534
FXUS02 KWNH 140706
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
305 AM EDT Mon Jul 14 2025

Valid 12Z Thu Jul 17 2025 - 12Z Mon Jul 21 2025

...Central Gulf Coast heavy rain threat...


...Overview...

A fairly typical summertime pattern will remain in place through
much of the medium range period with an expansive and building
upper ridge stretched across the Southern U.S. and progressive
shallow troughs moving through the northern stream flow. Convection
is likely along and ahead of a couple of cold front through the
northern tier and into the East. Farther south, a tropical wave
being monitored by the National Hurricane Center for development in
the northern Gulf will bring heavy rain threats to parts of
Florida and especially portions of the central Gulf Coast.
Meanwhile monsoonal moisture increases through the period in the
Four Corners states to the south- central High Plains. Upper
ridging from the southern Plains to the East will promote summer
heat through late week into next weekend.


...Guidance/Predictability Assessment...

Model guidance has persistently shown agreement for a low
amplitude and progressive pattern, but with variability in the
details and timing of shallow shortwave and longwave troughs within
it. These details affect frontal placement and QPF, but a general
model compromise worked well for the first part of the period to
handle these differences. A couple of shortwaves rounding a ridge
over the northeast Pacific show more uncertainty, especially late
period with more trough amplification over the Pacific Northwest. A
trend towards half ensemble means/half deterministic worked well
as a starting point for days 6 and 7.

The National Hurricane Center is monitoring a tropical wave, with
low probability of development, as it drifts across northern
Florida into the northwest Gulf by the start of the medium range
period. There is good agreement on the presence of a surface
reflection, but a lot of uncertainty on how strong this is or if it
even develops into a full tropical system. This especially impacts
the distribution and amounts of QPF. The NBM is heavier than much
of the deterministic guidance, with the GFS and ECMWF on the low
end (and likely too low). The WPC QPF trended heavier than
continuity for this system, but still lower than the NBM at this
point.


...Weather/Hazards Highlights...

A surface low pressure system (which the National Hurricane Center
is monitoring with low probabilities of tropical cyclone
development) will be retrograding into the Gulf by midweek after
crossing Florida, and potentially reaching the central Gulf Coast
Thursday-Friday. Moisture above the 90th percentile looks to reach
the central Gulf Coast by the medium range, after a wet early part
of the week in Florida. Given the moisture, ample instability, and
forcing from whatever surface is present, this warranted an upgrade
to slight risk from portions of Louisiana, and far southern
Mississippi and Alabama for both Day 4/Thursday and Day 5/Friday. A
Marginal Risk is included on both the Day 4/Wednesday and Day
5/Thursday Excessive Rainfall Outlook (ERO) for those areas. Heavy
rain may linger in the Gulf Coast region into next weekend as well.

Much of the nation from the Rockies eastward will be active with
typical summertime convection in a warm and unstable airmass. A
cold front shifting into the Ohio Valley/East Thursday and Friday
will support showers and thunderstorms with ample moisture and
instability, resulting in a heavy to excessive rainfall threat.
Both the Thursday and Friday ERO shows a very broad Marginal Risk
across these regions and stretching back westward into the Middle
Mississippi Valley and south-central Plains where the potential for
west- east training of convection may be higher. There is
considerable spread with the model guidance regarding heavy rain
amounts and placement, so the Marginals are quite broad in order to
cover the widespread threat. Generally this is a low- end and
isolated flash flooding threat equating to a Marginal Risk, but
some areas may eventually need embedded Slight Risks in future
cycles if models converge. Another front to the west will support
renewed rainfall threats across the northern Plains/Upper Midwest
next weekend.

Farther south, monsoonal moisture will gradually increase in
coverage across the Southwest/Four Corners/southern Rockies region.
Marginal Risks are in place across much of Arizona and New Mexico
and stretching into Colorado for both Thursday and Friday. Areas
like burn scars and urban areas would be of greatest concern for
flash flooding. The monsoon pattern should continue into next
weekend.

Temperatures in the High Plains to the northern/central Plains
will be well below normal (on the order of 10-15 degrees) for this
time of the year into late week, but should warm closer to average
by the weekend. Modestly above normal temperatures in the East
looks to equate to some major (level 3 out of 4) HeatRisk for
Thursday into Friday, but this should moderate and shift southward
into the Southeast next 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






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