Flash Flood Watch 7, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
309 AM MDT MON AUG 1 2011

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

SCATTERED SHOWERS CONTINUE TO MOVE THROUGH NORTH CENTRAL WYOMING
THIS MORNING. MOST THUNDERSTORM ACTIVITY WEAKENS AS IT APPROACHES
THE WYOMING BORDER...THOUGH SOME THUNDERSTORM ACTIVITY IS POSSIBLE
ACROSS SOUTHERN WYOMING THIS MORNING.

SHOWERS AND THUNDERSTORMS WILL REMAIN ACROSS THE CWA TODAY IN
RESPONSE TO THE COMBINATION OF A COLD FRONT MOVING THROUGH THE AREA
AND ANOTHER MONSOONAL PUSH OF MOISTURE. THIS FRONT WILL INCREASE
SHOWER COVERAGE ACROSS THE WESTERN MOUNTAINS AND VALLEYS THROUGH THE
AFTERNOON HOURS. SMALL HAIL...DANGEROUS LIGHTNING AND GUSTY WIND
WILL BE THE PRIMARY THREATS ASSOCIATED WITH ANY ACTIVITY.
ADDITIONALLY...MODELS INDICATE ELEVATED PWAT VALUES ACROSS THE
AREA IN RESPONSE TO THE MONSOONAL PUSH OF MOISTURE. THIS INCREASE INDICATES
THAT SOME STORM ACTIVITY MAY HAVE PERIODS OF HEAVY RAINFALL. FLASH
FLOODING MAY BE A CONCERN WITH SOME STORM ACTIVITY TODAY. COOLER
TEMPERATURES EXPECTED TODAY WITH THE PASSAGE OF THE FRONT.

PERIODS OF SHOWER AND THUNDERSTORM ACTIVITY WILL THEN BE OVER THE
AREA FOR THE NEXT COUPLE OF DAYS DUE TO CONTINUED DISTURBANCES IN
THE GENERAL SOUTHWESTERLY FLOW. GUSTY WIND AND LIGHTNING WILL REMAIN
THE MAIN THREAT WITH MOST STORM ACTIVITY. THIS SOUTHWESTERLY FLOW
WILL HELP TO USHER IN DRIER AIR OVER THE FORECAST AREA FOR TUESDAY.

.LONG TERM...THURSDAY THROUGH MONDAY

ISOLATED TO SCATTERED THUNDERSTORMS WILL CONTINUE INTO THURSDAY AND
FRIDAY WITH THE BEST CHANCES ACROSS THE NORTH AND EAST.  A DRIER
AIRMASS WILL EVENTUALLY PREVAIL ACROSS THE AREA OVER THE WEEKEND
INTO EARLY NEXT WEEK.  TEMPERATURES WILL BE NEAR NORMAL THROUGH THE
PERIOD.

MEDIUM RANGE GLOBAL MODELS IN OVERALL AGREEMENT WITH SUBTLE CHANGES
IN LARGE-SCALE FEATURES THIS MORNING.  UPPER HIGH CENTERED TEXARKANA
EARLY IN THE PERIOD GRADUALLY SHIFTS WESTWARD ACROSS THE SOUTHERN
ROCKIES OVER THE WEEKEND.  TROUGH OFF THE WEST COAST WILL KICK OUT A
GOOD CHUNK OF ITS ENERGY ACROSS THE INTERMOUNTAIN WEST INTO THE
NORTHERN ROCKIES THURSDAY NIGHT AND FRIDAY.  FOCUS OF CONVECTION
WITH THIS SYSTEM WILL BE ACROSS STATIONARY FRONTAL BOUNDARY/LEE SIDE
TROUGH NEAR THE MONTANA BORDER AND EAST OF THE BIG HORN MOUNTAINS
THURSDAY AND FRIDAY.  DRIER WSW FLOW TO THE SOUTH AND WEST WILL KEEP
THUNDERSTORM ACTIVITY MORE ISOLATED.  RETROGRESSION OF UPPER HIGH TO
THE SOUTHERN ROCKIES OVER THE WEEKEND WILL EFFECTIVELY PINCH OFF
MONSOONAL MOISTURE WITH WSW FLOW ADVECTING IN A MUCH DRIER AIRMASS
ACROSS MOST OF THE AREA.  WARM TEMPERATURES...MUCH LOWER RELATIVE
HUMIDITY AND BREEZY AFTERNOON/EVENINGS WILL INCREASE THE FIRE
DANGER...ESPECIALLY AFTER POTENTIAL LIGHTNING-CAUSED IGNITIONS FROM
THE PRECEDING ACTIVE PERIOD.  ISOLATED THUNDERSTORMS WILL BE MOSTLY
CONFINED TO THE FAR NORTH AND IN THE VICINITY OF THE BIG HORN
MOUNTAINS OVER THE WEEKEND.

&&

.AVIATION...

