Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
842 PM EDT Fri Jun 09 2023
Day 1
Valid 01Z Sat Jun 10 2023 - 12Z Sat Jun 10 2023
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH DAKOTA...
The only Slight risk area remaining is across portions of central
and western SD. Slow moving convection is ongoing along an axis of
enhanced lower level convergence near a surface trough and ahead
of southward dropping cold front. Shear profiles are pretty weak,
but strong upper level diffluence is noted across the
region...likely allowing cells to persist/organize a bit more than
the weak shear would otherwise allow. This combined with the
persistent convergence will continue to support some slow moving
convection across the area for the next several hours. As the
evening progresses instability will gradually erode, and the front
will push south of the area...thus the heavy rainfall risk should
decrease by the overnight hours. In the meantime 18z HREF
neighborhood probabilities of 3"+ are over 40%, and EAS
probabilities of 1" are 20-30%. This supports the idea of
scattered 1" QPF coverage, and localized amounts exceeding 3"
across central/western SD. Amounts of this magnitude are also
supported by recent HRRR runs and MRMS QPE estimates. While this
region has not been as wet over the past couple weeks as MT,
isolated to scattered FFG exceedance is expected, which may result
in some flash flood impacts.
Elsewhere a broad Marginal risk covers much of MT into the
Northwest, and much of the central Plains. Over MT/ID/WA/OR the
risk appears to be on a downward trend as instability gets eroded,
thus think a Marginal risk should cover the remaining
threat...with mainly isolated flash flooding still a concern over
these areas. Convection over KS/NE should organize into one or
more convective lines that will progress southeastward through the
overnight hours. In general the expectation is that this activity
will become more progressive with time...thus while non-zero, the
flash flood risk should stay generally localized in nature over
this region.
Chenard
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
411 PM EDT Fri Jun 09 2023
Day 2
Valid 12Z Sat Jun 10 2023 - 12Z Sun Jun 11 2023
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE PLAINS, ARKLATEX, AND THE MIDWEST...
...2030Z Update...
...NE/IA...
In coordination with LSX/St. Louis, MO; EAX/Kansas City, MO;
DMX/Des Moines, IA; and OAX/Omaha, NE forecast offices, the
inherited Slight Risk was shrunk quite a bit to favor the MO River
Valley between NE and IA. This area of the country has been
running very dry, with 14-day AHPS Climatology guidance suggesting
much of western IA and MO at under 50 percent of normal
precipitation and it's even drier off to the east towards St.
Louis. Further, there is some question as to how widespread the
storms will be, and as such the signal for heavy rain is lower.
MUCAPE values look to only peak between 1,000 and 2,000 J/kg,
though PWATs will be sufficiently high at around 1.5 inches, which
isn't unusual for this part of the country, but certainly is
plenty of moisture to support thunderstorms. Given the very dry
antecedent conditions, the uncertainty as to how widespread the
storms will be, and that much of the area (especially in IA) is
agricultural land that is hoping for rain, the flash flooding
threat is determined to be low, so much of the area has been
downgraded to a Marginal. For along the MO River through Omaha,
rainfall today has moistened things up a bit, and some of the
storms have been robust, dropping 1" of rain in 20 minutes, so the
Slight was maintained in and around Omaha.
...Arklatex Region...
The Slight Risk area is largely the same, but there was a small
expansion southward included as the guidance hints at more
widespread 2-4 inch rainfall totals from strong/severe
thunderstorms on Saturday through this region. Energy moving along
the southern branch of the jet stream will be enhanced by the
approaching positively tilted trough which will be causing the
convection further north. With additional moisture available due
to proximity to the Gulf, the storms are likely to build to the
south with time, requiring the southward expansion. FFGs are high
in the region due to recent dry weather, so the flash flooding
threat even with those higher amounts of rain should be limited.
...Intermountain West...
No significant changes were made to the inherited Slight and
surrounding Marginal Risk areas. Very wet antecedent conditions
will help to make up for lesser amounts of rain expected Saturday
as compared with previous days, as such, the inherited risk areas
look good.
Wegman
...Previous Discussion...
Northern High Plains...
Anomalous moisture continues early on before dropping off and
southward as an upper level shortwave potentially splits, with
some energy moving north into Canada and some undercutting the
ridge and dropping southward. Instability lingers early on, so
the existing Slight Risk still makes sense, with storms forming
initially across MT before dropping southeast across portions of
WY and western SD/NE.
Midwest...
A shortwave drops south around a forming closed low across
southeast Ontario, with the overall system on a strengthening
trend. A low- to mid-level low drops southeast and lures PW
values up to 1.5-1.75" into portions of KS, MO, NE, and IA.
