Friday, February 27, 2015

Long Range Ensembles Predict Incoming Spring-Like Weather

Long range ensembles are indicating a much warmer weather pattern is on the way for much of the country that has been held hostage by brutal cold in the last month.

PSU
Click to enlarge
The above image shows 500mb geopotential height anomalies from the GFS ensembles, projected over the Northern Hemisphere and valid for March 1st. In this graphic, we see a massive ridge of high pressure, the same one which has allowed for such a cold and snowy February, meandering westward over the north-central Pacific, as opposed to the northeast Pacific and Gulf of Alaska. This comes as a strong trough drops into the Southwest and Baja California. In response, with the strong upper level low previously positioned over Greenland, now over Europe, a ridge is able to form over the Central and East US. It looks like this ridge will be suppressed a bit, but warmer weather is on the way for those in the Plains, Midwest, Ohio Valley, and Northeast, among other areas.

PSU
By March 7th, ensembles are indicating the ridge remains in the north-central Pacific, but an upper level low has now developed in the Gulf of Alaska. Unfortunately, this then results in a ridge forming over the Western US, as the graphic above shows. Consequentially, the semi-permanent Arctic long wave trough (better than using 'polar vortex', apparently) is being pushed back into North America, setting up another period of cold weather for the Central and East US. This would likely last for a handful of days, right between February 5-10 or so.

But... finally... finally!... relief comes.

PSU
In the long-long range, to March 11th, ensembles see our ridge forcing itself north in the north Pacific into the Aleutian Islands, along the jet stream, where the "polar vortex" is stationed just off to the north. The net result for us is another trough setting up over the western section of North America. You weather enthusiasts know this as a negative Pacific-North American (PNA) pattern, with a trough in the west and warmth in the East.

This looks to be our new pattern, going strictly by these ensembles. Stormy weather in the West with predominantly warm weather out east.

To summarize:

- A brief warm-up is expected in the final days of February and early days of March.
- Another cold blast can be expected around March 7th.
- The pattern may then shift to a warmer set-up for the middle half of March.

Andrew 

Wednesday, February 25, 2015

March 1-2 Potential Winter Storm

Model guidance has been indicating a winter storm will track across the middle of the country, bringing accumulating snow to those further south of where much of the wintry weather has occurred this winter.

Tropical Tidbits
The image above shows the GFS forecast for precipitation type and intensity, valid for Sunday night. We see light to moderate, possibly even heavy snow falling across the Midwest, Great Lakes, and Ohio Valley. A classic signal of winter finally on its way out, the rain/snow line is displaced pretty far north in comparison to where it has been in recent days and weeks, with rain being a concern in southern Illinois into southern Ohio. A bit of mixed precipitation could impact those in the central Plains.

Instant Weather Maps
Snowfall projections have been waving back and forth with the axis of heaviest accumulations, but the latest GFS pegs a swath of 6-10" accumulations across the central Plains into the Midwest and central Great Lakes, with Kansas, northern Missouri, central Illinois and northern Indiana receiving the most snow.

To summarize:

- Model guidance is anticipating a winter storm to affect the country over the next few days.
- Snowfall on the order of 6-10" may be expected.
- While the track of this storm is still not nailed down yet, the central Plains and Midwest ought to see the most intense snow accumulations.

Andrew 

Sunday, February 22, 2015

Second Round of Harsh Arctic Air Flowing Southward

The second round of intense cold air in under a week is on the way for millions in the Northern United States.

Tropical Tidbits
Click images to enlarge
The above image shows the latest GFS model forecast for Monday morning. On this chart, we see temperatures in the negative-teens across Wisconsin, Illinois, Minnesota, Iowa, Michigan, Indiana, and Ohio. The most intense cold is projected to hit northern Wisconsin and southwestern Michigan, but that doesn't take away from the cold in the other aforementioned areas.

