Area Forecast Discussion
Issued by NWS Phoenix, AZ
FXUS65 KPSR 252054
Area Forecast Discussion
National Weather Service Phoenix AZ
154 PM MST MON JUL 25 2016
.UPDATE...Updated Fire Weather 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.
Storms underway across the Mogollon Rim this early afternoon and
along the weak 300/200mb jet streak/deformation zone draped across
the Four Corners. While wind speeds are not overly strong, the
gradient between calm winds and 30kts this AM along with the
stretching motion between ridge flow to our east and IT/MCV
circulations to our Southwest have unweighted enough of the
atmosphere. Still ample moisture surface in place and some available
instability, however last few frames of SPC Mesoanalysis page
indicate plenty of CIN covering SW AZ and much of Maricopa County
currently. Also southeast AZ is still quiet, slowly clearing of
debris clouds from this early morning`s Sonoran convection.
Storms over the eastern/northern AZ mountains will continue and
eventually fill down into the higher terrain of Southern Gila County.
Cannot rule out some isolated activity on the foothills on the
eastern periphery of the Phoenix Metro, but even isolated coverage
into the Lower Deserts looks slim tonight. As with previous evenings
across the Deserts, Rim convection will send some outflow winds into
the Lower Elevations and given how quiet SE AZ remains at time of
this writing, that looks to be the only outflow game in town tonight.
Relying on intersecting outflows to tap into already marginal CAPE
fields, unless southeast AZ starts to fill in rapidly, storms should
generally stay over the mountains tonight for Phoenix. For points
west of Phoenix, additional debris clouds will continue to move
across the desert from Mexico, clearing to the west/northwest through
the evening. The forecast for Tuesday looks to be similar to today,
with generally low-grade Monsoon pattern continuing and
destabilization of the atmosphere reliant on where debris clouds
linger from this evening`s activity.
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. Morning forecast guidance and limited model spread
increased confidence enough to add a degree or two to forecast values
as UL ridging settles overhead. 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.
Thursday through Monday: A warming and drying trend is expected
through Thursday as high pressure builds across northern Arizona.
Some increase in convective activity is expected Friday through
early next week 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
.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected.
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