Alert archive / Arizona / Severe Thunderstorm Warnings in 2020

Severe Thunderstorm Warning 5, NWS Flagstaff, AZ

July 23, 2020Coconino County, Arizona

NWS Flagstaff, AZ issued this severe thunderstorm warning at Jul 23, 2020, 10:56 AM MST for Coconino County, Arizona. It was in force for 28 min. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued: Jul 23, 2020, 10:56 AM MST (17:56 UTC)
Expired: Jul 23, 2020, 11:24 AM MST
In force: 28 min
Issued by: NWS Flagstaff, AZ
Area: Storm-based polygon
Hail: 1.0 in
Wind: 60.0 mph

County Coconino County, AZ

The radar

The Flagstaff radar (KFSX), 150 km from the middle of the area, began a volume at 17:59 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Flgstf/Belemont, AZ (KFGZ), launched 12:00Z, 5.9 hours before the alert went out and 68 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 391 J/kg
Mixed-layer CIN: -44 J/kg
Mixed-layer LCL: 1401 m above ground
0-6 km bulk shear: 31 kt
0-1 km storm-relative helicity: 49 m²/s²
0-3 km storm-relative helicity: 79 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this severe thunderstorm warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Flagstaff, AZ wrote its last area forecast discussion before this severe thunderstorm warning went out at Jul 23, 9:48 AM MST, 1 hour 8 minutes earlier.

Area forecast discussion, Jul 23, 9:48 AM MST, 1 hour 8 minutes before

Area Forecast Discussion
National Weather Service Flagstaff AZ
948 AM MST Thu Jul 23 2020

.SYNOPSIS...Widespread storm coverage is expected today through
Saturday as a favorable monsoon pattern takes hold. More typical
monsoon storm coverage is expected Sunday through the middle of
next week.

&&

.UPDATE...Increased southerly flow is observed this morning, in
response to an unusually strong low pressure system over central
California and high pressure to our east. This flow pattern has
resulted in a significant increase in lower level atmospheric
moisture over the past 24 hours (5 AM Bellemont Sounding Precipitable
Water up to 0.83", Phoenix near 1.80"). At 945 AM, most of
northern Arizona was seeing partly cloudy skies, certainly not
enough cloud cover to hamper daytime heating. With this increased
moisture, higher instability will exist today than previous days,
and a few stronger storms are possible. Storm motion should be
toward the north-northeast at 10-15 mph, with some training cells
possibly resulting in locally heavy rain amounts and flooding.
This threat covers all of northern Arizona, but especially areas
south of I-40. Made some minor forecast updates this morning, to
increase rain chances in the Winslow, Holbrook, St Johns areas as
the southerly flow should push storms off the rim into these areas
this afternoon. Otherwise, current forecasts are in good shape.

&&

.PREV DISCUSSION /450 AM MST/... An increase in lower-level
moisture combined with some enhanced dynamics will result in
greater shower and thunderstorm coverage today and into the
weekend. In fact, isolated thunderstorms have been continuing
through the night already.

Models are consistent in keeping moisture entrenched across the
area through early next week with active monsoon weather expected
daily.

&&

.AVIATION...For the 18Z package...Shower and thunderstorm
activity will become more widespread through the afternoon and early
evening hours. The stronger storms will be capable of producing MVFR
and localized IFR conditions. While the intensity of storms will
likely decrease after sunset, expect areas of precipitation to
continue into the overnight hours. Aviation discussion not updated
for amendments.

&&

.FIRE WEATHER...Expect widespread showers and thunderstorms today
and Friday. Many locations will see wetting rainfall through this
forecast period. Winds will be light and low haines indices.

Saturday through Monday...An active monsoon pattern will bring
scattered showers and thunderstorms each day, with near normal
temperatures.

&&

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

&&

PUBLIC...JJ/KD
AVIATION...TPS
FIRE WEATHER...TPS

For Northern Arizona weather information visit
weather.gov/flagstaff

In the hours before

Special weather statement, Jul 23, 10:31 AM MST, 25 minutes before

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The office that day

Everything else NWS Flagstaff, AZ issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 22, 5:11 PM MST	Flash Flood Warning Considerable damage threat	FGZ	Gila, Yavapai	3 hr
Jul 23, 10:31 AM MST	Special Weather Statement	FGZ		29 min
Jul 23, 11:46 AM MST	Special Weather Statement	FGZ	Coconino	44 min
Jul 23, 11:53 AM MST	Areal Flood Advisory	FGZ	Apache	2 hr
Jul 23, 12:59 PM MST	Areal Flood Advisory	FGZ	Apache, Navajo	3 hr
Jul 23, 1:07 PM MST	Special Weather Statement	FGZ	Yavapai	23 min
Jul 23, 1:46 PM MST	Flash Flood Warning Considerable damage threat	FGZ	Coconino	3 hr
Jul 23, 2:16 PM MST	Flash Flood Warning Considerable damage threat	FGZ	Yavapai	3 hr
Jul 23, 2:44 PM MST	Severe Thunderstorm Warning	FGZ	Coconino, Yavapai	31 min
Jul 23, 4:46 PM MST	Special Weather Statement	FGZ	Yavapai	29 min

Nearby

Severe Thunderstorm Warnings in Arizona, 2020 Every severe thunderstorm warning in 2020

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.