January 17-21 Potential Winter Storm

There is potential for a disturbance in the January 17-21 timeframe.

Tropical Tidbits

The above image shows 500mb vorticity values across the Western Pacific from the (soon to be retired) GFS model, valid the morning of January 11th. Here, we see elevated vorticity values pushing east from the mainland of Asia. Of note is the shortwave evident just west of Japan, as the depression in the 500mb contour lines shows. This is the storm system we are watching.

A look at mean sea level pressure (MSLP) values for this same timeframe indicates the storm would be crossing almost squarely over the middle of Japan. Using the Typhoon Rule for timeframe, extrapolating the date of this graphic out 6-10 days, we come up with a possible storm in the US during a January 17-21 timeframe.

ESRL

The above image shows teleconnection forecasts from the ESRL agency shows the Pacific North American index dropping to near-neutral levels when this storm is projected to strike. Add in the moderately-positive NAO forecast, and chances are this storm will mainly take a west-to-east track, and is unlikely to "cut" north or south in any drastic manner.

To summarize:

- A storm system may impact the US during the January 17-21 timeframe.
- Indications are this storm could affect primarily the mid-section of the country.

Andrew

January Outlook: Thaw Gives Way to Final Winter Punch

This is the long range January outlook. In this post, we'll discuss the reasoning behind my expectation for a mid-month thaw, then followed by a return to wintry weather to close January and open February.

Paul Roundy

The above image shows a Hovmoller diagram of forecasted Outgoing Longwave Radiation (OLR) anomalies between 7.5 degrees North and 7.5 degrees South latitude, on a global longitude scale. The blue colors indicate negative OLR anomalies, which depict enhanced convection in that latitude slice, at a given longitude alignment. Similarly, yellow colors indicate suppressed tropical convection, also known as positive OLR anomalies. The MJO waves are shown by solid red lines, with more lines indicating a stronger MJO wave. Dashed lines highlight the suppressed phase of an MJO wave.

Taking a look at this chart, we currently see our Madden-Julian Oscillation wave progressing at a somewhat slow rate eastward, now located around 140 degrees East longitude. Using our MJO OLR composite, with blue and yellow colors having the same meaning as shown in the paragraph above, we can confirm that we are currently in a Phase 5 MJO, just about to switch to Phase 6.

BOM

Now, as the Hovmoller diagram shows, we expect our wave to push into that Phase 6 mark before it begins dissipating, and a new wave begins forming way off to the west. The dissipation of our current wave and generation of the new wave should happen around January 21st, meaning the current wave will be free to push through into Phase 6 (possibly Phase 7), generally a phase favoring warmer than normal temperatures in the US.

In late January, the other shoe drops.

The new MJO wave looks to form in time for the final week or so of January, pushing east at a slower rate than our ongoing wave. It will form and strengthen at around the 65 degree East longitude line at this date, which correlates to Phase 1 or Phase 2 on our chart directly above.

Meteonetwork

The chart above shows 500mb geopotential height anomalies during February, in a Phase 2 MJO wave. Notice the pattern encompassing the Central and Eastern US; strong negative height anomalies are present from south-central Canada into the Northeast. The strength of this anomaly tells me it's more than a simple trough. The longwave pattern here says this may be a piece of the tropospheric polar vortex being shunted south into North America due to blocking high pressure east of Greenland. Luckily, the MJO doesn't drive the whole pattern, so it doesn't automatically mean the vortex will be down to visit again. However, it does give an idea of what late January could be like.

As the MJO wave moves further east in February, the pattern will once again turn warm. But for now, late January and early February are looking wintry across the US.

To summarize:

- A warm pattern is likely in the middle of January.
- It is possible a final burst of wintry weather strikes the Central and Eastern US in the final days of January into early February.

Andrew

Tropospheric Polar Vortex May Deliver Record Cold on January 7-9th

Nearly one year to the day after the tropospheric polar vortex was sent into southern Canada to bring record-breaking cold into the United States, model guidance is unleashing another round of record cold to kick off 2015.

