When will we see more Arctic Cold?

[donsutherland1]

Although, the extended range forecasts from the 1/26 0z GFS ensembles and 1/26 12z and 18z runs of the operational GFS did not really resemble the classic pattern associated with cases in February when the Arctic Oscillation (AO) was -3.000 or lower, the 1/26 0z Reforecast Ensembles were much closer to the classic pattern.

First, it should be noted that the latest ensemble guidance shows increasing support for the AO’s falling to and below -3.000 beginning around February 8:



The composite 500 mb height anomalies associated with all days in February (1950-2009) on which the AO was -3.000 or below was:



The following shows hours evolution of the 500 mb height anomalies forecast for hours 312 through 360 on the 1/26 0z run of the Reforecast Ensembles:



In short, the forecast height anomalies are trending toward the classic pattern one would expect to see with an AO of -3.000 or below. More importantly, one sees the NAO transitioning toward a strong Greenland block even as a negative EPO is developing. Such a dual blocking regime, if it becomes established, could allow for at least one outbreak of severe cold. Such a cold outbreak would have the potential to bring a new freeze to parts of Florida and readings into the 20s in southeast Texas and perhaps even upper 30s in south Texas.

In general, such a pattern is colder than normal. Data for select cities follows:



With a colder pattern getting into place coupled with an active subtropical jet, there will be opportunities for snow. Since 1950, 10/14 (71%) of February Kocin-Uccellini snowstorms (snowstorms of the kind featured in their seminal work Northeast Snowstorms) occurred with a negative AO. Six of those ten storms occurred with the AO at -1.000 or below.

At present, two storm possibilities are shown on the Reforecast Ensembles around hour 216 and hour 360:

Hour 216:


Hour 360:


In sum, the pattern is evolving consistent with the idea that February will likely wind up colder and snowier than normal in the East, wetter than normal on the West Coast, Southwest, and in the Gulf States. The Reforecast Ensembles currently provide the closest match to what one would expect with a severely negative AO in February. It will be interesting to see how the pattern evolves in the coming days.

[srainhoutx]

Although, the extended range forecasts from the 1/26 0z GFS ensembles and 1/26 12z and 18z runs of the operational GFS did not really resemble the classic pattern associated with cases in February when the Arctic Oscillation (AO) was -3.000 or lower, the 1/26 0z Reforecast Ensembles were much closer to the classic pattern.

First, it should be noted that the latest ensemble guidance shows increasing support for the AO’s falling to and below -3.000 beginning around February 8:



The composite 500 mb height anomalies associated with all days in February (1950-2009) on which the AO was -3.000 or below was:



The following shows hours evolution of the 500 mb height anomalies forecast for hours 312 through 360 on the 1/26 0z run of the Reforecast Ensembles:



In short, the forecast height anomalies are trending toward the classic pattern one would expect to see with an AO of -3.000 or below. More importantly, one sees the NAO transitioning toward a strong Greenland block even as a negative EPO is developing. Such a dual blocking regime, if it becomes established, could allow for at least one outbreak of severe cold. Such a cold outbreak would have the potential to bring a new freeze to parts of Florida and readings into the 20s in southeast Texas and perhaps even upper 30s in south Texas.

In general, such a pattern is colder than normal. Data for select cities follows:



With a colder pattern getting into place coupled with an active subtropical jet, there will be opportunities for snow. Since 1950, 10/14 (71%) of February Kocin-Uccellini snowstorms (snowstorms of the kind featured in their seminal work Northeast Snowstorms) occurred with a negative AO. Six of those ten storms occurred with the AO at -1.000 or below.

At present, two storm possibilities are shown on the Reforecast Ensembles around hour 216 and hour 360:

Hour 216:


Hour 360:


In sum, the pattern is evolving consistent with the idea that February will likely wind up colder and snowier than normal in the East, wetter than normal on the West Coast, Southwest, and in the Gulf States. The Reforecast Ensembles currently provide the closest match to what one would expect with a severely negative AO in February. It will be interesting to see how the pattern evolves in the coming days.

Thanks Don. Your input is very valuable and we thank you for taking time out of your busy schedule to post. We look forward to further updates in the days ahead.

