186
FXUS65 KPSR 021721
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1021 AM MST Sun Jun 2 2024

.UPDATE...Updated 18z Aviation Discussion.

&&

.SYNOPSIS...
A stagnant weather pattern will keep hot and dry weather
conditions over the region for most if not all of the upcoming
week. Expect slightly above normal temperatures through Tuesday
before hotter temperatures are likely starting Wednesday. An
Excessive Heat Watch has been issued for Wednesday and Thursday
for much of south-central Arizona with highs potentially reaching
110 degrees across portions of the lower deserts. Temperatures
should then trend back toward seasonal normals next weekend as a
weak weather disturbance passes through the region.

&&

.DISCUSSION...
Current satellite imagery showing clear skies and upper level
objective analysis is virtually unchanged from what we have seen
the last several days. The Desert Southwest remains positioned in
between a progressive wave pattern across the Northwestern U.S.
and Southwest Canada and the sub-tropical high over Mexico. This
will continue to provide dry westerly flow and slightly above
normal temperatures through around Tuesday before the pattern
finally shifts.

As we have mentioned in previous AFDs, the main forecast concern
will be the even hotter temperatures for the latter half of this
week. By Tuesday, guidance shows the sub-tropical ridge building
over the east-central Pacific before quickly moving eastward over
the Southwestern U.S. on Wednesday. At the same time, a weak cut-
off low is expected to develop west of central Baja and this
disturbance should eventually move through our region at some
point Friday into next weekend.

H5 heights are forecast to rise from the current 583-585dm to
around 590dm on Wednesday before peaking at around 592dm over the
eastern half of Arizona on Thursday. These heights would just
reach into the 90th climatological percentile for early June,
while giving a decent boost to temperatures starting Wednesday.
The latest NBM forecast temperatures shows highs over the lower
deserts between 106-110 degrees Wednesday before peaking at
107-112 degrees Thursday. These expected highs would mostly fall a
few degrees short of daily records with the exception of the 111
degrees which is the current record high for Phoenix on Thursday.
According to the NWS HeatRisk, some locations would reach into
Major HeatRisk, especially on Thursday across south-central
Arizona. Given this threat, we have issued an Excessive Heat Watch
for much of south-central Arizona on Wednesday and Thursday. By
Friday, guidance shows the cut-off low starting to move northward
up the Gulf of California which if the timing holds would begin to
bring some slight cooling to our area. If the cut-off low is
slower, excessive heat conditions could extend into Friday.

As the cut-off low starts to approach our area from the south
later this week, some weak moisture advection into our region is
expected to occur. There has also been a notable uptrend in
potential moisture over the past several model runs, but it is
still of fairly low confidence due to considerable differences
among ensemble members. The GEFS is the most bullish on the
moisture with PWATs increasing to 175% of normal by Saturday, but
even these anomalous PWAT values would still only represent
fairly limited moisture given this is our driest time of year. NBM
PoPs have likely yet to reflect this increase in moisture as the
lower deserts are still at 5% or less while the high terrain is
upwards of 10-15% for Friday and Saturday. Given the time of year,
getting decent rain chances is extremely unlikely, but it is
definitely something that will be monitored over the next several
days.

&&

.AVIATION...Updated at 1720Z.

South-Central Arizona including KPHX, KIWA, KSDL, KDVT; and
Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation concerns are expected during the TAF period. Winds
over metro Phoenix sites will follow diurnal trends with moments
and variability during directional shifts and occasional afternoon
gusts near 20 kts. Familiar late afternoon/evening breeziness is
likely (>90%) at IPL with gusts 20-25 kts, with daytime gusts near
20 kts expected at BLH. A FEW high clouds will filter in over the
region during the forecast window, but skies will be mostly clear
otherwise.

&&

.FIRE WEATHER...
Little to no change in the weather pattern will keep seasonably
dry and hot conditions in place over the next few days. Expect
lower desert highs between 100 and 105 degrees, or 3-5 degrees
above average each day. MinRH values will continue to run between
5-10% across the majority of the area each day, while overnight
recoveries will continue to range from poor to fair at around
25-40% over the eastern districts to 35-50% over the western
districts. Winds will remain fairly light following diurnal
tendencies with periodic afternoon gusts of 15-20 mph. The latter
half of the week will see even hotter temperatures with potential
for highs around 110 degrees Wednesday through Friday over
portions of the lower deserts. There will also eventually be a
slight improvement in humidities by next weekend along with a low
end chance of some isolated thunderstorms over the Arizona higher
terrain.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Watch from Wednesday morning through Thursday
     evening for AZZ534-537>546-548>555-559>562.

CA...None.
&&

$$

DISCUSSION...Kuhlman
AVIATION...RW
FIRE WEATHER...Kuhlman/Lojero