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

Valid 00Z Sat Jul 22 2017 - 00Z Mon Jul 24 2017

...The hot and humid conditions plaguing the eastern U.S. from the central
Plains to the Mid-Atlantic region will continue into the weekend...

...Heavy rain and severe weather will be possible in the Upper Midwest,
Great Lakes, and Ohio Valley and will shift to the northern Mid-Atlantic
region by the weekend...

...Monsoonal moisture moving into the Southwest in addition to the central
and southern Rockies will bring a threat of localized flash flooding...

The upper level ridge that spans from the central Plains to the
Mid-Atlantic states will continue to maintain the hot and humid conditions
across these regions through Friday and Saturday.  Many states in the
Plains, Middle Mississippi Valley, and even the Southeast have excessive
heat warnings and heat advisories; high temperatures are expected to reach
near or at the century mark and heat indices climbing to 110 degrees or
higher.  The Mid-Atlantic region and a large portion of North Carolina
also have heat advisories in addition to a small area of excessive heat
warnings. On Saturday, a cold front will push southward across the Plains
and Mississippi Valley and will bring relief from the heat by Sunday
across these areas. High temperatures are expected to cool down and be
closer to seasonal average.  However, hot and humid conditions will still
continue for the Mid-Atlantic and the Carolinas on Sunday as the front
will not move through these areas until early next week. 

A wavy frontal boundary that will stretch from the Upper Midwest and Great
Lakes to the Ohio Valley and Mid-Atlantic region will be the dominant
feature that help focus showers and thunderstorms along it through the
weekend.  With plenty of instability and moisture present, convection
leading to flash flooding and severe weather will be possible in these
regions. Tonight and into early Saturday morning, most of the convection
is expected to occur in the Upper Midwest/Upper Great Lakes.  Throughout
most of Saturday, showers and thunderstorms will move along the boundary
across the Ohio Valley and lower Great Lakes.  By Saturday night and into
Sunday, the focus of heavy rain and severe weather shifts to the northern
Mid-Atlantic.  See WPC's excessive rainfall outlook and SPC's convective
outlook for specific information on flash flooding and severe weather,
respectively. 

Monsoonal moisture combining with weak energy aloft will fire off showers
and thunderstorms across the Southwest and the central/southern Rockies on
Friday through Sunday.  Most of this activity can be expected in the late
afternoon and early evening as daytime heating will help trigger the
convection.  Some of these thunderstorms could produce heavy downpours and
lead to localized flash flooding. 

Daytime heating will also lead to afternoon showers and thunderstorms
across the Gulf Coast states.  Meanwhile, a front approaching British
Columbia bought bring light precipitation to northwestern Washington on
Saturday. 


Reinhart


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