000
FXUS65 KPSR 192057
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
157 PM MST Fri Oct 19 2018

.SYNOPSIS...
Warmer temperatures with readings near to slightly above normal
will last into tomorrow, but more unsettled weather will move in
later tomorrow and last into early next week. Rain chances
tomorrow afternoon will favor higher terrain locations,
especially across central Arizona. There will be a slight cool
down Sunday into early next week under partly cloudy skies and
lingering rain chances mainly north and east of Phoenix. Drier
conditions will move into the region by the middle of next week
with temperatures remaining near seasonal normals.

&&

.DISCUSSION...
The next weather system to affect our region is currently
centered off the northern coast of Baja California with this
system retrograding slightly tonight into early tomorrow morning.
The flow will become more southerly tomorrow, allowing moisture
to be advected into the region, however PWATs are expected to be
no more than a little over an inch. The greatest moisture will
exist near and east of the Colorado River and this is where the
greatest precipitation chances will also exist. With the trough
just to our west, there will be some weak dynamical support, but
overall it shouldn`t be a major factor. The threat for thunderstorms
will be there with enough shear to support some organized storms,
but storm movement will be around 20kts likely limiting the flood
threat outside of any cells that manage to train over the same
area. There is an outside chance of some small hail and gusty
winds, but it doesn`t seem all that likely given the brief period
of 500-1000 J/kg of MLCAPE. Hi-res models seem to keep showing a
similar trend, isolated showers during the day, mostly across the
higher terrain, with activity really ramping up after 00Z Sunday,
with an axis of showers and perhaps a thunderstorm or two
developing along western Pinal and Maricopa counties. Showers and
isolated convection then fade overnight with redevelopment of
showers possible once a gain early Sunday morning, but mainly
across Maricopa and Pinal counties.

The upper level low will begin to shift to the northeast on Sunday
shifting our winds more out of the southwest. South-southeasterly
moist low level flow will still be present across the eastern
half of Arizona on Sunday, so shower and thunderstorm chances will
shift a bit eastward on Sunday. Best rain chances Sunday look to
be north of Phoenix with more isolated activity across south-
central Arizona. Models are less clear on how much shower or
thunderstorm activity there will be on Sunday, but we are
thinking it will be a bit less than on Saturday. Temperatures on
Sunday will drop a few degrees off of Saturday`s highs, but
should remain close to normals.

There has been a slight shift in the models for Monday as a
stronger upper level Pacific jet is now shown entering the base of
the trough over the region. This should allow the trough to
deepen again with its center now over the Great Basin. Jet
positioning will become favorable for creating an area of moderate
vertical ascent late Monday over eastern Arizona. Plenty of
lingering low level moisture in combination with the jet dynamics
and weak southwesterly upslope low level flow should provide
another round of showers east of Phoenix. Rain chances will
greatly diminish by around noon Tuesday as the jet shifts eastward
and the upper level trough weakens again.

Drier air will gradually filter in from the west later Tuesday
into Wednesday while the trough finally exits well to the
northeast. Temperatures should hover around seasonal normals
through at least the middle of next week, but there are signs of a
potential warm up late next week into next weekend as a strong
Pacific ridge begins to shift eastward into the Desert Southwest.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:
Winds and LLWS late in the overnight and morning hours continue to
be the primary concerns for the TAF period. Gusty E-NE winds up to
20 knots will continue at KPHX and possibly the other terminals
through about 20Z before they decrease to around 10-15 knots
later this afternoon. High pressure northeast of the region will
allow easterly winds to persist aside from possibly a brief period
of more N-NE winds between 01-05Z. LLWS concerns will arise once
again between 09-16Z Saturday as 25-30 knot easterly winds 1-2 kft
AGL rapidly decrease towards ground level. These stronger winds
will mix down to the surface a bit earlier than yesterday around
16Z and persist through the afternoon with gusts to 25 knots
expected. An increase in moisture will support scattered to broken
7-8 kft ceilings late in the overnight hours throughout the day
tomorrow with very isolated showers possible.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns under mostly clear skies through Saturday
morning. Surface winds will favor a northerly direction this
afternoon with winds up to 15 knots at KBLH. Light westerly winds
will occur at KIPL overnight and tomorrow morning before shifting
back to northerly late tomorrow morning.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Monday through Friday:
Low pressure over the region will keep wetting rain chances
elevated during the Mon-Tue timeframe across south-central
Arizona. The best chances for rain continue to be over the high
terrain north and east of Phoenix. There is also a potential for
isolated thunderstorms as well on Monday. Dry conditions and
slightly lower humidities should return during the Wed-Fri period
as winds aloft become more westerly. Winds should remain at 15-
20mph or less area-wide. Minimum humidities in the 25-50 percent
range Mon (lowest over SE CA) will fall into the 20-40 percent
range (lowest over SE CA) by Thursday.

&&

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

&&

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

$$

DISCUSSION...Hernandez/Kuhlman
AVIATION...Hopper/Rogers
FIRE WEATHER...Percha/Hernandez

NWS PSR Office Area Forecast Discussion