Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/08/22

Area Forecast Discussion

National Weather Service Flagstaff AZ

 851 PM MST Fri Oct 7 2022

.SYNOPSIS...Unsettled weather will continue with the greatest
shower and thunderstorm chances this weekend into the middle of
next week. Look for decreasing chances later next week as drier
air moves in. Mild daytime temperatures are forecast through the
period.

&&

.UPDATE...Only a stray shower or thunderstorm across all of
northern Arizona during the mid evening. The chances of getting
spooked by a surprise thunderstorm the remainder of the night is
near zero. The overnight precipitation chances were updated to
better account for this trend. Otherwise, the forecast is in good
shape.

&&

.PREV DISCUSSION /201 PM MST/...The weather over the next few days
across northern Arizona will be largely influenced by a slow
moving upper low, currently situated across Baja California.
Afternoon GOES imagery in tandem with RAP mesoanalysis revealed a
plume of moisture slowly pivoting around the northern periphery
of this system. With daytime heating, we`ve seen a gradual uptick
in the coverage of convection. The upward trend in showers and
storms will persist this afternoon and 12 UTC HREF PMM and NBM
PPI products appear to be capturing the evolution of this quite
well. The greatest PoPs (50-70%) are confined to the White
Mountains, eastern half of the Mogollon Rim and into the Black
Hills with lower PoPs (under 20%) along the AZ/UT border. The
severe weather threat will be hampered by paltry deep layer shear
(under 15 knots). Instability values are advertised to remain at
or below 1000 J/kg and this may support some modest upward
vertical motion in updrafts. This will promote a hail and gusty
outflow wind threat with the strongest storms. PWAT values are
around the 75th percentile for this time of year and so brief
heavy rainfall resulting in a low-end flash flood threat remains
a possibility. Where convection trains or back builds, the flash
flood potential will increase. PoPs fall to under 40% during the
overnight period tonight, mainly across the White Mountains where
modest warm/moist advection may persist.

For tonight and into early Saturday morning, the aforementioned
warm/moist advection regime is expected to promote bouts of
drizzle/mist/fog/low clouds for areas south of I-40 and east of
the I-17 corridor. 30-50% probability of visibility below 2 miles
are advertised by the HREF for locations south and east of a St.
Johns to Show low to Cibecue line. As a result patchy to areas of
fog have been inserted into the worded forecasts. The potential
for dense fog exits in spots, but confidence is much too low for
any headlines. Trends will be monitored this afternoon.

An additional round of showers and storms will take shape on
Saturday as another westward push of moisture unfolds. Current
indications suggest that the moisture surge may not be quite as
robust as initially though with probability of PWATs above 1"
remaining largely below 10% (except across the southern reaches of
Yavapai County). CAMs do imply a greater areal coverage of
convection and as a result, I`ll include mentionable PoPs across
most of northern Arizona (the exception will be far northern
portions of the Kaibab). While deep layer shear is forecast to
remain under 20 knots, forecast soundings for areas near and south
of the Mogollon Rim do exhibit inverted V type profiles. This in
conjunction with 0-3 km theta-e differences running between 10 and
15 K will facilitate another gusty outflow risk with winds perhaps
as great as 40-50 mph with the strongest cells (if they can
materialize).

The coverage of showers and thunderstorms is expected to take a
gradual downturn for the latter half of the weekend as slightly
drier northeasterly flow develops. Across Navajo Nation and Hopi
Tribal Lands, PoPs dwindle down into the 20-30 percent range.
Across the Mogollon Rim and into the White Mountains, PoPs range
from 30 to 80% as wind trajectories here will be more east and
southeasterly (thereby pumping modest moisture northward).

For next week, the upper air pattern should mimic more of a Rex
Block with our current low across Baja not making much progress
eastward. Further inhibiting any movement of this synoptic
feature will be an increase in mid-level heights across the
Pacific Northwest. Previously, it was advertised that a potent
"Inside Slider" event was on the table with an anomalously deep
low plunging southward through the Great Basin. An examination of
the cluster analysis reveals that a majority of the European and
GFS ensemble members now favor more of a Rex Block which would
spell cool, cloudy, and potentially rainy/stormy weather across
northern Arizona. ECMWF/GFS ensembles upper air patterns are more
in line with the Grand Ensemble while the Canadian forecast system
(both the deterministic and ensemble components) still advertise
more of an inside slider type event. For now the official forecast
will remain aligned with the latest NBM, but if the Canadian
forecast systems are to verify, we`ll need to bring temperatures
down by a good 10 to 15 degrees.

&&

.AVIATION...For the 06Z TAF package...Mainly VFR conditions are
expected through the period. Scattered showers and storms during the
daytime hours will locally reduce visibility and lead to gusty,
erratic winds. Otherwise, light easterly winds are expected.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered afternoon showers and
thunderstorms are expected across northern Arizona through Sunday.
Lightning, heavy rain, and gusty, erratic winds are possible with
any storms. Otherwise, light easterly winds and slightly below
average temperatures are expected.

