Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/01/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 513 PM MST Mon May 31 2021

.UPDATE...
Updated Aviation discussion.

&&


.SYNOPSIS...
Seasonably dry and warm conditions will persist under mostly clear
skies through tomorrow. High temperatures will warm slightly by the
middle of the week but a persistent weak upper level low and a
slight uptick in cloud cover and moisture may be enough for isolated
showers and thunderstorms in Arizona most afternoons. Showers and
storms are most favored over the higher terrain north and east of
Phoenix but an isolated shower or thunderstorm can not be entirely
ruled out for the Phoenix area the second half of the week.

&&

.DISCUSSION...
Today`s upper level analysis shows a high-amplitude wave pattern
with a strong high pressure ridge axis over the PAC NW into W Canada
and a large, weak longwave trough from offshore Baja to the 4-
Corners and S/central Rockies. UL RAP analysis also shows an H5 low
pressure circulation beginning to develop into a cut-off low near-S
of Phoenix with upstream N flow across the Intermountain W on the
E flank of the ridge.

METSAT showed clear skies across the region with convective CU and
isolated mostly light showers/sprinkles radar returns forming across
N and E AZ. Mid level WV imagery showing slightly elevated moisture
in those same areas. Various UL vort max anomalies were also noted N
and S of the area. Local ACARs soundings evolution showed several
degrees of cooling aloft from 650 mb and upwards, with midday PW
increased from ~0.35" yesterday to almost 0.70" today.

On this sunny Memorial day expect yesterday`s near normal trend to
continue today with highs topping out in Phoenix and the lower
deserts at 99-101 degrees, and a couple of degrees warmer out west.

Models now agree on the upper low cutting off and retrograding
towards the SW over Central Baja by tomorrow as the strong high
pressure ridge shifts east and builds over the W US States to create
somewhat of a rex block pattern. The cut-off low is expected to
remain mostly stationary through Thu as the ridge maintains strength
over the West US while only shifting slightly east also through
Thu. As a result there is good confidence of a warming through Wed
with moderate heat risk and highs of 103-105 degrees in Phoenix
and the lower deserts, and 104-108 out west. Highs are then
expected stay close to this range through Sat.

The lingering low pressure system will also make for low-end
shower/storm chances each afternoon and evening for much of the
week. The HREF family and the NMM6Km are in good agreement on very
isolated, weak high-terrain/Mogollon Rim showers/storms today-
tomorrow, afternoon-evening. These would be high-based storms
with dry lightning and gusty outflow wind potential with little
to no rainfall. 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 showing PW spiking near
0.85" late this week. In addition there are no IVT moisture plumes
currently depicted in ensembles with this system.

The Clusters analysis for Thu favor the stationary closed low over
Central Baja with the massive ridge still parked over the W US. For
Friday they favor a flattening  ridge to the N and the ridge axis
shifting into the NE Plains with flattened lingering high pressure
and weak flow over the Desert SW. For QPF a minority of clusters
still favor very isolated showers/storms including the lower
deserts. This is where the NBM picks up on an uptick on POPs for
Thu evening and night from less than 10% to near 15% through very
early Fri morning.

However the much more likely and bullish solution favored by the
Clusters is dry conditions associated with the strong mid-late
week high pressure building and the maintenance to near 104
degree high temps through Saturday and a few degrees warmer out
west.

&&

.AVIATION...Updated at 0013Z.

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

A weak upper trough over the Desert Southwest and far northwest
Mexico is aiding the development of isolated thunderstorms over
the higher terrain of Arizona. Storms currently over southeast
Yavapai and northwest Gila Counties are slowly drifting toward
metro Phoenix. However, they are expected to dissipate before
reaching the Valley floor. But, some modest outflow from those
storms may enter northern and eastern portions of the metro area.
For the TAF sites, KDVT would most likely be affected - if at all.
Otherwise, surface winds will follow familiar warm season diurnal
patterns with relatively long lived upvalley/westerly winds this
evening before trending to downvalley/easterly directions.
Anticipate redevelopment of upvalley/westerly flow by midday.
There will be isolated thunderstorms over the higher terrain
Tuesday afternoon. At this time, it is anticipated that there will
be more storm coverage over southern Gila County which could make
for a little better potential for outflow winds reaching the
Valley floor in the evening. Skies will be mostly clear except for
minor amounts of debris cloudiness this evening AOA FL120 followed
by distant storm development over the mountains Tuesday
afternoon.


Southeast California/Southwest Arizona including KIPL and KBLH:

There is a weak upper trough over the Desert Southwest and far
northwest Mexico. But, skies will be clear except for minor
amounts of mid and high clouds. Surface winds will favor
southeasterly at KIPL through the day Tuesday with little to no
downvalley/westerly winds tonight. Southerly winds will be favored
at KBLH through Tuesday with afternoon and early evening gustiness
(20-25kts).

&&

.FIRE WEATHER...
Thursday through Monday:
Expect max temps to remain slightly above normal through Saturday.
A gradual increase in moisture is likely to bring some isolated
thunderstorms mainly over the AZ high terrain, with lower desert
storms not entirely out of the question, though much less likely.
However, wetting rains are not anticipated, so these isolated
storms may pose a dry lightning threat. Min RH values will remain
quite low, mostly staying between 7-12% each day. Daily max RHs
will mostly range from 20-30% with higher readings across the
western deserts. Winds will remain light to moderate through the
bulk of the period, but with typical afternoon breeziness most
days. Outflow winds, even from distant thunderstorms, cannot be
ruled out for any particular day either.

&&

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

&&

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

$$

DISCUSSION...Sawtelle
AVIATION...Hodges/Benedict
FIRE WEATHER...Sawtelle/Hodges