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Short Range Public Discussion
(Caution: Version displayed is not the latest version. - Issued 1956Z Jul 29, 2021)
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Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 356 PM EDT Thu Jul 29 2021 Valid 00Z Fri Jul 30 2021 - 00Z Sun Aug 01 2021 ...Severe thunderstorms likely from the Middle Mississippi Valley to the Mid-Atlantic through Friday morning... ...Excessive rainfall with isolated flash flooding possible over parts of the Northeast through Friday morning... ...Potentially heavy rainfall fueled by monsoonal moisture could produce scattered flash flooding in the Southwest and Central Great Basin for the first half of the weekend... ...Widespread Heat Advisories and Excessive Heat Watches/Warnings are in effect for much of the central US and Pacific Northwest... A low pressure wave positioned over the Lower Great Lakes with a cold front trailing southwest through the Ohio Valley to the Central High Plains and a warm front pushing ahead over the Mid-Atlantic and Northeast will be the focus for much of the activity affecting the eastern half of the CONUS during the short-range period. An unstable, moist airmass within the warm sector is expected to interact with upper-level shortwave energy and forcing at the surface via the cold front to generate scattered thunderstorms as well as multicell clusters. Due to the potential for these storms to become severe and produce damaging gusts and possibly a tornado or two, the Storm Prediction Center has issued a Slight Risk for severe thunderstorms for the Ohio Valley, Central Appalachians, and Mid-Atlantic through Friday morning. Because southeastern Pennsylvania, southern New Jersey, northern Delaware, and northeastern Maryland have the greatest likelihood of experiencing these conditions, an Enhanced Risk of severe thunderstorms has been issued for these areas. Taking into consideration the potential for localized flash flooding in the Northeast due to antecedent saturated soils and expected rainfall totals of 1 to 3 inches with the passage of this system, the Weather Prediction Center has issued a Slight Risk of Excessive Rainfall for the region through tomorrow morning. Overnight tonight the western tail end of the cold front is expected to become stationary over the Central High Plains and combine with a low pressure wave that slowly drifts from southern to northern Colorado. As the wave becomes embedded within the front it is expected to lift further north into Nebraska with a warm front extending out to the east across the state. This warm front will serve as the focus for convective development on Friday as it interacts with a moist and unstable boundary layer. As afternoon vertical wind profiles become more favorable a cluster of severe thunderstorms will likely develop. Seeing as these storms could generate large hail and gusty winds, the Storm Prediction Center has issued a Slight Risk of severe thunderstorms for parts of eastern Nebraska from Friday morning until Saturday morning. Localized flash flooding will be possible Friday through Saturday along a northwest-southeast axis from southern South Dakota to Tennessee due to the potential for these storms to produce rainfall totals of 1 to 2+ inches in 24 hours. Southeastern Missouri will be at greatest risk for flash flooding on Saturday, therefore, the Weather Prediction Center has issued a Slight Risk of Excessive Rainfall for the area beginning Saturday morning. Shifting focus to the Southwest, Great Basin and Central/Southern Rockies, showers and thunderstorms are expected to continue throughout the period as the pressure pattern aloft aids the transport of monsoonal moisture into the aforementioned regions. Anomalously high precipitable water values are expected to combine with upper-level energy as well as surface instability due to diurnal heating to produce heavy rainfall on top of already moist soils. Given the potential for high rain rates, antecedent wet conditions, and scattered burn scars throughout the affected areas, the Weather Prediction Center has issued a Slight Risk of Excessive rainfall for parts of the Southwest through Friday morning due to the possible occurrence of localized flash flooding. On Friday, the flash flooding concern is expected to spread north into the the Central Great Basin and Central Rockies, prompting the issuance of Slight Risk areas in those regions for Friday along with the Southwest. By Saturday the flash flooding risk is expected to shift even further north into the Northern Great Basin while simultaneously abating in the Southwest. As such, for Saturday a Slight Risk for Excessive Rainfall has been issued for the southern Oregon/Idaho border and parts of the Central Rockies. Widespread Heat Advisories are currently in effect from the Central Plains/Ohio Valley to the Lower Mississippi Valley/Southeast as hot afternoon temperatures and high humidity are expected to mix to generate heat index values between 100 and 110 degrees, with isolated higher values possible. Excessive heat warnings are also in effect for parts of Kansas, Missouri, Oklahoma, and Mississippi. Throughout northern California and the Pacific Northwest Excessive Heat Watches and Warnings as well as Heat Advisories are also in effect for areas where temperatures on Friday are forecast to be 10+ degrees above average, with highs reaching the upper 90s and low 100s. The main concern with these hot temperatures and/or high heat index values is the onset of heat related illness if the proper precautions aren't taken. Residents within the previously mentioned 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 to safeguard their health. Elsewhere, tropical moisture being pumped into the Gulf Coast states and Florida will help fuel the development of daily showers and thunderstorms through Saturday. Anomalously high precipitable water values over Florida could allow rain rates within these storms to reach 1.5 - 2 inches per hour, which may lead to isolated flooding, primarily in urban areas, through Friday morning. Lastly, Air Quality Alerts are currently in effect for portions of Idaho, Montana, Wyoming, Colorado, Minnesota, and Iowa due to smoke from ongoing wildfires out west and in Canada being advected into their areas by the prevailing northerly-northwesterly winds. Zavadoff Graphics available at