Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
800 PM EDT Sat Jun 03 2023
Day 1
Valid 01Z Sun Jun 04 2023 - 12Z Sun Jun 04 2023
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN HIGH PLAINS...
...Southern/Central Plains...
Convection is expected from the Central Plains to the Mexico/Texas
border into the Red River Valley of the South has generally had
more diffuse organization than previous days. Mid-level troughing
elongated across the Plains combined with modest left-exit jet
level diffluence and a residual surface trough has driven deep
layer ascent through the day. With effective bulk shear of 30-35
kts, this could result in some storm interactions/more organized
clusters moving generally 10-15 kts as progged by the layer
Corfidi vectors. Although the signal for training overall is
modest today, with rainfall rates possibly reaching 2.5"/hr at
times, any short term training or repeated rounds could quickly
result in runoff issues, especially where soils are most saturated
from 14-day rainfall that has been more than 300% of normal across
much of west/central Texas into western OK and southern KS.
The Slight Risk area in this region remains unchanged, as
convection in the risk area has been slow to move. Although the
model signal is vague for any more organized areas of convection
leading to more focused heavy rainfall, heavy rainfall remains in
the cards. The Slight Risk is strongly driven by antecedent
conditions from recent rainfall leading to compromised FFG as low
as 1.5"/3hrs which should be exceeded in an isolated to widely
scattered basis. Any storm that moves across this region could
quickly lead to additional runoff concerns.
While the rest of the area remains in a broad MRGL risk, that
thunderstorms near the Rio Grande have congealed into a slowly
forward propagating MCS with rain rates exceeding 2"/hr and push
E/SE into the RGV or western TX Hill Country tonight. Some cells
appear to be forming ahead of the line which could merge in. This
convective area is moving south of yesterday's heavy rainfall
footprint. Have left the risk area there Marginal but Slight Risk
impacts cannot be ruled out.
...Northern Rockies/Intermountain West...
Convective coverage has been fairly sparse across the region. The
Slight and Marginal Risk areas across the Northern Rockies have
been removed since we're passing the peak of the afternoon
convective activity.
...Florida...
Post-Tropical Cyclone Arlene is turning almost due east, and is
expected to scrape the Cuban coast overnight. This subtly enhanced
ascent combined with the continued modest diffluence aloft and a
surface trough/convergence axis/old frontal zone will provide
sufficient ascent for convection for a little while longer across
the southern Florida peninsula. Overnight, convection with heavy
rainfall is possible in the Keys as Arlene's remnant low moves by.
Hourly rain totals to 2.5" and local amounts to 5" cannot be
ruled out, so looped the Marginal Risk area around the FL Keys to
cover the possible threat.
Roth/Weiss
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
357 AM EDT Sun Jun 04 2023
Day 1
Valid 12Z Sun Jun 04 2023 - 12Z Mon Jun 05 2023
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN HIGH PLAINS...
...Southern to Central Plains into the Central to Northern
Rockies...
No significant changes anticipate to the blocking pattern across
much of the nation during the day 1 period. A closed upper high
will remain centered across the Northern Plains with an elongated
area of troffing extending northwest to southeast on the western
side of this ridge from the Northern Rockies into the Central to
Southern High Plains. PW values in this elongated trof axis will
remain above average, especially from northeast Colorado into
Montana where PW anomalies will run 2+ standard deviations above
the mean. Weak vorts in the high PW axis will again support
another day of widespread scattered convection stretching from the
Southern to Central Plains into the Central to Northern Rockies.
This entire region has seen much above average precip over the
past few weeks, with many areas having observed values 300 to 600%
of normal. This will continue the risk of isolated flash flooding
where any additional day 1 rains fall across areas that have
received recent heavy amounts. With confidence low with respect
to where any heavy day 1 totals will occur, much of this region
was kept in marginal risk. The one exception continues over the
Southern High Plains from far northeast New Mexico, across the
Texas/Oklahoma Panhandle region and southwest Oklahoma, where a
slight risk area was maintained. This region has seen heavy rains
over the past two days in the general same region and has a larger
region of high 1"+ HREF probabilities for the upcoming day 1
period.
