Area Forecast Discussion
Issued by NWS Glasgow, MT
Issued by NWS Glasgow, MT
256 FXUS65 KGGW 171954 AFDGGW Area Forecast Discussion National Weather Service Glasgow MT 154 PM MDT Tue Sep 17 2024 .DISCUSSION... KEY MESSAGES: 1) Scattered severe thunderstorms can be expected mainly this evening in a south to north corrider mainly east of a Glasgow- Jordan line. Damaging wind and large hail will be major threats, but heavy rain cannot be ruled out. 3) Western zones could see a significant rain event tonight through Thursday morning. Lower amounts for eastern zones. A Hydrologic Outlook was issued today for this plus the threat for higher stream runoff from central Montana (i.e. Flatwillow Creek). WEATHER PATTERN OVERVIEW: An upper low near the Wasatch of northern Utah will lift into eastern Montana later tonight and become vertically stacked. This structure will only allow it to drift slowly northeastward, not exiting Montana until Wednesday Night. The unusaully high humidity for this time of year (current dewpoints have reached the upper 50s to lower 60s!) to materilize into heavy rain for much of central Montana through Wednesday Night. SPC continues to have most of the CWA in a Slight Risk, but the corridor east of Glasgow to Jordan line looks to have the highest chance at this point for hail. Wind looks to be scattered across the CWA. Timing looks to be best in the evening as the storms move north. The DESI Grand Ensemble showed a 40 to 60 percent chance of 2 inches of total rainfall for SW Phillips and Petroleum counties. This promped the issuance of a Hydrologic Outlook. Another concern are the streams that feed from central Montana, particularly the Flatwillow Creek. The SW zones could see strong winds from about 6 pm Wednesday till about 6 pm Thursday with a tight surface gradient on the SW side of the surface low. At this point, winds speeds will likely stay below High Wind Warning criteria but a Lake Wind Advisory is likely for Fort Peck Lake. Temperatures closer to seasonal average will settle across the region behind the front starting on Wednesday. The upper level low will depart to the northeast on Thursday taking the rain with it. Temperatures will remain close to average through the end of the weekend. FORECAST CONFIDENCE & DEVIATIONS: There is moderate confidence of strong to severe storms occurring late this afternoon through early Wednesday morning. High confidence of rainfall greater than 1" occurring in Phillips and Petroleum counties, with low to medium confidence of 1" of rain further east. TFJ && .AVIATION... Last Updated: 2000Z CATEGORY: VFR then MVFR late tonight. DISCUSSION: Scattered showers and thunderstorms, some of which could be strong to severe with large hail and damaging wind will move north this evening. Ceilings then will lower to MVFR levels later tonight and remain there except for KSDY Wednesday. Lower ceilings (IFR) can be expected over central and southeast Montana. WINDS: E or SE at generally 10 kts or less, but higher at KSDY with speeds at 20-25kts. TFJ && .GGW WATCHES/WARNINGS/ADVISORIES... None. && $$ weather.gov/glasgow