Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Fri May 21 2021 Valid 12Z Fri May 21 2021 - 12Z Sun May 23 2021 ...Additional heavy rain associated with a developing low pressure center over the western Gulf of Mexico could impact areas from Texas Gulf Coast to Louisiana today followed by eastern Texas tonight... ...Thunderstorms could become severe ahead of a cold front through the High Plains for the next couple of days... ...Late-season snow will linger across higher elevations from the Sierra Nevada to the northern Rockies into the weekend... ...Critical Risks of fire danger remain in place for portions of the central Great Basin and Southwest... Southeasterly winds circulating around a large high pressure system centered over the northeastern U.S. will continue to direct a stream of tropical moisture from the Gulf of Mexico toward the western Gulf states. Meanwhile, latest observations indicate that a low pressure center is forming in the western Gulf of Mexico as it begins to move northward toward the western Gulf Coast. The National Hurricane Center is monitoring this area for the potential for tropical cyclone formation. Heavy rain ahead of this developing circulation continues to move across coastal Louisiana early this morning. Additional heavy rain could impact areas from the Texas Gulf Coast to Louisiana today as the developing low pressure center moves toward the western Gulf Coast. The continued threat of heavy rain will keep a Slight to Moderate Risk of flash flooding over southern Louisiana to the upper Texas coast today. 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 remain 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. Kong/Tate Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php