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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1957Z Jun 15, 2019)
 
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Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
357 PM EDT Sat Jun 15 2019

Day 1
Valid 1806Z Sat Jun 15 2019 - 12Z Sun Jun 16 2019

1800 UTC update

Some additional minor changes to the previous Excessive Rainfall
Outlook.  The marginal risk area was extended into far nw IA and
far eastern SD.

1600 UTC update

Only some minor changes made to the previous Excessive Rainfall
Outlook.  The slight and marginal risk areas were extended farther
south from central OK into north central TX as per latest hi res
consensus for heavy rains pushing farther south in the 0000-1200
UTC Sunday time period.  The slight risk area was also extended
slightly farther to the south across southern IL and southern IN.

Oravec

...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...

Decaying mesoscale convective systems moving across the Ohio
Valley early in the period (Sunday morning) will likely lead to
ongoing precipitation within this region.  At the surface, a cold
front will continue to sink south Sunday.  This will act as a
focus for shower/thunderstorm activity throughout the remainder of
the afternoon/evening.  Mid-level energy moving atop the boundary
will act to enhance precipitation, as noted previously by the
decaying MCS.  Sufficient moisture and surface convergence along
and south of the front will help supply lift.  Instability and
moisture will also pool south of the front with CAPE values
climbing well above 2000 J/kg and with precipitation water values
around 1.75 inches, respectively.  The 850mb southwesterly flow
will be fairly strong, 35-45 knots, especially early Sunday
morning and again later Sunday night as the nocturnal low level
jet strengthens. This will help organize convection Sunday
afternoon/evening south of the front.  Therefore the placement of
the front will largely impact the overall precipitation extent
with model variability still quite high for Day 2. Trimmed QPF a
bit given the instability and moisture convergence seem a bit
weaker across this region with some subsidence noted with the
exiting MCS.  Also, cloud cover may limit destabilization later in
the afternoon/evening.  While there is quite a bit of uncertainty
with respect to the typical ingredients needed, kept the Slight
Risk across portions of southern OH/PA and much of the windward
side of the high terrain in WV.  This is due to the activity
expected on Day 1 (through tonight) and lower flash flood guidance
as of today.  There may be a chance to remove the Slight Risk area
if QPF amounts continue to dwindle.     


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

A shortwave crossing the Plains will nudge a cold front and
associated surface low south and east toward the Lower MS Valley
Sunday. Convection associated with this mid-level energy (likely a
mesoscale convective system) may be ongoing Sunday morning which
will have large implications on convective initiation and
propagation throughout the day as residual boundaries may develop.
This has resulted in varied high-resolution model solutions in
terms of QPF totals. Regardless, heavy rain ingredients are
present as Gulf moisture will advent north into eastern portions
of the southern Plains and Lower MS Valley. Precipitable waters of
1.75+ inches aided by 40kt low level southerly flow is 1.5
standard deviations above the mean for this region.  This combined
with strong moisture flux across east TX and far southeast OK will
result in pooling of moisture east of the dryline and south of the
aforementioned cold front.  With plenty of instability in place
(>3000 J/kg CAPE) and mid-level vorticity slowly crossing atop
surface/moisture convergence, feel convection will develop across
portions of east Texas with potential redevelopment Sunday late
afternoon into the overnight with a strengthening low level jet.
With rain rates above 1.5 inches and potentially multiple rounds
of convection, especially across the eastern half of TX Sunday
through Sunday night, kept the Slight Risk, though adjusted it
south across southeast OK and northeast TX. FFG values are fairly
high for this region with below normal precipitation observed the
past 2 weeks.  While confidence is a bit higher with respect to
the convective activity across eastern TX, feel southeast OK may
encounter subsidence behind the morning MCS which may preclude
additional precipitation activity.  For right now, etched out the
region with the best overlap of heavy precipitation ingredients.
However, fully anticipate the Slight Risk area to adjust with
subsequent updates.

...Central High Plains...

Shortwave activity moving through WY into NE will imitate
convection across portions of the Front Range moving into the
central Plains Sunday afternoon evening.  With modest
instability/moisture in place and differential heating at the
surface with some upslope convergence noted, expect
shower/thunderstorm initiation across the lee side of the Rockies,
quickly moving into the Plains Sunday evening into the overnight.
Hourly rain rates above 1 inch are possible as the convection
moves into a more favorable environment across southwest NE.  With
hourly FFG as low as an inch and portions of this region receiving
>200% of normal precipitation the last 2 weeks, felt a Marginal
Risk of flash flood was warranted.   


Pagano

Day 3

The Day 3 outlook will be updated by 2030Z.


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