Alert archive / Utah / Areal Flood Warnings in 2012

Areal Flood Warning 41, NWS Salt Lake City, UT

September 11, 2012Washington County, Utah

NWS Salt Lake City, UT issued this areal flood warning at Sep 11, 2012, 10:52 AM MDT for Washington County, Utah. It was in force for 8 hr. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued
Sep 11, 2012, 10:52 AM MDT (16:52 UTC)
Expired
Sep 11, 2012, 6:45 PM MDT
In force
8 hr
Issued by
NWS Salt Lake City, UT
Area
Storm-based polygon
Flood severity
None

County Washington County, UT

The radar

The Cedar City radar (KICX), 66 km from the middle of the area, began a volume at 16:53 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

Las Vegas, NV (KVEF), launched 12:00Z, 4.9 hours before the alert went out and 207 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-pSkew-T log-p diagram, Las Vegas, NV at 12:00Z on 2012-09-11Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 2 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Las Vegas, NV at 12:00Z on 2012-09-11The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 17 square meters per square second.1939Sfc1 km3 km6 km9 kmRMLM
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
2 J/kg
Mixed-layer CIN
-171 J/kg
Mixed-layer LCL
1725 m above ground
0-6 km bulk shear
9 kt
0-1 km storm-relative helicity
17 m²/s²
0-3 km storm-relative helicity
37 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 areal flood warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Salt Lake City, UT wrote its last area forecast discussion before this areal flood warning went out at Sep 11, 3:22 AM MDT, 7 hours 30 minutes earlier.

Area forecast discussion, Sep 11, 3:22 AM MDT, 7 hours 30 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
322 AM MDT TUE SEP 11 2012

.SYNOPSIS...INCREASING MOISTURE ACROSS UTAH WILL BRING SHOWERS
AND THUNDERSTORMS TO MUCH OF UTAH THROUGH WEDNESDAY. SUBSTANTIALLY
DRIER AIR WILL SPREAD SOUTH ACROSS THE NORTHWEST WEDNESDAY AND
STATEWIDE THURSDAY.

&&

.DISCUSSION...WATER VAPOR SATELLITE LOOP SHOWS A DISTURBANCE LIFTING
NORTHEAST INTO SOUTHWEST ARIZONA...WITH A SECOND DISTURBANCE
APPROACHING FRONT CENTRAL CALIFORNIA. A DEEP CLOSED LOW HAS FORMED
OVER THE CANADIAN ROCKIES WITH A TROUGH CROSSING THE NORTHERN
ROCKIES.

RUC INDICATES COPIOUS MOISTURE (PRECIPITABLE WATER VALUES RANGING
FROM 1.0"-1.4") HAS SPREAD ACROSS SOUTHERN AND CENTRAL UTAH...WITH
VALUES CLOSER TO A QUARTER INCH RESTRICTED TO FAR NORTHWEST UTAH.
COOL FRONT ASSOCIATED WITH AFOREMENTIONED TROUGH HAS SLIPPED INTO
NORTHWEST UTAH BRINGING MUCH DRIER AIR INTO THAT PORTION OF THE
STATE. DEWPOINTS ARE CURRENTLY IN THE 40S EASTERN VALLEYS AND WELL
INTO THE 50S ACROSS CENTRAL AND WESTERN VALLEYS. THE EXCEPTION IS
FAR NORTHWEST UTAH WHERE VALUES ARE CLOSER TO 20F. THIS REPRESENTS
AN INCREASE OF 15-25F EXCEPT A DECREASE OF 10-20F FAR NORTHWEST
UTAH DURING THE PAST 24 HOURS.

