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

January Long-Range Outlook: La Nina Pattern Expected to Dominate

This is the long-range outlook for the month of January, and is one of the more unfortunate posts I have to write. At this time, it does appear my winter forecast is in trouble, primarily with respect to the Eastern US, based on how January is shaping up. Let's jump right in.

Paul Roundy

The above image shows a long-range Hovmoller forecast, on a time-by-longitude scale. For this chart, we want to focus on the colors, where yellow indicates suppressed tropical convection, and blues represent enhanced tropical convection from an area encompassing 7.5º North latitude to 7.5º South latitude. The other item we want to watch for is the solid red lines, which indicate the presence of a Madden-Julian Oscillation (MJO) wave. These are almost always accompanied by enhanced tropical convection signals (the blue colors).

On this graphic, notice how we see an MJO wave moving from 135E at the start of the New Year, to about 170E before it dies out near the International Date Line at 180º. If you put this into terms of the Madden-Julian Oscillation, it means the MJO will be moving through Phases 4, 5 and 6 before dying out just before reaching Phase 7. There are a total eight phases in the MJO, and Phase 4-6 are classified as 'La Nina pattern' phases. Similarly, Phases 8-2 tend to be associated with 'El Nino pattern' phases; I personally see Phases 7 and 3 as 'transitional phases'. Therefore, we can determine that we will be entrenched in a primarily-La Nina pattern until this MJO wave dies out close to January 20th, and a new wave commences around ~65E longitude to close out January. Long-long range forecasts into February also take this second wave through La Nina phases, a bad signal for winter weather fans in the East.

Nicholas Schiraldi

The image above shows the GFS forecast for atmospheric angular momentum, or AAM over the next 16 days. Notice how the GFS takes the AAM well into low territories, near phases 1-4. These phases and general Low AAM pattern are highly characteristic of a La Nina-dominated weather pattern, and this jives well with the indications we have been receiving from tropical forcing, as was described above.

So, what exactly does a La Nina pattern entail?

NOAA

The above image shows a general overview of the atmosphere during a La Nina-dominated pattern. During such a pattern, high pressure will take over the Gulf of Alaska and general Northeast Pacific regions, as the polar jet stream rides up into Alaska, before plummeting south into the Rockies. As a result, a general wet and cool pattern takes hold of western Canada and the North Plains. In the United States, high pressure and warm weather will take hold of the Southeast and East US, something we've been seeing, and ought to continue to see for the coming month. This ridge then provides an excellent 'blockade' that can force storm systems from the south to come north, and dump precipitation into the Great Lakes, Midwest, Plains, and even the Ohio Valley at times. That's why we see a 'wet' outline in the areas mentioned above (this outline is centered a bit to the east of where I believe this 'wet' pattern may set up).

Let's split this up into three portions, to better serve our forecasting purposes.

Early January
The early part of the month is likely to favor a cold Central and East US, as a lobe of the polar vortex ventures dangerously close to the United States. This time period is likely to feature multiple winter storm threats, which may affect the East US as well as the Central US. More examination of ridging in the Southeast will be needed, as far as knowing where the individual storms may track.

Middle January
The middle part of the month is likely to feature a warmer than normal East US, but long range model guidance is indicating this warmth may eventually push westward to encompass the Great Lakes and much of the Midwest. Time will tell on how this outlook unfolds, but a warm East and Central US may be a good bet, as the aforementioned MJO wave moves into phases unfavorable for warmth in those areas.

Late January
The closing part of the month is likely to feature a return to some cooler conditions, primarily in the eastern third of the country as a new MJO wave forms in phases favorable for a chill in the East. However, the final days of January and opening days of February could see warmth return to the East, if this new MJO wave moves quickly to La Nina phases.

The parts that would be included in the Summarization have been highlighted in red above.

Andrew

January 6-10 Potential Winter Storm

Model guidance is latching onto what could be our first shot at a strong winter storm, in the January 6-10 timeframe.

Tropical Tidbits

The above image shows 500mb geopotential height values in colored shadings, and MSLP values in contoured lines, across the West Pacific on New Years Eve. In this image, we see a strong low pressure crossing Japan, with a minimum central pressure value of 991 millibars, before sliding north and east towards the Aleutian Islands. If we apply the Typhoon Rule, which states that weather phenomena occurring in the West Pacific is reciprocated in the United States six to ten days later, we may extrapolate this to mean a strong storm could impact the US in a January 6-10 timeframe.

