Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/02/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 501 PM MST Tue Jun 1 2021

.UPDATE...
Updated Aviation discussion.

&&


.SYNOPSIS...
Temperatures will warm through the middle of the week with afternoon
highs in the 102 to 107 degree range along with moderate heat risk
for many places through the rest of the workweek. A persistent weak
upper level low and a slight uptick in moisture will result in a
chance of isolated showers and thunderstorms over the higher Arizona
terrain most afternoons. Showers and storms are most favored to
remain north and east of Phoenix but an isolated shower or
thunderstorm may survive into the lower desert areas near Phoenix.
A cooling trend is possible late in the weekend and early next week
as low pressure increases from the west.

&&

.DISCUSSION...
The upper level RAP mesoscale analysis indicates N to E flow
aloft on the north side of a closed cut-off low circulation over
offshore Baja. A small vort max in NW MX is rotating out in front
of the low. The skies are mostly clear across our region with
northerly flow across the western States in advance of the strong
ridge of high pressure building inland. Theres also some weak
elevated CAPE south of Gila County. METSAT showed mostly clear
skies across the region with convective CU and isolated mostly
light showers/sprinkles and an isolated storm cell on radar
returns forming across N and E and SE AZ. Mid-level WV shows some
slightly elevated moisture across the lower deserts and some
light patchy moisture with the cut-off low near Baja.

Local ACARs soundings evolution showed W flow below 700 mb and NE
flow above that with some elevated moisture near H5 and an above
average PW near 0.65" which is near to slightly increased from
yesterday. Yesterdays high in Phoenix was 101 degrees. The
month of May ended with 11 days of 100 degree plus days which is
very near the normal of 100+ degree days for May in Phx. Today
the warm-up continues with a highs of 102 to 104 in and around
Phoenix and 103 to 106 out west.

The models agree on the Baja cut-off low remaining mostly stationary
through Thu as the ridge maintains strength over the West while only
shifting slightly east also through Thu. As a result there is good
confidence of the elevated heat persisting into Saturday. This will
result in up to moderate heat risk and highs of 103-106 degrees in
Phoenix and the lower deserts, and up to 104-109 out west. Highs are
then expected stay close or just under this range on Sat.

The lingering low pressure system will also make for low-end
shower/storm chances each afternoon and evening through the late
work week. The HREF family and the NMM6Km are still in good
agreement on very isolated, weak high-terrain/Mogollon Rim
showers/storms every afternoon and evening through Fri. These
storms would be high-based storms with dry lightning and gusty
outflow winds with little to no rainfall. The HRW FV3 may once
again be a slightly more bullish outlier favoring slightly better
coverage of storms E and near Phx.

Although the low will be in position to rotate small vort
disturbances across the area for a few days, it is still fairly
weak and unable to attract more pronounced mid level (and BL)
moisture, with the GEFs plume now showing PW spiking near 0.77"
late this week. In addition there are still no IVT moisture plumes
currently depicted in ensembles with this system.

For Sat the Clusters analysis favors the ridge axis to the north
flattening and shifting E with weak zonal troughing near the PAC
NW. There is also flattened lingering high pressure and weak flow
over the Desert SW along with dry conditions being favored.
Tuesday Clusters depict differing positions of a W coast to W US
trough with clusters 3 and 4 showing a slight potential for light
QPF for central and S-Cent AZ likely associated with isolated
showers and storms. There is slightly better confidence however
for lower temperature from Sun and early next week associated with
increasing low pressure from the W.

&&

.AVIATION...Updated at 0000Z.

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

A weak upper low is centered near the Baja Spur. Just upstream is
a high amplitude ridge of high pressure with an axis near the West
Coast. There is just enough moisture and instability to have isolated
thunderstorms over east central AZ late this afternoon. As of this
writing, the nearest storms to metro Phoenix were near Globe and
producing westward moving outflow winds nearing the Gila/Pinal
border. Storms are not expected to survive over the lower deserts
and the outflow is anticipated to weaken substantially as it nears
far southeastern portions of metro Phoenix early this evening.
Confidence in a distinct wind shift at KIWA too low to reflect in
the TAF at this time. Even lower confidence in that occurring at
the other TAF sites. But, it bears watching. Otherwise, anticipate
typical warm season surface winds with upvalley/westerly
directions being favored this evening (occasional gusts 15-20kts)
before transitioning to downvalley/easterly directions (well
after 07Z for PHX). Upvalley/westerly directions resume
midday/early afternoon Wednesday. Anticipate isolated afternoon
storms over the higher terrain on Wednesday though perhaps with
a little less potential for outflows to reach the metro area.
As for sky cover, anticipate some minor amounts of debris cloud
tonight but otherwise, no significant cloudiness.


Southeast California/Southwest Arizona including KIPL and KBLH:

A weak upper low is centered near the Baja Spur. Just upstream is
a high amplitude ridge of high pressure with an axis near the West
Coast. The end result though will be only minor amounts of high
clouds and familiar warm season surface wind patterns with
some afternoon gustiness (20-25kts). For KIPL, there looks to be a
period tonight of south-southwest directions before resuming
southeasterly.


&&

.FIRE WEATHER...
Friday through Tuesday:
Isolated thunderstorms, mainly over the AZ higher terrain, could
drift into portions of Maricopa and Gila Counties, including the
Tonto NF Thursday-Friday. The main threats with any storms, even
distant ones, will be lightning and gusty outflow winds of 25-40
mph. Otherwise, the subtle moisture increase will not do much to
improve RH with afternoon values dropping into the 7-15% range and
overnight recoveries mostly in the 20-35% range. Outside of
outflows, winds will generally be light to occasionally moderate
and follow typical diurnal/terrain influences with afternoon
breeziness.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

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

$$

DISCUSSION...Sawtelle
AVIATION...AJ
FIRE WEATHER...Sawtelle/AD