Weather Service Report

FXUS65 KPSR 241122

Area Forecast Discussion
National Weather Service Phoenix AZ
422 AM MST MON OCT 24 2016

.UPDATE...Updated Aviation Discussion.


A low pressure system northwest of the region continues to draw a
considerable amount of subtropical moisture into the Desert
Southwest. This will lead to a threat of isolated showers and
thunderstorms through tonight. Showers and a few thunderstorms are
possible over southeast California and southwest Arizona through
early afternoon and then mainly late this afternoon and early
evening over south central Arizona. Drier and warmer conditions will
return by the middle of the week.


The potential for showers and thunderstorms today continues to
dwindle, but the chance is still there. Model advertised moisture a
couple days ago briefly had levels reaching near max climo values,
but models have since backed off some. PWATS will still likely reach
near 1.25 inches in some locations which is plenty sufficient for
this time of year. Even with this decent moisture, the lack of any
strong forcing mechanism will pose a problem for shower and
thunderstorm development. Thus far a few showers have been seen
across La Paz county, but the bulk of the overnight activity has been
to the west of our area.

Much of this moisture is a result of the increasing southwesterly
flow to our west, well south of the deep Pacific low off the Pacific
NW coast. As moisture levels increase today, a strong upper level jet
max will also nose into our region. Positioning of the jet max favors
areas to our northwest for better divergence aloft, but we will
remain under an overall weak difluent region for much of the day.
Latest hi-res convective allowing models show little development at
all today, but global models along with the SREF still point toward
at least some activity over our CWA today. As other previous shifts
have done, we have again trimmed PoPs some with mostly slight
chances remaining over the lower deserts and low end chances over
higher terrain areas. Best chances for any thunderstorms today will
first be over La Paz County late this morning into early this
afternoon, closer to the favored left front entrance region of the
jet. Another area of thunderstorm potential will be over south-
central Arizona late this afternoon and early evening as a weak
shortwave trough moves through. This area should destabilize enough
due to better diabatic heating resulting in CAPES of a few hundred

Much drier air aloft will overtake the region from west to east
starting late this evening as the jet max shifts into New Mexico.
Low level moisture will remain over most of Arizona into Tuesday
which may give rise to a few showers or maybe a thunderstorm over the
higher terrain of east-central Arizona. Flow aloft turns out of the
northwest as upper level ridging pushes northward out of Mexico.
500mb heights rebound quickly with 585dm heights already over the
area by Tuesday afternoon. This will lead to another warming trend
for the middle of this week. Highs may approach record levels in some
areas with readings likely topping out into the 90-95 degree range
starting Wednesday. This upper level ridge will get displaced
slightly to the east late Thursday into Friday as a strong upper
level low moves east northeastward toward the central California
coast. Much of the moisture with this system will remain over
California with only slight chances of showers over southeast
California. The displaced upper level ridge is forecast to remain
just to our east through the coming weekend keeping temperatures well
above normal with little to no chance of any rain.


.AVIATION...South-Central Arizona including KPHX, KIWA, and KSDL:
Southeast California/Southwest Arizona including KIPL and KBLH:

The next weather system will result in increasing mid- and high-
level clouds and a chance for showers and storms through the TAF
period. The greatest chances will exist over KBLH and KIPL this
morning through early this afternoon and over KPHX, KIWA, and KSDL
early this afternoon into this evening. Since activity will be more
sparse in nature, there is low confidence in exact spatial coverage
of storms. However, due to more favorable conditions this afternoon
and evening in south-central Arizona, have mentioned VCSH for Phoenix
terminals during the later part of the period. Outside of any
storms, winds will remain on the light side, mainly aob 10kts, and
follow normal diurnal headings. Skies will remain mostly cloudy, with
cloud heights generally aoa 10kft. 

Aviation discussion not updated for amended TAFs.


Wednesday through Sunday... 

High pressure redeveloping over the Desert Southwest will bring dry
conditions and well-above normal temperatures to the region on
Wednesday and Thursday. Another weather system brushes the Desert
Southwest late Thursday through Friday for an increase in humidities
and a slight chance of showers - mainly for southeast California and
southwest AZ. Warmer and drier weather is expected to return for
next Sunday. No strong winds are anticipated through the forecast
period. Minimum humidities stay near 20% and overnight recovery
remains at least good.


Spotters should follow standard reporting procedures. 




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