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

------------=_1564344556-118394-1469
Content-Type: text/plain

FOUS30 KWBC 282009
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
408 PM EDT Sun Jul 28 2019

Day 1
Valid 16Z Sun Jul 28 2019 - 12Z Mon Jul 29 2019

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN
PORTIONS OF THE NORTHERN PLAINS TO THE UPPER MIDWEST...

16Z Update...

...Southeast Texas and Southern Louisiana...
In addition to minor adjustments to the outlook areas over the
Plains, Great Lakes and Northeast, a Marginal Risk was added to
portions of Southeast Texas and southern Louisiana.  With the 12Z
run, HREF 40km neighborhood probabilities for amounts exceeding 2
inches during the afternoon-evening hours have increased across
this area.  Southwesterly low level flow is supporting PWs 1.8 to
2 inches, with scattered convection beginning to develop with the
increase in daytime heating.  Weak flow through the low to mid
levels is expected to support slow-moving cells.  Despite
relatively high flash flood guidance values (3-4 inches for 1-hr),
these storms may have to the potential to cause localized runoff
concerns, especially over poor drainage areas.

Previous Discussion...

...Northern Plains to Upper Great Lakes...
Deepening moisture and increasing instability ahead of a short
wave trough moving from SD into MN before merging into a long wave
trough crossing the Canadian Prairies feeds convection capable of
producing excessive rainfall Sunday into Sunday night. There
remained good model agreement with the large scale pattern, though
continued time and position differences with the surface low made
for differences with the QPF. Given the instability gradient
(higher CAPEs south), WPC QPF tended to align on the southern
periphery of the multi-model spread -- close to a blend of the
HREF mean, NBM, and WPC bias-corrected ensemble QPF.

Ongoing convection early this morning across SD into MN will be
reinvigorated today as the low deepens upon tracking toward Lake
Superior. The developing convection is fed 1.75 to 2 inch
precipitable water air (which is 2.5 standard deviations above the
mean) on a 30 to 40 knot low level southwest flow. Lift ahead of
the long wave trough should allow the convection to expand in
coverage, and become better organized as it moves over southern
and central MN into northern and central WI. Expect a sharpening
instability gradient N-S though the surface warm front, with a
model consensus of 2000-2500+ MUCAPEs across the southern
periphery of the Slight Risk area.

This airmass could support hourly rainfall totals near 1.5 inches
and there is a multi model signal for 2 to 2.5 inches of rainfall
over central MN to the Lake Superior shore. Three hour flash flood
guidance values are generally 1.5 to 2.5 inches over portions of
MN into WI (including the Minneapolis metro area), and these
numbers could be exceeded where convection trains ahead of the
front. Based on this, a Slight Risk was maintained over much of
southern and central MN into northern WI and the western UP along
with some more of eastern SD to cover the ongoing storms in the
morning.


...Central Plains...
A cold front trailing the shortwave trough crossing the northern
plains will push into IA/MO Sunday night. Southwesterly low level
flow ahead of the trough will bring PWs up to 1.75 to 2 inches
Sunday night from eastern KS to eastern IA. Scattered convection
developing late Sunday afternoon over eastern NE/western IA could
organize and track east while propagating south given westerly
mean flow and northerly propagation vectors. Despite 3hr FFG of
2.5 to 3 inches, localized repeating cells could raise flash flood
concerns and a Marginal Risk was raised that extends to across IA
to southwest MO.


...Northeast...
Moisture and instability south of a frontal boundary extending
from southern Ontario into northern ME could feed convection
capable of producing heavy rainfall Sunday afternoon and evening.
Weak short wave energy in the mid level flow south of the front is
expected to interact with 1.25/1.50 inch precipitable water air
and 1000/2000 J/KG of MLCAPE stretching from western NY/western PA
across NY state into northern and central New England during peak
heating.

The weakly difluent flow ahead of the short wave could allow small
clusters of storms to move across this area, generally following
the best instability axis, but much of the activity is expected to
be fairly short lived in nature. For the most part, the mid-level
flow should be sufficient to keep the convection progressive,
limiting an organized flash flood threat. In addition, much of the
area has been fairly dry over the past seven days, with three hour
flash flood guidance values generally over 2.50 inches. While
there could be some locally heavy rainfall, the overall threat for
more than isolated short-term runoff issues is low, thus the
Marginal Risk over this area.

