Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 272121
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
220 PM MST Mon Mar 27 2017

.SYNOPSIS...
A Pacific cold front will affect the region through Tuesday with
gusty winds and patchy blowing dust. The strongest winds will
develop over portions of southwest Arizona and Southeast California
this evening. A few light showers 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 sharp midlevel trough axis was nearing the Colorado River Valley
this afternoon with more pronounced height falls crossing into SE
Nevada/NW Arizona. With the focused jet streak and cold air aloft
still lagging on the western periphery of the trough, further
deepening of this system is anticipated through the four corners
region through Tuesday. Objective analysis pinpoints the true cold
front still to the NW over srn Nevada/NW AZ, however a pre-frontal
trough and a steepening pressure gradient were already materializing
through SE California. Eventually after sunset, this front will surge
south overtaking this pre-frontal feature and creating more robust
mountain wave activity descending into lower desert communities.

With the intensifying system and vorticity center propagating into
southern NM Tuesday, the sfc pressure gradient will be maintained
through much of central and western Arizona. The preponderance of
model output indicates a 25-35kt H8-H7 LLJ developing around the
Lower Colorado River Valley tomorrow, part of which will be
transported through the boundary layer via mechanical mixing
processes. Have kept Wind Advisory headlines (and associated mention
of blowing dust ans sand) going though the strongest gusts may be
tied more towards terrain features before rapidly weakening late
Tuesday afternoon. Also given the first vestiges of vegetative
drying, have issued a Red Flag Warning in western Arizona (see
PHXFWFPSR for more details).

Otherwise, short range ensembles and a large subset of operational
models show enough elevated moisture, orographic ascent, and
supportive dynamics for light showers later tonight and Tuesday
across terrain features east of Phoenix. With clouds bases 8-10K ft,
dry subcloud air should limit most activity to virga over lower
elevations, though even a sprinkle is possible around the Phoenix
metro. Although QPF amounts are rather meager, objective POPs have
been trending consistently higher given the excellent dynamics
associated with the vorticity center over southern Gila County.

Models are in fairly good agreement of a transient ridge building
over the area Wednesday into Thursday pushing lower elevation
temperatures back into the upper 80s. However, 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. While the
details are still uncertain, the system does look cooler than the
current one, though precipitation amounts do look rather slim again.
As with all these passing upper level troughs, this system look to
produce strong gusty winds again sometime during the end of the
week.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:
The main aviation weather impact through Tuesday will be an increase
in wind. Increasing westerly winds early this afternoon will become
breezy at times with gusts as high as 20-25 kt late this afternoon.
Winds will subside somewhat overnight, though a switch over to an
easterly direction is not anticipated. Few to scattered mid clouds
this afternoon should clear out sometime this evening. Winds will
again become gusty out of the west northwest Tuesday afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:
Increasing winds will bring breezy to windy conditions this
afternoon with gusts approaching 25-30 kts. There will be a slight
chance of blowing dust and blowing sand, particularly near KIPL late
this afternoon and this evening. Winds will diminish somewhat at
KIPL after midnight, but remain gusty at KBLH. Even stronger winds
are anticipated at KBLH on Tuesday with gusts to 35-40 kts at times.
Another period of blowing dust is possible further norther near KBLH
Tuesday. Any blowing dust or sand that develops also has the
potential to briefly reduce visibilities.

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 to 7 PM MST Tuesday for AZZ131-132.

     Wind Advisory from 3 AM to 7 PM MST Tuesday for AZZ020-021-026.

CA...Red Flag Warning from noon to 7 PM PDT Tuesday for CAZ231.

     Wind Advisory from 6 PM this evening to 3 PM PDT Tuesday for
     CAZ030>033.

&&

$$

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DISCUSSION...MO/Wilson
AVIATION...Kuhlman
FIRE WEATHER...Hirsch


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