Severe Thunderstorm Warning 56, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
Issued by National Weather Service Tucson AZ
1047 AM MST Wed Aug 10 2022

.UPDATE...
Updated 18z Aviation section.

&&

.SYNOPSIS...
Elevated chances for showers and thunderstorms will continue the
rest of the week and into next week, with slightly higher
potential Friday through Sunday. Occasionally heavy rainfall,
localized flash flooding, gusty winds and localized blowing dust
will be possible. High temperatures will remain below to near
normal through the forecast period.

&&

.DISCUSSION...
Another August night with nocturnal convection is upon us. A
close study of GOES-18 imagery of the middle and upper water vapor
channels reveals a pronounced circulation passing near Nogales
this morning. It emanated from the mid level shear axis/frontal
boundary in place draped across southern New Mexico/Texas and on
up toward the Ohio River Valley. This westward traveling wave is
encountering pockets of conditionally unstable parcels (per SPC OA
and verified with PHX ACARS sounding data) near the 700 mb layer
with around 500 J/kg of energy. Various 00Z CAMs have latched on
to this and generate some continued but decreasing convection
into Maricopa/Pinal Counties through 12Z, though intensity is not
very high in-line with CAPE values. Shear is also marginal at
best (10-15 kt). Given trends and less than favorable environment,
will cancel FA.A at this time. While some heavy rain is still
possible, the potential (10%) does not remain high enough to
warrant the watch.

At the synoptic scale, we still have the mid level high anchored
well to our northeast, near Cheyenne, WY, and a well defined mid-
level low off the northern California coast. A 700 mb front
extends in a large arc from MI-TX-UT. The Desert SW is caught in
the warm/moist sector ahead of the CA low and on the southern
periphery of the high, where a plume of anomalously high PWAT
values extend all the way into Washington. Over the next few days,
the low will lift toward Vancouver and weaken while the high
drifts to the southeast. This will essentially result in little
day-to-day change for our forecast area through Friday. Deep ESE
flow will remain entrenched with continued MCVs and other
perturbations shearing off the mid-level front drifting westward
and across our forecast area in a high moisture environment with
modest instability. Thus rain chances will remain elevated. Latest
HREF data do suggest a strong signal for outflow winds across
Pinal County this afternoon (70% chance of 30+ kt) but sporadic
elsewhere. Something else to watch for the following days will be
if any substantial PV anomalies develop and drift just off the
northern Baja coast by the end of the week.

Toward the weekend, as the larger systems reposition, there are
indications that the meridional flow within the moisture plume
will increase. Should any PV anomalies be sitting off the US/MEX
coast near San Diego, they would be apt to be ingested by this
enhanced flow and carried northward, enhancing the convective
potential across our western CWA this weekend and possible
lingering into early next week. While the bulk of EPS data support
a more typical albeit wet monsoon pattern, the EPS EFI continues
to suggest that there is a low end potential (5%) for significant
rains across our western CWA during this period. Meanwhile, as the
high shifts southeast this will push the mid-level front further
into NM and AZ, increasing shear and potentially enhancing
mountain convection that spills into lower elevations.
Uncalibrated EPS data show a broad area of 20-30% probability for
1/2"+ rain across our Arizona zones Sat/Sun though calibrated and
fuller NBM data bring that down a bit (10-20%). Regardless, there
is the potential for convection to be a bit more active and
focused perhaps as early as Friday and continuing through the
weekend.

Temperatures will continue to run near or below normal through the
forecast period, highly dependent of course on convective activity
and remnant cloud cover. Yesterday is a good example where cloud
cover earlier in the day helped keep KPHX somewhat cool with a
high of 98F which was below the NBM 25th percentile forecast.
Temperature uncertainty increases the next several days and will
be highest Sunday, decreasing slightly thereafter. HeatRisk will
likely continue in the Low category across our AZ zones with
Moderate into SE CA.

&&

.AVIATION...Updated 1747Z.

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

Main aviation weather concern will be the potential for
thunderstorm activity and associated outflow winds to affect the
terminals later this evening. In the meantime, conditions will
remain tranquil through the late afternoon with east to southeast
winds predominating through most of the morning hours followed by
a westerly shift by the late morning into the early afternoon
hours. Speeds will generally remain aob 10 kts. Thereafter, will
be monitoring the potential for thunderstorm activity and
associated outflows, mostly predominating from the east-southeast,
affecting the area terminals between 02-04Z. However models are
also showing an outflow from the north that could briefly impact
terminals on the northern edge of the Phoenix metro around 01Z.
At this time, there is a 50% probability of winds exceeding 30
kts with any surging outflows.

Southeast California/Southwest Arizona including KIPL and KBLH:

KIPL: Southeasterly winds aob 10 kts will predominate. An isolated
afternoon thunderstorm cannot be ruled out in the vicinity,
however, confidence is too low at this time to mention in TAF
package.

KBLH: Mostly southerly winds aob 10 kts will prevail through the
period. A round of thunderstorms originating from La Paz County
may affect the terminal this afternoon and perhaps again in the
early evening.

&&

.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...None.
CA...None.
&&

DISCUSSION...Iniguez
AVIATION...Lojero/Hardin
FIRE WEATHER...Iniguez