Area Forecast Discussion
Issued by NWS Glasgow, MT
Issued by NWS Glasgow, MT
236 FXUS65 KGGW 052058 AFDGGW Area Forecast Discussion National Weather Service Glasgow MT 258 PM MDT Sun May 5 2024 .DISCUSSION... KEY MESSAGES: - Long duration rainfall pattern for northeast Montana from Monday through Wednesday night. Weather Prediction Center has issued a Slight Risk for Excessive Rainfall for the 24 hr period ending on 6am Tuesday. - The general probability of exceeding 1 inch, 2 inches, and 3 inches of total rainfall during this aforementioned period ranges from 60-90%, 40-70%, and 10-30%, respectively. - There is a High Wind Watch for much of the area for very strong winds Monday night through Tuesday night, leading to crosswind concerns on area roadways. WEATHER PATTERN OVERVIEW: Multiple low pressure systems will move into northeast MT from the south this evening, and then again tomorrow afternoon. The surface low tonight will be associated with a band of thunderstorms that is centered over Garfield, McCone, and Prairie county according to high resolution weather models such as the HRRR, HRW FV3, and NAM NEST. There is moderate to high (50 to 60 percent) confidence of these storms producing a gust over 50 mph at the surface from 4 PM this afternoon through midnight. This surface low will weaken Monday morning, and another surface low will ride the border of SD and ND into northeast MT, which will bring an increase in winds Monday evening through Tuesday night. Therefore, a High Wind Watch is in effect from 6PM Monday through midnight Wednesday for Phillips, Valley, McCone, and Richland counties southward. Significant rainfall will accompany the surface low on Monday, and an upper level trough will help maintain this rainfall through Wednesday night. Refer to the Key Messages for rainfall amount probabilities. CONFIDENCE AND POTENTIAL DEVIATIONS FROM BASE FORECAST: There is high (70 percent) of the majority of the area receiving over one inch of rainfall, with moderate (50 percent) of rainfall exceeding 2 inches from Monday through Wednesday night. There is low (30 percent) confidence of a dry slot setting up between a north south line from Opheim to Jordan westward from Harlem to Lewistown based on the deterministic NAM. However the GFS, ECMWF, and Canadian models are in agreement on significant precipitation occurring. There is high (70 percent) confidence of areas There is moderate to high (50 to 70 percent) confidence of winds gusting over 60 mph on a line from Whitewater to Wolf Point to Sidney southward Monday night through Tuesday night. -Stoinskers/GAH && .AVIATION... LAST UPDATED: 2000Z FLIGHT CAT RANGE: VFR, becoming MVFR after 12Z Monday, becoming IFR after 15Z. DISCUSSION: After 00Z, showers and thunderstorms will spread across the area lasting into the night. Then widespread rain showers will begin moving into KGDV and KSDY by 12Z, and KOLF and KGGW by 15Z. There is high (90 percent) confidence ceilings will deteriorate below 1000 ft AGL after 15Z. This is as the surface low pressure system moves into southeastern MT, which will also bring sporadic low level wind shear to KGDV between 06Z Monday and 12Z Monday as well. WIND: Southeast 20 to 28 kts with gusts to 35 kts, decreasing to 10 to 16 kts after 06Z. For KGGW and KGDV, expect a switch to northwest at 10 to 15 kts after 17Z Monday, increasing to 20 to 30 kts with gusts to 40 kts after 21Z. For KOLF, expect a switch to northwest at 10 to 15 kts after 23Z Monday, increasing to 20 to 30 kts after 03Z Tuesday. && .HYDROLOGY... A potent spring storm will make its way into northeast Montana late tonight and last through Wednesday night. There is high (70 percent) confidence of rainfall exceeding 1 inch area wide, with moderate (50 percent) confidence of exceeding 2 inches, and low (20 to 30 percent) confidence of exceeding 3 inches of total rainfall. Areal creeks and rivers are expected to rise later in the week for locations that receive over 2 inches of rain, so there is moderate to high confidence flood products will be necessary for low lying locations mid to late week. && .GGW WATCHES/WARNINGS/ADVISORIES... Lake Wind Advisory until 6 PM MDT Monday for Central and Southeast Phillips-Central and Southern Valley-Garfield-McCone- Petroleum. High Wind Watch from Monday evening through Tuesday evening for Central and Southeast Phillips-Central and Southern Valley- Dawson-Garfield-McCone-Northern Phillips-Petroleum-Prairie- Southwest Phillips-Wibaux. && $$ weather.gov/glasgow