260
FXUS65 KFGZ 042042
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
142 PM MST Tue Jun 4 2024

.SYNOPSIS...Hotter temperatures and mainly dry conditions are
expected for the latter half of this week as high pressure builds
over the Southwest. Temperatures begin to cool gradually for this
weekend with the potential for a few showers and thunderstorms.

&&

.DISCUSSION...Besides for a few cumulus clouds bubbling over the
high terrain this afternoon, much of the mid to upper-level cloud
cover has cleared out as a high pressure ridge continues to
position itself over much of the West coast and into the Great
Basin. Temperatures will increase significantly each day through
Friday as this high pressure is expected to strengthen.

The main story for the next three days will be the temperatures as
daytime highs are forecast to be 5-10 degrees above average on
Wednesday, followed by 10-15 degrees above average for Thursday
and Friday as geopotential heights peak. A handful of record highs
are forecast for both these days across northern Arizona. At this
time, the Excessive Heat Warning remains in effect for Thursday
into Friday for elevations mainly below 4000 feet.

By Thursday, a weak, upper-level low pressure system off of the
Baja coast shifts northeastward as the axis of the ridge migrates
eastward with the center more over New Mexico. This synoptic setup
will allow for light southerly flow to develop into Arizona,
resulting in a gradual increase in mid-level moisture. Given the
daytime heating and a bit more moisture in place, slight chances
(15-20%) for isolated showers and thunderstorms remain in the
forecast for Thursday afternoon, mainly confined to the higher
terrain, i.e. the Kaibab Plateau, Mogollon Rim, and the White
Mountains. With the surface layer expected to remain quite dry
during this time (RH values of 5-12%), any storms that do develop
will likely be the hybrid, high-based type, which means the
threat of dry lightning and gusty outflows increases. Given that
ERCs (Energy Release Component) across much of northern Arizona
have risen into that 90th percentile threshold (very dry fuels),
any lightning strikes with very little rainfall (<0.10") could
potentially result in new fire starts. The threat should decrease
by the evening as convection cuts off.

Temperatures gradually cool, returning to near normal (within 5
degrees of average) by this weekend as the ridge becomes less
amplified and heights decrease. Slight chances for isolated
showers and storms persist mainly along the NM/AZ border towards
the east, increasing in coverage on Sunday as the upper-level low,
mentioned previously, ejects on shore and over Arizona.

As we head into next week, confidence is increasing in a return of
above average temperatures with little moisture thanks to guidance
from the CPC and WPC`s Days 6-9 Cluster Analysis tool. Shower and
storm chances could persist through Tuesday of next week, however,
the majority of the ensemble members from the GEFS and EPS suggest
a drop off in PWAT values thereafter, roughly half of what they
should be this time of year according to SPC sounding climatology.

&&

.AVIATION...Tuesday 04/18Z through Wednesday 05/18Z...VFR
conditions persist. Generally W-NW winds 5-15 kts, though some
variability in direction expected. Light and variable winds
forecast to return around 03Z.

OUTLOOK...Wednesday 05/18Z through Friday 07/18Z...VFR conditions
continue to persist. Light and variable winds generally 10 kts or
less forecast for much of Wednesday, becoming W-SW 5-15 kts
Thursday afternoon. Isolated TS/-TSRA possible Thursday along a
KGCN-KFLG-KJTC line between 18Z Thursday - 06Z Friday.

&&

.FIRE WEATHER...Wednesday through Thursday...Warming temperatures
and light and variable winds for Wednesday. Afternoon RHs will fall
into the low teens to single digits. Temperatures near record highs
Thursday as winds become more focused out of the SW 5-15 mph. Dry
thunderstorms will develop mainly along the Mogollon Rim Thursday
afternoon. Little change in afternoon RH.

Friday through Sunday...Near record heat persists Friday before
temperatures cool 5-10 degrees over the weekend. Dry thunderstorm
threat will become more confined to the White Mountains each
afternoon. Both afternoon and overnight RHs increase over the
weekend.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...

Excessive Heat Warning from 10 AM MST /11 AM MDT/ Thursday to 8
PM MST /9 PM MDT/ Friday for AZZ005-006-037.

&&

$$

PUBLIC...LaGuardia
AVIATION...RKR
FIRE WEATHER...RKR

For Northern Arizona weather information visit
weather.gov/flagstaff