textproduct: Great Falls

KEY MESSAGES

- Cooler temperatures and breezy north winds with a few showers through Tuesday.

- Overnight low temperatures in the upper 20s Tuesday night.

- Warmer but with a continued chance for showers and a few thunderstorms later this week into the weekend.

DISCUSSION

- Meteorological Overview:

A highly amplified upper level pattern is in place with ridging in the NE Pacific and deep troughing across central/eastern Canada. Energy diving south around the Canadian trough will maintain a cyclonic northerly flow across MT through Tuesday with a cooler airmass and surface high pressure building southward into the area today and maintaining below average temperatures through Tuesday. Gusty north winds with the initial cold front and surge of higher pressure across central and southwest MT this morning will decrease some by late morning but expect breezy to windy conditions to be fairly widespread across north-central MT this afternoon and again Tuesday afternoon beneath moderate northerly mid level flow. Moisture in this cyclonic northerly flow is fairly shallow and largely below 600MB but is supporting an area of showers moving south across north- central MT this morning with weak afternoon instability and northerly uspslope flow supporting widely scattered showers this afternoon and again Tuesday. Daytime temperatures will be around 10 degrees below seasonal averages today and tomorrow with the coldest temperatures likely Tuesday night/early Wednesday morning as clouds and winds decrease, allowing overnight minimum temperatures to reach the upper 20s across much of the area.

The larger scale upper level pattern de-amplifies later this week with model ensembles showing broad upper level ridging shifting inland and supporting a return to near and above average temperatures through next weekend. There are however several embedded disturbances including a shortwave tracking through NW flow around Thursday and another crossing the region next weekend. There is uncertainty still with the timing and strength of each of these disturbances but each will bring an increased risk of showers and potentially some thunderstorms. Hoenisch

- Forecast Confidence & Scenarios:

Wind gusts in excess of 40 mph are most likely (>50% probability) this morning through the N-S oriented southwest MT valleys as surface high pressure surges south from Canada with wind gusts peaking again in these areas tonight as additional pressure rises occur. Similar probabilities for gusts in excess of 40mph exist today across portions of Hill, Blaine and Fergus counties as well as the Judith Gap area beneath stronger mid level northwesterly flow where winds will peak this afternoon.

AVIATION

04/06Z TAF Period

The cold front should clear central MT by dawn before continuing southward into the southwest later this morning. Northerly winds gusting up to 40 kts at times will be the initial concern, followed by increased showers, scattered to broken MVFR/IFR clouds, and mountain obscuration. Scattered shower and isolated thunder activity will maintain periodic degraded flight categories during the second half of the TAF period, especially for areas near higher terrain. Winds will begin to decrease in a north to south fashion this afternoon, but will remain gusty over the narrow north to south oriented valleys of central and southwest MT. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 57 34 53 30 / 40 10 20 0 CTB 55 30 51 27 / 20 0 10 0 HLN 58 34 54 30 / 30 10 20 0 BZN 60 30 51 25 / 20 20 30 10 WYS 60 29 48 20 / 10 10 20 10 DLN 63 32 54 27 / 10 10 10 0 HVR 58 27 54 26 / 10 0 10 0 LWT 52 28 48 25 / 50 10 40 10

TFX WATCHES/WARNINGS/ADVISORIES

None.