Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 250916
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
216 AM MST Thu May 25 2017

.SYNOPSIS...
The high pressure system over the region that produced above normal
afternoon temperatures will weaken tonight as several weather
systems move into the western states. Although dry weather is
forecast, gusty afternoon southwest winds can be expected through
Saturday. Also, afternoon temperatures on the lower deserts will
cool into the 90s, or below normal temperatures. Dry weather with
warmer temperatures are expected beginning Sunday and continuing
through next week.

&&

.DISCUSSION...
Considerable high level cloudiness spans much of the AZ and SE CA
International Border this early morning, moving SW to NE. Upper
ridge axis that brought us a stretch of warm weather has cleared
well to our east this morning as broad troughing spans from the
central Canadian provinces, down through the northern Rockies and
through northern CA. Subtropical jetstreak enhancement began last
evening over Baja California, evident in cirrus blowoff over the
Baja Spine streaming into the area overnight. Mid-level height
falls and 1000-500mb thicknesses have begun to trend downward as
troughing sinks and turns to swing into the area. Combination of
height falls and upper jet proximity have created gusty pass level
winds across southeast California already this evening and those
will persist as well as expand down into the lower desert
elevations with the strongest winds focused along and west of the
Colorado River Valley. Gusts for the western CWA and southwest
Arizona will range 30 to 40 mph by the afternoon and 20 to 30 mph
for the south-central AZ deserts. Visibility and air quality
impacts are anticipated in the dust/sand prone areas, especially
across southeast California. Subtle CAA and theta-E ridging will
support a temperature cool down starting today with 8 to 12
degrees of cooling anticipated. Temperatures will cool further
still as troughing persists over the Great Basin and Southwest for
the end of the week and early weekend, with slightly below normal
temperatures forecast through Saturday.

High amplitude ridging will build back over the West Coast over
the weekend and transition back into the Southwest for Sunday and
Monday. Desert temperatures will head north of triple-digit
readings again.

By late Monday and into early next week, high amplitude wave
pattern over the Pacific and western CONUS will begin to be
undercut by a strong Pacific jet. A piece of energy becomes
cutoff from the upper jet streak/storm branch, developing off-
shore northern Baja Tuesday. To our east, high pressure
circulation will develop over TX through the 850-700mb layer. Low
and mid-level flow will become southerly in nature, drawing
moisture northward into the eastern portions of Arizona. Slight
chances for afternoon and evening thunderstorms remains for the
eastern most portions of southern Gila county through midweek.
Breezy south to southwest winds are also expected to reappear
Tuesday and Wednesday afternoons. Temperatures will trend slightly
cooler with more atmospheric moisture and lower heights in the
region again, near late May/early June normals.

&&

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

Moderate to strong southwesterly flow aloft will continue through
Thursday. Southwest and west breeziness will continue to weaken
tonight (more slowly over the Imperial Valley). Breeziness returns
Thursday afternoon. In between, for metro Phoenix, anticipate a
period of relatively light southeasterly surface winds (roughly
09Z-17Z). Otherwise, expect the mid-high high clouds to continue
decreasing from west to east.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
Saturday through Wednesday:
Wind speeds will weaken by Saturday, compared to earlier in the
week, as a pronounced area of high pressure builds over the Great
Basin. Temperatures will also be near or slightly below seasonal
normals on Saturday, with highs in the low-mid 90s. Warmer
temperatures will occur by Sunday, with highs near 100 degrees,
and will remain similar each day through the middle of the week.
Winds will also be generally light during this period.

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. However, confidence in any rain or
lightning potential is still low this far out.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter reports should not be needed.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory until 5 AM PDT Friday for CAZ562.

     Wind Advisory from 2 PM this afternoon to 5 AM PDT Friday for
     CAZ566.

&&

$$

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DISCUSSION...Nolte
AVIATION...AJ
FIRE WEATHER...Vasquez


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