213
FXUS65 KFGZ 050324
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
824 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.

&&

.UPDATE...Mostly clear skies this evening as high pressure sits
just to the west. Overnight temperatures should be a couple of
degrees warm than previous nights and then rise well above normal
for Wednesday afternoon.

Afternoon forecast package is on track, with no major changes
needed this evening. Previous discussion continues below.

&&

.PREV DISCUSSION /422 PM MST/...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...Wednesday 05/00Z through Thursday 06/00Z...VFR
conditions will persist. Look for light and variable winds
generally less than 10 kts.

OUTLOOK...Thursday 06/00Z through Saturday 08/00Z...VFR conditions
are forecast. Afternoon winds west to southwest at 5-15 kts with
gusts as high as 25 kts on Friday. Isolated thunderstorms
possible Thursday along a KGCN-KFLG-KJTC during the afternoon and
evening. Storm threat shifting eastward on Friday to mainly along
and south of a KSOW-KSJN line.

&&

.FIRE WEATHER...Wednesday and Thursday...Hot and dry with near
record high temperatures. Light and variable winds on Wednesday
becoming southwest at 5-15 mph on Thursday. Afternoon RH values 5-
15%. There will be just enough mid-level moisture for dry
thunderstorms mainly along the Mogollon Rim Thursday afternoon.

Friday through Sunday...Near record heat persists Friday before
temperatures cool 5-10 degrees over the weekend. The dry
thunderstorm threat will become more confined to the White Mountains
each afternoon. Both afternoon and overnight RH values 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...Humphreys/LaGuardia
AVIATION...McCollum
FIRE WEATHER...McCollum

For Northern Arizona weather information visit
weather.gov/flagstaff