January 21-25 Potentially Significant Winter Storm

It's looking as if a winter storm will impact the United States between January 21st and January 25th. As of now, this storm has potential to be a strong one.

Tropical Tidbits

The above image shows mean sea level pressure (MSLP) and precipitation values for the morning of January 15th over the West Pacific. In this graphic, we see a strong low pressure system moving up the eastern coast of Japan, delivering heavy precipitation to areas offshore of the island nation. A look at 500mb vorticity values (not shown) depicts this storm phasing with another piece of energy to strengthen and mature the energy into a substantial event.

If we recall that the Typhoon Rule states weather phenomenon occurring in East Asia is replicated here in the United States about 6-10 days later, we should expect a storm system, possibly strong, to hit the US in a January 21-25 timeframe. The orientation of this storm striking the east coast of Japan tells me it may come up from the South US and hug the East Coast here in the US.

Interestingly enough, model guidance is approving of this theory.

Tropical Tidbits

The new GFS (the old GFS model was retired with this morning's 12z / 6AM central time runs, and replaced by what was known as the GFS-Parallel model) is showing a storm system developing in the Southeastern US on January 23rd. Here, we see a large swath of heavy rain, likely containing thunderstorms draped across the Gulf Coast into the Mid-Atlantic, as well as a heavy snow swath spread across the Ohio Valley and into the Northeast. This is something like I would expect to see happen with the way our energy acts when it skirts around Japan in the earlier graphic we analyzed.

Tropical Tidbits

By the evening of January 23rd, we find our storm has moved offshore, dragging an impressive liquid precipitation shield behind it, which then drags behind it a very cold airmass to introduce the anticipated cold blast to close out January. A strong snow swath remains present, but the most intense snow appears to strike Long Island in New York, as well as other coastal spots. Lighter, but still impressive snows then impact more inland regions.

To summarize:

- A storm is expected to impact the United States between January 21 and January 25.
- This storm has the potential to be strong, per current guidance.

Andrew

Long Range Outlook: Dynamic Pattern Unfolding into February

This is the Long Range Outlook, covering the period from mid-January (present day) to around the middle of February.

Tropical Tidbits

The above image shows 500mb geopotential height anomalies across the West Pacific, projected from the GFS ensembles and valid on January 13th. Notice the strong ridge forcing itself north to the west of Japan, likely bringing substantial warmth along with it. If we apply the Typhoon Rule to this situation, which states weather phenomenon occurring in Japan is reciprocated 6-10 days later in the United States, we should expect a period of warm weather commencing around January 15th to 17th, evidenced by a gradual warming trend unfolding in short range forecasts here at home. The Typhoon Rule supports such warmth lasting for about 3-5 days, before a storm system ushers in another wave of cool air. From here, we go to our impending cold blast.

Paul Roundy

A look at the hovmoller diagram above will help us diagnose the atmosphere. We see our current Madden-Julian Oscillation (MJO) wave moving eastward to the 180 degree longitude mark by around the 18th of January. From here, typical MJO phase space diagrams (not shown) show the index moving into territory too weak to identify the phase, but that's just because another MJO wave is forming out by the 50E longitude line, around January 21st. This positioning around the 50E line puts us in a Phase 1 MJO event, as seen below.

BOM

This chart shows typical alignment of outgoing longwave radiation (OLR) values by MJO phase in the west-central Equatorial Pacific. Notice that we see negative OLR anomalies (blue colors) in the hovmoller diagram around January 21st near that 50E longitude line, which matches up with Phase 1 (top-left panel) in this graphic immediately above. This, along with some Typhoon Rule support, should enable a sharp Arctic blast to round out January, possibly to begin February. I do have concern that this wintry return may be weaker than what is currently advertised, as stormy weather over Japan only lasts about 24 hours, if that. This should be a cold event lasting anywhere from 2-5 days for the USA.

As we move ahead into February, things get a little dicey.

JMA

We saw a notable stratospheric warming event strike to kick off the New Year, with temperatures at the 30hPa level only now settling back down to normal levels, as the graphic above displays. Let me please clarify: This was not a Sudden Stratospheric Warming (SSW) event. In order to deem an event a true SSW, wind direction in the stratosphere must either significantly slow or even reverse, in addition to intense warming of temperatures. We saw the latter, to some degree, while the former wasn't as prevalent as we needed. For this reason, it's referred to as just a notable warming event.

The concept right now is that this warming event will lead to more wintry weather about 2-4 weeks down the road from when the warming occurred, which brings us to that late January-early February period. With unfavorable indications from Japan, though, I worry that the cold (while intense) may not stick around for long. In order for that to happen, we may need another warming event, ideally a true SSW. However, even that prospect is quickly fading, as we see a strengthening of the upper polar vortex in coming days and weeks.