Tropical Tidbits
The GEM model, with its notorious cold bias, agrees with the GFS model. Here, we see a swath of bone-chilling cold in southern Minnesota and Iowa, where temperatures are forecasted to approach -30 degrees. This is more than likely overdone, but the general trend of very cold temperatures similar to the GFS stands in Wisconsin, Illinois, Michigan, Indiana, Ohio, and even into the Dakotas.

Other model guidance, mainly the NAM model, is favoring a warmer solution than the two depicted above. It comes out to the GFS/GEM models and their ensembles, against the NAM/SREF models/ensembles. The National Weather Service appears to be favoring the NAM model / warmer forecast, even though morning observations in the Dakotas and Minnesota support a more GFS-like evolution. Regardless of what happens, another very cold morning is in store tomorrow.

To summarize:

- Another bout of harsh Arctic air is on the move south.
- Temperatures could drop into the negative-teens in some spots.
- Uncertainty still exists with how cold it will get.

Andrew 

Thursday, February 19, 2015

Long Range Outlook (Made February 19, 2015)

This is the updated long range outlook, made on February 19th, and valid for late February into the first half of March.

Tropical Tidbits
Click to enlarge
We're currently seeing a portion of the semi-permanent Arctic low pressure vortex intruding into the United States, with anomalously low 500mb geopotential height values appearing in the colored shadings and analysis in the graphic above. This anomaly has been forced by a strong ridge pushing into Alaska from the northeast Pacific and west coast of North America. Over the next few days, cold air intrusions should continue as this ridge flexes its muscles and persuades additional Arctic air masses to collapse into the lower latitudes.

ESRL
I want to now go over the teleconnections over the next two weeks, which can help us diagnose the pattern heading into the 14-31 day period.

Top left: PNA Forecast
Top right: NAO Forecast
Bottom left: WPO Forecast
Bottom right: EPO Forecast

A quick refresher on the PNA, NAO, WPO and EPO...
The Pacific North American index involves what the atmosphere does in the northeast Pacific and the western coast of North America. When we see a stormy pattern in place over these regions, we call such a pattern a negative PNA, due to the below normal height anomalies in this region. In a similar sense, when high pressure dominates that same region, we call that a positive PNA. A negative PNA will bend the jet stream to give the storms to the Plains and the Deep South regions, frequently initiating high pressure system formations over the Central US. A Positive PNA will bring about an opposite response to high pressure (HP) over the West, and will have the stormy pattern evolve over the East US.

The North Atlantic Oscillation involves the presence of a high pressure system over Greenland (negative NAO) or the presence of a low pressure system over Greenland (positive NAO). In the negative NAO, the jet stream will buckle into the Northeast to allow storms and cold to thrive in that region. The positive NAO denies this region any of these benefits.

The WPO (West Pacific Oscillation) and EPO (East Pacific Oscillation) are very closely related. In the negative phase of the WPO, a strong ridge exists over the Bering Sea, which can allow for sustained cold weather in the Central and Eastern United States. The negative phase of the EPO gives similar results, though the ridge is positioned in the Gulf of Alaska instead. The positive phase of both the EPO and WPO see warm weather prevail in much of the US, as stormy weather replaces the ridges in each respective region.

The positive PNA and negative EPO have worked in tandem to indicate this strong ridge blossoming into the Gulf of Alaska and general northeast Pacific. In the upcoming couple of weeks, model guidance is indicating we see the ridge shift further offshore to the west, as the PNA dip from positive to negative shows. Over time, ensemble guidance is telling us that this ridge could keep shifting west, resulting in the EPO actually moving positive for the first time in a while. The positive EPO signal, however, is weak, and will have to be watched for a 'false positive', both literally and metaphorically. If this forecast does verify, we can expect a warm-up in the early days of March.

Tropical Tidbits
Ensembles indicate we will see a ridge of high pressure pushing into Japan on the morning of February 21, as the graphic above shows. Using the Typhoon Rule, which states weather phenomena occurring in Japan is reciprocated in the United States 6-10 days later, we can anticipate a warm-up for millions that have undergone a brutal February in the final days of the month, likely into early March. From there, confidence decreases, but a return to an average or cooler than normal pattern may be expected.

