Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 210223
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
723 PM MST Sun Aug 20 2017

.SYNOPSIS...Expect isolated to scattered thunderstorms during much
of the upcoming week. The greatest coverage of thunderstorms should
occur east to south of Tucson, but the lower deserts will not be
completely left out. Daytime temperatures will be close to seasonal
averages.

&&

.DISCUSSION...Very little in the way of convection today across
southeast Arizona, with just a few showers/thunderstorms this
afternoon. KEMX radar still indicates isolated shower activity
ongoing over far eastern portions of Pinal county. Otherwise, most
of the activity today was confined to the higher terrain across the
northern half of the state, from the Mogollon Rim northward.

While moisture remains decent across the area, with PW values on the
KTWC 00Z sounding holding in above 1.2", there is very little in the
way of instability and/or synoptic/mesoscale lifting features to
kick off convection. Given ongoing precipitation trends, guidance
figures and the latest AZ WRF-NAM/WRF-GFS model runs, have trimmed
back precipitation chances for the rest of tonight and overnight
periods. Also made a few other minor adjustments to the grids and
will ship out grid/text updates shortly. For more information on the
latter periods of the forecast, please refer to the PREV DISCUSSION
section below.

&&

.AVIATION...Valid thru 22/03Z.
A slight chance of -TSRA/-SHRA mainly east of KTUS thru 21/17Z, then
isolated to scattered -TSRA/-SHRA aft 21/17Z. Otherwise, VFR
conditions with cloud decks at 8k-12k ft AGL. Surface wind variable
in direction mainly less than 12 kts, although brief gusts to near
35 kts in vicinity of TSRA. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Expect isolated to scattered thunderstorms favoring
locales east to south of Tucson this week. Normal diurnal wind
trends will occur aside from any gusty and erratic thunderstorm
outflows. Daytime temperatures will remain close to seasonal
normals.

&&

.PREV DISCUSSION...Synoptically, we have a nice low near the
southern California coast with high pressure to our east. A general
southerly flow between these features has brought deeper moisture
back into the picture over the past 36 hours. We have enough
moisture for thunderstorms with precipitable water values ranging
from 1.2 to 1.5 inches across the area. We`re just not getting
enough lift to tap into the conditional instability in any
meaningful way. The debris cloud from last night`s convection breaks
up just long enough to build additional cu fields before putting a
break on the solar insolation. We`ll keep a few showers overnight,
but nothing organized as a weak mid level impulse lifts north of the
area.

By tomorrow, the low near southern California will nudge a little
further east, wrapping in a little bit of drying from the southwest.
Isolated coverage should be the most we can manage Monday into
Tuesday, with storms tending to cling to the mountains.

Upward trend for thunderstorms Wednesday and Thursday as an impulse
wrapping around the high center lifts from Mexico into our area.

A pattern change by next weekend with strong high pressure over
western states. If that shifts to a position northwest of our area
that will give us another break.

&&

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

&&

$$

Discussion...Zell
Prev Discussion...Meyer/Rasmussen

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