Inflow at 850 hPa and effective bulk shear should be increasing,
particularly late in the period when the low-level jet tends to
ramp up Saturday night into Sunday morning which portends
organized convection. CAPE values upstream are forecast as high
at 3000 J/kg on the 21z SREF guidance during daytime heating,
falling towards 1000 J/kg overnight. The guidance (outside the
00z NAM) has a cohesive signal for heavy rainfall in and around
the offset KS/MO/NE/IA border junction where mid-level heights are
diffluent, with the guidance having a decent signal for local 3-5"
amounts. Flash flood guidance values, particularly outside MO,
are modest, but the Kansas City urban area would naturally be
susceptible to heavy rainfall. The ingredients available could
support hourly rain totals to 2.5", which would be a problem in
such an urban area. The Slight Risk area for these region remains
similar to continuity per the above parameters. A broad Marginal
Risk area continues to surround the Slight due to some lingering
spread seen in the 00z NAM and 00z UKMET solutions.
Portions of CA/NV...
An anomalously strong closed low drops into CA Saturday into
Sunday. Precipitable water values remain elevated, with moisture
increasing in the Central Valley as the cold low develops and
moves in. Instability shouldn't be a problem as temperatures
aloft decrease. Believe a Marginal Risk of excessive
rainfall/flash flood should continue Saturday into Sunday. Hourly
rain totals up to 1.5" should be possible where cells backbuild,
train, and/or merge.
ArkLaTex to the Central Gulf Coast...
As a southern stream shortwave phases with a deepening positively
tilted upper trough, PWs rise towards 2" along a section of the
polar front making some progress eastward. Low-level
inflow/effective bulk shear appear to be sufficient for convection
with some level of organization, which would support hourly rain
totals to 2.5" somewhere between eastern TX, LA, and MS. The
guidance is honing in on a cohesive heavy rainfall signal with
local 4-6" amounts in the ArkLaTex, so introduced of a new Slight
Risk area in that region.
Roth
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
411 PM EDT Fri Jun 09 2023
Day 3
Valid 12Z Sun Jun 11 2023 - 12Z Mon Jun 12 2023
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
COLORADO & THE TENNESSEE VALLEY...
...2030Z Update...
No big changes were made to either of the risk areas on Sunday.
The guidance remains in good agreement so much of the changes were
cosmetic, including expanding the TN Valley Slight risk area just
a bit to the north into KY. Otherwise the surrounding Marginal
risk area was shrunk a bit to account for recent dry weather
allowing much of the expected rainfall to be absorbed into the
ground or by the flora of the area. Afternoon convection is likely
to redevelop across much of the Intermountain West and along the
CO Front Range, where the Slight was left unchanged with this
update. Continued antecedent wet conditions will favor lesser
amounts of rain still being capable of producing isolated flash
flooding from the Sierras of CA up into MT.
Wegman
...Previous Discussion...
Great Lakes/Midwest/Ohio Valley/Tennessee Valley...
A broad area of locally heavy rainfall is expected in the eastern
portion of the country as a deepening closed cyclone drops into
the Great Lakes and phases with a shortwave moving eastward from
the southern Plains. The best signal for heavy rainfall is in the
TN Valley, where strengthening low-level inflow, CAPE of 2000+
J/kg, and PWs of 1.5-2" are forecast. There appears to be enough
effective bulk shear for convective organization. These
ingredients allow for hourly rain totals to 2.5". 00z UKMET
guidance indicates local 4"+ amounts, while the 00z Canadian
Regional advertises local 7"+ amounts. Outside of northernmost
GA, the region has seen much below rainfall over the past week.
However, with the rain rates expected, particularly in urban
areas, widely scattered to scattered instances of flash flooding
are expected despite the recent dryness, so raised the risk level
in the TN Valley to a Slight Risk. Coordination with JKL/Jackson
KY and the LMK/Louisville KY forecast offices kept the Slight Risk
area out of southernmost KY.
In and near Colorado...
Upslope flow behind a frontal zone imports moisture from the
southern and central Plains into eastern Colorado, with PWs
exceeding 1" in easternmost CO in a col point in the mid-level
flow. CAPE is expected to rise towards 1000 J/kg. With the
mid-level flow opposing the low-level flow, enough effective bulk
shear should exist for organized convection, which could allow
hourly rain totals to rise to 2" where cells train and/or merge.
Once cold pools becoming dominant, organized convection should
plow east to southeast into the low-level flow, increasing storm
scale inflow. The guidance has a good signal for local amounts of
2". Flash flood guidance is rather low, so a scattered risk of
flash flooding is anticipated as both hourly and three hourly
flash flood guidance values are exceeded. The Slight Risk area
was shifted southward from continuity to better match the current
model guidance.
Remainder of the West...
An anomalously deep closed low pivoting through southern CA into
southern NV will help cause pockets of 1000+ J/kg of CAPE and PWs
of 0.75-1.25". This is expected to cause isolated heavy rain
concerns particularly at elevation across portions of the West and
northern Rockies. Where cells train and/or merge, hourly totals
of 1.5" are possible. Considering recent wetness, the existing
Marginal Risk area looks reasonable at this time.
