Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 171631

Area Forecast Discussion
National Weather Service Tucson AZ
931 AM MST Thu Aug 17 2017

.SYNOPSIS...Dry westerly flow will shut down thunderstorm chances
into Friday. A moisture increase from the south will gradually
bring isolated to scattered thunderstorms back to the region this
weekend and especially early next week. High temperatures within
a few degrees of normal will prevail.


.DISCUSSION...Generally clear skies over SE AZ this morning
although mid/high cloudiness continues to stream NE from leftover
storm complex in Mexico as mentioned in previous discussion
section below. Precipitable water on this morning`s sounding
showed 0.77 inch, still below normal. Should be enough mid level
moisture later today though to result in buildups over the
mountains, especially east of Tucson. However there is still not
enough moisture or instability in the atmosphere for thunderstorms

Temperatures this morning are running 1 to 4 degrees warmer than
this time yesterday. With considerable sunshine, we should be able
to eclipse Wednesday`s highs and Tucson will approach the 100
degree mark. That would be the first occurrence of 100 or warmer
at the airport since the 11th of August.

Current forecast of a ramp up in moisture and thunderstorm
chances into early next week looks on track. No adjustments needed
for now.


.AVIATION...Valid thru 18/18Z.
Mainly clear skies will prevail through the period. Expect normal
diurnal wind trends less than 12 kts. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...Dry westerly flow aloft will continue into Friday.
Isolated to scattered showers and thunderstorms will then return
this weekend into early next week. 20-foot winds will generally be
terrain driven at less than 15 mph apart from any thunderstorm


.PREV DISCUSSION...A moderate westerly flow continues with well
below average moisture for mid August. Even international border
areas were showing dew points in the 40s yesterday. Precipitable
water values are ranging from .6 to .8 inches across the area,
with below average values around 1 to 1.3 inches even in southern
Sonora. Southwest Chihuahua and especially Sinaloa were pretty
active yesterday, with the monsoon pushed back deeper into Mexico.

It`s too early to call it quits, and that trend will reverse over
the next 72 hours as northern portions of Mexico get active
again. The complex in northern Sinaloa will help push deeper
moisture through Sonora, staging in southern Sonora and western
Chihuahua tomorrow and then northern portions of the those states
Friday. We`ll be picking up a southerly component to our flow as
this happens, with weak troughiness to our northwest and some
reconsolidation of the ridge to our east. By this weekend, all of
these trends will have pushed deeper moisture back into our corner
of the state along with New Mexico. After the ramp-up over the
weekend, we should be in good shape for storms the first half of
next week.






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