textproduct: Great Falls

KEY MESSAGES

- Warmer and drier Wednesday and Thursday. - Next weather system arrives Friday, bringing cooler temperatures along with some periods of rain/mountain snowfall. - Another weather system brings even cooler temperatures and more widespread precipitation to Montana, with more chances for mountain snowfall.

DISCUSSION

- Meteorological Overview:

In the wake of a series of upper level systems earlier this week, a weak ridge embedded in northwesterly flow will bring a period of warmer but breezy weather to North Central Montana Wednesday and Thursday. This period of warmer weather will come to a quick end on Friday as a decaying upper level trough moves through Southern British Columbia and Alberta into Montana, which will bring cooler temperatures, along with some showers of rain and mountain snowfall as it pushes through. The cooler temperatures will linger behind this system, which will set up the next, stronger system to produce widespread precipitation with snow expected above 7000 feet, which would include some of the higher mountain passes. A brief period of warmer and drier weather is expected late Sunday and Monday before the unsettled pattern resumes by the middle of next week.

- Forecast Confidence & Scenarios:

Winds today and Thursday: Westerly, cross barrier flow will bring some gusty winds to North Central and Southwestern Montana Wednesday and Thursday. While winds are not expected to be strong enough to reach high wind criteria (58 mph for most, 75 mph along the Rocky Mountain Front), gusts to 35-50 mph will be possible across the area, especially on Thursday when winds will be strongest.

Mountain Snowfall this weekend: A strong upper level low will move into the Treasure State over the weekend, bringing well below average temperatures along with copious amounts of moisture. The cooler temperatures will bring snow levels down to 7000 feet above sea level, which will result in widespread mountain snowfall to areas above 7000 feet. Current forecasts keep snowfall amounts under 6 inches at the moment, but some of the highest terrain still have around a 10 percent chance of snowfall amounts over a foot over the weekend. Ludwig

AVIATION

09/06Z TAF Period

High confidence in VFR condition across all terminals through the entirety of the TAF period. A ridge of high pressure will continue to push east into Montana bringing warmer temperatures and breezy conditions. The timing is consistent across all terminal with winds beginning to increase and turn more southwesterly between 16z and 19z. Conditions remain clear with widespread clear to mostly clear sky and high cloud bases. Winds are of greatest across north central Montana specifically terminals KCTB, KHLN, KGTF, and KHVR where gusts of 25-30kts are expected from a west/southwest direction. Region wide, gusts from the SW up to 20kt are expected. -JR

For KGTF: Winds will begin to increase 09/14z offering a brief period of favorable wind direction from the southwest. Winds will quickly ramp up to 10G20KT with a low (30%) chance of crosswinds exceeding the 15kt threshold. By 09/17z winds become more westerly (240-260 degrees) with high confidence (>60%) of gusts with a crosswind component of 15-18kt. Winds become nearly due west (270 degrees) by 09/20z increasing the crosswind component of sustained winds near/above the 15kt threshold. Winds remain consistent till 10/02z when they begin to wane/shift southwest. -JR

PRELIMINARY POINT TEMPS/POPS

GTF 76 54 81 47 / 0 0 0 70 CTB 69 50 71 41 / 0 0 0 60 HLN 75 49 83 52 / 0 0 0 60 BZN 76 44 83 47 / 0 0 0 10 WYS 69 29 71 35 / 0 0 0 0 DLN 77 41 81 44 / 0 0 0 0 HVR 75 49 81 43 / 0 0 0 30 LWT 72 49 83 45 / 0 0 0 60

TFX WATCHES/WARNINGS/ADVISORIES