FXUS65 KPSR 200514

Area Forecast Discussion
National Weather Service Phoenix AZ
1014 PM MST Fri Jan 19 2018

.UPDATE...Updated Aviation Discussion.


High pressure will prevail across the region today with above normal
temperatures and dry conditions. A notable storm system will move
into the Southwest later today and into Saturday. While it still
does not look like a very wet system,it will result in increasing
winds and a significant drop in temperatures. After a cool Saturday
and Sunday, temperatures will slowly rebound heading into the first
part of next week.


Mostly clear skies with only very thin cirrus are observed this
afternoon across the region, as temperatures heat up into the
mid-70s. Bigger weather changes are on the horizon, however, as an
upstream trough is digging southeastward along the California
coast. The edge of colder air aloft was observed in the morning
sounding from Vandenburg AFB, and this will continue to rapidly
spread eastward. Surface observations show the position of the
cold front entering the Los Angeles Basin and Mojave Desert of
California as of 1:30 PM MST. The current timing of the cold front
suggests that it will enter southeast California early Saturday
morning, before spreading into south-central Arizona by late
Saturday morning. This will substantially limit diurnal heating
tomorrow with persistent low-level cold advection occurring
throughout the day. Winds will also kick up a bit due to the
relatively strong low-level thermal gradient in place, but speeds
are expected to remain below criteria.

Due to the progressive nature of this system, the amount of
moisture will remain fairly limited. As previously advertised,
this will likely remain an event more favorable for precipitation
north and east of the Phoenix area across the higher terrain.
Current forecast trends suggest precipitation will start across
northern Arizona during the late morning, and spread southeastward
across northeastern Maricopa and southern Gila Counties by
afternoon. The temperature profile aloft will be very cold, and
will result in snow levels initially starting around 6500 ft and
falling to near 4000 feet by late Saturday evening. Regardless,
accumulations across south-central Arizona should be fairly
light. A few light showers are also possible across the lower
deserts, including the Greater Phoenix area, but any rainfall
totals are currently expected to be very light.

Well below-normal temperatures will persist into Sunday with
highs only expected to reach the upper 50s in most lower desert
locations. Not much change to the previous thinking in terms of
the cold overnight temperatures, with lows forecast to generally
remain close to or above freezing in most areas with exception to
localized outlying spots.


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

On Saturday morning expect a strong cold front to move into the area
with breezy westerly winds, lowering CIGS and a chance of rain
showers through much of the period. Tonight a light wind regime
will continue until early morning. Expect the cold front`s arrival
between 11-16Z with breezy southwesterly winds 8-11kt gusting to
14-18kt. This system will also bring light to moderate rain
showers along with low cloud CIGS from 5-9K and FEW-SCT low
clouds near at 3-4K. The chances for rain showers will continue
into Saturday evening.

Southeast California/Southwest Arizona including KIPL and KBLH:

With a strong cold front currently sweeping through southeast CA
expect breezy to occasionally windy westerly winds near 14kt gusting
to 20-25kt at KIPL. Winds at KBLH are expected to be southwesterly
at 8-12kt tonight becoming westerly to northwesterly and breezy by
early to mid morning at 8-12kt gusting to 17-20kt. Expect mostly
cloudy skies tonight with high cloud CIGS and FEW-SCT low to mid
clouds at 4-10K.

Aviation Discussion not updated for amended TAFs.


Sunday through Thursday:
Anticipate a warming trend during the first half of next week.
Accordingly, humidities will trend downward though overnight
recovery will remain good. Winds will be light and favor north and
northeasterly directions. During the latter part of next week, a
passing weather system will bring cooler temperatures and stronger
winds. At this time, rain chances will be slight at best and will
be limited to the higher terrain of south-central AZ.


Spotters should follow standard reporting procedures.




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NWS PSR Office Area Forecast Discussion