Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 281044
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
344 AM MST Tue Mar 28 2017

.SYNOPSIS...
A Pacific trough will affect the region through Tuesday with
gusty winds and patchy blowing dust. The strongest winds will
continue over portions of southwest Arizona and Southeast
California before dying down Tuesday evening. A few showers and
thunderstorms are also possible across high terrain areas of
central Arizona. Otherwise, high pressure will redevelop across
the region Wednesday and Thursday ahead of another weather system
moving into the Desert Southwest over the weekend.

&&

.DISCUSSION...

A positively tilted upper level trough continues to dig south and
east across our area this morning creating a broad area of ascent
over southeast Arizona. Strong positive vorticity advection
combined with cooler air rushing in at 500mb has created
convective showers this morning just behind the leading edge of
the trough. Most of these showers have been light given the dry
atmosphere below them and relatively high based (~10 kft). A few
of the showers across the Phoenix metro and in SE Arizona this
morning have been strong enough to generate in cloud lightning
with just a few cloud to ground strikes being observed.

As this system digs further south and east, the backside of the
trough will be positioned nearly square over the Lower Colorado
River basin. This will act to enhance 850mb winds to roughly 40
kts over the area during the early morning hours (15Z) on Tuesday.
As surface heating takes place, higher momentum air will
undoubtedly mix to the surface bringing gusts up to 40 mph.
Blowing dust and sand are expected to accompany these gusty winds
which could result in briefly lowered visibilities.

Closer to Phoenix, winds will be much lighter with gusts forecast
to be below 25 mph on Tuesday. Models indicate the highest
amounts of low level moisture, and subsequently instability, will
remain to our east today in Gila county. Most models have a few
hundred J/kg of CAPE materializing there this afternoon, which in
combination with the westerly upslope flow, should be enough to
initiate convective shower activity with a chance of a weak
thunderstorm. Some model solutions indicate light precipitation
could form over far eastern portions of Maricopa county today as
well.

The trough shifts off to our east late in the day on Tuesday which
should help weaken winds dramatically Tuesday evening and diminish
any chance of precipitation in Gila county by early Wednesday
morning. Beyond this, a transient ridge builds in which will help
warm temperatures across our entire CWA with highs reaching the
upper 80s by Thursday.

Models show yet another trough diving down from the Pacific
Northwest and into our area on Friday. This will cause a rather
sharp cooling trend Friday with highs at least 10 degrees cooler
than Thursday. This transition to a cooler airmass will
subsequently increase pressure gradients and drive another round
of windy conditions, especially out in SE California and the
Colorado River Basin. Although at this point, they do not look as
strong as what we will be experiencing on Tuesday. As with our
current trough, the best chance of precipitation will remain in
Gila county with amounts remaining rather light.

All major global circulation models agree that this trough will
linger through Saturday but major differences arise beyond that.
Because of this, there is very low confidence in the forecast for
early next week as each one of the models has their own unique
solution. For now, have gone with a blended approach and have kept
temperatures near seasonal normals.


&&

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

Wind will be the primary aviation impact over the greater Phoenix
area over the next 24 hours as a strong upper low moves east across
the state. Continued locally breezy west to northwest winds will
affect the terminals well past midnight and the chances of winds
turning east at KPHX later tonight are small. Expect more breezy
west/northwest winds Tuesday afternoon with gusts to near 25 kt
likely. There may be a few showers in the area through midnight
tonight with most cloud decks in the FEW-SCT category with bases
genly aoa 8k feet. Coverage too isolated to put in the TAFs at this
time. By Tuesday morning skies should be genly clear as strong
subsidence aloft moves into the area.

Southeast California/Southwest Arizona including KIPL and KBLH:

Gusty northwest to north winds will be the main weather impact
across the western deserts, affecting both KIPL and KBLH over the
next 24 hours. Strongest winds will likely develop at KBLH; gusts
over 25kt are likely from the northwest for the rest of tonight with
a continued increase in wind during the early to mid morning
Tuesday. Strong north wind will blow down the lower CO river Tuesday
with peak gusts in excess of 35kt at times. May see some blowing
dust but at this time confidence is a bit low on restricted vsbys so
will not mention this in the TAF. Winds a bit less at KIPL,
especially overnight tonight, but we can expect winds to pick up
during the morning Tuesday with peak gusts to 25kt likely. Skies to
be genly clear at the TAF sites next 24 hours hours.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Wednesday through Sunday:
The weather pattern will remain quite active across the Desert
Southwest through early next week, though in general precipitation
is not expected, except in the higher terrain well north and east
of Phoenix. Main weather impact will be breezy conditions, which
are expected to redevelop Thursday and Friday associated with the
next low pressure system. With RHs generally remaining below 15
percent, elevated fire danger will again be a possibility across
southeastern California, particularly Friday afternoon.
Thereafter, the low pressure system will likely move through
Arizona during the weekend, bringing below normal temperatures
along with a general decrease in wind and an increase in
moisture.

&&

.SPOTTER INFORMATION STATEMENT...

Spotters should follow reporting procedures with criteria reports
this week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Red Flag Warning from noon today to 7 PM MST this evening for
     AZZ131-132.

     Wind Advisory until 7 PM MST this evening for AZZ020-021-026.

CA...Red Flag Warning from noon today to 7 PM PDT this evening for
     CAZ231.

     Wind Advisory until 3 PM PDT this afternoon for CAZ030>033.

&&

$$

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DISCUSSION...Wilson
AVIATION...CB
FIRE WEATHER...Hirsch



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