FOUS30 KWBC 121947
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 PM EDT Wed May 12 2021

Day 1
Valid 16Z Wed May 12 2021 - 12Z Thu May 13 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL GULF COAST...

1600 UTC update

Only some minor changes made to the marginal risk area along the
central Gulf coast. The previous area was trimmed slightly to the
south and slightly on the eastern end over the Florida panhandle
based on latest hi res guidance and where heaviest rains fell over
the past 24 hours.

Oravec

0900 UTC discussion

In general not expecting any widespread heavy rainfall today, and
the flash flood risk should stay rather low. The ongoing
convection is expected to remain progressive as it tracks across
the Gulf Coast this morning, and the upstream environment behind
this activity is pretty worked over. Thus not anticipating any
development too organized behind this ongoing line. However, the
actual surface front is hanging back, so the central Gulf Coast
will remain south of the main frontal boundary for much of the
day. Can not rule out some development closer to this front today
into this evening, and given the wet antecedent conditions,
localized heavy rainfall with any cells may result in an isolated
flash flood risk. If it were not for the antecedent conditions, no
risk of excessive rainfall would be needed today. But given the
increasingly saturated ground and front hanging back...the safe
option is to maintain the Marginal for now, in case some
redevelopment is able to occur over any more sensitive locations.

Chenard


Day 2
Valid 12Z Thu May 13 2021 - 12Z Fri May 14 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF EXTREME SOUTHEAST FLORIDA...

At the start of the forecast period (13.12z), shortwave currently
crossing the central Gulf Coast will be exiting well off the NE
Florida coast but supporting slow southward building of the high
and sag of the frontal zone across central FL. By midday,
filtered insolation and weak southerly surface flow should support
increasing instability along/ahead of the front but also mild
capping to build up instability. Strengthening northeasterly flow
will sharpen the front and increase sfc to boundary layer moisture
flux convergence to develop strong thunderstorms. Additionally,
the tail end of 3H jet will be oriented favorably for right
entrance divergence and larger scale ascent/outflow to enhance
clustered updrafts.

GFS/ECMWF soundings and TPW forecast depicts west to east deep
moisture axis ideally oriented for mid-cloud entrainment to
accompany low-level flux suggesting 1.75-2" values and strong flux
convergence to support very efficient rainfall production for
thunderstorms after 21z, likely focused along the eastern coast
where sfc flow is enhanced due to sea-breeze/onshore flow. As
such rainfall rates in excess of 2-3"/hr are possible. Weak
shear/mean layer flow may support greater than desired pulse
nature but there are suggestions of weak organized clusters that
would support very slow motions for high rainfall totals in 1-2
hours. 12z HREF probabilities support this with 2"/hr rates in
the 30% range but also 6hr totals of 3" and 5" at 60-70% and
25-30% respectively (mostly between 21-06z).

While, ground conditions are dry and FFG is in typical very high
range, Hi-res CAMs and other global guidance are honing in on best
forcing to near enough to Southeast Florida urban centers. Given
the magnitude of rates and potential 3-5" localized totals, there
is sufficient confidence to support a Marginal Risk of Excessive
Rainfall across the urban corridor of southeast Florida.
Potential for thunderstorms over current Day 1 period could even
increase localized rapid inundation flooding risk and will be
monitored for tonight's update moving into the Day one period.

Gallina


$$
--- SBBSecho 3.12-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1)

FOUS30 KWBC 222000
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
359 PM EDT Sat May 22 2021

Day 1
Valid 16Z Sat May 22 2021 - 12Z Sun May 23 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
TEXAS, THE HIGH PLAINS, AND THE SOUTHERN/CENTRAL ROCKIES...

...Central/Eastern Texas...
A weak surface low pressure system will continue to drift
northwest between the weakening trough in the West and ridge in
the East. Still anticipate convection to become more widespread
through the afternoon with localized multiple rounds of heavy rain
and isolated flash flooding.

