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Area forecast discussion
National Weather Service Phoenix Arizona
840 am MST Friday may 24 2013
low pressure center over the Pacific northwest is expected to keep
the region under dry southwesterly flow aloft...with breezy
conditions at times into next week. Anticipate little change in
temperatures through Saturday. Thereafter...a trough along the
West Coast is anticipated to deepen which will lead to some modest
cooling Sunday and Monday with some more noticeable cooling Tuesday
not much change in the weather pattern for our area this
morning...as dry southwest flow aloft persists across the
area...ahead of an upper trough parked along the West Coast. Infrared
imagery at 8 am showed sunny skies around Arizona and southeastern
California...and area radiosonde observations continued to show southwesterly flow through most of
the column. Low/middle level gradients remain sufficiently tight to
give another day of breezy conditions during the afternoon and
evening hours. Flg/tus 12z soundings showed 15-20kt below 700mb and
this will mix to the surface later today under nearly full sunshine.
With 500mb heights remaining high...near 580dm over the southern
deserts...high temperatures today will stay slightly above seasonal normals
and the warmest deserts should reach to 100 degrees...or at least
into the upper 90s. The current high of 100 at Phoenix today may be
reached but it is possible that it will come up a degree or two
short...given that both tus and flg showed a couple degrees of
cooling over the past 24 hours below 700mb...and central deserts are
currently running a few degrees cooler than yesterday. Overall
forecasts are in fine shape and no updates are needed.
areawide weather has been on the quiet side this week and slightly
warmer than expected the past couple days. The deep upper low over
the Pacific northwest is not quite having as much of a cooling
effect over the Desert Southwest as anticipated.
However...temperatures have cooled noticeably across our western
zones and slightly below normal temperatures are expected through
the weekend there. Farther away from the cooler
airmass...south-central Arizona remains above normal with metropolitan
Phoenix readings around 100 the past couple days. Not expecting any
noticeable change in temperatures across south-central Arizona today
or even into Saturday.
By Sunday...the persistent upper low over the Pacific northwest
finally weakens and becomes more of an open trough. A shortwave does
Peel off the main low and dives southward into the Great
Basin...thus lowering heights across the Desert Southwest. This is
expected to have a slight cooling effect across the region...but the
more significant cooling won't occur until the middle of next week.
Through Monday...dry southwesterly flow maintains it/S hold across
the region...but changes in the flow starting Tuesday.
A fairly strong shortwave trough is forecast to slide southeastward
from the North Pacific Sunday into Monday coming onshore in
California Monday night. The large scale troughing pattern across
the western United States and a 120kt upper jet will aid in the
quick progression of this shortwave into our region by Tuesday.
Model differences are still problematic with the operational
European likely on the overly strong side of the spectrum and the
Gem on the opposite side of the spectrum with the main shortwave
ending up across the Pacific northwest. The European and GFS
ensemble means are fairly close to each other in speed and strength
with more spread seen within the European ensemble members. Given
this...have trended the current forecast toward the GFS...GFS
ensemble mean...and European ensemble mean. This still results in a
modest cooldown of 5-10 degrees for the middle of next week...and
especially Tuesday and Wednesday with the potential for decent middle
and high level moisture and resulting cloud cover. Precipitation
chances still look fairly low given overall fairly dry airmass. Have
elected to mostly ignore the operational European quantitative precipitation forecast forecast for
the region given it/S overly strong solution...but have at least
included slightly higher than climatology probability of precipitation for Tuesday into Wednesday.
If other model solutions start trending toward the stronger
European...higher probability of precipitation will be needed.
south-central Arizona...including kphx...kiwa...ksdl...southeast
California/southwest Arizona...including kipl and kblh...
Dry southwest flow aloft will keep skies clear to mostly clear
through the taf period. Winds are expected to follow the usual
diurnal trends in direction and speed...with westerly breezes
developing during the afternoon and evening hours.
Aviation discussion not updated for amended tafs.
Sunday through Thursday...
low pressure that is expected to remain along the West Coast on
Sunday and Monday is forecast to move inland over the Desert
Southwest on Tuesday and Wednesday...then off to the east into the
Central Plains on Thursday. Dry southwest to west flow ahead of this
low center will keep skies mostly clear and temperatures near normal
on Sunday and Monday...with cooler temperatures...an increase in
cloudiness...and gusty winds likely on Tuesday and Wednesday...as
the low passes through the region. Warmer temperatures are then
expected on Thursday as ridging begins to build in from the west.
Single digit minimum humidities are expected on Sunday and
Monday...with somewhat higher values on Tuesday and Wednesday...then
falling back into the single numbers and low teens on Thursday.
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