134
FXUS02 KWBC 171935
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
335 PM EDT Fri May 17 2024

Valid 12Z Mon May 20 2024 - 12Z Fri May 24 2024


...Overview...

An upper trough and surface low will be exiting the East Coast by
the start of the period, but may linger in the western Atlantic for
a day or two before getting pushed out to sea by the next system
behind it. Meanwhile, a shortwave will push into the northern
Plains/Upper Midwest early in the week along with a modest surface
reflection and potential for at least locally heavy convection
across the north- central U.S.. An upper low is forecast to drop
into the Northwest behind this system around midweek bringing
another cold front and unsettled weather to the West.


...Guidance/Predictability Assessment...

Models are in reasonable agreement on the overall synoptic pattern
across the CONUS during the medium range period. A general model
blend consisting of the 00z EC/UK/CMC and 06z GFS were used on days
3 and 4, with higher weighting toward the EC and GFS. The 00z ECE
and 06z GEFS were introduced to the blend on day 5 in place of the
favored EC/GFS weighting as well as the UKMET. The 00z CMCE
replaced the 00z CMC on day 6 and was continued through the end of
the period with the ensembles making up the bulk of the blend on
days 6 and 7.


...Weather/Hazards Highlights...

An upper shortwave and leading cold front pushing slowly through
the Plains/Upper Midwest early in the week will help fuel showers
and thunderstorms from the north-central Plains into the Great
Lakes, with potential for at least locally heavy rainfall given
ample anomalous moisture and instability present. Both the Days 4
and 5 (Monday-Tuesday) Excessive Rainfall Outlooks show just broad
marginal risks across this area, and in some places may be
dependent on activity towards the end of the short range period as
well. Farther West into the Rockies, some moderate snowfall may
fall in the higher elevations. After Tuesday, expect northeastward
progression of the surface low to push the trailing cold front and
accompany rain/storms farther east and south with some more
uncertain potential for heavy rainfall in the eastern and southern
U.S. for Wednesday-Thursday. Approach/arrival of another upper low
as currently advertised by midweek or so would produce somewhat
more organized precipitation across the Northwest, and potential
for heavy snow in the mountain, and snow levels dependent on the
depth of the upper low.

Expect South Texas to see multiple days of hazardous heat during
the period with highs persistently running 10-15F above normal with
max heat index values possibly reaching at least 110F. Highs near
or over 100 degrees could stretch farther north across the southern
High Plains at times as well. Some daily records for highs/warm
lows will be possible. Above normal highs will also track East
across the Midwest and Northeast Monday-Wednesday but should
moderate by Thursday as the cold front pushes through the region. The
forecast pattern will favor below average highs over the Northwest
to northern Plains for most of next week.


Kebede/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










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