This is a multi-part message in MIME format...

------------=_1563843523-2024-4104
Content-Type: text/plain

FOUS30 KWBC 230058
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
857 PM EDT Mon Jul 22 2019

Day 1
Valid 1942Z Mon Jul 22 2019 - 12Z Tue Jul 23 2019

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE TENNESSEE VALLEY AND CENTRAL APPALACHIANS...AS WELL AS A
PORTION OF THE NORTHERN MID ATLANTIC...

...Lower Mississippi Valley through the Tennessee Valley into
Central Appalachians, and portions of the Mid Atlantic and
Northeast...
The first batch of excessive rainfall continues across portions of
southern New England early in the period, as the storms follow the
deepest moisture and edge of the instability gradient offshore
this evening. Based on extrapolation, the flash flood threat
across southern New England should wane as storms move offshore,
along with the best instability and moisture.

Further south across NJ/PA into the southern Appalachians, There
is a lull in the activity as the airmass across this region has
been overturned by earlier storms. However, the airmass change
lags the frontal boundary, and the moisture and instability remain
in place through 23/05z along and east of the Interstate 95
corridor. It remains unclear how much the airmass can recover
after the previous storms, but in deference to the most recent
HRRR runs, the Slight Risk remains in place through the overnight
hours, though it is possible that the greatest threat could end
before 23/06z. Based on input from WFO PHI, the Moderate Risk was
left in place over a portion of eastern PA into northwest NJ, as
this area was hit hard by earlier flash flooding.

Finally, across KY/TN, the airmass remains relatively unaffected
by the earlier convection passing to the north, as convection
follows the best instability axis into eastern TN/eastern KY
before 23/03z. As the storms track eastward, they will tap in to
the 2.00+ inch precipitable water air just ahead of the front. As
the mid level flow parallels to the slowly sinking frontal
boundary, training remains the primary flash flood threat, as
hourly rainfall rates could top out near 2.00 inches (which is
supported by the most recent HRRR runs). High resolution guidance
suggests that local 3.00/4.00 inch rainfall amounts are possible
before the instability is shunted southward with the front. Based
on this, the Moderate Risk was left in place for the evening
hours.


...Portions of the Southwest into the Southern High Plains...
Monsoonal moisture across portions of the Southwest into the
southern High Plains will fuel heavy to excessive rainfall, mainly
during the evening into the early overnight hours

There are three areas of concern for this outlook period. The
first is southeast NM, where a low level easterly flow continues
to feed deepening moisture (as precipitable water air values top
out near 1.50 inches) and 2000/3000 J/KG of MUCAPE across west TX
into southeast NM. An MCV dropping south from northeast NM will
provide sufficient lift to support convection along the
instability axis. Storms or small convective clusters could train
along the TX/southeast NM border during the evening hours,
resulting in hourly rainfall rates near 1.50 inches.

The MCV drops southeast to the far western TX Panhandle before
23/06z, as the instability either slowly weakens or becomes more
elevated. Some of the high resolution guidance (including the most
recent HRRR runs) have been slow to pick up in the development,
even though the most recent RAP runs have depicted the placement
and movement of the MCV well. Thus, the flash flood threat could
continue into the early morning hours.

The second area of concern is northwest NM, where convection
forming in the differential heating over the terrain in northwest
NM. The convection is expected to be more scattered in nature than
southeast NM, as the mid level forcing under the ridge here is not
nearly as impressive. However, slow cell motions to the south
could result in cell mergers and short term training, which could
support hourly rainfall rates over an inch. Three hour flash flood
guidance values here are as low as 1.50 inches, so a flash flood
threat will continue until the activity until the instability in
place becomes exhausted, which could occur as later as 23/06z.

The third area of concern is a small portion of south central AZ,
mainly for the evening hours. There is a multi model signal for
convection developing over nearby Mexico to track over south
central AZ this evening. The convection follows a monsoonal
moisture plume (with precipitable water values nearing 1.75
inches, which is near two standard deviations above the mean) on
the broad southeast flow under the mid level ridge in place over
the Southwest. Being just east of the mid level ridge position,
slow northwest cell motions are expected (generally under 10
knots) into south central AZ. The slow cell motions could foster
an environment for cell mergers and short term training, which in
turn could result in hourly rainfall rates approaching 1.50 inches
(which is supported by members of the 12z model suite, as well as
the last few runs of the HRRR).

Instability over this area is impressive, with the most recent
HRRR/RAP soundings showing local 2000/3000 J/KG of MUCAPE in place
through 23/06z. Model soundings also indicate that the cap remains
in place for much of the evening into the early overnight, which
could limit the areal extent of the convective coverage. However,
with the ingredients of flash flooding in place, a Slight Risk was
left in place here.

Hayes



Day 2
Valid 12Z Tue Jul 23 2019 - 12Z Wed Jul 24 2019

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

...Southeast Virginia/Carolinas/Georgia...
A cold front will continue to move southeast Tuesday across the
southeastern CONUS before stalling over northern FL Tuesday night.
A low level wave looks to develop over the Carolinas through the
day and provide a focus for thunderstorm development. Moisture and
instability ahead of the front are above normal given the recent
heat. Prefrontal activity has been occurring ahead of this cold
front which will continue Tuesday over eastern VA/NC/SC/GA. Shrank
the Slight Risk area to be around and north of this surface low
track with less in GA. Most models indicate weakening activity
Tuesday evening over southern GA as the front gets strung out, but
a Marginal Risk was maintained there and west to the central Gulf
Coast given the ample moisture despite high FFG and areas of
drought.

...Southern New England...
A wave along the cold front moving off the northeastern seaboard
Tuesday allows a plume of 2 inch PW air to cross southern New
England. This high moisture, along with some instability should
allow some prolonged heavy rain around the north side of the low.
Therefore, a Marginal Risk was introduced for roughly Boston and
south/east.

...Four Corners States...
The ridge centered over the Four Corners brings monsoonal moisture
up from the eastern Pacific and Sea of Cortez across AZ. Air with
a positive 2 to 2.5 standard deviation moisture anomaly lifted
over the AZ terrain with instability and a low mean wind warrants
a flash flood threat. Expanded the Marginal Risk to include more
upslope portions of the Mogollon Rim. A Slight Risk may be
warranted for portions of this area given the continued monsoonal
flow.

Southerly flow up the eastern slopes of the NM/CO Rockies brings
one inch PW with instability over the terrain will set off
afternoon thunderstorms centered on the San Juans of CO. Light
northerly mean flow, counter to the low level flow will make for
particularly slow storm motions, so the Marginal Risk was
maintained.

Jackson



Day 3
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 is
expected across this region Wednesday afternoon. Within the upper
levels, the jet streak will slowly sink south allowing the right
entrance region to become positioned over southern GA into
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 which could result in convective training. As a
result, isolated flash flooding is possible, with high flash flood
guidance taken into account. 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. Expanded the
Marginal Risks to once again include AZ and added the Slot Canyon
region of southern UT where thunderstorms are possible. Southerly
flow up the eastern sides of the CO/NM Rockies will again provide
moisture to storms firing over the high terrain, so a Marginal
Risk was again centered on the San Juan mountains.


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...


$$




------------=_1563843523-2024-4104
Content-Type: text/plain; charset="US-ASCII"
Content-Disposition: inline
Content-Transfer-Encoding: 7BIT

= = =
To unsubscribe from WX-STORM and you already have a login, go to
https://lists.illinois.edu and use the "Unsubscribe" link.  Otherwise email
Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.
------------=_1563843523-2024-4104--

--- SBBSecho 3.07-Linux
 * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)