RADAR TRENDS INDICATE A GOOD DEAL OF ELEVATED CONVECTION ACROSS
SOUTHERN AND CENTRAL UTAH ATOP OF WHAT LOOKED LIKE AN EARLIER
OUTFLOW THAT HAS MOVED INTO SOUTHERN UTAH. MEANWHILE...COPIOUS
CONVECTION AND VERY COLD CLOUD TOPS (PER IR SATELLITE) IS
APPROACHING FROM NEVADA DRIVEN BY THE APPROACHING CALIFORNIA
DISTURBANCE. ARIZONA IS BECOMING MORE ACTIVE AS THE DISTURBANCE TO
THE SOUTH APPROACHES. ALL THIS POINTS TO A VERY ACTIVE CONVECTIVE
DAY.

GIVEN THE COMBINATION OF MOISTURE (+2 TO +3 STANDARD DEVIATIONS FROM
NORMAL) AND DYNAMICAL LIFT...FLASH FLOOD WATCH FOR CENTRAL AND
SOUTHERN UTAH THROUGH THIS EVENING LOOKS ON TARGET. FLASH FLOOD
PRONE AREAS INCLUDE SLOT CANYONS AND NORMALLY DRY WASHES OF SOUTHERN
UTAH...AND RECENT BURN SCARS ACROSS SOUTHERN AND CENTRAL UTAH.

THE COMBINATION OF INCREASED CLOUD COVER AND PASSAGE OF A SHALLOW
COOL FRONT WILL SUPPORT COOLER TEMPERATURES THROUGH MID WEEK.

MOISTURE LINGERS ACROSS SOUTHERN UTAH TOMORROW AS THE TRAILING
DISTURBANCE PASSES THROUGH. CONVECTIVE COVERAGE WILL THIN OUT BUT
STILL POSE A HEAVY RAIN THREAT FOR SOUTHERN UTAH BEFORE DECAYING
DURING THE EVENING HOURS. GFS AND EUROPEAN MODELS SHOW A STRONG
DRYING TREND THEREAFTER INTO THE WEEKEND AS A RIDGE BUILDS FROM
THE WEST.

NEXT APPROACHING DISTURBANCE LOWERS HEIGHTS AS IT APPROACHES SUNDAY
WITHIN NORTHWEST FLOW ALOFT. ADDED MENTION OF CONVECTION SUNDAY IN
THE TERRAIN AS IT APPEARS THAT MOISTURE WILL RECOVER SOMEWHAT IN
ADVANCE OF THIS FEATURE. DRY NORTHWEST FLOW EXPECTED EARLY NEXT WEEK.

&&

.AVIATION...THE SLC TERMINAL WILL SEE VFR CONDITIONS THROUGHOUT THE
DAY. SOUTHERLY WINDS ARE EXPECTED TO SHIFT TO THE NORTHWEST BETWEEN
15Z AND 17Z WITH THE PASSAGE OF A COLD FRONT...BUT THERE IS A 30
PERCENT CHANCE THIS WILL OCCUR AN HOUR OR TWO LATER THAN EXPECTED.
THERE IS ALSO A 30 PERCENT CHANCE THAT OUTFLOW FROM THUNDERSTORMS IN
THE VICINITY OF THE TERMINAL WILL PRODUCE PERIODS OF GUSTY AND/OR
ERRATIC WINDS THIS AFTERNOON THROUGH EARLY THIS EVENING.

&&

.FIRE WEATHER...COLD FRONT REMAINS OVER NORTHERN UTAH THIS MORNING
WITH SHOWERS AND THUNDERSTORMS CONTINUING OVER CENTRAL AND SOUTHERN
UTAH. THE FRONT WILL MOVE SOUTHWARD TODAY...BRINGING DRIER AND MORE
STABLE AIR BEHIND IT. HOWEVER...NUMEROUS SHOWERS AND THUNDERSTORMS
WILL DEVELOP OVER THE REMAINDER OF THE DISTRICT BY THIS
AFTERNOON...BRINGING A HIGH POSSIBILITY OF WETTING RAIN. THE FRONT
WILL MAKE IT TO SOUTHERN UTAH WEDNESDAY...SO CONVECTION WILL BE
CONFINED TO THAT AREA THEN. HIGH PRESSURE WILL BRING A DRY AND
STABLE AIRMASS TO THE ENTIRE DISTRICT THURSDAY. MOISTURE WILL MAKE
ITS WAY BACK INTO THE DISTRICT OVER THE WEEKEND.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...FLASH FLOOD WATCH THROUGH THIS EVENING FOR
     UTZ004-008-010-012>016-019>021-517-518.

