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FOUS30 KWBC 231606
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1205 PM EDT Tue Jul 23 2019

Day 1
Valid 16Z Tue Jul 23 2019 - 12Z Wed Jul 24 2019

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
MONTANA, THE SOUTHERN MID ATLANTIC, SOUTHEAST, & CENTRAL GULF
COASTAL REGION...

...Far southeast Virginia..eastern Carolinas...south central
Georgia...southern Alabama...western Florida Panhandle...Central
Gulf Coast...
The strong surface frontal boundary will continue to press
southeast Tuesday through the Southeast and southward through the
Lower Mississippi Valley and Southern Plains.  The synoptic set up
remains very favorable for widespread heavy precipitation totals
ahead of this boundary from the central Gulf coastal
region...across the Southeast and into the Southern Mid Atlantic.
Across these areas...very favorable right entrance region jet
dynamics will accentuate lift in the axis of pw values in the
range of 1.75-2"+...supporting the likelihood of widespread heavy
precipitation totals. The simulated radars from the 0000 utc hi
res guidance...which has a bias of being weak with reflectivity
compared to observed radar reflectivity...is showing a well
defined convective squall line developing Tuesday afternoon across
these regions with hourly rainfall rates of 1-2" possible as the
line progresses southeastward.   Neighborhood probabilities from
the href show widespread 80-90% probabilities of 2"+ across this
region...and a narrower probability of 45-80% of 3"+ totals.  The
marginal and slight risk areas were expanded farther to the
southwest from the previous issuance into the Southeast and
Central Gulf Coastal region to cover the higher href probabilities
of 2 and 3"+ totals.  The marginal risk was also extended into far
south Texas where localized heavy totals of 1-2" are possible. The
marginal risk area was also maintained over southeast New England
for Tuesday morning when a period of heavy rains with rates of
.50-1"+ per hour are possible.

...Southern California...Southwest into the Southern Rockies...
A closed upper high is forecast to remain in place in the vicinity
of the Four Corners on Tuesday.  This will favor the persistence
of above average monsoonal pw values...1 to 2+ standard deviations
above the mean...stretching on the south and southwest sides of
the closed high across the Southwest into Southern California.
With clearing skies, scattered monsoonal convection likely with
isolated heavy totals and isolated runoff issues possible, even
into the valleys of southern AZ.  Href probabilities of 1"+
amounts highlight the areas from the Peninsular Range of Southern
California...through the Mogollon Rim of Arizona into southern New
Mexico and far Southwest Texas.  The 1"+ probabilities also
highlight the Southern Rockies from north central New Mexico into
south central Colorado.  Across these areas...a marginal risk was
also denoted.

...Northern Great Basin into the Northern Rockies...
A slight risk area was introduced for western MT within the
broader marginal risk introduced earlier this morning.  An upper
trough progresses inland across these areas Tuesday night/early
Wednesday morning, which could increase effective bulk shear and
organize convection.  ML CAPE is already on the rise, and it's
possible convective initiation would be quite early, close to 18z
around the time a weak upslope flow into western MT is expected.
Model qpfs are not too impressive across these areas...but
scattered convection likely in the region of well defined upper
difluence expected ahead of these height falls over the Northern
Great Basin into the Northern Rockies.  With pw values rising to
1.5 to 2.5 standard deviations above the mean Tuesday night/early
Wednesday -- into the 0.75-1.25" range -- isolated totals of 1-2"
possible, which could occur in one hour given the ample moisture
available.

Roth/Oravec


Day 2
Valid 12Z Wed Jul 24 2019 - 12Z Thu Jul 25 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF FLORIDA AND GEORGIA AS WELL AS THE FOUR CORNERS REGION...

...Northern FL/Southeastern GA...
A cold front will become stalled across the region and off the
southeast coast by early Wednesday. With a decent moisture and
instability gradient present combined with mid-level impulses
riding atop the aforementioned surface boundary, convection will
likely develop with efficient rain makers. Precipitable water
values of 2+ inches will be transported by 15-25 knot
southwesterly winds. Marginal MUCAPE values of 1000+ J/kg are
expected across this region Wednesday afternoon. Within the upper
levels, the jet streak to the north will slowly sink south
allowing the right entrance region to become positioned over
southern GA and northern FL, promoting additional lift. Mean wind
around 20 knots from the southwest will become aligned with
corfidi vectors in terms of both speed and magnitude for a period
of time Wednesday afternoon/evening. This will likely result in
shower/thunderstorm activity training across portions of the
northeast Gulf Coast region along the FL coast between Tampa and
Tallahassee. Given this, there is the potential for isolated flash
flooding with high flash flood guidance taken into account.
Therefore, the Marginal Risk was maintained.

...Four Corners...
Mid/low-level monsoonal flow around the persistent Four Corners
high will provide moisture with instability and upslope flow to
promote convective initiation along higher terrain of the Four
Corners states Wednesday afternoon/evening. Continued light mean
flow will mean slow storm motions and the potential for the
activity to spread off the terrain into the plains. Therefore, the
Marginal Risk was maintained across portions of AZ and the Slot
Canyon region of southern UT. Southerly flow up the eastern sides
of the CO/NM Rockies will again provide moisture to storms firing
over the high terrain, so the Marginal Risk remains centered on
the San Juan mountains.


Jackson/Pagano

Day 3
Valid 12Z Thu Jul 25 2019 - 12Z Fri Jul 26 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF FLORIDA AND GEORGIA AS WELL AS THE FOUR CORNERS REGION...

...Northern FL/Southeastern GA...
Rinse and repeat from Day 2 (Wednesday/Wednesday Night) with
respect to the stationary boundary which remains draped across
northern Florida (through Thursday night) which is the continued
focus for shower/thunderstorm activity.  Given this pattern has
shown little movement from the previous 24 hours, any
precipitation that did fall on Day 2 may allow soils to become
slightly more sensitive to additional rainfall.  However, these
sandy soils can take quite a bit of rain with soil recovery quick
to occur.  Regardless, with a continual feed of high precipitable
water across this region, lingering instability and mid-level
impulses moving atop the surface front, expect a couple additional
rounds of precipitation across this region. Areal average
precipitation within this region will range from around 0.75 to
over 1.25 inches. Therefore, decided to introduce a Marginal Risk
in basically the same location as seen on Day 2.

...Four Corners...
Mid/low-level monsoonal flow will persist across the Four Corners
region Thursday afternoon into the overnight as the mid-level
high/ridging provides moisture and impulses which when combined
with instability and upslope flow will promote convective
initiation along higher terrain. Continued light mean flow will
mean slow storm motions and the potential for the activity to
spread off the terrain into the plains. A slight difference with
respect to the synoptic pattern as observed on Day 2, a trough
crossing the northern Rockies will promote additional lift,
especially across the higher terrain in CO/NM.  Therefore expect
higher QPF totals and thus introduced a large Marginal Risk area
across this region. In addition have a Marginal Risk across a
portion of northern AZ into the higher terrain of south UT.

Pagano


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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