[Portastorm]

Absolutely! It is good to see you again this far west

Thank you so much Don for your post. Looks like February could be quite a month for many of us.

[xironman]

Thanks Don for posting! It is a great opportunity to for us to learn. Hope remains alive for February. This current cold snap seems to be really effecting the MA and it looks like the SE will get some good snows this weekend.

[srainhoutx]

While everyone is watching the current storm unfold, I'm going to bump this up concerning "Longer Range Forecasts" for February...

[donsutherland1]

A very quick update...

1. Parts of the southern Plains across to southern VA and northern NC will enjoy a big snowfall, which has been well-modeled. Farther east, any northward shift in the models should be small given the strength of the polar vortex.

2. There is growing ensemble support that the Arctic Oscillation could crash to severely negative levels after the first week in February.

3. Given the above, I suspect that any events in the February 4-7 timeframe will probably present an opportunity for a widespread snowfall in the Mid-Atlantic and southern New England regions. Suppression may be somewhat more of a concern than their tracking inland. Already, the GFS has slowly shifted the storm track for an event forecast for that timeframe to the east.

4. In the extended range, the Reforecast Ensembles are still leading the way with a classic look for strong blocking. The 1/28 0z GFS ensembles have taken an important step in that direction.

5. On or around February 10, the EPO could be negative or trending negative. Hence, the guidance is slowly putting the pieces together for a generally cold February in the eastern third to half of the USA, along with southern Ontario and southern Quebec.

[cycloneye]

Good to see you back Don with your always comprehensive analysis of all the factors.

[srainhoutx]

Thanks Don. Just had a chance to look at the 00Z GFS ensembles. For those of us in the Southern Plains regions, thing do look interesting and may offer more chances for a colder regime during February. The STJ looks to remain active as well.

[srainhoutx]

Don, I as well as other members have been watching the data showing a SSW (Sudden Stratospheric Warming) MMW (Mid-winter Major Warming) event. What are your thoughts regarding the February 10-13th time frame for areas E of the Rockies? Thanks for posting and we look forward to your thoughts.

[Stephanie]

Great to see you don!

The Mid Atlantic has seen a nice thaw - looks like we're going to be smacked back into Winter's Reality.

[Ptarmigan]

Well written as usual Don! February looks to be interesting.

[srainhoutx]

Several things to watch for regarding mid February. We have a SSW (Sudden Stratospheric Warming) MMW (Major Mid-winter Warming in the troposphere as well as a switch in wind flow that translates cold air downward) as well as a tanking –AO (-3.000+) as well as a –PNA. There are signals that a –EPO and a slightly +PNA will occur. MJO is entering phase 8. While this all may sound like a bunch of weather nut jargon, these are in fact strong indications of a major pattern change back to a very cold regime for the eastern 2/3 of the CONUS. Operational guidance is playing catch up with the pattern shift. It may take 5-7 days before we see the OP guidance latch on to the upcoming change. The STJ is going to be rather active and we see this in guidance next week. A very potent storm looks to affect the area around Wednesday/Thursday of next week. A time frame to watch for in the longer range is around the 12th-15th of February. Although the cold will not be as severe as we saw in early January, it does appear that a 1050+ mb high will slide across the North Pole into N America. A cross polar flow will likely occur as well. If the ensembles are correct, we could see a rather chilly/stormy period from mid February until the end of the month. Could this forecast be incorrect? Most certainly! Weather is a very humbling hobby/profession, but the signals are rather strong to just ignore for those that watch longer range forecasts. Discuss away and throw me under the bus…

[donsutherland1]

Thanks Stephanie.

[donsutherland1]

Today, the AO had fallen to -2.250. The ensemble forecast is very bullish on the AO's falling to -3.000 or below.