The retrograding eastern ridge will continue to shift the best
moisture transport west from western LA to east TX through the
early afternoon. Precipitable water values will increase to around
2 inches (aided by 20-30 knot southeasterly low level flow) which
is over 2.5 standard deviations above the mean. Coincident with
this transition will be diurnal heating leading to better
instability through the afternoon. MUCAPE values will range
between 500-1000 J/kg. Thus, anticipate convection to blossom with
rain rates exceeding 1.5 inches/hour. Areal average precipitation
will range from 0.5-1.5+ inches with locally higher amounts in 12Z
guidance centered in north-central TX. Therefore, the Marginal
Risk area was expanded north a bit.


...Southern/Central Rockies and adjacent High Plains...
The trough in the west will continue to weaken as it shifts north
and east through the forecast period. Mid-level impulses will
round the trough and cross existing surface boundaries with pooled
moisture and instability helping to focus convection, especially
on the High Plains. This activity will likely continue through the
evening hours with the strengthening low level jet. Thus, multiple
rounds of heavy rain could lead to localized flash flooding.

Precipitable water values will increase across the region to
around 0.75-1.25 inches aided by southern flow (both from the
Pacific and Gulf of Mexico). Values will be 2+ standard deviations
above the mean. Instability climbing to above 2000 J/kg MUCAPE by
the afternoon with convection locally enhanced by low level
upslope flow. In addition, subtle mid-level impulses aloft will
interact with lingering surface boundaries which will likely act
as a focus for convection from the afternoon into the
evening/overnight hours. Rain rates may exceed 1 inch/hour with
multiple rounds of precipitation resulting in localized higher
hourly storm totals. Areal average precipitation will vary quite a
bit with some locations observing 3+ inches. 12Z guidance
consensus has a main QPF axis farther west over the northern
Plains, so the Marginal Risk was shifted north up to the southern
edge of the Nebraska Sandhills. Burn scars were also taken into
consideration when maintained the risk area in the CO Rockies.

Jackson/Pagano


Day 2
Valid 12Z Sun May 23 2021 - 12Z Mon May 24 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CENTRAL/SOUTHEASTERN TEXAS...

21z Update...
...Central Texas to Middle Texas Coast...
Early morning convection today (May 22) helped to lower FFG values
exist along the Middle Texas Coast. This is generally aligned
with increasing confluence and theta-E flux across throughout the
day 2 period but significantly enhancing after 24.00z that will be
capable of intense rates over 2"/hr. This is supported by about
half of the Hi-Res CAMs and solid response out of the 12z NAM,
ECMWF and CMC solutions, providing confidence. Given this and in
coordination with local forecast offices, a Slight Risk was
introduced.

...Upper Midwest...
Hi-Res CAM and global guidance trended a tad eastward resulting in
a shift of heaviest rainfall solutions. As such, small adjustment
removing portions of western MN were taken, while bringing the
Marginal Risk Area across Southern half of WI to Lake Michigan.

...Western Dakotas...
At the start of the forecast period, 23.12z, a compact shortwave
within the parent Western closed low will be advancing northward
across W CO into the Northern High Plains. Deep moisture will be
streaming northward across the High Plains on 25-30kts of LLJ
throughout the day. Given the strong height-falls, the western
branch of the LLJ &TROWAL will develop pulling 3-4 Std. Dev of
moisture flux into the Hi-Plains of E MT. This will help to surge
the Warm Front northward.

