GaWx

The 18Z GFS has a whopping 1060 mb surface high west of Hudson Bay at hour 138! Other runs and models have shown something similar for then. This kind of thing being repeatedly shown and it now being only 6 days out tells me that the pressure may not be overdone. For comparison, the record highest SLP for all of Canada in March is only 1 mb higher and that is way up in northern Nunavut! Also, the highest SLP on record for that area west of Hudson Bay is only ~1058 mb for all months, not just March. That alone is enough to tell me we're likely dealing with a very highly anomalous setup, which may lead to something historic for the US down the road in terms of cold and wintry weather. The map below has the all time record highest SLPs in Canada for all months. Note the 580 just N of NW Manitoba (1058 mb): https://www.wpc.ncep.noaa.gov/research/roth/SLPrecords.html

That's just an ordinary 1060 mb high at hour 138 of the 18Z GFS plunging down. Nothing to see here. Move along.

Not everybody wants the same thing. I try to leave my feelings out of these discussions as much as possible. For example, I don't want tornadoes anywhere near me, but don't complain if they're discussed. Discussing them doesn't make them occur and if anything it increases awareness of the danger. Anyway, the 12Z Euro was unreal but likely overdone as I said. Cold is often dry. Nothing unusual about that at all. Of course, that doesn't mean it will play out that way ultimately.

What Met1985 said. This is literally a wx forecasting discussion thread. Why wouldn't we discuss this stuff, especially with it being so different from almost the entire winter and potentially highly anomalous for mid March? It is what it is. Besides, this discussion may allow some people to prepare for the cold to mitigate potential damage.

The 12Z Euro has 850 temps down to -10 to -11 C in my area at 12Z on March 12th! Although it is likely overdone, that could very well be the coldest 850 so late in the season. I mean that's very cold for midwinter, much less March 12th.

Freezes are showing on the 12Z GFS for many inland areas March 10-12. That would be the first time for three in a row since very early February should they verify. Plus some areas get another on March 16th. Would at least feel like winter for a change. Also, great upslope snow potential is showing for the NC mountains at least. 12Z GEFS is the coldest run yet for March 9th-11th+.

I'm not believing the 12Z ICON's 1060 SLP just west of Hudson Bay at 144 (for 12Z on March 8th). That would beat the alltime high SLP record of ~1058 mb in that area for ANY month, much less just for March. It also would be near the 1061 March record for all of Canada, which is way up north in N Nunavut per this site: https://www.wpc.ncep.noaa.gov/research/roth/SLPrecords.html But the model consensus has been for very high SLPs (1050+) in that region for then, regardless of how high it will actually get. So, that will be interesting to follow.

We will see how long and strong the cold period will be, assuming it comes at all. The models have been cold biased for most of the last few winters due largely to under forecasted SE ridging. Maybe the cooldown will end up being weak and short per what wncsnow just posted. It will be mid-March by then after all. Nobody knows of course and that's the kind of speculation this thread is here for. Regardless of what ends up happening, I think it will be noteworthy in that there will at the very least be a major pattern change to sharply colder for an unknown period of time starting after the next week or so vs how it has been most of this winter to date due to the very weak SPV (see AO forecast info below). The model consensus is still calling for the longest period of chill by far since the last half of December. Regarding wintry precip, that is always a crapshoot in the SE, especially outside of the mountains, especially south of NC, and even moreso for all of the non-mountainous SE in mid March. Hopefully, some locations will luck out and get some of note with good upslope snow for the mountains at the very least with any luck. Meanwhile, the trend toward a stronger and longer -AO period during the first half of this month (likely due to the lagged effects of a very weak and displaced SPV) continues with today's 0Z update: 0Z GEFS based AO forecasts for March 6th: 2/26 run: -0.1 2/27 run: -0.5 2/28 run: -1.3 3/1 run: -1.5 3/2 run: -1.9 For March 10th: 2/28 run: 0.0 3/1 run: -0.9 3/2 run: -2.0 Also, the EPS has continued its downward trend of the AO since its 0Z 2/27 run.

The trend toward a stronger and longer -AO period during the first half of this month (likely due to the lagged effects of a very weak and displaced SPV) continues with today's 0Z update: 0Z GEFS based AO forecasts for March 6th: 2/26 run: -0.1 2/27 run: -0.5 2/28 run: -1.3 3/1 run: -1.5 3/2 run: -1.9 For March 10th: 2/28 run: 0.0 3/1 run: -0.9 3/2 run: -2.0 Also, the EPS has continued its downward trend of the AO since its 0Z 2/27 run.

The trend toward a stronger and longer -AO continues.

I think that the seemingly ever-present NW trend of storm tracks from run to run as well as an overall cold E US bias of models much past 5 days and especially out 10+ days is probably partially related to the warm Atlantic fighting back. But if so, why do the models not get adjusted in updates to take these biases into account after all of these years? Is sparse initialization data over the Atlantic the main issue keeping the models largely clueless?

I've read from pro mets that the SER is enhanced by the record warmth in the MC of the W Pacific in addition to it being enhanced during La Nina. But is the SER also made stronger by the AMO? The AMO has been about as high during the last few years as during any other period: https://psl.noaa.gov/data/correlation/amon.us.long.data If the high AMO, itself, is also a significant SER strengthening factor, I could see your idea being plausible. Could it be that the overall warm Atlantic (including GOM) from the equator to 70N (one definition of the AMO) is resisting and thus providing its own blocking (manifested by the persistent SER)?

