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Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 331 AM EDT Sun Apr 30 2023
Valid 12Z Sun Apr 30 2023 - 12Z Tue May 02 2023
...Heavy rainfall and severe thunderstorms likely across Northeast and Mid-Atlantic on Sunday...
...Locally significant, multi-day snowfall event for U.P. of Michigan through early work week; Well-below-average temperatures across Great Lakes and Ohio Valley Sunday through Tuesday...
...Above-average temperatures to continue across interior Pacific Northwest, Great Basin, and Intermountain West, as cooler weather arrives on Sunday for immediate coast...
 The main weather headline for the last day of April will be the heavy rainfall potential throughout the Mid-Atlantic and Northeast as a strengthening storm system tracks along the Eastern Seaboard. Sunday will be a wet and chilly day for the entirety of the region, as the surface low tracks just inland, allowing for anomalously moist air originating from as far south as Florida to push onshore, increasing the chances for heavy rainfall and producing region-wide rainfall totals of 1"+. The heaviest totals will be confined to coastal and interior northern New England, where upwards of 3-5" of rain, in addition to rainfall rates approaching 1"/hr will be possible, resulting in the issuance of a Slight Risk of Excessive Rainfall for northern Massachusetts, New Hampshire, and southern Maine. Further south, a second Slight Risk is in effect for New Jersey, eastern Pennsylvania, southern New York, and the Baltimore/Washington D.C. urban corridor, as although rainfall totals will not be as excessive as in previously mentioned areas, the combination of 1-2" of rain and saturated soils, given the recent rainfall, may lead to areas of flooding as showers and thunderstorms develop on Sunday. Severe thunderstorms will also be of concern across the Carolinas and Mid-Atlantic ahead of the frontal passage during the early to midday Sunday hours, with damaging winds and isolated tornadoes possible, resulting in the Storm Prediction Center placing much of the region under a Slight Risk for Severe Thunderstorms. Conditions will improve from south to north, with the heaviest axis of precipitation pushing through northern New England during the early Monday morning hours, although the weather will remain damp and cool through Tuesday.
Meanwhile, a deepening, highly anomalous, and nearly stationary upper-low presiding over the Great Lakes will lead to much below-average temperatures and localized heavy snowfall across northern Wisconsin and the Upper Peninsula (U.P.) of Michigan through Monday. Shortwave energy traveling around the base of the upper low will lead to a rapid deepening of a surface low over Lake Superior and the Ontario Province late Sunday into Monday, with several locations potentially approaching both April and May monthly low-pressure records. Strong northwesterly winds on the backside of the strengthening surface low, in conjunction with cold air advecting southward and orographic lifting, will lead to a localized swath of 1-2ft of snow across higher elevations of the interior U.P. of Michigan. Given the late-season snow, surface temperatures hovering around freezing during the event will lead to very heavy wet snow, which may result in downed trees and powerlines. The snow will diminish on Tuesday as the system weakens and slowly pushes eastward as high pressure builds in. Furthermore, a broader area of much-below-average temperatures (10-20 degrees F below average), encompassing much of the Midwest, Great Lakes region, and Ohio Valley, will be possible through Tuesday, as daytime highs struggle to reach 50F, and numerous locations approach or break daily record low maximum temperatures.
Elsewhere, above-average temperatures across the Intermountain West, Great Basin, and interior Pacific Northwest will continue through the forecast timeframe as persistent upper-level ridging supports temperatures 15-25 degrees above normal. Widespread high temperatures in the 80s are expected throughout interior sections of the Pacific Northwest, while locations further south, including California's Central Valley and the Mojave/Sonoran deserts, reach the 90s and even 100s in localized areas on Sunday. However, a storm system and attendant cold front pushing onshore early Sunday will result in more seasonable temperatures returning to the immediate coast, with cooler temperatures spreading inland on Monday and Tuesday. Furthermore, scattered showers, thunderstorms, and high-elevation snow will also be possible across the West and northern/central Rockies during the start of the work week.
 Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php

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