Strong convective response to the DPVA from the shortwave should
occur by early to mid-afternoon across E MT/WY, though anomalous,
the moisture will be limited so rainfall efficiency should be
limited. As the line expands and advances east, it will intersect
the warm front and deeper moisture across W SD, where total PWats
will be nearing 1.0", so flux convergence may support rates of
1.25-1.5" toward 21-00z (and CAPEs over 1500 J/kg). Shear
profiles may support embedded rotating updrafts, which may further
enhance low level entrainment and flux convergence resulting in
sub-hourly totals of 1.5-2". Dry ground conditions are the
dominant, limiting feature across the area with NASA SPoRT 0-40cm
soil saturation ratios below 30%, these embedded streaks of higher
rainfall totals are less likely to soak into the ground with
enhanced localized run-off, perhaps resulting in small
basins/watersheds flooding in short duration. CSU First Guess ERO
suggests probabilities of exceedance for day 2 in the 15-20%
range; typically due to the methodology of training against the
GEFS across the High Plains into the West tends to yield higher
ranges of probability...it does provide sufficient confidence to
suggest a Marginal Risk of Excessive Rainfall and Flash Flood
potential exists. In agreement with local forecast offices, we
have introduced a broad Marginal Risk over the lowest FFG values
of Western North and South Dakota.

Gallina

---Prior Discussion (09z)---
...Central Texas to the Middle Texas Coast...
In the wake of a remnant low to mid-level low tracking northward
through northern Texas/Oklahoma early Sunday morning, an axis of
high precipitable water values (1.7 to 2.1 inches, or +2 to +3
standardized anomalies) will remain focused from the western Gulf
of Mexico into the middle Texas coast and portions of central
Texas. Aloft, a mid-level shear axis will remain oriented from
south to north across the region with embedded vorticity maxima.
850-300 mb mean flow is forecast to be on the weak side across
central/southern Texas, ranging between 5 and 15 kt. Meanwhile,
850 mb flow will remain roughly perpendicular to the coast and
vary between 10 and 25 kt, with the Gulf of Mexico acting as a
source region for moist and unstable air. Stronger 850 mb flow
allows for backward propagating Corfidi vectors, supportive of
backbuilding and training.

While there are differences with the degree of instability
forecast for the afternoon hours, the high moisture environment
should be able to support tall/skinny CAPE profiles as depicted by
the NAM. Forcing for ascent will be aided by smaller scale
vorticity maxima along the mid-level shear axis. The coarser
resolution models support a relative max in QPF across central
Texas to the coast with roughly 0.5 inches to 1.5 inches, but the
NAM_nest and FV3_LAM are perhaps too aggressive with smaller scale
maxima of 3-6 inches (NAM_nest locally higher). The potential for
2-4 inches on a localized basis atop wetter than average soils
supports a Marginal Risk.

...Upper Midwest...
A Marginal Risk was added to southern Minnesota, northeastern Iowa
and central/southern Wisconsin to account for the potential of
localized flash flooding. Anomalous precipitable water values will
travel northward through the Plains into the Upper Mississippi
Valley, on the west side of a ridge centered over the Tennessee
Valley. At the surface, a front will extend roughly west to east
across Minnesota into Wisconsin, with the nose of the moisture
axis intersecting the front near the Minnesota/Wisconsin border
(precipitable water values along the front of 1.5 and 1.8 inches).
Deeper-layer mean flow will be roughly parallel to the frontal
boundary which may support some repeating/localized training of
thunderstorms.

Differences in the latitude of the front remain, with the GFS and
FV3_LAM north of the remaining model consensus. 12 hour hi-res QPF
was available through 00Z/24, showing unanimous consensus for 2-4
inches locally across the Marginal Risk area. Additional heavy
rain will be possible beyond 00Z in the vicinity of the slow
moving frontal boundary. Despite the relative lack of rain over
the past two weeks, flash flood guidance values are only about 1.5
to 2.5 inches in 3 hours across a majority of the region, and
these values could be surpassed Sunday into Sunday night.

Otto

Day 3
Valid 12Z Mon May 24 2021 - 12Z Tue May 25 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL ALLEGHENY PLATEAU AND ALLEGHENY MOUNTAINS AND PORTIONS
OF CENTRAL TEXAS TO THE MIDDLE TEXAS COAST...

