875
FXUS65 KPSR 052305 AAA
AFDPSR

Area Forecast Discussion...UPDATED
National Weather Service Phoenix AZ
405 PM MST Wed Feb 5 2025

.UPDATE...Updated 00z Aviation Discussion.

&&

.SYNOPSIS...
High pressure across the region will continue to slowly weaken the
next several days allowing temperatures to retreat from recent near
record levels, though still 5 to 10 degrees above normal. Dry
conditions will persist through the first half of next week, albeit
with occasional breeziness and temperatures eventually falling much
closer to the seasonal normal.

&&

.DISCUSSION...
Strong subtropical ridging over the SW Conus continues to be
steadily eroded as zonal jet energy and subtle shortwaves stream
across the Great Basin helping depress midtropospheric heights.
Forecast confidence is excellent that westerly quasi-zonal flow will
persist through the weekend keeping H5 heights stable in a 573-579dm
range. Numerical guidance spread is somewhat wider than would be
anticipated under such a pattern, and likely associated with
uncertainty in timing and coverage of periods of thicker cirrus
cover spreading into the region downstream from broadly cyclonic
flow over the East Pacific. Nevertheless, readings some 5F-10F above
the seasonal normal will be common the remainder of the week.
Mandated NBM POP forecasts late in the week are still advertising
unreliable output across SE California given the pattern of a
decaying cold front and shallow moisture trapped along the coast,
and have cut these forecast values rather significantly.

Early next week, the entire hemispheric pattern will have shifted
east with broad troughing over eastern Canada/US and high amplitude
ridging along the west coast of North America. This pattern
configuration will favor some form of longwave troughing development
over the western Conus with the majority of ensemble membership
suggesting weak, positively tilted troughing initially carving out
more defined cyclonic flow inland. This should result in marked
midlevel height falls as H5 values likely tumble into a 560-568dm
range over the forecast area. Numerical spread understandably
increases during this period with ensemble variations growing,
however confidence is still elevated that temperatures cool back
into a near to possibly even slightly below normal range. Despite
this introduction of a troughing pattern, moisture intrusion will
likely still be muted with low level mixing ratios solidly below 4
g/kg and total column PWAT under 0.50". Just beyond this forecast
period during the latter half of next week, prospects of better
quality, deep moisture advection and favorable jet dynamics may
become juxtaposed over the Southwest yielding an extended period of
unsettled weather. While ensemble spreads is quite large, the
overall pattern would support good chances for mountain snowfall
across northern and eastern Arizona with modest chances for light
showers in lower elevations of south-central Arizona.

&&

.AVIATION...Updated at 2305Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are anticipated through the TAF period under
clear skies. Winds will remain light, mostly AOB 7 kts, and will
follow typical diurnal patterns. Directions should maintain a
prevailing westerly component until late tonight, followed by a
shift back to westerly winds between 20-21Z tomorrow afternoon.
KSDL and KDVT can expect to experience more S/SW flow tomorrow
afternoon. Expect periods of variability to precede these diurnal
transitions.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will generally favor west at KIPL and south southwest at
KBLH, with extended periods of variability likely through this
afternoon and into early this evening. Expect wind speeds to
remain light, mostly AOB 7 kts, though gusts up to 22kts at KIPL
are possible tomorrow morning into tomorrow afternoon. Clear
skies will prevail through the TAF period.

&&

.FIRE WEATHER...
Weak high pressure will remain over the region the rest of the week
providing a continuation of the above normal temperatures and dry
conditions. MinRHs over the next few days will mostly range between
20-30% over the western districts to 15-25% over the eastern
districts. Winds will remain fairly light, except for some afternoon
and evening breeziness with gusts up to around 20 mph mainly across
the western districts. Starting this weekend into early next week,
the weather pattern will gradually shift to allow for temperatures
to cool back into the normal range with continued dry conditions and
low humidities.

&&

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

$$

DISCUSSION...18
AVIATION...Whittock/Ryan
FIRE WEATHER...Kuhlman