000
FXUS65 KPSR 160857
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
157 AM MST Fri Apr 16 2021

.SYNOPSIS...
Temperatures will remain near normal for the next few days with
most locations staying in the 80s. Conditions will generally be
dry, but a few showers will be possible on Sunday across the high
terrain north and east of Phoenix. Additionally, breezy conditions
are expected each afternoon, with the strongest winds on Sunday.
Above normal temperatures will resume early next week with highs
climbing into the low 90s across the lower deserts. Another
potential system during the middle of next week may bring somewhat
cooler temperatures and increased breezy conditions.

&&

.DISCUSSION...
An amplified upper level ridge remains anchored over the Pacific
Northwest this morning with a downstream trough over the Great
Basin. Somewhat below normal heights and upper level temperatures
allowed high temperatures to drop just a couple of degrees below
normal yesterday. Meanwhile, a modest upper level jet impinging on
the area from the southwest is allowing for some weak upper level
lift, which is generating cirrus clouds across the area. Over the
next 24 hours the upper level configuration will remain largely
unchanged, with the exception of some shortwave ridging building
to the west as the upper level jet weakens. The end result will be
slightly less cloud cover and therefore minimally warmer
afternoon temperatures.

By Saturday, and especially Sunday, the trough over the Great
Basin will begin to push eastwards, away from the area. As this
occurs, a portion of the trough will split and remain over
Arizona, leading to the development of a closed low. Considering
the track of this system, it will be quite moisture starved, with
any saturation confined to levels at or above 700 hPa. With that
said, upper level lapse rates look to be quite steep with
unusually cool mid level temperatures as well. In fact, 500 hPa
temperatures will fall below the 10th percentile of the NAEFS
climatology for this time of year. Taken together, these factors
should be sufficient to allow for a few high based showers to form
over the high terrain on Saturday and in particular Sunday
afternoons. Model soundings continue to depict very low values of
CAPE (less than 200 J/kg) will develop on Sunday afternoon, and as
such, an isolated thunderstorm may also be possible. As the low
pressure begins to move east of the forecast area on Sunday the
steering flow aloft will switch to northeasterly at 15-20 kts,
which may allow for a few of these showers to move into northern
and eastern portions of the Phoenix metro area. The odds of
accumulating rainfall are very low, but nonzero. A better bet
would be gusty outflow winds near any such showers.

The other forecast concern for Sunday will be the wind potential.
In response to the upper level low, surface pressure will also
lower over Arizona on Sunday. Meanwhile, high pressure will become
established over the Great Basin. The corresponding pressure
gradient will send a surge of dry northerly winds down the
Colorado River valley, leading to increased fire danger. As of
now, it appears that wind speeds will likely remain sub advisory.

Upper level heights and temperatures will rebound for the early
part of next week as the next trough passes well to the northeast
of the forecast area. NBM temperatures probabilities show a 75-80%
chance of exceeding 90 degrees Tuesday and Wednesday. High
pressure over the southern Great Plains will induce an easterly
pressure gradient next Wednesday, leading to yet another very
breezy day with high fire danger across the forecast area.
Ensemble forecasts are in good agreement that another trough will
develop over the southwestern United States during the middle to
end of next week. WPC cluster analysis shows near unanimous
agreement on the development of this trough, but with considerable
variability in its timing, amplitude, and exact placement.
Considering its continental track, it will undoubtedly have very
little moisture associated with it and the risk of rainfall is
minimal. However, the discrepancies mentioned will affect the
level of breeziness and cooling that occurs across the forecast
area.

&&

.AVIATION...Updated at 0550Z.

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

Mostly light westerly winds will continue well into tonight. A
late switch to easterly winds is expected during the early morning
hours on Friday with westerly winds returning early Friday
afternoon. Occasional locally breezy afternoon gusts into the
teens or low 20s is possible, especially in the N-NE Valley
terminals of KDVT and KSDL during the mid to late afternoon. BKN
high cloud CIGS around 25kft will continue through Friday
afternoon with additional BKN decks around 20kft by midday Friday
along with areas of virga and/or isolated sprinkles across the
region. Skies should then scatter out during the early evening
along with light winds and normal diurnal patterns.

Southeast California/Southwest Arizona including KIPL and KBLH:

Persistent W-NW winds will continue through Friday morning when
light SE-SW winds will begin to be favored. SCT-BKN high cloud
CIGS/decks around 25kft will continue with additional BKN decks
around 20kft by Friday morning along with virga and/or isolated
sprinkles across the area. Skies will then scatter out during the
mid afternoon.

&&

.FIRE WEATHER...
Sunday through Thursday: Continuation of breezy afternoons and
gradually warming temperatures are expected through much of the
period. Sunday could see an enhanced period of northerly winds
down the Lower Colorado River Valley and across southeast
California. There will be a low (20-30%) chance of light rain
areas north and east of Phoenix on Sunday, though wetting rains
are quite unlikely. An isolated thunderstorm can`t be ruled out
as well over the higher terrain. For the most part, slight
downward RH trends are expected. They will remain quite low
(10-20%) during the afternoons with overnight recovery very
location dependent (15-30% for most locations). Increasing breezy
conditions will be possible during the middle of next week.

&&

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

&&

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

$$

DISCUSSION...Hodges
AVIATION...Sawtelle
FIRE WEATHER...Iniguez/Smith

NWS PSR Office Area Forecast Discussion