Area Forecast Discussion
Issued by NWS Phoenix, AZ
FXUS65 KPSR 301154
Area Forecast Discussion
National Weather Service Phoenix AZ
454 AM MST Sun Apr 30 2017
.UPDATE...Updated Aviation and Fire Weather Discussions...
One more day of slightly below-normal temperatures can be expected
today, before a substantial warming trend into next week. The
first 100 degree temperatures are likely Thursday and Friday
across the Phoenix metro. Dry conditions, mostly clear skies, and
generally light winds will prevail throughout the week as high
pressure builds over the Southwest.
A pronounced midlevel cyclone was located over central Kansas this
morning, with much of the Southwest remaining in dry
northwesterly flow. Broad cyclonic flow will persist across much
of the interior CONUS as this feature advances northeastward into
the upper Mississippi Valley, keeping heights aloft suppressed for
at least another couple days. Slightly below-normal temperatures
are a safe bet for today across south-central Arizona, where highs
will remain in the 80s across the lower deserts. A weak upper
disturbance will move southeastward across the Great Basin on
Monday, but will not have much influence on sensible weather, and
the warming trend will continue unabated as widespread highs in
the 90s make a return.
The trend for rising heights will continue through mid-week as an
amplified ridge builds across the Intermountain West.
Consequently, the first 100 degree day of the year for Phoenix
appears likely to occur on Thursday, with temperatures peaking on
Friday. The current forecast appears to be just shy of record
levels on Friday (record high of 105 for Phoenix). Additionally, a
modest increase in moisture aloft may occur across the Southwest,
and support the development of a few very light showers across
the higher terrain during the afternoon on Thursday and Friday,
but chances for any measurable precipitation still appear minimal
at this time.
In the extended period, models continue to signal a major change
in the large-scale pattern with the development of an anomalously
deep closed low along the Pacific coast. Details are quite murky
at this time, especially this far out, but the expected slow-
moving nature of this system should draw in sufficient moisture
for showers across parts of the Southwest. Much cooler
temperatures are also a possibility, along with strong south
winds, but with a tight baroclinic gradient surrounding this
feature, narrowing down specific values at this range is difficult
as the forecast will be very sensitive to the exact track of this
system. Nevertheless, it will be worth monitoring closely
throughout the week.
South-Central Arizona including KPHX, KIWA and KSDL:
Timing wind shifts will be the only real aviation consideration
through tonight under clear skies. Winds will generally remain
below 10 kts, but some gusts this afternoon may exceed 15 kts.
Southeast California/Southwest Arizona Including KIPL and KBLH:
No major aviation concerns through early Monday. Winds will mostly
be on the light side, but some afternoon breeziness is likely,
especially at KBLH.
Aviation discussion not updated for amended TAFs.
Tuesday through Saturday:
A ridge of high pressure will slowly build over the west next
week with the lower deserts making another run at 100 degrees
during the latter half of next week. No strong wind events are
anticipated. Minimum humidities will remain low - below 15% for
most areas with the low deserts generally in the single digits.
Overnight recoveries will range from 25-35% and up to 40% in the
elevated portions of Gila county. Low pressure will likely
approach the region on Saturday allowing for cooler temperatures,
but a drastic increase in winds and fire danger.
.SPOTTER INFORMATION STATEMENT...
Spotter reports will not be needed through at least the middle of
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