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FOUS30 KWBC 042013
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
413 PM EDT Sun Aug 04 2019

Day 1
Valid 1926Z Sun Aug 04 2019 - 12Z Mon Aug 05 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST, SOUTHERN ROCKIES, SOUTHERN HIGH PLAINS, DAKOTAS,
AND SOUTHEAST...

...Southwest...Southern High Plains...Southern Rockies...
An upper high remains centered near the Four Corners. Above
average precipitable water values 1.5 to 2 standard deviations
above the mean will support potential for additional locally heavy
and isolated excessive rainfall in what will likely be another
round of widespread scattered convection.  Temperatures at 700 hPa
of ~15C indicate that locations closer to sea level in the deserts
should remain capped, with activity mostly confined to the
topography.  The marginal risk area was not changed appreciably
from the previous issuance and takes into account recent radar
trends.

...Southeast/Mid-South...
A broad marginal risk area exists across the region near a pair of
weak fronts.  The upper trough axis is forecast to remain oriented
from the Upper Ohio Valley into the Tennessee Valley and Central
Gulf Coast, supporting the potential for additional convection
across the above mentioned regions that received heavy rains over
the past 24 hours.  HREF neighborhood probabilities for 2"+
amounts are high across this area...generally in 60-70%
range...which could occur in one hour given the moisture present.
Adjustments were made to the area to account for the more
significant instability pools which are leading to pockets of
heavy rain across KY, southwest TN, and northwest MS.

...Dakotas & West-central Minnesota...
A surface frontal boundary dropping southeast across the Northern
Plains into the Upper Mississippi Valley will remain the focus for
convection this afternoon into night.  While there is a large
spread in QPF details..there is consensus for moderate to locally
heavy precip totals in an axis of increasing instability...ML CAPE
values are currently 2000-3000 J/kg in eastern ND and western MN.
Adjustments were made to the area based on radar trends.

Roth/Chenard/Oravec


Day 2
Valid 12Z Mon Aug 05 2019 - 12Z Tue Aug 06 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PLAINS AND THE SOUTHEAST U.S. ON MONDAY...

...Central Rockies and Adjacent High Plains...
Monsoon moisture should still be located over portions of the
Central Rockies...trapped within the broad anticyclonic flow over
the region.  That should set the stage for another round of
scattered afternoon and evening convection.  Current thinking is
that the convection should largely being unfocused in terms of
synoptics...leaving forcing on the mesoscale or smaller as
important players in initiating and sustaining convection.  The
GFS continued to show the highest Precipitable Water values along
the Colorado and New Mexico front range where PW values are
forecast to be at or above 1 inch.

...Central Plains...
Minor changes were made to the Marginal Risk from the earlier
issuance across portions of the central Plains northeast toward
the Upper Mississippi River Valley, with some adjustments to the
northeast aligning with the latest model signal for heavy
rainfall. Locally heavy rainfall of 1-2 inches will be possible
along/ahead of a slow-moving frontal passage. Higher moisture
pooling ahead of the front, characterized by PWs of 1.5 to 1.75
inches along with warm cloud depths of 3-3.5 km, suggest
possibility of efficient rain producing thunderstorms. Rainfall
totals of 1+ inch in one hour will be possible.

...Southeast U.S....
A lingering surface boundary combined with higher than normal
precipitable water values (2.0-2.2 inches) across the eastern
Carolinas coastal plain will favor locally intense rainfall rates
Monday afternoon into the early morning hours on Tuesday. The
latest HREF continued to show probabilities of locally heavy
rainfall and the Colorado State University first guess fields
suggested probability of flash flooding in the 5-10 percent range,
indicating potential for some ponding problems within areas of
poor drainage. No changes were made to the existing Marginal Risk
from the earlier issuance.

Bann/Taylor


Day 3
Valid 12Z Tue Aug 06 2019 - 12Z Wed Aug 07 2019

...MARGINAL RISK OF FLASH FLOODING ACROSS THE SOUTHWEST U.S. AND
LOWER GREAT LAKES REGIONS...

...Arizona to Colorado and New Mexico...
Monsoonal moisture will remain in place across portions of the
Southwest states, circulating around a sprawling upper high
anchored over New Mexico. Another push of deeper moisture is
slated to arrive across portions of southern Arizona and
potentially into far southern Nevada Tuesday night/Wednesday
(particularly shown by the latest GFS). However, the rest of the
deterministic models hold the deeper moisture back into Arizona
during the Day 2 period. As such, after coordination with VEF, the
Marginal Risk was adjusted out of Nevada at this time. Elsewhere,
only minor changes were made where PWs 1.5 to 2.0 SD above the
climatological mean are present. With the favored upslope flow
initiating and sustaining convection, locally intense rainfall
rates will be possible.

...Lower Great Lakes Region...
Along and ahead of an approaching cold front, higher moisture is
expected to pool across portions of northern Indiana, northern
Ohio, and western Pennsylvania. Precipitable water values of 1.5
to 1.75 inches are expected, which generally are at or above the
90th percentile for the area this time of the year. Additionally,
the latest model guidance indicates warm cloud depths of 3 to 3.5
km will be present during the afternoon/evening hours. With
sufficient instability and lift in place, efficient rain producing
thunderstorms are likely with some probabilities of exceeding 1
inch in 1 hour in places. With the front taking on a more
west/east orientation and storm motions likely to be parallel to
the mean flow, some training thunderstorms will be possible. The
main limiting factor against flash flooding is the drier than
normal conditions observed in the last 7-14 days (subsequently
higher FFG). However, the Colorado State University first guess
ERO fields do show 5-10 percent probabilities and with
coordination from IWX/CLE/PBZ, a Marginal Risk was introduced.

Taylor


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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