Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 270320

Area Forecast Discussion
National Weather Service Phoenix AZ
820 PM MST THU MAY 26 2016

A broad area of low pressure will persist over the western United
States through the beginning of next week yielding somewhat cooler
than normal temperatures and dry conditions. Strengthening high
pressure much of next week will finally bring a warming trend with
high temperatures pushing near 100 degrees by the middle of the week.


Upper trough heights are slow to exit the Southwest States and Four
Corners today allowing for one more afternoon of mountain showers and
thunder across northern portions of the state. Far enough removal
from the upper cold core of this system kept conditions across our
forecast area dry with sensible weather notes some very limited CU
coverage and still breezy afternoon conditions. Cooler temperatures
were also felt and enjoyed across the area, with Phoenix coming in 13
degrees below late May normals. We peaked at 85F today with today`s
normal value at 98F. Dry northwest flow is transitioning into the
area from the west part of the downstream flank of a broad Pacific
high pressure circulation. After mild temperatures today and tonight
we`ll be looking for a warm-up into the holiday weekend back solidly
into the 90s and even warmer by next week as the upper ridge boosts
area thicknesses and subsident motion over the region.


The center of a seasonally deep midtropospheric wave has shifted
very near the four corners early this afternoon with large scale
synoptic ascent focused downstream into the southern Rockies and
plains states. Shallow convection had rapidly developed over NE
Arizona in concert with strong sfc heating and unusually cold
temperatures aloft. Putting this system into context, KFGZ 12Z
sounding sampled H5 temperatures at -21.1C which is a record low for
the date; and virtually all other midlevel height and temperature
parameters fall in the lowest 95th percentile for the end of May.
While some deeper convection and showers are likely over higher
terrain the remainder of the day and into this evening, steering flow
will deflect action away from the local forecast area while stronger
subsidence rotates into the region behind behind the circulation

Objective analysis already indicates modest warming and height rises
aloft, which will only escalate in magnitude on Friday. However,
some measure of broad troughing will still linger through the region
limiting the total amount of warm air advection aloft. Given the
late May sun angle and clear skies, insolation and deep mechanical
mixing should compensate somewhat for the cooler environment in the
midlevels; and afternoon highs should rebound some 5F or so from
Thursday readings. A near persistence type forecast will prevail
through the entire holiday weekend as a weak negative remains quasi-
stationary over the SW Conus and H6 heights hover in a 576-582dm
range. Guidance spread through this period remains unusually low
with standard deviations between models generally only 1F returning
excellent forecast confidence of a pleasant holiday weekend.

Heading into the middle of next week, ensemble guidance becomes more
chaotic and unsettled as solutions start to diverge between members.
However, the preponderance of the guidance suggests that the large
scale western CONUS trough break down and shift east as an upper
ridge develops along the west coast. This will lead to continued dry
but warmer conditions Tuesday through Thursday. By Tuesday, the
warmer western deserts should eclipse the 100F with another couple
degrees of warming likely by Wednesday. Phoenix will approach 100F
Tuesday and likely breach this threshold beyond that. However, this
is hardly unusual for the beginning of June where average highs sit
at 100 anyways.


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

Dry northwest flow aloft is transitioning into the region and will
promote continued clear skies and lighter winds than experienced over
the last few days. Phoenix area terminals will see easterly AM winds
return, possibly a few hours lagged than usual with light
southwesterly winds carrying on through the evening. Typical
directional headings developing for KIPL and KBLH with light speeds
overnight. No weather impacts to aviation operations to occur for the
TAF period.

Aviation Discussion not updated for amended TAFs.


Sunday through Thursday...
With a dry airmass still in place, continued warm daytime high
temperatures in the mid 90s through Monday will warm up to the upper
90s to near 100 on Tuesday and nudge as high as the upper 90s to
lower triple digits beginning Wednesday. Occasionally breezy
southerly and southwesterly winds are expected each afternoon
beginning Monday with gusts of 15 to 20 mph, then winds becoming a
bit more breezy on Wednesday with gusts of 17 to 23 mph. Along with
the warm weather will come minimum relative humidities in the 8 to
12 percent range beginning Monday and lasting through the end of the


Spotter activation is not expected.




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