Area Forecast Discussion
Issued by NWS Glasgow, MT
Issued by NWS Glasgow, MT
330 FXUS65 KGGW 062129 AFDGGW Area Forecast Discussion National Weather Service Glasgow MT 329 PM MDT Mon May 6 2024 .DISCUSSION... KEY MESSAGES: - High Wind Warning remains in effect for most locations south and west of Fort Peck Lake. Strongest winds which could lead to damaging impact are expected overnight tonight through Tuesday. Crosswind concerns and dangerous chop on Fort Peck Lake are heightened. - Widespread periods of moderate to heavy rain will persist through Wednesday night. A Hydrologic Outlook as been issued for the area receiving the heaviest rainfall. - Flood concerns increasing for small streams Tuesday and Wednesday, leading to rises along the Milk River late in the week. WEATHER PATTERN OVERVIEW: The slow-moving strong spring storm system will sit and spin over this region for the next several days. Most of the associated heavy rain will last through Wednesday morning. By the weekend, a flat ridge will push in from the Pacific Northwest across the northern Rockies. CONFIDENCE AND POTENTIAL DEVIATIONS FROM BASE FORECAST: Probabilities for high wind have decreased slightly with both speed and area. Still looking at high probability (70-90%) for wind gusts over 55 mph for Phillips county (excluding the north), Petroleum and Garfield counties. For Prairie county, the high winds will be mostly in the west over the Big Sheeps, and Valley county will see the strongest winds across the ridge tops near Fort Peck Lake. So have upgraded these zones to a High Wind Warning. Other zones in northeast Montana will have much lower probability for reaching high wind criteria. Rainfall amounts for the region from today through Wednesday night remain very high. Probability for at least 1 inch is over 70% for the entire region. Confidence for 2 inches or more drops off to 30-50% east of Opheim, Poplar and Glendive while staying at 60-90% for most of the area to the west. Probability for more then 3 inches is not insignificant, setting at 30-40% for Malta, Glasgow and Jordan, and peaking at 60% around the Little Rockies. With the widespread high precipitation amounts, flooding will become a concern from midweek into the weekend. Updated RFC river point forecasts are showing sharp rises for the Milk River at Tampico and Glasgow by the end of the week. Small stream flooding and impassable gravel roads are also expected mainly for Phillips, Valley and Garfield counties. BMickelson && .AVIATION... PATTERN: The unusually strong and slow-moving spring storm system, will continue to push wave after wave of moderate to heavy rain across the area for at least the next few days.. A region of dry air will act to slightly diminish rainfall amounts especially near the Montana/North Dakota border. FLIGHT CONDITIONS: MVFR to borderline IFR will persist through most of this TAF cycle. IFR is possible in the bands of heaviest rainfall. WINDS: The slow-moving storm system is accompanied by a nearly stationary cold front. East of the front, winds remain light from the east. Behind the front northwest winds will are increase to the 25G35KT range. The location of this wind shift will waffle back and forth across NE MT over the next few days. KGGW and KGDV may occasionally see these stronger winds, but will also revert back into light and variable. BMickelson && .HYDROLOGY... Widespread heavy rainfall has impacted many locations already since this morning. Smaller creeks and streams are expected to begin rising this evening especially near and west of MT Highway 16. The responsible storm system is large and slow-moving and is very efficient is producing multiple bands of precipitation. As the storm system stalls over our area through the next few days, rainfall accumulations are expected to exceed 1 inch for most locations, and 2 inches for many other locations. A few isolated areas could receive in excess of 3 inches. Low-lying areas and poor-drainage areas will easily begin ponding water this afternoon and evening. Small creeks and streams will soon rise and begin to run. All of this water will eventually flow into the larger, main stem rivers in the next few days with some sudden rises being possible. It is not yet known whether the Milk River will reach minor flood stage this weekend. We will continue to monitor conditions and provide updates as needed. BMickelson && .GGW WATCHES/WARNINGS/ADVISORIES... High Wind Warning until midnight MDT Tuesday night for Central and Southeast Phillips-Central and Southern Valley-Garfield- Petroleum-Prairie-Southwest Phillips. && $$ weather.gov/glasgow