Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 406 PM EDT Thu May 20 2021 Valid 00Z Fri May 21 2021 - 00Z Sun May 23 2021 ...Even more rainfall could cause additional flooding and flash flooding for eastern Texas into Louisiana... ...Thunderstorms are expected over parts of the central U.S., with severe weather possible in the Northern/Central High Plains through tonight... ...Late-season snow will continue across higher elevations of the West, with well over a foot of snow likely in the Northern Rockies... ...Critical Risks of fire danger remain in place for portions of the Central Great Basin and Southwest... Ample moisture from the Gulf of Mexico will continue streaming into the central U.S. over the next few days, and upper-level energy moving from the Plains to the Midwest should continue to trigger showers and thunderstorms over the region. Additional rainfall totals of up to 3 inches are possible for southeastern Texas into parts of Louisiana, which have already seen several days of heavy rain, and flooding is ongoing in some areas. The next rounds of rain should serve to exacerbate ongoing flooding and could lead to numerous instances of flash flooding. A Moderate Risk of excessive rainfall is in place through tonight, and Flash Flood Watches are in effect along the western/central Gulf Coast. Lessening rain totals by Friday, but still some modest rainfall potential, has led to a Slight Risk of excessive rainfall in place for Friday for southeastern Texas and southwestern Louisiana. A deep upper-level low is forecast to drop slowly southward across the West and persist there over the next couple of days. This feature providing lift combined with a frontal system moving slowly across the north-central U.S. will lead to scattered showers and thunderstorms across the Northern/Central Plains and Midwest. A Slight Risk of severe thunderstorms is in place through tonight for northern and central parts of the High Plains mainly for wind and hail threats. Isolated strong to severe thunderstorms are possible for the Mississippi Valley as well. Additionally, isolated flash floods are possible for eastern North Dakota/northwestern Minnesota through tonight where locally heavy rain could occur if thunderstorms train over the same area. Underneath the upper low, temperatures are expected to be substantially below normal over the West. High temperatures are forecast to be more than 30 degrees below average for portions of Montana, with temperature anomalies of 20 degrees below normal common for the Intermountain West. These cold temperatures will support lowering snow levels across the West, so snow is likely for the Cascades, Sierra Nevada, and higher elevations of the Intermountain West. But the greatest snow totals are expected in the Northern Rockies, and Winter Storm Warnings are in effect for portions of Montana where snow totals should be well over a foot. Meanwhile, the upper-level pattern will support gusty winds across the interior West, and combined with dry conditions, fire danger will continue. Critical Risks of fire weather are delineated for much of the Central Great Basin and Southwest through Saturday, and the interior valleys of California and the Southern High Plains are under Elevated Risks as well. Elsewhere, the northeastern U.S. can expect increasing chances for showers and thunderstorms for the end of the week along a meandering front. Warmer than average temperatures are forecast to continue for the Great Lakes/Ohio Valley and Northeast/Mid-Atlantic over the next several days, with highs rising well into the 80s and even into the 90s. Tate Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php