Area forecast discussion 
National Weather Service Phoenix Arizona 
320 PM MST Thursday Nov 27 2014 




Synopsis... 
a warm and dry stretch of weather will affect the region through the 
upcoming weekend under high pressure aloft. High temperatures will 
be the warmest today and then slowly cool through early next week 
while still remaining well above seasonal normals. A low pressure 
system is expected to affect the western states next week bringing a 
slight chance of light showers Tuesday into Wednesday and cooler 
temperatures. 


&& 


Discussion... 
rest of today through Sunday... 
the rest of the warmth in the lower levels certainly reached the 
surface this afternoon likely aided by the pressure gradient across 
much of Arizona. Temperatures in the Phoenix area have already 
climbed well into the 80s with Sky Harbor tying a record for the 
date at 86 degrees. Friday will only be a little bit cooler as the 
ridge starts to weaken and we have some high clouds. This very 
gradual trend continues through the weekend. Anticipate more high 
clouds on Sunday as a weakened short wave moves through the 
southwesterly flow aloft. Meanwhile...a new low pressure system 
takes shape off the West Coast becoming centered west of northern 
California by Sunday afternoon. Also by this time...moisture from 
tropical latitudes moves northeastward toward the Baja California peninsula. 


Monday through Thursday... 
differences in the medium range models become more evident by Monday 
with the GFS positioning the upper low closer to the coast than the 
European model (ecmwf) and Gem. The latter also depict a more cutoff situation with 
the low. The GFS also has a more substantial subtropical jet and 
moisture plume than the the European model (ecmwf) and Gem. However...the low weakens 
as it moves inland. While the GFS has trended down substantially in 
its quantitative precipitation forecast the past couple days...it seems to have settled on a window 
of Tuesday afternoon into Wednesday for precipitation over our area. The 
experimental GFS-13km also supports this. The gefs probabilities are 
also well into the double digits. Contrast that with the ecwmf and 
Gem which keep at least some measure of ridging over US as the 
system dissipates moving into the Pacific northwest. The ecens mean 
supports the idea of weakening and some sort of ridging though a bit 
less than the operational run. With the persistence of the GFS/gefs 
in holding on to probability of precipitation...left the extended as is. If we wind up 
getting precipitation next week it is not looking like it will be much. 
Otherwise there should at least be some thick cloud cover around 
Tuesday/Wednesday to nudge high temperatures downward. Extended temperatures may need some 
upward adjustment if less troughing pans out. 




&& 


Aviation... 
south-central Arizona including kphx...kiwa...and ksdl... 
southeast California and southwest Arizona...including kipl and 
kblh... 


Upper level ridge over the Desert Southwest will allow for mostly 
clear skies and light winds at all terminals through at least 
Friday. Winds will favor typical diurnal trends at all 
sites...generally 5 kts or less. Regarding the Mulch fire near Luke 
Air Force base...this should only have an impact on slant visibilities as 
winds should be too light to carry dense smoke to any of the main 
Phoenix terminals. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
Saturday through Wednesday... 
high pressure will remain in control through Monday...resulting in a 
continued period of mostly clear skies and dry conditions. Single 
digit humidities with fair overnight recoveries will be common 
through the weekend. Still monitoring the potential for a large 
upper level storm system to move through the area by the middle of 
next week. Some model differences have become more and more evident 
over the past few runs...thus confidence in exactly how the forecast 
will evolve next week is low. Still hanging onto the idea of 
increasing rain chances and elevated humidities by 
Tuesday/Wednesday. 


&& 


Psr watches/warnings/advisories... 


Arizona...none. 


California...none. 


&& 


$$ 


Visit US on facebook...twitter...and at weather.Gov/Phoenix 


Discussion...aj 
aviation...leins 
fire weather...leins 



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