Let's dive into February a bit deeper.

Kyle MacRitchie

The above image once again shows forecasted outgoing longwave radiation (OLR) anomalies, but now forecasted well out into the spring. Due to such low confidence, we're only going to look at the long range OLR forecast as an indicator of what may come, not necessarily as something that's "set in stone". Notice how we see our ongoing MJO wave fading near the 21st of January with the dissipation of negative OLR anomalies, as well as our second wave forming well off to the west. As the Paul Roundy hovmoller showed, this second wave slowly shifts east as we move into February, but then note what this forecast predicts in the middle and late stages of February. We see the MJO stalling out around the 160E longitude mark. Going back to our MJO OLR composite image earlier in this post, we see this correlating to Phase 6, also known as the warm weather phase. Here's a graphic displaying a Phase 6 MJO event in February, to give you an idea of what we could see if this forecast verified.

Meteonetwork

We see a strong ridge unfolding across the East US into the Ohio Valley and Great Lakes during this February Phase 6 MJO event, with stormy weather impacting the Pacific Northwest. Ridging is shunted south and east across the Northeast Pacific, into the Southwest US. This should be particularly concerning for winter weather fans in the East, because this set-up does have additional support. Model guidance is expecting the atmosphere as a whole to dive into a La Nina-esque pattern, which is shown like the image below.

NOAA

During a typical La Nina pattern, we tend to see strong high pressure across the Gulf of Alaska, before the jet stream buckles south and delivers cold weather into the North Plains and Northwest. Ridging then is provoked in the East US (the reason why cold weather fans in the East see La Nina's in their nightmares). This, of course, is not a perfect correlation, but you can make key connections between the typical La Nina environment, as well as the projected Phase 6 MJO event in February. This would not bode well for a cold and stormy end to winter for most east of the Rockies, unfortunately.

On a side note, many have asked why I am using the MJO in my forecasts, since we are currently in the pro-warmth Phase 6, but cold weather is prevailing. I continue to use the MJO because it usually provides a good idea as to where we are going in the future. The MJO's effects were being overruled by a very strong ridge along the West Coast; remember that the MJO is not the sole player in this atmosphere, and that's being exhibited well. We are currently seeing warmth return to the US as that ridge breaks down in accordance with the warm MJO phase.

Even when the MJO seemed to be failing, it still managed to reflect itself well in the atmosphere. Shown below is a side-by-side comparison of the last few days of January 500mb geopotential height anomalies (left), as well as typical 500mb height anomalies during a January Phase 6 MJO event, in an ENSO atmosphere reflective of this one. The comparison isn't perfect, by any means, but it's there.

ESRL and Meteonetwork

To summarize:

- Warmer than normal weather is expected around a January 15-23rd period.
- A storm system may impact the country around January 21-25.
- Cooler than normal weather is expected in the final days of January, possibly into February.
- There is increasing potential for a warming trend in the middle of February back to above-normal temperatures.

Andrew

Model Discussion - January 10, 2015

ESRL

ESRL Ensemble Guidance Analysis
Prepared January 10 2015

Short-Medium Range (00hr to 144hr)

Guidance retracts strong upper level low from South Canada into Greenland, a textbook signal of the North Atlantic Oscillation (NAO) active in its positive phase. This is seen well in sustained ridging across much of the country, primarily the northern half, in most of the period. Positively tilted shortwave drops into the Southwest and slowly exits into the Southern Plains under the ridge, permitting for a southern track. This may allow for precipitation development in the mid-section of the country, though exact placement and precipitation type is in question. Have a good feeling wintry precipitation will not be favored due to generally seasonal temperatures in the aforementioned North US, where ridging will be present. Regardless of storm evolution, overall warm temperature pattern is favored.

Long Range (144hr to 360hr)

Strong ridge cell then evolves in the West US and shifts east with the departure of the aforementioned trough along the East Coast. Ridge continues pushing east and amplifies in the Central US with the assistance of a longwave trough pattern moving into the Pacific Northwest, allowing for above-normal warmth in much of the land east of the Rockies. As this ridge slowly departs into the Canadian Maritimes, troughing pattern in the Gulf of Alaska is decimated and replaced by a ridge, forming a connection to the other ridge in the Maritimes. Intensification of the ridge along the West Coast of North America permits the evolution of the active Pacific North American (PNA) index in its positive phase, likely reflected later in the period as a negative East Pacific Oscillation (EPO) signal. Aforementioned ridge that moves east of the Canadian Maritimes has some ensemble support to form an east-based negative North Atlantic Oscillation (NAO) signal, agitating a much more wintry pattern to end January compared to that in the short term. Some indication of subtropical jet stream amplification is evident, though uncertainty is too high to evaluate such a potential at this time.

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