Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Thu Aug 17 2023

Valid 12Z Thu Aug 17 2023 - 12Z Sat Aug 19 2023

...Hot/record temperatures to shift focus out of the Northwest and into
the central U.S.; Critical Risk of Fire Weather in the Northwest...

...Showers, thunderstorms, and an increasing risk of flash flooding for
the Southwest...

...Scattered shower and thunderstorm chances continue along the East
Coast...

An upper-level ridge shifting from the Northwest eastward over the central
U.S. will continue to be the driver of an expansive heatwave. One more day
of oppressively hot temperatures are forecast for the interior Northwest
and portions of the Northern Rockies/adjacent High Plains Thursday. Highs
will generally be in the upper 90s to low 100s, near record-tying/breaking
levels for portions of the Northern Rockies. In addition, low relative
humidity and some gusty winds on top of the hot temperatures has resulted
in a Critical Risk of Fire Weather from the Storm Prediction Center for
portions of eastern Washington and northwest Montana Thursday and Friday.
A Pacific system/cold front pushing southeast across the region late
Thursday and into the day Friday will bring an end to the more dangerous
heat for this region, with highs remaining hot but returning to more
reasonable, summer-time temperatures generally in the low 90s. As the
ridge shifts east, temperatures will begin to soar into the upper 90s to
low 100s over western portions of the Northern/Central Plains on Friday.
This eastward shift in the ridge will also bring temperatures back up into
the mid- to upper 100s in Texas and low 100s for the Lower Mississippi
Valley, near record-tying/breaking levels, after a brief reprieve for many
the past couple of days. The ridge unfortunately looks to settle in and
lead to a long-duration heatwave over the central U.S. into next week.
Please see WPC's Heat Key Messages for more information on this expansive
heat wave.

An upper-level closed low lingering over the California coast will
continue to provide support aloft for daily shower and thunderstorm
chances over portions of the Southwest/Great Basin. Anomalously high
moisture in the region will lead to locally heavy downpours with the risk
for some isolated flash flooding, particularly for more sensitive
locations such as urban areas, burn scars, dry washes, and slot canyons.
Enhanced lift aloft and higher instability will result in a locally higher
risk of a few scattered instances of flash flooding over portions of
southwest Utah and northwest Arizona on Friday, with a Slight Risk of
Excessive Rainfall (level 2/4) in place. Confidence has increased in
significant heavy rainfall/flooding impacts from increasing moisture
streaming into southern California and the Southwest from Hilary in the
eastern Pacific, but this will likely begin just beyond the current
forecast period during the day Saturday. High temperatures broadly across
the southern tier of the West will range from the 70s along coastal
California, 80s in the Four Corners region, and low to mid-90s for the
Central/Southern Rockies and Great Basin. Heat-related advisories/warnings
are in effect Thursday for the central California Valleys for highs in the
mid 100s and the Desert Southwest for highs into the 110s before a return
to more typical summertime temperatures Friday.

Elsewhere, a frontal system passing through the Great Lakes will continue
to bring a chance for showers and thunderstorms through early Thursday
before shifting into the interior Northeast by Thursday afternoon and New
England by Friday. Some locally heavy downpours/isolated flash flooding
and an instance or two of gusty winds will be possible. Cooler
temperatures will follow behind the front, with highs in the 70s to low
80s for much of the Midwest/Northeast. Over the Southeast, a lingering
frontal boundary will provide the focus for mainly afternoon showers and
storms. Highs will be near average from the southern Mid-Atlantic through
the Southeast and into Florida, with upper 80s to low 90s expected. 

Putnam

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