Two ensemble members bring the AO to historic negative readings for February (-5.000 or below). Since 1950, there have been just two years (6 days) on which the AO was -5.000 or below in February:

2/13/1969 -5.282
2/14/1969 -5.074
2/15/1969 -5.102
2/16/1969 -5.064
2/5/1978 -5.291 (monthly record)
2/6/1978 -5.026

Composite temperature anomalies for the AO are as follows:

-3.000 or below in February (1950-2009):


-5.000 or below in February (1950-2009):


For purposes of comparison, here are the temperature anomalies being forecast on 2/7 when the AO is around its lowest point:

Reforecast ensembles:


GFS ensembles:


Finally, for purposes of comparison, the following are some charts for New York City for February when the AO was -3.000 or below, -2.999 to -0.001, and 0 or above:



All said, the reforecast ensemble guidance has a much better fit with the composite anomalies for extremely negative AO cases. As a result, I believe the February 5-11 period will likely prove colder than normal in the Mid-Atlantic and New England regions rather than warmer than normal as suggested by the GFS ensembles. Prior to that or in the early stages of the period, I suspect that the storm shown on the GFS for the 2/4-7 timeframe will either be suppressed or bring accumulating snow to a large portion of the Mid-Atlantic and New England states rather than its cutting inland or bringing all rain.

[srainhoutx]

Thanks for the update Don! I see the overnight OP runs have come around and blocking looks very strong. -AO continues to decline and +PNA is now suggested out W. Appears the colder regime is on track and will begin the treck across the NP in early February. We look forward to your thoughts as well as others.

[jinftl]

I would imagine that sustained and prolonged outbreaks of arctic cold at levels that would rival the coldest temps seen in a given winter at any one location do start to become less likely of taking place as we progress through February. After mid-month, average temps really start to climb across the U.S., along with the length of day and sun angle.

While epic snowstorms are certainly possible into March (with large temp swings that could bring a few very cold days into the South), prolonged arctic invasions have only about 2 to 3 weeks left to take place in my opinion across all but the northernmost regions of the lower 48.

Case in point, take a look at the avg high/low temps for the following dates in February at these locations:

Philadelphia
2/1 = 39/25
2/14 = 42/27
2/28 = 46/30

Chicago
2/1 = 31/16
2/14 = 34/19
2/28 = 39/23

Houston
2/1 = 64/42
2/14 = 66/44
2/28 = 70/47

[vbhoutex]

No argument whatsoever with your post Jinftl. February is normally our snowiest month as well as being the time we usually have our last chance at a really big shot of arctic air(not that it can't happen later, because we have had some cold shots in March to take us below freezing), which I would presume would have to be Arctic in origin. But normally, we are through with freezing weather of any magnitude by late Feb. or at the latest early Mar. here in Houston. IIRC, and that does get fuzzy sometimes, we have seen a few times to freezing in April over the last 38 years I have been in Houston, but I think it is like 2 times.
Still watching the current pattern and how it is evolving. One more strong shot of Arctic air to our area is, imo, probable within the next 2 weeks. With the continued active Southern jet we can only hope for a "February surprise" precipitation wise. BTW, the low this am was 30.3ºf at my house in W. Houston.

[srainhoutx]

CPC Super Ensemble Output this morning suggests an interesting pattern ahead with at last 4 storm threats in the +8 day time frame and very strong blocking...notice some of the analogs as well...

[srainhoutx]

After a chilly weekend in Houston wth 20 degree+ departures from climo, the January Thaw is quickly becoming a memory. While we head into a transition period toward a pattern change, we will likely see a very active STJ and split zonal flow keeping the coldest air to the N in Alaska, Northern Canada and points across the North Pole. Our neighbors to the east look to have a very strong winter storm next weekend. -AO continues a rapid decline (-3.156 today). The ensemble data suggest a -AO nearing the -5 range during the mid February time frame. A -NAO is also suggested via the ensembles as well as a +PNA. CPC updated graphics do show we are heading to a below average in temps and above average in moisture as MJO enters phase 8. Operational models are beginning to latch on to the pattern change as well. We shall see what lies ahead, but trends look for much 'cooler/stormier' weather near Valentines Day and beyond for TX as well as SE TX IMHO.

http://www.cpc.noaa.gov/

[vbhoutex]

CPC Super Ensemble Output this morning suggests an interesting pattern ahead with at last 4 storm threats in the +8 day time frame and very strong blocking...notice some of the analogs as well...

That 2/12/73 analog is the one that caught most of my eye!!