FXUS65 KTWC 171733
Area Forecast Discussion
National Weather Service Tucson AZ
1030 AM MST Tue Jul 17 2018
.SYNOPSIS...Plenty of moisture and instability will remain in
place to support daily showers and thunderstorms through at least
the middle of the week. Some storms will generate strong winds
and heavy rain. Partial drying from the east may lead to reduced
thunderstorm coverage by the weekend, along with hotter
.DISCUSSION..A significant shift in the weather pattern will take
place today through the rest of the week. The northern extent of an
inverted trough will continued to pass through the area today, with
drying and subsidence aloft limiting thunderstorm chances. Recent
HRRR solutions focus most of the shower and thunderstorm activity
across central and western Pima county, and near the International
Border for this afternoon and evening. Current forecast still looked
on track, so no updates necessary this morning.
.AVIATION...Valid through 18/18Z.
Isolated to scattered -SHRA/TSRA mainly west of KTUS this morning
and then once again area-wide this afternoon and evening. Cloud
bases 8k-12k ft AGL with SCT-BKN clouds above 20k. Winds remain
below 12 kts through the period, with stronger gusts possible
around TSRA. Aviation discussion not updated for TAF amendments.
.FIRE WEATHER...A shift in the weather pattern will begin to
take place, bringing in drier air and reducing rain chances.
However, isolated storms could still develop, especially over the
higher terrain. Temperatures also gradually warm through the week.
20-ft winds remain below 15 mph, although the Upper Gila River
Valley will experience gustier northwesterly winds at times.
.PREV DISCUSSION...The northern periphery of an inverted trough
exiting Chihuahua into Sonora is nosing into our area and helping to
maintain a large area of showers with isolated embedded
thunderstorms now west of Tucson. The easterly flow is quick enough
that we're already seeing decent clearing behind the area. We're
also seeing a dry punch in these easterlies on the back side of the
inverted trough, with precipitable water values down to around 1
inch through much of Chihuahua and New Mexico. Add in a little
subsidence behind this feature and thunderstorm development in
eastern areas is expected to be more limited today than recent
weeks. Our main focus will be areas southwest and west of Tucson
this afternoon, with wet microburst activity possible.
Over the next 72 hours, we'll keep an easterly flow as the ridge
slowly intensifies and reconsolidates northeast and east of our
area. Thursday is looking like a possible strong outflow day from
higher terrain into lower deserts, otherwise we will start to see a
bit less thunderstorm coverage with partial drying upstream in
eastern areas as can be seen on multi-level water vapor imagery, as
well as persistent trends in both operational and GEFS/NAEFS
ensemble means. Add the return of weaker flow, and mid level warming
with the proximity of the strengthening ridge for an overall
downturn in convection. In turn, we will see temperatures climbing
back to several degrees above average over the weekend and possibly
into early next week. The monsoon isn't going away, but it will slow
down a bit as we rely on only our southerly moisture source for a
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