You'll notice I haven't used tropical forcing in this post; that's because the ridge in the West is just so overpowering that the Madden Julian Oscillation can't do much of anything.

To summarize:

- A cold pattern is expected to round out February.
- A warm-up is expected for the last days of the month into early March.
- The first half of March should be characterized by a generally average to slightly below-average temperature pattern. There are hints of some stormy weather in early March.

Andrew

Monday, February 16, 2015

Chicago, Milwaukee Bracing for Severe Arctic Cold

Midwestern cities such as Chicago and Milwaukee are bracing for cold that could drop temperatures well into the double-digit negatives. This sort of cold has been seen recently east of Lake Michigan, but will make its first appearance of the month in more western regions this workweek.

Tropical Tidbits
Click images to enlarge
The above image shows the latest GFS model forecast for air temperatures on Thursday morning at 6AM, fresh off the presses. We see temperatures near Madison, Wisconsin plummeting to -15 degrees Fahrenheit, with Minneapolis seeing similar readings. Chicago looks to be under the gun for -10 to -15 degree temperatures, while Springfield, IL may see relatively warmer values.
There is model discrepancy with respect to how cold this air mass will be. The GFS model is favoring a much colder solution, as we see above, while the short-range NAM model (not shown) is favoring a warmer solution. One model has to cave at some point; it's a waiting game to figure out which one. For now, better safe than sorry.

Tropical Tidbits
Friday morning is the tricky forecast for these Midwestern cities. Skies will be clear for swaths of the Midwest, and with much of the area under a snow pack, temperatures could drop even lower than Thursday morning readings. However, in addition to the NAM model favoring a warmer air mass, warm air advection will be ongoing across the Plains into the Midwest. Discrepancies remain with respect to how fast this warmer air will push into the Midwest, and how intense it will be. For now, I'm taking more of a wait-and-see approach, but preparing for the worst. Again, better safe than sorry.

Purely for eye candy, as in this will not verify, check out the Canadian model air temperature forecast for Friday morning.

Tropical Tidbits
To summarize:

- The Midwest may undergo its most severe wave of cold weather this season, with cities such as Chicago, Milwaukee and Minneapolis going below the -10 degree F benchmark.
- Unusually high uncertainty still exists surrounding the intensity of this cold air on both Thursday and Friday. Any updates to this post will be made on either our Facebook or Twitter pages.

Andrew

Saturday, February 14, 2015

February 15-19 Potential Snowstorm and Ice Storm

The February 15 through 19 period is increasing in likelihood that we will see a winter storm, potentially with an ice storm component.

Tropical Tidbits
Click images to enlarge
The image above shows the GFS forecast for precipitation type over the United States for the morning of February 16th. Here, we see precipitation breaking out over the Southern Plains and along the Gulf Coast as a low pressure system advects northeast-ward. In this forecast, we see a snow shield placed from southern Illinois into Missouri, Arkansas, and the Tennessee/Kentucky area, with rain blossoming in Texas, Louisiana, and southern Mississippi. We also see a rather broad swath of sleet, potentially freezing rain in southeast Oklahoma, central Arkansas, and northern Mississippi. This freezing rain/sleet delineation could prove to be a serious issue for those in the South, especially with memories of the ice storm from last year still fresh.

Tropical Tidbits
By the evening of February 16th, the low pressure system responsible for this precipitation is trekking along the Gulf Coast, located along the Mississippi/Alabama border in this graphic. A rain shield encompasses Louisiana, Mississippi, and a good chunk of both Alabama and Georgia. Snow is falling in eastern Tennessee, the western Carolinas, and extreme western Virginia, with a small band of freezing rain / sleet in northern Mississippi and Georgia. It's encouraging to see the freezing rain shield shrink from our last image, but as freezing rain is so tricky to predict, I wouldn't take that part of this forecast verbatim.

