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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0903Z Jun 15, 2019)
 
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Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
503 AM EDT Sat Jun 15 2019

Day 1
Valid 12Z Sat Jun 15 2019 - 12Z Sun Jun 16 2019

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF
ILLINOIS, INDIANA, AND OHIO EXTENDING THROUGH SOUTH CENTRAL
MISSOURI AND ALONG THE EASTERN KANSAS/OKLAHOMA BORDER...

...Northern Ohio Valley/South Central Great Lakes Region...
At the start of the forecast period, a strong closed low will be
be pressing a strong cold front and drier air across the northern
and lower Great Lakes, while a southern stream subtle shortwave
and associated mature MCS are progressing across the Central
Plains into the Lower Missouri River Valley.  Northwesterly flow
out of the Pacific stream, is also providing some stream
confluence across the Central MS River Valley into portions of the
eastern Midwest (IL/IND/OH), adding to focus moisture flux
convergence and channeled mean steering flow from WSW to ENE
across these states.  Warm advection early this morning is pumping
deep moisture pocket with total PWats in the vicinity of 1.75". 
The MCS should continue to roll through the northern Ohio River
valley through early afternoon, but with strong warm advection,
post convective environment will be rebuilding instability as
great as 2500-3000 J/kg upstream in MO/IL that will likely
reinvigorate additional round of thunderstorms along the
rear-inflow jet axis/or mid-level confluence axis across IL-IND. 
This should support some training environments, supporting 2-4"
rainfall corridor(s).   While there is agreement toward a
southward shift of the instability axis and confluence boundary in
the Hi-Res CAMs, the precise latitude remains contingent on many
factors (IE MCS placement) and proximity to the northern stream
pressing cold front.  As such, there is sufficient uncertainty to
precise corridor of heaviest rainfall training, and so WPC has
broadened a Slight Risk of Excessive Rainfall to cover a large
area of central IL/IND and Ohio with a Marginal Risk extending
into northeast PA, remaining locations in OH/IND/IL.

...Central/Southern Plains into Missouri...

Upstream, a more robust shortwave is tracking across the Four
Corners and is expected to eject into the Southern High Plains
around peak heating.  A surface low will respond with solid
deepening supporting isallobaric response with strong
northeasterly flow across SE CO/SW KS and a dry-line bulge across
the TX panhandle.  This will support a strong/moisture convergence
signal breaking out convection that will be initially severe, but
will not be able to meander much along the convergence axis across
SE CO into NW OK/SW KS.  GOES-WV and global guidance supports a
faster trend with this shortwave and so moisture return will
likely limit convection coverage along the front range of the CO
Rockies, so have pulled the Marginal Risk to focus further
southeast.

Toward 00z, LLJ will back to more southerly and aiding moisture
convergence at the northeast inflection of the surface wave, where
instability will also build to around 4000+ J/kg and support Total
PWats around 1.5".  Cell motions will be stalled/support
backbuilding with a fairly stationary convective complex to
develop across S central KS/northern OK.  HREF probabilities
suggest 2"/hr rain-totals in this region around 50-60% with
similar probabilities of 3"/3hrs, which would likely exceed the
corridor of regionally lower FFG values (I-35 corridor).  The
shortwave will continue to progress eastward through the early
overnight and LLJ will strengthen and veer leading to strong
convergence along the boundary left by the tonight's MCS and
general confluence boundary that extends along the OK/KS border
into Southern MO generally along I-44 in MO.  There will be ample
moisture/instability in place and fairly unidirectional steering
flow to support some training, but cold pool and slow southward
propagation may limit overall totals relative to the greater QPF
signal further west.  Additionally, there is some potential for
warm sector convective clusters across N TX/SE OK that may disrupt
best moisture flux convergence per Hi-Res CAMs; still in
coordination with local NWS forecast offices, introduced a Slight
Risk area to connect across to the Slight Risk over the Central
MS/Ohio River Valley.

...Upper Mississippi River Valley...
Pacific stream shortwave currently over the Canadian southern
Prairies continues to be blocked by the deeper closed low
downstream, leading to increased shearing of the wave into
confluent flow across the upper Red River of the North into the
Upper Mississippi River Basins, with the surface frontal zone
generally draped through the region.  Relatively clear skies and
modest moisture lingering along the frontal zone, will support
midday growth of instability across S MN into NE IA, generally
expected to be around/above 2000 J/kg by late afternoon. 
Thunderstorms will have the potential to be slow moving into the
shear axis leading to spotty 1-3" rainfall totals.  FFG is about
1.5/2.25 in 1/3hr time frame across this region and so there is a
lower end risk of isolated flash flooding.  As such, have expanded
the Marginal Risk of Excessive Rainfall to best align with
sufficient instability for strong/efficient updrafts and lowered
FFG.  While instability is a bit more limited near the best
forcing/shortwave across the Red River Valley, the FFG is
considerably lower, and so slow moving cells will have equal
potential for exceeding FFG with possible flash flooding.

