363
FXUS02 KWBC 140700
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 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 agremeent 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 aross 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 northern High Plains will cool dramatically by
Wednesday with highs around 15 to 25 degrees below normal.
Temperatures there should slowly warm closer to average late week.
Temperatures look to be a few degrees cooler than average for the
south-central U.S. for much of the week as clouds and rain hold
temperatures down. The Great Lakes and Northeast will see warmer
than average temperatures Wednesday and Thursday under an upper
ridge, with somewhat widespread Major (level 3/4) HeatRisk showing
up in those areas and points southward mid-late week. In the
Northeast, a cold front will allow temperatures to cool toward
normal by next wekeend. Meanwhile the Southeast should be near
normal most days, for typical summer heat and humidity.


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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