Tropical Tidbits
By early morning on February 18th, the storm has transferred offshore and is beginning to strengthen over warm waters along the coast of the East US. Snow continues to fall in much of North and South Carolina, with rain prevailing in southern Georgia and much of Florida. Heavier bands of snow are already impacting coastline locations in the Mid-Atlantic and Northeast, with New Jersey on the northern fringe of this heavy snow shield. From there, the storm continues north and east.

Snow accumulation charts are unreliable in this case, as some methods for snowfall will accidentally count freezing rain and sleet as snow, unrealistically amplifying snow totals. Thus, it would be unwise to show a snow total chart for those in Arkansas, where that unrealistic amplification of totals is likely to occur.

WxCaster
I want to now look at the forecasted freezing rain accumulation chart from the short-range NAM model over the Eastern US. In this chart, we can see where freezing rain is most likely to occur. Again, because freezing rain is so hard to predict in advance, take this with a relative grain of salt. Regardless, let's see who may be affected. The highest freezing rain totals appear in western South Carolina, where accumulations of 0.50" to 0.75" could be found. Significant accumulations of 0.25" to 0.50" extend through the rest of the Carolinas, and isolated spots of similar totals stretch back through northern Mississippi, Georgia and Alabama, all the way to southern Arkansas. While you shouldn't expect to see this chart verify exactly as-is, it gives you a good idea as to who may be affected by freezing rain from this storm.

To summarize:

- A storm system in the Southern US looks to bring wintry precipitation to states such as Arkansas, Mississippi, Alabama, Georgia, Tennessee, Kentucky, and the Carolinas.
- Accumulating snowfall is possible, particularly in Tennessee and Kentucky.
- Accumulating freezing rain is possible, particularly in southern Arkansas, northern Mississippi, Alabama, Georgia, and the Carolinas.

Andrew

Thursday, February 12, 2015

Anomalous Upper Level Low to Deliver Intense Cold in East US

An anomalous upper level low connected to the swirling mass of cold air in the Arctic looks to deliver a punch of brutally-cold air, impacting the East US the strongest.

PSU
Click images to enlarge
The above image shows the GFS ensemble mean spread forecast for the 500-millibar field on the top panel, with increased spread/uncertainty among ensemble members shown by shaded colors. That spread can also be seen in the individual member colored lines. The bottom panel shows anomalies for the 500-millibar field, with cool colors indicating negative anomalies, and warm colors depicting positive anomalies.

In this image, we note a strong upper level feature pushing south from Canada, with anomaly values reading 3.27 units below normal, maximized in western New York into western Pennsylvania as the purple colors show. Judging by the numerical denotations on that bottom panel, 500-millibar values could flirt with the 500-dm benchmark along the US/Canada border, indicative of a very strong (and very cold) upper level low.

Tropical Tidbits
Forecasts from computer models suggest sub-zero temperatures will be the theme throughout a significant swath of the North US. Latest guidance suggests temperatures in west New York and Pennsylvania will easily drop below -10 degrees Fahrenheit, with some locations getting very close to -20 degrees F. Locations further to the west, particularly in the Midwest and Great Lakes, may also come close to -15 degrees, with some areas dropping down to that -20 degree F benchmark. All in all, this is looking dangerously cold, potentially life-threatening.

To summarize:

- The first part of a multi-wave cold blast looks to impact the North US this weekend.
- Cold weather will be maximized in the Northeast, where temperatures could reach lows of -20 degrees Fahrenheit.
- Travel is strongly advised against due to the life-threatening nature of this cold air.
- Make sure to seek out assistance now for neighbors, friends, and/or family that may have trouble sustaining heat in their homes, or could be adversely affected by this cold.

Andrew

Long Range Outlook (Made February 12, 2015)

This is the Long Range Outlook, valid for the middle and end of February into the start of March.

