Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 358 PM EDT Tue Sep 17 2024 Valid 00Z Wed Sep 18 2024 - 00Z Fri Sep 20 2024 ...A coastal low brings a threat of flash flooding to the Mid-Atlantic today with precipiation chances lingering through Wednesday... ...A strong low pressure system will bring unsettled weather to the northern/central Rockies and Plains with severe thunderstorms expected this evening in the northern/central High Plains... ...Very heavy rainfall expected in Montana on Wednesday with some flash flooding possible... An area of low pressure, previously labeled as Potential Tropical Cyclone Eight, will continue to slowly move north across the Carolinas towards the Mid-Atlantic over the next day or so. Moist, onshore flow will support persistent showers and thunderstorms across portions of North Carolina and the southern Mid-Atlantic through early Wednesday, and locally heavy rainfall could result in isolated to scattered instances of flash flooding. Flood Watches are in effect for portions of southeastern Virginia and North Carolina. Precipitation chances will expand northeastward into southern New England through the day Wednesday, though intensity should begin to decrease overall, resulting in a lower threat for flash flooding. Coastal flooding will also be a concern with a prolonged period of onshore winds along the Mid-Atlantic coast. By Thursday, this system will begin to shift offshore into the Atlantic and high pressure will build behind it. Meanwhile, a strong low pressure system moving across the Intermountain West this afternoon will begin to emerge into the northern/central Plains this evening, strengthening in the lee of the Rockies. Widespread showers and thunderstorms are forecast with this system in the vicinity of the low pressure center and along and ahead of the trailing cold front. Some thunderstorms may become severe this evening in the northern and central High Plains, and the Storm Prediction Center has highlighted this area with a Slight Risk of severe thunderstorms (level 2/5) with an embedded Enhanced Risk (level 3/5) over the central High Plains. Severe storm hazards include significant damaging winds and isolated large hail. Further north, anomalously moist, strong easterly upslope flow along the northern Rockies will lead to thunderstorms and very heavy rainfall tonight and especially on Wednesday. A Slight Risk of Excessive Rainfall (level 2/4) covers portions of north-central Montana where several inches of rain (2-4"+) are possible, leading to a heightened risk of flooding. Winds are also expected to be rather gusty as the low strengthens, prompting some high wind-related warnings and advisories for portions of the northern High Plains. Gusts as high as 60 mph will be possible, particularly along the Front Range of the Rockies. Additional isolated thunderstorms are expected ahead of the eastward moving cold front through the Plains on Wednesday and into the Upper Midwest by late Wednesday and into Thursday. More favorable overlap of strong upper-level winds with an accompanying trough and increased moisture/instability will lead to the threat of some additional severe weather Thursday. There is a Slight Risk over portions of eastern Minnesota, northwestern Wisconsin, and northern Iowa for isolated large hail and damaging winds. Another system approaching the Pacific Coast will bring some scattered showers and storms to the coastal Pacific Northwest this evening, spreading southward into northern California and the central Great Basin on Wednesday. The rain will be relatively modest for most areas, with the highest expected in the Sierras, where a bit of snow may mix in at the higher elevations. Temperature-wise, much of the northern-tier of the central/eastern U.S. as well as the Plains will remain much above average Wednesday and Thursday. Highs will be into the mid- to upper 80s for portions of northern New England and the Upper Midwest Wednesday, and a handful of near record-tying/breaking highs approaching 100 will be possible for portions of the southern Plains on Thursday. Meanwhile, temperatures will be well below average across the West behind the strong Plains system, with many highs in the 60s across the Great Basin and only in the 80s for portions of the Desert Southwest. Highs will generally be near average in the Southeast (80s-90s) and Mid-Atlantic (70s-80s) the next couple of days. Putnam/Dolan Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php