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FXUS65 KPSR 161254 CCA
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
438 AM MST Sun Dec 16 2018

.UPDATE...Updated Aviation and Fire Weather Discussions...

&&

.SYNOPSIS...
Mild weather will continue today with temperatures a few degrees
above seasonal normals. There will be off and on periods of thicker
high clouds through Monday night associated with a pair of weak
systems. There will be a very slight chance of showers developing on
Sunday night and again on Monday night over the high terrain east of
Phoenix. Strong high pressure will then build back over the region
for the latter half of next week with temperatures potentially
nearing record highs late in the week.

&&

.DISCUSSION...
Tonight`s satellite imagery is showing an area of mid and high
clouds streaming north-northeast into S-central AZ ahead of a NW
MX/N. Baja CA upper low pressure system. H5 analysis shows the low
pressure system`s closed circulation currently centered over the NW
coast of Baja CA. Current radar shows some very light virga and/or
sprinkle returns drifting into S. Yuma county and SE AZ from NW MX
ahead of the low pressure system. High-res models suggest that some
of the virga and isolated sprinkles will drift across the deserts
today.

Today the relatively weak NW MX low pressure system will move east
along the MX-AZ border with its main influence staying mostly south
and east of the CWA. The system will bring a gradual increase in
moisture beginning this afternoon through tonight with a very slight
chance of showers developing in the higher elevations east of
Phoenix and in Pinal county from late this afternoon, tonight and
into Monday. However, the moisture bump with this system is expected
to be modest with models showing PWs peaking at only about 0.5 to
0.6 in. In addition, no significant rainfall is expected in those
areas with this system.

On Monday the low exits to the east as the next open wave trough
moves east into the Intermountain W. The southern extent of its axis
moves through S. CA Monday and digs a little further southeastward
into AZ on Monday night. This rather weak system brings a modest
amount of moisture with it with its spike in PW being even less than
the previous system to less than 0.5 in. As a result there is only a
very slight chance of showers in the deserts with only slightly
better chances across the high terrain areas north and mostly east
of Phoenix on Tuesday night and into Tuesday morning.  No
significant rainfall is expected with this system either. Although,
this pair of systems will manage  to cool us down a few degrees with
highs cooling to the upper 60s for Monday and Tuesday.

On Tuesday a ridge axis slides east into the Intermountain W and SW
US.  On Wednesday a warming trend begins as the ridge then
reinforces its presence and builds in amplitude and expands over the
W US. By late Thursday afternoon the strong ridge axis will extend
from AZ through the N Rockies as H5 heights are forecast to peak
near 585dam over the area--near the 99th percentile for all
climatological values for this time period. Forecast high
temperatures for Thursday and Friday are well into the 70s, or at
least 10 degrees above normal, and could come fairly close to the
record highs for those dates.

&&

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

No significant aviation concerns at the TAF sites into Monday.
Winds will continue to be light and weakly favor typical diurnal
patterns, with dominant winds overall favoring the east. KPHX
will struggle to turn to the west later today and should just see
a brief period of very light/variable winds. SCT to BKN high
clouds will continue through this afternoon before scattering out
a bit this evening into tonight.

Southeast California/Southwest Arizona including KIPL and KBLH:

Winds will continue to be light and often times light and variable.
No aviation concerns for at least the next 24 hours.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Tuesday through Saturday:

Strong high pressure will build into the region from the west
during the middle part of the week allowing for a warming trend
and eventually well above normal temperatures late in the week.
Dry conditions will persist through the period under generally
light winds. Min RH values initially on Tuesday near 30 percent
will gradually lower closer to 20 percent by Friday. Overnight
recoveries will be good to excellent throughout the period.

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

&&

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

$$

DISCUSSION...Sawtelle
AVIATION...Kuhlman
FIRE WEATHER...Kuhlman

NWS PSR Office Area Forecast Discussion