Before we get started, please read this infographic from the National Weather Service to understand what the polar vortex is and is not.

NWS

*Note: The controversial phrase 'polar vortex' is used in this article for purposes of communication to the public, instead of 'Massive Arctic Semi-Permanent Upper Level Low', which would not only be too long to type over and over again, but is also not as effective at communicating this threat to others. 

Tropical Tidbits

The above image shows the European model ECMWF's forecast of 500mb geopotential height anomalies, for the evening of Wednesday, January 7th. Note how we see strong high pressure forcing its way into the Arctic from the Bering Sea. This dislodges the tropospheric version of the polar vortex, and seemingly splits it into two bodies; one just east of Greenland, and another in the East US. That dark blue area represents the lobe of the polar vortex, and if you closely observe the 500mb height contours on this chart, you can see that the lobe gets as far south as the border of New England and Canada before shooting east. The GFS model agrees on this polar intrusion.

So... what can we expect for this latest cold blast?

Tropical Tidbits

Now switching to the American GFS model, as ECMWF temperature products are pay-to-view and may not be posted on this website, we see the cold really begins to set in on the morning of January 7th. We see temperatures on the surface of -25 degrees Fahrenheit over the Dakotas, with major cities like Des Moines, Chicago, Milwaukee, and Minneapolis all sub-zero. Similar to the Arctic air outbreak last January, this is pure Arctic air. This is dangerous and potentially life threatening, IF current forecasts are correct.

Tropical Tidbits

By Thursday morning, the cold recedes from the Plains to some degree, but hits the Great Lakes hard, as Chicago goes sub-negative-15 degrees on January 8th, with similar fates meeting the Quad Cities, Madison, and even Gary, Indiana. It's very possible that any snow cover put down by the January 3-5 winter storm, as well as the January 5-6 clipper, may intensify this cold blast further than models are predicting.

Although I can not post temperature forecasts of the ECMWF model, here are a few key points that I can paraphrase for you:
- Temperatures by midday Wednesday are sub-zero north of a line from Springfield, IL to North Platte, NE.
- Temperatures on Thursday morning bottom out around -22 degrees F in central Wisconsin, with widespread double-digit sub-zero temperatures around the Midwest and Great Lakes. Madison, Minneapolis, and Chicago all hover around -15 to -20F.

To summarize:

- Model guidance is in agreement on a record-breaking cold blast to hit the United States on January 7th and 8th.
- Temperatures, if forecasts are correct, will plunge below -20 degrees Fahrenheit in the North Plains and Upper Midwest, with double-digit negative temperatures widespread across the Midwest, Plains, and Great Lakes.
- High uncertainty still exists with this event, but confidence is gradually rising.
- Residents across the United States must be watchful of future forecasts, as this will be a deadly cold wave if it comes to fruition.

Andrew

January 5-6 Potentially Significant Clipper Snowstorm

Model guidance is starting to realize the potential for a rather significant clipper storm in the January 5-6 period.

Instant Weather Maps

The above image shows the 0z GFS snowfall projection for this clipper storm over a 24-hour period, ending on the afternoon of January 6th. We see a very strong clipper system dropping snowfall in the range of 6-10" across eastern Iowa, southern Wisconsin, and northern Ohio into Michigan. Northern Indiana and Northern Illinois are hit especially hard, with a stripe of 9-10" accumulations. The clipper then goes on the drop amounts over 6" in northwest Pennsylvania, with additional shovel-able snow spreading across New York and other portions of the Northeast.

Instant Weather Maps

Let's fast-forward to the most recent GFS forecast, which is the 12z forecast. In this 24-hour snowfall accumulation chart, valid for the early-evening of January 6th, we see high snowfall amounts over the eastern Dakotas into Minnesota and Iowa, extending far into Wisconsin, Illinois, Indiana, Ohio, and the Northeast. Here, the hardest-hit regions look to be eastern Iowa into northwest Illinois, where amounts are maximized to the 8-10" range.

