textproduct: Great Falls

KEY MESSAGES

- It will be windy across North-central, Central, and Southwestern Montana on Wednesday and Thursday.

- Showers and thunderstorms return Tuesday and continue through at least the end of the work week.

- It will warm up through Tuesday then cool off to end the work week.

DISCUSSION

- Meteorological Overview:

This afternoon there is an upper-level ridge over North-central, Central, and Southwestern Montana. This will allow temperatures to warm up with mostly dry weather. On Tuesday the upper-level ridge remains over North-central, Central, and Southwestern Montana. This will allow temperatures to warm up to above seasonal averages. Tuesday evening an upper-level shortwave will move through the ridge and bring showers and thunderstorms to Southwestern Montana. On Wednesday an upper-level trough begins to move over North-central, Central, and Southwestern Montana. This will allow temperatures to cool down slightly with showers and thunderstorms across the area. Due to strong southerly flow aloft and strong low-level winds it will be windy across North-central, Central, and Southwestern Montana on Wednesday with the strongest winds along the Rocky Mountain Front and in north-south orientated valleys.

On Thursday the upper-level trough remains over North-central, Central, and Southwestern Montana. This combined with strong southerly flow aloft and strong low-level winds will bring another day of windy conditions to the area. On Thursday there will be another day of showers and thunderstorms. On Friday an upper-level low is over Washington and Oregon with southwest flow over North- central, Central, and Southwestern Montana. This will allow temperatures to be around seasonal averages with another day of showers and thunderstorms and breezy conditions. -IG

- Forecast Confidence & Scenarios:

On Wednesday and Thursday there is a 40 - 80% chance for wind gusts of 45 mph or greater across Southwestern Montana. On Wednesday and Thursday there is greater than a 50% chance for sustained winds of 40 mph or greater in the Madison River Valley. As a result a High Wind Watch was issued for the Madison River Valley from Wednesday afternoon through Thursday evening. On Wednesday and Thursday there is a 30 - 60% chance for wind gusts of 35 mph or greater across North-central Montana. On Friday there is a 40 - 80% chance for wind gusts of 30 mph or greater across North-central, Central, and Southwestern Montana with the greatest probability in Southwestern Montana and along the Rocky Mountain Front.

On Tuesday there is a 15 - 30% chance for thunderstorms across North- central, Central, and Southwestern Montana. On Wednesday there is a 15 - 30% chance for thunderstorms across most of North-central, Central, and Southwestern Montana. On Friday there is a 15 - 30% chance for thunderstorms across Southwestern Montana. On Tuesday there is a 50% chance for a quarter inch of rain or greater across Northwestern Beaverhead County.

On Saturday and Sunday there are significant differences in the track of the upper-level pattern in the deterministic models and ensembles. One scenario is that the closed low remains situated over Washington/Oregon. This would keep status quo weather with seasonal temperatures and precipitation chances. Another scenario is that the closed upper-level low splits with one part going south and the other portion going up into Canada. This would bring breezy conditons to Hi-Line with some precipitation primarily confined to the Hi-Line. A third scenario is that the upper-level low moves east and weakens some. This would bring cooler and wetter conditions to North-central, Central, and Southwestern Montana. -IG

AVIATION

31/18Z TAF Period

VFR conditions are expected to prevail for the next 24 hours as high pressure moves though Montana. Winds will largely be light and variable. Only concern is a 30% chance of a shower near KWYS late Tuesday morning. SHRA/TSRA will eventually move into SW MT during the afternoon Tuesday.

For KGTF: With light and variable winds in the forecast, there is a near zero percent chance of crosswinds over 15 kts through 18z Tuesday. The chance will increase on Tuesday afternoon as some southeasterly winds gust to around 15 kts. Ludwig

PRELIMINARY POINT TEMPS/POPS

GTF 48 85 56 81 / 0 0 20 50 CTB 45 82 51 76 / 0 0 10 50 HLN 48 86 51 79 / 0 10 60 70 BZN 46 81 48 78 / 0 20 70 30 WYS 36 68 36 65 / 10 40 60 10 DLN 44 81 45 76 / 0 10 80 40 HVR 46 88 54 86 / 0 0 10 40 LWT 47 83 53 82 / 0 10 20 30

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Watch from Wednesday afternoon through Thursday evening for Madison River Valley.