textproduct: Great Falls

KEY MESSAGES

- One more night of widespread sub-freezing temperatures tonight. - Temperatures gradually warm through the rest of the work week with warmest readings likely Thursday and Friday.

- Mainly afternoon and early evening showers each day through Wednesday with an isolated thunderstorm possible.

DISCUSSION

- Meteorological Overview:

The upper level trough extending from Canada southwest across the western US will gradually weaken while shifting east over the next several days. A cyclonic northwesterly flow aloft lingers across the Northern Rockies and MT through Wednesday with weak embedded disturbances and limited moisture combining with daytime heating to support the diurnal development of scattered showers and perhaps an isolated thunderstorm or two each afternoon through Wednesday.

One more night of widespread sub-freezing temperatures is expected tonight with a return to seasonal temperatures beginning Tuesday. Upper level ridging builds across the NW US Thursday and Friday for mainly dry conditions area-wide with afternoon temperatures warming above seasonal averages and likely to peak on Friday with afternoon temperatures in the upper 60s to low 70s. Hoenisch

- Forecast Confidence & Scenarios:

Through this evening, widely scattered showers will primarily be focused across southwest MT and north along the continental divide. On Tuesday and Wednesday, the coverage of showers and possible thunderstorms will be a bit broader across western portions of north-central MT as well as much of central and southwest MT. Through this evening, precipitation associated with any showers will primarily be snow. Tuesday and Wednesday, snow levels rise to around 6000 ft or higher, however enough cold air aloft remains in place to support graupel or very small hail down to the surface with more intense shower activity.

Longer range model ensembles are in general agreement on the broader pattern evolving this weekend as upper ridging amplifies offshore of BC with Pacific energy diving south along or offshore of the US west coast. Meanwhile, energy coming over the Eastern Pacific ridge looks to dive south through central Canada, carving out a broader trough that deepens into the N-central US by early next week. Uncertainty exists in the timing of energy moving south out of Canada by later this weekend and the extend of any moisture moving out of the SW US low. In any case, some cooling is likely to begin this weekend with low confidence in the amount of cooling and occurrence of precipitation. Hoenisch

AVIATION

27/18Z TAF Period

Passing shortwaves will maintain periods of scattered to broken low VFR/MVFR clouds, mountain obscuration, and widely scattered rain/snow showers for the duration of the period. Most of this activity will occur over central and southwestern MT, especially over and near areas of higher terrain. KWYS will observe the most persistent degraded conditions. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 27 56 33 58 / 10 30 20 30 CTB 23 55 30 57 / 10 20 10 10 HLN 29 56 33 58 / 10 30 20 50 BZN 24 54 30 57 / 10 30 20 50 WYS 17 46 22 50 / 40 30 10 50 DLN 25 54 31 58 / 10 20 0 20 HVR 24 59 29 59 / 0 10 0 0 LWT 24 52 29 54 / 10 30 10 40

TFX WATCHES/WARNINGS/ADVISORIES

None.