Flash Flooding in Arizona, June 26, 2022

Area Forecast Discussion...UPDATED
National Weather Service Flagstaff AZ
940 AM MST Sun Jun 26 2022

.SYNOPSIS...Monsoonal flow will continue to bring showers and
thunderstorms to central and northern Arizona well into next week.
Gusty winds, localized heavy rainfall, and lightning will be the
primary concerns.

&&

.UPDATE...The overall short term forecast is in good shape with
just a few minor tweaks needed. PoPs were boosted a little bit
more near and northeast of the rim where HREF PWAT probs of over
1" are near 100%. Most of the hi-res NWP supports nudging PoPs
upward (now around 70-80%) across this area as well. Elsewhere, PoPs
will remain in the 40-70% range. The main hazards today are expected
to remain heavy rain with isolated instances of flash flooding,
especially if any of the deeper/slower-moving convection can take
place over any of the burn scars. Some pocket change sized hail
cannot be discounted with stronger updraft pulses, especially near
and east of the I-17/US HWY 89 corridor where CAPE values may
approach or even exceed 1000 J/Kg. Still, deep layer wind shear
remains modest with values near and below 25 knots.

&&

.PREV DISCUSSION /235 AM MST/...through Tonight...Area of showers
remain over eastern Arizona this morning, and should continue to
dwindle through the remainder of the early morning hours. High
pressure remains to the northwest over Nevada, keeping monsoonal
moisture flowing into the region, especially along and south of
the Mogollon Rim. Showers and thunderstorms are expected to
develop again late this morning initially across the high terrain
then increasing over much of the area through the afternoon.
Guidance from the 00Z HREF shows a swath of surface-based CAPE of
around 750-1000 J/Kg mainly along and east of I-17/US-89, thus,
the current thinking for the greatest coverage this afternoon
will be over the eastern-half of Arizona. 0-6 km shear remains
fairly weak, so another day of fairly slow storm motion is
expected. The slow storm motioned combined with increased moisture
(PWATs generally 0.80"-1.00") will lead to an increased flash
flood potential over the area today. This will be especially true
over any recent burn scars, where less rainfall is needed to
produced significant impacts. Outside of the heavy rainfall, gusty
outflow winds and small hail will be possible with any stronger
thunderstorm.

Monday...Showers and thunderstorms develop again on Monday as
well, however, a majority of the instability and deeper moisture
is expected to remain along and south of I-40. Flash flooding in
areas of heavy rainfall will again remain a concern across eastern
and central Arizona. Additionally, wind shear increases a bit
more Monday afternoon, leading to the potential for a few strong
to possibly severe storms to develop. The most likely area for
stronger thunderstorms looks to be over Yavapai and Gila Counties.

Tuesday through Saturday...Heights begin to decrease slightly as
the ridge begins to drift eastward by the middle of next week. As
the ridge moves overhead, a slight decrease in coverage looks
possible on Tuesday. However this is short lived, as moisture
quickly returns to the area by Wednesday with renewed southerly
flow as the ridge becomes centered over New Mexico. The monsoon
looks to remain through much of the next week; thus daily showers
and thunderstorms will continue to be a threat over the region.
Localized flash flooding and strong, gusty outflow winds will
continue to be the main hazards through the upcoming week.
Outside of the storms, near-normal temperatures and mainly light
winds are expected to prevail.

&&

.AVIATION...For the 18Z TAF package...Scattered SHRA/TSRA will
clutter the northern AZ airspace late this morning and into the
evening. Lightning, gusty/erratic outflow winds, and brief +RA
are forecast. Occn'l MVFR vsby may accompany +RA. Confidence is
greatest in intermittent TSRA at FLG...INW...SEZ...and PRC. The
potential for TSRA is non-zero at PGA and GCN, but for now I'll
forecast TS INVOF these aerodromes. Prevailing winds should
largely be out of the east/southeast...except at SEZ where a few
more hours of NE downslope winds are on tap. SHRA/TSRA is expected
to dissipate after 03 UTC.

&&

.FIRE WEATHER...The early monsoon pattern will continue to bring
scattered thunderstorms each afternoon both today and Monday.
Lightning, gusty outflow winds and flash flooding from heavy rain
are possible, especially over recent burn areas. Outside of
storms, expect generally light winds.

Tuesday through Thursday...Shower and thunderstorm chances will
continue each afternoon, favoring areas along and south of the
Mogollon Rim. An increase in activity is possible late next week.

&&

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

&&

PUBLIC...Bain/Humphreys
AVIATION...Bain
FIRE WEATHER...MCT

For Northern Arizona weather information visit
weather.gov/flagstaff