Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 262109

Area Forecast Discussion
National Weather Service Phoenix AZ
209 PM MST Wed Jul 26 2017

.UPDATE...Updated aviation and fire weather discussions.


Drier air moving into the region will result in a lower chance of
storms for much of the work week. Decreasing cloudiness and
moisture will support a warming trend through Thursday with near
normal highs. Moisture begins increasing late Thursday and will
usher in an increased chance of storms across the CWA Thursday
night through the weekend. Subsequently, high temperatures
decrease as well...most noticeably over south-central Arizona.


Quiet weather will continue through the day where our most
concerning question is to see just how hot temperatures will
climb. Phoenix has already hit a high of 103 degrees, before 1PM,
so adding three or perhaps four degrees to that figure is not out
of the question. A study of the GOES-16 visible satellite reveals
mostly clear skies but for some high clouds filtering through the
area. The 500 millibar high pressure situated over central New
Mexico is allowing for drier southwesterly air aloft to filter
over the area. This morning, surface dew points were still in the
mid 60s through parts of central Arizona while the sounding
revealed a much more delightful 1.6 inches of precipitable water.
Even better, we should see the PW values drop a little more
through the next day or two. The lower desert will have very
little, if any, CAPE to work with during the next two days.

In addition, the atmosphere over much of Arizona will endure some
warming aloft. At 12Z, the Phoenix sounding indicated the 500 mb
temperature was a little cooler than -4 deg C, and the
southwesterly flow aloft will help warm that layer an additional
degree or two by tomorrow. An isolated storm or two might be
possible over the mountains in Gila County tonight and Thursday,
but with nearly no CAPE and warming aloft, one would be hard
pressed to find much convection over the lower desert. However,
the drier atmosphere will lead to slightly warmer temperatures
peaking 2-5 degrees above normal.

Thunderstorm chances creep back into the area by Friday evening.
The center of the 500 mb high migrates a closer to the Four Corners
which will induce a more storm-favorable southeasterly wind flow,
and allow additional moisture to penetrate into the area. There
are also a few disturbances rotating around the 250 mb high, which
is centered over the south-central US, that will enhance
atmospheric dynamics to be more supportive for storm development
as they move closer to the region. While day-to-day variability
will matter, storm chances will remain in the forecast into early
next week. Although the best chances for rain will remain over the
higher elevations, all places across the CWA will have at least a
shot at some rain. Moreover, the additional moisture will also
usher in high temperatures a few degrees below the seasonal



South-Central Arizona including KPHX, KIWA, and KSDL:
Very few aviation weather concerns looking into tonight. Winds
will remain relatively light and follow typical diurnal
directional patterns. No real chance for storms at the terminals
with mostly some passing high clouds overhead.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will remain relatively light and favor a southerly
direction. No real chance for storms with only a few passing high
clouds. Otherwise, no major aviation weather concerns through

Aviation discussion not updated for amended TAFs.


Saturday through Wednesday:
Thunderstorm chances will remain in the forecast through the
weekend with all locations having at least a decent chance and
rain. Storm chances decrease through Wednesday, with the best
chances by then being confined mostly to the higher terrain north
and east of Phoenix. Given the moisture levels, minimum relative
humidities will stay well above 15 percent with good overnight
recoveries. Winds will otherwise be light outside of any
thunderstorm related winds.


Spotters should follow standard reporting procedures.




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