{"id":415105,"date":"2025-11-28T19:24:29","date_gmt":"2025-11-28T18:24:29","guid":{"rendered":"https:\/\/climatescience.press\/?p=415105"},"modified":"2025-12-27T03:38:20","modified_gmt":"2025-12-27T02:38:20","slug":"early-winter-onslaught-lurking","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=415105","title":{"rendered":"Early winter onslaught lurking"},"content":{"rendered":"\n
\"A<\/figure>\n\n\n\n

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From CFACT<\/a><\/p>\n\n\n\n

By Joe Bastardi<\/a><\/p>\n\n\n\n

\"A<\/figure>\n\n\n\n

I got Grok to blend the AI ensemble, Euro ensemble, GFS ensemble and CFSV2 for the front 10 days of December. Keep in mind that Weatherbell.com had targeted early cold Thanksgiving to Christmas from our August 29 Winter forecast based on the parameters we use to set up the winter, chief among them at the time, the back weighted ACE index in relation to normal from mid-season on. This is a novel idea we also used to predict the cold surge of 2022 and last year during that time<\/p>\n\n\n\n

So Grok came up with this<\/p>\n\n\n

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\"A<\/figure>\n<\/div>\n\n\n

When asked what this ranked in the front 10 days of December, which, btw is a little over 10% of the DJF heating season, it gave the above map<\/p>\n\n\n\n

Historical Context for Early December (Days 1\u201310) Temperature The blended forecast map I generated represents a strong cold anomaly across the northern and central U.S. for approximately November 30\u2013December 10, 2025 (aligning with early December\u2019s first 10 days). To rate it against the last 30 years (1995\u20132024, using the 1991\u20132020 climatology baseline), I compared the key anomaly values (\u221210\u00b0F to \u221218\u00b0F in the Upper Midwest\/Great Lakes core, \u22125\u00b0F to \u221210\u00b0F across the broader northern tier, and near-average to mildly positive in the South) to historical December data from NOAA\u2019s National Centers for Environmental Information (NCEI) and other sources.Key Metrics for Ranking<\/p>\n\n\n\n

Region<\/th>Forecast Anomaly (\u00b0F)<\/th>Historical 30-Year Range (Dec Mean Anomaly)<\/th>Percentile Ranking (Coldest = Lower Percentile)<\/th>Notes\/Comparable Years<\/th><\/tr>
Upper Midwest\/Great Lakes (e.g., Minneapolis, Chicago)<\/td>\u221210 to \u221218<\/td>\u22122 to \u221215 (coldest tercile: \u2264 \u22128; avg. SD ~4\u20136\u00b0F)<\/td>5th\u201315th percentile (among coldest 10\u201320% of Decembers)<\/td>Extremely rare; comparable to 1995 (\u221212\u00b0F regional avg., La Ni\u00f1a cold blast) or 2010 (\u221210\u00b0F, polar vortex). Only 3\u20135 events in 30 years hit \u221210\u00b0F+ deficits.<\/td><\/tr>
Broader Northern\/Central U.S. (e.g., Dakotas to Northeast, south to Plains\/Ohio Valley)<\/td>\u22125 to \u221210<\/td>\u22121 to \u22128 (coldest tercile: \u2264 \u22124; avg. SD ~3\u20135\u00b0F)<\/td>10th\u201325th percentile (coldest quarter)<\/td>Unusual but not record-shattering; seen in 8\u201310 of 30 Decembers (e.g., 2000, 2014 La Ni\u00f1a years). Sharp north-south gradient matches 20% of cold events.<\/td><\/tr>
Southern U.S. (e.g., TX\/FL to Carolinas)<\/td>0 to +6 (mild pockets +4 to +8)<\/td>+1 to +5 (warmest tercile: \u2265 +3; avg. SD ~2\u20134\u00b0F)<\/td>60th\u201380th percentile (mildly warm third)<\/td>Typical for La Ni\u00f1a; occurred in ~60% of Decembers. Matches 2020\u201321 early season (+4\u00b0F South vs. cold North).<\/td><\/tr>
National Contiguous U.S. Average<\/td>~ \u22123 to \u22125<\/td>\u22120.5 to \u22123 (coldest tercile: \u2264 \u22121.5)<\/td>15th\u201330th percentile (coldest third overall)<\/td>One of the 5\u20139 coldest early Decembers in 30 years; contrasts warming trend (U.S. Decembers warmed ~0.5\u20131\u00b0F\/decade since 1990s).<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Overall Rating vs. Last 30 Years<\/p>\n\n\n\n