GaWx

I’ve been thinking “prime time” winter storm opportunities in the SE wouldn’t likely start til ~2/18-19 but with colder dominating starting ~2/15.

For the SE, the last few days of the 12Z GFS don’t look good at 500 mb for sustained cold air. Too zonal imo. And then up at Chicago and MSP, the coldest was an AN mid 20s. Most of the recent runs looked better to me. It doesn’t matter much because it is just the low accuracy late GFS and the 12Z GEFS looks better at H5 and is similar to recent GEFS.

And now the OHC is down to only ~+0.10:

The late portion of the 12Z GFS was ugly. No two ways about it. Hopefully it will turn out to just be an outlier. Let’s see what the more credible late GEFS shows.

I don’t see a delay based on the consensus. It appears to me that the 3 major ensembles are still suggesting ~Feb 15 for a cold front generated by a Canadian high to first reach the SE. The strong increase in a +PNA still starts ~Feb 13. Now regarding the potential for significant nonmountain wintry precip, that has generally been targeting on the extended models for quite some time ~Feb 18-19 for the first decent chance per following individual ensemble member tracks. Anyone can look back at my posts on this timing in this thread. The more difficult challenge imo will be to see whether or not the predicted cold will be accompanied by precip or else be dry. That’s often a challenge as Arctic air is by its nature dry. My hope is though that an El Nino induced split flow will set up the SE for a nice winter storm. But getting the right combo of features and the right timing is always a challenge. That’s why it often takes only one major storm to make for an AN snow season.

0Z GFS and 6Z GFS (image below) have what is very likely a split major SSW by Feb 16-7. **Edit: 0Z GFS gets down to +6 at the end...so not quite a reversal.** Unlike the reversal of Jan 17, this warming would be the more typical near simultaneous and would be right on the anniversary of the one from last winter. Unlike the simultaneous one from last winter, this one wouldn’t have a strong -PNA to fight and would already have a -AO and possibly also a -NAO. Perhaps this is related to the 1/17/24 reversal. This wasn’t even hinted at until @mitchnickalerted us on Jan 23 as a stronger than climo SPV had been forecasted for most of Feb. The implications for especially the E US during very late Feb and especially Mar would be interesting:

I agree that the week centered on Jan 3 would be +2.1, not +1.9, if it were to match up with this cyclonicwx. Also, the week centered on Jan 24 would be +1.6, not +1.7. I don’t know why they don’t always match up. Good finding on your part, regardless.

Keep in mind that these CANSIPS maps are based on the somewhat colder 1981-2010 climo vs the 1991-2020 climo that you used in your Feb composite map. So, CANSIPS anomalies would be a bit colder if they had used 1991-2020. OTOH, CANSIPS may tend to be a little colder than other seasonals. Regardless, this new run is colder for Feb and Mar in the SE US than last month’s run and colder in much of the E US in Mar.

Brand new CANSIPS for Feb: colder than prior run in SE (as is also the case for Mar): keep in mind that this is based on the colder 1981-2010 climo (vs the warmer 1991-2020). It not surprisingly has a mild ridgy Dec/Jan next winter with La Niña. So, enjoy El Niño while you can!

Do you have predictions for the second half of Feb (say, Feb 15-29) in Asheville with regard to both temperature anomaly and snowfall? If so, what are they?

Wrong. The 12Z EPS 360 (last map of the run) is colder in the SE than the 12Z GEFS 360 and the 18Z GEFS 354 at both 2 meters and 850 mb. Check them out at Tropical Tidbits.

The 12Z UKMET is further S than other models and the strongest by far with the upcoming storm. It is so strong that the text output classifies it as a tropical cyclone out in the Gulf despite it having no real tropical characteristics. Dewpoints are too low, SSTs are only in the low to mid 70s (see image below), and it is under a strong upper low. But maps do suggest a slight low level warm/wet core vs its surroundings: https://www.pivotalweather.com/model.php?m=ukmet&p=sfctd_b-imp&rh=2024013112&fh=108&r=conus&dpdt=&mc= On Sun evening the run has it max out with sustained winds at 59 knots/68 mph along with a SLP way down at 978 mb/28.85”. It looks to me like this UKMET run is likely on crack: MET OFFICE TROPICAL CYCLONE GUIDANCE FOR NORTH-EAST PACIFIC AND ATLANTIC GLOBAL MODEL DATA TIME 1200UTC 31.01.2024 NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 96 HOURS FORECAST POSITION AT T+ 96 : 26.9N 88.1W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 04.02.2024 96 26.9N 88.1W 993 44 0000UTC 05.02.2024 108 28.3N 84.7W 978 59 1200UTC 05.02.2024 120 29.1N 82.6W 981 44 0000UTC 06.02.2024 132 28.6N 81.5W 990 40 1200UTC 06.02.2024 144 CEASED TRACKING

Consistent

That last (“at the buzzer” ) warm burst for all anyone knows MIGHT be enough to barely attain a +2.00 for the unrounded NDJ ONI, but it could still go either way. (Rounded +2.0 NDJ in the table remains a near certainty.) A lot for the unrounded is riding on the relationship this month between OISST and ERSST. The Aug-Dec ERSST anomaly averaged 0.08 warmer than OISST. Before anyone asks, whether or not the unrounded turns out to be +2.00+ will have no impact on Feb wx prospects. This is just for fun, documentation, bragging rights, and the contest.

