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Extended Forecast Discussion
 
(Latest Discussion - Issued 0657Z Apr 16, 2024)
 
Version Selection
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Tue Apr 16 2024

Valid 12Z Fri Apr 19 2024 - 12Z Tue Apr 23 2024


...Overview...

The pattern during the medium range period should transition
towards more progressive flow after the start of the period on
Friday, as an Omega block over the northeast Pacific into western
North America and the northern U.S. tier begins to break down. A
cold front through the East late this week will be accompanied by
some showers and thunderstorms, with the Northeast drying out
thereafter. From the Southern Plains into the Southeast, a slow
moving cold front and shortwave energy will increase the heavy
rainfall potential, particularly from central Texas into the Lower
Mississippi Valley on Saturday. By early next week, general
troughing will be present across both the West and East coasts,
with upper ridging in between, and generally fairly dry conditions
across the CONUS.


...Guidance/Predictability Assessment...

Latest guidance shows good agreement Friday and Saturday as an
upper low shifts into southeast Canada and energy out of a deep low
in the Gulf of Alaska shifts towards the Northwest U.S.. By Sunday,
there remains quite a bit of variability on the strength and timing
of the energy as it moves inland and towards the Northern Plains.
The GFS and CMC are more progressive/weaker with the system vs
yesterdays 12z ECMWF which showed a weak closed low moving slowly
eastward. The new 00z run tonight has trended faster and more in
line with the GFS and CMC. The ensembles and the ECMWF-
initialized AI/ML models also seem to show better support for a
more progressive system, but with continued variability. After
this, there are some differences in the details of energy rounding
the base of the Eastern U.S. trough, and even greater uncertainty
by Monday-Tuesday with another trough moving towards the West
Coast.

The WPC forecast today used a blend of the deterministic models for
Days 3-4, gradually transitioning towards the ensemble means, along
with the GFS and CMC for some added system definition. 


...Weather/Hazards Highlights...

A cold front moving through the Northeast Friday-Saturday will be
accompanied by some generally light precipitation and storms, with
the southern portion slower to move or possibly stalling briefly
into the weekend across the Southern Plains-Southeast region.
Anomalous
moisture and instability present in the vicinity of the wavy front
favors a low-end Marginal Risk area on Friday from near the
confluence of the Ohio/Mississippi Rivers southwest through parts
of Texas. This overall area should have some potential for storm
training with higher rain rate potential, though guidance signals
do not show great coherence for details yet. Also most of this area
has been rather dry as of late, which should inhibit the overall
flash flood threat. Favorable flow into the Central Rockies should
work to enhance precipitation there too, with some snow in the
highest elevations. By the weekend, weak shortwave energy reaching
into the Southern Plains should help to further enhance
precipitation across Texas and vicinity on Saturday with increasing
heavy rain potential. Given how wet the southern TX to southern AR
region has been lately, opted to introduce a slight risk on the
Day 5 Excessive Rainfall Outlook across this area, with a broader
marginal risk encompassing the greater Southern Plains/Lower
Mississippi Valley/into parts of the lower Tennessee Valley. The
system currently expected to brush the Northwest during the weekend
may bring some light to locally moderate precipitation.

By Friday and beyond, much of the Northeast should gradually cool
behind a cold front. Meanwhile, the upper trough over the northern
tier states and eventually into the East will support below normal
temperatures (with greater anomalies for highs than lows) for most
east of the Rockies but Florida by next weekend. Above normal
temperatures across the Southwest should gradually expand northward
underneath a building Western U.S. ridge and progress eastward
into the Rockies early next week. Northern parts of the West may
stay near normal due to the upper shortwave/cold front crossing the
region this weekend.


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