Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 262244
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
344 PM MST Sun Feb 26 2017

.UPDATE...
Updated Aviation section.

&&

.SYNOPSIS...
Cooler than average temperatures will persist the next several days
as two fast moving weather disturbances move into the region. The
first system today will produce only minimal showers while a second
disturbance Monday night and Tuesday will have an excellent
potential for spreading widespread rain across the area. Dry
conditions and much warmer temperatures will return for the latter
half of the week.

&&

.DISCUSSION...
Water vapor imagery from this afternoon shows a weak upper impulse
moving through Arizona, which was associated with sprinkles and very
light showers across central Arizona. Given the dry boundary
layer, precipitation actually reaching the ground has been
minimal. This feature will continue quickly shifting eastward,
ahead of the amplifying upper trough off the Pacific Northwest
coast. As the trough approaches the Southwest, it will phase with
a plume of moisture over the eastern Pacific.

Forcing for ascent will increase tomorrow morning as an upper-
level jet intensifies across the southern Great Basin. Given the
orientation of the moisture plume, the most favorable area for
initial precipitation development appears to be across far
southeast California into western Arizona tomorrow afternoon. This
should quickly spread eastward to encompass most of Arizona by
tomorrow evening, with a high likelihood for widespread rainfall
occurring in most locations overnight. Typically favored upslope
areas within southerly or southwesterly flow regimes are expected
to receive the highest precipitation totals. QPF amounts have been
increased slightly in the latest forecast update in line with WPC
guidance, with storm total amounts expected to generally range
from 0.6-0.9 inch around the Phoenix area, with over an inch
likely north and east of Phoenix. Lighter amounts (less than 0.5
inch) are generally expected over southwest Arizona into southeast
California.

The shortwave trough and an associated surface frontal wave will
begin accelerating eastward on Tuesday, with a rapid reduction in
precipitation chances from west to east occurring during the day.
Showers should linger into late Tuesday afternoon across eastern
Maricopa and southern Gila counties before clearing the forecast
area by Tuesday evening. A secondary wave embedded within large-
scale cyclonic flow over the western U.S. will move through early
Wednesday, with the only notable effect on sensible weather being
to keep temperatures cool for one more day.

Broad ridging will envelope most of the west into late next week,
but mid-level heights will remain generally suppressed as the
storm track remains active across the Pacific Northwest.
Regardless, drier conditions and a substantial warming trend
appear probable into the weekend, with temperatures likely to
reach the low-80s across many locations Saturday and Sunday.

&&

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

Breezy to locally windy conditions (gusts 20-30 kts) will weaken
this evening. Otherwise, winds will be light. Skies will be
mostly clear the rest of the afternoon and much of the night
before a stronger weather system moves in during the day Monday
leading to thick cloud cover, scattered to numerous showers, and
breezy conditions. Showers will begin to develop over the Phoenix
area after 18Z Monday with numerous showers developing Monday
evening.


Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Tuesday through Saturday...
A Pacific low pressure system will bring lingering rain mainly to
eastern Arizona on Tuesday followed by considerable drying
starting Wednesday. Below normal temperatures are expected
through Wednesday with a significant warming trend likely late
in the week. Breezy conditions are expected on Tuesday most areas
with breezy conditions persisting down the Lower Colorado River
each afternoon through at least Thursday. Increased humidities
with minimum readings between 25 to 40% on Tuesday will dry out
starting Wednesday with afternoon readings closer to 15% over the
deserts through the rest of the period.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter reports will not be needed through the weekend.

&&

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

$$

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DISCUSSION...Rogers
AVIATION...AJ
FIRE WEATHER...Kuhlman



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