Tropospheric NAM = AO 0Z GEFS based AO forecasts for March 6th show that the trend is downward: 2/26 run: -0.1 2/27 run: -0.5 2/28 run: -1.3 3/1 run: -1.5 For March 10th, yesterday's 0Z GEFS had 0. Today's had -0.9. The 12Z EPS has a stronger -AO through most of its run through March 14th and that continues its downward trend since the 0Z 2/27 run.

Tropospheric NAM = AO 0Z GEFS based AO forecasts for March 6th: trend is downward: 2/26 run: -0.1 2/27 run: -0.5 2/28 run: -1.3 3/1 run: -1.5 For March 10th, yesterday's 0Z GEFS had 0. Today's had -0.9. The 12Z EPS has a stronger -AO through most of its run through March 14th and that continues its trend since the 0Z 2/27 run.

1. The 12Z EPS held consistent with the prior colder E US trend and has a stronger PNA trend in the 11-15 vs prior runs. 2. The -AO continues to trend in the stronger direction on the EPS and other models out near day 10. I wouldn't be surprised if this continues. I suspect this is because of the very weak SPV. The 10 mb winds at 60N dipped all of the down to -19 m/s yesterday, indicative of a very weak strat. A strong -AO is a primary effect of a successfully down-welled weak strat onto the troposphere.

The -AO continues to trend in the stronger direction out near that time. I wouldn't be surprised if this continues. Could this be because of the very weak SPV? The 10 mb winds at 60N dipped all of the down to -19 m/s yesterday, indicative of a very weak strat. A strong -AO is a primary effect of a successfully down-welled weak strat onto the troposphere.

No worries. Indeed, that's how it is looking. But my point was about any assumption that the Arctic blocking, itself, would play out as was projected yesterday considering how the current blocking didn't even start to be recognized by the daily GEFS forecasts until within 10 days. The models have an extra challenge when the SPV is very weak. Look at today's GEFS mean vs yesterday's. Yesterday's had the AO on day 10 (3/10) near zero. Today's for 3/10 has it still down at -0.9.

The chances of the upcoming March NAO ending up sub -0.5 is pretty good considering how displaced/weak is the strat and how negative it is progged to be for the first 10 days. Since 1950, there have been 20 of these out of 73 (just over 1 in 4 chance). I did some calculations based on these 20 for RDU: 1. Temperature: 7 MB, 5 B, 7 N, 1 A (60% MB to B, 35% N, 5% A) AVG -2.8 2. Snow/IP (I didn't do ZR): - Measurable in 8 of 20 (40% of these vs 33% of all) - 4"+ in 3 of 20 (15% of these vs 10% of all)(all 3 cold) - Max 9.3" (1969) - Average: 1.2" vs longterm average for all of 1.1" (so not bad but not much difference from average considering the high percentage that were cold)

Today's NAO of -0.9 was the most negative day in February since February 28th of 2018, which was 16 days after the 2/12/2018 major SSW. As recently as just 11 days ago, the GEFS mean had today's NAO only down to zero with runs a couple of days earlier than that still positive for the last days of Feb. Also, it wasn't but 4 days ago that the GEFS had the AO stay positive through the entire run. The point is that the models were slow to see this blocking, which illustrates well the difficulty the models have with the troposphere starting by week 2 after an SSW vs the much easier to forecast strat out several weeks. Looking ahead: with today's renewed plunge of the 60N winds at 10 mb (to -18 or -19 m/s, which is significantly lower than the -13 m/s of the mid Feb major SSW) and thus a weak and extremely displaced SPV, folks shouldn't assume that the NAO, AO or anything else is anywhere near set in stone once looking ahead to week two, especially after day 10. Currently, the GEFS has on day 10 the NAO rise back to -0.4 and the AO rise back to 0. Will these actually verify?

A map that averages 51 members with 8 BN way out at hour 300 is a very strong BN signal and means a lot more than merely taking a day's climo average and subtracting 8 degrees. Thus, I think Michael Muccilli is looking at this the wrong way.

When an ensemble run's mean of dozens of members shows 8 BN for a period of a week or so, that implies that individual members for their respective coldest individual days will be much colder than 8 BN. There'd likely to be many cases of 20 or more BN on certain days for certain members.

The 12Z EPS is by a good margin the coldest run yet for much of the E US!

The 12Z EPS is by a good margin the coldest run yet for much of the E US!

The 12Z EPS is by a good margin the coldest run yet for much of the E US!

The correlation of a -NAO with BN SE temps is higher during March vs all other months: https://psl.noaa.gov/cgi-bin/data/correlation/corr.test1.pl?iregr=1&var=Air+Temperature&level=Surface&mon1=3&mon2=3&iy[1]=&iy[2]=&ilead=0&ilag=0&type=3&timefile=&customtitle=&labelc=Color&labels=Shaded&cint=&lowr=&highr=&scale=&switch=0&proj=USA&xlat1=&xlat2=&xlon1=&xlon2=&custproj=Cylindrical+Equidistant&level1=1000mb&level2=10mb&Submit=Create+Plot Edit: Also, the correlation to BN in the SE during March is higher for -AO and -NAO vs any other indices such as +PNA.