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Office: PSR

FXUS65 KPSR 162346 AAB
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
445 PM MST Tue Aug 16 2022

.UPDATE...Updated 00Z Aviation Discussion.

&&

.SYNOPSIS...
Temperatures will climb to near to slightly above
normal through Wednesday, with daily isolated showers and
thunderstorms. Beginning late Wednesday, deep monsoonal moisture
will return to southern Arizona leading to much better chances for
showers and thunderstorms. Heavy rainfall and localized flooding
are likely to impact portions of south-central and eastern Arizona
later this week, with chances peaking on Friday through Sunday.
Temperatures are also forecast to cool to well below normal with
highs across a good portion of the lower deserts falling into the
nineties or even upper eighties by Friday.

&&

.DISCUSSION...
A broad area of ridging remains in place across the northern
portions of the United States and Canada with near or below normal
heights across the Desert Southwest. There are several mesolows in
the area, including one southeast of Phoenix that will drift up
towards our forecast area this afternoon. Further east near the
Big Bend area of Texas, a much stronger upper level low is slowly
drifting west, but for now is not impacting the forecast area.
Visible satellite shows partly sunny skies, with a few
thunderstorms popping up over the higher terrain. ACARS soundings
show a cap at the top of the boundary layer, which should keep
storms from proliferating in the valleys too much for now,
especially near Phoenix.

For this afternoon we are looking at scattered storms developing
over the higher terrain, especially southeast California where
moisture and instability profiles are a bit better. HREF guidance
shows high confidence (50-70%) chance of gusty outflow winds of at
least 35 kts over southeast California today with a lower
(20-40%) chance of such winds for the rest of the forecast area.
Because PWAT remains elevated at 1.7-2.1", locally heavy rain will
also be a threat. Further, with weak winds aloft, storms will not
move very quickly. For the Phoenix area, sufficient
destabilization for storms is in question, but it does appear that
a few storms will pop up this afternoon or evening with a 10-20%
chance of rain in any given location. As for temperatures, warm to
hot conditions will continue through Wednesday with highs in the
103-107 range for the lower deserts, but with elevated moisture
levels it will not feel like our more typical dry heat.

For the Wednesday through early Friday period we will see an
increasing storm threat in response to the previously mentioned
upper level low centered near the Texas/Mexico border. Several
factors will work together to enhance the storm threat as it
approaches. First, mid level winds in the 600-400 mb layer will
shift to northeast and strengthen. This will act to strengthen
wind shear and the steering flow from off the higher terrain.
Second, an influx of deep moisture on Wednesday will send PWAT
values close to 2" for much of the area. Third, there will be some
forced ascent as the storm system approaches. These factors
should allow for numerous high terrain storms to develop along the
Rim with a decent (30-50%) chance of these storms moving into the
valleys of Arizona from the northeast during the afternoon hours.
Should this scenario unfold all of our typical monsoon hazards
would be possible, but wind and dust typically dominate in
northeast flow events. Heading into Thursday and especially Friday
it may be that excessive cloudiness limits storm chances
somewhat, but this outcome will depend on what happens in the
previous days in large measure. There is also still some
uncertainty with respect to the track of the low pressure area,
and if it tracks further south than modeled our risk of storms
would diminish.

Friday will be a transitional day for what looks to be the main
event and potentially a significant precipitation event for
south-central Arizona. Setting the stage will be a strengthening
trough to the northwest of the forecast area, which will put
southern Arizona under excellent diffluent flow aloft with
strongly forced ascent, especially on Saturday. Low level moisture
transport will strengthen, with PWAT climbing above 2", which is
near the max NAEFS climatology for this time of year and above the
99% percentile. Further, due to the proximity of the trough and
the other upper level low (which will still be south of the area),
wind shear will increase. Taken together, these factors strongly
support widespread and potentially heavy precipitation. ECMWF EFI
precipitation depicts values of 0.7-0.9 across the area on
Saturday. The shift of tails is relatively minimal, and a perusal
of the ensemble reveals good consistency in precipitation totals
compared to usual. What this likely means is higher confidence in
most locations getting a good soaking, rather than a few locations
getting a lot of rain while most others get little to none.
Accordingly, WPC QPF continues to show potentially large storm
totals of 1-3" between Friday and Sunday evening for south-central
Arizona. Lower totals of less than 1" are forecast for SE
California during this period. It is anticipated that a flood
watch will eventually be needed for south-central Arizona if the
forecast remains consistent.

Temperatures will also cool off considerably by Friday with highs
falling well into the 90s over a good portion of the lower deserts.
If models end up being correct with the amount of clouds and
rainfall over the area later this week, some lower desert areas
likely won't get out of the 80s on Saturday. The NBM even has a 20%
chance that the Phoenix area fails to reach 85F for the high on
Saturday. Widespread rain chances may also linger into Sunday, but
models mostly show waining upper level support by early Sunday while
the disturbance to our south weakens considerably. By early next
week, there is fairly good ensemble agreement our region will see a
gradual drying trend with northerly upper level flow becoming more
dominant.

&&

.AVIATION...Updated 2345Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Current light westerly winds are expected to continue thru shortly
after midnight, then becoming typical easterly drainage winds
thereafter. Thunderstorm chances to remain low thru tonight as most
activity will remain focused across the high terrain. It's not out
of the question to see a few isolated vicinity showers pop up across
the metro this evening, but confidence (10-20%) chance remains too
low to include anything more then VCSH in the TAFs at this point.
Chances are a little more likely (20-30% chance) that current
westerly winds could be enhanced a bit from outflows from t-storms
over SW Maricopa County, but confidence remains low on if/when any
outflows impact the terminals, Expect SCT-BKN clouds to remain
mostly aoa 8 kft through this evening. After winds shift to easterly
late tonight, expecting these easterly winds to continue thru early
afternoon Wednesday, then switch to typical westerly winds during
the mid-afternoon hours.

A better chance (40-60%) exists for t-storms impacting the terminals
Wednesday afternoon/evening as moisture/instability increases across
the region. Have added VCTS in the TAFs at this point (given
uncertainties in timing), with winds likely shifting to a
northeasterly direction. There are also indications that lighter
SHRA/isolated T-storm activity could persist well into Wednesday
night as well.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds through the period will mostly favor a southerly to
southeasterly component outside of any potential thunderstorm
outflows. It appears that the t-storm activity that developed across
the region is diminishing at this hour, thus have only included VCSH
in the 00Z TAF suite for the next few hours, with only a remote (10-
20%) chance that t-storms will directly impact either SE CA
terminal. Chances for SHRA/t-storm activity increase again Wednesday
afternoon/evening, but remain too low (10-20%) to include anything
more than VCSH in the TAFs at this point.

&&

.FIRE WEATHER...
Daily chances for mostly isolated thunderstorms are expected
through Wednesday afternoon areawide with chances increasing
across southeast and south-central Arizona by Wednesday evening.
A weather disturbance along with deep tropical moisture are then
expected to impact much of Arizona as early as Thursday, likely
peaking at some point Friday into Saturday. This will provide
widespread wetting rains and cooler temperatures across the area,
especially across southeast and south-central Arizona. Humidities
will remain fairly elevated through mid week with afternoon
minimum RH values into a 25-30% range, before climbing back upward
later this week as even higher moisture levels return and
temperatures cool off. Impacts from thunderstorm activity will
increase starting Thursday with strong winds, heavy rainfall, and
flooding all possible through the upcoming weekend. Winds through
the majority of the period will remain light, with the exception
of nearby thunderstorms or thunderstorm outflow generating
stronger gusts.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Hodges/Kuhlman
AVIATION...Percha
FIRE WEATHER...Kuhlman



