628
FXUS65 KPSR 211741
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1041 AM MST Thu Nov 21 2024

.UPDATE...Updated 18z Aviation Discussion.

&&

.SYNOPSIS...
High pressure over the region will bring slightly above normal
temperatures into the weekend with lower desert highs in the
upper 70s to around 80 degrees through Saturday. Dry conditions
will continue through at least the weekend with skies eventually
becoming fairly cloudy starting Sunday. For the first half of
next week, expect near normal temperatures to return and mostly
cloudy skies, but little if any chance of precipitation.

&&

.DISCUSSION...
A deep Pacific trough continues to sit nearly stationary off the
Pacific Northwest coast streaming an atmospheric river into
northern California and Oregon, while allowing for high pressure
to build over our region. Since Tuesday, an upper level ridge has
moved over the Desert Southwest with H5 heights now near 585dm, or
easily into the 90th percentile of climatology for this time of
year. Little change is expected with the synoptic setup over the
next couple of days with the ridge remaining parked over our
region and H5 heights peaking as high as 588dm later today. Dry
atmospheric conditions with surface dew points mainly in the teens
will persist with additional warming today into Friday pushing
daytime highs into the upper 70s across the western deserts to
at or just above 80 degrees in the Phoenix area. Skies are
forecast to remain mostly clear through Saturday with only some
thin high cirrus moving through the region.

Over the weekend, the Pacific trough is forecast to shift farther
to the south with the first AR mostly dying out as it moves into
southern California on Saturday, but there looks to be a second
weaker AR setting up to hit southern California Sunday night
through at least Monday. As this shift occurs, the ridge over our
region will get flattened out and eventually pushed to the south.
Temperatures are still expected to remain above normal into early
next week, but we will see a marked increase in cloud cover
resulting in a much narrower diurnal temperature range. As the
weaker AR hits much of southern California, the mid and upper
level moisture will stream through our region starting Sunday and
likely last into the middle part of next week. PWATs are forecast
to increase to at least 150% of normal over much of the region,
but nearly all of the moisture will be aloft with surface dew
points only increasing into the 30s to as high as the 40s across
southeast California. Given the lack of good low level moisture
and little to no forcing mechanisms for precipitation
development, the bulk of the area will remain dry throughout the
period. NBM PoPs yesterday did show some 10-20% chances over
higher terrain areas, but even that has dropped mostly down to
below 10%. For now, we are most likely just going to see a few
days of overall cloudy skies starting Sunday with highs mostly in
the low to mid 70s and lows in the mid 40s to mid 50s.

&&

.AVIATION...Updated at 1740Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and
Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns will exist through Friday morning
under periods of high clouds and otherwise mostly clear skies.
Light wind speeds, AOB 6 kts, will persist, with N-NW flow
developing in the early to mid afternoon before shifting to the E
later in the evening.

&&

.FIRE WEATHER...
High pressure will persist across the region into the weekend
with temperatures running a few degrees above normal. Dry
conditions are expected through at least Saturday with MinRHs
around 10% across the lower deserts to 15% in higher terrain
areas before humidities increase Sunday into early next week
under fairly cloudy skies. The weather pattern will continue to
support overall light winds with only some periodic light breezes
mainly during the morning hours and focused along ridgetops.

&&

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

$$

DISCUSSION...Kuhlman
AVIATION...Whittock
FIRE WEATHER...Kuhlman