PSU
Ensemble guidance close to 9 days out from today shows a pattern highly conducive to cold weather across North America. We see a strong ridge positioned across the west coast of North America, pushing into Alaska. The alignment of this ridge closer into the Gulf of Alaska as opposed to along the shoreline indicates a negative East Pacific Oscillation (EPO) pattern. This sort of pattern allows for sustained northwest flow (winds out of the northwest) in the Central US, and this is well shown by the strong upper level low buckling south into the Great Lakes. Short range projections show very cold temperatures slamming much of the nation, hitting the northern Ohio Valley and Northeast very hard in particular. This cold pattern looks to be enhanced by some ridging, albeit suppressed, south of Greenland. I am concerned that the ridge not being positioned closer to Greenland could make this cold weather more progressive and not as long-lasting as current ensembles are making it out to be, though those details can be sorted out further down the road. For now, the opening days of this 7-31 day forecast period are looking very cold.

PSU
By Hour 348, which is about 14 days out from today, we see a shifting of the members mentioned above to the west. Our negative EPO ridge has now been shunted west, and now occupies the Bering Sea into waters to the southwest. The strong upper level low still remains on our side of the hemisphere, but the core of this low has been retracted into the North Atlantic, with a leg of negative height anomalies stretching out to the Rockies. As a result, the general idea is that more progressive flow can be expected as we round out February, which should be able to moderate any cold blasts near the end of the month. We also see ridging coming up offshore of the East Coast, which could put an end to what looks to be an incredibly cold and snowy February for millions in the East.

Albany
We now turn to tropical forcing to help us identify the pattern for the beginning days of March. Looking at the bottom panel, we see a significant swath of enhanced tropical convection blossoming just south and east of the subcontinent of India, depicted by the deep blue shadings. If we match the positioning of these anomalies to the eight phases of the Madden Julian Oscillation, we can expect the emergence of a Phase 3 or Phase 4 event, as the composite chart below shows.

BOM
Generally, Phase 3 events support cooler than normal temperatures in the United States, while Phase 4 composites indicate warmth prevails across the country. Purely due to how February looks to shape up, I would favor a chillier outlook to kick off March. This method of persistence forecasting tends to work well, particularly when the pattern seems to 'lock in' to a certain temperature alignment; in this case, a cold Central and East US, with warmth in the West.

CPC
Looking even further out, just for kicks, let's go over sea surface temperature anomalies, under the surface. Anomalies show the 'warm part', the upwelling phase of a Kelvin wave moving eastward at a depth of about 100 to 200 meters. We're currently seeing the 'cold part' of that Kelvin wave, the downwelling phase, hitting the surface from about the 100 west longitude line on eastward. The warmth from the upwelling is already at the surface in the Central Pacific, and this could be setting up a more El Nino-like pattern. I personally find this to be plausible, as El Nino winters are notorious for a slow start and furious end, as we're seeing in real time right now in the East US.
In springs with an El Nino, temperatures in the North US will generally be warmer than normal, while the opposite scenario plays out in the South, with colder than normal temperatures. It remains to be seen if this will play out in the March-April-May period, but it'll be something to watch.

To summarize:

- A very cold pattern will unfold over the next 7-14 days.
- There are hints of a warmer pattern coming around for the period beyond 14 days, but this needs to be watched for potential failure.
- It is expected that the East will remain overall below normal throughout the entire period in temperatures. A similar story, though not as cold, may be expected in the Central US.
- Snowfall should favor the East US in this entire pattern, though a shift to a more inland track could occur in late February if model guidance ends up being correct.

Andrew

Saturday, February 7, 2015

February 22-27 Potential Winter Storm

Model guidance has been hinting at a rather strong winter storm impacting the United States around a February 22-27 period.

Tropical Tidbits
Click images to enlarge
The above image shows the GFS forecast of 500mb geopotential height values (colored shadings) and mean sea level pressure contours over the West Pacific, valid on February 16th. In this image, which is from the GFS model run on the morning of February 4th, we see a very strong low pressure system crossing Japan and moving away from the country as it does so, with a minimum central pressure here of 987 millibars. This is a very strong system, but one might argue that can be expected from long range guidance, which can/does tend to over-amplify storms in long-range forecasts.

Since that forecast was made, at least 5 other GFS runs came in with very similar solutions, meaning this could be a valid storm potential. You'll notice that the timeframe isn't exactly the same on each graphic, but the storm impacting Japan between February 16-17 is generally agreed upon.

