Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Thu Jul 13 2023

Valid 12Z Thu Jul 13 2023 - 12Z Sat Jul 15 2023

...Heavy rain and flash flood potential returns to the Northeast Thursday
and Friday...

...Additional rounds of severe weather and flash flooding persist across
the Mississippi Valley and Plains over the next couple days...

...Significant heat wave continues to expand across much of the western
and southern tier of the U.S....
 
Shortwave energy rotating around a broad upper-level low over the Hudson
Bay will lead to increased lift ahead of a cold front pushing into the
Ohio Valley and Northeast from the west, triggering renewed development of
showers and thunderstorms Thursday. Southerly flow ahead of the front will
draw deep moisture back northward after conditions dried out the last
couple of days, as well as prompt storm motions parallel to the boundary
and more likely to lead to repeated rounds of rainfall. A Moderate Risk of
Excessive Rainfall (level 3/4) has been issued for southern Vermont and
adjacent Upstate New York where additional heavy rainfall will pose a
rapid increase in the risk for flash flooding following the intense
rainfall and flooding earlier this week. A separate Slight Risk (level
2/4) is in effect for the Upper Ohio Valley where another focused area of
heavy rainfall is expected. Strong flow aloft as well as moderate
instability will also lead to a few robust, organized thunderstorms
capable of large hail, damaging winds, and a couple of tornadoes for the
Interior Northeast/Upper Ohio Valley. A Slight Risk of severe weather
(level 2/5) has been issued by the Storm Prediction Center for the region.
The heavy rain threat will shift slightly southeastward Friday ahead of
the the slow-moving cold front with a Slight Risk of Excessive Rainfall
for southern New England and the coastal Mid-Atlantic.

A complex Summer-time pattern continues to unfold across portions of the
Mississippi Valley/Plains, with multiple focus areas of heavy rain and
severe weather expected. Moderately strong northwesterly flow containing
embedded shortwaves atop a quasi-stationary frontal boundary as well as
lingering convective outflows will continue to trigger multiple focused
corridors of showers and thunderstorms. High moisture to the south and
pooling along the boundary will help promote very heavy downpours with
intense rainfall rates and the risk of flash flooding. The tendency for
storms to grow upscale into organized convective systems will increase the
areal coverage of rainfall and heavy rain totals. On Thursday, an ongoing
convective system as well as additional development during the day has
prompted a Moderate Risk of Excessive Rainfall over central Mississippi
where significant rain totals over several inches are possible. A Slight
Risk is in place more broadly across the Lower Mississippi Valley to the
central Gulf Coast. Additional storms, potentially an organized convective
system, are expected Friday along and ahead of the boundary from the
Central Plains southeast into the Lower Mississippi Valley with a Slight
Risk in effect. Further west, more isolated, scattered storms are
expected, but pooling moisture and upslope flow along the foothills of the
Rockies will provide instability for robust thunderstorm development. A
Slight Risk of severe weather has been issued for portions of the
Central/Southern High Plains Thursday for the risk of large hail and some
damaging winds. A focused corridor of thunderstorms, and perhaps a
convective system, is forecast ahead of the front on Friday through
southern Kansas and northern Oklahoma, with yet another Slight Risk of
severe weather. 

Meanwhile, a stagnant upper-level high in place over the
Southwest/northern Mexico that has led to hot temperatures over portions
of the Southwest and South-Central U.S. this week will continue to build
in coverage, particularly to the northwest over the Great
Basin/California/Pacific Northwest. Widespread heat-related advisories and
warnings are in place across the Central/Southern Plains and Lower
Mississippi Valley as well as portions of the Desert Southwest as a
significant heatwave intensifies across the southern tier of the country.
Forecast highs will be in the upper 90s and low 100s for locations in the
eastern half of the Plains and the Lower Mississippi Valley which, when
combined with very high humidity, will lead to oppressive heat indices in
the 110-115 degree range. A frontal boundary and convective outflows
sliding into northern portions of the Southern Plains/Lower Mississippi
Valley will likely bring a bit of relief Friday. To the west, while there
will be less humidity, air temperatures will soar much higher into the mid
100s for west Texas and New Mexico and into the 110s for the Desert
Southwest. A few record-tying/breaking temperatures are possible. The heat
will begin to build northward into California, the Great Basin, and the
Pacific Northwest on Friday, with highs into the 90s and low 100s. Heat
advisories also remain in effect for south Florida where relatively warm
temperatures in the mid-90s and heat indices up to 110 continue. In
addition to the oppressive heat during the day, overnight lows will remain
abnormally warm, bringing little relief from the heat overnight. Numerous
near record-tying/breaking warm lows are expected. Unfortunately, the long
term outlook through the weekend and into next week is for an increasingly
significant and oppressive heat wave.   

Putnam


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