Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tucson Arizona
210 PM MST Tuesday Aug 4 2015
Synopsis...drier and hotter conditions will continue across
Southeast Arizona into middle week...with little or no thunderstorm
activity. As high pressure shifts back east of the area...increasing
moisture will bring an increasing thunderstorm trend later in the
week into early next week. As this happens temperatures will fall
back closer to seasonal averages.
Discussion...as expected we're seeing meager cumulus fields across
most of Southeast Arizona this afternoon. Dry and relatively stable
for early August...just a few buildups approximating early stage
storms over a couple of mountains. An unfavorable ridge position and
orientation overhead has temporarily shut down the monsoon...with
declining moisture trends noted on CIRA layered precipitable water
imagery even across northern Sonora and northwest Chihuahua. The
high pressure combined with less moisture has helped push our
temperatures to well above climatology today and should again tomorrow.
Please see the climate section below for additional details.
Additional moisture will begin to try to creep back in from the south
Wednesday with a few storms possible near the international border
as Sonora and western Chihuahua become more active. Overall another
dry and hot day for Southeast Arizona as the ridge starts to weaken.
The high center should have reconsolidated immediately east of the
area by Thursday afternoon...with the moisture deepening as it does
so. The flow will still be on the weak side...but the atmosphere
should be in a position to support thunderstorms again by later
Thursday afternoon. A nice 700 mb Theta-E ridge is setting up west of
Tucson as the moisture returns from the south and high pressure
remains too close for eastern areas. So the forecast focus Thursday
will be mainly west and south of Tucson...emphasizing Santa Cruz
County and the tohono o'odham nation.
A weak impulse in the strengthening southerly flow should increase
coverage and possible organization of storms Friday from Tucson
eastward. As this happens...the low lifting through the region to
our northwest will try to reintroduce a westerly component to our
flow across western areas...so a reverse of Thursday storm trends.
Over the weekend we meander with a generally weak flow across
Southeast Arizona. Then strengthening high pressure with a stronger
ridge axis immediately downstream Monday and Tuesday should be more
favorable for storms. Add in another impulse in the southerly flow
pushing into Southeast Arizona Monday and there you are.
Aviation...valid through 06/00z.
Few-scattered clouds at 8-12k feet above ground level mainly near terrain east of ktus through
05/05z. Mostly clear skies after 05/05z. Surface winds generally less than
12 kts with a few higher gusts during the afternoon/early evening
hours. There is a slight chance of afternoon showers and
thunderstorms on Wednesday afternoon... mainly near the
international border and in the White Mountains. Aviation discussion
not updated for taf amendments.
Fire weather...dry conditions are expected across most of Southeast
Arizona today...along with above normal temperatures. Daytime
minimum relative humidity values will fall into the 10 to 20 percent
range through Wednesday. Increasing precipitation chances are then
expected into the upcoming weekend as high pressure shifts from
nearly overhead eastward into the Southern Plains. Outside of any
thunderstorm wind gusts...20-ft winds will generally be terrain
driven and less than 15 miles per hour. However...there will be some afternoon
and early evening breeziness...especially in the Gila Valley River
Valley near Safford.
Climate...strong high pressure will build over the area today into
Wednesday...bringing hot early August temperatures to the
area...with a few spots approaching or tying record highs. Not all
locations in Southeast Arizona will get into the near record heat. Below are the
sites that will be at or within three degrees today and Wednesday.
Date Aug 04 Aug 05
forecast rcd/year forecast rcd/year
Tucson International Airport 107 109/1994 108 108/2009
Fort Thomas 105 107/1995 106 109/2009
Safford ag station 104 106/2009 105 108/1995
With a forecast high of 107 at Tucson Airport today...this will mark
the 7th time since 1895 that August hit 105 or hotter when it didn't
occur in July. The previous six occurrences were in
1914/1919/1945/1962/1975 and 1977.
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