Area forecast discussion
National Weather Service Phoenix Arizona
230 PM MST Friday may 24 2013
..update to aviation and fire weather discussions...
&&
Synopsis...
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 Sunday. Thereafter...a trough along the
West Coast is anticipated to deepen which will lead to some modest
cooling Monday with some more noticeable cooling Tuesday and
Wednesday.
&&
Discussion...
a large area of low pressure remains anchored along the West Coast
this afternoon with the main upper low centered in the vicinity of
the Pacific northwest coast. Arizona remains under persistent southwest flow
aloft...keeping skies mostly clear and allowing for afternoon
breeziness. 500 mb heights remain somewhat elevated...near 580dm across
southern Arizona...and as such high temperatures remain near or slightly above
seasonal normals with warmest deserts approaching 100 degrees.
For the next few days...no significant changes to the weather
pattern are expected...at least none that will change our sensible
weather very much. A series of pv anomalies/vorticity maxes rotate around
the main upper low and into the Pacific northwest...keeping persistent southwesterly
flow aloft in place across Arizona through the weekend and into early
next week. 500 mb heights/thicknesses change little over this time and
as such high temperatures will remain in the middle 90s to around 100 Saturday
into next Monday. Forecasts indicate that there will be an increase in
high clouds Monday for partly sunny skies...but until then expect
mostly sunny or sunny days and clear nights. Afternoon and early
evening breezes will be on tap tonight into Monday as well as middle
level gradients remain somewhat tight.
Forecasts agree that a large and rather progressive upper trough will
develop along the Pacific northwest coast...then slide southeastward and into
our region by next Tuesday. Model differences are still problematic
with the operational European likely on the overly strong and wet
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...which would be likely given the time of
year and very low probability of precipitation expected by climatology. 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.
Dry westerly flow aloft will follow on Thursday for mostly sunny
skies...along with warming temperatures.
&&
Aviation...
south-central Arizona...including kphx...kiwa...ksdl...southeast
California/southwest Arizona...including kipl and kblh...
Mostly clear skies and breezy winds will persist for the terminals
through the evening hours. Kipl and kblh winds will gradually
transition from southerly to swstrly headings closer to sunset while
the phx terminals can expected southwesterly breezes. Sustained
winds expect generally 15 kts or less with gusts of 20 to 25kts.
Aviation discussion not updated for amended tafs.
&&
Fire weather...
Monday through Friday...
large area of almost stationary low pressure across the northwest
U.S. Will begin to open up into a more noticeable troughing pattern
by Monday. A series of dry weather systems will move through the
predominately southwest flow...persisting afternoon and early
evening winds while also introducing a mild cooling trend. With
current forecast model guidance...winds look to be their strongest
late Tuesday into Wednesday...however at this time remaining below
critical fire weather thresholds. Humidities will see a slight
increase midweek with the cooler temperatures and potential for some
weak low level moisture advection...ahead of the most promising
weather system at this time. Overall...conditions for the southwest fire
districts will remain dry as dry westerly flow returns to the region
late week. Near normal temperatures with a return to single digit
daytime humidities are expected.
&&
Psr watches/warnings/advisories...
Arizona...none.
California...none.
&&
$$
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Discussion...cb/Kuhlman
aviation...Nolte
fire weather...Nolte
