Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 211552

Area Forecast Discussion
National Weather Service Tucson AZ
851 AM MST Fri Jul 21 2017

.SYNOPSIS...Scattered to numerous afternoon and evening
thunderstorms will prevail into early next week. The greatest
daily thunderstorm coverage should occur east to south of Tucson
with reduced thunderstorm activity across the western deserts. A
less favorable pattern may temporarily bring reduced thunderstorm
coverage around the middle of next week.


Moist air remains in place across the region with another near
record precipitable water sounding from KTUS this morning at just
over 1.8". Despite the appearance of dry air on water vapor imagery
to the west, nearly all of the lower deserts are swamped with pwats
that are well into the 95th percentile. Regional satellite imagery
reveals a fair amount of cloud cover along the AZ/NM border and also
suggests a weak remnant MCV over Greenlee County.

Hi-res models including UA WRFs, HRRR, HRRRx, and NCAR ensemble seem
to have a decent handle on the current weather and all indicate
convection blossoming in the mountains east of Tucson by late
morning. No doubt the MCV will play a role at some point later this
afternoon in triggering storms. With northerly flow around 10-15kts,
this should help get storms off the mountains and take another run
at Tucson. It`s a little less clear of a picture west of Tucson
where numerical guidance suggests it`s a bit drier than reality.
I`ll hang onto some low PoPs west of Tucson toward Ajo since these
areas have been active the past few days but the bulk of the
activity will almost certainly be east. I made minor adjustments to
PoPs based on 06z/incoming 12z model data but the forecast looks in
great shape overall.


.AVIATION...Valid thru 22/18Z.
VFR conditions with cloud decks generally 5k-10k ft AGL with BKN
layers above, and surface wind variable in direction mainly less
than 12 kts. SCT TSRA developing after 21/18Z and lingering through
22/06Z. Winds vicinity TSRA could gust 40+ kts. Aviation discussion
not updated for TAF amendments.


.FIRE WEATHER...Scattered to numerous mainly afternoon and evening
thunderstorms will continue into early next week with locally heavy
rain and strong winds. Temperatures will remain below normal with a
continuation of elevated humidity levels through Tuesday. Wednesday
onward conditions will become a bit drier and warmer with somewhat
less convection. From 20-foot winds will mainly remain below 15 mph
with the exception of strong outflow winds in the vicinity of


Outflow from earlier storms north of the area along with weak upper
level diffluence is helping to push and pull scattered showers with
isolated embedded thunderstorms up around the area this morning.
Otherwise, a bigger picture is showing cloud tops continuing to warm
with partial clearing here and there. Copious available moisture
continues with precipitable water values ranging from 1.5 to 1.7
inches. Weak shear and modest storm level flow will again make heavy
rain and isolated wet microburst activity a concern.

We`ll keep enough moisture around for decent storm chances into
early next week. Weak troughiness developing to our northwest may
actually stack a westerly component to our flow and temporarily push
deepest moisture into Chihuahua and New Mexico around Tuesday or
Wednesday. Potential to give us our first break of any significance.
Don`t count your chickens before they hatch though.






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