AWUS01 KWNH 201801
FFGMPD
AZZ000-NVZ000-CAZ000-210000-

Mesoscale Precipitation Discussion 0952
NWS Weather Prediction Center College Park MD
201 PM EDT Sun Aug 20 2023

Areas affected...much of southern California and adjacent areas of
southern Nevada and far western Arizona

Concerning...Heavy rainfall...Flash flooding likely

Valid 201800Z - 210000Z

Summary...Tropical Storm Hilary continues to make steady
north-northwestward progress toward the Southwestern U.S.. Areas
of heavy rainfall should cause flash flooding at least through 00Z.

Discussion...Widespread areas of light to moderate rainfall
continue to stream northward ahead of the approach of Hilary,
which was recently located near the northern Baja California
Peninsula. Rain rates have generally remained in the 0.2-0.5
inch/hr range across southern California so far, with the heaviest
rain recently noted in/near higher terrain north of Los Angeles
and just south of El Centro in far northwestern Mexico over the
past hour or so. These rain rates have resulted in a few impacts
so far. Models/CAMs suggest that rain rates within this general
axis (from Los Angeles northward toward Death Valley and southern
Nevada near Pahrump) could increase as the center of Hilary gets
closer, with spots of 0.5+ inch/hr rainfall expected as low-level
wind fields increase over time.

A somewhat more concerning scenario should unfold from along and
just east of the Peninsular and eastern Transverse ranges into the
southern Sierra through 00Z. As Hilary moves closer to these
areas, low-level wind fields will increase dramatically, with a
distinct southeasterly component of flow interacting favorably
with local orography to provide lift. Additionally, strong
low-level warm/moist advection and surface heating should allow
for added destabilization to both 1) bolster updraft strength and
coverage while 2) eventually increasing rain rates. Eventually,
heavier precipitation (such as the near 1 inch/hr rain rates
observed just south fo El Centro) should migrate northward into
southern California and further increase the flash flood risk.
These rates could persist for a few hours in tandem with Hilary's
storm motion. Areas of 2-4 inch rainfall totals are likely, and
this thinking is generally in line with the 12Z runs of the
high-resolution Nam and HREF.

Additional thunderstorm activity should also materialize along the
Lower Colorado River Valley, although the flash flood potential is
somewhat in question there as fast storm motions limit the amount
of rainfall in any given spot. It appears that more organized
training of convection will be needed for a more appreciable flash
flood threat to materialize across eastern portions of the
discussion area (closer to the Lower Colorado River) through the
evening.

Cook

ATTN...WFO...HNX...LKN...LOX...PSR...REV...SGX...VEF...

ATTN...RFC...CBRFC...CNRFC...NWC...

LAT...LON 38231643 37511562 36391459 35181471 34111442
33031429 32421479 32301716 32801790 33951911
34971939 36641939 37651876 38221764

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AWUS01 KWNH 211150
FFGMPD
NVZ000-CAZ000-211800-

Mesoscale Precipitation Discussion 0957
NWS Weather Prediction Center College Park MD
750 AM EDT Mon Aug 21 2023

Areas affected...Southeast CA Deserts...Much of Central Nevada...

Concerning...Heavy rainfall...Flash flooding likely

Valid 211200Z - 211800Z

SUMMARY...Tail end of moisture flux band associated with Post T.C.
Hilary. Additional 1-2" across areas already flooded could
possibly reaggravate situations locally.

DISCUSSION...GOES-W WV suite denotes Hilary has fully transitioned
and melded with extratropical deep cyclone west of CA with
trailing tail-end of broad warm conveyor belt denoted across S CA
and NV. CIRA LPW also depicts core of moisture is starting to
shift north and bifurcate through depth across the southeast
deserts of CA into south-central NV. Sfc to 700mb still shows
core of enhanced moisture through the Lower Colorado Valley nosing
into the S NV and through central NV with .33 to .5" across the
two layers (sfc-850 & 850-700) respectively. However, the 700-500
layer has enhanced drying overlaying this enhanced moisture, but a
narrow band of enhanced moisture up to .5" does exist through the
Imperial valley through the Mojave to west of Las Vegas. As such,
a narrow overlap resulting in totals near 1.5-1.7" still exists
near the CA/NV boarder centered over and west of the Spring
Mountains. Winds through this area continue to be strong with
20-25kt at 850 becoming 40-50kts at 700mb, but fairly
unidirectional through great depth. Even 500-300mb flow is
unidirectional likely to allow this overlapping area of enhanced
moisture to stream northward further into central NV throughout
the remainder of the morning.

While instability is very limited, there are hints of 250-500 J/kg
of MUCAPE and with favorable right entrance ascent to 60-70kt 3H
jet core near 120W, a few shallow but vertical cores of convection
remain possible through the morning hours. Starting across the
Mojave Desert currently, and streaking northward into northern Nye
county and eventually toward Eureka county toward late
morning/noon. Showers will likely be best enhanced along spines
of the Ranges where any localized mountain circulation can enhance
low level moisture flux convergence. Hi-Res CAMs continue to
appear plausible with fairly good agreement in placement and
timing to provide some increased confidence. As such, rates up to
1"/hr and localized spots of 2-2.5" remain possible. This alone
may have resulted in possible flash flooding conditions, but given
the recent heavy rainfall across the area...flash flooding is
considered to be likely to reaggravate ongoing flooding across the
area of concern through 18z, but diminishing with time and from
south to north.

