Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 270305

Area Forecast Discussion
National Weather Service Phoenix AZ
803 PM MST Fri May 26 2017

Dry and tranquil weather will persist into the weekend with
afternoon high temperatures very typical for the end of May into the
90s and lower 100s. Temperatures will warm somewhat into the
beginning of next week with some scattered mountain storms possible
by the middle of the week.



A series of low pressure systems that move into the western states
and provided below normal temperatures today will move east of the
region tonight.  A warmer airmass with higher atmospheric heights
will slowly build this weekend resulting in clear skies with a
warming trend. The 100 degree mark on the deserts will be breached
again Sunday. Much lighter afternoon winds are also expected.
Current forecasts look good. No short term updates necessary.


A temporary cool down today and Saturday will give way to warming
temperatures and above normal highs starting Sunday. The cool down
is taking place because of a large scale troughing that moved into
the Western U.S. A significant shortwave trough embedded within the
large scale flow will move through the Great Basin into tonight
while another barely noticeable is currently moving through Arizona.
Very dry conditions over the region will keep skies clear despite
the shortwave trough passage. The area will also have to contend
with another breezy to windy day today as surface low pressure
deepens over the Great Basin providing a modestly strong northwest
to southeast pressure gradient. Wind gusts this afternoon will
approach 30 mph in many locations, but higher gusts are expected
over higher terrain locations of southeast California and eastern
Arizona. This has also prompted a Wind Advisory to be issued through
early Saturday morning for far southwest Imperial County. Very
little change in the forecast has been made through the weekend and
the previous forecast still applies.


General mid continent troughing and a series of shortwaves over the
Rockies will keep H5 heights locally dampened in a 576-582dm range
today with only modest increases through the weekend as the core of
lower heights aloft translates into the Great Lakes. A more split
flow regime will predominate over the western Conus early next week
as high amplitude ridging through the Pacific Northwest is undercut
by an active subtropical jet into the Southwest. The end result will
be temperatures oscillating not horribly far from the seasonal
average, yet potentially better moisture availability than would be
expected at the end of May.

The majority of height falls and cooling aloft has locally
stabilized as the primary troughing circulation spins over the
Rockies and the trailing trough axis becomes less defined into the
Southwest. As a result, cooling around the H8 layer will be
maximized today with afternoon highs some 4F-8F cooler than
Thursday. Low level thermal profiles will rebound rather quickly
through the weekend with most lower elevation communities once again
breaching the 100F threshold (and very close to the seasonal normal)
by Sunday. Otherwise, any remaining strong winds will abate with the
weakening pressure gradient this morning; and only the more typical
afternoon gusts will prevail through the weekend.

Through the first half of next week, a more active subtropical jet
will bring at least one lower amplitude disturbance into the
Southwest domain though the details regarding timing, intensity, and
moisture availability remain varied among ensemble member output.
Ahead of this wave, heights and temperatures aloft will temporarily
spike and pockets of afternoon highs in a 105F-110F range will be
common Monday and Tuesday. Taking a GFS/ECMWF blend (which also
approximates a full ensemble blend), a quasi-cutoff feature will
drift into the Baja/northern Mexico allowing substantial backing of
winds in the H8-H7 layer through the four corners. Most model output
suggests notable moisture advection up the Rio Grande Valley and
juxtaposed with weakly forced ascent associated with the shortwave,
isold/sct thunderstorms will be possible along the Rim, White
Mountains, and portions of southern Gila County.

The forecast for the second half of next week remains highly
uncertain with model spread growing abruptly in a partially blocked
flow pattern. Have mostly ignored the operational 00Z GFS and its
follow-up deeper shortwave and closed low as an outlier versus
almost all other ensemble members. The 00Z ECMWF looks far more
agreeable when compared to other medium range guidance keeping an ill
defined trough lingering towards the four corners and yielding a
forecast very close to climatology.


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

Dry westerly flow aloft will result in clear skies and lighter
afternoon winds through Saturday. Through 06z Sat, clear skies. West
wind 5 to 10 knots. From 06z Sat through 20z Sat, clear skies. Light
south to southeast wind under 7 knots.

Aviation discussion not updated for amended TAFs.


Monday through Friday:

A return to above normal temperatures will occur Monday as high
pressure builds across the Great Basin. Dry conditions will also
persist though winds will generally be light. A weak Pacific low
pressure system will develop and move eastward towards the Southwest
and could result in a slight chance for thunderstorms across the
higher terrain of east-central Arizona, including southern Gila
County, Monday through the latter portion of the work week. Any
associated rainfall totals would likely be very light, and there is
some potential for isolated dry lightning strikes. As the weak low
moves east and across the area high temperatures will gradually
trend back towards seasonal normals. Minimum RH values across the
deserts will mostly range between 10 and 18 percent each day, with
higher amounts over the higher terrain of southern Gila county
expected as moisture returns from the east.


Spotter reports will not be needed through the middle of next week.


CA...Wind Advisory until 3 AM PDT Saturday for CAZ562.


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