Area Forecast Discussion Issued by NWS Phoenix, AZ
000
FXUS65 KPSR 191133
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
433 AM MST Tue Mar 19 2024
.UPDATE...Updated 12z Aviation Discussion.
&&
.SYNOPSIS...
Weakening low pressure will once again bring rain chances to parts
of the Desert Southwest this afternoon before the system finally
exits the region by Wednesday. High pressure will then take over
for the remainder of the week, ushering in the return of dry and
tranquil conditions while promoting above-normal temperatures
through at least the start of the weekend. Cooler and more unsettled
conditions are likely to return by the end of this weekend/start of
next week.
&&
.DISCUSSION...
Early morning upper-air analysis reveals the persistent upper-low
continuing to spin over the Desert Southwest, with the center of
circulation now focused over the Imperial Valley. This system`s
westerly retrograde has ceased, and it will again push east as we
go through the day today. With eastern parts of our CWA still
likely to be under the influence of positive vorticity advection,
and with models continuing to favor a decent regional moisture
profile, showers and thunderstorms will once again be a
possibility (20-40%) this afternoon across northern and eastern
Maricopa County and southern Gila County, with greater chances
over high terrain locations just outside of our forecast area. Hi-
res guidance continues to show relatively high SBCAPE values for
these areas (200-400 J/kg) along with 0-6 km shear values between
25-50 kts, resulting in an environment favorable for the
development of multicellular convection, and even a marginal chance
of a supercell. However, due to the weakening trend of the
aforementioned low, the amount of upper-level forcing available will
likely be a limiting factor for how much robust convection occurs.
Nonetheless, isolated showers and thunderstorms capable of producing
gusty winds, and small hail are expected over the previously
mentioned areas. Any additional rainfall will be light (0.01-0.10")
barring any heavier activity which could result in locally higher
totals.
Enhanced atmospheric moisture will not be limited to only high
terrain areas of south-central Arizona. Global models show above-
average moisture levels stretching across the lower desert regions,
which will promote destabilization when combined with abundant
daytime heating this afternoon. Hi-res guidance shows forecasted
SBCAPE values ranging from 100-300 J/kg across southwestern
Arizona and southeastern California, which may allow for a few,
very isolated pop-up showers and thunderstorms, especially for
areas around enhanced terrain features. As for the Phoenix metro,
a similar situation is expected to play out. Instability over the
Valley will be the highest across the region, with SBCAPE values
approaching 500 J/kg, though widespread thunderstorm activity is
unlikely given that the axis of greatest lift will be just off to
the east by the time peak solar heating takes place. However,
given the unstable environment, isolated convective activity
popping over high terrain features such as the Estrella Mtns and
the White Tanks is possible (10-20%) this afternoon. QPF totals
from these showers or storms will be minimal, with most areas
likely seeing less than 0.10".
Temperatures over the next several days will continue their upward
trend as the long-lived low pressure system continues to weaken
before finally moving out of the region by Wednesday. Temperatures
this afternoon across the lower deserts will range between the mid
70s to around 80 degrees, warming to the upper 70s to mid 80s by
Wednesday as high pressure takes over for the remainder of the week.
By Thursday, many locations will likely experience their warmest
temperatures so far this year with NBM MaxT forecasts calling for
widespread afternoon highs in the middle to upper 80s for lower
elevation communities. Although probabilities of reaching 90 degrees
for areas in and around the Imperial Valley have dropped slightly
since yesterday morning, a 20-40% chance of reaching that mark for
the first time this year remains.
The aforementioned high pressure will usher in a much more tranquil
pattern for the rest of this week and at least into the start of
this weekend, but global ensembles depict another potent trough
impacting much of the western CONUS by the end of the weekend which
would likely result in a quick pivot back towards wetter and cooler
conditions across the Desert Southwest. Ensembles are in good
agreement regarding this systems evolution, with only subtle
differences in strength, orientation, and timing, so this will be
something to keep an eye on going forward.
&&
.AVIATION...Updated at 0550Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The main aviation concern through the TAF period will be the
potential for the development of isolated-scattered showers/storms
and gusty winds from any outflows this afternoon and early
evening. Current thinking is that the terminals are safe from any
need for VCSH mention, as chances are too low (<20%). Any robust
convection is likely to remain anchored to the higher terrain
features (e.g. the Estrella`s) in the immediate metro area. Light
and variable winds through the overnight hours should turn
easterly by mid-morning. All sites will then do their typical
diurnal switch to westerly this afternoon. Depending on
shower/thunderstorm activity during the early afternoon hours,
there could be outflows that could enhance the westerly flow prior
to a stronger outflow signal turning winds out of the north
during the early evening hours. With any outflow, particularly if
the convection early this afternoon is robust, gusty winds could
reach the 20-25 kt range for brief periods. FEW-SCT high clouds
are anticipated through the TAF period, with FEW-SCT CU clouds
developing during the afternoon hours with bases aoa 7-8 kft.
Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are expected through the
forecast period. Winds at both terminals will remain light, aob 5
kt, through the TAF period. At KBLH, current northeasterly winds
will become variable later this morning before going westerly
late Tuesday afternoon. At KIPL, current westerly winds will
become northwesterly late Tuesday morning and then go back
westerly Tuesday evening. FEW-SCT high clouds are anticipated
through the TAF period, with FEW CU clouds developing tomorrow
afternoon with bases aoa 8 kft.
&&
.FIRE WEATHER...
Low pressure will continue to promote chances for showers and
storms across the higher terrain areas of the eastern districts,
with very slight chances of an isolated shower or thunderstorm
around enhanced terrain features of the western districts. Winds
outside of any thunderstorm activity will be light with occasional
afternoon breeziness. MinRH values over the next few days will
remain above 20-25% before decreasing later this week as high
pressure sets in. Temperatures will hover right around normal
today before quickly warming to above seasonal normals during the
latter portion of the week.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Smith
AVIATION...Young/Berislavich
FIRE WEATHER...RW