Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
844 PM EDT Sun Oct 01 2023
Day 1
Valid 01Z Mon Oct 02 2023 - 12Z Mon Oct 02 2023
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHEAST
PORTIONS OF THE FLORIDA PENINSULA...
...Florida Peninsula...
0100 UTC Update -- Based on the latest observational and
mesoanalysis trends, along with recent HRRR and HREF runs, have
curtailed the northern portions of the Slight Risk out of the
Space Coast and much of the Treasure Coast. 18Z HREF exceedance
probabilities for the overnight (>1-2"/hr rates and >3"/12 hrs
between 00-12Z) are not as robust compared to last night-early
this morning, however are sufficient to maintain a Slight Risk
across SE FL along and ahead of the front, especially given the
current trends/more numerous cells.
...New Mexico/West Texas and western portions of the Oklahoma
Panhandle...
0100 UTC Update -- Based on the latest convective trends
(satellite/radar/mesoanalysis), along with the recent HRRRs and
18Z HREF exceedance probabilities, have expanded the Marginal Risk
to include the remaining portion of southeast and south-central NM
and much of West TX. Expanding thunderstorm coverage with periods
of training will maintain an isolated flash flood threat across
eastern NM into portions of western TX through 05Z. Rainfall rates
of 1-2"/hr will be possible in isolated areas. For further
information, please refer to the latest mesoscale precipitation
discussion or MPD #1122, which is in effect until 0530 UTC.
Hurley
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
346 PM EDT Sun Oct 01 2023
Day 2
Valid 12Z Mon Oct 02 2023 - 12Z Tue Oct 03 2023
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN HIGH PLAINS OF NEW MEXICO AND TEXAS...
...20Z Update...
...Southern High Plains...
No major changes were made to the ERO risk areas for Day 2/Monday.
The Slight Risk remains in place for eastern NM and portions of
the TX Panhandle as a deep trough ejects out of the Rockies, which
when added to increasing Gulf moisture ahead of the trough will
result in widespread shower and thunderstorm development in the
Slight Risk area. Training will be the primary concern as the
storms largely struggle to move east, instead tracking NNE to NE.
Expect heavy rainfall rates as high as 2 inches per hour with the
strongest storms. NASA Sport imagery shows the area is at to a bit
below normal as far as soil moisture conditions go, so it will
likely take multiple rounds of storms to result in widely
scattered flash flooding except where any bigger towns or flood
sensitive areas are hit with the heavier rains.
...Florida...
The front over the center of the Peninsula now will make its way
to the southern tip of the state by Monday/Day 2. Predominantly
easterly flow will allow for a renewed round of convection in the
Miami-Ft. Lauderdale area, and as with the past few days will be
slow moving and moisture-laden. Thus, the threat for flash
flooding remains in the urban areas predominantly. Out over the
Everglades it's much more difficult for heavy rains to result in
flash flooding, so the Marginal Risk area was trimmed from the
west to highlight the greatest threat being in the urban areas.
For the Keys, any excessive rainfall induced flooding would likely
be compounded by tidal flooding.
Wegman
...Previous Discussion...
...Southern High Plains of New Mexico and Texas...
Confidence has increased enough to warrant an upgrade of the New
Mexico/west Texas Marginal to a Slight Risk. The Southern High
Plains will be under the influence of deep diffluent flow from a
potent upper trough propagating through the West on Monday. This
will be coupled with the arrival of a strong upper jet aloft and
favorable low level jet dynamics. Cape values in the 1000-1500J/Kg
range and moisture anomalies well over 2 standard deviations
(1-1.5in") should support thunderstorm activity (some severe) with
excessive rainfall potential.
...Florida...
Albeit weaker than today's threat, Monday's heavy rainfall threat
will shift to southern Florida as the surface front, which will
continue to be the focus for storms, shifts southward. Instability
will weaken on Monday so any excessive rainfall threats will
likely be few and far between. The main threat from potential
heavy rainfall will be over urban areas.
Kebede
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
346 PM EDT Sun Oct 01 2023
Day 3
Valid 12Z Tue Oct 03 2023 - 12Z Wed Oct 04 2023
,...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS
OF THE GREAT PLAINS AND THE EAST COAST OF FLORIDA...
...20Z Update...
Once again no major changes were made to the inherited forecast.
Over the Plains, the Marginal Risk area looks good for the
uncertainty as to where the strongest storms will develop. The
overall area was nudged a row of counties east, and trimmed on the
western side, particularly across western SD, where the center of
the low is expected to track, which will end the rainfall threat
more quickly. More of ND may be able to be trimmed with future
updates due to lack of instability on the northern side of the
low, but the confidence wasn't quite there to make that change.
...Florida...
An easterly wave is expected to move into the Space Coast Tuesday
and especially Tuesday night. This area has been hard-hit with
rainfall the past few days, and so while the rainfall forecast at
this point is meager along the coast, there remains some chance
that slow-moving/training storms could cause localized flash
flooding, especially right along the coast. This is a
low-confidence Marginal, and any bigger changes in frontal
position could result in bigger changes to the Marginal Risk area.
Wegman
...Previous Discussion...
