346
FXUS02 KWNH 150637
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
237 AM EDT Tue Jul 15 2025

Valid 12Z Fri Jul 18 2025 - 12Z Tue Jul 22 2025

...Central Gulf Coast heavy rain threat into next weekend...


...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
upper troughs moving through the northern tier states. Convection
is likely ahead of a cold front across the interior eastern U.S.
and north of a warm front across the Midwest. Farther south, the
National Hurricane Center continues to monitor the potential for a
low pressure area currently east of Florida to develop into a
tropical cyclone and reach the central portion of the Gulf Coast
during the latter half of this week. Regardless of development,
heavy rainfall and flash flooding threats are increasingly likely
for parts of the central Gulf Coast later this week and into the
weekend. Meanwhile, monsoonal moisture will be in place through the
period in the Four Corners states to the south-central High
Plains. Upper ridging from the southern Plains to the Southeast
will promote summer heat into early next week.


...Guidance/Predictability Assessment...

A low amplitude and progressive synoptic weather pattern across
the northern tier states will remain in place through much of the
medium range period. Model and ensemble guidance has been very
consistent in showing this, but continues to show plenty of
uncertainty in the details and timing of shortwaves within the
greater longwave trough. These details affect the timing and
placement of surface fronts and QPF. A blend of the deterministic
solutions seemed like a good starting point for the first half of
the period, increasing to 50/50 ensemble mean and deterministic by
the second half to account for greater uncertainty.

The National Hurricane Center now shows a moderate chance of
tropical development of an area of low pressure just east of
Florida as it drifts westward into the northern Gulf. Much of the
guidance suggests the presence of a low, but there is a lot of
uncertainty in the strength. The ECMWF and GFS are the least
enthusiastic with development and thus have relatively
underwhelming QPF amounts. The CMC, UKMET, and especially the ICON
show more potential and significantly more QPF. These solutions
however, do have support from some of the AI and ensemble guidance.
The WPC QPF tonight continued to trend heavier than continuity,
and is near or just slightly higher than current NBM values. This
seems warranted given moisture values in the 90th-95th percentile
as advertised by much of the guidance.


...Weather/Hazards Highlights...

An area of low pressure is forecast to move east across northern
Florida this week and reach the central Gulf Coast late this week.
Regardless of any kind of tropical development, moisture above the
90th percentile looks will impact the central Gulf Coast by the
medium range leading to heavy to excessive rainfall. There is
enough consistency in the model timing of the heavy QPF and the
abundance of tropical moisture for an upgrade to a moderate risk on
the Day 4/Friday Excessive Rainfall Outlook (ERO) across southern
Louisiana. A broader slight and marginal risk is maintained from
far east Texas into parts of Mississippi, Alabama, and the Florida
Panhandle. Moisture in this area may be slower to move given the
larger scale ridge in place, and so a slight risk seemed warranted
for the Day 5/Saturday ERO as well across Louisiana. Moderate
rainfall may extend into Sunday as well but with much more
uncertainty.

Much of the nation from the Rockies eastward will be active with
typical summertime convection in a warm and unstable airmass during
the period. A cold front shifting into the Ohio Valley/East on
Friday will support showers and thunderstorms with ample moisture
and instability, resulting in a heavy to excessive rainfall threat.
Both the Thursday and Friday EROs show a very broad Marginal Risk
across these regions and stretching back westward into the mid-
Mississippi Valley. There was enough agreement in the guidance for
the addition of a slight risk across parts of the central
Appalachians on Friday with ample moisture in an area of relatively
low flash flood guidance. There is also increasing model agreement
for a synoptic pattern that favors the setup of west-to- east
training of convection to the north of a lifting warm front ahead
of a developing low pressure wave on Friday into Saturday.
Therefore, slight risks are in place for both Friday and Saturday
on the EROs associated with this activity.

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 Friday and Saturday. 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
looks to remain near or below normal (on the order of 5-10 degrees)
for this time of the year through much of the period, with some
moderation at times. Elsewhere, despite temperatures being near or
only a few degrees above normal, the persistence of ridging over
the Southeast will keep a moderate to major HeatRisk in place for
the region, stretching westward with time into the
Tennessee/Mississippi Valley.


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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