Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 221214
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
514 AM MST Sun Jan 22 2017

.UPDATE...To Aviation and Fire Weather Discussions...

&&

.SYNOPSIS...
A break in the weather is expected early today, however another
Pacific storm will approach the area later in the afternoon.
Increasing clouds are expected this afternoon, with a slight chance
of showers developing over portions of southeast California,
spreading east across the remainder of southern Arizona later
tonight and Monday. Snow levels Monday afternoon and night will be
between 5 and 6 thousand feet. A drier and much colder airmass will
settle over the region Tuesday through Thursday, resulting in some
of the coldest low temperatures of the year.

&&

.DISCUSSION...
Arizona is now seeing a very brief break in the active weather
pattern as a short wave ridge has pushed into the desert southwest
ahead of yet another deep, cold and wet Pacific upper trof. The
ridge is rather flat in nature and as such will allow significant
amounts of mid and high level cloudiness to spill through it today
for mostly cloudy skies. On the back side of the ridge, a 170kt jet
will slam into central California and southern CA will see yet
another significant atmospheric river barrel inland today and
tonight. With the flat nature of the ridge combined with the deep
moisture pushing into far southern CA, scattered showers are
expected to develop over the far SE California deserts today with a
few light showers working into portions of the western AZ deserts,
mainly west/northwest of central Phoenix. Despite the presence of
the ridge and higher heights aloft, the thick cloud cover will keep
high temperatures down below normal again today, mostly in the low
to mid 60s over the warmer lower deserts.

Operational guidance from models such as the GFS, NAM and ECMWF as
well as GEFS, SREF and NAEFS ensemble guidance are all on board with
yet another wet and cold Pacific trof moving slowly across the area
early in the week bringing scattered to numerous showers to the
deserts. The deep low will come in slowly with a series of
disturbances moving through the trof and across the area; the most
significant wave with the best qg forcing looks to move through
Monday into Monday night with the most widespread showers focused
across south-central Arizona. Look for rain chances in the greater
Phoenix area to climb to around 70 percent by Monday afternoon with
chances over 90 percent across the higher terrain of southern Gila
county. Rain totals with this event should be a bit less than the
previous system, with central deserts to see around one quarter of
and inch and totals up to around 0.75 inches in the higher terrain
east of Phoenix. At this time, it appears that the threat of thunder
will be minimal but it will not be zero. We don`t have thunder
mentioned in the forecast but there will likely be some enhanced
convective cells which could pump up rainfall amounts locally so some
higher terrain spots might see totals reaching or exceeding one inch
with this system. Confidence in rains over one inch is low however.

From Tuesday into Wednesday the last of the disturbances will swing
east across the area, but should do little in terms of bringing any
rain to the area. For the most part, flow aloft becomes more and
more subsident as mid level q-divergence fields increase and by
Wednesday afternoon there will be just a very slight chance of a
shower mainly east of Globe with mostly sunny skies present across
the lower central and western deserts. High temperatures Monday into
Wednesday will stay well below normal with Tuesday and Wednesday to
be the coolest days; the greater Phoenix area will likely stay
mostly in the mid 50s both of those days. Low temperatures Wednesday
and Thursday morning will be quite cold with some of the outlying
central deserts likely to drop to around freezing, and Phoenix
should see a low around 38 both days. We will need to keep on eye on
the potential for a freeze warning for some of the deserts during
this mid week cold period.

For the Thursday through Saturday time frame, it looks to be a dry
period for the deserts as subsident northwest flow aloft persists
across the area. There will be a weak trof pushing though the flow
and across the four corners area; this feature appears dry at this
time, and this is supported by NAEFS POPs in the single digits at
best. The trof passage will keep a lid on any warming and high temps
will stay below normal, mostly in the low 60s over the central
deserts and maybe mid to upper 60s over the western AZ and far SE CA
deserts.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA,and KSDL:
Easterly winds to prevail today and into the overnight hours with
speeds 5-8kts. BKN-OVC CIGs between 8-11kft will continue to stream
in from the west, ahead of the next weather system forecast to move
through the area late Sunday overnight and into Monday. Another round
of shower chances accompany this system, but should hold off over the
western AZ deserts and higher terrain north of the Phoenix area until
early Monday morning before becoming VC for the terminals.

Southeast California/Southwest Arizona including KIPL and KBLH:
BKN-OVC skies of 8-10kft will continue to stream in from the west
ahead of the next Pacific weather system. Morning winds will be on
the light side before increasing out of the south by midday 8-14kts.
Low- level moisture will enter southeast California after 23/00Z, and
could result in cloud bases approaching 5kft, especially at KBLH.
Some light showers may develop over the mountains to the west before
crossing into the southeast CA deserts overnight as southwesterly
winds become elevated and gusty after 23/02z.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Tuesday through Saturday: Weakened but broad and dry troughing will
settle over the west Tuesday and Wednesday keeping flow aloft
westerly. Additional weak shortwaves may move on-shore over southern
CA but fall apart before reaching the districts in southeast CA.
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 will stay at or below seasonal
normals as minimum humidities gradually dry into the 20 to 40 percent
range through the week. 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.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

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

$$

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DISCUSSION...CB
AVIATION...Nolte
FIRE WEATHER...Nolte



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