000
FXUS65 KPSR 212125
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
225 PM MST Mon May 21 2018

.SYNOPSIS...
A seasonably warm and dry weather pattern will continue through the
week along with clear to mostly clear skies. Daytime temperatures
near to slightly below seasonal normals through Wednesday will
temporarily warm late in the week with many location again flirting
with 100 degrees. Another dry weather disturbance may swing through
the area over the weekend taking some of the edge off the heat.

&&

.DISCUSSION...
An upper low spinning over central California is poised to begin a
weakening phase and lift into the Great Basin over the next 36
hours. A nicely defined concentric cold core will only brush the
forecast area with modest height falls deteriorating throughout the
day with the decaying system. Other than shallow marine moisture and
saturation around the immediate cold core, this system will merely
be another producing some breezy conditions and a brief cooling
trend. The greatest concern for wind and associated impacts will
align through far SW Imperial County once again this evening where
differential heating and mountain rotors could invigorate stronger
gusts and blowing dust around sunset. At this time, the setup
doesn`t appear to be hazardous; however, the timing and system
dynamics could necessitate a brief and small advisory this evening.

While the aforementioned upper low lifts well to the north and east
through Wednesday, height aloft will only slowly recover with H5
readings only edging from 576dm to 582dm into Wednesday evening.
Another seasonally deep trough will deepen west of the California
Thursday allowing ridging to finally amplify over the SW Conus with
H5 heights finally reaching closer to 585-588dm. Corresponding
recovery with respect to temperatures at the surface will also be
nearly as gradual with only a few locations flirting with the 100F
threshold Thursday and Friday.

Model spread increases over the weekend as the upper low moves into
central California and parts of the Southwest. The GFS has been a
bit more aggressive pushing the low further inland before lifting
northeast through Nevada while the European had tracked the low
further north. There has been a trend among operational members of
bringing more notable height falls into the forecast area over the
weekend (similar to the GFS), however then stalling the cold core
circulation over the Great Basin. Ensemble members are not quite so
bullish on the magnitude and equatorward depth of the cold core, yet
do support a similar scenario. Therefore, have pushed temperatures
even cooler over the holiday weekend more in line with the ensemble
mean, but not quite as cool as the operational members.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:
Breezy conditions will develop this afternoon ahead of a dry low
pressure system in Southern California. Westerly gusts up to 25
kts can be expected through this evening with the typical drainage
winds returning late tonight. Similar conditions are expected
tomorrow although winds are forecast to be slightly weaker. This
means several hours of southerly crosswinds will be possible at
KPHX on Tuesday morning before eventually switching west. Ceilings
will not be an issue through the TAF period with just some
passing high clouds.

Southeast California/Southwest Arizona including KIPL and KBLH:
Strong westerly/southwesterly flow is expected at KIPL/KBLH this
afternoon and evening ahead of an approaching low pressure system.
Currently, winds are from the east at KIPL but should abruptly
switch to the west early this afternoon.  When they do, gusts will
reach 25-30 kts with slightly weaker winds at KBLH. Also concerned
that some patchy blowing dust may develop at KIPL late this
afternoon/early evening but have not included it in the TAF for
now. Winds weaken substantially tonight and stay relatively light
through Tuesday afternoon.

&&

.FIRE WEATHER...
Thursday through Monday:
Dry conditions will prevail across the districts through the holiday
weekend with temperatures several degrees above normal Thursday and
Friday cooling back near average over the weekend. Afternoon minimum
humidity levels will mostly fall in a 5-10% range following
generally poor overnight recovery. Wind speeds will begin to
increase Friday across SE California, then across the remainder of
the districts on Saturday. Wind gusts approaching a 25-30mph range
will be possible leading to an elevated fire danger, particularly on
Saturday.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter activation will not be needed.

&&

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

&&

$$

DISCUSSION...MO/Kuhlman
AVIATION...Wilson
FIRE WEATHER...MO

NWS PSR Office Area Forecast Discussion