Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Sun May 23 2021 Valid 12Z Sun May 23 2021 - 12Z Tue May 25 2021 ...Another round of late-season snow moving into the northern Rockies as above normal temperatures linger across the northern Plains to parts of the eastern U.S... ...Scattered Thunderstorms through the Plains will produce locally heavy rains, isolated Flash Flooding and the risk of Severe Weather... The mid to upper level flow will remain highly amplified across the lower 48 over the next two days with a strong closed low lifting northeast from the Great Basin and through the Northern Rockies, while an upper level ridge along the Mississippi pushes east into the Southeast. In this flow regime, a low pressure system is forecast to intensify as it lifts northward through the Rockies today. This will bring another round of mountain snow across the northern Rockies with a soaking cold rain for the lower elevations, possibly mixing with wet snow into tonight. The intensifying low will also push a strong frontal boundary across the High Plains where thunderstorms could become severe today and into tonight. The low pressure system should continue to move north into the Canadian prairies on Monday but the snow will be slow to taper off in the northern Rockies as winds become strong and gusty from the west to northwest. The strong winds will then spread eastward across the northern Plains by Tuesday as the low begins to move eastward. Farther south across the Plains, the threat of severe thunderstorms should diminish slightly on Monday as the main energy associated with the low lifts into southern Canada. However, the tropical plume of moisture from the Gulf of Mexico remains open for the next few days as winds continue to circulate around a large high pressure system over the eastern U.S. This will support at least scattered thunderstorms from the western Gulf Coast up across many of the Plains states into Tuesday. This may lead to locally heavy rains, isolated flash flooding and continued threat of severe weather. Given this highly amplified weather pattern, temperatures are expected to be 10 to 20 degrees below average in the West in contrast with equally above average temperatures from the northern to central Plains eastward across much of the Mississippi Valley and eastern U.S. Some record high temperatures are possible today in the urban corridor from Boston to Washington DC, where highs are forecast in the upper 80s to low 90s. Meanwhile, the fire weather threat across portions of the Four-Corner region should gradually diminish as the low pressure system moves away. Interestingly, the above average temperature region will also encompass all of the historical region of the Brood X periodic cicada. This will ensure additional warming of the soil and expansion of the regions of emergence and continued active cicada singing where they have already surfaced. Kong/Oravec Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php