Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EDT Sun Apr 14 2024

Valid 12Z Wed Apr 17 2024 - 12Z Sun Apr 21 2024


...Overview...

A storm system exiting the Upper Midwest/Great Lakes early in the
period will continue to bring a threat for at least locally heavy
rainfall to parts of the Upper Midwest/Ohio Valley Wednesday into
Thursday. Behind this, another upper trough/low will skirt the
northern tier states before ultimately evolving into somewhat more
amplified troughing across the Ohio Valley-Northeast late this
week. Upper ridging should build over the Northwest by next weekend
ahead of another amplified trough across the northern Pacific and
the overall pattern across the CONUS turns more zonal/relatively
quiet.


...Guidance/Predictability Assessment...

Model guidance remains reasonably agreeable on the large scale
pattern through the period, but plenty of differences in the
smaller scale details and timing of systems. The main
uncertainties during the medium range period will be with the
second, more broad, upper low across central-eastern Canada and any
shortwave energy that swings through the base of the trough
through the Ohio Valley/Northeast late week. This presents timing
inconsistencies of the surface front through the East and
associated generally light precip along it. Additional energy may
drop southward through central Canada next weekend, possibly
skirting the northern tier, and there are some differences in the
strength of ridging across the West as well. Otherwise, the pattern
trends pretty quiet overall across the CONUS, except for possible
energy through the Southwest which models are showing inconsistency
with how much this may increase QPF across Texas by next Sunday.
The WPC forecast tonight was based on a blend of the deterministic
guidance Days 3-5, increasing the means to help smooth out the
smaller scale differences by days 6-7.


...Weather/Hazards Highlights...

Precipitation will be ongoing from the Upper Midwest into the Ohio
Valley associated with a deep surface low moving through the Upper
Midwest on Wednesday. Given ample moisture and instability and a
threat for at least locally heavy rainfall, a broad marginal risk
remains in place for the Day 4 Excessive Rainfall Outlook
(Wednesday- Thursday morning) from the Upper Great Lakes to Ohio
Valley and central- northern Appalachians. Some potential for
severe weather as well along the cold front, per discussions out of
the Storm Prediction Center. Behind the low, some gusty winds
could be possible across the Upper Midwest region.

The next upper trough right on its heels could bring some notable
snow to mainly the higher elevations of the northern/central
Rockies mid-week. As systems progress, rain and convection are
forecast to move into the eastern U.S. into late week, while
lingering across the south- central U.S. as the frontal system
stalls briefly. After this, conditions should mostly dry out across
the CONUS leading into next weekend, but some enhanced rainfall may
make its way back into Texas ahead of weak shortwave energy slides
into the Southwest.

Expect a broad area of above normal temperatures over the eastern
third of the country into the southern Plains Wednesday-Thursday,
with advancing frontal systems slowly trimming the western side of
the warmth. Expect highs in the eastern U.S. to be around 10F or
so above normal with anomalies for morning lows tending to be
several degrees higher. The upper trough across the northern tier
states will bring below normal highs into the northern
Rockies/High Plains by next Wednesday- Thursday while gradually
expanding farther south and east behind the secondary cold front
late week. Above normal temperatures across the Southwest should
gradually expand northward underneath a building Western U.S.
ridge.

Santorelli


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw