Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/10/22

Area Forecast Discussion

National Weather Service Phoenix AZ

 529 PM MST Tue Aug 9 2022

.UPDATE...
Updated Aviation section.

&&

.SYNOPSIS...
Elevated chances for showers and thunderstorms will continue the
rest of the week and into early next week. Occasionally heavy
rainfall, localized flash flooding, gusty winds and localized
blowing dust remain likely through early next week. High
temperatures will remain below to near normal through the forecast
period.

&&

.DISCUSSION...
The midlevel Monsoon ridge remains optimally located near the S-Cent
Rockies with moist E undercutting flow through the mid-upper
levels aloft. WV imagery reveals a very moist airmass across the
region with a number of E waves/inverted troughs pushing W and NW
into/through various parts of the region including N, E and S-SE
AZ, SE CA/La Paz Cty, where GOES imagery and radar also indicated
an area of scattered showers and storms, with localized flash
flooding occurring this afternoon, including I-10 E and W of
Blythe.

Early afternoon radar also showed widely isolated to
scattered distant thunderstorms across the high terrain of N, E
and S-SE AZ. Both the E AZ/W NM and S-SE AZ storms were
associated with additional, possibly linked E wave(S) advancing
from those areas. The latest ACARS soundings showed an
anomalously moist airmass with PW maintaining near 1.7->1.9" while
mesoscale analysis indicated PW of 1.5->2" and Mean W of 10->14
g/kg across SW-W and S-Cent AZ and into SE CA. MU and SB CAPE had
also increased to >1.7-1.8K j/kg around Phoenix and >2k j/kg
across the W deserts.

In a seemingly virtual repeat of yesterday, HREF members still favor
pronounced convection with locally heavy rainfall developing this
afternoon across S Gila Cty and near Globe and burn scar areas
before descending into the lower deserts and parts of the Phoenix
Metro during the evening hours. With the regional Flood Watch now
underway through late tonight, and with the WPC Day 1 ERO
indicating the large "Slight Risk" area, any convection that
develops will have sound potential to produce locally heavy
rainfall as well as localized flash flooding.

Also like yesterday the HRRR has once again become an outlier and
has again backed off on that scenario by both delaying and
weakening the convection coming off of the high terrain this
evening. This is the result of a festering MCV, light showers and
cloudy/mostly cloudy conditions that significantly delayed surface
heating this morning across most of the Phoenix Metro. This
supported elevated levels of CIN well into the day around Phoenix.

However the 12Z HREF ensemble still indicated a gusty SE outflow
this evening pushing into the Phoenix metro and N Pinal as well as
colliding outflow signals late tonight W-SW of Phoenix. The
potential for patchy blowing dust moving NW remains possible,
although remains most likely for N Pinal Cty and the SE-E Phx
Metro Valley where there is a 10-30% chance of max sustained storm
outflow wind speeds of >35 mph this evening.

Also like a repeat of yesterday`s progs, tomorrow the HREF and
ensembles are in agreement on an increase in storm chances and
coverage from E to W across the region with POPs increasing to near
50% for Phoenix and the lower deserts and the E AZ high country, and
20-30% for SW AZ and SE CA.  Some HREF members start with some
shower activity W of Phoenix in the Wed morning hours moving in from
in S-SE AZ. However the main convection will likely start in E-SE AZ
associated with the next E wave(S) and will push into the Phoenix
Metro and the lower deserts Wed evening.

For Wed evening the HREF indicates an even better 30->50% chance
of max sustained storm outflow wind speeds of >35 mph from both
the S-SE and E and locally dense blowing dust. Also indicated is a
>10% chance of sustained max outflow winds >57 mph along the
infamous I-10 dust corridor just south or the CWA (or S of Eloy
AZ near Picacho Peak). This would likely be followed by locally
heavy rainfall and additional localized flash flooding in the high
country and the lower deserts.

Looking more broadly for the rest of the week and into the
weekend, major weather features include the mid level anticyclone
centered near Four Corners and a rather deep upper level low off
the northern CA coast. The low is expected to lift north,
amplifying the anticyclone and shifting the center a little
further north and east through the week. This will enhance the
undercutting easterly flow across Southwest. EPS/GEFS/CMC resolve
this, with H5 heights anomalously higher over the Pacific
Northwest, indicating an even broader easterly flow is likely by
this weekend. Until then, PoPs remain elevated with continued
chances of showers and thunderstorms each day across the entire
CWA.

Several EPS and GEFS members latch onto a significant wave moving
through the Southwest around Saturday (give or take a day for
uncertainty). The EPS-based EFI QPF data has an interesting
signal in that the majority of members are not forecasting
climatologically high rainfall, but there are a small minority of
members that are predicting QPF outside the model climate for
August. This aligns with an axis of enhanced instability and
moisture emanating north out of the Gulf of California and arcing
NNE into southern Idaho. Digging a little deeper through cluster
analysis of the global ensembles, the details of this will really
depend on the evolution of the upper level low to our northwest. A
deeper solution (favored by 1/3 EPS and 1/2 CMC but just one GEFS
members) would increase wind fields and moisture flux resulting
in greater precip potential. Even the NBM is indicating non-zero
chances for 24-hr QPF of 1"+.

Given the increased cloudiness and moisture through the forecast
period, high temperatures will likely (~80%) remain below daily
normals. Temperature variability is quiet high, especially around
the weekend with the potential influx of even higher moisture and
clouds (NBM IQR for Sunday`s high temperature is 96-105F).
HeatRisk levels will remain in the Moderate category across SE CA
through the week with Low expected across most of Arizona - thus
some heat impacts are possible especially for those with greater
exposure or those exerting themselves outdoors. With many schools
going back in session, it`s worth reminding kids (and
teachers/faculty) to pace themselves and hydrate appropriately.

&&

.AVIATION...Updated 0029Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Storms to the north, east, and south of the Phoenix over
southeast and eastern AZ have been isolated with newer development
over southwest Maricopa County. Outflow that had been approaching
from Pima County has weakened. Given the lack of more robust
activity, and convective inhibition evident in aircraft sounding
data, have removed the mention of VCTS from the TAFs. However,
storms over southwest/west Maricopa County could produce outflow
that potentially reach the the TAF sites. As has been seen a
number of times this Monsoon season, late night shower and
thunderstorm activity will be possible, but would expect it to be
weaker than last night and more isolated (if it happens at all).
Apart from outflows, light west and northwest winds will prevail
before trending toward light easterly late tonight. As for sky
cover, expect increasing mid and high clouds as the night
progresses followed by thinning during the day Wednesday.


Southeast California/Southwest Arizona including KIPL and KBLH:

KIPL: Thunderstorms are ongoing in the vicinity of KIPL with gusts
of 30-35 kts and blowing dust dropping visibility below 6SM.
Anticipate erratic winds and at least one downpour reducing vis to
between 2SM - 4SM along with ceilings to between FL070-090.
Anticipate significant decline in storm activity to begin by 02Z.
Winds will become lighter as well with variable directions before
southeasterly resumes overnight. There is potential for another
round of activity tomorrow afternoon.

KBLH: Earlier storm activity has likely helped stabilize things
over/near KBLH to preclude new storm development the rest of the
afternoon and evening. A round of late night/morning showers is
possible but confidence of those occurring at the airfield too
low to reflect in the TAF. Anticipate light and variable winds to
become southerly overnight and continue through the day Wednesday.
As for sky cover, anticipate variable amounts of mid and high
clouds with bases AOA FL120.


&&

.FIRE WEATHER...
A humid airmass will remain in place through the forecast period,
yielding elevated afternoon RH values and good overnight recovery.
Chances for wetting rains will continue for most areas almost
daily. Winds for the most part will remain light, with the
exception of thunderstorm outflows generating stronger gusts. The
fire danger threat is expected to remain low for the foreseeable
future.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch until 2 AM MST Wednesday for AZZ530>544-546-548>551-
     553>555-559.

     Flood Watch until midnight MST tonight for AZZ545-547-552-
     556>558-560>563.

CA...Flood Watch until 2 AM PDT Wednesday for CAZ560>570.

&&

$$

DISCUSSION...Sawtelle/Iniguez
AVIATION...AJ
FIRE WEATHER...Iniguez