Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/03/22

Area Forecast Discussion

National Weather Service Phoenix AZ

 500 PM MST Sun Oct 2 2022

.UPDATE...0z Aviation Discussion Below...

&&

.SYNOPSIS...
Shower and thunderstorm chances for Phoenix and parts of the lower
deserts could spike very early in the workweek and possibly again
very late in the workweek and next weekend. Otherwise mostly modest
storm chances will often favor higher terrain areas of south-central
and southwest Arizona today and well into the week. High temperatures
will remain slightly above normal, even with a minor cooling
trend during the latter part of the workweek.

&&

.DISCUSSION...
Today`s overall pattern hasn`t changed a great deal since yesterday
and remains largely non-progressive. A small cutoff UL low had
shifted into NE Sonora with satellite showing a good portion of its
clouds and moisture field shearing off further to the NE into S-SW
NM. The center of a much larger closed low to the N had moved NE
into cent MT with a fairly stationary rear flank axis extending
through cent CA. The large low remains flanked to the N, NW and W by
a high amplitude ridge and another UL ridge to its SE across TX and
the Central Plains forming a kind of rex block.

This puts the area under a neutral col pattern at H5. Local ACARS
soundings depicted somewhat moist ESE flow from near H6 down, and
drier-neutral W component flow from ~H5 up. Anomalously moist PWs
remain near or just off a temporal max of ~1.20-1.30" around
Phoenix, and >1.50" for SW AZ. The local morning soundings and
mesoscale analysis also indicated a moistened BL compared to
yesterday but a bit drier compared to earlier this morning. Dry
upper-mid levels were also seen.

Overall the column was more unstable than yesterday with late
morning SB/MUCAPE > 2,670 j/kg, and there was less MLCIN at -283
j/kg and a series of mid and upper level subsidence caps. GOES IR
METSAT also showed mostly clear skies with mean W ranging from 10
gm/kg around Phoenix to > 12 gm/kg for SW AZ-SE CA. Radar revealed
isolated thunderstorms popping across NW-Cent AZ ahead of a vort
max on the rear flank trough axis of the northern UL low.

Due to the waning proximity/influence of the Sonoran low, and the
increasing influence of the rear flank of the northern low, models
are in good agreement on a mix of changing parameters. A 5-day
drying trend through the BL, sfc and column is barely underway with
PWs just barely off their maxes. Ensembles, the HREF/family and
UAWRF-GFS also depict widely isolated, generally short-lived
storms/showers developing across the region today, similar to
yesterday, which seems likely.

These isolated cells will be capable of producing localized,
fleeting gusty outflows, some dust and brief, mainly light to
moderate showers. Most areas will not be impacted by this hit-and
mostly miss-activity with only slight 10-15% chance of showers and
storms for Phoenix, the lower and SW AZ to SE CA deserts. Highs will
not change much and will top out in the mid-upper 90s around Phoenix
and out west today. Then with a forecast short-term increase in
H5 heights through tonight, a degree warmer for highs tomorrow.

From tonight/tomorrow and the first part of the week models agree on
slowly shifting the N low pressure system slowly E into the N-Cent
Plains and building strong high pressure across the W and NW CONUS
by Tue. At the same time at least one or more short wave vort
disturbances with cold air dive off the rear flank of the main low
and rotate through N to E AZ tomorrow. Along with the associated
forecast falls in H5 heights and temps, this will produce modest to
moderate spikes in instability and forcing and will likely trigger
occasionally scattered convective storm activity across N, E and
even S-cent and SW AZ/SE CA Mon afternoon and evening.

In fact, the HREF & family members and UAWRF-GFS have now latched
onto this and are now fairly bullish on showers and thunderstorms
descending off the the N-Cent AZ high terrain into Phoenix, the
lower deserts and SW deserts by late tomorrow afternoon along with
two very pronounced N component outflows--one for Phoenix and the
whole E half of the CWA, and one for the entire W half of the CWA
for Mon afternoon to evening.

As a result Phoenix will enjoy a spike in Mon PM POPs to near
~20-25% during that time with a 30-~40% chance of max windspeeds
of 35 mph stretching from east to west across the entire N-Cent
CWA, including SW AZ and SE CA. The preferred WPC-NBM bias-
corrected QPF is little to none across the CWA.

As for the E AZ high terrain, more decent 30% storm chances start
Mon followed by 20% chances for the midweek and late week
periods. By midweek storm chances fall to less than 10% for
Phoenix and the lower deserts due to the forecast drying trend.
Highs will nudge down a couple of degrees in the mid 90s going
into the late week but will still manage to remain slightly above
normal.

For late week and next weekend ensembles and Clusters now favor
strong high pressure to the N-NW and anomalous low pressure
developing near cent Baja/GOC and the associated moist SE BL/sfc-
mid level flow. This could maintain slight rain chances for the
lower deserts and high terrain, although with plenty of model
spread and forecast uncertainty.

&&

.AVIATION...Updated 0Z.

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

Light and at times variable winds will continue through the
evening. PHX will likely veer around from SW to N, then E over the
next several hours. Overnight through the morning, light easterly
flow should prevail at most sites. The switch to westerly may not
occur tomorrow at Sky Harbor, with a period of southerlies
indicated at IWA/SDL/DVT. We are monitoring a quick-hitting upper
air disturbance which will arrive late tomorrow afternoon,
coinciding with peak heating. Chances for showers and
thunderstorms are around 20-30% at this time around the metro
after 22Z. Currently, this is noted with an increase in wind gust
potential and VCSH in the TAF package. Subsequent TAF packages
may require TS mention for tomorrow evening. Ceilings remain well
above thresholds through at least 03/22Z.

Southeast California/Southwest Arizona including KIPL and KBLH:

Winds at KIPL will generally favor the SE, while winds at KBLH
favor the S. Expect wind speeds to remain light, mostly aob 8 kts.
Any anvil debris will scour out tonight at BLH. Tomorrow will
feature an increase in clouds by afternoon with 20-30% chances for
storms, highest risk at BLH, after 22z. Wind gusts over 40 mph
cannot be ruled out in the vicinity of showers and storms.
Currently, this is noted with an increase in wind gust
potential and VCSH in the TAF package. Subsequent TAF packages
may require TS mention for tomorrow evening.

&&

.FIRE WEATHER...
Shower and thunderstorm chances this week will be primarily
limited to the higher terrain areas of south-central Arizona.
However, portions of the lower deserts will have the potential
for isolated thunderstorms today and Monday (best coverage Monday).
High temperatures will remain two to four degrees above average
through Wednesday followed by a modest cooling trend brings
readings very close to average for Friday and Saturday. MinRH
will range from 25-35% across the forecast area today before
decreasing by Wednesday to 15-20% lower elevations and 20-30%
higher terrain of south-central AZ. Anticipate a 3-8% increase by
Saturday. MaxRH will also trend downward through midweek (most
noticeably over southeast CA) but with relatively good overnight
recovery (lowest values of 30-35% over eastern Riverside County).
Apart from thunderstorms, winds will be light and favor terrain
driven diurnal patterns through Wednesday. The latter half of the
week, winds will favor easterly directions along with some
breeziness at times (most noticeably over south-central AZ).

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Sawtelle
AVIATION...Heil
FIRE WEATHER...AJ