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

------------=_1564430834-118394-1829
Content-Type: text/plain

FOUS30 KWBC 292007
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
406 PM EDT Mon Jul 29 2019

Day 1
Valid 16Z Mon Jul 29 2019 - 12Z Tue Jul 30 2019

...MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS MULTIPLE AREAS
TODAY...

...Eastern Portions of TX-OK through the Lower-Mid MS Valley,
western OH Valley, and Lower MI...
Low pressure will continue to move east across northern Ontario
today with an associated shortwave trough pushing east from WI to
MI into tonight. The greater forcing farther north over the
Midwest is still expected to make a more progressive cold frontal
passage while farther south of the more pronounced height falls,
the front will become more west-east orientated with time and
become quasi-stationary by Tuesday morning.

Overall, a marginal or isolated risk for excessive rainfall
remains over a fairly large latitudinal swath ahead of the upper
shortwave trough/surface front. Over the northern areas (mid MS
Valley-OH Valley-Lower MI), quasi-linear segments of pre-frontal
convection will feed off a modest thermodynamic profile -- with
PWs ~1.75" and MUCAPEs ~1000-1500 j/kg). Given the swift frontal
progression, any organized segments will likely forward propagate,
especially given the weak mid-level lapse rates ahead of the front
and (thus) the reliance on surface-based heating to foster any
upscale convective growth -- the result of which would promote
fairly productive cold pools/outflow boundaries.

Farther south toward the lower MS Valley, eastern TX and the Gulf
Coast, higher PWs (~2.00" and more robust deep-layer instability
(mixed layer CAPEs 2000-3000+ j/kg) would favor higher rainfall
rates, as noted by the HREF and experimental HREF probs of 1-2+
inches within an hour. However, weaker low-level inflow (greater
vertical wind shear) along with the weak mid level lapse rates
over this region as well will too limit the persistence of intense
rainfall rates before the ensuing cold pool/outflow decay. Given
higher flash flood guidance over the south, no areas of Slight
Risk have been identified as of this time.


...Portions of the Southwest...
A modest degree of 850-700 mb moisture flux, with PWs not overly
anomalous for late July underneath the upper ridge will pose a
marginal or isolated risk for excessive rainfall over southeast AZ
and southwest NM, particularly during the peak heating hours
through this evening. Weak deep-layer flow/low 0-6km bulk shear
values and thus pulse-type storm mode will inhibit any persistence
of the more intense rainfall rates. Shrank the northern portions
of the outlook area based on 12Z CAM guidance which is more
suppressed south.


...Portions of the Central High Plains...
Convection firing this afternoon across far eastern CO/western KS,
triggered by the peak daytime heating with an uptick in
southeasterly (upslope) low-level flow and moisture transport,
will propagate fairly swiftly to the SE per the Corfidi vectors.
Regardless, strong deep-layer instability (mixed-layer CAPEs
1500-2000 j/kg) will lead to some intense precip rates (including
hail) for a short period of time, which could cause runoff issues
in areas with lower FFG values. Most of the high-res CAMs show
isolated QPF totals between 1.5-2.5". This area was focused based
on FFG and 12Z CAM guidance.

Farther north, a weak mid-level impulse rounding the ridge axis
over the northern Rockies will promote late afternoon scattered
thunderstorms over eastern WY. These will shift east-southeast
with the mean flow into an environment of around 1500 SBCAPE over
far northwest NE. Low level southeasterly inflow is directly
counter to this mean flow, so there should be some propagation
issues/potential for training cells. PW increases to around 1.25"
which is not anomalously high, but the 3hr FFG is around 1.5
inches west of the Sandhills. Therefore, a Marginal Risk was
raised for an area of NE/SD/WY northwest of the Sandhills.

Hurley/Jackson





Day 2
Valid 12Z Tue Jul 30 2019 - 12Z Wed Jul 31 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER THE
SOUTHERN ROCKIES INTO THE SOUTHWEST...PARTS OF THE NORTHEAST...AND
THE CENTRAL GULF COAST...

...Southwest...
Mid-level ridge centered over New Mexico will gradually shift
westward continuing to drive monsoon moisture into the Southwest.
PWATs as high 2+" will pool near the Mexico/AZ border, more than 3
standard deviations above the climo mean, before advecting
northward in response to persisting low/mid level southerly flow
and a shortwave rotating around the periphery of the ridge. In
addition, a jet streak is progged to strength across the northern
Great Basin, placing the area within the favorable RRQ for ascent
coincident with the best MUCape which may approach 2000 J/kg. The
best moist advection may lag the strongest instability, but still
expect considerable coverage of convection from Arizona northeast
into SW Colorado.

Although coverage of thunderstorms may be scattered to widespread,
and HREF/GEFS probabilities for 1"/hr rain rates are moderate,
storm motions of 15 kts, utilizing the 0-6km mean wind as a proxy,
may inhibit anything more than localized flash flooding despite
low probabilities for 3" of rainfall focused in southern AZ. While
these rain rates and this amount of rain would likely exceed FFG,
after coordination with TWC/PSR have opted to maintain the MRGL
risk due to concern about storm motions and cloud cover
potentially limiting instability. Should a model signal become
more robust for heavy rainfall and flash flooding, a SLGT risk may
be needed with the day 1 update.


...Northeast...
Moisture and instability streaming northeast along and ahead of a
slowing cold front could feed convection producing heavy to
locally excessive rainfall over portions of the Northeast, mainly
across eastern OH and WV into western NY state during Day 2. A
ribbon of MUCape potentially exceeding 1500 J/kg could support
scattered to broken areas of convection, which in an environment
characterized by PWATs of 1-1.5 standard deviations above the mean
could support heavy rainfall. This will be most likely as
propagation vectors become aligned parallel to the boundary, and
ascent is aided by modest upper diffluence. Training of these
heavier cells could produce flash flooding. This will be most
likely in regions of the lowest FFG, which is as low as
1-1.5"/1hr, or 1.5-2"/3hr from WV through parts of upstate NY.
Although flash flooding is not expected to be widespread due to
cloud layer wind as high as 25kts, training of cells atop these
pre-conditioned soils has prompted a continuation of the MRGL risk.


...Central Gulf Coast...
High-res guidance indicates that clusters of thunderstorms, or an
MCS, on the tail end of a slowly sinking cold front will create
heavy rainfall across portions of LA and into the upper Texas
coast. Weak northerly flow will drive these clusters, or MCS,
southward towards the coast as a weak vort swings southeastward
around the expansive mid-level ridge to the east. This convection
will occur in an environment ripe for heavy rainfall due to PWATs
over 2 inches and MUCape 2000-3000 J/kg. Storm motions may be slow
before better organization leads to an outflow dominated system
which would likely drop faster to the S/SW into the 850mb moist
inflow. While there remains considerable uncertainty into the
positioning and strength of these features, there is enough
support in a favorable environment to introduce a MRGL risk as
rain rates may approach 2"/hr at times, and there are low
probabilities among the various ensembles for 3" of rainfall.
Despite the high FFG, excessive rain rates, especially in any
urban areas, could produce flash flooding and the MRGL risk was
coordinated with the local WFOs.


Weiss

Day 3

The Day 3 outlook will be updated by 2030Z.


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...


$$




------------=_1564430834-118394-1829
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.
------------=_1564430834-118394-1829--

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