Gallina


Day 2
Valid 12Z Sun Jun 16 2019 - 12Z Mon Jun 17 2019

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE OH VALLEY/LOWER GREAT LAKES REGION AS WELL AS PORTIONS OF THE
CENTRAL PLAINS...

...Ohio Valley/Lower Great Lakes...

A cold front will sink south on Sunday across portions of the Ohio
Valley and Mid-Atlantic regions before becoming nearly stationary.
This boundary will continue to be a focus for mid-level support
and surface/moisture convergence over much of the Ohio Valley.
Precipitable water anomalies along the front will be nearing +2
standard deviations, a with instability increasing to the south of
this boundary, organized convection is anticipated to span from
the Ohio Valley/Lower Great Lakes region into into northern
Pennsylvania. Confidence on where the boundary will stall is not
that high, which in turn results in a lower than average
confidence for the max QPF axis. A handful of model solutions are
signaling 1 to 3+ inches over central/southern Ohio and northern
West Virginia where FFG is a low as 1". These forecast amounts are
enough to raise the threat of excessive rainfall and flash
flooding, especially since the location of some of the maximums
are in flood-prone areas. A Slight Risk area was introduced for
southern Ohio, northern West Virginia and extreme western Maryland
and southwest Pennsylvania. The Marginal Risk covers eastern
Illinois to southern New York.


...Eastern portions of the Southern and Central Plains...

A shortwave crossing the Plains will send a cold front south and
east toward the central U.S. Gulf where moisture will be advecting
into the Plains and Midwest while pooling across the South.
Precipitable water anomalies will be near +1.5 standard deviations
above normal from eastern Texas to central Missouri. Organized
convection is expected along and ahead of the approaching front
from central/eastern Texas to central Missouri. Multiple solutions
are focusing the highest QPF over central/southern Oklahoma. This
region had been 200 to 600% of normal for much of May and has
recently had time to recover in regards to soil saturation. FFG
over much of the area is 1.5 to 2.5 inches. WPC QPF has areal
averages of the same amount with isolated areas of 3 inches
possible. The best moisture and forcing will be aligning toward
the tail end of the end day 2 forecast over southern Oklahoma and
western Arkansas. At this time, felt the Marginal Risk was
sufficient for the flash flooding risk.


Campbell/Pagano

Day 3
Valid 12Z Mon Jun 17 2019 - 12Z Tue Jun 18 2019

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE OHIO VALLEY/LOWER GREAT LAKES REGION IN ADDITION TO THE
SOUTHERN/CENTRAL PLAINS...

...Ohio Valley/Lower Great Lakes...

A surface wave traveling along the frontal boundary will lift
north into the Ohio Valley/Lower Great Lakes region. The best
forcing and moisture alignment will be over southern portions of
the Ohio valley and into the Appalachians/Mid-Atlantic region. QPF
amounts of 1 to 2.5+ inches over the higher terrain of Ohio and
West Virginia may be problematic for these flood-prone areas.
Local FFG in some locations are as low as 0.75" and with the
forecast amounts being nearly double or triple, the flooding risk
will be elevated. A Slight Risk was introduced for most of West
Virginia, southeast counties of Ohio, southwest Pennsylvania and
far western Maryland. Per collaboration with the local forecast
office in Sterling, Virginia, portions of western Virginia and
Maryland we not included at this time. While a couple local maxims
of 2 inches may be possible, the best signal for excessive
rainfall stays over West Virginia. A Marginal Risk spans from
eastern Kentucky to the Chesapeake and Delaware Bays.


...Oklahoma...

The shortwave crossing the Plains will begin to lift north and
east into the Midwest/Middle Mississippi Valley on Monday. The
associated surface cold front will slow over the eastern Plains
and become quasi-stationary over eastern Oklahoma. Meanwhile,
strong moisture transport will be present over Texas, Oklahoma,
Louisiana, Arkansas and Missouri- with a local max precipitable
water value of 2 inches near the AR-LA-TX-OK border. Strong
instability will increase northward from Texas to Oklahoma (CAPE
values of ~3000 to 5000 J/kg) and will tap into the pooled
moisture. The environment will be conducive for widespread
organized convection that will be capable of producing very
efficient rainfall. Multiple models are signaling the highest QPF
to occur over extreme northeast Texas, eastern Oklahoma and
western Arkansas in the amount of 1 to 4 inches. Hires shows
isolated maxes of 4 to 7 inches possible over this same area. WPC
QPF has an areal average of 1 to 3 inches. These amounts may reach
or exceed local FFG in a short period of time. A Slight Risk for
excessive rainfall and elevated flash flooding threat was issued.
A Marginal Risk covers from central Oklahoma, northeast Texas,
northern Louisiana, central Arkansas, southeast Kansas and
southern/central Missouri.

  
Campbell




Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt