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

------------=_1565020646-118394-5512
Content-Type: text/plain

FOUS30 KWBC 051557
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1156 AM EDT Mon Aug 05 2019

Day 1
Valid 16Z Mon Aug 05 2019 - 12Z Tue Aug 06 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST...UPPER MISSISSIPPI VALLEY INTO THE UPPER GREAT
LAKES..SOUTHERN APPALACHIANS...COASTAL CAROLINAS AND COASTAL
SOUTHEAST FLORIDA...

...Southwest...
Another day of widespread scattered convection possible in the
vicinity of the closed upper high forecast to remain centered near
the four corners this period.  With pw values forecast to remain 1
to 2 standard deviations above the mean across the Southwest and
potential for slow moving cells...locally heavy precipitation and
isolated runoff issues are possible.  The previous marginal risk
area was decreased in size and concentrated across the Southwest,
not extending northeastward into the Rockies.

...Upper Mississippi Valley into the Upper Great Lakes...
A surface cold front will be pressing southeast Monday across the
Upper Mississippi Valley and into the Upper Great Lakes.  Well
defined upper difluence ahead of the associated southeastward
moving shortwaves will enhance lift in the axis of above average
pw values along and ahead of this front.  Model consensus is for a
fairly broad area of moderate to locally heavy rains across these
areas. The previous marginal risk area across this area was
expanded northeastward to cover the areas where HREF neighborhood
probabilities were high...60-90%...for 1"+ rains.  The greatest
heavy rain threat across the northern portion of the marginal risk
area appears to be in the 1800 utc Monday to 0000 utc Tuesday time
frame...with the southern portion of the risk area having the
greatest heavy rain threat in the 0000 to 0600 utc Tuesday time
frame

...Southern Appalachians and Coastal Carolinas...
The mid to upper level trof axis will be pushing eastward from the
Central to Southern Appalachians and into the Southeast this
period.  Scattered convection likely ahead of this trof with two
marginal risk areas depicted.  One is across the Southern
Appalachians  from far northern Georgia into western North
Carolina where HREF neighborhood probabilities are high for 1 and
2"+ amounts.  With ffg values across this region relatively
low...there may be isolated runoff issues.

The other marginal risk area is along the coastal sections of
South Carolina and North Carolina.  This region is being
highlighted by the latest guidance for locally heavy rains and did
receive some locally heavy rains over the past 24 hours.

..Coastal Southeast Florida...
A marginal risk area was added across coastal Southeast Florida
for isolated urban runoff issues this afternoon.  Hi res models
are showing potential for heavy rains across coastal southeast
Florida...with this reflected in the HREF neighborhood
probabilities which are very high for 1 and 2"+ amounts...90%+ and
50-70%+ for 3"+ amounts. Per collaboration with WFO MFL, have
expanded the Marginal Risk to include much of South FL, while
adding a Slight Risk over central and eastern portions. South FL
will continue to reside along the subtropical jet during the
period, within a weakly-difluent upper flow pattern as the
southern periphery of the upper trough tracks slowly eastward
across the eastern Gulf. 12Z KMFL RAOB depicted a PW of 2.26" and
wet bulb zero heights near 15kft -- a highly favorable profile for
optimal rainfall efficiency, especially considering mixed-layer
CAPES between 2000-3000 j/kg. The latest HREF neighborhood
probabilities of 1 hourly QPF exceeding 2" tops out between 30-50+
percent over portions of the outlook area between 19 and 23Z, with
6 hourly probs of >3.00" between 50-90% across eastern areas
toward the Gold and Treasure Coasts.

Hurley/Oravec


Day 2
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.
Saw little reason to make signficant changes to yesterday's Day 3
Excessive Rainfall Outlook as it becomes today's Day 2 ERO in the
Nevada/Arizona portion of the forecast. 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...
Maintained the Marginal Risk area over the Lower Great Lakes
region which will be positioned 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
still 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. The 00Z HREF probabilities also indicate isolated areas
where the probability of exceeding an inch per hour rainfall rates
peak over 20 percent in the Day 2 period.  Given the spread of QPF
solutions and uncertainty with the timing of the cold front, still
think a Marginal Risk is appropriate.  This is reinforced by the
idea that conditions have been drier than normal conditions have
been observed the last 7-14 days.

Bann


Day 3
Valid 12Z Wed Aug 07 2019 - 12Z Thu Aug 08 2019

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ON
WEDNESDAY/WEDNESDAY NIGHT ACROSS THE CENTRAL PLAINS...

...Central Plains...
The approach of a cold front and associated amplifying mid- and
upper-level trough over the eastern thhird of the nation will
become the focus for convection, especially Wednesday night/early
Thursday morning, over the Central Plains. The GFS is most
aggressive of the global models in developing the heavy rainfall
over portions of Nebraska/Kansas/Missouri...but its idea was
supported by the 04/12Z ECWMF with the overall synoptic pattern.
By Wednesday evening, winds in the 925 mb to 850 mb layer are
forecast to become southerly and start to draw an airmass with
Precipitable Water values at or above 1.8 inches toward a frontal
boundary.  By 08/03Z, the GFS was showing PW values of 2.0 to 2.3
inches but am taking that as a signal that the GFS has already
started to convect.  With southerly low level flow accelerating to
between 25 and 30 kts which helps maximize the low level moisture
flux convergence.  At the same time, a 110 to 125 kt upper level
jet max arching from the Dakotas to Kentucky will put the Central
Plains in a favored region of upper level support in the early
morning hours on Thursday.

WPC manual QPF nudged the axis of heaviest precipitation shown in
the GFS eastward a bit in deference to the position of the upper
jet and mid level troughing.  The QPF signal in the ECMWF was less
focused than in the GFS...while the NAM and UKMET had a weak QPF
signal.  The Canadian had a signal for moderate rainfall placed
well to the east.  Consequently, the confidence in any one
solution is below average and the WPC QPF is likely to be adjusted
over time.  A Marginal Risk area surrounds the Slight Risk area in
deference to the uncertainty and due to the possibility enough
instability will result in briefly intense rainfall rates. If the
axis is close to the current forecast...an upgrade to a Moderate
risk may be needed given the rainfall amounts observed over parts
of Kansas over the past week or so.

...Northeast U.S....
Moisture will be drawn over the Northeast U.S. during the period
by persistent west to southwesterly flow that taps Precipitable
Water values at or over 1.5 inches through the period.  Difluence
in the upper level flow develops as an amolously deep trough over
Ontario approaches...which aids precipitation development due to
broad vertical velocities ahead of a shortwave embedded within the
synoptic scale trough.  The ECMWF was actually most aggressive
while the GFS was weaker but had a broader precipitation area.
Thinking was that there would be embedded higher rainfall rates
within a broader precipitation area.  The forecasted PW values
briefly reach 2.0 standardized anomalies...but were typically in
are generally in the 1.0 to 1.5 standardized anomalies range
during the period.  As a result, think a Marginal Risk will be
sufficient for now.

...Southwest U.S....
Monsoon moisture will still be present over the Southwest U.S.
during the period, although the overall threat looks ot be waning
late in the period as heights and thickness values increase in
response to a deepening system off the west coast of North
America.  Precipitable Water values still look to be in the 1.25
to 1.5 inch range (with highest values close to the international
border at the time of maximum daytime heating).  That should be
more than sufficient for convection to produce localized intense
rainfall rates...especially in the late and and early evening.

Bann



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...


$$




------------=_1565020646-118394-5512
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.
------------=_1565020646-118394-5512--

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