Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 260446
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
946 PM MST WED MAY 25 2016

.SYNOPSIS...
A broad area of low pressure will continue over the Western States
through the weekend bringing overall cooler than normal temperatures
and dry conditions. A more compact low pressure system moving through
the region today will bring gusty winds to much of the area.
Building high pressure for next week will likely bring a warming
trend pushing highs to near 100 degrees for the lower deserts by the
middle of next week.

&&

.DISCUSSION...
Breezy to windy conditions continue across much of the forecast ahead
of and along an initial frontal intrusion associated with an upper
low circulation near the AZ/CA/NV triple point this evening. Airmass
moisture continues to be at a premium with PWATs less than half an
inch from the Las Vegas RAOB and just shy of three-tenths of an inch
in Tucson. Had to rely on strong winds and steepening lapse rates in
the vicinity of the cold core circulation for any convective activity
during the daylight hours. Isolated thundershowers developed over the
northern portions of the JTNP during the afternoon, putting down a
few lighting strikes but unclear if any of the hydrometeors were
actually hitting the ground given the dry sub-cloud layers. Activity
quickly waned over our forecast area but continues right in the heart
of the upper circulation, mainly west of the Laughlin areaat time of
this writing. Main circ center will swing through central AZ this
evening, possibly genning up an isolated shower across northern
portions of La Paz and far NW Maricopa counties overnight before
continued draw in of dry moisture and subsident flow shuts off any
precip chances for the daytime Thursday. Made minor adjustments to
the PoP grids based on high-res precip forecasts and on-going precip
activity thinking it could clip the areas mentioned above. Mild
daytime temperatures in store for tomorrow in the wake of today`s
initial frontal intrusion and exiting upper low movement.

&&

.PREVIOUS DISCUSSION /ISSUED AT 205 PM MST/PDT/...
A compact but modestly strong upper level low moving eastward into
southern California will track through central Arizona tonight, but
there will be little change to sensible weather. Atmospheric profiles
ahead of this low show little if any moisture to work with, thus the
current mostly sunny skies. What moisture does accompany this system
will mainly stay across higher terrain areas of southeast California
and the northern half of Arizona. As of early this afternoon, a few
areas of high based cumulus are seen on visible satellite, all
located over higher terrain areas. Still showing a slight chance of a
shower or thunderstorm for JTNP through this evening and high res
models support some development. Winds are the main concern for the
rest of today into early tonight as the upper low moves through
central Arizona. Wind gusts of 25 mph across the deserts and up to 35
mph over higher terrain locations are expected through early evening,
possibly resulting in some patchy areas of blowing dust.

Models, including GEFS ensemble members, remain in good agreement
that dry weather with continued below seasonal normal high
temperatures will continue into the weekend under the influence of
large scale upper troffing that has been persistent across the
western CONUS. Subsident northwest flow aloft overspreads the area
late tonight eliminating any remaining threats for showers. The low
will usher in a cooling trend mainly to south central Arizona on
Thursday, dropping high temperatures into the middle 80s over the
lower deserts; Phoenix is forecast to fall to 86 degrees which is 12
degrees below seasonal normals for the date.

For Friday into the weekend, upper troffing is forecast to persist
across the western CONUS, although it will not be overly strong or
deep; for the most part a baggy trof sets up over the desert
southwest keeping dry southwest flow going across the area each day
with only a bit of high clouds embedded in the flow for mostly sunny
days and generally clear nights. With 500mb heights not really
falling all that much there will be somewhat of a warming trend with
high temperatures climbing into the low to mid 90s through Sunday;
these temperatures will still be a few degrees below normal. The
normal high on Sunday at Phoenix is 99 degrees, and the forecast is
for 96 degrees; it makes sense for temps to be slightly below normal
given the presence of weak troffing over the desert southwest during
this period.

Early next week, model ensemble spread becomes quite large and
operational runs from both the GFS and ECMWF argue that much of the
low pressure aloft over the western states will shift eastward as
upper ridging forms just off the west coast. As this occurs, heights
rise and high temperatures over the lower deserts climb putting the
warmer deserts into the upper 90s, possibly reaching around 100
degrees by Tuesday. Thus we are calling for a warming trend with
Phoenix set to reach 97 degrees next Tuesday. It will stay dry each
day with generally sunny days and clear nights across the area.

&&

.AVIATION...

South-Central Arizona including KPHX...KIWA and KSDL...
Southeast California/Southwest Arizona including KIPL and KBLH...

Low pressure passing through central AZ will continue to support
elevated westerly winds overnight for the Phoenix area terminals with
even some gusts of 20 to 25 kts. Typical morning easterlies may
develop into the terminals, but have a much later onset if they do
develop. Western terminals will continue to experience west winds
overnight, with speeds gradually decreasing in the wake of a mostly
dry surface front and upper low pressure system. Some nighttime
clouds may develop over south-central AZ mostly FEW to SCT in nature
AOA 12kft.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Saturday through Wednesday...
With dry southwesterly flow aloft expect slightly below normal yet
warm daytime high temperatures through Wednesday in the mid to upper
90s. Minimum relative humidities will generally range in the 7 to 12
percent range along with fair overnight recoveries. Occasionally
breezy southerly and southwesterly winds are expected each afternoon
with gusts of 15 to 20 mph.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected.

&&

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

$$

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



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