Area forecast discussion 
National Weather Service Phoenix Arizona 
946 PM MST Wednesday may 25 2016 


Synopsis... 
a broad area of low pressure will continue over the western states 
through the weekend bringing overall cooler than normal temperatures 
and dry conditions. A more compact low pressure system moving through 
the region today will bring gusty winds to much of the area. 
Building high pressure for next week will likely bring a warming 
trend pushing highs to near 100 degrees for the lower deserts by the 
middle of next week. 


&& 


Discussion... 
breezy to windy conditions continue across much of the forecast ahead 
of and along an initial frontal intrusion associated with an upper 
low circulation near the Arizona/CA/NV triple point this evening. Airmass 
moisture continues to be at a premium with pwats less than half an 
inch from the Las Vegas radiosonde observation and just shy of three-tenths of an inch 
in Tucson. Had to rely on strong winds and steepening lapse rates in 
the vicinity of the cold core circulation for any convective activity 
during the daylight hours. Isolated thundershowers developed over the 
northern portions of the jtnp during the afternoon, putting down a 
few lighting strikes but unclear if any of the hydrometeors were 
actually hitting the ground given the dry sub-cloud layers. Activity 
quickly waned over our forecast area but continues right in The Heart 
of the upper circulation, mainly west of the Laughlin areaat time of 
this writing. Main circ center will swing through central Arizona this 
evening, possibly genning up an isolated shower across northern 
portions of La Paz and far northwest Maricopa counties overnight before 
continued draw in of dry moisture and subsident flow shuts off any 
precip chances for the daytime Thursday. Made minor adjustments to 
the pop grids based on high-res precip forecasts and on-going precip 
activity thinking it could clip the areas mentioned above. Mild 
daytime temperatures in store for tomorrow in the wake of today's 
initial frontal intrusion and exiting upper low movement. 


&& 


Previous discussion /issued at 205 PM MST/PDT/... 
a compact but modestly strong upper level low moving eastward into 
Southern California will track through central Arizona tonight, but 
there will be little change to sensible weather. Atmospheric profiles 
ahead of this low show little if any moisture to work with, thus the 
current mostly sunny skies. What moisture does accompany this system 
will mainly stay across higher terrain areas of southeast California 
and the northern half of Arizona. As of early this afternoon, a few 
areas of high based cumulus are seen on visible satellite, all 
located over higher terrain areas. Still showing a slight chance of a 
shower or thunderstorm for jtnp through this evening and high res 
models support some development. Winds are the main concern for the 
rest of today into early tonight as the upper low moves through 
central Arizona. Wind gusts of 25 mph across the deserts and up to 35 
mph over higher terrain locations are expected through early evening, 
possibly resulting in some patchy areas of blowing dust. 


Models, including gefs ensemble members, remain in good agreement 
that dry weather with continued below seasonal normal high 
temperatures will continue into the weekend under the influence of 
large scale upper troffing that has been persistent across the 
western Continental U.S.. subsident northwest flow aloft overspreads the area 
late tonight eliminating any remaining threats for showers. The low 
will usher in a cooling trend mainly to south central Arizona on 
Thursday, dropping high temperatures into the middle 80s over the 
lower deserts; Phoenix is forecast to fall to 86 degrees which is 12 
degrees below seasonal normals for the date. 


For Friday into the weekend, upper troffing is forecast to persist 
across the western conus, although it will not be overly strong or 
deep; for the most part a baggy trof sets up over the Desert 
Southwest keeping dry southwest flow going across the area each day 
with only a bit of high clouds embedded in the flow for mostly sunny 
days and generally clear nights. With 500mb heights not really 
falling all that much there will be somewhat of a warming trend with 
high temperatures climbing into the low to mid 90s through sunday; 
these temperatures will still be a few degrees below normal. The 
normal high on Sunday at Phoenix is 99 degrees, and the forecast is 
for 96 degrees; it makes sense for temps to be slightly below normal 
given the presence of weak troffing over the Desert Southwest during 
this period. 


Early next week, model ensemble spread becomes quite large and 
operational runs from both the GFS and European model (ecmwf) argue that much of the 
low pressure aloft over the western states will shift eastward as 
upper ridging forms just off the West Coast. As this occurs, heights 
rise and high temperatures over the lower deserts climb putting the 
warmer deserts into the upper 90s, possibly reaching around 100 
degrees by Tuesday. Thus we are calling for a warming trend with 
Phoenix set to reach 97 degrees next Tuesday. It will stay dry each 
day with generally sunny days and clear nights across the area. 


&& 


Aviation... 


South-central Arizona including kphx...kiwa and ksdl... 
southeast California/southwest Arizona including kipl and kblh... 


Low pressure passing through central Arizona will continue to support 
elevated westerly winds overnight for the Phoenix area terminals with 
even some gusts of 20 to 25 kts. Typical morning easterlies may 
develop into the terminals, but have a much later onset if they do 
develop. Western terminals will continue to experience west winds 
overnight, with speeds gradually decreasing in the wake of a mostly 
dry surface front and upper low pressure system. Some nighttime 
clouds may develop over south-central Arizona mostly few to scattered in nature 
at or above 12kft. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
Saturday through Wednesday... 
with dry southwesterly flow aloft expect slightly below normal yet 
warm daytime high temperatures through Wednesday in the mid to upper 
90s. Minimum relative humidities will generally range in the 7 to 12 
percent range along with fair overnight recoveries. Occasionally 
breezy southerly and southwesterly winds are expected each afternoon 
with gusts of 15 to 20 mph. 


&& 


Spotter information statement... 
spotter activation is not expected. 


&& 


Psr watches/warnings/advisories... 
Arizona...none. 
California...none. 
&& 


$$ 


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


Discussion...Nolte 
previous discussion...cb/Kuhlman 
aviation...Nolte 
fire weather...Sawtelle 






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