Roth
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
343 PM EDT Fri Jun 09 2023
A daily risk for heavy showers and strong to severe thunderstorms
from the Southern Plains to the northern Rockies and westward into
the Great Basin is expected to be slow to dislodge through about
mid-week, as tropical Pacific moisture advects northward between a
strong central U.S. upper ridge and an upper low/trough parked
over California/Southwest early in the week. A weakening boundary
through the region should also help to enhance rainfall totals,
with particular concerns over areas that have seen well above
average rainfall over the past two weeks (northern and central
Rockies/western Great Plains). A Slight Risk area remains in
place on the WPC Day 4 Excessive Rainfall Outlook across
northeastern Colorado and small portions of neighboring states,
with a broad marginal risk extending from the Intermountain West
to the south-central Plains.
The closed low over the Great Lakes and trailing surface cold
front will advect copious moisture northward across the
Mid-Atlantic and Northeast, and in combination with ample
instability will likely produce storms with locally heavy
rainfall, with a Marginal Risk of excessive rainfall in effect for
Monday-Monday night, with lingering wrapping into northern New
England into Tuesday. Antecedent dry conditions and the
progressive nature of the front preclude anything more than a
broad Marginal Risk at this time. Elsewhere, ejecting shortwaves
from the Southwest also appear to favor additional rounds of heavy
rainfall and convection again around mid-week for parts of the
south-central Plains to the Mid-South and vicinity with copious
Gulf return moisture and instability intersecting a
quasi-stationary/warm front.
There will be two main areas of the U.S. that will likely have
above normal temperatures next week, with the first being across
the Dakotas and into Minnesota, Wisconsin, and Iowa where readings
are expected to be 5-15 degrees above mid-June averages. The
second and more impactful area should develop and spread across
Texas into the central Gulf Coast region as upper ridging becomes
better established over the region and temperatures slowly
increase to the south of a frontal boundary and associated
convection. Widespread mid-upper 90s are expected, with values
well into the 100s across the normally warmer locations across
southern Texas, along with increasing humidity levels. Some daily
record highs are possible, mainly mid-late next week. This heat
wave will likely have some staying power beyond next Friday and
also expand into the following week toward the Southeast U.S. as
per latest guidance from the Climate Prediction Center.
Elsewhere, underneath closed upper low development over the Great
Lakes/Midwest and also over the Southwest/California, temperatures
should feel more like the month of May next week.
Schichtel/Hamrick
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
343 PM EDT Fri Jun 09 2023
A daily risk for heavy showers and strong to severe thunderstorms
from the Southern Plains to the northern Rockies and westward into
the Great Basin is expected to be slow to dislodge through about
mid-week, as tropical Pacific moisture advects northward between a
strong central U.S. upper ridge and an upper low/trough parked
over California/Southwest early in the week. A weakening boundary
through the region should also help to enhance rainfall totals,
with particular concerns over areas that have seen well above
average rainfall over the past two weeks (northern and central
Rockies/western Great Plains). A Slight Risk area remains in
place on the WPC Day 4 Excessive Rainfall Outlook across
northeastern Colorado and small portions of neighboring states,
with a broad marginal risk extending from the Intermountain West
to the south-central Plains.
The closed low over the Great Lakes and trailing surface cold
front will advect copious moisture northward across the
Mid-Atlantic and Northeast, and in combination with ample
instability will likely produce storms with locally heavy
rainfall, with a Marginal Risk of excessive rainfall in effect for
Monday-Monday night, with lingering wrapping into northern New
England into Tuesday. Antecedent dry conditions and the
progressive nature of the front preclude anything more than a
broad Marginal Risk at this time. Elsewhere, ejecting shortwaves
from the Southwest also appear to favor additional rounds of heavy
rainfall and convection again around mid-week for parts of the
south-central Plains to the Mid-South and vicinity with copious
Gulf return moisture and instability intersecting a
quasi-stationary/warm front.
There will be two main areas of the U.S. that will likely have
above normal temperatures next week, with the first being across
the Dakotas and into Minnesota, Wisconsin, and Iowa where readings
are expected to be 5-15 degrees above mid-June averages. The
second and more impactful area should develop and spread across
Texas into the central Gulf Coast region as upper ridging becomes
better established over the region and temperatures slowly
increase to the south of a frontal boundary and associated
convection. Widespread mid-upper 90s are expected, with values
well into the 100s across the normally warmer locations across
southern Texas, along with increasing humidity levels. Some daily
record highs are possible, mainly mid-late next week. This heat
wave will likely have some staying power beyond next Friday and
also expand into the following week toward the Southeast U.S. as
per latest guidance from the Climate Prediction Center.
Elsewhere, underneath closed upper low development over the Great
Lakes/Midwest and also over the Southwest/California, temperatures
should feel more like the month of May next week.
Schichtel/Hamrick
