658
FXUS65 KFGZ 201758
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1058 AM MST Thu Jun 20 2024

.SYNOPSIS...Daily chances for showers and thunderstorms are
forecast through the weekend and into early next week, along with
warming temperatures.

&&

.UPDATE...Moisture from what is now Tropical Depression Alberto,
located central Mexico, has pushed across the eastern third of
Arizona. The deepest moisture and most unstable air mass according
to model soundings will be along and north of a line extending
from Heber to Show Low to Springerville and includes the Chuska
Mountains, Defiance Plateau and the Chinle Valley. Storms today
will move generally from south to north and will be capable of
producing 0.50 to 1.00 inch downpours, wind gusts in excess of 50
mph and localized storm runoff. The western boundary of the
moisture extends as far west as Flagstaff and Page but a mid-level
cap of relatively warm air will likely result in extremely
isolated storms that far west.

&&

.PREV DISCUSSION /428 AM MST/...Today...A large area of high pressure
sits over the eastern-half of the United States, with a trough
situated over much of the west. Meanwhile, Tropical Storm Alberto
is approaching the eastern coast of Texas and Mexico. As Alberto
moves across Mexico, the trough over the west begins to lift
northward and the ridge begins to retrograde. As a a result, a
surge of sub-tropical moisture is initiated into Arizona.

Surface dewpoints have already begun to rise into the 50s F and 60s
F across much of New Mexico and into far eastern Arizona, as the
moisture begins to inch closer to Arizona. PWATs look to rise to
around 0.75-1.00 inches over Arizona by this afternoon, well above
the 90th percentile for this point in the year. 00Z HREF guidances
shows strong support for destabilization later this afternoon,
with 700-1200 J/Kg of surface-based CAPE. 0-6km shear is a bit on
the lower-end but with the influence of the trough, areas across
northern Arizona could potentially see a few stronger
thunderstorms with 25-35 kts of shear.

Latest CAM guidance has the bulk of the activity this afternoon north
of a Grand Canyon to St. Johns line, with lesser coverage along the
Mogollon Rim as well. The greatest threat from this storms will be
gusty outflow winds, brief heavy downpours, and small hail. However,
a couple strong to severe thunderstorms can not be ruled out.

Friday...The greatest moisture looks to move in on Friday, with PWAT
values of around an inch for much of northern Arizona to upwards of
1.2 inches in the Lower Deserts. Even with the increased moisture,
coverage still looks best over northern and eastern Arizona during
the afternoon on Friday, and to a lesser extent over central Arizona.

HREF and CAM guidance does show an increase in 0-6 km shear as the
trough lifts northward. Thus, the threat for a couple of stronger
thunderstorms remains. Localized flash flooding will also remain
a possibility through the Four Corners region given the amount of
moisture available, however storm motions of 20-25 kts may limit
the residency time of any one storm.

Saturday into Next Week...By the weekend the ridge has shifted full
into New Mexico, moisture remains in place, keeping daily chances
for showers and thunderstorms in the forecast. However, as the
heights continue to rise with the ridge building into the Southwest,
temperatures begin to warm once again for the start of next week.
Coverage and intensity of showers and thunderstorms may begin to
wain into next week as subsidence increases aloft.

&&

.AVIATION...Thursday 20/18Z through Friday 21/18Z...Mainly VFR
conditions persist through the TAF period with FEW-BKN cloud
cover after 19Z. Expect isolated to scattered -SHRA/-TSRA from
20Z-03Z with brief periods of MVFR VIS and CIGS, confined along
and east of a KGCN-KFLG-KPAN line. Showers and BKN clouds look to
continue through the night near the Four Corners region.
Anticipate south-southwest winds, 20-30 kts, becoming south 5-15
kts after 03Z.

OUTLOOK...Friday 21/18Z through Sunday 23/18Z...Another round of
scattered to widespread -SHRA/-TSRA is expected on Friday from
19Z-03Z with showers continuing into the night. Greatest coverage
will likely be along the Utah and New Mexico borders. Moderate
chances for -SHRA/-TSRA continue through the weekend across all of
northern Arizona. Anticipate enhanced south to southwest winds on
Friday afternoon, 20-30 kts, becoming much lighter for Saturday
and Sunday, outside of any gusty outflows from storms.

&&

.FIRE WEATHER...Today and Friday...Increasing chances for
showers/thunderstorms from east to west today and Friday. South to
southwest winds 15-25 mph, with gusty and erratic winds in the
vicinity of storms. Increasing RH values from 15-30% today to 30-50%
on Friday.

Saturday through Monday...Chances for showers and thunderstorms each
day. South to southwest winds around 5 to 10 mph Saturday and Sunday
becoming more westerly at 5 to 15 mph Monday. Gusty and erratic
winds possible in the vicinity of storms. Decreasing moisture will
result in lower RH values, generally between 20-30%.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

PUBLIC...McCollum/Humphreys
AVIATION...LaGuardia
FIRE WEATHER...Meola

For Northern Arizona weather information visit
weather.gov/flagstaff