![]() ![]() GFS 500 MB Pattern For 12Z (5 AM MST) December 16th GEFS 500 MB Pattern For 12Z (5 AM MST) December 16th Rockies (not shown), putting a major dent into the 500mb ridge over western North America. One major step in this process occurs early this weekend (graphic below valid for 12 UTC (5 AM MST) 16 Dec), as a shortwave trough slides down the eastern side of the Canadian Rockies (shown below) and then cuts off westward off the U.S. ![]() Over the next 7-10 days, the global ensemble predictions systems are suggesting we will see a slight, but significant shift westward, bringing colder air from Canada into the West. In other words, this type of pattern has a tendency to remain nearly stationary, or even retrograde to the west. Over the past week, we've seen it remain nearly stationary. Start of Pattern Shift: These large scale patterns are controlled by processes called Rossby Wave Dynamics. Highly amplified flow (like we are currently seeing) is often associated with lower Rossby wave phase speed. GFS 12Z (5 AM MST) December 13th Pattern Analysis GEFS 12Z (5 AM MST) December 13th Pattern Analysis Here is the current analysis from this morning, 12 UTC (5 AM MST) 13 Dec: An anomalous ridge over the North Pole is making it difficult to establish circumpolar flow, leading to a highly amplified pattern. and Canada, and equally impressive troughs situated along both sides. This pattern has been characterized by an impressive 500mb ridge over most of the western U.S. has been under the influence of a strongly positive phase of the Pacific/North American (PNA) Pattern for some time. Scroll further down for the science behind this pattern change.Ĭurrent Pattern: The western U.S. Check out the CPC 6 to 10 Day and 8 to 14 Day outlooks to see more how this pattern may affect the weather patterns to end the year. It is unclear what exactly the southward extent of this colder air might be, or how long it will remain in place. This unsettled pattern could bring some increase precipitation potential for some areas of Montana. It is likely that areas west of the Rockies will see their first shot of Arctic air this winter beginning sometime in the December 21-24 time frame. Deterministic solutions are still valuable because they highlight the potential for individual shortwaves that are not apparent in the ensemble mean.Skillful use of the ensembles is the best way to obtain confidence at 7-10 day lead times.Aside from Montana (upslope precipitation), this will continue a dry pattern for the western U.S.The ridge will retrograde westward in 7-10 days, with the coldest air of the season likely west of the Rockies.The past several weeks have been very warm west of the Rockies, due to a persistent western North American ridge.Sign up for our daily forecast newsletter at /newsletters.Key Points | End Result l Science l Pattern Shift Thursday will be the “warmest” day with middle to upper 50s to around 60° expected. Keep the warm clothes out because morning lows Tuesday to Sunday will fall to the middle/upper 30s to around 40. Another weather disturbance will provide enough lift for a few showers beginning Saturday afternoon into Sunday morning. The forecast is for dry weather from Tuesday to Friday. Temperatures by 4:00 will be noticeably warmer in the western Hill County where the sun breaks through the clouds first. 75″ at La Grange at 1:30.Ĭlearing from west to east will occur during the afternoon. There were a few lightning strikes noted in northeast Fayette County during the 1:00 hour. AUSTIN (KXAN) - Showers with a few thunderstorms increased during the early afternoon with some heavy rain reported east of I-35, especially in Fayette County. ![]()
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