Flash Flood Warning 15, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
907 AM MST Sun Aug 23 2020

.SYNOPSIS...Isolated showers this morning will give way to
scattered afternoon and evening thunderstorms later today. A more
typical monsoon pattern remains on track to occur this week with
daily thunderstorm chances.

&&

.UPDATE...Slight adjustments were made to precipitation chances to
this afternoon and evening to match hi-res trends this morning.
Morning satellite shows continuing cloud cover over much of
Coconino County. It is possible that for portions of northern
Coconino County daytime heating may be limited from yesterday as
morning shower activity continues along with less sun peaking
through the low to mid level cloud deck. This could result in
less instability from yesterday for thunderstorm development.
Showers and thunderstorms are still expected with rich
precipitable water values, however these may not be as strong as
what we say yesterday.

Further south, sunshine is out this morning across much of the
southern and eastern portions of the area. These areas will have
ample time to become unstable before thunderstorm development.
Similar to yesterday, expect to see storms form along the high
terrain first before slowly moving into the lower terrain areas by
the late afternoon/evening. Hi-res models do indicate an early
start to some scattered convection over the Bradshaws near
Prescott. So, we could see an earlier start to thunderstorms in
Yavapai County than the last few days.

Threats remain largely the same today. Expect developing
thunderstorms to have gusty winds, hail, frequent lightning, and
heavy rainfall.

&&

.PREV DISCUSSION /334 AM MST/...Showers and isolated thunderstorms
have continued overnight and into the early morning hours today.
Look for expanding coverage of thunderstorms early this afternoon
and early evening. Continued monsoon activity will last through
much of this week.

This morning....GOES-17 infrared satellite imagery is
highlighting some low and mid-level cloud cover across much of
northern Arizona. Surface observations are show a few areas with
cloud bases down to around 5,000 feet above ground level along the
Mogollon Rim. Embedded within this sky cover are isolated showers
and thunderstorms that have persisted through the overnight
hours. Slight chances of precipitation for early this morning
remain limited to mainly Coconino, Yavapai and northern Gila
counties. Sky cover will slowly decrease through this morning.

Today....Model forecast soundings show a similar setup today as
we experienced on Saturday. Daytime heating will occur throughout
the morning with maximum temperatures likely being observed
shortly before afternoon cloud cover spreads across the region.
Maximum temperatures are expected to be around five to ten degrees
above normal today.

Thunderstorms will begin to initiate around the noon hour today.
These first thunderstorms will form over the higher terrain
features of the Chuska Mountains, Black Mesa, Kaibab Plateau,
along the Mogollon Rim and over the White Mountains. Weak
steering flow today will produce very slow move to nearly-
stationary thunderstorms which will drift in a general westerly to
southwesterly direction by mid-afternoon. High resolution guidance
then progs continued lower terrain thunderstorm activity through
early this evening.

The primary hazards today will be small hail, localized heavy
rainfall, lightning and strong outflow winds. While many
thunderstorms will remain below severe criteria, there is a chance
again today for some severe thunderstorms with larger hail and
very strong winds. Slightly higher precipitable water values
today could also produce more localized heavy rainfall today
compared to Saturday. Always be aware of the possibility for
ponding on roadways and slick driving conditions during the
monsoon season.

Late This Evening....Thunderstorm coverage is expected to
decrease tonight as cloud cover, remnant cold pools and decreased
daytime heating sets up a more stable boundary layer. Slight
chances for showers do persist though into early Monday morning.

Rest of the Week....The Four Corners high pressure will remain in
place through much of this week. The result will be a more
typical monsoonal pattern than what much of northern Arizona has
experienced this summer. Look for afternoon and early evening
chances of thunderstorms, highest over the higher terrain, each
day through the work week. Operational deterministic guidance
does show a shift and degradation of the high pressure by later
Friday. The result would be an affect on precipitation chances by
next weekend. Stay tuned.

&&

.AVIATION...For the 18Z package...VFR conditions and generally light
wind expected outside of convective activity over the next 24 hours.
Scattered showers and thunderstorms will develop again after 18Z
Sunday over the high country, shifting toward the lower terrain to
the southwest through the evening, with only isolated showers
possible after 04Z. TAF discussion not updated for amendments.

&&

.FIRE WEATHER...Look for scattered afternoon and evening
thunderstorms through Monday, with the most widespread activity
extending from the Coconino plateau along the Mogollon Rim to
the White Mountains. High temperatures are will be 5-10 degrees
above normal.

Tuesday through Thursday...Daily chances for showers and
thunderstorms will persist. Daytime temperatures will be slightly
above normal.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...NONE.

&&

PUBLIC...ET
AVIATION...DL
FIRE WEATHER...JJ

For Northern Arizona weather information visit
weather.gov/flagstaff