A rapidly developing mid-latitude cyclone, supported by a deep
upper-level trough will produce thunderstorms (some severe) and
moderate to heavy rainfall across the Great Plains on Tuesday.
Confidence has diminished a bit since the last issuance regarding
excessive rainfall over parts of the Northern Plains, therefore
the Slight Risk has been removed. The broad Marginal area remains
due to the potential for excessive rainfall, particularly over
parts of the Central Plains where favorable instability within
potential severe storms could enhance rainfall rates. PWATs will
be well over 1 inch across the Plains on Tuesday with impressive
low level winds.
Kebede
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
234 PM EDT Sun Oct 01 2023
The south-central U.S. will be an area of focus for widespread
heavy rain especially on Wednesday, as the right entrance region
of the jet will provide ample lift, and plenty of instability is
in place just ahead of the cold front. A Slight Risk remains in
place there in the Day 4/Wednesday Excessive Rainfall Outlook, as
despite the drought conditions, high rain rates that could
overcome the dryness are likely. By Thursday, the cold front will
push southeast and clear out rain potential on its backside, but
could still provide forcing for convection along and ahead of it
into southern and eastern parts of Texas and into the Lower
Mississippi Valley. Model guidance still varies with placement of
any heavy amounts, but ensemble and clustering signals are growing
to favor issuance of a small Slight Risk area over Texas for the
Day 5/Thursday ERO to cover the threat. Some lingering rain may be
possible in South Texas late week.
Farther north, the cold front should track through the
Midwest/Upper Great Lakes and the Ohio/Tennessee Valleys Wednesday
into Friday, the into the East heading into the weekend, producing
showers and thunderstorms along and ahead of it. This rain should
overall be lighter than farther south, but may be enhanced in the
Northeast especially in favored terrain, as the front could begin
to tap Atlantic moisture within southerly flow to increase
rainfall, especially considering preference for an amplified
supporting upper troughing by late week.
The amplified trough and the cold front will lead to cooler
temperatures than average while the upper ridges to the east and
west will support above normal temperatures. The Interior West
should see cooler temperatures than average especially through
midweek, with with lows 5-10F below normal and highs around 10-15F
below average, but warming to near normal for the latter part of
the week. Meanwhile warmer than average temperatures by around
15-20F above normal are forecast midweek for the Midwest into the
Great Lakes and the Interior Northeast, with highs in the upper
70s to low 80s. Some daily records for highs/warm lows may be
possible Wednesday. As the cold front and upper trough march east
into the latter half of the week, temperatures will cool to below
average across the central and then east-central U.S., limiting
the above normal temperatures to the Northeast. A trailing front
may reinforce the cooling trend by Friday-Sunday, and there could
be concerns for the first frost or freeze of the season to occur
in the northern High Plains. Approach/arrival of the eastern
Pacific upper ridge should raise temperatures along the West Coast
to above average, by as much as 5-15F, and some record warm lows
may be possible.
Schichtel/Tate
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
234 PM EDT Sun Oct 01 2023
The south-central U.S. will be an area of focus for widespread
heavy rain especially on Wednesday, as the right entrance region
of the jet will provide ample lift, and plenty of instability is
in place just ahead of the cold front. A Slight Risk remains in
place there in the Day 4/Wednesday Excessive Rainfall Outlook, as
despite the drought conditions, high rain rates that could
overcome the dryness are likely. By Thursday, the cold front will
push southeast and clear out rain potential on its backside, but
could still provide forcing for convection along and ahead of it
into southern and eastern parts of Texas and into the Lower
Mississippi Valley. Model guidance still varies with placement of
any heavy amounts, but ensemble and clustering signals are growing
to favor issuance of a small Slight Risk area over Texas for the
Day 5/Thursday ERO to cover the threat. Some lingering rain may be
possible in South Texas late week.
Farther north, the cold front should track through the
Midwest/Upper Great Lakes and the Ohio/Tennessee Valleys Wednesday
into Friday, the into the East heading into the weekend, producing
showers and thunderstorms along and ahead of it. This rain should
overall be lighter than farther south, but may be enhanced in the
Northeast especially in favored terrain, as the front could begin
to tap Atlantic moisture within southerly flow to increase
rainfall, especially considering preference for an amplified
supporting upper troughing by late week.
The amplified trough and the cold front will lead to cooler
temperatures than average while the upper ridges to the east and
west will support above normal temperatures. The Interior West
should see cooler temperatures than average especially through
midweek, with with lows 5-10F below normal and highs around 10-15F
below average, but warming to near normal for the latter part of
the week. Meanwhile warmer than average temperatures by around
15-20F above normal are forecast midweek for the Midwest into the
Great Lakes and the Interior Northeast, with highs in the upper
70s to low 80s. Some daily records for highs/warm lows may be
possible Wednesday. As the cold front and upper trough march east
into the latter half of the week, temperatures will cool to below
average across the central and then east-central U.S., limiting
the above normal temperatures to the Northeast. A trailing front
may reinforce the cooling trend by Friday-Sunday, and there could
be concerns for the first frost or freeze of the season to occur
in the northern High Plains. Approach/arrival of the eastern
Pacific upper ridge should raise temperatures along the West Coast
to above average, by as much as 5-15F, and some record warm lows
may be possible.
Schichtel/Tate
