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Short Range Public Discussion
(Caution: Version displayed is not the latest version. - Issued 1955Z Jul 28, 2021)
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Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 355 PM EDT Wed Jul 28 2021 Valid 00Z Thu Jul 29 2021 - 00Z Sat Jul 31 2021 ...Severe thunderstorms likely from the Upper Midwest to the Mid-Atlantic through Friday morning... ...Excessive rainfall with isolated flash flooding possible over parts of the Upper Midwest through Thursday morning... ...Potentially heavy rainfall fueled by monsoonal moisture could produce scattered flash flooding in the Southwest through Friday... ...Widespread Heat Advisories and Excessive Heat Warnings are in effect throughout the central US... A long, slow moving frontal boundary extending from the Central High Plains through the Upper Midwest to the Mid-Atlantic will be the focus for much of the activity over the CONUS during the short-range period. A low pressure wave set up over the Upper Midwest is expected to interact with upper-level shortwave energy and surface instability to produce both heavy rain and thunderstorms over the region. Taking into consideration the antecedent saturated soils and the potential for rainfall accumulations up to and exceeding 2" in 24 hours, which could lead to localized flash flooding, the Weather Prediction Center has issued a Slight Risk of Excessive Rainfall for portions of Wisconsin and Michigan through Thursday morning. As afternoon vertical wind profiles become more favorable, severe thunderstorms and supercells will likely develop throughout the Upper Midwest that hold the potential to produce damaging winds, large hail, and a few tornadoes. Much of Wisconsin and the surrounding areas have the greatest likelihood of experiencing these conditions, therefore, the Storm Prediction Center has issued a Moderate Risk of severe thunderstorms for portions of Wisconsin through Thursday morning. The low pressure wave and its associated frontal boundary are forecast to move from the Great Lakes area overnight and into the Ohio Valley/Mid-Atlantic by Thursday morning. Though rainfall totals are expected to be a bit lower than the previous day's, saturated soils throughout the regions due to 150-400% above normal precipitation will still make isolated flash flooding a concern. Additionally, a moist, unstable airmass extending from the Ohio Valley to the Mid-Atlantic could interact with the advancing cold front to produce linear thunderstorm clusters and supercells. Due to the potential for this storms to produce damaging gusts and possibly a tornado or two, the Storm Prediction Center has issued a Slight Risk of severe thunderstorms for the Ohio Valley, Central Appalachians, and Mid-Atlantic from Thursday through Friday morning. Shifting focus to the Southwest and Central Great Basin, showers and thunderstorms are expected to continue throughout the period as high pressure aloft aids the transport of monsoonal moisture into the region. Anomalously high precipitable water values are expected to combine with surface instability due to diurnal heating to produce hourly rain rates between 0.5 and 1 inches, with isolated higher amounts possible. Given these high rain rates, antecedent wet conditions, and scattered burn scars throughout the regions, the Weather Prediction Center has issued a Slight Risk of Excessive Rainfall for portions of Arizona, Nevada, Utah, and Colorado from Thursday through Friday due to the potential for localized flash flooding to occur. Widespread Heat Advisories are currently in effect from the Northern Plains/Upper Midwest to the Lower Mississippi Valley/Southeast as hot afternoon temperatures and high humidity are expected to produce heat index values between 100 and 110 degrees, with isolated higher values possible. The main concern with heat index values this high is the onset of heat related illness if the proper precautions aren't taken. Residents of these regions are urged to drink plenty of fluids, stay in air conditioned rooms, stay out of the sun, and reschedule strenuous activities to the early morning or evening. Excessive Heat Warnings are also in effect for portions of Minnesota, Kansas, Missouri, Oklahoma, and Mississippi. In Northern California and the Pacific Northwest, Excessive Heat Watches and Warnings as well as Heat Advisories are in effect for areas where temperatures on Friday are expected to be above average, with highs reaching the high 90s and low 100s. The Storm Prediction Center has issued an Elevated Risk of Fire Weather for portions of the Northern Plains through Thursday morning due to prevalent dry fuels throughout the region, low relative humidity values, and winds between 15 and 20 mph. Air Quality Alerts are in effect for portions of Washington, Idaho, Montana, Wyoming, and Colorado due to wildfire smoke from ongoing wildfires. Zavadoff Graphics available at