Tropical Tidbits

Tropical Tidbits

Tropical Tidbits

Tropical Tidbits

Tropical Tidbits
While this model remains inconsistent as far as showing this storm run-after-run, the general concept of a storm in this timeframe is still present (for now).

When we apply the Typhoon Rule, which states weather phenomena occurring in Japan is reciprocated in the United States 6-10 days later, we can extrapolate the storm in this February 16-17 timeframe to get a rough estimate of a February 22-27 correlation here in the US, padding in a couple days for uncertainty. But we may also be able to figure out where it tracks.

ESRL
The above image shows sea level pressure anomalies on the morning of January 24th, 2011. On this day, we saw a storm system cross Japan and rapidly strengthen as it began to exit the eastern coast of this country. Just for kicks, let's apply the Typhoon Rule here. If we do so, we likely saw a storm system impact the country between January 30th and February 3rd, 2011.
Some of you might remember that as the Groundhog Day Blizzard of 2011, which dropped close to 24" of snow in Chicago, IL, as well as incredible ice accumulations in the cold sector of this storm. When we compare the projected track of our mid-February storm in the GFS images above, we see that some (not all) forecasts have the upcoming low taking a similar track as the eventual-Groundhog Blizzard did. That's not to say I'm expecting another massive blizzard. I'm just trying to show where this storm could end up tracking, and that could be through the Midwest yet again.

Tropical Tidbits
There's also the chance we see this storm go through the East US and impact that area primarily. The reasoning behind this is the expected ridge-out-west and trough-out-east pattern which will likely deliver more than one round of accumulating snow to the East (more on this can be found in yesterday's post). The image above shows the GFS ensemble outlook at the very end of its run, depicting 500-mb geopotential height anomalies for February 22, 2015. We see a gradual departure of the trough in the East into Greenland, though the ridge in the West is still persisting. Personally, I'd bet more on the trough staying put purely out of persistence forecasting, but that's why you take model guidance with your own opinion. If this forecast did work out, however, the storm could impact the Central US and East US, whereas the trough staying put would result in an impact likely for the East.

CPC
If we factor in tropical forcing, we get yet another different picture. When the timeframe for this storm rolls around, enhanced tropical convection is forecasted (not shown here) to be placed in an area around and just east of the 90ยช East longitude line, which places us in Phases 4 or 5 of the Madden-Julian Oscillation (MJO). The above graphic shows precipitation anomalies on the left two columns; we'll ignore the colorful columns on the right for now. When we look at precipitation anomalies during Phase 4 and 5 in a January-February-March period, we tend to see the Central US into the Northeast getting in on storm activity. This could mean the storm in late February, if it happens to begin with, will hit both the Central US and East US, but anything beyond that is purely guessing.

To summarize:

- There are indications a strong storm could hit Japan in the middle of February.
- This could result in a strong storm in the United States between February 22 and February 27.
- It is not known who will/could be affected by this system yet.
- As the post thoroughly showed, significant uncertainty surrounds this event.

Andrew

Friday, February 6, 2015

Upcoming Pattern Very Favorable for East Coast Snowstorms

The upcoming pattern appears to be very favorable for snowstorms along the East Coast.

Tropical Tidbits
The above image shows the 500mb geopotential height anomaly field over North America, forecasted by the GFS Ensembles from February 11th to February 16th. In this graphic, we see a strong upper level low dipping down over the Bering Sea, forcing a strong ridge to blossom along the Western US. A Rex Block then forms in the Southwest, as an upper level low slides under the ridge. Usually, a Rex Block upstream creates zonal flow downstream, but instead of rather calm weather in the East US, we see a deep upper level low pushing its way into the Northeast. This looks to be the pattern for the next 2 weeks or so.

In this sort of pattern, sustained northwest flow (winds from the northwest) often leads to a 'clipper train', where a multitude of Alberta Clippers slides southeast-ward into the Central US. These clippers can then move east off the coast, and can intensify to produce heavy accumulating snow for the East US. I believe that this is a possibility, and could happen more than once in the next couple of weeks.

