169
FXUS65 KPSR 121110
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
410 AM MST Mon Aug 12 2024

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
Showers and storms will be again be possible this afternoon and
evening, but activity will mainly favor the higher terrain
locations. Drier air will work it`s way into the region for the
middle of the week causing a significant downtrend in monsoon
activity. Moisture looks to rebound slightly by the end of the
workweek and heading into the weekend leading to storm chances
returning to the region, mainly for the higher terrain locations.
Temperatures will remain largely unchanged through the week and run
slightly above normal.

&&

.DISCUSSION...
The overall synoptic pattern remains largely unchanged from the past
few days. The subtropical high pressure system is still centered
over Texas and stretches back westward into eastern Arizona. The
weak upper-level cyclonic circulation also remains situated over the
northern Baja peninsula. There is also a polar trough starting to
digging off the coast of the Pacific northwest. The leftover MCV
from yesterday morning`s activity can still be seen spinning in
southwestern Arizona and is slowly making its way into southeastern
California. Another weak mid-level wave can be seen in northwestern
Mexico and it is expected to move into southeastern Arizona later
this afternoon sparking convection down there. PWATs are in the 1.5-
1.7" range with this wave and the leftover MCV in southwestern AZ,
elsewhere PWATs range from 1.0-1.4" across the region. This is ample
moisture to support the development of storms later today,
especially in the higher terrain of Arizona. The environment does
support some showers and storms across south-central AZ, including
the Phoenix Metro, this evening. Latest forecast soundings show
MUCAPE values in the 1000-1500 J/kg range and do not show much in
the way of convective inhibition for this afternoon and evening. One
thing that may limit storms across the lower deserts this evening is
the lack of moisture. Models have been over doing PWAT values by
~0.2" and are initializing with PWAT values too high. Hi-res
guidance does continue to show storm activity struggling to survive
into the lower deserts this evening. With southerly/southeasterly
flow in place, convection surviving into the lower deserts tonight
will likely depend on how robust the storms in southeastern Arizona
get later today and if we can get deep/colliding outflow boundaries.

Tuesday will be the transition day for the overall synoptic pattern.
The aforementioned polar trough will continue to dig into the
Pacific northwest. This will lead to drier air starting to make its
way into the region, especially across the lower elevations. With
this drier air starting to make its way into the region any storm
activity on Tuesday afternoon and evening is expected to remain
across the higher terrain of eastern Arizona.

A big pattern change is still expected for the middle to latter half
of the workweek. The polar trough will continue to move into the
Pacific northwest causing the subtropical high pressure system to
relax and stretch out even more. With this pattern change we will
see the flow aloft become southwesterly, which will user in drier
air with PWATs decreasing to around 0.8-1.2" across the CWA. This is
unfavorable for monsoonal activity and will likely result in little
to no shower or storm activity across the CWA for the middle part of
the week.

Heading into Friday and the weekend, the subtropical ridge will
start to build once again across the southern Plains. This will
result in a return to southerly/southeasterly flow aloft. This shift
in the flow pattern aloft will allow for a slight increase in
moisture, with global ensembles showing PWATs returning to the 1.2-
1.4" range across the CWA. This increase in moisture will result in
an increase in shower and storm activity, with most of the activity
expected to be confined to the higher terrain locations.

Temperatures this coming week are forecasted to remain largely
unchanged. For the lower desert communities, afternoon high
temperatures are forecasted to be in the 100-110 degree range
through the week. For the higher terrain areas, afternoon high
temperatures are forecasted to be in the 90-100 degree range.
Thursday and Friday are currently forecasted to be the hottest days
of the week. With temperatures being near to slightly above normal,
HeatRisk will be in the Minor to Moderate range across the region.

&&

.AVIATION...Updated at 1110Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Chances for at least one outflow boundary and abrupt wind shift with
isolated storms on the fringes of the airspace this evening will be
the greatest weather concerns. Winds this morning may not fully
complete the easterly switch, and variable directions may be more
common before returning to a westerly fetch prior to noon. Cloud
decks 080-120ft AGL should also start to develop over higher terrain
areas with daytime heating.

Models suggest the most likely outcome being southerly outflows
sweeping into the metro early evening though other directions cannot
be completely precluded. If storm origins are more to the SW, then
outflows may become absorbed into the general west flow and not
create any immediate operational impact. Chances of direct TS
impacts are under 20%, so not included in this TAF package.
Eventually by mid/late evening, forecast confidence is moderate that
E/SE winds will eventually envelop the metro and predominate at all
terminals through the overnight.


Southeast California/Southwest Arizona including KIPL and KBLH:
Only the outside possibility of isolated TSRA around the region would
pose a weather impact under mostly clear skies. Any storm coverage
late this afternoon appears too isolated to include in this TAF
package. Otherwise, some form of a southerly wind component will be
preferred with occasional gustiness to 20 kt.

&&

.FIRE WEATHER...
Shower and thunderstorms chances will continue today, with the best
chances confined to the higher terrain locations. Shower and
thunderstorm chances tomorrow will be limited to just the higher
terrain locations. With any thunderstorm activity, there will be
strong winds along with the potential for gusty outflows to travel
long distances and cause sudden wind shifts. Thunderstorms will also
contain localized heavy downpours and frequent lightning. Drier air
will move into the region for Wednesday and Thursday with little to
no thunderstorm activity expected. Aside from thunderstorm winds,
the overall general winds will tend to follow their typical diurnal
tendencies with some afternoon upslope breeziness. MinRH values
today will be in the 20-30% range with a downward trend for the
middle of the week with MinRH values in the 10-25% range. Overnight
recoveries will be in the 30-50% range. Temperatures though the week
will remain largely unchanged and run near to slightly above normal.

&&

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

&&

$$

DISCUSSION...Berislavich
AVIATION...18
FIRE WEATHER...Berislavich