Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
221 AM EDT Fri Jul 26 2024

Valid 12Z Mon Jul 29 2024 - 12Z Fri Aug 02 2024

...Hazardous heat to shift into and northeast of the central
Plains...
...Showers/storms with locally heavy rainfall possible
over parts of the eastern half of the lower 48...


...Overview...

Guidance continues to show the pattern evolving toward a
strengthening southern Rockies/Plains upper ridge by the middle to
late part of next week as a retrograding Gulf Coast ridge merges
with the lingering ridge over the southern Rockies. This should
help set up what should be a prolonged period of hot weather over
many areas with the most anomalous heat expected over the Central
Plains. Shortwave energy moving through the Midwest with eventual
mean troughing that develops over the eastern U.S., will support a
broad area of showers/thunderstorms drifting across the eastern
half of the country. Energy feeding into an initial mean trough
aloft over the Pacific Northwest coast should bring some rainfall
to the region early next week. This energy should eject eastward
mid-late week as larger scale troughing takes shape over the
northeastern Pacific.


...Guidance/Predictability Assessment...

On the large scale, the latest models and ensembles show good
agreement on the overall pattern during the medium range period,
but some uncertainty still in the details of individual systems.
Across the East early next week, models continue to converge on the
merge of a shortwave through the Ohio Valley and a weak upper low
tracking into New England. There are some detail discrepancies on
the exact evolution, which has some implications on QPF
coverage/intensity across the East-Central to Eastern U.S.. There
is good agreement though that eventually mean troughing should
develop over the East mid to late next week as a ridge builds
upstream across the central and southern Plains. The next shortwave
will reach the West Coast around Monday-Tuesday and the UKMET is
notably slower with its progression eastward into the northern
Plains and was not included in tonight's forecast blend. Models
suggest this may spin up a weak upper low over the northern Great
Lakes late week.

The WPC forecast tonight used a blend of the 18z GFS with the 12z
ECMWF and CMC for the first half of the period. After this,
increased contributions from the ensemble means reaching fifty
percent of the blend by Day 7. Overall, this maintained good
agreement with the previous WPC forecast through Thursday.


...Weather/Hazards Highlights...

By Monday, there will be a broad corridor of above-climatology
precipitable water values extending from the Upper Midwest into the
Southeast, gradually shifting eastward with time. The Days 4 and 5
Excessive Rainfall Outlooks covering Monday-Tuesday night show
broad marginal risks across this region. There was enough agreement
in the guidance for small slight risks across portions of the
southern-central Appalachians where flash flood guidance is
typically lower. Much of the Eastern third of the country should
remain generally unsettled next week as a upper trough is slow to
budge out of the region. Elsewhere, above normal moisture
associated with a shortwave should bring some modest rainfall to
portions of the Pacific Northwest on Monday, with much lighter/more
scattered rainfall as the shortwave shifts inland. Monsoonal
convection over the Southwest should stay confined to southern
areas through midweek, though it may eventually expand a little
northward depending on the shape of the southern Rockies/Plains
ridge and upper level energy rotating around its western periphery.

The forecast pattern evolution will support an expanding area of
warmer than average temperatures across the Lower 48, possibly into
the Ohio Valley/Mid-Atlantic by next Thursday. The most persistent
and extreme high temperature anomalies should be over the Central
Plains where some locations should see multiple days with highs
10-15F or so above normal. The Northeast could see some highs reach
10F or so above normal early in the week. The experimental
HeatRisk likewise reflects an expanding area of Moderate to Major
risks of heat- related impacts from the weekend through next
Wednesday, and even some pockets in the Extreme category over the
central U.S. by next week. Forecast temperature anomalies would
yield highs in the upper 90s to 100s over the central Plains and
upper 80s to 90 or so farther northeastward. Climate Prediction
Center forecasts indicate some variation of this pattern may
persist into next weekend. Much of the West will likely see near to
slightly below normal highs through the first half of next week
before the strengthening ridge pushes temperatures somewhat above
normal by next Thursday. Lingering rainfall over the southern tier
should support near to below normal highs, especially over
southern/eastern Texas at the start of the week.

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