Area forecast discussion 
National Weather Service Phoenix Arizona 
340 am MST Tuesday may 3 2016 


Update...aviation and fire weather discussions. 


&& 


Synopsis... 
temperatures will quickly warm Tuesday and peak Wednesday under high 
pressure. Some lower deserts will approach triple digits. The heat 
will not last long as another storm system rolls in from the 
Pacific. Winds will increase Wednesday and be strongest Thursday 
leading to areas of blowing dust. Friday into the weekend will 
feature below normal temperatures...various cloud cover...and modest 
chances for rain. 


&& 


Discussion... 
overnight water vapor loops over the north.A. Continent this morning 
Herald a highly amplified wave pattern and ridging building over the 
southwest states. High pressure anchored over the intermountain west 
extends well north into Canadian northwest territories and is pinched 
between two deep troughs over the northeast Pacific and the 
central/eastern Continental U.S.. compact and trailing upper shortwave that 
brought scattered precipitation activity to the northern Arizona Mountain 
yesterday continues to weaken in terms of 500mb heights but maintains 
a subtle circulation as it slowly rotates eastward. Ridge heights 
over Southern California are pushing eastward and will begin to settle over 
the southwest states today and Wednesday...introducing a sharp 
warming trend to daytime temperatures. 


Consensus and NAM/GFS MOS have begun to advertise 100f for Phoenix 
on Wednesday. Understanding even the warm biased British Columbia guidance has the 
influence of the last few days of below average temperatures...felt 
comfortable enough nudging up forecast values to 100f for Phoenix. 
Climatological first observance over the last normal period /98-10/ 
falls on may 2nd...so we are close. Yuma still has to hit their first 
100f of 2016 also...with April 22nd their average first observance 
over the last normal period. Yuma could get close on Wednesday 
however...500mb heights begin to fall across the western forecast 
area zones by Wednesday /south of 580dm/ relegating their chances 
dependent to the warm air advection and strong southerly flow that begins during 
the day. 


While the warmth will be the main headline Wednesday...southerly 
winds will become noticeable stronger as the aforementioned Pacific 
trough begins to move into the West Coast. Winds will become stronger 
for Thursday as 55-plus knots 500mb and 80-plus knots 300mb jet noses into 
the area ahead of the main low circulation. Dust and associated visibility 
restrictions are present for Wednesday with a more local focus...but 
become a regional concern across the majority of the Lower Desert 
elevations Thursday. Forecast surface winds continue to sit within gefs 
upper percentile forecasts and near Wind Advisory thresholds. 
Combination of strong winds and low humidities lend themselves to 
fire weather concerns as well Thursday and as such a Fire Weather 
Watch has been posted for the central Arizona zones/districts just east of 
the Colorado River valley. By Thursday afternoon the upper low center in 
plotted north of the l.A. Basin...just off-shore. 


Moisture parameters...precipitable water outputs from GFS/gefs and mixing ratios 
from European model (ecmwf)...are beginning to focus on the first wave of actionable 
moisture in combination with a vorticity maximum/frontal passage for 
Friday...particularly in the afternoon hours. Strong upstream 
heights and ll jet winds down the California coast should be able to 
transport marine moisture inland for Friday with precipitable waters  heading north 
toward 0.75 inch values. Further improvement of gefs reforecast probability of precipitation 
and finer timing details lead ME to nudge forecast probability of precipitation for Friday into 
the chance category across south-central Arizona and also include mention 
of thunder. Timing of coldest temperatures aloft and lifted indices are not 
perfectly aligned with peak heating...but given vertical motion 
associated with the height falls transitioning into the area felt 
thunder mention was warranted. Significant cooling trend is still on 
tap...with highs dipping back into the 70s/low 80s for most desert 
locales and upper 60s/low 70s for the nearby foothills and higher 
terrain for Friday and Saturday. 


Heading into the weekend the forecast remains broadly covered by 
slight chance probability of precipitation...cooler temperatures and partly to mostly cloudy 
skies. This latest trough cutoffs...similar to systems earlier this 
Spring...and begins to send embedded shortwave/vorticity lobes through the 
region at various times. Latest deterministic and ensemble storm 
track forecasts eventually draw the system eastward by early next 
week with Pacific high pressure transitioning into the west. 


&& 


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


A high pressure system will build over the region. Stable conditions 
will result in mostly clear skies with light wind under 6 knots 
through at least 23z Tuesday. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 


Thursday through Monday... 
..Fire Weather Watch Thursday afternoon and evening across 
southwest and south central Arizona... 


Thursday...a Pacific cold front will move into Southern California 
Thursday afternoon. Ahead of the front...strong gusty south to 
southwest winds 25 to 35 miles per hour will develop over a large part of 
southwest and south central Arizona.. with minimum relative 
humidities falling below 15 percent...a Fire Weather Watch has been 
posted. 


Friday through Monday...behind thursdays cold front...a large cool 
Pacific low pressure system will become nearly stationary over the 
region. This will provide cooler afternoon temperatures...along with 
a relatively moist airmass. Minimum relative humidities will range 
from 20 to 25 percent. Afternoon southwest winds in the 15 to 25 miles per hour 
range will develop Friday...decreasing into the 10 to 15 miles per hour range 
Saturday through Monday afternoon. Additionally...a slight chance of 
afternoon showers are possible mainly over the mountains north 
through east of Phoenix. 


&& 


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


&& 


Psr watches/warnings/advisories... 
Arizona...Fire Weather Watch from Thursday afternoon through Thursday 
evening for azz132-133. 


California...none. 
&& 


$$ 


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


Discussion...Nolte 
aviation...vasquez 
fire weather...vasquez 



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