{ "number": 474, "headline": "December 28, 2024 Saturday Winter Weather", "standfirst": "Increasing risk for historic cold by January 8-11", "desk": "winter", "dateline": { "place": "Weather Trader", "state": null, "lat": null, "lon": null, "site_key": null, "site_name": null, "site_url": null, "accent": null }, "edition": "2024-12-28", "published": "2024-12-28T14:47:34.342000Z", "updated": null, "access": "free", "body_html": "
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Saturday Morning Update: Good morning!

8:45 AM ET Temperatures across the Lower 48

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Maine is holding onto the coldest temperatures across the Lower 48 this morning. Notably for me in Atlanta, the mountain cold-wedge remains in place with stubborn clouds and mist.

Temperature Anomaly | 8:45 AM ET

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Overall the Lower 48 is a whopping +13.1\u00b0F (above normal)

Saturday High Temperatures

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Into the 60s in the Ohio River Valley, also Nashville and Pittsburgh

Sunday Low Temperatures

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Very warm overnight across the East Central Lower 48.

Sunday High Temperatures

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Even warmer on Sunday with 60s pushing into Philadelphia. 70s into the Carolinas. 63 Million at/above 70\u00b0F for December 29 is quite a end of 2024 treat.

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Weather Headlines for Saturday

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ECMWF 00z precipitation type and MSLP next 7-days

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Heavy rain across South into the Ohio Valley from powerful storm system currently developing across Texas/Louisiana, which will track into Quebec by Monday.

Another area of Low Pressure tracks through the Plains into Ohio by next Wed/Thurs, and intensify over Quebec (again) with some snow on the backside in the much colder air.

The first polar front in a while arrives for Jan 2-3 for the Eastern U.S. as high pressure builds across the Midwest \u2014 and back in Canada setting the stage for the \u201cmain event\u201d the following week.

NWS | Total Precipitation Next 48-hours

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Large area of 2-inches+ rainfall from Louisiana into the Southeast including Atlanta and the Carolinas, and into the Mid-Atlantic.

2-day totals of precipitation in the 2\u201d to 4\u201d range across northern California into the Cascades where higher elevations will see enormous snowfall.

NWS | Total Snowfall Next 72-hours

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While the storm systems are relatively warm with Pacific moisture from subtropical origin atmospheric rivers, the air mass is cold enough at elevation to see many feet of snowfall.

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Total Precipitation next 7-Days | NOAA WPC

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Very wet pattern for Eastern U.S. for late December. Boatloads for Pacific Northwest.

ECMWF 00z Extreme Forecast Outcome

We need to talk about the updated ECMWF forecast from 00z through the next 2-weeks.

This is the \u201ccontrol run\u201d or unperturbed ensemble member, but it is only 1 solution out of 51. However, that doesn\u2019t mean it has a 2% likelihood of happening in reality. We need to look for agreement from the other ensemble members in a time window of 24-48 hours to account for spatial / temporal spread in the total ensemble.

However, the ensemble also provides valuable information about \u201ctail risks\u201d in the extended range. We can watch as the forecast date arrives if extreme solutions are becoming more/less likely. Suffice to say, this is a historical outcome that would not be pretty for the Southeast U.S.

A large cyclonic gyre encompasses eastern North America with the polar vortex anchored far to the south over Ontario. This is the \u201cwhole load\u201d and displacement of the typical TPV located over Hudson Bay or near Greenland.

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Height Anomaly is extreme with 540 dm heights into North Florida.

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And temperature anomaly of 45\u00b0F below normal for already cold January 10-11 across the Eastern U.S.

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Wind chill temperatures would be dangerous into South Florida.

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HOWEVER

And, this is where the valuable context comes into play. The median ensemble solution for the eastern U.S. is cold, but not historic. Instead, a low of 21\u00b0F would be rather seasonable in Atlanta.

But will the median outcome be the most likely forecast at Day 14? That\u2019s where more tools need to come into play with other models, cluster analysis, and expert analysis!

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EPS and GEFS Ensemble Mean 00z | Day 13

It seems the pattern shift to Arctic blast by January 8-11 is baked in the cake.

Over the next week, we must assess the risk of extreme outcomes.

15-Days Ensemble Median Snowfall

Interesting to see 0.1\u201d of snowfall showing up in North Georgia on the \u201cmedian\u201d accumulation map through 15-days. Significant Lake Effect + western Mountain snowpack building!

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75th Percentile Solution Through 15-days

This can be read as there is a 25% chance of at least 2\u201d of snowfall in Atlanta.

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Most Extreme Solution Through 15-days

Based upon the 00z ensembles (51-members) this would be most snowfall at any location with a 2% chance of happening [1-member] \u2026

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What does this mean? Even in the climate of January 2025 with \u201cglobal warmth\u201d we can still see 2\u201d of snowfall in Orlando assuming the most extreme upper-level \u201cpolar vortex\u201d displacement.

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Probability of 0.1\u201d+ Snowfall Next 15-days

Any snow over the next 15-days?

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Small chances into Florida \u2014 even 2% in Orlando. Better than 60% in Atlanta and the Carolinas.

ECMWF EPS 00z | 5-Day Chunk Temperature Anomaly

Days 1-5: December 28 - January 1

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Days 6-10: January 2 - January 6

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Very cold over Western Canada \u2014 poised to dump into the Lower 48 for 2nd week of January.

Days 11-15: January 7 - January 11

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Very significant cold anomaly across Eastern U.S. with [relative] warmth out west.

Snowfall Analysis | Season to Date October 1, 2024 \u2014 today

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Snowfall Last 7-Days

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Maps sourced from weathermodels.com designed and innovated by yours truly! Please subscribe there for real-time access to the newest maps, charts from all of the weather models including ECMWF.

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Saturday Morning Update: Good morning!

8:45 AM ET Temperatures across the Lower 48

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