Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Phoenix Arizona
910 am MST Wednesday Aug 27 2014
drier air will continue to move into the region today...ushering in
a drier and warmer pattern across the Desert Southwest through at
least early next week. High temperatures will return to near normal
values by Thursday...peaking between 105 and 110 Friday and
Saturday...before retreating slightly next week.
tail end of a shortwave trough is moving through Gila County this
morning...with a few lingering showers and isolated thunderstorms
noted on satellite and radar. WV imagery reveals the parent
circulation across eastern Utah with substantial middle level drying
stretching from south-central Arizona westward into central
California. Surface dewpoints have been slow to respond and are
generally in the low to middle 60s as of 16z.
Strong subsidence and middle level warm advection has already commenced
across southeast California and southwest Arizona and will continue
to spread westward this afternoon. The hrrr along with several other
local hi-res models indicate a few pop-up showers are possible well
east of Phoenix this afternoon...but the deserts will remain dry.
The inherited forecast indicated 10-20 probability of precipitation for this afternoon but
based on how quickly the shortwave is exiting the area...I made
slight reductions to probability of precipitation for later today. All in all it should be a
quiet day...no major updates necessary.
for Thursday through the weekend...zero probability of precipitation are in the forecast
during the period as a very dry northwesterly upper level flow
pattern persists across the Desert Southwest. The subtropical high
builds westward behind the exiting Pacific low with the high center
settling just off the Southern California coast. This will allow
500mb heights to build across our region and for an uptick in
temperatures. Highs will return to near seasonal normals already on
Thursday and then climb a couple degrees higher for Friday and
Saturday. Wouldn/T be surprised if a few locations across the
southeast California and southwest Arizona deserts hit 110 on Friday
The upper ridge will begin to break down on Saturday as a trough
moves into the Pacific northwest. Models are in excellent agreement
this trough will flatten the ridge to our southwest...but keep US
under a westerly to northwesterly dry upper level flow into next
Monday. Highs should start to trend downward starting Sunday as the
trough to our north slowly knocks down our upper heights. Some model
differences are shown near the end of the forecast period for next
Tuesday and Wednesday as the European begins to rebuild the
subtropical high to our southeast and possibly allows for some
minimal moisture return under weak southeasterly flow. The GFS keeps
the drier westerly flow aloft under a weaker sub-tropical high
centered still to our southwest. To account for the potential return
in monsoonal moisture...have introduced at least some low end slight
chance probability of precipitation for Tuesday and Wednesday across the higher terrain in
south-central Arizona including kphx...kiwa...and ksdl...and
southwest Arizona and southeast California including kipl and kblh...
Given the strong subsidence forecast to move into the area
today...weather concerns are minimal through Thursday. Mostly clear
skies and light diurnal winds are forecast at all sites.
Aviation discussion not updated for amended tafs.
Friday through Tuesday...
strong high pressure aloft and dry northwest flow will build over
the district through early next week. Even across Gila
County...chances for thunderstorms are almost zero through the
entire period. With temperatures at or slightly above the seasonal
average...afternoon humidities will range from the teens at lower
elevations to 20-30 percent over higher terrain. Fair overnight
recovery through the weekend will gradually increase...becoming good
or excellent by early next week. Wind speeds will be uncommonly low
through the weekend...with very little gusty character.
Visit US on facebook...twitter...and at weather.Gov/Phoenix