Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Sun Apr 14 2024

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


...Overview...

A low pressure 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 Great Lakes/Ohio Valley Wednesday
into Thursday. Behind this, another upper trough/low will skirt the
northern tier states but fight with a southern stream ridge to
determine how far south it may reach across the Ohio Valley to
Northeast late this week. At least a brief period of upper ridging
looks to 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 still some differences in the
smaller scale details and timing of systems. As the first Midwest-
Great Lakes low exits, the second broader upper low across south-
central to southeastern Canada shows variations especially with
troughing along its periphery. There are some timing
inconsistencies with the surface front swinging through the East
and its associated generally light precipitation as shortwave
energy may swing through the Ohio Valley/Northeast during the
latter part of the week. Farther south than the Ohio
Valley/Northeast, models seem to be gradually trending toward less
amplification of the trough, favoring more southern stream ridging.
On the western side of the upper low center, there is uncertainty
with how much energy is held back across the Northwest. GFS runs
have shown more energy there while the non-NCEP camp has more
ridging across the Northwest Friday-Saturday. The latter was
favored. Then upstream energy also shows model variations
especially by Sunday with potentially additional energy coming into
the Northwest. The WPC forecast maintained a multi-model
deterministic blend early in the period, and increased the
proportion of the GEFS and EC ensemble means to over half while
phasing out the GFS in particular by late period.


...Weather/Hazards Highlights...

Precipitation will be ongoing from the Upper Midwest into the Ohio
Valley associated with a deep low (both at the surface and in the
upper levels) moving through the Upper Midwest on Wednesday. Given
ample moisture and instability and a low threat for locally heavy
rainfall, a broad Marginal Risk remains in place for the Day 4
Excessive Rainfall Outlook (Wednesday-Thursday morning) for
portions of the Great Lakes and Ohio Valley. The Storm Prediction
Center is also watching severe potential near the Ohio River on
Wednesday. Gusty winds are possible for the Great Lakes region as
well as behind the low in the Rockies and the north-central Plains.

The next upper trough right on its heels could bring some notable
snow to mainly the higher elevations of the northern/central
Rockies midweek. 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. Then renewed moisture into Texas in particular
ahead of weak shortwave energy sliding into the Southwest could
create some enhanced rainfall totals there into the weekend, while
some rain could extend across the Southeast while the Northeast
dries out.

Expect a broad area of above normal temperatures by 5-15 degrees
over the southern half of the country Wednesday-Thursday, while the
northeastern quadrant of the U.S. gradually cools behind a cold
front. Meanwhile the upper trough across the northern tier states
will bring below normal temperatures (with greater anomalies for
highs than lows) starting in the northern Rockies/Plains midweek.
Cooler temperatures gradually expand farther south and east behind
the secondary cold front late week into the weekend, with near to
below average temperatures expected to reach everywhere but Florida
by next weekend. Meanwhile, above normal temperatures across the
Southwest should gradually expand northward underneath a building
Western U.S. ridge.


Tate/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