Area Forecast Discussion
Issued by NWS Phoenix, AZ
FXUS65 KPSR 240921
Area Forecast Discussion
National Weather Service Phoenix AZ
225 AM MST TUE MAY 24 2016
.Update...Aviation and Fire Weather Discussions.
A large region of low pressure will continue over the Western States
through the weekend. There will be day to day fluctuations in
temperatures and afternoon breeziness as the system waxes and wanes.
Overall though, temperatures will remain below normal and conditions
will remain dry.
Early this morning, dry southwest flow aloft was present across far
southeast California as well as Arizona, as seen in the recent 00z
plot data and the regional soundings. PWAT values for Tucson were
below 0.40 inches and surface dewpoints over the lower central
deserts were mostly in the 20s at 2 am. IR imagery early this
morning depicted generally clear skies area-wide.
A large area of low pressure has been in place and impacting the
weather across the western CONUS for the past few days and there
will be very little change in this basic large-scale weather pattern
for the upcoming week. Dry southwest to west flow aloft will persist
day to day, keeping high temperatures below seasonal normals every
day, with warmer deserts typically ranging from the upper 80s to mid
90s day to day. There will be locally breezy conditions most days as
well although winds will not be strong enough to reach wind advisory
levels at any time. For the most part we can expect sunny days and
clear nights with just occasional mainly thin high clouds embedded
in the flow. GFS and ECMWF operational runs as well as ensemble
guidance has been very consistent with this large scale upper trof
and confidence in the forecast including cooler than normal high
temperatures remains high.
One feature of note: operational runs from the NAM, GFS and ECMWF
continue to call for a small closed upper low to move inland from
the far southeast California coast during the afternoon on Wednesday
and this low will quickly race northeast and across northern Arizona
overnight Wednesday night. Despite strong UVV ahead of this low,
with a large bullseye of mid level Q-convergence forecast, moisture
values will be too low to support any convection or precipitation
with this system for the most part. By the time moisture starts to
increase from the west, stronger DVV/subsidence will work in behind
the exiting low eliminating any chance for measurable rain. We did
raise POPs a few percent to around 10 percent over the higher
terrain of Joshua Tree National Park Wednesday afternoon however;
given the strong UVV and some mid level moisture creeping in, and
MLCAPE values near 200 j/kg advertised, we cannot completely rule
out a stray shower or weak storm over the high terrain at this time.
Otherwise this low will mainly give some breezy conditions to the
central deserts ahead of its passage on Wednesday afternoon, and
usher in a modest cooling trend to south central Arizona during the
day on Thursday. Expect Thursday to be the coolest day of the week
with highs falling into the middle 80s; Phoenix is forecast to fall
to 86 degrees which would be over 10 degrees below seasonal normals.
South-Central Arizona including KPHX...KIWA and KSDL... and
Southeast California/Southwest Arizona including KIPL and KBLH...
A low pressure system and associated dry cold front will move
through southern California and western Arizona this afternoon. The
airmass is relatively dry, however gusty southwest winds are
expected. Through 18z Tue, south to southeast wind 8 to 10 knots.
Clear skies. From 18z Tue through 03z Wed. Clear skies. Increasing
southwest winds 15 to 20 knots.
Aviation Discussion not updated for amended TAFs.
Thursday through Monday...a series of low pressure systems will
continue to move into the western states mainly north of Arizona.
Although dry weather is forecast, the proximity of the low pressure
systems to Arizona will result in breezy to windy afternoons, 15 to
25 mph each day. Minimum relative humidities will range from 10 to
15 percent. fair overnight recovery is expected. Below normal
temperatures are also expected.
.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected.
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