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FOUS30 KWBC 250041
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
840 PM EDT Wed Jul 24 2019

Day 1
Valid 01Z Thu Jul 25 2019 - 12Z Thu Jul 25 2019

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHWEST...

...Southwest into the Southern Great Basin...
Little change was made to the coverage or position of a Slight
Risk that was shifted northward and westward earlier this
afternoon.  Late afternoon/early evening radar imagery showed
scattered convection over parts of the Southwest U.S..  Some of
the convection over the Desert Southwest was being focused and
supported by two vorticity maximum...one of which was over the
southwest corner of Arizona and the either was over the
northwestern part of the state.  The energy should continue to
support additional convection as they move into a moist and
unstable atmosphere.  A 22Z sounding from 1Y7 showed a
Precipitable Water value of 2.03 inches, nearly 1100 K per kg of
CAPE and a nearly saturated column in the mid levels.  The 00Z
soundings showed a decent gradient in Precipitable Water
values...with VEF values at 1.3 inches.  Despite the lower PW
values, forecast soundings still supported the idea of locally
intense rainfall rates, especially with the added support of the
upstream vorticity centers. Expect the convection to eventually
weaken with a corresponding decrease in rainfall rates later this
evening with the loss of heating.  Still noting that the HREF was
still highlighting probabilities for 1 and 2"+ amounts this
evening along the Peninsular Range of Southern
California...western Mogollon Rim of AZ...the southern
Sierra...through the Wasatch and the Southern Rockies of north
central NM into southwest CO.

...Northern Florida...
Early evening radar imagery was showing a decided decrease in
areal coverage and decreasing rainfall rates over the northern
Florida peninsula while only a small area of moderate rainfall was
being shunted out over the Gulf of Mexico.  There was a
quasi-stationary front draped across the area that separated
Precipitable Water values of 2.00 to 2.25 inches south of the
boundary with Precipitable Water values of 1.25 inches or less to
the north.  Opted to keep a small Marginal Risk area but suspect
that the heaviest rainfall has already occurred and any concerns
for flooding will be confined to a few spots which received local
rainfall amounts approaching 5 inches during the afternoon.

...Far eastern Montana...western North Dakota and western South
Dakota...
Shortwave energy pushing eastward around the north side of the
Four Corners centered upper high...has indeed shunted the best
focus for convection out over the Northern Plains and Adjacent
High Plains.  The numerical guidance has not been handling the QPF
well...but early evening radar imagery showed storms over
southwest SD and the northern Nebraska panhandle.  Will maintain a
Marginal Risk area ahead of these storms given some intense
rainfall rates associated with the convection...and HREF guidance
which supports convection building northward into parts of North
Dakota later tonight. The big factor working against widespread
problems with flooding is that these storms have been steadily
moving any chance of back-building storms looks limited at this
time. To the west, hoisted a separate Marginal Risk area over
southern Montana for short-term concerns where small and widely
scattered cells could produce locally heavy rainfall amounts
before the cells dissipate during the mid- to late-evening.

Bann



Day 2
Valid 12Z Thu Jul 25 2019 - 12Z Fri Jul 26 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST AND THE NORTHERN PORTION OF THE FLORIDA PENINSULA...

...Southwest...
Mid/low-level monsoonal flow will persist across the southwest
CONUS around a high centered on the Four Corners through the end
of the work week. Weak impulses such as the one that pushed
northwest across AZ today will provide enhanced lift beyond the
normal unstable airmass. Light mean flow will persist which will
continue to lead to slow storm motions and increased risk for
excessive rain. A greater rain threat for Nevada and west to the
Sierra Nevada from these impulses rounding the ridge warrants an
increased Marginal Risk. Given the moisture anomaly of 2 to 3
standard deviations over Nevada, there may need to be an upgrade
to a Slight Risk once a particular threat area can be identified.


...Northern FL/Southeastern GA...
A stationary boundary remains draped across northern Florida which
will be the focus for continual shower/thunderstorm activity
through Thursday night. A tight gradient of 2+ inch precipitable
water will exist across this region in addition to marginal
instability. With the upper level jet streak just to the north,
the right entrance region will assist with large scale forcing
along with mid-level impulses moving atop the surface boundary.
Therefore, anticipate convection to move from the northeast Gulf
of Mexico across the northern FL peninsula through the period.
This will result in areal average precipitation values around 1
inch with highest amounts across the northern FL peninsula.
Maintained the Marginal Risk across this area given the expected
precipitation activity from Day 1 which may help soils become a
bit more sensitive to additional rainfall and aide a continued
isolated flash flood risk.

Jackson

Day 3
Valid 12Z Fri Jul 26 2019 - 12Z Sat Jul 27 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE FOUR
CORNERS REGION AS WELL AS THE UPPER GREAT LAKES REGION...

...Four Corners Region...
Monsoonal moisture continues as the mid-level high/ridge axis
remains anchored across this region during the first half of the
forecast period. The high starts to shift to the south and west in
time, with shortwave activity moving into the California coast
thus resulting in the Pacific moisture feed becoming shunted. The
moisture within the mid-levels will be supplied by the
trough/front moving through the Central Plains. In addition,
mid-level impulses will shift farther south due to the retreating
high. Therefore, the best moisture/lift will be across southern CO
into NM. Precipitable water of 1.25 inches combined with pockets
of 2000+ J/kg will be available during the afternoon/evening
hours. Thus, expect convection to initiate along the terrain and
move southwest with time. Therefore the Marginal Risk was
maintained. Activity from UT terrain will likely spread from there
and with the large area of anomalously high moisture persisting,
the Marginal Risk was expanded over the greater UT area.


...Upper Great Lakes...
Shortwave activity shifting across Manitoba into Ontario drag a
cold front across the northern Great Lakes Friday into Saturday.
Moisture anomalies of 1 to 1.5 standard deviations accompany this
front, but given the progressive nature and relatively dry
conditions of the UP, the Marginal Risk was dropped. Areas in
northern WI are sensitive from organized weekend thunderstorms, so
this area will continue to need to be monitored.


...Gulf Coast...
A boundary persists across FL, likely sagging farther from
previous days. However, given the low FFG there no risk is raised
at this time. Farther west along the Gulf Coast there is a risk
for potential organization in the Gulf could raise the flash flood
risk, but as of now most guidance has heavy rain over the Gulf.
This will need to be monitored.


Pagano/Jackson


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


$$




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