Severe Thunderstorm Warning 5, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
214 PM MST Tue Jun 28 2022

.SYNOPSIS...The warm temperatures and isolated thunderstorm
activity will persist for the remainder of the afternoon across
northern Arizona. Deeper monsoon moisture arrives Wednesday
leading to increasing chances for thunderstorms and flooding rains
through Friday. A drying trend is looking more likely as we head
into the holiday weekend.

&&

.DISCUSSION...Radar is currently showing some isolated shower and
thunderstorm activity in the White Mountains as well as into
Yavapai County. Convective models do suggest this isolated
activity to continue into the evening hours with coverage
eventually extending into Mohave County. Localized flash flooding
for areas directly underneath any storms' core is possible during
this time. Convection should wind down by tonight with decreasing
cloud cover and average temperatures.

As the core of the high pressure system shifts eastward, an
increase in monsoonal flow and moisture is expected to take place
across Arizona. This will result in the development of scattered
to widespread shower and thunderstorm coverage for both Wednesday
and Thursday. The majority of the GEFS and ECMWF ensemble members
show a jump up in PWAT values for locations across northern
Arizona during this time as well as in CAPE according to model
soundings. With widespread PWATs around an inch or more at this
time, confidence has increased in the potential for scattered to
widespread flash flooding on both days, with highest POPs along
and west of HWY 89 & I-17 on Wednesday, then shifting to the east
on Thursday. Forecast rain rates of 0.50-1.00" per hour are likely
with even higher rates possible in some of the stronger storms.

By Friday, moisture and POPs begin to decrease as a longwave
trough develops off the west coast. Still think scattered storm
coverage is likely across the region on Friday, with the highest
chances in the White Mountains, due to the presence of lingering
moisture in the low to mid-levels. However, as we enter into the
holiday weekend, precipitation chances decrease significantly
across northern Arizona with only moderate chances confined to the
eastern Mogollon Rim and the White Mountains. A bit hesitant at
this time to completely take out chances for locations westward
along the Rim, however if you are hoping for more rain, then the
trend is not your friend. Ensemble guidance, including the NBM,
continues to suggest a downward trend in moisture with an increase
in southwesterly winds for Saturday, Sunday, and Monday most
likely due to impacts of that longwave trough off the west coast.
The outlier in terms of model guidance is currently the
deterministic GFS which shows scattered to widespread storm
activity continuing through the weekend. Can't completely
disregard it, especially still being a few days out, however
forecaster confidence is currently hitching itself to the ensemble
guidance and the drying trend.

After the holiday weekend, the forecast becomes unclear with
regards to the overall synoptic flow and progression of the high
pressure system. At this time, no significant signals exist
showing the dry pattern persisting or a return of widespread
storm activity, however the temperature trend is increasing which,
most of the time with the monsoon, correlates with decreased
moisture.

&&

.AVIATION....For the 00Z TAF package...Scattered cumulus clouds and
isolated storms across northern Arizona will continue into the
evening. Thunderstorms will possible producing brief periods of
localized MVFR this evening. More widespread activity expected by
18z tomorrow. Lightning, erratic, gusty winds, and heavy rainfall
will accompany thunderstorms. Light E-SE winds overnight becoming
breezy S-SW winds tomorrow afternoon. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...Scattered to widespread showers and thunderstorms
Wednesday due to southerly winds increasing moisture. Gusty winds,
lightning, and possible flash flooding will be the main thunderstorm
hazards. Similar conditions are expected Thursday.

Friday through Sunday...Precipitation chances remain over much of
the area Friday, however decreasing for Saturday and Sunday.
Expect generally S-SW winds and warm conditions during this time.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...Excessive Heat Warning until 8 PM
MST this evening FOR AZZ006.

&&

PUBLIC...LaGuardia
AVIATION...JM
FIRE WEATHER...JM

For Northern Arizona weather information visit
weather.gov/flagstaff

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