Flash Flood Warning 40, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1041 AM MST Thu Sep 4 2025

.SYNOPSIS...Hurricane Lorena will continue to push additional
moisture into Arizona through the end of the week/early weekend.
Although there still remains uncertainty with the trajectory of
Lorena, gusty winds, localized flash flooding, and frequent
lightning will be the primary hazards. By Sunday, drier
conditions quickly return across the state and continue through
next week.

&&

.DISCUSSION...Majority of activity still lingering this evening
remains over Phoenix's CWA, but a few isolated showers/storms have
pushed into southern Yavapai County. Not much is expected out of
the showers in our area, but we are still on the hook for another
active afternoon/evening later today. From writing this discussion
yesterday to now, Tropical Storm Lorena was upgraded to Hurricane
Lorena. Other than the upgrade in intensity, there still is
decent uncertainty with the track of this system and how far north
the heavy rainfall will push into Arizona. Even with the lack of
high confidence in excessive rainfall leading to flash flooding
concerns, a Flood Watch has been issued for Yavapai County and
Gila County for today (between 11 AM MST - 11 PM MST). This call
was heavily influenced by the Slight Risk issued by WPC that
covers portions of Yavapai County and Gila County. Even though
tropical moisture looks to hang around through Saturday, we'll see
how today pans out before considering extending the Flood Watch.

One of the main factors that could completely downplay how active
the afternoons/evenings get will be lingering debris clouds. Plus,
hi-res guidance didn't do too hot yesterday with the placement of
storms. There just isn't a great grasp on what's to come from
Hurricane Lorena, but we'll do our best to update the forecast
accordingly.

By Sunday, our weather story becomes more straight forward.
Arizona will gradually fall under a zonal flow, which will cut off
the bulk of our moisture and leave only a few isolated showers
across higher terrain. Then by the beginning of next week, a
trough sweeps across the region and further clears us out.

&&

.AVIATION...Thursday 04/18Z through Friday 05/18Z...VFR conditions
expected, brief MVFR in heavier SHRA/TSRA. Scattered SHRA/TSRA
between 04/18Z and 05/04Z throughout most of the region. Then
between 05/04Z and 05/13Z numerous SHRA/TSRA form in southern Utah
and trek south into northern Arizona. Expect the main area of
impact to be north of the Interstate 40 corridor as around 05/12Z
the showers begin to weaken as they approach the Interstate.
Expect winds around outflow boundaries 20-40kts, gusty and
erratic winds in the immediate vicinity of SHRA/TSRA, otherwise
winds west at 5-15kts.

OUTLOOK...Friday 05/18Z through Sunday 07/18Z...VFR conditions
expected, brief MVFR in heavier SHRA/TSRA. Expect daily SHRA/TSRA
between 18Z and 03Z each day through Sunday. Expect winds around
outflow boundaries 20-40kts, gusty and erratic winds in the
immediate vicinity of SHRA/TSRA, otherwise winds south to west at
5-15kts.

&&

.FIRE WEATHER...Thursday and Friday...Tropical moisture will bring
scattered to widespread showers and thunderstorms each afternoon.
Storms will be capable of producing heavy rainfall, frequent
lightning, and gusty/erratic winds. Outside of storm driven outflow
winds, look for westerly winds 10-20 mph. Expect minimum RH values
between 20-45% on Thursday, increasing to 30-60% on Friday.

Saturday through Monday...Scattered to widespread showers/storms
will stick around on Saturday, before northern AZ quickly dries out
Sunday and Monday. Main hazards will be heavy rainfall,
gusty/erratic winds, and frequent lightning. Outside of storm
driven outflows on Saturday, expect westerly winds 5-15 mph
through Sunday, becoming southwest 10-20 mph on Monday. Look for
minimum RH values between 30-60% Friday and Saturday, dropping to
20-45% on Sunday.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Flood Watch through this evening for AZZ008-018-037.

&&

PUBLIC...Konieczny
AVIATION...Bernhart
FIRE WEATHER...Konieczny

For Northern Arizona weather information visit
weather.gov/flagstaff