Severe Thunderstorm Warning 39, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
942 AM MST Tue Aug 9 2022

.SYNOPSIS...Deep monsoonal moisture will remain across much of
northern Arizona through the week. Scattered to widespread
thunderstorms are likely each afternoon during this time. Flash
flooding will again be the main threat, especially near recent
fire scars.

&&

.UPDATE...Scattered showers and thunderstorms are expected to
develop across the region this afternoon and evening, with the
greatest coverage expected mainly over the high terrain. Cloud
cover and earlier preciptation from a decaying MCS moving into
Mojave County has stabilized much of western portions of the
region, thus, likely contributing to a delayed start in storms
this afternoon. 12Z HREF guidance shows areas of mix-layer CAPE
values of around 500-1500 J/Kg this afternoon mainly along and
south of I-40. This combined with fairly weak (~15 kts) 0-6km
shear will limit the overall severe threat today. Flooding will
however remain a concern as PWAT values remain high, around 1.0 to
1.5 inches, although faster storm motion around 10-15 kts does
limit the overall threat outside of training storms.

Updated PoPs through the overnight to delay the start of
convection and reduce chances this afternoon.

&&

.PREV DISCUSSION /316 AM MST/...For today, a high pressure
circulation centered near the Four Corners will allow deep monsoon
moisture to become thoroughly entrenched across northern Arizona.
Surface dew points are generally expected to be above 60 F south
of the Mogollon Rim, with values in the 50s along and north of
the Rim. In addition, precipitable water is expected to range
from 1.0 to 1.75 inches, with the highest values across southern
Yavapai County.

In terms of instability, above 1000 J/kg is predicted to develop
along and south of the Mogollon Rim this afternoon, coincident
with the area of greatest moisture. North of the Rim, less
instability is anticipated, with CAPE likely ranging from 500-1000
J/kg. 0-6km Bulk shear will be low, with values in the 5-15 knot
range. In this moderate CAPE, but low shear environment, the
severe weather threat remains low, although a few strong storms
capable of producing hail up to 1 inch in size cannot be ruled
out.

Most high resolution model guidance shows the typical daily
trend, with storms forming over high terrain around noon, before
outflow boundaries initiate new storms within valleys during the
mid-afternoon and evening hours. The strongest of these storms is
expected to occur along and south of the Mogollon Rim as that is
where the greatest instability is forecast. Individual storm
motion will be toward the northwest between 10-15 mph. Due to the
uptick in monsoon moisture, and the relatively slow moving nature
of today's storms, the flash flood threat will increase. As a
result, a Flash Flood Watch has been issued for this afternoon and
evening for areas from the Mogollon Rim south, including the
White Mountains and Grand Canyon country.

From Wednesday into next week, an active monsoon pattern is
forecast to continue as high pressure strengthens over the
central United States and a moist southerly wind persists across
Arizona. Good chances for showers and thunderstorms are forecast
each day for the foreseeable future.

&&

.AVIATION...For the 18Z TAF package...Expect SCT-NMRS SHRA/TSRA and
ISOLD +TSRA along and south of a KSJN-KFLG-KGCN line from 18Z-03Z.
Activity more in the ISOLD-SCT range north of that line and AFT 03Z
Wednesday. Heavier cells will produce brief MVFR/IFR. Sfc winds
light. Aviation discussion not updated for TAF amendments.

&&

FIRE WEATHER...Scattered to widespread showers and thunderstorms
will bring good chances for wetting rainfall today and Wednesday.
The main hazards from these storms are flash flooding and strong
thunderstorm winds. Otherwise, expect light winds far from storm
activity with little change in temperatures.

Thursday through Saturday...Monsoon moisture will remain in place
bringing daily showers and thunderstorms. Winds will remain light
outside of storm activity with little change in temperatures.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Flood Watch through this evening for AZZ004-006>008-015>018-037-
038-104-106>108-115>118-137-138.

&&

PUBLIC...Humphreys/RR
AVIATION...Peterson
FIRE WEATHER...RR

For Northern Arizona weather information visit
weather.gov/flagstaff