Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/31/23
Area Forecast Discussion
National Weather Service Phoenix AZ
525 PM MST Wed Aug 30 2023
.UPDATE...Updated 00z Aviation Discussion.
&&
.SYNOPSIS...
Shower and thunderstorm potential will increase Thursday and Friday, with
additional activity Saturday before drying out. During this active
period strong to severe wind gusts, blowing dust, heavy rain and flash flooding
will be possible. Cooler conditions are also anticipated with the increase
in storms, followed by a gradual warming trend early next week.
&&
.DISCUSSION...
Latest water vapor imagery reveals drier than normal conditions
on the eastern flank of the anticyclone, which is centered across
northeastern Arizona. Meanwhile, further south, deeper tropical
moisture resides within a broad area of low pressure across the
Baja Peninsula. Latest ACARS sounding reveals a well-defined
subsidence inversion around 500 mb, where temperatures are sitting
around -5 degrees C.
Southeasterly flow has transported richer low-level moisture from
the Gulf of California to Yuma and the Imperial Valley. Dewpoints
reached as high as the lower 80s this morning, and the anomalous
humidity is resulting in heat indices as high as 115-125 degrees.
Further east across the Phoenix area, temperatures only bottomed
out at 93 degrees this morning, which will set a new record warm
minimum for the day. This is the 35th day this year with lows of
90 or above, which has already surpassed the previous record of 28
days set in 2020. Meanwhile, temperatures in the Valley have been
slow to rise this afternoon, likely owing to mixing ratios of 11
g/kg that extend up to 850 mb. Nevertheless, there is roughly a 50
percent chance of at least tying the record high of 113 degrees
at KPHX set in 2011. The Excessive Heat Warning remains in effect
this afternoon for the lower deserts but will be allowed to expire
this evening.
The warm ridge across Arizona will result in weak mid-level lapse
rates which will generally inhibit organized convection this
afternoon. Isolated activity will mainly be relegated to the
higher terrain east of Phoenix before drifting into Pinal County
this afternoon. An outflow boundary from this activity could
trigger an isolated cell across Maricopa County this evening,
though HREF probabilities remain less than 10 percent.
Conditions will become considerably more favorable for convection
Thursday afternoon as the ridge drifts eastward into New Mexico,
resulting in a weak southeasterly steering flow. Latest HREF
supports at least scattered activity with general propagation
towards the deeper moisture and into the lower deserts. Subsequent
outflow boundaries from the initial activity will trigger
additional moisture convergence and storm development across
central Arizona. Overall, this setup appears to be one of the more
favorable ones we have seen all Monsoon. HREF indicates a 70
percent chance of strong wind gusts across a large portion of
central Arizona and this will translate into higher than normal
chances of blowing dust. The strongest cells will also be capable
of producing frequent lightning, heavy rain and localized flash
flooding.
Shower and thunderstorm activity will continue to some degree
Thursday night and possibly into Friday morning as a PVD
associated with the aforementioned low pressure system lifts
northward through Sonora. There is quite a bit more uncertainty in
the CAMs Friday. However, at least conceptually, it could be
quite active as deeper moisture and forcing for ascent is pulled
northward through Arizona ahead of an anomalous upper low across
northern California. This is reflected in the latest NBM PoPs,
which have jumped to nearly 70 percent across Central Arizona
Friday. There is good agreement in the ECMWF ensembles PWATs will
approach 2 inches across the lower deserts Friday. With PWATs this
high, flash flooding will be a concern, particularly in a
corridor stretching from Tucson through Phoenix and towards
northwestern Arizona. ECMWF ensemble QPF even points to the
potential for a quick 1-2 inches of rain with the more intense
cells.
&&
.PREVIOUS DISCUSSION...
Heading into the weekend, another day of afternoon showers and
thunderstorms, favoring higher terrain areas is expected on
Saturday before drier conditions develop, as the California low
becomes transitory and ushers drier air into the region. With the
cloudier skies and rainfall Friday and negative height anomalies
traversing over the region this weekend into early next week,
below normal temperatures are in the forecast for several days.
This will feel like a breath of fresh air after the current heat
episode.
Taking a peak at the far extended forecast, ensembles are trending
towards ridging building into the region from the east, likely
north of 590 dam heights into southcentral AZ by Wednesday, Thus,
a warming trend is seen in the latest NBM forecast, with chances
for seeing at least one more day of 110 degree highs in the
Phoenix area around 30-40%.
&&
.AVIATION...Updated at 0025Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Generally diurnal wind patterns, with the exception of a weak
outflow primarily out of the easterly direction that may either
result in the early onset of the easterly wind shift or cause
winds to become variable for a period until well into the
overnight hours tonight. Easterly winds into tomorrow morning
will become westerly again mid to late morning, with some
gustiness to 20 kts. VCTS conditions are expected to develop
tomorrow afternoon, generally 23z or later. At this point,
anticipating winds shifting out of the southerly to southeasterly
direction to be gusty with 50-70% chances of gusts in excess of 30
kts going into tomorrow evening. Visibility reductions due to
blowing dust are anticipated to accompany these gustier winds.
Chances of TS conditions developing tomorrow evening are around
30-40%.
Southeast California/Southwest Arizona including KIPL and KBLH:
Southeast/southerly winds are expected to continue at KIPL and
KBLH through Thursday though there may be a few hours this evening
at KIPL with some variability. Gustiness at KBLH will weaken in
the late afternoon. Some gustiness resumes at KIPL tomorrow
morning. Otherwise, little cloudiness except for some cirrus
through tonight. There is potential for some debris showers to
brush the TAF sites after 15Z Thursday but potential too low to
reflect in the TAFs. Gusty southerly winds are expected to develop
mid-morning at both TAF`s and persist into the afternoon hours.
&&
.FIRE WEATHER...
A steady increase in humidity will translate into a cooling trend
and above normal normal chances of wetting rains Thursday and
Friday, particularly from Maricopa County eastward. Any storms
that develop will be capable of producing frequent lightning along
with strong and erratic wind gusts and localized flash
flooding. Below normal temperatures are anticipated in the wake
of this activity, followed by a warming and drying trend early
next week.
&&
.CLIMATE...
Phoenix Daily Temperature Records (Year last set)
High Low (warmest)
--------- -------------
8/30 113 (2011) 91 (2007)
Yuma Daily Temperature Records (Year last set)
High Low (warmest)
--------- -------------
8/30 114 (1998) 90 (1998)
El Centro Daily Temperature Records (Year last set)
High Low (warmest)
--------- -------------
8/30 116 (1984) 95 (2007)
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST this evening for
AZZ530>555-559.
CA...Excessive Heat Warning until 8 PM PDT this evening for
CAZ562>570.
&&
$$
DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Benedict
AVIATION...Young/AJ
FIRE WEATHER...Hirsch
CLIMATE...Salerno