FOUS30 KWBC 050046
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
845 PM EDT Tue Oct 04 2022

Day 1
Valid 01Z Wed Oct 05 2022 - 12Z Wed Oct 05 2022

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST AND THE SOUTHERN ROCKIES/HIGH PLAINS...

Southwest United States...
Felt it was a little too early to remove the Marginal Risk area in
portions of Arizona and New Mexico even though convection and the
threat for excessive rainfall should soon start to wane with the
loss of daytime heating.  Felt confident enough to remove the
portion of the Marginal Risk in Colorado but continued the
Marginal Risk area where surface-based CAPE and CAPE based on the
lowest 100 mb layer was nearing 500 J per kg.  These areas had the
most convection.  This was roughly coincident with where satellite
imagery showed two separate well-defined vort centers...one
eastern Arizona and the other over the central portion of New
Mexico...that were helping focus convection and sustain the
convection. Even expanded the Marginal area a bit into West Texas
where some training of cells has raised the prospect of flash
flooding or problems with run off in the short term. Point
forecast soundings suggest enough potential for propagation
through thunderstorm outflows (strong low-level lapse rates
through early evening and weak low-level shear) which still
suggests that precipitation potential should be limited to an inch
or less in most areas.



Mid-Atlantic...
There is still a non-zero probability for the occurrence of
excessive rainfall in association with a strong coastal low
overnight and some elevated instability to help enhance rainfall
rates locally. It still appears, however, that risk is still not
widespread enough to warrant an upgrade to a Marginal Risk.  If
rainfall rates were to approach Flash Flood Guidance thresholds
(around 0.5-1.0 inch/hr) it should be focused from parts of the
Delmarva into far southern New Jersey overnight where pockets of
elevated instability could briefly enhance rainfall rates over
areas where rain has fallen for several days in a row.  An area of
rainfall farther north should remain in a more stable environment
with lower rainfall rates.

Bann



Day 2
Valid 12Z Wed Oct 05 2022 - 12Z Thu Oct 06 2022

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST AND THE SOUTHERN ROCKIES/HIGH PLAINS...

...21Z Outlook Update...
The ongoing forecast is on track, with only minimal changes to the
Marginal area in Arizona.  Southeastern Arizona should remain just
ahead of a mid-level trough axis, allowing for afternoon
thunderstorms to develop in a similar regime as areas just to the
northeast in New Mexico.  Localized heavy rainfall could promote
excessive runoff at times, though the risk should remain isolated.

A few areas of higher rainfall totals (1-1.5 inches) could
materialize across southern New England and eastern Massachusetts.
 Very localized areas of ponding/runoff could materialize,
although antecedent conditions and soil moisture values are
relatively dry.  Any flash flood threat should be isolated at best
(less than 5% coverage).

Cook

...Previous discussion...

...Southwest...

The frontal boundary will continue to press southward into the
Southern Plains and portions of the Southern Rockies with
persistent showers and thunderstorms in its proximity. These
storms may be capable of producing moderate to heavy rainfall
across parts of the Southwest and Southern Rockies during this
period which will keep the threat for excessive rainfall elevated.
A Marginal Risk remain in effect for New Mexico and small portions
of eastern Arizona, southern Colorado and western Texas.

...Northeast...

The coastal low is expected to pull farther offshore during this
period although lingering showers and thunderstorms will remain
possible over the area. Rainfall amounts should stay below FFG
thresholds.

Campbell

Day 3
Valid 12Z Thu Oct 06 2022 - 12Z Fri Oct 07 2022

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PARTS OF
NEW MEXICO AND ARIZONA...

...21Z Outlook Update...
The Marginal Risk area in the Southwest has been nudged westward
across Arizona.  Recent guidance depicts thunderstorm development
across eastern Arizona and New Mexico during the afternoon.  A
mid-level wave near the area should gradually weaken while
drifting westward, allowing for a slight westward shift in
thunderstorm risk.  Locally heavy rainfall could cause excessive
runoff in a few areas - especially during and just after peak
heating hours.

Cook

...Previous Discussion...

The progression of the cold frontal boundary will slow during this
period as the northern stream begins to to pull away from the
upper low/trough over the Southwest. However this will continue to
be abundant moisture pooled that part of the country which will
help continue to support diurnally drive thunderstorms capable of
producing heavy rainfall. A Marginal Risk area is in across across
Arizona and New Mexico.

Campbell



Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt


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