...Allegheny Plateau and Central Mountains...
At the start of the forecast period, 24.12z, a convectively
induced shortwave will be in the vicinity of the Allegheny plateau
at a distant periphery of right entrance to Polar Jet streak over
SE Canada and northern New England. The anomalous eastern U.S.
ridge will continue to retrograde west, allowing for the streamer
of deep Gulf moisture (2-3 std. dev of normal) to atop the ridge
across the central Great Lakes, intersecting with the trailing
edge of a frontal zone crossing through the Northeast. While,
this shortwave is awkwardly timed coming through the region with
respect to instability, global guidance does keep some sort of
axis aligned with the moisture axis as well. Additionally, there
is likely to be ongoing scattered convection from the day 2 period
at the start, but solid 15-20kts of WNW inflow along the moisture
axis should support ample flux and nearly orthogonal orographic
ascent. In addition, this should turn propagation vectors into
the flow suggestive of a favorable back-building environment and
given generally unidirectional steering flow to the moisture axis
could provide opportunity for back-building cells to repeat.

A limiting factor would be generally dry to very dry ground
conditions in the vicinity per 0-40cm soil saturation ratios well
below 10% according to NASA SPoRT derived product. Still, complex
terrain and potential for sub-hourly rain totals at 1.5-1.75"/hr
rates could approach the naturally lower FFG values in the area.
As such, and in coordination with local forecast offices,
introduced a Marginal Risk of Excessive Rainfall across Northeast
WV, Southwest PA and adjoining portions of Eastern OH, and Western
MD.


...Central Texas to Middle Texas Coast...
At the start of the forecast period, there is likely to be ongoing
convection within the deep moisture plume oriented SE to NNW
across the central Texas Coast toward the Dallas-Fort Worth Metro.
Deep tropically rich moisture over 2-2.25" through the column and narrow/skinny unstable profiles will provide ample moisture
loading for efficient rainfall production. Scattered 2-3" totals
in coarser global guidance is more than sufficient to result in
flash flooding concerns given the saturated ground conditions. As
such a Marginal Risk is placed along the mean moisture flux axis
across Texas, once again for the Day 3 period. An upgrade to a
higher category is once again contingent on the placement of the
heavy rainfall over the next few days and so is too uncertain to
delineate at this time.

Gallina

$$
--- SBBSecho 3.12-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1)

FOUS30 KWBC 280805
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
405 AM EDT Fri May 28 2021

Day 1
Valid 12Z Fri May 28 2021 - 12Z Sat May 29 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS CENTRAL TO
SOUTH CENTRAL TEXAS...

...Central to south central Texas...
The surface cold front currently sinking southward into the
Southern Plains is expected to become stationary and oriented west
northwest to east southeast from eastern New Mexico into Central
Texas. Upstream shortwave energy pushing eastward from the
Southern High Plains will ride along this front and support
additional organized convection pushing southeast in the axis of
pw values 1.5-2+ standard deviations above the mean in the
vicinity of this boundary. There are some timing differences with
this convection, but general model agreement for potential of
organized activity moving southeastward late afternoon Friday into
Friday night/early Saturday. A slight risk area was added from
the previous outlook where the latest HREF neighborhood
probabilities are showing values of 50-80%+ for 2"+ totals,
40-60%+ for 3"+ totals and 5-20% for 5"+ totals this period.

...Southern to Central Appalachians into the Mid-Atlantic...
No significant changes to the broad marginal risk area depicted in
the previous outlook stretching across the Southern to Central
Appalachians into the Mid-Atlantic. The amplifying mid to upper
level trof across the Mississippi Valley will help surge a broad
region of pw values 1.5 to 2+ standard deviations above the mean
northeastward across these areas beginning this morning.
Convection likely to increase in this high pw axis along and ahead
of the associated cold front where very favorable right entrance
jet dynamics will accentuate lift. Simulated hi res radars are
showing the potential for more than one round of convection to
push eastward ahead of the front across the Southern to Central
Appalachians and into the Mid-Atlantic with .50-1"+ hourly totals
possible with each round. FFG values are lowest across the
Central Appalachians from southwest Pennsylvania, far western
Maryland, central West Virginia into portions of southwest
Virginia, with higher values south into the Southern Appalachians.
Given the strong upper dynamics and anomalous pw values, didn't
want to exclude any regions in the Appalachians where heavy rains
are possible. HREF neighborhood probabilities are very high
across the entire marginal risk area for 1"+ totals 80-90%+ and
30-70%+ for 2"+ totals this period. The marginal risk area was
maintained to the north of the west to east oriented frontal zone
expected in the vicinity of the Mason-Dixon line, across the urban
areas from Philadelphia to northern New Jersey. Rainfall rates
are not expected to be as great as across areas south of this
front, but with relatively low FFG values isolated urban runoff
issues possible from pockets of heavy overrunning rains pushing
northeast across this region.


