Flash Flooding and Damaging Wind in Arizona, July 17 to 18, 2018

Area Forecast Discussion
National Weather Service Flagstaff AZ
919 PM MST Tue Jul 17 2018

.SYNOPSIS...Expect a good chance of afternoon and evening showers
and thunderstorms through the remainder of the week and into the
weekend. The greatest coverage and highest potential for stronger
storms will be over portions of Coconino and Yavapai counties.

&&

.DISCUSSION...Scattered showers and thunderstorms are ongoing
across western Coconino and Yavapai counties this evening. The
remainder of the area is generally quiet. Latest hi-res model
guidance indicates the convective activity will gradually wind
down overnight. Expect another round of scattered showers and
storms on Wednesday, first forming off the higher terrain and
generally moving toward the west-southwest. The deepest moisture
remains along and southwest of the Mogollon Rim. Storm motion was
a bit faster today and this will continue on Wednesday, but flash
flooding will remain a concern across the region due to the
saturated soils and the moist airmass in place.

Current forecast handles this well and no updates are needed this
evening.

&&

.PREV DISCUSSION /205 PM MST/...Deep moisture and marginal
instability will continue to be the rule through Thursday, with
the highest moisture values southwest of the Mogollon Rim. Higher
shear values today may start to overcome the slow start, due to
earlier debris cloud cover and rain-cooled air. Wednesday should
be a bit more active, barring any complex development tonight.

Steering flow will remain easterly through Thursday, before
turning more southerly late this week and into the weekend. This
will likely keep deeper moisture into at least the western and
central portions of the CWA, while pushing storm activity back
farther north.

By late in the weekend and early next week, models suggest some
strengthening of the mid-level high and an intrusion of drier air
from the north. We anticipate some decrease in activity during
this time frame, but a complete stoppage is unlikely.

&&

.AVIATION...For the 06Z package...Scattered shower and thunderstorm
activity will gradually diminish through the overnight hours. The
strongest storms will produce localized MVFR/IFR conditions.
Scattered showers and storms will develop again after 18z Wednesday,
initially over the higher terrain. Aviation discussion not updated
for TAF amendments.

&&

.FIRE WEATHER...Expect scattered to numerous afternoon and evening
showers and thunderstorms Wednesday and Thursday. Storm motion will
generally be east to west, with portions of Coconino and Yavapai
counties likely seeing the most activity.

Friday through Sunday...Flow becomes more southerly during this
period, ensuring that deep moisture remains in at least the western
and central zones. Some minor drying may develop Sunday as flow
turns northerly heading into early next week.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...NONE.

&&

PUBLIC...TPS/Peterson
AVIATION...TPS
FIRE WEATHER...Peterson

For Northern Arizona weather information visit
weather.gov/flagstaff