Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 111121 AAA

Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
420 AM MST Wed Dec 11 2019

.UPDATE...Updated aviation and fire weather discussion.


High pressure under mostly clear skies will bring slightly warmer
daytime temperatures through Saturday as highs climb to around 70
degrees each day. A weak but mostly dry weather system for Sunday
into Monday should bring cooler temperatures into early next week
with readings closer to seasonal normals.


After a three week period of active weather, the weather pattern
across the Southwestern U.S. looks to calm down over the next week
or so. Boundary layer conditions continue to dry out with surface
dew points now mostly in the lower 40s. Fog formation early this
morning is very unlikely in most areas due to the high clouds
overhead and drier conditions, but we can`t rule out some light
fog in the more favorable rural desert areas where winds are
calm. A fast moving dry shortwave trough currently moving through
California is providing the high level clouds over the region, but
once the trough axis exits to the east by late afternoon, skies
will clear out quickly.

Increasing upper level heights will be seen Thursday into Friday
as a strong ridge of high pressure to our west nudges into our
region. This will provide some modest warming allowing daytime
highs to climb to between 70-73 degrees over the lower deserts by
Friday. This ridge will quickly flatten out later Friday and
eventually start to drift to our south on Saturday as an upstream
trough moves into northern California. Saturday should still be
quite pleasant with highs still roughly 4-7 degrees above normal,
but there should be some increasing high cloudiness later in the

Models still show a Pacific trough mostly passing by to our north
Sunday into Monday, but the base of the trough will likely track
through northern Arizona at some point. Though this system will
be fairly moisture starved, it will be on the colder side and thus
may be able to bring a few light showers across northern and far
east-central Arizona later Sunday. This trough should lower
daytime highs across our area back into the 60s into early next
week, or closer to seasonal normals.


.AVIATION...Updated at 1120Z.

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

Mostly BKN cirrus decks will move across the greater Phoenix area
this morning, by afternoon there should be clearing resulting in
mainly FEW-SCT high cloud decks for the rest of the TAF period.
Winds will be very light, weakly favoring typical diurnal
tendencies. There will be many light/variable or event calm wind
readings at the TAF sites, especially KDVT and KSDL. There are
really no aviation concerns at the TAF sites for at least the next
24 hours.

Southeast California/Southwest Arizona including KIPL and KBLH:

SCT-BKN cirrus decks will be present during the TAF period with the
most significant cloud cover during the morning today. Look for very
light winds over the next 24 hours. At KBLH winds should weakly
favor the north but there will likely be many observations of
light/variable. Really, there are no aviation concerns over the next
24 hours.


Friday through Tuesday: Dry conditions under increasing high
pressure aloft will prevail through Saturday before a weak low
pressure system affects the region Sunday into Monday. Moisture
levels with the late weekend system should be rather dry, hindering
precipitation chances although there is a slight chance of rain or
high elevation snow Sunday afternoon and overnight Sunday night over
high terrain east of Phoenix. Above normal high temperatures Friday
and Saturday give way to somewhat cooler conditions Sunday into
early next week as highs fall slightly below normal by Monday.
Minimum humidity levels initially should stick around 25-35% much of
the period, potentially lowering slightly into early next week.
Winds will stay light through Saturday before some breezy conditions
move in for Sunday and Monday. Light winds return again Tuesday as
weak high pressure aloft returns to the area.


Spotters should follow standard reporting procedures.




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