Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 192149
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
250 PM MST Wed Jul 19 2017

.SYNOPSIS...Scattered to numerous afternoon and evening thunderstorms
will prevail through this weekend. The greatest thunderstorm
coverage should occur east to south of Tucson with lesser
thunderstorm activity west of Tucson. Below normal daytime
temperatures will also prevail into the weekend.

&&

.DISCUSSION...Another active afternoon across portions of southeast
Arizona with storms firing across Cochise, Santa Cruz, Graham,
eastern Pima and eastern Pinal counties so far. Expect shower and
storm development to continue through the rest of the afternoon and
into the evening hours tonight before diminishing. Overall, flash
flood threat is down from the last couple of days with relatively
fast steering flow/storm motion. Drier air noted earlier in the day
on water vapor and Blended Total Precip Water imagery has overspread
northern Greenlee and Graham counties and shut down convection for
the time being in those areas. PW values in these areas have fallen
into the 0.70-0.90 inch range with visible satellite imagery
indicating just some flat cumulus clouds. Very little convective
activity also noted upstream in western New Mexico under the core of
drier air. Otherwise, storms are firing all along and out ahead of
this dry air boundary residing over far eastern Cochise, Graham and
southern Greenlee counties attm.

Not much change in thinking with the forecast going forward. The
western half of the state will begin to dry out Thursday and Friday,
with the eastern half of the state remaining quite moist and active.
A weak upper low/inverted trough is progged to move northward from
Chihuahua, Mexico and set up along the Arizona/New Mexico border
Thursday into Friday enhancing storm development across eastern
portions of the forecast area. In addition, the brisk steering flow
of today will become light Thursday into Friday, so storms that do
form those days will have an increased flash flood potential. The
overall pattern then shows very little change Saturday through
Monday of next week, as deep moisture once again surges northward
across the state increasing precipitation chances areawide, but
especially from Tucson and points south and east. Some drying is
then noted mid to late next week, but the latest models runs are not
quite as aggressive with this drying. Grids/text products show a
lowering of pops next Tuesday and Wednesday in response to this
drying, especially west of Tucson.

Daytime high temperatures will remain below normal into early next
week and then near normal mid to late next week.

&&

.AVIATION...Valid thru 21/00Z.
Scattered to numerous TSRA/SHRA this afternoon/evening, then
isolated to scattered -TSRA/-SHRA mainly west/northwest of KTUS late
tonight into early Thursday morning. Scattered to numerous TSRA/SHRA
developing again Thursday afternoon. Otherwise, VFR conditions with
cloud decks generally 5k-10k ft AGL, and surface wind variable in
direction mainly less than 12 kts. Aviation discussion not updated
for TAF amendments.

&&

.FIRE WEATHER...Scattered to numerous mainly afternoon and evening
thunderstorms will continue the rest of the work week with locally
heavy rains. A bit of an uptick in the number of storms is likely
later this weekend into early next week. Temperatures will remain
below normal with a continuation of elevated humidity levels. 20-
foot winds will mainly remain below 15 mph with the exception of
strong outflow winds in the vicinity of thunderstorms.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

Zell

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