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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1905Z Apr 09, 2024)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
305 PM EDT Tue Apr 9 2024

Valid 12Z Fri Apr 12 2024 - 12Z Tue Apr 16 2024


...Overview...

The vigorous storm system affecting the East at the start of the
forecast period on Friday will continue to track over eastern
Canada and push its trailing front eastward as the supporting
upper trough lifts northeastward. Some areas of rain and snow may
linger over the Northeast into Saturday. A trailing Rockies/Plains
upper ridge will bring initial western warmth into the central
U.S. with parts of the Plains seeing highs 15-25F above normal
during the weekend. Guidance is starting to stabilize for the deep
upper low dropping into the eastern Pacific during Friday-Saturday,
bringing a brief period of precipitation into California during
the weekend. However after Saturday there is still timing spread
for the upper low between California and the Plains, with some
influence from differences in upper troughing expected to push
gradually into the Northwest. This upper low will most likely reach
the Plains by next Tuesday and support a fairly strong surface low
at that time.

...Guidance/Predictability Assessment...

On day 3, a general model blend consisting of the 00z EC/UKMET/CMC
and 06z GFS was used, due to the general model agreement regarding
the presence of an omega block pattern over the CONUS. By day 4 we
shifted toward a Euro weighted GMB because it was more consistent
than the GFS with respect to the digging West Coast trough. The EC
also clustered reasonably well with the CMC, UKMET and ensemble
means over the West Coast as well. There's much more spread on day
5 and that's reflected in a blend containing 6 different pieces of
guidance. The 00z deterministic Euro is still favored but the 00z
ECE and 06z GEFS were introduced to the GMB to account for spread
in the Western mid-level low.

By day 6, we've gone with an equal blend of the 00z EC/ECE/CMCE and
06z GEFS. The operational GFS still has the mid-level low center
stationed over southern California while the favored blend
positioned it near and around the Four Corners region. This same
blend is continued through day 7.

...Weather/Hazards Highlights...

The windy system tracking out of the Great Lakes as of early Friday
will still support anomalous moisture over the Northeast in the
strong southerly flow along/ahead of the cold front sweeping
through the region during the day. A Slight Risk of Excessive
Rainfall leading to Flash Flooding was introduced, in coordination
with GYX, over portions of southern Maine and the White Mountains
of ME/NH. Increased QPF trends, snow melt, and orographic
enhancement were some of the supporting factors for the upgrade
from the Marginal that remains over portions of Upstate New York,
and central/northern New England. Colder air will filter in with
the passage of the front which may result in areas of mixed
precipitation type or changeover to all snow by Friday night and
persisting into Saturday.

The upper low dropping southward over the eastern Pacific late this
week should approach/reach California during the weekend. While
moisture anomalies do not appear too extreme with this system, the
depth of the upper system offers potential for some localized
moderate to heavy rain bands. Such activity could lead to some
runoff issues given fairly high soil moisture anomalies currently
existing along the coast. Thus the Day 5/Saturday ERO depicts a
Marginal Risk area along approximately the central half of the
California coast where the best average of guidance suggests
potential for rainfall enhancement. Some precipitation in the
Sierra Nevada may be in the form of snow. As the upper low
progresses eastward, it should produce precipitation of varying
intensity across the Great Basin and Four Corners states, followed
by increasing coverage/intensity of rainfall over the Plains by
next Tuesday as it develops potentially strong low pressure. The
Northwest may see some light precipitation late this week and
perhaps another period of rain/mountain snow early next week with
the arrival of an upper trough. Farther east, a weak wave/frontal
system may produce some rain over parts of the Ohio Valley/Great
Lakes through Mid-Atlantic during at least a part of the weekend.

The Northeast will see unseasonably warm lows early Friday ahead of
the cold front crossing the region during the day. Behind the
front, parts of the Ohio Valley/Great Lakes into central-northern
Appalachians will see a brief period of cool daytime highs Friday-
Saturday. Farther west, from Friday through the weekend an area of
above normal temperatures will shift from the West/High Plains
into the central U.S. Highs should reach up to 10-20F above normal
on Friday while parts of the northern/central Plains may see plus
15-25F anomalies during the weekend. Some of this warmth with
lesser anomalies (plus 5-15F) will likely spread into most of the
East from Sunday onward. Persistence of a mean trough aloft may
hold daytime highs closer to normal over the Northeast though. The
upper low tracking in from the eastern Pacific will bring below
normal highs into California and the Southwest during Sunday-
Tuesday while farther north an upper trough and leading cold front
should promote modestly below normal readings over the Northwest
by early next week.

Kebede/Rausch


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