...Florida...
The remnants of Arlene expected to pass to the south of South
Florida early Sunday with any associated heavy rains on the north
side likely having already pushed to the southeast of the southern
portion of the peninsula by the beginning of the day 1 period.
In its wake, another day of scattered to widespread afternoon
thunderstorms is likely across the southern half of the Florida
Peninsula as the upper trof that the remnants of Arlene have been
rotating through pushes across the Florida peninsula. HREF
probabilities are high across the southern half of the Florida
peninsula for 1 and 2"+ amounts. This may lead to isolated flash
flooding, especially in urbanized areas where hourly rate of 1 to
2" are possible.
Oravec
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Sun Jun 04 2023
Day 2
Valid 12Z Mon Jun 05 2023 - 12Z Tue Jun 06 2023
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN HIGH PLAINS...
...Southern Plains through the Northern Rockies...
With little in the way any significant changes to the overall
large scale flow across the central portion of the nation day 2,
the day 2 Excessive Rainfall Outlook is very similar to the day 1
outlook. PW values are forecast to remain above average from the
Southern to Central Plains through the Central to Northern
Rockies. Similar to the day 1 period, shortwave energy embedded
in this high PW axis will support another day of widespread
scattered convection across these areas. A slight risk area was
continued from northeast New Mexico into the Texas/Oklahoma
Panhandle region. There continues to be somewhat better agreement
that this area will see a better chance of organized heavy precip
than other areas in the high PW axis. As stated in the day 1
discussion, isolated flash flooding is possible across the entire
area given recent rainfall amounts that have been as much as
400-600% of normal.
...Sierra Nevada...
One of the biggest changes to the large scale flow across the U.S.
during the day 2 period will be the closed mid to upper level low
approaching the central to southern California coastal region.
Increasing upper difluence Monday afternoon to the north and
northeast of this closed low will support scattered convection
through the Sierra, northern California and portions of the
Northern Great Basin. With PW anomalies rising to 1 to 2+
standard deviations above the mean in this upper difluent region,
locally heavy rainfall amounts of up to an inch possible. With
stream flows remaining much above average through the Sierra,
isolated flash flooding is possible Monday afternoon into Monday
evening.
Oravec
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
406 AM EDT Sun Jun 04 2023
Day 3
Valid 12Z Mon Jun 05 2023 - 12Z Tue Jun 06 2023
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS
NORTHEASTERN NEW MEXICO...
The story remains the same for the upcoming day 3 period with
little changes to the overall stagnant blocked pattern across the
nation. Another day of widespread scattered convection likely
from the Southern to Central High Plains, northward through the
Central to Northern Rockies into the Northern High Plains. There
is model consensus for a westward shift in the axis of heaviest
rains over the Southern High Plains day 3. This will remove
portions of central Texas from the marginal risk area. A slight
risk area was maintained over northeast New Mexico where model
consensus is for a max precip area. This is a region where upper
difluence strengthens day 3 well to the east of the upstream
coastal California mid to upper level low. This will bring three
days of potential heavy rains over this region, warranting the
continuation of a slight risk. Similar to the day 1 and 2
periods, given recent heavy rains, 400-600% of normal through
portions of this area, isolated flash flooding will again be
possible from the additional day 3 heavy rain potential across the
remainder of the broad marginal risk area extending into the
Central to Northern Rockies and Northern High Plains. There is
also a model signal for a precip max along the western Gulf coast
from the middle to upper Texas coast into southwest Louisiana.
With recent rains not as anomalous across this area as other areas
in the Southern Plains, the threat was kept at marginal for the
time being.
...Northern Sierra/Northern California into portions of the Great
Basin...
The closed low that approached the central to southern California
coast day 2 is not expected to move much day 3. This will keep a
favorable upper difluent pattern in place to the north and
northeast of this system and support another day of scattered
convection. Consensus is for a broader region of upper difluence
compared to previous days, resulting in a broader area of
potentially locally heavy rains in what will again be an axis of
above average PW values stretching across Northern California into
the Great Basin. This is reflected in a larger marginal risk area
than on day 2 extending into northern California, southern Oregon,
northern Nevada and far southwest Idaho. Stream flows are above
average across much of the marginal risk region with isolated
flash flooding possible.
