textproduct: Great Falls

KEY MESSAGES

- Areas of fog this morning.

- Mild and mainly dry conditions prevail through Thursday.

- Pacific weather system brings windy and cooler conditions by the weekend

DISCUSSION

- Meteorological Overview:

An upper level ridge centered over MT and surface high pressure over the northern US plains will maintain very light flow aloft and at the surface across the region through tonight. Except for some areas of fog this morning, primarily across the plains but also in some SW MT valleys, mainly clear skies and light winds will prevail with afternoon temperatures reaching the 70s. A southwesterly flow develops Tuesday through the rest of the week, bringing some additional warming with afternoon temperatures as much as 10-15 degrees above average through Thursday. A weakening upper level disturbance tracking out of the Southwestern US across WY by mid- week will bring risk for showers and perhaps an isolated thunderstorm to portions of SW MT late Tue/Tue night. A larger scale upper trough from the North Pacific begins to move onshore Friday with a cold front sweeping east across the Northern Rockies and MT late Friday or early Saturday. Gusty winds are likely to accompany and follow the frontal system along with cooler temperatures by the weekend.

- Forecast Confidence & Scenarios:

Looking ahead to the late week/weekend system, there is reasonable model agreement on a potent shortwave ejecting across the Northern Rockies, which would favor a fairly energetic frontal passage and associated winds. Probabilistic model guidance keeps the risk for strong (>50mph) winds around 20% less, and there is still a fair amount of timing uncertainty, but this will continue to be monitored as the week progresses. Hoenisch.

AVIATION

21/06Z TAF Period

Main concern overnight will be fog potential over mainly the eastern half of the CWA. Fog is beginning to develop at 05z around Lewistown. The fog should continue to develop overnight and spread further east towards Havre/West Yellowstone and possibly as far west as Helena. The fog could be dense at times with LIFR conditions at times. Most of the fog should diminish by 17z Mon, with generally quiet weather conditions expected Mon afternoon. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 79 48 80 49 / 0 0 0 0 CTB 76 44 77 47 / 0 0 0 0 HLN 76 45 77 49 / 0 0 0 10 BZN 73 41 75 45 / 0 0 0 10 WYS 67 30 68 34 / 0 0 0 30 DLN 72 41 73 42 / 0 0 10 20 HVR 79 46 80 49 / 0 0 0 0 LWT 75 44 79 48 / 0 0 0 10

TFX WATCHES/WARNINGS/ADVISORIES

None.