Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
737 PM EST Mon Jan 22 2024
Day 1
Valid 01Z Tue Jan 23 2024 - 12Z Tue Jan 23 2024
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE UPPER TEXAS COAST THROUGH WESTERN LOUISIANA...
0100 UTC Update -- Based on the latest observational and guidance
trends, we were able to remove the outlook areas along the CA and
southwest OR coasts, along with the Central Valley and western
slopes of the Sierra. In addition, the western peripheries of the
Marginal and Slight Risk areas across eastern TX-OK were trimmed
as well per the aforementioned trends and current mesoanalysis,
while the Slight was removed out of the ArkLaTex region given the
lack of instability (even elevated) and thus more limited
hourly/sub-hourly rainfall rates.
Hurley
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
322 AM EST Tue Jan 23 2024
Day 1
Valid 12Z Tue Jan 23 2024 - 12Z Wed Jan 24 2024
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
EASTERN TEXAS INTO THE ARK-LA-TEX AND SURROUNDING PORTIONS OF
NORTHWEST LOUISIANA AND SOUTHWESTERN ARKANSAS...
...Eastern Texas to the Mid-South...
A brief window of relatively drier conditions is expected for much
of the early morning as the shortwave impacting the region
overnight lifts to the northeast through the mid Mississippi
Valley. However, heavy precipitation is expected to quickly
redevelop back to the west as upstream energy continues to amplify
an upper trough moving across the Southwest. Amplifying southerly
flow will support a resurgence of deeper moisture across eastern
Texas and the lower Mississippi Valley, as a stronger shortwave
trough ejects eastward into the Southern Plains. PWs over 1.5
inches (2.5 standard deviations above normal) will begin to extend
north across eastern Texas and the lower Mississippi Valley late
today into early Wednesday. This moisture (along with ample
instability and large-scale ascent) will support the development
of organized convection around midday across eastern TX. Rainfall
rates of 1-2"/hr will be supported by the environment, as
convection becomes linear and fairly progressive towards the east.
Soils have become locally saturated over the past 24 hours with
2-4" of rainfall having already fallen (per MRMS estimates)
resulting in FFGs as low as 1-2". As a result, numerous flash
floods are likely from portions of eastern TX through the
Ark-La-Tex. This area with the highest risk for flash flooding is
generally encompassed by the Moderate Risk, and includes the
region where 00z HREF exceedance probabilities are maximized (with
40-km neighborhood probabilities of up to 80% for 3" exceedance
and between 20-40% for 5" exceedance). Given the potential for
localized totals of 4-6" over already saturated areas, some
locally significant flash flood events are possible (particularly
over more sensitive low-lying areas and poor drainage urbanized
terrain).
...Southeastern Arizona...
An amplified upper trough along with anomalous moisture will
continue to support precipitation across the region early in the
period. While widespread heavy amounts are not expected, some
additional locally heavy amounts (1"+) may produce some isolated
runoff concerns early in the period.
Churchill/Pereira
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 AM EST Tue Jan 23 2024
Day 2
Valid 12Z Wed Jan 24 2024 - 12Z Thu Jan 25 2024
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM FAR EAST
TEXAS AND CENTRAL LOUISIANA THROUGH NORTH-CENTRAL MISSISSIPPI AND
NORTHWESTERN ALABAMA...
...Central Gulf Coast through the Mid-south and Tennessee/Ohio
Valleys...
An upper trough over the Southwest will make meaningful progress
eastward on Wednesday, as a 40-50 kt low level jet out of the Gulf
will be racing northward up the Mississippi River Valley by
Wednesday morning. A digging longwave trough will support the
right entrance region of a 120 kt southerly jet centered over
central TX and OK. The area east of it, where the western side of
the Moderate Risk is located will be highlighted for the greatest
atmospheric lift in this setup. Training thunderstorms stretching
as far west as Houston will be ongoing over central and southwest
LA northeast into western MS. These storms will be capable of
1-2"/hr rainfall rates, and localized 24-hr totals will likely
reach 3-6" across the Moderate Risk area. When added to rainfall
that occurred on prior days, the result will likely be numerous
urban, small stream, creek, and small river flooding. Locally
significant flash flooding will be possible, especially in those
areas where the ongoing storms Wednesday morning are most
persistent. This is mostly likely to be across central Louisiana,
but could extend into surrounding portions of far eastern TX,
northern LA, and central MS.
On Wednesday afternoon through the overnight, the upper-level jet
will continue strengthening to 130 kt over the mid-Mississippi
River Valley, as the LLJ from the Gulf continues to stream air
with PWATs as high as 1.75 inches into the Southeast. This will
allow the storms that could be ongoing from the morning and
afternoon hours to persist northeastward into northern
Mississippi, Alabama, and potentially as far north as central
Tennessee. A couple factors come into play in this part of the
country...there's a bit more orographic assistance, especially
into Tennessee, but this will be the first significant round of
rain for this area, which is still warming up from the recent cold
snap. The result is despite somewhat dry soils (below average for
this time of year), thawing ground, high rainfall rates, and
rainfall totals that could locally exceed 4 inches in 24 hours
will likely be enough rainfall to overwhelm many small streams,
creeks, and any urbanized areas to result in scattered to numerous
instances of flash flooding. The thawing ground and vegetation
still in "winter mode" should allow much of the rainfall to
translate to runoff instead of being absorbed (as the soils act
more like hydrophobic clay when frozen). Into the southern
Appalachians, remaining snow cover from recent winter storms will
contribute to additional runoff to the local river systems in the
form of snowmelt. This factor has allowed for some expansion of
the Slight and Marginal Risk areas northeastward, and additional
expansions further east into the mountains and further northeast
into the Ohio Valley are possible with future updates.
