Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tucson Arizona
855 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...water vapor imagery...05/00z upper-air plots and most
recent model data show a ridge axis nosing eastward across Arizona
and into New Mexico. A swath of dry middle-upper level air is still
evident and extends from the eastern Pacific waters across southern
Arizona and into parts of New Mexico and the central and Southern
Plains. This evenings ktwc 05/00z sounding revealed a precipitable water of 0.98
inches and a lifted index of plus 1.
Infrared satellite imagery shows scattered thunderstorms continuing to our
south and southeast over parts of northeast Sonora and northwest
Chihuahua...with all of this activity moving to the south southwest.
Closer to home...no returns within my forecast area and the
inherited forecast of zero rain chances for the remainder of the
night is right on track.
As of 03z (8 PM mst)...temperatures across the region ranged from
the lower 80s to the upper 90s...with the Tucson International Airport
reporting a temperature of 98 degrees f...after achieving an afternoon high of
106 degrees f...which was 9 degrees f above normal for this date. These
readings seem to be on track with respect to the inherited overnight
low temperatures...so no changes are planned at this time.
For details regarding the forecast beyond tonight...please refer to
the previous discussion below.
Aviation...valid through 06/06z.
Mostly clear skies after 05/06z. 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...a slight threat for showers and thunderstorms will
occur Wednesday afternoon and early evening...mainly along the
international border as well as the White Mountains. Increasing
precipitation chances are expected late this week and 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 River valley near Safford.
Climate...strong high pressure will continue over the area 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 on Wednesday.
Date Aug 05
Tucson International Airport 108 108/2009
Fort Thomas 106 109/2009
Safford ag station 105 108/1995
With the high of 106 degrees at the 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.
Previous discussion...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.
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