Forecast-Discussion

000
FXUS65 KPSR 210422
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
920 PM MST Fri Apr 20 2018

.SYNOPSIS...
An exiting weather system today will bring breezy conditions with
warming conditions west of Phoenix. Building high pressure this
weekend will result in a significant warming trend with high
temperatures reaching into the middle 90s by Monday. The very
warm and dry conditions will last through the middle of next week
with highs nearing 100 degrees over the warmest desert locations.

&&

.DISCUSSION...
At 8 pm this evening, the closed low that brought strong wind and
blowing dust to the lower deserts yesterday continued to lift out to
our northeast, allowing dry, subsident northwest flow aloft to
spread into the lower deserts. One final vort trof was pivoting
around the back side of the departing low, moving through east
central Arizona, and as it moved thru the area a low/mid level cloud
band developed from central Phoenix eastward into the higher
terrain. Very little precip occurred with this wave, just a few
light showers were seen earlier on radar over higher terrain areas
mainly east of Globe but nothing in the Phoenix area. High temps
today cooled nicely in the wake of this trof, with the Phoenix area
falling into the mid to upper 70s. The high in Phoenix reached just
78 degrees today although this cooling will not be long lasting.
Expect to rebound back to around 90 tomorrow and then into the mid
90s by Sunday.

Winds today were much less than yesterday with just minor breeziness
reported and most gusts were below 25kt today. Winds will continue
to taper off following sunset and lack of mixing, and with
subsidence moving in, the cloud band east of Phoenix will quickly
dissipate leaving behind genly clear skies for the rest of tonight.
Forecasts look to be in good shape and no updates are needed at this
time.

.PREVIOUS DISCUSSION...
An upper low was centered near the 4 Corners early this afternoon
which has kept lingering breeziness going and enabled some
additional cool air to filer eastern portions of the forecast area
(including metro Phoenix). Some modest instability is evident in the
cloud cover affecting much of northern Arizona. There are even some
weak radar echoes there. A short wave on the western side of the low
is evident in the water vapor imagery and is well depicted in the
models. HRRR and some other hi-res guidance depict increased
coverage of radar echoes as it swings southeastward late this
afternoon and evening. Precip chances for our forecast will be
slight and limited to portions of southern Gila County.

Transient ridging tracks across the western states over the
weekend for a warming trend. Of note there is a split in the
Westerlies far offshore which will enable a weak short wave to
undercut the ridge on Sunday. This will produce little more than
thick high clouds. By Tuesday, the flow consolidates as a low
deepens off the West Coast. Expect some more high cloudiness
emanating from subtropical latitudes. Temperature guidance in
pretty good agreement that highs will still be well into the 90s.

Substantial model spread is seen across the Southwest U.S. for
the latter half of next week. Overall model consensus shows a deep
upper level low potentially becoming cut-off from the main flow
during the period. Very little change is seen across the Desert
Southwest for next Wednesday with continued very warm temperatures
and dry conditions. Forecast confidence is low thereafter as
temperatures will be highly dependent on how long the upper low
sits off the West Coast. For now it looks like the well above
normal temperatures are to remain over the region through at least
next Thursday, possibly longer.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:

Gradients have relaxed significantly as the large upper low
continues to lift off to the northeast. Winds have tapered off and
will become light diurnal (light east) after midnight. After that
expect continued rather light winds following normal diurnal
tendencies in the Phoenix area through Saturday evening. Skies to be
genly clear next 24 hours. No aviation concerns at any airfield for
the next 24 hours at least.

Southeast California/Southwest Arizona including KIPL and
KBLH:

Dry west flow aloft moving into the area for genly clear skies next
24 hours. Winds to be on the light side, with light/variable common.
Winds may favor the south at KBLH during the afternoon on Saturday.
No aviation concerns for at least the next 24 hours.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Sunday through Friday...

A pattern of warm and dry weather will predominate the region
throughout the period. Above normal max temps in the 90s and min RH
values in the single digits are expected to persist through
Friday. Overnight recovery is expected to remain poor to fair.
Otherwise generally light winds with occasional seasonable breezes
can be expected through midweek next week. Strengthening
breeziness is anticipated late next week.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters are encouraged to follow standard reporting procedures.

&&

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

$$

DISCUSSION...CB
PREVIOUS DISCUSSION...AJ/Kuhlman
AVIATION...CB
FIRE WEATHER...AJ/Sawtelle

NWS PSR Office Area Forecast Discussion