I'm unable to share certain graphics of other models on this website due to copyright concerns, but it appears the Canadian GGEM model does not have this clipper system. However, the ECMWF model does have this clipper potential, with a decent amount of GFS ensemble members also backing the solution. Regardless, there's quite a bit of uncertainty here.

To summarize:

- Model guidance is indicating a strong clipper system may strike the Plains and Midwest to start the next workweek.
- Amounts off of one model point to maximum 6-10" accumulations.
- High uncertainty still exists with regards to amounts, storm track, and even the existence of the storm.

Andrew

January 3-5 Potential Winter Storm & Ice Storm Threat

The tables have turned (yet again) on the forecast models, as guidance is favoring a northward track for this storm system. Additionally, some guidance is seeing a major ice storm threat.

TwisterData

The image above shows observed 500mb vorticity values and height contours as of this morning. We can see our primary piece of energy located in the West, digging to the south and slightly to the west as it begins to close off in the Southwest. Interestingly enough, this will be the same piece of energy that will bring the rare snowfall to the area that news agencies have been reporting on. Eventually, this energy will eject into the Plains, and that's where the real action begins.

TwisterData

By 102 hours out, we see our primary piece of energy has moving into the Midwest, and we also see another piece of energy diving south from the North Plains to interact with the primary energy. This interaction is critical to the evolution of this storm. If the system coming south from Canada is delayed, or speeds up, this storm will take on an entirely different approach, which is why model guidance still retains some problems with sorting this storm out. Lately, guidance has agreed on this storm being a "cutter" event, where the wintry precipitation will impact the Great Lakes, Plains and Midwest (those of you who read my previous post know this as the track I did not side with), but beyond that consensus, there isn't a whole lot of agreement.

We'll analyze three different model forecasts in today's discussion.

Tropical Tidbits

The above image shows the latest GFS model's forecast of accumulated snowfall out to next Monday. We see the track this storm has taken in this projection, with the bullseye of the snow hitting northeastern Missouri. A heavy swath of snowfall extends northeast from that corner of Missouri, where an additional 6"+ of snow is forecasted through the Quad Cities, Chicago, Milwaukee, and into North Michigan. This solution has been one that has shown up rather consistently, particularly in recent runs of all guidance, as the trend has been to go north. However, as was stated above, model disagreements are still evident.

Tropical Tidbits

The above image shows the snowfall forecast off the GFS-Parallel model, the incoming upgrade to the current GFS model. This forecast has one band of snow dropping about 6" or 7" in much of northern Illinois, while what may be a second band delivers similar amounts in central Wisconsin. The intriguing part about this model is its poor verification, especially as of late. It remains to be seen how this model does with this storm, but so far, recent history suggests one ought to be wary of this model's forecasts.

Lastly, but certainly not least, we need to discuss this ice storm threat.

CMC/EC

The above image shows forecasted precipitation types from the Canadian GGEM model, valid for the morning of January 3rd. We initially see a swath of moderate to heavy rain across the southern Midwest into the Ohio Valley, but areas north (particularly the western Great Lakes into Indiana and Ohio) are under the gun for a significant ice storm. Earlier projections, made not even 24 hours ago, favored freezing rain accumulation of 0.8" in Chicago, IL, though this model has since lowered those totals to a "better" 0.4" outlook of freezing rain. The GGEM model isn't the best at verification, either, so I wouldn't get hung up on this forecast. I would, however, keep an eye on forecasts for the potential for an ice event, should these ominous outlooks continue to surface.

To summarize:

- Model guidance is coming into agreement on a winter storm impacting the Plains, Midwest and Great Lakes.
- Some forecasts are predicting a major winter storm to hit the aforementioned regions, while other forecasts favor rain. Still others favor a miss to the south.
- There is some indication of an ice storm threat, but due to model uncertainty I wouldn't begin worrying yet.

Andrew