Monday through Wednesday...Daily chances for afternoon showers and
thunderstorms remain. Expect seasonably cool temperatures and light
winds outside of storms.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

PUBLIC...McCollum/Bain
AVIATION...BAJ/Meola
FIRE WEATHER...BAJ/Meola

For Northern Arizona weather information visit
weather.gov/flagstaff



Area Forecast Discussion

National Weather Service San Diego CA

 144 PM PDT Fri Oct 7 2022

.SYNOPSIS...
An upper-level low over northwestern Mexico will lead to offshore
flow with warming expected west of the mountains through
tomorrow. Increasing moisture along the northern periphery of the
low will flow into Southern California, leading to daily chances
of thunderstorms mainly in the mountains and eastern valleys; this
could disrupt the marine layer the next few days, with low cloud
coverage patchy along the coast at times. Another low dropping
down the West Coast early next week will move the low east, but
could also enhance the chance of showers over all of southwest
California before much drier conditions arrive later in the week.

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

At 1 PM, patchy low cloud coverage is occurring along the
immediate coast in San Diego County, and cumulus clouds are
brewing in the mountains. A 582 DM low is churning over northern
Gulf of California and a 588 DM high is centered over northern
California. This is leading to offshore flow, which will mean
warming for areas west of the mountains today, and slight cooling
for the mountains and deserts. Highs will be 2 to 7 degrees above
normal for most areas, with the exception of the mountains where
temperatures will be near to slightly below normal. Little change
in temperature is expected for tomorrow.

Increasing moisture is occurring along the northern periphery of
the low, with a slight chance of thunderstorms for this afternoon
across the mountains and eastern valleys. The 20z SPC RAP analysis
shows SBCAPE values of 500 J/kg from the mountains, westward, and
MUCAPE values of 500-1000 J/kg, increasingly favorable low- and
mid-level lapse rates and rising dew points into the 60s.
Thunderstorms will be possible this afternoon over the mountains
and may drift west-southwestward into the valleys this evening.

The closed low will persist across northwestern Mexico through
this weekend, with continued chances for showers and
thunderstorms. The highest moisture surge looks to occur on
Sunday, when ECMWF ensemble members shows PWAT values of 1.3 to
1.5 inches for Imperial. The most likely scenario seems to be
thunderstorms forming over the mountains and drifting into the
valleys, potentially even reaching the coast at times this
weekend.

The upper low will eventually be absorbed into the mean flow on
Monday, finally progressing eastward. A large-scale pattern change
is expected early next week as another low strengthens across the
West Coast and progresses southeastward into the region. This will
lead to the return of onshore flow, cooler temperatures and a
deeper marine layer. Lingering moisture combined with the dynamic
lift of the approaching vorticity maximum could result in more
steady precipitation on Monday or Tuesday. Highs will fall
slightly below normal for Tuesday and Wednesday.

&&

.AVIATION...
072045Z...Coast/Valleys...SCT-BKN007-015 at the coast and over the
coastal waters becoming BKN-OVC005-013 and spreading 20 miles inland
through 16Z Saturday with vis reductions of 1-4 miles in FG and HZ
after 09Z. Scatter out for the valleys 16-18Z Saturday, and 18-21Z
at the coast. Low clouds could persist through most of Saturday
afternoon at the coast, including at KSAN and KCRQ. Afternoon TSRA
over the mountains will drift southwest into the valleys, perhaps as
far as the coast with the stronger cells.

Mountains/Deserts...SCT-BKN100-150 with scattered thunderstorms over
the mountains with tops to 30,000 feet MSL. Northeast winds aloft
will push the storms southwest off the mountains and into the
Valleys.

&&

.MARINE...
Thunderstorms are possible over the coastal waters Saturday
afternoon. If a thunderstorm does move over water, strong winds will
bring choppy, short-period seas.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

PUBLIC...Schenk
AVIATION/MARINE...Moede



Area Forecast Discussion

National Weather Service Tucson AZ

 120 PM MST Fri Oct 7 2022

.SYNOPSIS...A low pressure system will linger over northwest Mexico
and southern Arizona with a chance of showers and thunderstorms
through this weekend. Temperatures will remain near or below
average for early October.

&&

.DISCUSSION...Latest WV satellite imagery shows the mid/upper low
that we`ve been dealing with for the past several days continues to
spin across the northern Gulf of California. This low is cut-off
from the mean flow so it will continue to be very slow to fill and
eject eastward through the weekend. With PWAT values generally 0.75
to 1 inch across the region, combined with cooler than normal mid
level temperatures for this time of year, sufficient instability
will be realized to result in scattered mainly afternoon and evening
showers and thunderstorms. Storm development initiated to the south
of Tucson mainly across Santa Cruz County into east central Pima
County and we do expect storms to generally push off to the
northwest this afternoon as we`ll be in southeast flow on the
northeast flank of the mid/upper low. Main concerns will be similar
to that of the past few days including local/brief heavy rain, gusty
winds and small hail with the stronger storms. Also wouldn`t be
surprised if a couple of spots mainly west of Tucson see blowing
dust as DCAPE values in excess of 1000 J/KG are noted via RAP
mesoanalysis data. Showers and thunderstorms will gradually diminish
after sunset.

