Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 250446

Area Forecast Discussion
National Weather Service Phoenix AZ
946 PM MST Thu May 24 2018

.UPDATE...Updated aviation discussion.


Near normal temperatures and dry weather will persist over the
region through the holiday weekend, though breezy conditions will be
common Friday and Saturday as a low pressure system moves into
northern Arizona. Warmer temperatures are likely next week with
highs reaching over 100 degrees for most communities.


With one low pressure trough lifting into the northern Rockies and
Plains, a secondary series of shortwaves were intensifying just off
the California coast causing amplification of shortwave ridging
over the forecast area. 12Z sounding data over Arizona sampled 3dm
H5 height rises falling in a 582-587dm range, or near the 90th
percentile. Correspondingly, afternoon temperatures were spiking
towards the middle/upper 90s (or near to slightly above normal). The
set of disturbances over the eastern Pacific will eventually
consolidate into more of a single circulation center this weekend,
only slowly progressing across the Southwest and Great Basin. This
system will eventually open and lift into the northern Plains after
the holiday, although southwest flow will persist over the forecast
area only allowing gradual increases to heights and temperatures
next week.

Rather subtle height falls will begin to enter SE California Friday
afternoon as the aforementioned shortwaves move onshore over the
central coast. Though westerly flow over the San Diego mountains
will promote some stronger downslope winds into the western portions
of Imperial County, the temporal alignment of synoptic weather
features is not quite optimal for the type of winds to create
widespread, dense blowing dust and sand. The most concentrated
baroclinicity/theta-e gradient will be relegated closer to the coast
in San Diego County and most pronounced height falls will still be
more removed from the CWA. Have kept dust/sand mention valid for the
SW corner of Imperial County as similar events in the past couple
weeks have yielded near advisory threshold winds and localized
dust/sand issues for this area.

The upper level trough will continue to track into Nevada Saturday
with better height falls sweeping through the forecast area and the
trough base finally encompassing Arizona. Winds speeds Saturday will
increase eastward across southern Arizona while remaining modestly
strong across western Imperial County. A loosely defined frontal
boundary will also propagate into central Arizona enhancing
baroclinicity and winds within the mixing layer. Model output
indicates speeds in the H8-H7 layer around a 20-25kt range which
should easily be tapped during mixing. Kept a mention of blowing
dust and sand through SW Imperial County while the majority of the
region could see some minor suspended dust.

Saturday undoubtedly will be the coolest day over the next week as
highs only reach the upper 80s to middle 90s across the lower
elevations. The trough will fill somewhat Sunday allowing winds to
diminish considerably, but lower heights will remain planted over
the Southwestern U.S. through Monday. Temperatures will begin to
climb Sunday as airmass modification takes place and 500mb heights
rise from a low point of 575-578dm Saturday to 582-585dm by Monday
afternoon. The early weekend cooling will indeed be short lived as
temperatures should breach the 100F threshold in the major, lower
elevation population centers Monday afternoon.

The trough will finally lift well out of the region starting
Tuesday, but the large scale troughing pattern over eastern Pacific
and Western U.S. is forecast to continue through the rest of next
week. At this point, it looks like the trough will set up just far
enough to our west that heights aloft will continue to rise across
the Desert Southwest. Models are in good agreement through next
Wednesday with high temperatures rising up to the 105 degree mark,
but eventually the trough to our west should get ejected eastward
bringing some cooling late next week. The end to the dry conditions
is nowhere in sight, but at least there are indications we will see
a couple periods of high clouds next week.


South-Central Arizona including KPHX, KIWA, and KSDL:
Gusty winds have largely died down tonight across area terminals.
Expecting typical diurnal wind shift out of the east between
09-11Z early Friday morning. Could see a prolonged period of a
stronger southerly component tomorrow to winds (around 10 kts),
before an eventual shift to west by 23Z at both KPHX and KIWA.
Clear skies will continue.

Southeast California/Southwest Arizona including KIPL and KBLH:
Breezy west winds are expected overnight at KIPL, with gusts up to
25 kt possible from modest sundowner winds across Imperial County.
Should see gusts subside by 10Z, before picking back up early
Friday afternoon with gusts again to around 25 kt expected. Winds
will be less gusty at KBLH, although a few to 20 kt still expected
Friday afternoon.

Aviation Discussion not updated for amended TAFs.


Sunday through Thursday:
Dry conditions will continue to prevail across the districts next
week with no sign of substantial moisture anytime in the near
future. Temperatures will become seasonably warm after the holiday
with afternoon highs some 5F or so above average. Afternoon humidity
values will fall to around 10% following poor to only locally fair
overnight recovery. Winds will obtain a typical late morning/early
afternoon upslope gustiness with somewhat stronger speeds possible
Wednesday afternoon.


Spotter activation will not be needed.




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