Other model guidance supports a weaker system moving over Japan, meaning we will need to monitor the region in coming days. If the storm crosses Japan at a weaker intensity, the storm here in the US would likely be weaker as well.

Purely for 'eye candy', here's the latest GFS projection of a storm in the East US on January 6th. This graphic isn't a forecast you should count on to verify.

COD

To summarize:

- A storm system may impact the US between January 6-10.
- Storm strength is still uncertain, and all aspects exhibit very high uncertainty at this juncture.

Andrew

January 3-5 Potential Major Winter Storm

** This post is dedicated to the lives potentially lost on the QZ8501 flight, reported missing last night. **

The potential for a winter storm in the January 3-5 period appears to be growing.

TwisterData

The above image shows 500mb vorticity values across the United States from the GFS model, valid for the afternoon of January 2nd. Here, we see a rather potent piece of energy pushing eastward across the southern Plains at a neutral tilt. This energy is the piece we will be watching to impact a significant portion of the Central and East US. As of now, there are two tracks: one takes the system north and lays down plowable snowfall in the Great Lakes (Madison, WI or Chicago, IL), while the other track goes into the Ohio Valley, putting down snow in that area, even into the Northeast.

I'm going to go through the different mechanisms for this storm, and why ingredients are here for both a north and south track.

TwisterData

Shown here is the mid-level wind speed chart from the GFS model, valid at the same time as the first image we looked at. Notice the streak of enhanced wind speeds rounding the base of the trough/storm system in the South Plains. This streak of strong air is a textbook signal for a strengthening storm system, as the storm will then attempt to attain a 'negative tilt', where those vorticity values in that top image will try and "push" in a southeast direction. This negative tilt indicates the storm has reached peak intensity, and is now a mature storm. Additionally, it allows the storm to curve northward, and qualify the northward track.

Tropical Tidbits

Here's the snowfall projection off of the most recent GFS model forecast, giving you a good idea for where snow would fall if this northern track were to verify. Northeast Iowa into much of southern and central Wisconsin would see amounts near or in excess of 6", with similar amounts nearing 12"+ in Michigan. The GFS has continued to trend north as time has gone on, and is now reaching 'outlier' status, as other model guidance comes in south.

Tropical Tidbits

Here's the Canadian GEM model forecasted 500mb geopotential height values (color) and MSLP values (contoured lines) for the afternoon of January 3rd. We see our storm system displaced well south of the GFS track, with this forecast leading the low pressure system over western Tennessee, eventually into the Mid-Atlantic, producing accumulating snow as it does so. The GFS-Parallel model, the successor to the current GFS model, is also siding with this GEM projection of a further south track. This southern track would deliver snows to portions of Indiana, Ohio, and into the Northeast, finally adding a bit of winter for those regions.

Now, it's time for a bit of analysis.

TwisterData

Let's use the same image now as we did to kick off this post. As we see the energy push into the Southern Plains, notice how the longwave trough over Canada seems to almost converge with that ridge in the Southeast, right over the Midwest. This tightening up/coming-together of contour lines is a process called 'confluence'. Confluence works by piling up air, as those contour lines press together. At the surface, this results in high pressure. My concern is that model guidance (the GFS model in particular) is not accurately accounting for this high pressure. The formation of high pressure right where the storm is supposed to track would usually see the storm forced southward, similar to what the GEM and GFS-Parallel are showing. 
Adding to this concern is that all model guidance has a known bias to be too slow with the progression of Arctic air southward. Lo and behold, we have a strong Arctic high pressure system on the heels of this storm system, and if models are retaining this bias, it's quite possible the storm ends up shunted to the south, giving snow to the Ohio Valley and Northeast.

Tropical Tidbits

The image above shows the projection for 500mb geopotential height values (colored regions) and MSLP values (contour lines) for December 29th over the West Pacific. We see a low pressure system has formed on the southeastern coast of Japan, and is moving east-northeastward along the coast. As time progresses, this low will eventually shift out to sea and away from Japan.

Our Christmas Eve storm was expressed well by this Typhoon Rule application, and this storm looks rather similar to the track the storm took in Japan preceding the Christmas Eve event. The only difference here is this time around, the low pressure system drifts out to sea instead of cutting up the eastern coast of Japan. This is a huge red flag, and tells us that this storm may very well go further south and east than current model guidance is suggesting. Given the success this predictor has had in the past few years I've used it, there is reason to believe this system could go further south and east. 

