Area forecast discussion 
National Weather Service Phoenix Arizona 
902 am MST Tuesday Oct 21 2014 


Synopsis... 
gradual drying will occur this week...but there will be one last day 
of slight chances for showers and thunderstorms across the mountains 
north and east of Phoenix today. Some warming is expected by middle 
week...lasting through Saturday with highs 5-10 degrees above 
normal. A cool down is expected to take place on Sunday into early 
next week bringing temperatures back to near seasonal normals. 


&& 


Discussion... 
temperatures as of 8 am MST are running in the upper 60s and low 70s 
area wide...except for the northern portion of Arizona where it 
remains a bit cooler with temperatures in the middle 40s. The next short wave 
trough feature is moving through the Great Basin this 
morning...bringing showers and clouds to Idaho/Montana/Wyoming/and 
parts of Utah. Some middle-high level clouds will continue to stream 
across the southwest as this trough pushes through the Rocky 
Mountains today and Wednesday. Very little change in the forecast 
was made this morning...just some tweaks to account for current 
conditions. Temperatures still look on track to reach near seasonal 
normals. 


&& 


Previous discussion.../issued 413 am MST/PDT /... 
the upper level low that has brought daytime shower and thunderstorm 
activity the past two days is now over southwest New Mexico...while 
another upper level system...mainly focused across the Great 
Basin...will drag a weak trough axis through Arizona today. 
Lingering low level moisture and sufficient daytime heating will 
again allow for some isolated showers and thunderstorms across 
eastern Arizona this afternoon with slight chance probability of precipitation over far 
eastern Gila County. Dry conditions will remain across the lower 
deserts even though precipitable water values will remain near one 
inch as warm middle level temperatures and the lack of any forcing 
mechanism inhibits any shower or thunderstorm development. 


High temperatures this afternoon will be similar to Monday...but a 
warm up is expected starting Wednesday. The Pacific Ridge is 
forecast to build northeastward into the Desert Southwest over the 
next few days allowing 500mb heights to rise to around 588dm. Model 
guidance over the past couple days has trended warmer for the 
Wednesday through Saturday timeframe and have adjusted our highs 
upward slightly to accommodate. The warmest day should end up being 
Friday as the ridge axis passes over Arizona late Thursday into 
early Friday. For Friday...readings in the middle 90s should be 
common across the lower deserts and a forecast high of 95 at Phoenix 
is just one degree shy of the record for the day. 


A less clear picture is shown for this weekend into early next week 
as significant model differences are shown for Sunday and Monday. 
The European and the Canadian models are now showing a fairly strong 
pv anomaly breaking off from a North Pacific low and sliding 
southeastward into or near the Desert Southwest sometime Sunday into 
Monday. The GFS remains much weaker and further north with this 
feature. Either way...little to no moisture is currently shown to 
accompany this potential shortwave trough...but will have to monitor 
for any changes over future model runs. Long range models do agree 
that an overall troughing pattern will take over starting Sunday 
allowing for a significant cool down...probably back to near normal 
or highs in the lower to middle 80s across the lower deserts. 


&& 


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


Through 03z Wednesday...mostly clear skies. Light wind under 8 knots. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
Thursday through Monday... 
a strong high pressure will build over Arizona and remain in place 
through Friday...then gradually weaken this weekend as a few weather 
systems move into the western states north of Arizona. Except for 
considerable high clouds this weekend...dry weather with above 
normal afternoon temperatures will continue. Minimum relative 
humidity will generally range from 17 to 20 percent...except near 35 
percent in the southern Gila County. Light wind is generally 
expected...however gusty south winds 10 to 20 miles per hour will likely 
develop along the Colorado River valley Saturday afternoon. Mostly 
good recovery is expected at night. 


&& 


Psr watches/warnings/advisories... 


Arizona...none. 


California...none. 


&& 


$$ 


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


Discussion...Dewey 
previous discussion...Kuhlman 
aviation...vasquez 
fire weather...vasquez 



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