Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 261016
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
315 AM MST THU MAY 26 2016

.Update...Aviation and Fire Weather Discussions.

&&

.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. 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...
Early this morning, an upper level low pressure system could be seen
spinning over northwest Arizona, moving towards the east/northeast.
Not much in terms of clouds or precipitation associated with the low
as seen in the 1 am IR satellite imagery, and in fact most of the
lower deserts were clear. PWAT values were low as well with just
0.14 inches seen at Flagstaff and 0.29 inches at Tucson. Surface
dewpoints over the south central deserts were up over the past 24
hours but were not overly high mostly ranging from the mid 20s to
mid 30s. Progs call for the upper low accelerate to the northeast
and move into northwest New Mexico this afternoon, with a subsident
northwest flow aloft overspreading the deserts leading to mostly
sunny skies. The main impact from this low will be somewhat cooler
high temperatures across south central Arizona day; the greater
Phoenix area will see high temps fall into the middle 80 today.

In the wake of the departing upper low, heights will rise on Friday
and temperatures will climb back into the low 90s across the warmer
lower deserts under mostly sunny to sunny skies as drier subsident
northwest flow aloft continues across the area. Latest GFS and ECMWF
guidance as well as GEFS spaghetti ensemble members agree that over
the weekend a baggy upper trof will develop over the deserts
southwest. This will be a dry system, no precip and little if any
cloud cover is expected however it will serve to keep our high
temperatures below seasonal normal levels. Most of the warmer lower
deserts will stay in the middle 90s for the most part Saturday and
Sunday.

As we move into the first half of next week, GEFS ensemble guidance
becomes very chaotic and unsettled and solutions start to diverge
between the operational GFS and ECMWF models. However, preponderance
of the guidance suggests that the large scale troffing that has
impacted the western CONUS for some time will break down and shift
east as an upper ridge develops along the west coast. This will lead
to continued dry but warmer conditions Monday through Wednesday. By
Tuesday the warmer western deserts should reach to around 100
degrees with another degree or two of warming likely by Wednesday.
Phoenix is forecast to reach 99 on Wednesday, and that number would
still be a degree below normal, but depending on the strength of the
building ridge, we could easily see Phoenix hit or exceed 100 by the
end of the 7 day forecast period.

&&

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

A weak Pacific low pressure system will continue to cover the region
today. The airmass will remain dry for mostly clear skies, however
gusty west winds will develop during the afternoon hours. Through
18z Thu, light south to southeast wind under 7 knots. Clear skies.
From 18z Thu to 02z Fri, increasing west to southwest wind 10 to 12
knots. Clear skies.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Saturday through Wednesday...a series of weak low pressure systems
will continue to move into the western states. Although dry weather
is forecast, the proximity of the low pressure systems to Arizona
will result in breezy afternoons, with 15 to 20 mph winds each day.
Minimum relative humidities will range from 10 to 15 percent. Good
overnight recovery is expected. A slow warming trend will develop
with afternoon temperatures approaching seasonal normals by
Wednesday.

&&

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

&&

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

$$

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DISCUSSION...CB
AVIATION...Vasquez
FIRE WEATHER...Vasquez



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