For this weekend, much of the same as the low will slightly nudge
northeast from its current position on Saturday so another day of
scattered mainly afternoon into evening showers and thunderstorms
are expected. By Sunday, the low will be over southern Arizona with
continued scattered shower and thunderstorm chances mainly from
Sells eastward.

While the low will shear and eject east on Monday limiting
mentionable PoPs to areas fairly east of Tucson, the larger scale
blocking pattern will prevent a complete scouring out of the
moisture. Another weak system is progged for Tuesday into Wednesday
with slight chance PoPs mainly to the north and east of Tucson.
Thereafter, drier northwest flow aloft should prevail but confidence
is low.

Temperatures will generally remain several degrees below normal into
early next week, then warming to near normal levels by the middle of
next week.

&&

.AVIATION...Valid through 09/00Z.
SCT-BKN clouds at 7k-12k ft AGL through 08/06Z with ISOLD-SCT
TSRA/SHRA for terminals across Santa Cruz, Pima and southern Pinal
counties through 08/03Z. Brief IFR visibilities, small hail and wind
gusts to 40 mph+ are main impacts with activity.  Storm movement
will be 10-15 kts from ESE to WNW. FEW-SCT clouds after 08/06Z with
overnight return to east-southeast breezes at or about 10 kts most
areas through 08/17Z. Outside of thunderstorm outflows, typical SFC
winds generally less than 10 kts, with higher gusts during the
afternoon hours. Storm focus Saturday shifts eastward for Cochise
county terminals.  Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Isolated to scattered afternoon and evening showers
and thunderstorms are expected through the weekend. The main threats
will be strong and gusty outflow winds, isolated areas of heavy
rainfall and dangerous lightning. Outside of thunderstorm outflow
winds, 20-foot winds will remain less than 15 mph into this
evening, with some gusty east/southeast winds today and Saturday.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

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Area Forecast Discussion

National Weather Service Las Vegas NV

 207 PM PDT Fri Oct 7 2022

.SYNOPSIS...A large cutoff low pressure system over southern
Arizona and northwest Mexico through the weekend will bring
sufficient moisture back over northwest Arizona and southeast
California for isolated afternoon showers and thunderstorms. The
system will pull away early next week followed by a ridge of high
pressure.
&&

.SHORT TERM...through Sunday night.

Most of the region will see little change in the dry and warm
weather which has been persisting for the past few days as a large
cutoff low spins over southern Arizona and northwest Mexico. The
counterclockwise circulation of the system will pull limited
moisture from northern Arizona down over Mohave and eastern San
Bernardino counties the next couple days leading to increasing
coverage of showers and thunderstorms...especially over southern
Mohave County Saturday afternoon. The latest HRRR and HREF indicate
the potential for strong thunderstorm winds gusts over 40 mph over
southern Mohave County and the lower Colorado River Valley,
including Lake Havasu, late Saturday afternoon. We will have to
monitor that potential tomorrow. The overall pattern begins to
change Sunday as a short wave trough drops down through eastern
Washington and Oregon into northwest Nevada. This will begin to
nudge the cutoff low toward the east, but it won`t make much
progress until after Sunday. Meanwhile, sufficient moisture and
instability in the lingering northeast flow will lead to persistent
chances for Sunday afternoon thunderstorms over central and southern
Mohave County. Temperatures will not vary too much with highs only
dropping a degree or two by Sunday.

.LONG TERM...Monday through Friday.

The weak trough digging from northwest Nevada over southern
California late Monday will converge with the northwest Mexico
cutoff low and lead to broad upward forcing over our region with
chances for showers or thunderstorms expanding a little over the
mountains of southern Nevada and Inyo County California...especially
the southern Sierra. So, the weather will be a little more unsettled
Monday, but impacts appear fairly minor for now with convection
confined mainly to the mountains. Model ensembles indicate the
interacting systems are forecast to slowly pull away Tuesday and
Wednesday followed by a high amplitude ridge likely developing along
the West Coast leading to a dry northwest flow over our region the
second half of the week. Although there are a few outlier solutions
that dig a deep trough over the Intermountain Region and retrograde
it over southern Nevada/California during the same time, this
appears to be much less likely scenario. The latest NBM keeps
conditions dry and mild over our region Wednesday through Friday
with highs 85-90 degrees across the desert zones.
&&

.AVIATION...For Harry Reid...No significant weather is anticipated
during through Saturday. East-northeast winds around 6-8 knots will
occur during the afternoon hours flipping to west-southwest after
sunset and overnight.

For the rest of southern Nevada, northwest Arizona and southeast
California...VFR conditions and winds generally less than 10 knots
favoring typical diurnal directions can be expected across most of
region through Saturday. The exception is northwest Arizona and
where a few afternoon showers and thunderstorms will be possible.
Outflow from storms may impact sites in lower the Colorado River
Valley Saturday afternoon.
&&

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&

$$

SHORT TERM/LONG TERM/AVIATION...Adair

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