Special Weather Statement, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
206 PM MST Tue Jun 29 2021

.SYNOPSIS...Thunderstorm activity will increase today and continue
through Wednesday and Thursday with areas of locally heavy rain,
frequent lightning, and gusty winds expected. Storm coverage is
forecast to decrease somewhat from Friday into the early part of
next week.

&&

.DISCUSSION...Thunderstorms have initiated over the Coconino
Plateau and Mogollon Rom over toward the White Mountains, with
steering flow taking these storms gradually southward. Another
area of storms initiated over Black Mesa on the Navajo Nation and
is expected to continue to develop south/southwest this
afternoon/evening. The greatest threats will be cloud to ground
lightning, locally heavy rain, and strong wind gusts. Locally
heavy rain and strong wind gusts have the greatest likelihood of
occurrence south of the Mogollon Rim where precipitable water
values are a bit greater and surface temperatures are warmer.

HREF mean precipitable water forecasts are for values around 0.2"
greater on Wednesday than the analyzed values are today as
moisture continues to work its way into Arizona. A threat of
localized heavy rain and strong wind gusts will continue into
Wednesday afternoon/evening. Storms may have a bit greater
westerly component to their motion on Wednesday as we will be
located to the south of a weak low over Utah, though enough
northerly flow should exist to again allow storms developing over
the high terrain to move into the lower elevations.

Weak southerly flow aloft is expected from Thursday into Friday as
the low over Utah weakens and a high begins to build westward
into Arizona. Enough moisture should remain in place for shower
and thunderstorm chances each day, though perhaps with coverage
not quite as extensive as today and Wednesday. By the weekend, the
EPS mean location of the high near the AZ/UT state line would
place the majority of northern Arizona in light easterly flow.
Again, we should see some shower/thunderstorm activity from the
moisture in place, but the higher heights and the light steering
flow may eventually decrease rainfall coverage. Temperatures are
forecast to climb to near normal values for the weekend.

For the early to middle part of next week, a low-grade monsoon
pattern is currently expected. Around 10% of ensemble members
forecast a trough in westerly flow approaching around Tuesday,
which would greatly decrease atmospheric moisture. The other 90%
maintain a high somewhere in the area, though the details of
exactly where that high is matter as far as moisture and storm
coverage.

&&

.AVIATION...For the 00Z package...SSW-moving showers/thunderstorms
stretching from near Supai to KCMR to KPAN will build southward
through the afternoon/evening hours and could produce MVFR
cig/vsby as well as strong wind gusts from variable directions.
Another area of storms from KPGA-KRQE moving SSW could also
produce these conditions. Expect minimal storm coverage after
04-05z. Another round of showers/storms is forecast after 17-18z
Wednesday. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Numerous showers and thunderstorms are expected
Wednesday afternoon/evening with moderate to heavy rainfall
in the strongest storms. Scattered storm coverage is expected
Thursday, with afternoon relative humidity remaining largely in
the 25-35 percent range.

Friday through Sunday...Isolated to scattered showers and storms
are forecast. Haines indices of 4-5 are forecast this weekend
mainly north of Interstate 40.

&&

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

&&

PUBLIC...AT
AVIATION...AT
FIRE WEATHER...AT

For Northern Arizona weather information visit
weather.gov/flagstaff

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