Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 240351

Area Forecast Discussion
National Weather Service Phoenix AZ
855 PM MST Mon Jan 23 2017

The last in the recent series of Pacific storm systems will move
through the area tonight and Tuesday. The threat for rain and
mountain snow showers are forecast to linger over central and
eastern Arizona through late tonight, otherwise clearing from the
west to east is expected. A much colder and drier air-mass is
forecast to settle over the region Tuesday through Thursday,
resulting in some of the coldest low temperatures of the season
Wednesday and Thursday mornings. Mostly clear skies and slightly
warmer temperatures will return next Friday and the weekend.



As expected, the colder front that brought locally heavy rain to
parts of SE CA as now moving across South-Central AZ at this hour.
Light to moderate shower activity ahead of the front has dropped up
to 1/3 inch of rain over much of lower elevation areas of northern
Maricopa County, with up to 0.75 of an inch falling over the higher
terrain north and east of Phoenix. A final push of shower activity
is now moving through the region as the sfc cold front moves
through. Perhaps another 0.05 to 0.20 inch of rain could fall over
the lower deserts of south-central AZ before the rain ends for good
later this evening, as indicated on latest HRRR and 3km NAM model
output. Rain and snow showers will likely linger into Tuesday
morning over southern Gila County and the higher terrain of extreme
northern and eastern Maricopa County. A few inches of snow is still
expected above 6000 feet tonight and early Tuesday, with flakes
falling as low as 4000 feet. As far as the short-term forecast is
concerned, other than some adjustments to the hourly
temp/dewpoint/wind grids to better reflect current trends, inherited
forecasts are still looking good.


Later Tonight...

Clearing skies are expected tonight, but with lingering showers
forecast over the higher mountains east of Phoenix on Tuesday, namely
southern Gila County zone 24.

Tuesday through Thursday...

A much colder and drier airmass is forecast to settle over the
region Tuesday through Thursday following Mondays cold front.
This incoming airmass is the coldest so far this season, and
although not extremely cold, will be enough to drop minimum
temperatures on the lower deserts into the low to mid 30s,
possibly 28 degrees both Wednesday and Thursday mornings. Mostly
clear skies area also forecast, again with the exception of a few
lingering snow showers over the mountains east of Phoenix Tuesday

Friday through Monday...

Dry northerly flow aloft will continue to keep temperatures below
normal through the period. With mostly clear skies, night-time
temperatures on the deserts will also remain below normal, from the
middle 30s to middle 40s.


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

Modest cold front moving through metro Phoenix as of 21Z with
isolated to scattered showers and variable ceilings ranging from 4-
7 kft MSL. Higher mountains obscured. Anticipate higher ceilings and
a temporary cessation of shower activity roughly between 22Z-02Z
over the lower elevations (no break for higher terrain). Then,
scattered to numerous light showers redevelop for a few hours
(bases 5-7 kft MSL) followed by clearing after 06Z-07Z (lingering
until about 10Z over higher terrain). Surface winds will favor
westerly directions through about 10Z before trending southeast.

Southeast California/Southwest Arizona including KIPL and KBLH:

Isolated showers will continue through 03Z with areas of ceilings 6-
8 kft MSL and localized 5-7 kft MSL before clearing. Southwest and
west winds with gusts to 30 kts will continue until about 02Z-03Z
before weakening.

Aviation discussion not updated for amended TAFs.


Wednesday through Sunday: Weakened but broad and dry troughing will
settle over the west Wednesday keeping flow aloft westerly with low
level winds north to northwesterly but rather light. Quasi-zonal
flow will develop into the region as high pressure attempts to build
into the west and various shortwave systems ride over the ridge
flow. Temperatures initially will be well below normal but will
gradually warm during the five day period, becoming near seasonal
seasonal normal by Sunday. Humidity values will start highly
elevated with minimum RH values 30-45 percent, gradually drying
during the week and lowering into the mid to upper teens by the
weekend. One stronger storm system passing through the Four Corners
during the late week/early weekend will produce enhanced easterly
surface flow over the Mogollon Rim and northerly flow down the
Colorado River Valley, introducing breeziness and periodic gustiness
from the north and northeast for the districts.


Spotters should follow standard reporting procedures.


AZ...Winter Weather Advisory above 6000 feet until 5 AM MST
     Tuesday for AZZ024.



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