{ "number": 167, "headline": "December 28, 2023 Thursday update", "standfirst": "Quiet weather continues again across Lower 48 but cooling is on the way", "desk": "notebook", "dateline": { "place": "Weather Trader", "state": null, "lat": null, "lon": null, "site_key": null, "site_name": null, "site_url": null, "accent": null }, "edition": "2023-12-28", "published": "2023-12-28T22:02:55.765000Z", "updated": null, "access": "free", "body_html": "

Thursday afternoon temperatures were not too bad across the Lower 48 especially in the sunshine. 50s and 60s in the Southeast. Only about 5 million people were below freezing mark.

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A quiet weather pattern over the next 10-days looks likely across much of the Lower 48 except for weak Clipper systems across the Great Lakes and the West Coast storm this weekend. Heading into the following weekend (January 6-7) would be a chance at a East Coast system. There is some ensemble support for a Nor\u2019easter, and there should be more cold air available (finally).

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Friday Low Temperatures | December 29, 2023

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Lower 48 average low temperature has slipped again to 29\u00b0F with almost 100 Million population at/below freezing (< 1/3 of U.S. population). More area (67%) of the Lower 48 below freezing, so continues to be a good example of why you should always population or energy weight for impacts.

Friday High Temperatures

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Florida and the Southeast is again the \u201ccoolest\u201d relative to climatology with temperatures more than 12\u00b0F below normal. The northern half of the Lower 48 remains unseasonably warm with the Dakotas > 20\u00b0F above normal. Of course, it\u2019s usually pretty cold in late December, so this will get them above freezing!

Temperature Outlook Next 2 Weeks

The Northern Hemisphere land masses remain very, very warm compared to typical early winter temperatures as the El Nino rages. However, there are signs of changes including a massive cold pool formation over Greenland and Northern Europe. It will take a while to wipe out the continental warmth, but it will happen.

Week 1: December 28, 2023 - January 4, 2024 [EPS Mean 12z]

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Week 2: January 4, 2024 - January 11, 2024 [EPS Mean 12z]

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The Earth loses about 0.4\u00b0F compared to climatology as the Northern Hemisphere cools dramatically. You can see blue on the maps again over North America.

The Canadian Arctic sees cooler than normal air-mass development. Is this a shift to a much colder and wintry pattern by mid-January across the entire Lower 48 as a weak to moderate Stratospheric Warming and split polar vortex event reaches its crescendo? I think so!

3 to 7 Day Precipitation Outlook

Lower 48 next 72-hours precipitation forecast from WPC (18z) issuance

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Next 3-days Precipitation Totals | WPC 18Z issuance
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7-Day Total Precipitation | California | WPC 18z Issuance

Good rainfall (+mountain snow) totals for California over the next week.

Looking forward through 10-days from the ECMWF HRES precipitation anomaly, except for the immediate west coast and apparently SE Texas in the 9-10 day range, the Lower 48 remains quite dry compared to normal. That is a change/flip from previous weeks with infusion of Pacific moisture.

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Snowfall Forecast Next 15-days

The probability of 3-inches or more falling from the ECMWF EPS 12z forecast across the Lower 48 in the next 15-days.

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Note: when you see snowfall probabilities across Southern states:

There is non-zero but not much better chances for snowfall across the Southern USA. Again, we do not sound the alarm since this not actionable unless the values really increase to 50% in the short and medium-range e.g. 3-7 days.

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We usually do ensemble sorting and not averaging [ensemble means] in the medium and long range b/c so many zero events get mixed in. It would be better to caveat the snowfall amounts by \u201cif if snows, then how much\u201d and then provide a % chance of snow, and a range of outcomes. [More on that with Weather Trader products to come.\u2019

Here\u2019s an example from Boston for total snowfall from the 51-members of the ECMWF EPS (12z).

There are certainly chances of big storms > 12-inches of snow, but plenty more in the zero column. So, the ensemble mean is around 3-inches. But, that\u2019s not the best way to use the ensembles with snowfall or precipitation since the distributions are heavily skewed to the right.

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2024 Global Tropics

Ghost town across the Southern Hemisphere, which is not what we expect in an El Nino summer in the Southern Hemisphere. Nothing in the next 10-days according to ECMWF HRES 12z.

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Thursday afternoon temperatures were not too bad across the Lower 48 especially in the sunshine. 50s and 60s in the Southeast. Only about 5 million people were below freezing mark.

A quiet weather pattern over the next 10-days looks likely across much of the Lower 48 except for weak Clipper systems across the Great Lakes and the West Coast storm this weekend. Heading into the following weekend (January 6-7) would be a chance at a East Coast system. There is some ensemble support for a Nor\u2019easter, and there should be more cold air available (finally).

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