Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/19/22
Area Forecast Discussion
National Weather Service Phoenix AZ
405 PM MST Sun Sep 18 2022
.UPDATE...
Updated Aviation
&&
.SYNOPSIS...
Dry conditions will continue through Monday under mostly clear
skies. There will be a gradual increase in moisture through midweek
along with a chance of showers and storms beginning Tuesday.
Slightly below normal temperatures are anticipated midweek, followed
by a warming and drying trend into the weekend.
&&
.DISCUSSION...
Latest water vapor imagery reveals a dry southwesterly flow between
a closed low off the northern California coast and a broad
anticyclone across the southern Plains. Meanwhile, latest
mesoanalysis and ACARS soundings indicate PWATs range from roughly
0.5 to 0.7 inches, which is below average for mid-September. The dry
air is also evident at the surface and dewpoints are generally in
the mid 30s to lower 40s. With the relatively dry air promoting
favorable conditions for radiational cooling, temperatures early
this morning dropped as low as mid 60s in the outlying areas near
Phoenix.
After a respite in the Monsoon the past few days, an increase in
moisture will herald a return to the threat of showers and
thunderstorms this week. The moisture is already apparent on
satellite imagery with areas of CU developing across western New
Mexico and southeastern Arizona. Latest HREF indicates the chance of
storms will arrive as early as Monday afternoon, particularly across
eastern Arizona. Although showers are generally not expected in the
Phoenix area, the extended HRRR suggests convection in Pinal and
Gila Counties could produce an outflow boundary capable of producing
blowing dust. This is an outlier though and probabilities generally
remain below 10 percent.
Models remain in good agreement the gradual increase in moisture
will continue Tuesday through Thursday, with PWATs potentially
peaking as high as 2 inches Wednesday night. This is quite anomalous
for this time of year and may approach all-time records per the SPC
sounding climatology. However, it is unlikely this will translate
into widespread, heavy rainfall given the lack of discernible
forcing or PVDs.
In the battle between the aforementioned upper low to the west and
ridge to the east, model consensus indicates the high will
predominate, resulting in somewhat above normal temperatures aloft.
This will yield weak mid-level lapse rates and generally hinder
instability. Nevertheless, latest NBM PoPs suggest most spots will
see at least some rain in the Tuesday-Thursday time frame. But given
abundant moisture, the strongest storms will also be capable of
producing localized flooding.
The cutoff low is expected to open up and eject eastward Wednesday-
Thursday per the latest NCEP cluster analysis. Drier air behind this
system will overspread the intermountain West. However, the threat
of showers and storms will linger through Friday across Arizona.
Latest ECMWF ensemble suggests the increasing insolation may
contribute to higher CAPE. The instability combined with the
residual 20 kt deep layer-shear points to the potential for strong
storms Friday, particularly from Phoenix north and eastward.
Thereafter, a warming and drying trend remains likely for next
weekend.
&&
.AVIATION...Updated 2305Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather issues will exist through Monday evening with only
a modest increase in mid/high cloud decks. W/SW winds should hold
longer into the evening/overnight than recent days. Light east winds
with periods of nearly calm conditions are likely Monday midday, and
the transition to the traditional afternoon west wind may not occur
particularly quickly.
Southeast California/Southwest Arizona including KIPL and KBLH:
Clear skies will persist through the period with trends in winds
nearly identical to the past 24 hours. Uncertainty becomes tied to
magnitude and persistence of wind gusts this evening at KIPL, while
somewhat weaker winds will be preferred at KBLH.
&&
.FIRE WEATHER...
Dry conditions will prevail across the lower deserts through Mon.
Although S Gila Cty will see a decent 30% chance of showers and
storms by Mon evening. Min RH in the low-mid teens today will
improve to the upper teens-20% Mon. Winds will favor familiar
diurnal patterns with overall light speeds, but with periodic
afternoon breezes to around 20 mph through Mon. A decent return of
moisture continues through at least midweek bringing good to
excellent, 40-60%, chances for showers and storms across the eastern
Arizona high terrain by Tue along with at least slight 10-20%
chances for the lower deserts. The lower desert chances improve to
decent 30% chances for Wed-Thu. Max Ts will generally run near to
slightly above seasonal normal through the week and into next
weekend. Min RH will improve to ~30% for S-Cent AZ by Wed and fall
to near 20% for late week and next weekend. Outside of storms, winds
will overall be light and favor normal diurnal slope/valley
patterns, but with somewhat higher afternoon speeds and gusts to
around 20 mph most days through the first half of the week.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Hirsch
AVIATION...18
FIRE WEATHER...Sawtelle/Kuhlman