SHORTWAVE LIFTING NORTH AND THEN NORTHEAST THROUGH NEVADA AND UTAH
EARLY THIS MORNING WILL TRAVERSE WESTERN/CENTRAL WYOMING ON MONDAY.
VFR CONDITIONS WILL PREDOMINATE BUT MVFR VISIBILITIES WILL OCCUR
WITH AFTERNOON CONVECTION. LOCALIZED VISIBILITIES COULD BE IFR WITH
STRONGEST AFTERNOON CONVECTION. TOUGH TO FURTHER PIN-POINT TIMING
AND EXACT LOCATIONS IN THIS SCENARIO. PRECIPITABLE WATER VALUES HAVE
CONTINUED TO CLIMB AND DEW POINTS IN THE CENTRAL BASINS HAVE FINALLY
RISEN. SHOWERS AND THUNDERSTORMS WILL BE WIDESPREAD ALONG AND WEST
OF THE CONTINENTAL DIVIDE AS THE SHORTWAVE LIFTS ACROSS THE REGION.
DYNAMICS WILL BE SUFFICIENT TO KEEP CONVECTION GOING THIS MORNING
WITH THUNDERSTORMS BECOMING MORE PREVALENT DURING THE AFTERNOON.
ENVIRONMENT FAVORS HEAVY RAIN AS THE MAIN HAZARD WITH KJAC...KBPI...
KPNA AND KRKS TERMINALS. SCATTERED COVERAGE EXPECTED EAST OF THE
DIVIDE WITH MOST CONVECTION BEING DIURNALLY DRIVEN. INVERTED-V
ENVIRONMENT WILL TRANSITION TO MORE SATURATED ENVIRONMENT BY LATE
THIS MORNING AND THEREFORE FAVOR HEAVY RAIN FOR THE REMAINDER OF THE
FORECAST PERIOD. SURFACE PRESSURE GRADIENT WILL GENERATE SOUTHWEST
WIND 12-25KTS FROM LATE MORNING AT KRKS AND KCPR TO EARLY AFTERNOON
AT OTHER TERMINALS. THE EXCEPTIONS WILL BE KCOD AND KWRL WHICH WILL
SEE SURFACE FRONT DRIVEN SOUTH THROUGH THE BIG HORN BASIN FROM ABOUT
16Z AT KCOD TO 18Z-19Z AT KWRL. THIS BOUNDARY WILL REACH KRIW/KLND
AROUND 23Z AND KCPR BY 01Z/TUE. FRONTAL PASSAGE WILL HINDER
INSTABILITY AND DEEPER CONVECTION AT KCOD AND KWRL. HOWEVER...FRONT
WILL LIKELY SERVE AS A FOCUSING MECHANISM AS IT MOVES INTO CENTRAL
BASINS LATE THIS AFTERNOON. UPSLOPE FLOW BEHIND THE FRONT IN THIS
REGION SHOULD AID CONTINUED SHOWERS/STORMS FROM 00Z-06Z/TUE.
POSSIBILITY OF FOG EXISTS AT KBPI...KJAC AND KCPR EARLY TUESDAY
MORNING WITH CLEARING SKIES...CALM WINDS...AND LOW TEMPERATURE-DEW
POINT SPREADS.

&&

.FIRE WEATHER...

MOIST CONDITIONS EXPECTED TODAY. COOLER TEMPERATURES WILL ALSO BE
PRESENT AS A COLD FRONT MOVES THROUGH THE AREA. SOME GUSTY WIND IS
EXPECTED ACROSS FAVORED LOCATIONS FOR THIS AFTERNOON. SHOWERS AND
THUNDERSTORMS WILL ALSO BE POSSIBLE ACROSS THE MAJORITY OF THE
FORECAST AREA FOR THE NEXT COUPLE OF DAYS. LIGHTNING AND GUSTY WIND
WILL BE THE PRIMARY THREATS WITH ANY ACTIVITY. IN
ADDITION...PRECIPITABLE WATERS WILL BE ELEVATED FOR MONDAY
POTENTIALLY BRINGING PERIODS OF MODERATE TO HEAVY RAINFALL WITH
STORM ACTIVITY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

SHORT TERM...BRANHAM
LONG TERM...AEM
AVIATION...CNJ
FIRE WEATHER...BRANHAM

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
1010 AM MDT MON AUG 1 2011

WYZ012-013-023-024-011915-
JACKSON HOLE-SALT RIVER AND WYOMING RANGES-STAR VALLEY-
TETON AND GROS VENTRE MOUNTAINS-
1010 AM MDT MON AUG 1 2011

NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS WILL SPREAD NORTH INTO
THE STAR VALLEY...JACKSON HOLE AND SURROUNDING MOUNTAINS INTO THE
AFTERNOON. EXPECT LOCALLY VERY HEAVY RAINFALL.  WIDESPREAD RAINFALL
AMOUNTS OF 0.15 TO 0.30 INCHES ARE EXPECTED THROUGH THE MORNING WITH
LOCAL AMOUNTS AROUND ONE INCH.  CAMPERS AND HIKERS SHOULD BE
PREPARED THE ONSET OF HEAVY DOWNPOURS AND POSSIBLE RAPID RISES IN
SMALLER CREEKS AND STREAMS THIS MORNING.

19

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
1014 AM MDT MON AUG 1 2011

WYZ002-014>016-012015-
ABSAROKA MOUNTAINS-UPPER WIND RIVER BASIN-WIND RIVER MOUNTAINS EAST-
WIND RIVER MOUNTAINS WEST-
1014 AM MDT MON AUG 1 2011

NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS WILL SPREAD INTO
THE SOUTHERN ABSAROKAS...WESTERN WIND RIVER MOUNTAINS...UPPER WIND
RIVER VALLEY AND SURROUNDING AREAS INTO THE AFTERNOON. EXPECT
LOCALLY VERY HEAVY RAINFALL. WIDESPREAD RAINFALL AMOUNTS OF 0.15 TO
0.30 INCHES ARE EXPECTED THROUGH THE MORNING WITH LOCAL AMOUNTS
AROUND ONE INCH. CAMPERS AND HIKERS SHOULD BE PREPARED THE ONSET OF
HEAVY DOWNPOURS AND POSSIBLE RAPID RISES IN SMALLER CREEKS AND
STREAMS THIS MORNING.

19