Unisys
A look at sea surface temperatures shows how potent this environment is. For now, we'll focus on the East Coast. Notice all the oranges and reds immediately along the coastline, extending a bit east. Those are very warm waters, with well-above normal anomalies being detected. Consequentially, any clippers that move off the coast and threaten the East will have unusually warm waters to work with, which could very well enhance snowfall totals.

To summarize:

- The upcoming pattern is favorable for accumulating snowfall in the East US.
- This pattern may support more than one event of plowable snow.
- Extreme cold may affect the Northeast, at times.

Andrew

Tuesday, February 3, 2015

February 16-20 Potential Arctic Outbreak

There appears to be the risk of an outbreak of cold air between a February 16-20 period.

Tropical Tidbits
The image above shows 500mb geopotential height anomalies over the West Pacific, forecasted by the GFS model and valid on the morning of February 10th. In this image, we see a very strong upper level low displaced just north of Japan, with contours telling me this is a sub-500dm upper level low- a very strong storm. When we use the Typhoon Rule, which states weather phenomena occurring in Japan is reciprocated in the United States 6-10 days later, a strong upper level low could approach the United States from the north in a February 16-20 period. It's too early to tell definitively, but this could correlate to a lobe of the tropospheric polar vortex plummeting south towards the mid-latitudes. Again, it's too early to tell right now.

ESRL
Long range ensemble forecasts for the middle of this timeframe are already beginning to see strong upper latitude blocking leading to a new wave of cold weather for the Central and East US, as those blue colors shown over North America. We will need to watch upcoming forecasts to see how they change.

ESRL
For comparison, here's the chart of 500mb geopotential height anomalies over Japan on December 27th, 2013. We saw a very strong upper level low drop south into southern Japan, which then correlated to the infamous cold blast which originally made the phrase 'polar vortex' go viral. Forecasts above don't see the impending upper level low dropping as far south, which is why I'm thinking this upper level low will approach the region, and not necessarily induce a period of incredibly frigid temperatures, like we saw last winter.

To summarize:

- A strong upper level low looks to drop south to scrape northern Japan in the next week.
- As a result, we could see a period of below-normal, possibly well below-normal temperatures between February 16th and February 20th.

Andrew

Monday, February 2, 2015

February 10-15 Potential Winter Storm

I'm watching for the potential for wintry weather in the February 10-15 period.

Tropical Tidbits
The image above shows 500mb geopotential height values for the morning of February 5th, with mean sea level pressure (MSLP) contours superimposed. In this graphic, we see two areas of low pressure over the Western Pacific. The more dominant system is located south and east of Japan, with another piece of energy just west of this island nation. In the forecast hours after this graphic, it appears the energy west of Japan transfers to the storm east of Japan. From there, the dominant low moves generally northeast, away from Japan. When we use the Typhoon Rule, which states weather phenomena occurring over Japan is reciprocated in the US 6-10 days later, a storm in the US might be expected in a February 10-15th period, adding a day for some uncertainty I have on timing. Additionally, the transfer of energy over Japan tells me we could be looking at a transfer scenario from the Midwest/Great Lakes/Ohio Valley into the Northeast.

ESRL
We can take a look at teleconnections to get a glimpse at what this storm might do. For this post, we'll pay attention to the top-right North Atlantic Oscillation (NAO) outlook. Notice how the index rises from negative to neutral territory right in the timeframe of this potential winter storm. The NAO switching phases is known to be a red flag for snowstorms in the Northeast, as the risk of snow events in that area tend to rise when this switching of phases occurs. This could support the idea of a transfer storm to the Northeast, like the GFS showed (in a likely overdone projection) in its 12z forecast:

Tropical Tidbits

To summarize:

- Model guidance is indicating a winter storm may impact the country in a February 10-15 period.
- As of now, a transfer low from the North-Central US to the East Coast may be a likely solution.
- As usual, high uncertainty still exists.

Andrew