Office: TWC FXUS65 KTWC 162030 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 128 PM MST Tue Aug 16 2022 .SYNOPSIS...Shower and thunderstorm chances will continue. A slight downward trend in storm activity is expected this evening before ramping back up the second half of the week into the weekend. Temperatures will remain near seasonal averages through Wednesday, lowering to nearly 10 degrees below normal this weekend. && .DISCUSSION...A wetter period can be anticipated starting tomorrow through the weekend as a low pressure system with tropical origin impacts the region. This system was centered just south of the Texas Big Bend today and will track farther westward the next few days. Models were in good agreement with this low bringing an influx of deep moisture into the region as it moves closer and becomes somewhat stalled over NW Mexico/NRN Gulf of California this weekend. Needless to say, rain chances and rainfall amounts will be on the increase as early as tomorrow but more so Friday into the weekend. ECMWF was noticeably wetter than the GFS with the ECMWF ensemble QPF derived Extreme Forecast Index (EFI) highlighting Saturday for more widespread heavy rainfall amounts. This scenario would suggest a transition from a localized flash flooding threat to a more longer term flooding concern by early next week, if not sooner. Please refer to the hydrology section in this product for more details. Otherwise, high temperatures will hover below seasonable readings, especially Friday into the weekend. && .AVIATION...Valid through 18/00Z. SCT-BKN clouds 7k-12k ft AGL. ISOLD-SCT SHRA/TSRA developing and persisting thru 17/04Z mainly from Tucson south and westward. With the stronger TSRA, expect cloud decks to lower to 4k-6k ft AGL, wind gusts to 45+ kts, vsby reductions, and mountain obscurations. Outside of any TSRA, SFC wind generally less than 10 kts and favoring a NWLY direction through the early evening hours and variable in direction at other times. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Expect a daily chance of showers and thunderstorms through the upcoming weekend, with increasing precipitation chances late in the week into the weekend. The main threats will be strong gusty winds and heavy rainfall/flash flooding. There is the potential for precipitation outside the normal afternoon/evening cycles. Outside of thunderstorm outflows, wind trends will be light and follow typical diurnal patterns. && .HYDROLOGY...A low pressure system with tropical origin was centered just south of the Texas Big Bend area today. This low will track westward bringing an influx of deep moisture to the region as early as Wednesday but more so this weekend. Latest models showed this low pressure system becoming somewhat stalled south of the International Border over Northwest Mexico/northern Gulf of California through the weekend. As this system moves closer, rain chances and rainfall amounts will be on the increase areawide, peaking late Friday and Saturday. While flash flooding will be a concern, mainstem rivers and larger washes will likely experience significant flows by Monday, if not sooner. The river forecast outlook, based on the latest QPF, indicated a few river systems of concern such as the Gila River upstream from the San Carlos Reservoir. That said, conditions may transition from localized flash flooding to longer term flooding concerns. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson
Office: FGZ FXUS65 KFGZ 162014 AFDFGZ Area Forecast Discussion National Weather Service Flagstaff AZ 114 PM MST Tue Aug 16 2022 .SYNOPSIS...An active monsoon pattern will continue across northern and central Arizona through the upcoming week. Heavy rainfall leading to flash flooding will continue to remain a threat, especially Thursday into the weekend. Cooler temperatures are also expected into this weekend. && .SHORT TERM (through Wednesday Night)...After morning fog lifted across portions of the high country, daytime cumulus began developing. Thunderstorms are now maturing over the White Mountains and Grand Canyon North Rim. Expect storm coverage to increase into the afternoon, but remain less widespread than yesterday's. Plenty of available moisture will allow some storms will drop copious amounts a rain. As a result, flash flooding is possible in vulnerable areas today. .LONG TERM (Thursday through Monday)...A tropical disturbance continues its push westward over northern Mexico. Once the system is over Senora, moisture is advected northward into Arizona beginning on Thursday. By Friday and Saturday, GEFS and ENS ensemble guidance show deep monsoonal moisture over Arizona, with PWAT values approaching 2 inches over the lower deserts and 1-1.5 inches across the high country (nearing the 90th percentile for this time of year). As a result, an active monsoon period is expected to finish out the week. Uncertainty with what areas will see the greatest impacts however remains high at this point in time, as they will largely be dependent upon remnant convection and debris cloud from the day before. Nevertheless, heavy rainfall leading to flash flooding will be a concern across central and northern Arizona, especially in areas more sensitive to heavy rainfall (recent burn scars, slot canyons, and low-water crossings). Heights begin to fall more sharply as the system moves over Arizona on Friday and Saturday. As a result, well below normal temperatures (~8-14 degrees below normal) are expected over much of the region. Temperature begin to rebound for the start of the upcoming week, as the trough (and its associated moisture) move eastward out of the region. While daily shower and thunderstorm chances do look to remain, a slight downward trend in coverage looks plausible as moisture lessens over the region. Ensemble guidance supports this thinking, though it will largely be dependent upon the influence of a weak trough approaching the West Coast on the ridge driving the monsoonal flow. && .AVIATION...For the 00Z TAF package...Primarily VFR conditions with light winds are expected over the next 24 hours, outside of thunderstorms. Much of the showers and thunderstorms will diminish after 00Z Wednesday, with lingering activity remaining east of a KGCN-KFLG line through 06Z. There is a slight chance for patchy morning fog, primarily in the higher terrain, which could result in IFR conditions. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Daily scattered showers and thunderstorms are expected each afternoon through Thursday, especially over the higher terrain. Gusty, erratic winds, and flash flooding will be likely. Friday through Sunday...More widespread shower and thunderstorm activity is expected Friday into the weekend. Flash flooding and gusty winds will remain the primary hazards. Well below normal temperatures are also expected. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...BJ LONG TERM...Humphreys AVIATION...BJ FIRE WEATHER...Humphreys For Northern Arizona weather information visit weather.gov/flagstaff