Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 301610
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
910 AM MST MON MAY 30 2016

.SYNOPSIS...
A slow moving low pressure system across the desert southwest will
persist through Tuesday yielding cooler than normal temperatures and
mostly dry conditions. Thereafter, high pressure builds over the
regions resulting in a sharp warming trend. By the weekend, many
lower desert locations will reach the 110 degree mark.

&&

.DISCUSSION...
A slow moving and weak shortwave has now moved into far western AZ
this morning with KTWC 12Z sounding data sampling just enough
moisture around the H7 layer and increased SW flow to allow for
upslope induced CU/ACCAS over the White Mountains. Otherwise outside
of some deformation banding across far NW AZ, moisture values remain
well below 5 g/kg through the entire column for the majority of the
area. Best performing high resolution models still depict sct
showers along the Mogollon Rim this afternoon in association with
this deformation/divergent region in N AZ. Other than some
decaying/diffuse outflow boundaries trying to push south, no impact
should be felt locally. In the short term, some adjustment to
dewpoints were made as the discontinuity and gradient across the
forecast area was greater than anticipated. Also, made some minor
adjustments to temperatures and sky cover based on observational
trends. Overall, a fairly nice holiday Monday for the region
considering the heat that will be experienced later this week.

&&

.PREVIOUS DISCUSSION...
/453 AM MST MON MAY 30 2016/
Today through Wednesday...
As the low slowly drifts east-southeastward, it will try to tap into
moisture from the Plains as well as subtropical moisture from Baja
and Sonora. Being that it is weak, the moist advection will be
meager. However, both hi-res and larger scale models depict
convection developing over northern AZ today with more coverage
Tuesday. With the low center dipping south of the Mexico border by
Tuesday afternoon, northeasterly steering flow will help move storms
from the Rim and Yavapai County into south-central AZ. This would
primarily affect southern Gila and northern Maricopa Counties. The
nature of the convection will be high based and shallow given the
very modest moisture availability.

Thus, no real precip opportunity but rather there will be gusty wind
potential and thus blowing dust potential. Our local WRF-NMM is the
most aggressive with the coverage and even has La Paz County and
Pima County getting into the mix. Other models (including NCEP WRFs
and UofA WRFs) are not as optimistic. Held on to the patchy blowing
dust in the grids for late Tuesday afternoon and evening but pared
back the area. By Wednesday afternoon, the low will be centered over
the Sonora/Chihuahua border. With lingering moisture and
northeasterly steering flow, added mention of slight chance t-storms
for our higher terrain zone northeast and east of metro Phoenix for
Wed. aft/eve.

As for temperatures, they will be a little bit below normal today and
near normal Tuesday (slightly above near and west of the Lower
Colorado River Valley). There will be additional warming Wednesday as
the low exits and the ridge advances inland. That will be the first
day of this week for 100 degree mark over the Phoenix area.

Thursday through Sunday...
The short story is that a strong ridge keeps building inland with
500mb heights in the 592-594dm range Friday and Saturday. NAEFS
depicts 850mb temps reaching and exceeding the 90th percentile both
of those days (especially Saturday). This pattern will result in well
above normal temperatures (even for early June) with most lower
deserts reaching the 110 degree mark Friday and Saturday. One minor caveat
is a backdoor front pushing against the Continental Divide late in
the week which could conceivably keep temps over south-central AZ
slightly below forecast but probably would only be felt over the
higher terrain - if at all. The ridge starts shifting eastward Sunday
in response to an advancing low pressure system leading to slight
cooling (more noticeably for southeast CA).

&&

.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL...
A weak low pressure system will move into Arizona today, though no
direct aviation weather impacts are anticipated through Tuesday
morning. Winds will generally remain less than 10 kt and follow
typical upslope/downslope patterns across the Phoenix area.

Southeast California/Southwest Arizona Including KIPL and KBLH...
Lighter than normal winds are expected through Tuesday. At KIPL,
directions will vary while at KBLH, winds will generally retain a
southerly or easterly component.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Wednesday through Sunday...
A strong high pressure system is forecast to build into the region
providing some of the warmest afternoon temperatures of the year by
the weekend. Afternoon temperatures will be 5 to 8 degrees above
normal. Typical afternoon and evening southwest winds 10 to 15 mph
are expected each day. Good recovery is expected at night. Minimum
relative humidities are generally expected in the 8 to 12 percent
range.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Watch from Friday morning through Sunday evening
     for AZZ020>023-025>028.

CA...Excessive Heat Watch from Friday morning through Sunday evening
     for CAZ031>033.

&&

$$

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DISCUSSION...MO/AJ
AVIATION...Hirsch
FIRE WEATHER...Vasquez


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