Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 032033
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
132 PM MST Wed Jun 3 2020

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.SYNOPSIS...
Expect hot temperatures through tomorrow as strong high pressure
remains over the region. A low pressure system will move through the
region Friday, causing winds to increase and temperatures to begin
cooling. Winds will decrease by Saturday as temperatures drop to
below normal values and remain as such into early next week.

&&

.DISCUSSION...

The overall synoptic pattern will remain fairly stagnant the rest of
today and into Thursday, with a warm southerly flow over the
forecast area, promoting increasing height/thickness values. H7
temperatures per the HREF mean will climb from around 12C this past
Tuesday afternoon to 14C Thursday afternoon. This is expected to
result in widespread lower desert highs near/just above 110F this
afternoon and again on Thursday afternoon. While afternoon record
high temperatures seem mostly out of reach, record warm lows remain
possible through Friday morning. NBM- based probabilities for
reaching/exceeding HeatRisk "High" levels remain near 70 percent for
Wednesday and Thursday. The Excessive Heat Warning will remain in
place through Thursday.

A jet streak diving southeastward out of the Gulf of Alaska will
finally dislodge the cut-off low from its current position,
ejecting it into Arizona on Friday. This has been the forecast
scenario for a while now and latest ensembles are now showing very
good agreement on this scenario. The low will be transitioning into
an open wave as it moves northeastward, which may trigger some
showers and thunderstorms, mainly over northern/eastern Arizona. A
few ensemble members do keep it a closed low a little longer as it
lifts into Arizona, and should that happen, the potential for
showers/storms would be higher for the lower deserts of central
Arizona than currently forecast (around 10-15%. Winds will increase
across the region as the pattern change occurs, leading to gusty
conditions Friday afternoon. Although forecast wind/RH values at
this time still appear to remain below critical thresholds, the
combination of these strong winds, very dry conditions, and a bumper-
crop of fine fuels from last winter`s rains, possibility of dry
lightning, and current ongoing fire activity will definitely raise
Fire Danger levels across the region. Wind gusts may climb high
enough to warrant an advisory in southwest Imperial County, with
some potential to extend into the Imperial Valley. Another impact
will be cooling temperatures Friday, which will cause the heat
warning to come to an end Thursday.

For the weekend and into early next week, the upstream jet streak
will cause a pattern realignment, with broad troughing through the
Western CONUS. Temperatures will fall into the below normal category
for several days, with 3-4 consective days of high`s in the 90`s
looking more-and-more likely for next week. Overnight lowers will
also be much cooler than what we are currently experiencing, with
widespread lower-desert lows in the 60`s (and even a few upper 50`s)
a good bet. Heights may begin to show a rebound toward the middle of
next week, with temperatures creeping back up into a more typical
range for mid June.

&&

.AVIATION...Updated at 1755Z.

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

Light diurnal winds are favored through the TAF period at all
terminals. Speeds should remain around 8 kts or less, but will
likely see intermittent increases to 10-12 kts this afternoon
with gusts up to 18 kts. Skies over the metro area will remain
clear through tonight, then mid and high clouds increase from the
south Thursday morning.

Southeast California/Southwest Arizona including KIPL and KBLH:

This morning`s isolated showers/virga have all dissipated and
skies will continue to clear over the next few hours. Skies will
then remain clear until an increase in high clouds midday
Thursday. Winds will favor the south at KBLH through the period,
with morning variability. KIPL will see primarily a south-
southwest to west wind. Both terminals will generally see light
winds, but with afternoon and evening speeds up to 10-12 kts.

&&

.FIRE WEATHER...
Saturday through Wednesday:
Low pressure over the region to keep temperatures several degrees
below average through the entire period. Humidity values will remain
low, near 10 percent, during the afternoon with overnight recovery
in the 30-40 percent range. Even though these elements remain well
below critical thresholds, the fire danger will remain heightened.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Thursday for AZZ537-
     540>544-546-548-550-551.

     Excessive Heat Warning until 8 PM MST Thursday for AZZ530>536-
     538-539-545-547-549-553>556-559>562.

CA...Excessive Heat Warning until 8 PM PDT Thursday for CAZ561>570.

&&

$$

DISCUSSION...Percha/Iniguez
AVIATION...Benedict
FIRE WEATHER...Percha/Smith



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