481
FXUS65 KFGZ 302130
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
230 PM MST Sun Jun 30 2024

.SYNOPSIS...The active monsoonal pattern continues through
Wednesday with scattered showers and thunderstorms, light winds,
and seasonable temperatures expected each day. Then, a warming
and drying trend develops for the holiday weekend as high pressure
strengthens towards the west.

&&

.DISCUSSION...As predicted, thunderstorms have developed early
this afternoon across the White Mountains and portions of
southern Coconino County, moving northward at about 10-20 mph. No
indications of any severe storms at this time, however, the main
concern continues to be the threat of heavy rain and flash
flooding. Current dewpoints are in the 50-60F range along and
south of I-40 and should continue to increase northward as the
afternoon progresses. Shower and storm coverage is forecast to
increase during this time and persist into early this evening.

Then, things get interesting tonight as a subtle shortwave comes
up from the south and tracks across northern Arizona, southwest
to northeast. This disturbance will likely result in increased
shower activity overnight with greatest chances across Yavapai and
southern Coconino counties. Overcast skies with moderate to heavy
rainfall at times is anticipated along with areas of steady,
stratiform rain. With a longwave trough draped over the
Intermountain West, dry southwesterly flow should inhibit this
moisture advection, from the south, from reaching farther north
than the Grand Canyon. POPs have been adjusted this afternoon for
tonight, using the latest hi-res guidance, with the greatest
chances extending from Prescott to Polacca on the Navajo Nation.

By sunrise Monday morning, shower coverage should decrease
becoming more isolated with scattered activity continuing near the
Four Corners. Southwesterly flow increases a bit for Monday
afternoon as a trough passes by towards the north. Another round
of shower and storm activity remains in the forecast for Monday
afternoon, however, confidence is on the lower side at this time
in regards to overall coverage as cooler, overcast conditions
could lead to limited convection.

Cloud cover clears Monday night and into Tuesday as surface to
mid-level moisture remains in place. Weak westerly flow develops
by the afternoon, but given the moisture and anticipated clear
skies Tuesday morning, thunderstorm activity could be more
abundant compared to Monday with a few hi-res model solutions
showing signs of this potential scenario. As of now, chances are
confined to locations mainly along and south of I-40, however,
this could increase in coverage northward with even greater
chances towards the south for Tuesday. Something to keep our eye
on.

One more day of isolated to scattered showers and thunderstorms
is likely on Wednesday before a drying and warming trend develops
for Thursday and Friday as high pressure strengthens towards the
west. Confidence continues to increase in 5-10 degree above
average temperatures returning for the 4th of July and into the
holiday weekend with little to no chances for precipitation thanks
to dry, northwest flow. Ensemble guidance continues to show a
strong, high pressure ridge developing over much of the West Coast
for next weekend and into early next week. This is not a favorable
position for a ridge in regards to monsoonal activity as being on
the eastern side of this high pressure system results in much
drier northerly flow. However, depending on the overall strength
of this high and potential convective activity in Mexico, moisture
could try to sneak northward into Arizona.

&&

.PREV DISCUSSION /823 AM MST/...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.

&&

.AVIATION...Sunday 30/18Z through Monday 01/18Z...Scattered to
widespread showers and thunderstorms are expected from ~19Z-02Z
with greatest chances along and east of a KPAN-KSEZ-KFLG-KGCN
line. Brief periods of MVFR VIS and CIGS are likely during this
time. After 03Z, expect widespread -SHRA and MVFR conditions to
persist with heavier showers for KPRC-KSEZ-KFLG until ~12Z-14Z.
Besides for gusty and erratic outflow winds from any storms,
anticipate south-southwest winds, 10-20 kts, for this afternoon,
becoming south-southeast, 5-15 kts, after 03Z.

OUTLOOK...Monday 01/18Z through Wednesday 03/18Z...The active
pattern continues with showers and storms expected each day,
tapering each night. Afternoon winds, 10-20 kts, out of the
southwest on Monday, followed by west-northwest winds for Tuesday
and Wednesday.

&&

.FIRE WEATHER...This Evening through Tuesday...The active monsoonal
pattern continues through Tuesday with scattered showers and
thunderstorms each afternoon. Activity looks to increase this
evening and persist overnight, with greatest chances and coverage
across Yavapai, northern Gila, and southern Coconino counties. Main
threats include brief, heavy rainfall rates of 1-2 inches per hour
and gusty outflows. Outside of any outflow winds, anticipate
southwest winds, 15 to 20 mph, becoming west on Tuesday.

Wednesday through Friday...One more day of isolated to scattered
showers and thunderstorms is likely on Wednesday before a drying and
warming trend develops for Thursday and Friday as high pressure
strengthens towards the west. Daytime temperatures of 5-10 degrees
above average return for both Thursday and Friday with afternoon
humidity near 15%. West-northwest winds, 15 to 20 mph, are forecast
on Wednesday, followed by north-northwest winds on Thursday and
Friday.

&&

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

&&

$$

PUBLIC...LaGuardia/RR
AVIATION...LaGuardia
FIRE WEATHER...LaGuardia

For Northern Arizona weather information visit
weather.gov/flagstaff