For now, I'll set my sights on this storm tracking to the south, more in line with what the GEM/GFS-Parallel are showing. The GFS model, in addition to being too far north, may be too quick with the storm, so other guidance appears to be good to use at this time. The combination of potential model error, as well as expected high pressure issues, in addition to the Typhoon Rule, is too much for me to put faith in the northern solution. The GEM snowfall prediction is shown below (this event's snowfall would be through the upper Ohio Valley into the Northeast).

Tropical Tidbits

To summarize:

- Model guidance is now confirming the possibility of a storm in the January 3-5 timeframe.
- A southward track is expected at this time, with snow hitting the upper Ohio Valley and Northeast.
- Substantial uncertainty still exists.

Andrew

January 3-5 Potential Winter Storm

It's looking like the next threat of a winter storm will arrive in time for the first few days of the New Year.

TwisterData

On December 31st, a strong trough is expected to drop into the West US and close off, as the circular 500mb geopotential height contours show above. This cyclone closing off in the West slowly drifts eastward, and that's the first thing we must watch for. A common model bias involves guidance closing off these troughs too quickly. For those located in the Plains and Midwest hoping for a snowstorm, you want this trough to close off quickly. A later close-off of the trough would result in a further south track, which might be in the cards of this is an instance of that model bias. For now, however, the trend has been to close off the energy earlier and earlier.

Tropical Tidbits

This image shows the projected 500mb vorticity values for January 3rd, the same type of chart as above. Off of the latest GFS model projection, we can see the energy now located in Indiana, taking on a negative tilt, as the contours seem to be "pushing" in a southeast-ward direction. When the system initially exits the Southwest, it will have a positive tilt. In order for those north of Kentucky to have a shot at a good snowstorm, this storm needs to attain a negative tilt rather quickly, as the GFS has done above.

Tropical Tidbits

The 500mb geopotential height anomaly chart off the ECMWF, valid for January 3rd, shows a similar situation as the GFS is predicting. We see our energy in southern Minnesota and northern Arkansas attaining a negative tilt. Although I don't have access to the smaller-interval charts from the ECMWF, it's not a stretch to assume this storm takes a similar path as the GFS model, as well as the Canadian GGEM model (not shown).

There are a few, rather significant items standing in the way of this being a 'likely' winter storm for the Midwest.

Tropical Tidbits

The image above shows the projection for 500mb geopotential height values (colored regions) and MSLP values (contour lines) for December 29th over the West Pacific. We see a low pressure system has formed on the southeastern coast of Japan, and is moving east-northeastward along the coast. As time progresses, this low will eventually shift out to sea and away from Japan.

Our Christmas Eve storm was expressed well by this Typhoon Rule application, and this storm looks rather similar to the track the storm took in Japan preceding the Christmas Eve event. The only difference here is this time around, the low pressure system drifts out to sea instead of cutting up the eastern coast of Japan. This is a huge red flag, and tells us that this storm may very well go further south and east than current model guidance is suggesting. Given the success this predictor has had in the past few years I've used it, there is reason to believe this system could go further south and east.

Tropical Tidbits

Also of concern is that massive Arctic high pressure system to the north in Canada, pressing southward into the United States. It is well known that model guidance has a bias to be too slow with the progression of Arctic high pressure systems southward. Applying this to our storm here, this means that model guidance might be forecasting this low pressure system to be too far north. Consequentially, this would result in the storm going further south and east.

When you shed all the more 'uncertain' parts to this forecast, you end up with a model consensus favoring a northward track, and the Typhoon Rule in favor of a southward track. Usually, I would go in favor of the Typhoon Rule and predict a further south track, but we have a strong streak of mid-level winds rounding the base of the trough on the latest GFS, which is a big signal for a storm to go negative-tilt, and in this case, go north. Add up all the model biases and predicted phasing of the subtropical & polar jet streams for this event, as well as a suspicious timeframe for the system in Japan, and there's too much uncertainty to decide on one particular track at this time.

To summarize:

- There is the potential for a winter storm to impact the Central and Eastern United States between January 3-5 (good confidence).
- There is too much uncertainty to tell whether this storm will hit the Midwest and Great Lakes, or stay south in the southern Ohio Valley.
- With good Arctic air already in place prior to this storm, accumulating snowfall is a good bet at this time.

Andrew