Oravec


Day 2
Valid 12Z Sat May 29 2021 - 12Z Sun May 30 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL & SOUTHERN HIGH PLAINS AND SOUTHEAST TEXAS...

...Southeast Texas into far Southwest Louisiana...
Global guidance suggests there may be a weakening ongoing
convective complex in the vicinity of Central Texas at the start
of the forecast period, 29.12z. The GFS and ECMWF continue to
support an MCV traveling southeast along the trailing trof/frontal
zone that is draped across the Northwest Gulf and coastal
southeast Texas/southwest Louisiana. Ample remaining instability
and moisture pooled along the boundary may help to feed any
ongoing thunderstorms, but even the strongest solutions suggest
weakening (5-15kts) of southerly component inflow from the south
for isentropic ascent along any outflow induced boundaries from
the complex. Hi-Res CAMs are nearly vacant of convective
activity, providing reduced overall confidence in the global
solution's manifesting. However, if there are cells, they are
likely to be efficient rainfall producers with 1.75" of total PWAT
but given weaker flux convergence, they may not be all that
excessive; however, they will be moving across compromised soils
where 2-week precip anomalies per AHPS remain 300-500% of normal.
Even though there has been some recent improvement per NASA SPoRT
0-40cm soil saturation, all the factors suggest maintaining a
Marginal Risk mainly for the earliest time periods on Saturday
morning into the afternoon.

...Central and Southern High Plains...
The base of a northern stream trof axis will be crossing out of
the northern High Plains, though weak lingering positive tilt
troughing will exist over the Four Corners. This will support
southerly low level flow across the Central Plains, while also
increasing return moisture across the Southern High Plains by the
end of the forecast period. As the northern shortwave progresses
northward, the trailing frontal zone will drop south along the
intersection of the High Plains, maximizing moisture flux
convergence with its slow southward progression; combine this with
diurnal upslope components and insolation to support a ribbon of
increased instability across the Central High Plains. Convection
will develop in the mid-afternoon/early evening. Clusters nearest
the frontal zone may slow a tad and build up-scale for localized
heavy rainfall given slower mean flow and cell motions. While some
Hi-Res CAMs are particularly aggressive and result in areal 2-4"
totals, there is typical placement uncertainty. Lower FFG values
across the Southern Platte River Valley and generally well above
normal soil saturation, suggest a Slight Risk may be needed
further north.

However, strong low level flow, may reduce overall totals as
clusters may propagate further south, faster with general eastward
march off the higher terrain after night-fall. Additionally,
stronger moisture return that was easterly through the day will
veer slowly over the southern High Plains of NM/and the TX/OK
panhandles. As such, the focus for stronger upscale enhancement
continues to shift south into early Sunday morning. Again, some
solutions such as the NAM-Conest and FV3CAM show extreme rain
totals, but this is typical bias, though UKMET/ECMWF and recent
NAM solutions suggest better clustering further south too with
2-3" areal average QPF values. Overall, these model solutions
should result in a Slight Risk, particularly given the higher than
normal soil saturation; however, the precise placement and pace of
southward propagation provides too much uncertainty to place a
Slight Risk category at this time.

Gallina


$$
--- SBBSecho 3.12-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1)