Area Forecast Discussion
Issued by NWS Phoenix, AZ
FXUS65 KPSR 251800
Area Forecast Discussion
National Weather Service Phoenix AZ
1100 AM MST MON JUL 25 2016
.UPDATE...Updated Aviation Discussion.
An increase in moisture and cloud cover over the region is expected
to take some edge off the heat and provide somewhat better chances
of showers and thunderstorms through the middle part of this week.
The best opportunity for rainfall will occur over the higher terrain
north and east of Phoenix, with lesser chances heading west into
southeast California. A better chance for showers and thunderstorms
is then forecast for the end of the week and into the upcoming
weekend, as deeper moisture begins to move into the region from the
south and southeast.
Debris clouds will continue to thin into the late morning as several
MCVs travel westward across the region. Morning satellite loops
indicate two, possibly three, separate circulations skirting through
the area. The first over northern Baja, second exiting Sonora into
the GoCA and third weakly moving over central portions of the Rim
this AM. In addition, broader mid-level IT/wave activity was
analyzed over ABQ down through Chihuahua this AM. Broad weak deformation
zone noted on satellite loops and morning RAOB charts as well, with
300/200mb winds over portions of the Four Corners 25-30kts with calm
UL winds over the southern Rockies/New Mexico. This morning looks to
be a near repeat of the past couple mornings, including Mexican
convection getting a much later start into the evening and clouds
tops warming/decaying even early into our shift. Also received
another GoCA surge event this AM, albeit fairly shallow, wrapping
into the Phoenix area and producing westerly AM winds. 12z RAOB from
the Yuma Proving Grounds indicates quick drying off the surface...but
still averaging about 10 g/kg to just above the 850mb sfc before
further drying occurs below morning LCL.
Conceptually today should play out like the past few afternoons, with
activity developing over the Rim first after midday while
southeastern AZ will get a later into the day start on their storms.
Handful of CAMs today converging on a outflow-driven/fairly isolated
storm coverage solution for the Phoenix area. Outflow intrusion
possible from the north to northeast by the early evening hours,
reducing initial concerns for dust from that direction. While LL
moisture remains somewhat excessive in terms of the Monsoon profile,
fair bit of sounding CIN, warming of the 500mb sfc from the southeast
by the afternoon (forecast temps progged to go from -7C on the
current RAOBs to approx -4C) and reliance of several outflow
intersections to capitalize on any instability later into the day
makes chances for storms look rather low for the Phoenix Metro today.
Scaled back PoPs slightly for the evening while increasing values on
the periphery from Wickenburg through southern Gila County.
.PREVIOUS DISCUSSION /Issued at 440 AM MST/PDT/...
Today through Tuesday...
Lack of available moisture and rather warm air aloft (500mb temps in
the -5C to -6C range) is expected to limit the amount and coverage of
any showers/storms that do develop, with the greatest threat for most
locations being gusty winds/blowing dust. The forecast for Tuesday
looks to be similar to today, although convective activity could be
reduced somewhat if significant debris cloudiness from today`s storms
lingers very long into Tuesday morning.
Wednesday and Thursday...
A reduction in convective activity looks likely during this period
as ridging aloft strengthens over the region and some drying of the
airmass occurs. 500mb heights are expected to approach 596dm by
Thursday, with many lower desert locations once again seeing highs
at/above 110F. The euro is the most aggressive model in terms of the
warming, taking the high at Phoenix Sky Harbor all the way up to
116F on Thursday! However, we are currently leaning towards the
somewhat cooler GFS, since lingering moisture/cloudiness is expected
to hold temperatures down somewhat. Convective development during
this period will likely be mainly confined to the higher terrain
north and east of Phoenix, with just a few storms (at most) making
their way into the lower deserts each day.
Friday through Sunday...
Although we are still expecting a uptick in the monsoon activity
during this period, as easterly winds aloft increase and moisture
levels rise further, there now appears to be a drying trends showing
up in the latest model suites, especially on Friday. This is likely
due to the fact that the global models seem to be having a tendency
so far this summer to weaken the upper-level ridging that has
persisted over our region too much, and also pushing the main ridge
axis too far to our north. This results in the airmass ending up
drier and more stable, resulting in less convective activity.
South-Central Arizona Including KPHX, KIWA, and KSDL:
Scattered showers and thunderstorms are expected to develop across
the higher terrain north and east of Phoenix this afternoon. Latest
model guidance suggests an outflow boundary from these storms will
move into the Phoenix area this evening. Best estimate on timing is
around 03z with winds out of the north or east. Gusts have the
potential to reach 30 kt as the boundary moves through. Easterly
winds will then persist overnight before becoming light and variable
Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation weather impacts anticipated. Winds will generally retain
a southerly component at both KIPL and KBLH, occasionally reaching 20
kt at KBLH through the period.
Aviation Discussion not updated for amended TAFs.
Wednesday through Sunday...
Monsoon moisture working its way back into the region will bring
chances for afternoon and evening thunderstorms each day. The best
chances for wetting rains will be over the higher terrain east of
Phoenix through the Friday with lesser chances over the lower
deserts of south-central and southwest Arizona and only slight
chances over southeast California. Some increase in convective
activity is expected this weekend as deeper moisture begins to move
into the region. Temperatures to remain slightly above normal through
the entire forecast period. Minimum humidities should fall in the
15-30 percent range through Thursday and rise into the 20-35 percent
range starting Friday.
.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected.
Visit us on Facebook...Twitter...and at weather.gov/phoenix