WY...NONE.
&&

PUBLIC...ROGOWSKI
FIRE WEATHER...TRAPHAGAN
AVIATION...TRAPHAGAN

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)

FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION
VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP (ALL LOWER CASE)
Hazardous weather outlook, Sep 11, 3:00 AM MDT, 7 hours 52 minutes before
HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
300 AM MDT TUE SEP 11 2012

UTZ001>016-019>021-517-518-WYZ021-121300-
CACHE VALLEY/UTAH PORTION-NORTHERN WASATCH FRONT-
SALT LAKE AND TOOELE VALLEYS-SOUTHERN WASATCH FRONT-
GREAT SALT LAKE DESERT AND MOUNTAINS-WASATCH MOUNTAIN VALLEYS-
WASATCH MOUNTAINS I-80 NORTH-WASATCH MOUNTAINS SOUTH OF I-80-
WESTERN UINTA MOUNTAINS-WASATCH PLATEAU/BOOK CLIFFS-
WESTERN UINTA BASIN-CASTLE COUNTRY-SAN RAFAEL SWELL-
SANPETE/SEVIER VALLEYS-WEST CENTRAL UTAH-SOUTHWEST UTAH-
UTAHS DIXIE AND ZION NATIONAL PARK-SOUTH CENTRAL UTAH-
GLEN CANYON RECREATION AREA/LAKE POWELL-CENTRAL MOUNTAINS-
SOUTHERN MOUNTAINS-SOUTHWEST WYOMING-
300 AM MDT TUE SEP 11 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE WESTERN TWO THIRDS OF
UTAH AND SOUTHWEST WYOMING.

.DAY ONE...TODAY AND TONIGHT

NUMEROUS SHOWERS AND THUNDERSTORMS WILL AFFECT CENTRAL AND
SOUTHERN UTAH THROUGH THIS EVENING. SOME OF THESE STORMS WILL
CONTAIN HEAVY RAINFALL WITH THE POTENTIAL TO CAUSE FLASH FLOODING.
FLASH FLOOD PRONE AREAS INCLUDE SLOT CANYONS AND NORMALLY DRY
WASHES OF SOUTHERN UTAH...AND RECENT BURN SCARS ACROSS THE STATE.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

FLASH FLOODING CANNOT BE RULED OUT ACROSS SOUTHERN UTAH
WEDNESDAY...THOUGH STORM COVERAGE WILL BE LESS THAN TODAY.

DRIER AIR WILL FILTER INTO THE AREA FROM THE NORTH TONIGHT
AND GRADUALLY SPREAD ACROSS THE REMAINDER OF UTAH BY THURSDAY
MORNING ENDING THE FLASH FLOOD THREAT.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

ROGOWSKI

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)

FOR INFORMATION ON POTENTIAL TRAVEL IMPACTS VISIT...
HTTP://WWW.UDOTTRAFFIC.UTAH.GOV/ROADWEATHERFORECAST.ASPX

In the hours before

Local storm report, Sep 11, 10:49 AM MDT, 3 minutes before
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The office that day

Everything else NWS Salt Lake City, UT issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 10, 6:08 PM MDTSpecial Weather StatementSLCTooele22 min
Sep 11, 12:20 PM MDTAreal Flood WarningSLCKane4 hr
Sep 11, 12:27 PM MDTFlash Flood WarningSLCWayne4 hr
Sep 11, 1:45 PM MDTFlash Flood WarningSLCWashington3 hr
Sep 11, 4:20 PM MDTFlash Flood WarningSLCWayne3 hr

Nearby

Areal Flood Warnings in Utah, 2012Every areal flood warning in 2012

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.