Oravec
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Sun Jun 04 2023
A daily diurnal risk for heavy showers and thunderstorms will be
maintained through the period from the southern Plains to the
northern Rockies and westward into the Great Basin as tropical
Pacific moisture is funneled northward in between a strong central
U.S. ridge and an upper low parked over California. For now, the
day 4 Excessive Rainfall Outlook continues to depict just one
large Marginal risk area for this region, however embedded Slight
risk areas may become necessary if heavy rains focus over
antecedent wet areas. By day 5, the marginal risk region is
largely the same as day 4, but did add a slight risk for parts of
central/eastern Montana given more favorable moisture and dynamics
and considering antecedent conditions in this region. The risk may
extend past day 5 as well as a frontal boundary becomes
established over the region.
Elsewhere, a front through the Great Lakes/Upper Midwest should
focus showers and storms ahead of it across the Northern
Plains/Upper Mississippi Valley early to mid week. In the
Northeast, the deepening upper trough/lows should favor pockets of
rainfall into Friday as moisture gets wrapped back into especially
northern Maine from a lingering low pressure system near the
coast. In Florida, a lingering weak front should support unsettled
conditions over the Sunshine State with better heavy rain chances
in southern Florida late week as deeper moisture gets pulled north.
Central U.S. ridging aloft will maintain an axis of above normal
temperatures from the northern Plains south-southeast to the
Mid-South, with plus 5-10F anomalies for highs possible most days.
Moderation back towards normal is expected next weekend as
lowering heights moves into the region. The Northwest will be the
other focus for very warm temperatures, with highs 10-20F or so
above normal Wednesday and Thursday. Expect near to below normal
temperatures over the Northeast and at times into the Mid-Atlantic
beneath upper troughing. Clouds and periods of rainfall should
keep highs 5-10F or so below normal over the southern half of the
Rockies/High Plains for most of the period and the upper low
reaching southern California Monday will also bring a cooling
trend into the southwestern U.S. next week.
Santorelli
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Sun Jun 04 2023
A daily diurnal risk for heavy showers and thunderstorms will be
maintained through the period from the southern Plains to the
northern Rockies and westward into the Great Basin as tropical
Pacific moisture is funneled northward in between a strong central
U.S. ridge and an upper low parked over California. For now, the
day 4 Excessive Rainfall Outlook continues to depict just one
large Marginal risk area for this region, however embedded Slight
risk areas may become necessary if heavy rains focus over
antecedent wet areas. By day 5, the marginal risk region is
largely the same as day 4, but did add a slight risk for parts of
central/eastern Montana given more favorable moisture and dynamics
and considering antecedent conditions in this region. The risk may
extend past day 5 as well as a frontal boundary becomes
established over the region.
Elsewhere, a front through the Great Lakes/Upper Midwest should
focus showers and storms ahead of it across the Northern
Plains/Upper Mississippi Valley early to mid week. In the
Northeast, the deepening upper trough/lows should favor pockets of
rainfall into Friday as moisture gets wrapped back into especially
northern Maine from a lingering low pressure system near the
coast. In Florida, a lingering weak front should support unsettled
conditions over the Sunshine State with better heavy rain chances
in southern Florida late week as deeper moisture gets pulled north.
Central U.S. ridging aloft will maintain an axis of above normal
temperatures from the northern Plains south-southeast to the
Mid-South, with plus 5-10F anomalies for highs possible most days.
Moderation back towards normal is expected next weekend as
lowering heights moves into the region. The Northwest will be the
other focus for very warm temperatures, with highs 10-20F or so
above normal Wednesday and Thursday. Expect near to below normal
temperatures over the Northeast and at times into the Mid-Atlantic
beneath upper troughing. Clouds and periods of rainfall should
keep highs 5-10F or so below normal over the southern half of the
Rockies/High Plains for most of the period and the upper low
reaching southern California Monday will also bring a cooling
trend into the southwestern U.S. next week.
Santorelli