Gallina

ATTN...WFO...LKN...REV...VEF...

ATTN...RFC...CBRFC...CNRFC...NWC...

LAT...LON 40901541 40321495 39271494 38261493 36911494
34911498 34431560 34901637 35941733 38621843
40231814 40881719

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AWUS01 KWNH 211227
FFGMPD
IDZ000-ORZ000-WAZ000-211830-

Mesoscale Precipitation Discussion 0958
NWS Weather Prediction Center College Park MD
826 AM EDT Mon Aug 21 2023

Areas affected...Eastern Oregon...West-central Idaho...

Concerning...Heavy rainfall...Flash flooding likely

Valid 211230Z - 211830Z

SUMMARY...Sharp/stationary deformation zone with persistent highly
anomalous moisture flux and occasional embedded convective
elements capable of 1"+/hr. Localized spots of 2-3" are possible
through 21z, resulting in flooding and possible localized flashy
conditions at times.

DISCUSSION...GOES-W WV depicts nearly full transition of Hilary to
a classic baroclinic cyclone with impressive baroclinic leaf
developing across N CA into Oregon with broad shortwave ridging
expanding over the area of concern and expanding anticyclonic
cirrus arching through the entrance to the 110+kt 3H Jet along the
western US/Canadian boarder. This is providing strong vertical
ascent across the region, while the core of deep layer moisture
associated with Post T.C. Hilary has been lifting through western
NV toward the region. Concurrently, low level flow through the
Snake River Valley in ID has backed with 700mb accelerating to
over 25kts from the southeast (increasing to 50kts in the next few
hours). Low to mid-60s surface Tds and overall total PWats
increasing to over 1.3", perhaps as high as 1.5", which would be
at or near local record values using surrounding RAOB history but
is nearly 5-6 standard deviations from monthly averages. While
mid-level temperature profiles are fairly moist adiabatic, there
is still some warm air advection to support some weak mid-level
unstable air with MUCAPE values near 500 J/kg.

Given the strength of moisture flux convergence into the
strengthening deformation/frontogenetical band from NW NV to
east-central OR into north-central ID, a broad shield of
precipitation is forming along the band with KCBX already showing
some embedded convective elements along the the upwind edge at
this time. Those elements are likely to settle further north but
begin to remain relatively stationary with cell motions likely to
be along the arch to support training potential. Those small
convective cores are likely to support rates up to 1" maybe
1.25"/hr within the broader .25-.33"/hr shield. Given duration of
3-6+ hours, spots of 2-3" are possible. Orographic ascent across
the SE facing terrain is a bit more atypical, especially given the
deeper moisture that may expose topography/channels/creeks that
have not experienced these types of rates and may result in
increased mud flows as well. These rates, totals and topography
are likely to induce at least highly localized flash flooding
conditions through the late morning into early afternoon period.

Gallina

ATTN...WFO...BOI...MSO...OTX...PDT...

ATTN...RFC...CNRFC...NWRFC...NWC...

LAT...LON 46661518 45811499 45051531 44041616 43251690
42681743 42261793 42081855 42241902 43171930
44281883 46021727 46641620

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MIKE POWELL wrote to ALL <=-

SUMMARY...Tail end of moisture flux band associated with Post
T.C. Hilary. Additional 1-2" across areas already flooded could
possibly reaggravate situations locally.

One of the local meteorologists was reporting on tropical storm Hilary
during the news and absent-mindly said "Tropical Storm Hillary Clinton"!


¯ ®
¯ BarryMartin3@MyMetronet.NET ®
¯ ®


... Little known facts: cow farts come from the dairy air.
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One of the local meteorologists was reporting on tropical storm Hilary
during the news and absent-mindly said "Tropical Storm Hillary Clinton"!

That does not shock me. :) The Babylon Bee did a satirical piece about
how TS Hilary was not as potent at landfall as forecast due to "Russian interference" in our weather. :D

Mike


* SLMR 2.1a * Pregnancy is a side effect of sloppy birth control.
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Hi Mike!

One of the local meteorologists was reporting on tropical storm Hilary during the news and absent-mindly said "Tropical Storm Hillary Clinton"!

That does not shock me. :) The Babylon Bee did a satirical
piece about how TS Hilary was not as potent at landfall as
forecast due to "Russian interference" in our weather. :D

So the Russians are sneakier than the Chinese? (Sly referral to the
balloons incidents.)


¯ ®
¯ BarryMartin3@MyMetronet.NET ®
¯ ®


... Him: "What's the Microsoft anti-spyware tool called?"
Me: "FDISK."
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