Area Forecast Discussion
Issued by NWS Glasgow, MT
Issued by NWS Glasgow, MT
527 FXUS65 KGGW 181513 AFDGGW Area Forecast Discussion National Weather Service Glasgow MT 913 AM MDT Wed Sep 18 2024 .DISCUSSION... Going foreast still intact through tonight. With the area of heaviest rain mainly west of Phillips and Petroleum, the threat for flooding may be diminished, but not confident enough to cancel the Hydrologic Outlook. Flatwillow Creek in southern Petroleum County has begun to rise and will likely do so into tomorrow (Thursday). TFJ KEY MESSAGES: 1) Phillips and Petroleum Counties may see some heavy rain at heavy rain at times today. Lower rainfall amounts are expected to the east. A Hydrologic Outlook is in effect for this plus the threat for higher stream runoff from central Montana (i.e. Flatwillow Creek). Rainfall is expected to end tonight. 2) A High Wind Warning has been issued from 9 am this morning until 9 pm this evening for strong NW winds. The strong NW winds today will be confined to the SW zones of the forecast area. The NW winds will spread east across the forecast area tonight at lower wind speeds but will be strong enough for a Lake Wind Advisory for tonight and Thursday. WEATHER PATTERN OVERVIEW: The surface low was located near the U L Bend area of Fort Peck Lake at 08z (2am MDT) this morning with the upper low over south central Montana. The surface and upper low will be stacked over eastern Montana today and will slowly drift NE across the region today and move to the NE tonight. Heavy rain is expected on the west side of the low today with dry slotting on the east side of the low. This means that Phillips and Petroleum Counties will be the eastern edge of the heavy rain today. The remainder of the forecast area will have periods of dry weather today mixed in with isolated to scattered showers and thunderstorms in an unstable atmosphere. The showers and thunderstorms will continue at times tonight as the stacked low moves NE out of Montana and diminish Thursday morning. The probability of 2 inches or more of total rainfall for SW Phillips and Petroleum Counties remains between 50 and 70 percent for today and tonight. Will maintain a Hydrologic Outlook for this area. Another concern are the streams that feed from central Montana where even heavier rain is possible, particularly the Flatwillow Creek. Areas SW of the low today will have strong NW winds with a tight surface gradient. The probability of a 60 mph wind gusts for Petroleum County is high enough (70 percent) that a High Wind Warning has been issued from 9 am this morning to 9 pm this evening. Winds will be much lighter to the NE of this area today being closer to the low. The strong NW winds will spread east tonight with lower speeds but they will be strong enough that a Lake Wind Advisory is likely for Fort Peck Lake tonight and Thursday. The upper level low will depart to the northeast on Thursday taking the rain with it. The next upper trough moves through on Friday with a cold front that will bring below normal temperatures on Saturday. FORECAST CONFIDENCE & DEVIATIONS: High confidence of rainfall greater than 1" occurring west of Malta and Winnett today and tonight with low confidence in the location and timing of any showers and thunderstorms to the east. High confidence in the strong NW winds over Petroleum County but medium confidence on whether or not a gusts to 60 mph will occur. Used the NBM 90 percent with Petroleum County winds today and did increase the base probability of precipitation at times today and tonight to provide a better hour to hour consistency. && .AVIATION... Last Updated: 0845Z CATEGORY: VFR most of the time with occasional MVFR today and tonight. DISCUSSION: The TAF sites will be in the dry slot of a strong stacked low today which will result in VFR conditions most of the time. An unstable atmosphere will allow for showers and thunderstorms at times especially this afternoon and tonight that could bring a period of MVFR conditions. Also, some low clouds are expected late tonight as the low exits the region which could bring some MVFR ceilings. WINDS: SE to south today 5 to 15 knots this morning increasing to 10 to 20 knots this afternoon. The surface low moving NE across the TAF sites will bring a period of variable winds in the late afternoon and early evening (22Z to 03Z). Then winds will be NW at 10 to 20 knots late tonight. && .GGW WATCHES/WARNINGS/ADVISORIES... High Wind Warning until 9 PM MDT this evening for Petroleum. && $$ weather.gov/glasgow