011 
FXUS65 KPSR 291153
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
453 AM MST Mon Mar 29 2021

.UPDATE...
Updated 12Z aviation discussion. 

&&

.SYNOPSIS... 
Very warm and dry conditions are on tap all week with high 
temperatures reaching 90 degrees for the first time this year as 
early as today. A weather system passing by well to the north on 
Tuesday will lead to breezy to locally windy conditions and a 
slight dip in temperatures. Stronger high pressure will then set 
in for the latter half of the week and into the weekend with high 
temperatures in the lower to mid 90s Thursday through Sunday.

&&

.DISCUSSION...
A strong upper level ridge currently over the region with 500mb
heights around 582dm, or near the 97-99th percentile of the climo
period will bring the warmest day of the year so far today. Highs
today are expected to top out near 90 degrees in the Phoenix area
to the lower 90s across the western deserts, likely marking the
first 90 degree day of the year for some areas. Some high 
cloudiness will move in from the southwest mostly across southern 
Arizona by this afternoon, but it likely will not affect 
temperatures all that much. A Pacific trough now moving through 
the Pacific NW is forecast to track southeastward later today, 
mostly bypassing our region, but it will briefly suppress heights 
aloft. 

The main impact with this passing trough will be increased winds
on Tuesday after a dry "cold" front surges southward during the 
morning hours. Daytime wind gusts of 25-30 mph will be possible 
across the Lower CO River Valley. Very dry air will also filter in
from the north during the day Tuesday, while strong daytime mixing
aids in lowering surface dew points and humidities further. The 
breezy to windy conditions and very low humidities will also lead 
to elevated fire weather conditions across the Lower CO River 
Valley. Elsewhere, gusty winds of 20-25 mph at times are expected 
in the afternoon. The lower heights aloft and slight cooling 
behind the cold front will keep highs mostly in the lower 80s 
across the western deserts to the mid 80s in the Phoenix area.

Starting Wednesday, a large upper level ridge that is currently 
taking shape well off the West Coast will migrate eastward over 
the Western U.S. This will bring additional warming across our 
region through the end of the week as the ridge axis eventually 
settles just to our east, keeping 500mb heights mostly between 
580-584dm. After the slight dip in temperatures Tuesday, highs 
Wednesday are likely to reach near 90 degrees in the Phoenix area 
to the mid to upper 80s across the western deserts. 

Ensemble guidance remains in very good agreement showing the 
strength and expansiveness of the ridge, but temperature spread is
still a bit high for Thursday due to some potential clouds from a
weakening cut-off low likely to move into our region from the 
southwest late Thursday into early Friday. Although this low will 
be fairly dry and warm, it may bring some high level clouds 
potentially affecting temperatures Thursday. However, NBM median 
temps for Thursday are still mostly calling for the lower 90s. Any
clouds from the cut-off low should exit the region early Friday, 
while temperatures are likely to warm a bit further with forecast 
highs in a 93-97 degree range. Similar readings are forecast for 
Saturday, but the NBM does point toward Saturday as having the 
best potential for seeing upper 90s, likely threatening the 
record of 97 degrees in Phoenix. Latest probability for Phoenix 
tying the record of 98 degrees on Friday is 15%, while Saturday's 
probability of getting to 97 is 35%. 

Some relief from the expected early April heat may arrive by early
next week as a slow moving trough looks likely to approach the 
West Coast by Sunday or next Monday. Increased high level clouds
and gradual lowering of heights aloft will hopefully start a
modest cooling trend Sunday into early next week.

&&

.AVIATION...Updated at 1153Z.
 
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: 

Minimal aviation impacts are expected through Tuesday morning as 
light diurnal winds persist under high cirrus clouds. Easterly or 
variable 5-10 knot winds this morning will become westerly at 5-10
knots by 20-21Z with a couple hours of light southerly winds 
possible prior to the switch. Very brief 15-20 knot wind gusts 
will be possible this afternoon, but they are not included in any 
of the TAFs due to their sporadic nature and low confidence in 
occurrence at any one site.

Southeast California/Southwest Arizona including KIPL and KBLH:

Aside from gusty winds this afternoon, minimal aviation impacts 
are expected through Monday evening. Winds will generally remain
westerly to southerly in response to a broad upper level trough 
digging into the region. Relatively light 5-10 knot winds will 
persist through early afternoon before 15-20 knot gusts impact the
region this afternoon and evening. KBLH will have more south- 
southwest headings, whereas KIPL will have westerly headings. 
Winds should gradually subside overnight, with a slight chance of
low-level wind shear issues late in the overnight hours. Skies 
will remain clear aside from a few high cirrus passing overhead. 

&&

.FIRE WEATHER... 
Wednesday through Sunday:
High pressure and warmer than normal temperatures will prevail
through the period with typical afternoon breezes. Very dry
conditions will be likely leading to afternoon minimum humidity
levels in the single digits (low teens across mountainous
locations) while overnight recoveries generally top out only in
the 15-30% range. 

&&

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

&&

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

$$

DISCUSSION...Kuhlman
AVIATION...Hopper
FIRE WEATHER...Feldkircher/Kuhlman