Chilly and Wet Pattern

A transition to a more amplified pattern will occur, which will usher in big changes for the eastern United States–including the Southern Plains next week. The combination of positive PNA (see Figure 1), negative AO (see Figure 2), and negative NAO (see Figure 3) will be conducive for a strong north Pacific ridge (into Alaska) and high-latitude blocking (see Figure 4). This synoptic setup, along with a well established snow pack (see Figure 5), would allow for a deep trough to setup for areas east of the Rockies.

Figure 1: PNA Forecast

Figure 2: AO Forecast

Figure 3: NAO Forecast

Figure 4: 500mb Height Anomaly Map: GEFS(Next Wednesday)

Figure 5: Current snow and ice cover

For the Southern Plains, a cold front looks to advance into the region early next week. The guidance is struggling on the exact timing, which is expected during an amplified pattern, but a Monday or Tuesday time frame looks likely–and temperatures will stay well below average for much of the upcoming week (see Figure 6). This will generate showers and thunderstorms for this region (mainly along and east of I-35), which is much needed–many areas are slipping into a drought. It is possible a few post-frontal showers may occur immediately behind the cold front.

Figure 6: Surface Temperature Anomaly Map: GEFS (December 5th-December 10th)

Eyes then turn to the west. Guidance is indicating a disturbance or two may ‘ride’ over the ridge out west and down into the southern Rockies. Depending on the timing and strength of the disturbance(s), it is possible light precipitation may develop during Wednesday and/or Thursday time frame for Texas and Oklahoma. Again, the timing and strength of the disturbance(s) is questionable, and the amount of moisture is unknown, but we will need to keep a close eye on this setup since anomalously cool air will be in place. It is not out of the question that wintry precipitation chances may be possible. At this time, the greatest chance would be for western Oklahoma and western Texas.

The wintry precipitation chances are NOT set in stone, but I am keeping a close eye on next week. The guidance should become more certain with the evolution of the synoptic pattern by this weekend, and thus a more detailed forecast will be provided then once the finer details are known. The cold air will advance eastward into the Northeast, Mid-Atlantic, and Southeast by mid-next-week. This cold air will remain in place for this region through the weekend. Matthew will have a detailed article out tomorrow on the impacts for this region.