Pereira/Hurley/Jackson


Day 2
Valid 12Z Mon Jul 29 2019 - 12Z Tue Jul 30 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN ROCKIES INTO THE SOUTHWEST...AS WELL AS THE LOWER
MISSISSIPPI VALLEY INTO THE OHIO VALLEY...

...Southern Rockies into the Southwest...
As the mid level ridge reasserts itself over the Southwest states,
the monsoonal flow becomes reestablished over the Southwest and
Southern Rockies during Day 2. While the best thrust of moisture
is expected across southern AZ (where precipitable water values
rebound to near 1.75 inches before 30/12z), the best instability
is expected across the Southern Rockies into the Sangre de Cristo
Mountains. An axis of 500/1000 J/KG of MLCAPE is expected to
develop from the Front Range of the Rockies in CO into northern
and southwest NM, peaking near 30/00z.

The developing storms will tap 1.00 inch precipitable water air on
a low level southeast flow to produce local 1.00 inch rainfall
amounts over the higher terrain, where the storms will be almost
stationary against the upslope flow. Once maximum heating occurs,
the storms will begin to move slowly west northwest with the weak
mid level flow, retaining the potential to produce hourly rainfall
rates between 0.50/1.00 inches away from the terrain. Three hour
flash flood guidance values are as low as 1.50 inches in these
areas, so a low end flash flood threat is expected. Based on the
above, a Marginal risk was placed over the higher terrain and
adjacent locations.

Further west across southeast AZ, the moisture plume from northern
Mexico possesses more moisture than
CO/NM, but instability could end up being the limiting factor for
a more organized flash flood threat. Scattered storms could
produce local 1.00 inch rainfall amounts over the higher terrain
before moving out into lower terrain, but the general lack of
forcing would suggest that the storms should be short lived. Slow
cell motions under the ridge position could allow for cell mergers
and short training. Based on the above, the Marginal Risk was
extended across southeast AZ for Day 2.


...Lower Mississippi Valley into the Ohio Valley...
Moisture and instability extending ahead of a slowing cold front
are expected to feed convection that could produce locally heavy
rainfall from the Lower MS Valley into the OH Valley during Day 2.
The best moisture feed ahead of the front is expected across MO
into AR/OK, mainly between 29/18z and 30/06z. Model soundings
showed an axis of 1500/2500 J/KG of MLCAPE in line with the
deepest moisture, and developing storms are expected to drop
southeast with the mid level flow.

Slow storm motions along the front as it becomes quasi stationary
in the 1.75/2.00 inch precipitable water air pooled near the front
could allow hourly rainfall rates to approach 2.00 inches, mainly
over AR around 30/00z. After that, there is a model signal that a
cold pool could form with storms over AR, resulting in the storms
dropping south into northern LA as they weaken.

Three hour flash flood guidance values are generally above 2.50
inches from MO into northeast OK, and above 3.50 inches over much
of the Lower MS Valley. Slow storm motions (especially early,
before any outflow driven storms form) could produce rainfall
amounts near the lower end of the spectrum, especially over
portions of AR and southern MO. Based on the above, a Marginal
Risk was placed over much of the Lower and a portion of the Mid MS
Valley for Day 2.

Further northeast along the front, the axis of moisture and
instability extends into the OH Valley, where storms along the
front across slow as the mid level flow becomes more parallel to
it. The 00z NAM CONUS Nest indicated the potential for hourly
rainfall rates to approach 1.50 inches over IN/OH and northern KY.
Three hour flash flood guidance values here are generally above
2.50 inches, but short term training in the higher moisture air
environment could allow storm totals to reach close to these
values. Based on this, the Marginal Risk was extended into the
Ohio Valley for Day 2.

Hayes

20Z Update: No noteworthy changes were necessary for the Day 2
excessive rainfall outlook, and the previous discussion remains
valid for this forecast period. /Hamrick



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...


$$




------------=_1564344556-118394-1469
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.
------------=_1564344556-118394-1469--

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