Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 211613
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
915 AM MST Sat Jan 21 2017

.SYNOPSIS...
A series of Pacific storms will continue to affect the desert
southwest into the early to middle part of next week. The strongest
and wettest of them will move east and out of the area today into
tonight as rain chances diminish from the west. Snow accumulation
will be above 5500 feet. A Winter Storm Warning remains in effect
for the mountains east of Phoenix through this afternoon. A break in
the weather is expected later tonight and early Sunday, however
another Pacific storm is expected into the region later Sunday
through next Tuesday. Dry but cool weather will settle over the
region for the middle of next week.

&&

.DISCUSSION...

Morning weather balloon data showed the disturbance that moved
through AZ overnight was rapidly approaching western New Mexico.
Although rain and snow showers had been diminishing in intensity
across central AZ, a cold unstable airmass should continue shower
threats into the afternoon hours.

The modeled sounding for Phoenix showed the potential for afternoon
congestus clouds at 54 deg F, with much more low level moisture from
southern CA pouring over the coastal range the southern half of the
state.

Updates this morning were to continue a chance of showers over
Phoenix and surrounding deserts through late afternoon. Upslope rain
and snow showers will be most widespread over the mountains north
through east of Phoenix.

Although the Winter Storm Warning continues for the mountains of
southern Gila County above 5500 feet through 11 am mst, which is
above all population centers, we have no idea how much snow fall in
the mountains overnight. The remote RAWS observation site at 5700
feet northeast of Globe stopped recording rain at 0.72 inches in
contrast to other lower elevation amounts in the 1 to 2+ inch range.

The next weather system will approach the region later Sunday and
Monday. Precip chances will spread from west to east, or southeast
CA to south central AZ later Sunday. Models suggest another plume of
deep low level moisture with the frontal zone, with the potential
for another bout of moderate to heavy upslope precip over the
mountains east of Phoenix, or in southern Gila County.

Except for the minor precip probability updates for this afternoon,
the remainder of the forecasts look ok for now.



.PREVIOUS DISCUSSION...549 AM MST...

At 230 am, a potent winter storm continued to push east across the
area with most of the showers on radar located across higher terrain
areas north and east of central Phoenix. The impressive area of 100
percent POPs that were in effect for last evening (pretty much from
the CO river east) worked out extremely well; Maricopa County Flood
Control District gages depicted basically 100 percent coverage
across the network, with most of the reports above about one quarter
inch, and many locales well above one half inch. Phoenix set6 a
daily rain record yesterday at 0.86 inches with much of that total
occurring during the evening hours. Even though showers have greatly
dissipated from areas west of Maricopa County, IR imagery continued
to show quite a bit of cloud cover spreading into the desert
southwest for partly to mostly cloudy skies.

Operational guidance as well as GEFS ensemble guidance remains very
consistent in exiting the strong trof off to our east today and
allowing a somewhat more subsident northwest flow to spread into the
area. POPs will steadily decrease from the west today with scattered
showers expected across south central AZ into the afternoon (more
numerous over the higher terrain of southern Gila County) and by
this evening there will be just a few lingering showers over the
high terrain east of Phoenix and partly cloudy skies over the lower
deserts. Expect another cool day today with desert highs mostly
ranging from the upper 50s to low 60s. Overall, for the next several
days at least, the presence of continued significant cloudiness
along with a cooler air mass and occasional showers will keep our
high temperatures running well below seasonal normal each day.
Phoenix will struggle to climb above 60 on any day through about
next Thursday.

Cooler air will continue to filter in behind this exiting trof,
allowing the snow level to gradually fall below 5000 feet by mid
morning today. By the time the snow level really lowers the precip
will be mostly over. For now, significant snows should remain above
5500 feet and only affect higher terrain areas mostly to the east of
Globe. We will keep the Winter Storm Warning through 11 am today for
areas above 5500 feet; no problems have been reported so far as of 3
am due to the potential heavy snow however.

Flat short wave ridging moves into the area Sunday, but with another
atmospheric river barreling into far SE California during the day,
there will be quite a bit of clouds streaming through the ridge for
mostly cloudy skies and scattered showers across portions of far SE
CA as well as La Paz County. Any rain totals Sunday will be very
light however. For Sunday night into Monday night we will see yet
another wet and cold Pacific low push through the desert southwest
and Arizona bringing another wave of precip to the area. Best
chances for rain and higher elevation snow will occur later Monday
and Monday night across south central Arizona with rain chances
above 70 percent over higher terrain areas east of Phoenix. Rain
chances should be around 50 percent Monday over the central deserts
but most rain totals should stay below one quarter of an inch. We
could see totals above that over southern Gila County though. This
cold and wet low will actually move in as a series of disturbances
moving through the main upper low and the last in this series of
waves will push through Tuesday into early Wednesday. It is not
expected to bring much in terms of rain; as it progresses through
the area the flow aloft becomes more subsident with pronounced mid
level q-divergence present, so skies will actually become mostly
clear during the day Wednesday behind the exiting wave.

Dry subsident northwest flow will dominate our weather Thursday into
Friday for mostly sunny days and clear nights.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA,and KSDL:
Elevated, and at times gusty, west to southwest-oriented surface
winds will persist for much of the day for the Phoenix terminals.
Surface cold front is tracking into eastern Arizona this morning,
where desert rain and mountain snow showers persist. Could see
additional light showers back across the Phoenix area through midday,
so maintained VCSH during the morning. Dry air moving in from the
west will lift CIGs above 5kft with some FEW-SCT low level clouds
possible over nearby terrain. Enough moisture will remain in the
boundary layer today that congested CU fields are possible during the
warmer afternoon and may fill in around 7-8kft.

Southeast California/Southwest Arizona including KIPL and KBLH:
SCT-BKN clouds will remain in the wake of last night`s surface cold
front passage, with bases ranging 8-12kft. Surface winds will hold
west-southwest with elevated readings and occasional gustiness. Rain
shower activity for the deserts will remain well east of the
terminals and in Arizona for the day.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Monday through Friday: Unsettled conditions with another round of
precipitation will continue Monday ahead of high pressure building
into the region. Rainfall amounts will be less than those from the
weekend and chances for wetting rains are not as widespread. High
pressure will gradually rebuild across the area Tuesday and
Wednesday, resulting in a drying trend though temperatures will
remain below normal. Fire danger will remain low through the period
due to the persistent and anomalously moist conditions.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter reports of rain and snow will likely be needed later this
week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Winter Storm Warning until 11 AM MST this morning for AZZ024.

CA...None.
&&

$$

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DISCUSSION...Vasquez/CB
AVIATION...Nolte
FIRE WEATHER...Nolte/Hirsch


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