{ "number": 469, "headline": "December 23, 2024 Monday Winter Weather", "standfirst": "Clipper system in Great Lakes and Northeast into Tuesday", "desk": "winter", "dateline": { "place": "Weather Trader", "state": null, "lat": null, "lon": null, "site_key": null, "site_name": null, "site_url": null, "accent": null }, "edition": "2024-12-23", "published": "2024-12-23T14:23:48.094000Z", "updated": null, "access": "free", "body_html": "
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Quick note: ECMWF has a new A.I. ensemble system called AIFS-CRPS with impressive skill that exceeds the current physics based IFS (EPS) system. Soon, data will be provided from the 0.25\u00b0 resolution model \u2014 and hopefully the weights to reproduce the forecasts, and generate our own. This will be a game changer. ECMWF has been running an experimental, low-resolution (~1.0\u00b0) AIFS ensemble, and even that system has shown remarkable skill. The new AIFS-CRPS will be a step upgrade.

AIFS-CRPS [pre-print]

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For the usefulness of a weather forecast it is important to account for forecast uncertainties. Ensemble forecasts are run to estimate the probability density of the atmospheric state at a future time [Lewis, 2005, Leutbecher and Palmer, 2008]. In physics-based numerical weather prediction (NWP), this is achieved via running the forecast model from a range of perturbed initial conditions and by introducing stochastic perturbations into the forecast model itself. The aim is to generate a well calibrated ensemble. This means that on average, the ensemble standard deviation needs to match the root-mean square error of the ensemble mean (e.g., Fortin et al. [2014]), and the predicted probability of an event should accurately reflect the observed probability of it occurring.

Good morning! Monday starting off very cold across the Mid-Atlantic and Northeast.

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Temperatures well below zero in the interior of New York and New England.

This is more than 30\u00b0F below normal for December 23.

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Calm conditions under strong high pressure (1036 mb) allows significant radiational cooling especially over snow-covered ground. Temperatures crashed and will only recover into the 20s later on Monday.

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Weather on Monday

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Yet another Clipper system across the Great Lakes into the Northeast on Tuesday.

Weather through Midnight | HRRR simulated radar

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NWS expects 3-6\u201d of snow across Michigan on a diagonal line from Manistee to Port Huron. However, as the Clipper moves east overnight into New England, the snowfall will weaken to lighter accumulations \u2014 but YES we will still see snowfall Tuesday morning in New York City for sunrise. It will be beautiful for Christmas Eve!

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At about 10 AM, HRRR has a light band of snowfall from Boston to NYC to Philadelphia! An inch or so in an hour of moderate snowfall should be expected.

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Will this Clipper system outperform like last week? HRRR model snowfall does have > 1\u201d across NYC.

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ECMWF Precipitation Type and MSLP Next 6-days

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Gulf of Mexico moisture streams northward up the Mississippi River valley over the next several days leading to heavy rainfall accumulations \u2014 maybe upwards of 4-6\u201d.

The West Coast continues to be hammered by atmospheric rivers.

Much warmer air will sweep across the Midwest and Great Lakes after Christmas, so any precipitation would be rain.

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Looking ahead into 2025 for the Pattern Flip

Quite an enticing pattern for winter storm wish-casters across the Eastern U.S. with a large trough sitting over a large area in the ensemble mean \u2014> first week of January.

Much colder Canadian Arctic air will finally replace the much above average warmth across western Canada and the Lower 48 into January 1-2, 2025.

So, we have 8-days or so of above average warmth to end 2024.

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Monday High Temperatures

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More than 57 million will fail to get above freezing especially across the Northeast on Monday. Widespread 50s across the Rocky Mountain west!

Tuesday Morning Temperatures | Christmas Eve

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Still very cold across New England in the teens! Temperatures will finally warm up during the day to above freezing, barely!

Tuesday High Temperatures

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Wednesday High Temperatures | Christmas Day

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Seasonably chilly in the low-30s across the Great Lakes and Northeast for Christmas Day. In the upper-50s to lower 60s from Nashville, Atlanta, down to Macon.

8:30 AM ET Temperatures across the Lower 48

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More than 186 million now below freezing this morning.

Temperature Anomaly | 8:30 AM ET

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Overall the Lower 48 is still 5.4\u00b0F (above normal) with warmth west of the Mississippi crushing the extreme cold centered upon NYC.

Total Precipitation next 7-Days | NOAA WPC

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WPC now showing area of 4-6\u201d centered over Texarkana and large area of 2-inches to 4-inches centered on Little Rock.

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NWS WPC with large areas of 12-18\u201d of rainfall along the NorCal coast up into Washington. And, that could be conservative!

10-day Ensemble Median Snowfall

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Sadly, not expecting any major snow threats after the Clipper exits into the Atlantic on Tuesday. The Western U.S. does cool down so more widespread snowfall at lower elevations. Regardless, the atmospheric rivers will dump 8-feet or more in the Cascades.

Probability of 3\u201d+ Snowfall Next 10-days

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Looking for a major storm with 3\u201d of snowfall threshold \u2014 and nothing else on the radar. The huge hole in Canada exemplifies the extreme warmth in Alberta and Saskatchewan \u2014 relative to normal \u2014 of course. It\u2019s still not shorts and t-shirt weather!

ECMWF EPS 00z | 5-Day Chunk Temperature Anomaly

Days 1-5: December 23 - December 27

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The cold overnight lows across the Northeast = strong 5-day average cold signal.

Days 6-10: December 28 - January 1

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Coast to coast well-above normal warmth with > 30\u00b0F anomaly over Canada.

Days 11-15: January 2 - January 6

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The coldest anomaly in the Day 11-15 period centered on Florida!

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

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Snowfall Month-to-Date | December 2024

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Not too bad for December! We\u2019ll look back and see these maps \u2014 and say, wow, that was a snowy month in 2024.

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.

", "body_key": null, "teaser_html": "

Quick note: ECMWF has a new A.I. ensemble system called AIFS-CRPS with impressive skill that exceeds the current physics based IFS (EPS) system. Soon, data will be provided from the 0.25\u00b0 resolution model \u2014 and hopefully the weights to reproduce the forecasts, and generate our own. This will be a game changer. ECMWF has been running an experimental, low-resolution (~1.0\u00b0) AIFS ensemble, and even that system has shown remarkable skill. The new AIFS-CRPS will be a step upgrade.

AIFS-CRPS [pre-print]

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