457
FXUS65 KFGZ 301523
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
823 AM MST Sun Jun 30 2024

.SYNOPSIS...An increase in shower and thunderstorm activity is
expected for the newt few days, before decreasing again from about
mid-week onward. Expect light winds and seasonable temperatures
early in the week, before a strong warming trend develops for the
holiday weekend.

&&

.UPDATE...Precipitable water is increasing across northern
Arizona this morning due to a combination of southerly flow
drawing moisture rich air into the state from the Gulf of
California, as well as from outflows associated with a decayed
thunderstorm complex that collapsed south of Tucson last night.
Precipitable water measured from the upper-air sounding taken here
in Bellemont, AZ this morning showed a value of 0.78", which is
up from 0.57" the morning before. High-resolution model guidance
predicts that by this afternoon, precipitable water will range
from 0.75" to 1.5" area-wide.

Along with the increasing moisture comes an increase in
instability for thunderstorms as well. Whereas yesterday`s CAPE
values were largely <= 500 J/kg along and south of the Mogollon
Rim, today CAPE values are expected to range from around 200 J/kg
near the Grand Canyon to 900 J/kg south of the Mogollon Rim and
near the Four Corners. 0-6 km bulk shear collocated with the
highest instability varies between 15-25 knots. These shear values
mean the threat for organized, rotating storms is low, but cannot
be completely ruled out. Storm motion is forecast to be toward
the north between 10-20 knots, with the thunderstorm anvils moving
in the same direction, potentially shading out downstream
activity.

With everything considered, expect an increase in storm activity
today, with the greatest activity east of a line from Prescott to
Flagstaff to the Four Corners. Severe weather potential for today
can be characterized by a moderate threat for flooding, with a
low to moderate threat of large hail and downburst winds. Given
the active day expected across the entire state, some high
resolution model guidance predicts additional rounds of showers
and thunderstorms pushing into the area from the south overnight.

&&

.PREV DISCUSSION /350 AM MST/...A strong outflow, emanating from a
decayed thunderstorm complex south of Tucson earlier tonight, is
moving northward to the Phoenix area this morning. We are already
seeing some light rain shower development in the mid-levels ahead
of this outflow, with more development likely by 4-5AM, as the
boundary layer outflow enters southern Yavapai County. This is all
set up from the southerly flow over eastern Arizona, due to a
ridge to our east and the continued presence of a trough over the
Pacific NW. We expect further development this afternoon,
especially from the I-17 corridor north and northeast, as higher
moisture values stream into the area. By tonight, the overall
pattern remains the same, but MCS development shifts northward,
setting up a potential for nocturnal activity in our CWA, as
active outflows push north and west overnight.

Due to the cloud cover and rain-cooled air that potentially may
develop tonight and early Monday, it could actually be a down day
for Monday afternoon, leaving Tuesday as the next active period.

By Wednesday, the Pacific NW trough finally dislodges and move east.
However, instead of the sub-tropical high reestablishing itself, it
will retreat eastward and allow an even stronger Pacific high to
take its place. This pattern may displace moisture southward as
early as Wednesday, perhaps totally drying our CWA by Thursday and
Friday. This could end up being a very hot pattern for the holiday
weekend. But, there is some disagreement in high placement after Day
5 or so, we will have to wait and see.

&&

.AVIATION...Sunday 30/12Z through Monday 01/12Z...Scattered
SHRA/TSRA after 19Z, with more widespread activity developing
from south to north after 02Z. Periods of MVFR conditions and
gusty, erratic outflow winds possible in and around TS. Winds S/SW
around 10 kts with gusts 15-20 kts.

OUTLOOK...Monday 01/12Z through Wednesday 03/12Z...Daily chances
for SHRA/TSRA each afternoon. Periods of MVFR conditions and gusty,
erratic outflow winds possible in and around TS. Winds SW 10-15
kts on Monday, becoming W 5-10 kts on Tuesday.

&&

.FIRE WEATHER...Today and Monday...Scattered showers and storms are
expected across much of northern Arizona each day, some activity may
continue into the overnight. Gusty, erratic winds possible in and
around thunderstorms. Near-normal to below normal temperatures,
along with southwest wind 10-25 mph.

Tuesday through Thursday...Chances for showers and thunderstorms
continue through Wednesday, with drier conditions returning for
Thursday. Warming temperatures, along with west winds 5-10 mph
through Wednesday, becoming northwest 10-15 mph on Thursday.

&&

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

&&

$$

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

For Northern Arizona weather information visit
weather.gov/flagstaff