The ensemble means remain in agreement on the major pattern change at H5 to start ~Feb 13, when the +PNA first rapidly intensifies and which is consistent with what the extended models started showing over 3 weeks ago. So, as we see it getting closer with little or no can kicking, confidence increases. Within a few days, the SE gets cold on the models. For example from the 12Z GEFS: how often do SE 850s this cold show on day 16 of the GEFS? Now note on the 12Z GEFS map below the green area well to our WSW. That represents the El Niño supported moist subtropical jet. Combined with the cold transporting +PNA (cold aided by -AO/-NAO), we’d have a classic split flow, which is the most favorable pattern to induce the possibility of a GOM Miller A based major SE winter storm. Extended models have been suggesting the first enhanced chance for one of these ~Feb 18-19 based on examining the last few days of runs’ individual members’ SLPs. That green area is moving generally toward the E during the last frames. So, it’s possible that it would get to the SE then and allow the moist flow to overrun the SE cold. WSW to SW H5 flow over the SE is usually needed for a big widespread storm. We can get that kind of flow from that ST jet, which has WSW H5 flow, moving E. But the +PNA can’t be too overpowering or else H5 flow might remain W or WNW over the SE and thus be dry. And the cold can’t modify too much once the moist flow arrives or it could be too warm. Always the delicate balance/timing. But at least there’s an opportunity being strongly hinted during favorable Nino climo of mid to late Feb.

YW. I could see it (if it occurs) possibly helping to allow this pattern change to maintain itself for a longer period into March. I don't have any feel for the idea of a more extreme change due to this. For mid-Feb I'd say no because of the lag. Could it intensify in late Feb/early March because of it? I suppose that's possible but I'd think it would be hard to prove.

Fwiw, the 12Z GFS like the 6Z GFS, has at the very least close to a major SSW/10 mb wind reversal on Feb 16. Trends on the ensembles the last 5 days have markedly started trending in that direction after showing virtually no chance as recently as just 5 days ago. The ensembles have a history over the years of not even starting to see these all that well until just over two weeks out, which is similar to the the last few days of trends. Also, if there were to be an actual mid-Feb major SSW, the wind reversal date may creep forward a couple of days to say, ~Feb 14. If there were to be one, the typical response in the troposphere would start ~1-3 weeks afterward. However, the ensemble means are/have been suggesting independent of any mid-Feb SSW a major pattern change at 500 mb to start ~Feb 13 and likely continue for at least a couple of weeks. So, it might be difficult to discern any effects from a mid-Feb SSW.

End of 6Z GEFS (for Feb 16) is setting up for potential SE wintry mischief (say, for ~Feb 18) with a split flow getting established and similar to what the extended models had been hinting at.

The Jan 2024 SOI ended up at +3.96, easily the 2nd most +SOI Jan of 19 strong+ Ninos and not too far behind Jan of 1931’s +6.4: https://data.longpaddock.qld.gov.au/SeasonalClimateOutlook/SouthernOscillationIndex/SOIDataFiles/MonthlySOIPhase1887-1989Base.txt Keep in mind the La Niña-like extreme cold pattern of midmonth (coldest in Plains/upper MW and then with much less intensity anomalywise SE)

This end of the Jan 31 6Z GFS is close to a major SSW on the anniversary of the one of last winter, Feb 16:

I’ve also been wondering about that fly in the ointment the last few days despite a still good looking pattern at H5. Also, the CFS ensemble means have been trending warmer for March while trending colder for Feb. We’ll see!

The long awaited (for ~3 weeks) and hoped for major pattern change of mid Feb seems to be more or less on track at the end of the regular ensemble runs now. Here’s the nice split flow at the end of the 12Z GEFS/El Nino says hello: The extended models have been hinting at Feb 18-19 as the first period for an enhanced chance for a SE Miller A/GOM winter storm. We’ll see. The end of the regular runs is still too far out to be considered anything close to trustworthy territory but it’s a nice baby step.

Look at how much the WCS daily PDO has risen recently. It was up to -0.20 as of Jan 27: Edit up to -0.17 on Jan 28

But this is already happening. It says this is a 2023 upgrade. The 100 ensemble members already run to day 46 every day on the 0Z run rather than the old twice per week runs.