Severe Thunderstorm Warning 158, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1001 AM MST Fri Aug 24 2018

.SYNOPSIS...Deep monsoon moisture will bring another round of
afternoon and evening thunderstorms today. Drier air advecting
into the region will lead to a downturn in shower and thunderstorm
activity later in the weekend into early next week.

&&

.DISCUSSION...Ample moisture remains in place over much of
northern Arizona setting the stage for another active monsoon day.
Surface dewpoints range from the mid 50s to around 60 degrees
indicating significant low level moisture in the region.
Additionally, mostly sunny skies are allowing for sufficient heating
of the boundary layer this morning. Expect convection to develop
by midday with the most widespread showers and thunderstorms along
the Rim from Flagstaff southeast to the White Mountains. A
complex over northern Mexico will likely provide additional
moisture and lift later this evening to the southeast portion of
the region. This could keep shower and thunderstorm activity
going well into the evening hours in southern Navajo and Apache
counties. We will continue to monitor this potential.

A few minor changes were made to precipitation chances, but the
overall forecast remains on track.

&&

.PREV DISCUSSION /444 AM MST/...Flood water from storms yesterday
is still flowing down the Agua Fria and Paria Rivers this morning.
This water should recede by mid morning. The rain from yesterday
also helped fog to form in a few areas. Most notable was along
I-40 between Flagstaff and Williams. This fog should also burn off
by mid morning.

Moisture values (from satellite) have changed very little over
this portion of northern Arizona since yesterday morning...still
an inch or higher. Some drying has taken place over southern
Nevada in the past 24 hours (1.4 inch yesterday vs 0.8 inch this
morning).

Cloud cover over northern Arizona is thinner than yesterday
morning. This will allow an earlier start to storms. An active day
is expected across northern Arizona today. Storm motion west and
north of Flagstaff is expected to be southwest to northeast.
Storms south and east of Flagstaff are expected to move more south
to north. Many areas across Yavapai County have received heavy
rain over the past few days. Additional heavy rain over these
areas will generate more runoff rather quickly.

Drier air will continue to slowly advect into the region over the
weekend resulting in a continued decrease in convection. However,
enough moisture will remain in the White Mountains for scattered
to numerous storms each afternoon.

A drier airmass will remain in place early next week so we are
only expecting isolated monsoon activity each afternoon. Long
range model guidance indicates these drier conditions could last
well into next week.

&&

.AVIATION...For the 18Z package...Scattered showers and thunderstorm
are expected this afternoon with the most active areas along the Rim
from KFLG southeast to the White Mountains. IFR possible in the
stronger storm cells. Storm activity decreasing after 02Z. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Monsoon moisture will remain over the district
with good chances for showers and thunderstorms again today and
Saturday. Expect scattered storms to develop each afternoon with the
greatest coverage along the Mogollon Rim southeast to the White
Mountains.

Sunday through Tuesday...Drier air will move into the region leading
to decreased shower and thunderstorm activity. Scattered showers and
thunderstorms are still expected in the White Mountains region each
afternoon.

&&

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

&&

PUBLIC...TPS/MAS
AVIATION...MCT
FIRE WEATHER...KD

For Northern Arizona weather information visit
weather.gov/flagstaff