Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 271246 AAA
AFDPSR

Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
545 AM MST Thu Jul 27 2017

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

&&

.SYNOPSIS...
Drier air over our region will result in a lower chance of storms
for much of the work week. This will allow our warming trend to
continue into Thursday with highs slightly above normal. Moisture
begins increasing late Thursday and will usher in an increased
chance of storms across the CWA Friday through the weekend.
Subsequently, high temperatures decrease as well...most noticeably
over south-central Arizona.

&&

.DISCUSSION...

Another quiet evening across our CWA with just some high and mid
level clouds overhead associated with decaying convection to our
south and east. A 500 mb high continues to sit over New Mexico
putting much of our region under a southerly flow aloft. Models
continue to indicate that PW values will hit a minimum today
before a more moist easterly flow sets in. The latest sounding
from Phoenix (03Z) show about 1.5 inches of PW to work with today
although values will possibly drop slightly lower than that this
afternoon.

Temperatures this morning are running several degrees (+8 for
KPHX) above what they were at this time yesterday due to the added
cloud cover and warmer temperatures observed yesterday afternoon.
High temperatures will continue to warm today despite a subtle
lowering of 500 mb heights as no outflows moved through our area
yesterday to cool the boundary layer. While moisture across the
CWA is forecast to be slightly lower this afternoon, an
approaching easterly wave and a SE steering flow aloft should help
nudge convection into Gila County this afternoon. As these storms
march towards the valley later this evening, appreciable CIN
(150-200J/kg) and very little CAPE should prevent most, if not all
storms from moving into the valley. However, remnant outflows
could certainly move through the metro later this evening.

Depending on which model you are looking at, and even which run,
an abundant amount of mid level clouds (remnant from previous
convection) could move over south-central either Friday and/or
Saturday. This will certainly impact daytime temperatures which
should cool highs 5-7 degrees F over Thursday. However, this will
create a difficult forecast as additional cloud cover (and less
CAPE) makes it challenging to pinpoint which days could be more
or less active. For now, we have our PoP forecast following the
moisture trends, which will be increasing this weekend. Much
uncertainly lies beyond this period but a very gradual drying
trend seems to be evident in the numerical models. For now, have a
downward trend in PoPs next week with a slow rise in daytime
temperatures.

&&

.AVIATION...

South-Central Arizona including KPHX, KIWA, and KSDL:

Still expecting very slim chances for storms to affect the greater
Phoenix area today and this evening as storms should pretty much
remain confined to the higher terrain of southern Gila County.
Should any wind shifts occur, they would likely not happen until
after around 05Z when east/southeast winds would move in with speeds
mostly below 15kt. Otherwise, expect SCT-BKN mid and high decks this
morning with clearing by afternoon. Later this evening we should see
more mid and upper level debris clouds move in from the east with
CIGS genly 12k feet or higher. Light variable or light east winds
this morning at the terminals becoming west by 19-20z or so with
speeds 12kt or lower.

Southeast California/Southwest Arizona including KIPL and KBLH:

Another day with pretty much no chance for storms to affect the
western deserts or the TAF sites. We are looking at winds to persist
mostly from the south at KBLH with speeds below 15kt, and at KIPL
light west winds should turn southeast after noon before returning
to the southwest later this evening. Otherwise just occasional
mainly high cloud decks moving across the terminals. No real
aviation concerns at the TAF sites through tonight.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Saturday through Wednesday:
Thunderstorm chances will remain in the forecast through the weekend
with all locations having at least a decent chance of rain. Storm
chances then gradually 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 mostly above 20 percent with good overnight
recoveries. High temperatures will be mostly below seasonal normals
this weekend, then gradually climbing to slightly above normal
levels by Wednesday as storm chances dwindle and moisture decreases.
Winds will otherwise be light outside of any thunderstorm related
winds.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

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

$$

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DISCUSSION...Wilson
AVIATION...CB
FIRE WEATHER...Deemer/CB



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