Area Forecast Discussion
Issued by NWS Phoenix, AZ

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050
FXUS65 KPSR 261005
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
305 AM MST Wed Apr 26 2017

.SYNOPSIS...
A series of mainly dry Pacific weather disturbances will move across
the western states through early next week. These systems will keep
afternoon temperatures near or slightly below normal, along breezy
afternoons and evenings. One stronger disturbance on Friday will
likely bring windy conditions and has the potential to produce a
slight chance of afternoon showers over the eastern Arizona
mountains.

&&

.DISCUSSION...
An upper level trough axis has shifted well into New Mexico early
this morning with increasing subsidence and modest warming aloft
over SE California and Arizona. The warming aloft will lead to
highs increasing a few degrees over Tuesday`s readings with the
Phoenix area reaching near 90 degrees and the SE California and SW
Arizona lower desert locations reaching into the lower 90s. Winds
will again be breezy today, but gusts should mostly remain below
25 mph. Similar conditions are expected for Thursday as dry
northwest flow continues.

Much better model agreement is now shown for the next low
pressure trough bringing a closed low southward through eastern
Utah into the Four Corners area Friday night. This will bring a
cold frontal boundary southward through Arizona Friday afternoon
through early Friday night. Some limited mid level moisture ahead
of the front will likely result in some scattered showers and a
very remote chance of a thunderstorm over the high terrain north
and east of Phoenix. Can`t completely rule out a shower or two
making it off the high terrain into the south-central Arizona
deserts, but a very dry sub-cloud layer should only result in
virga or sprinkles. Very dry air will usher in behind the cold
front with surface dew points likely crashing into the single
digits late Friday afternoon and evening. Another windy day is
likely on Friday with a high likelihood of some areas being under
Wind Advisory. The strong winds and lowering humidities on Friday
will likely bring dangerous fire weather conditions once again.

Ahead of the cold front on Friday, highs should reach into the
upper 80s across the deserts. Cooler air ushering in behind the
cold front will allow for a fairly mild but breezy day on
Saturday as highs should only top out between 80-85 degrees.
Rapidly building heights and warming aloft will take place
Saturday night into Sunday as the upper level trough shifts
eastward into the Southern Plains. This will return temperatures
back to near normals on Sunday and a few degrees above normal for
Monday.

Considerable model spread exists after Monday with potential for
yet another upper level trough digging southward through the Great
Basin and Four Corners area. The operational GFS is on the
extreme side bringing a closed low through eastern Arizona while
the operational European keeps it much farther north and east,
essentially showing ridging over the Desert Southwest. The GFS
and European ensemble means are somewhere in between the
operational solutions. For now we are keeping our forecast mainly
based on the ensemble means calling for near normal temperatures
with continued dry and breezy conditions.

&&

.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL:

Wind gusts have become less frequent this evening, but westerly
winds around 15 kt are persisting across Phoenix area terminals.
Should expect to see a continued weakening trend into early
Wednesday morning, with an eventual shift to an easterly direction
occurring after 12Z. Westerly winds will strengthen once again
Wednesday afternoon, but will be weaker than Tuesday, around 8-14
kt at the surface. Cloud cover will also decrease through
Wednesday morning, remaining above 25 thousand feet.

Southeast California/Southwest Arizona Including KIPL and KBLH:

Westerly winds around 10 kts should persist through much of the
next 24 hrs across KIPL and KBLH, with only a modest strengthening
expected Wednesday afternoon. Little to no cloud cover is
anticipated.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Friday through Tuesday:

Temperatures will continue to hold at or above seasonal averages
today, with minimum RH values mostly below 15 percent as dry
northwest flow aloft persists over the area. Expect afternoon
westerly breezes especially over south central Arizona. A cooling
trend will settle into the region as mostly dry storm systems sweep
through the Great Basin and down through the Southwest. Outside of a
slight chance at some light showers over high terrain of Gila County
Friday into Saturday, widespread dry weather will cover the
districts. Dry afternoons with 5-10% will be common with overnight
humidities varying between mostly fair to good. Active storm track
through the West will keep afternoons breezy for the district, with
upslope west winds and occasional gusts possible through week`s end.

There continues to be potential for widespread dangerous fire
weather conditions Friday into Saturday as windy conditions develop
across most of the area - especially south-central Arizona on Friday
- and minimum RH values drop into the single digits across much of
the lower desert. The cooling trend may help mitigate some of the
fire danger potential however but this is something to keep our eyes
on as we move towards the latter part of the week.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter activation will not be needed through the middle of next
week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

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DISCUSSION...Kuhlman
AVIATION...Rogers
FIRE WEATHER...Hernandez



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