Churchill/Wegman
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
330 AM EST Tue Jan 23 2024
Day 3
Valid 12Z Thu Jan 25 2024 - 12Z Fri Jan 26 2024
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL
GULF COAST THROUGH THE SOUTHERN APPALACHIANS...
Heavy rainfall may still be ongoing across portions the southeast
into Thursday morning, though the intensity is likely to be waning
as activity gradually begins to make some meaningful eastward
progress. While the highest totals (locally 2-3") are likely to
occur into the southern Appalachians (where a strong low-level jet
will interact with terrain to enhance totals), additional totals
of 1-2" farther southwest into LA/MS/AL could be more impactful
given the potential 2-6" totals across much of those areas on
Wednesday. For that reason, the inherited Slight Risk was expanded
a bit westward, though the high-end Slight probabilities are
currently confined to East TN, northern GA, and surrounding
portions of northeast AL and western NC/SC.
Churchill
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
221 AM EST Tue Jan 23 2024
An amplified upper ridge will build over the West Coast by Friday
that should prove slow to shift eastward across a warmer and
stabilized West through next Tuesday. A series of amplified
eastern Pacific systems will lift offshore and bring an axis of
long fetch moisture up on the western periphery of the shielding
ridge, with main focus into favored terrain within coastal areas
from the Pacific Northwest to northern California. WPC Excessive
Rainfall Outlooks (ERO) for Day4/Friday and Day5/Saturday offer
Marginal Risk threat areas over NW California/SW Oregon and the
Olympics to highlight best guidance signals and leads into
additional wet coastal weather potential later weekend into early
next week.
A significant rainfall episode over the South will linger into
Friday/Saturday as deep moisture feed in advance of the last major
southern stream shortwave in the series works across the region
and lifts energetically northeastward on the western periphery of
a slow to recede Southeast/East downstream upper ridge. A
remaining threat for leading heavy rain and thunderstorms through
the Gulf Coast states into the Southeast/southern Appalachians and
vicinity with system approach/passage and enhanced frontal
wave/deepening low focus has prompted issuance of a Day 4/Friday
Slight Risk area ERO over the central Gulf Coast States with a
surrounding Marginal Risk Area Day4/Friday extending up
through/lee of the southern Appalachians Day 5/Saturday. Areas in
vicinity of the track of the initially closed upper center may
also see locally heavier downpours as highlighted by the
Day4/Friday Marginal Risk area ERO over Oklahoma/north Texas. This
lifting/shearing of this feature favors a moderate precipitation
swath northeastward across the Mid-South and Ohio Valley through
the central Appalachians, Mid-Atlantic and New England through the
weekend. While within a widespread and significantly warmer
pattern, enough cooled air may remain in place to allow potential
for some snow along with some windy conditions on the far northern
edge of the broad precipitation shield into the interior Northeast
by Sunday as aided with a deepening low track up/off the East
Coast. This storm should become strong enough to be a maritime
hazard off the Mid-Atlantic then New England Sunday into Monday.
Schichtel
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
221 AM EST Tue Jan 23 2024
An amplified upper ridge will build over the West Coast by Friday
that should prove slow to shift eastward across a warmer and
stabilized West through next Tuesday. A series of amplified
eastern Pacific systems will lift offshore and bring an axis of
long fetch moisture up on the western periphery of the shielding
ridge, with main focus into favored terrain within coastal areas
from the Pacific Northwest to northern California. WPC Excessive
Rainfall Outlooks (ERO) for Day4/Friday and Day5/Saturday offer
Marginal Risk threat areas over NW California/SW Oregon and the
Olympics to highlight best guidance signals and leads into
additional wet coastal weather potential later weekend into early
next week.
A significant rainfall episode over the South will linger into
Friday/Saturday as deep moisture feed in advance of the last major
southern stream shortwave in the series works across the region
and lifts energetically northeastward on the western periphery of
a slow to recede Southeast/East downstream upper ridge. A
remaining threat for leading heavy rain and thunderstorms through
the Gulf Coast states into the Southeast/southern Appalachians and
vicinity with system approach/passage and enhanced frontal
wave/deepening low focus has prompted issuance of a Day 4/Friday
Slight Risk area ERO over the central Gulf Coast States with a
surrounding Marginal Risk Area Day4/Friday extending up
through/lee of the southern Appalachians Day 5/Saturday. Areas in
vicinity of the track of the initially closed upper center may
also see locally heavier downpours as highlighted by the
Day4/Friday Marginal Risk area ERO over Oklahoma/north Texas. This
lifting/shearing of this feature favors a moderate precipitation
swath northeastward across the Mid-South and Ohio Valley through
the central Appalachians, Mid-Atlantic and New England through the
weekend. While within a widespread and significantly warmer
pattern, enough cooled air may remain in place to allow potential
for some snow along with some windy conditions on the far northern
edge of the broad precipitation shield into the interior Northeast
by Sunday as aided with a deepening low track up/off the East
Coast. This storm should become strong enough to be a maritime
hazard off the Mid-Atlantic then New England Sunday into Monday.
Schichtel
