Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
332 AM EDT Fri Jul 21 2017

Valid 12Z Fri Jul 21 2017 - 12Z Sun Jul 23 2017

...Hot and humid conditions are expected to persist from the Central
Plains and Middle Mississippi Valley to the Mid-Atlantic states Friday and
Saturday...

...Heavy rain and severe storms will be possible along a wavy frontal
boundary stretched from the Upper Midwest and Great Lakes to the Ohio
Valley and northern Mid-Atlantic region...

...Monsoonal moisture will keep localized flash flooding a threat from the
Southwest into the Southern and Central Rockies over the next few days...

Hot and humid conditions will persist beneath upper ridging expanding from
the Central Plains and Middle Mississippi Valley to the Mid-Atlantic
states Friday and Saturday.  Widespread excessive heat warnings and heat
advisories remain in effect where daytime temperatures in the mid to upper
90s will combine with high dew points to create triple digit heat indices.
 Locations across the Central Plains and Middle Mississippi Valley should
see some relief from the heat Saturday night into Sunday as the ridge
suppresses aloft and a cold front sinks southward through the region.   

North of the excessive heat, rain and thunderstorms will focus along a
wavy frontal boundary expected to stretch from the Upper Midwest and Great
Lakes to the Ohio Valley and northern Mid-Atlantic region Friday and into
the weekend.  Given the amount of available moisture and instability,
developing convection will have the potential to become organized and
produce flash flooding and severe weather.  Please refer to WPC's
excessive rainfall forecasts and SPC's convective outlooks for the latest
information on the threat for flash flooding and severe weather.

The combination of monsoonal moisture and weak impulses of energy aloft
will help foster additional days of afternoon/evening convection and
localized flash flooding across portions of the Southwest and
Southern/Central Rockies Friday and Saturday.

Elsewhere, daytime heating will help trigger afternoon showers and
thunderstorms within a moist airmass in place across the Southeast and
Gulf Coast states, while a frontal system approaching British Columbia
could bring mostly light precipitation into the extreme northwestern
corner of the Nation.


Gerhardt


Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php