10:00 AM | Heavy rain event on Thursday triggers pattern change to noticeably colder

[00Z GFS Ensemble 2-meter temperature anomaly forecast map for days 1-5; courtesy NOAA, "tropicaltidbits.com"]

Discussion

Near term

So far the month of November has been well above normal in the Mid-Atlantic region (Philly +7.1°, DCA +5.0°, NYC +6.4°), but it looks like the overall mild pattern is going to change noticeably to colder for the last ten days of the month and perhaps right even into early December and all of this is going to be triggered by a heavy rain event on Thursday. After a mild day to start the work week, there will be a temporary setback in the mild temperatures on Tuesday as a back door cold front slides southward through the Mid-Atlantic region during the overnight hours. High temperatures on Tuesday afternoon will be some ten degrees cooler than what is expected later this afternoon. Milder air pushes northward again on Wednesday and Thursday riding in on increasingly strong south-to-southwest winds and a strong cold front will be approaching from the west. Heavy rain is likely from the cold frontal system late Wednesday night and Thursday in the I-95 corridor and this event will trigger the temperature pattern change to colder beginning by this upcoming weekend.

[00Z GFS Ensemble 2-meter temperature anomaly forecast map for days 6-10; courtesy NOAA, "tropicaltidbits.com"]

Longer term

Last night’s GFS Ensemble run at 00Z shows nicely the changes that are coming not only here to the Mid-Atlantic region for the last ten days of the month, but also to much of the nation as well. The first map (top) shows the overall temperature anomalies across the US for days 1-5 (16NOV-21NOV). Warmer-than-normal conditions (oranges) dominate in the eastern US with mainly colder-than-normal (blues) weather out west during this current 5-day stretch. Beyond that, the 6-10 day (21NOV-26NOV) temperature anomaly forecast map (middle) shows big changes in the Mid-Atlantic region with colder-than-normal (blues) conditions and it is similarly cold throughout most of the nation away from the southwestern states. Does the cold hold beyond that time period? The 11-15 day (26NOV-01Dec) temperature anomaly forecast map (bottom) indicates it certainly will with colder-than-normal weather continuing in most of the nation right from Thanksgiving into the beginning of December. As far as snow is concerned, there are signs for some threats in the Northeast US in the weekend after Thanksgiving or the early part of December and we’ll monitor those chances in the days ahead.

[00Z GFS Ensemble 2-meter temperature anomaly forecast map for days 11-15; courtesy NOAA, "tropicaltidbits.com"]