Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 240505
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1105 PM MDT THU JUL 23 2015

.SHORT TERM...TONIGHT THROUGH FRIDAY (ISSUED AT 310 PM MDT)

WV IMAGERY SHOWING TROF RIDGE TROF FROM W TO E ACROSS THE
CONUS...WITH EMBEDDED SMALL SW ENERGY CURRENTLY MOVING ACROSS NRN TO
NERN WY...AND ANOTHER UPSTREAM OVR NERN NV/NRN UT HEADED THIS WAY.
SFC HAS LOW P OVR THE NERN CORNER OF WY WITH WEAK COLD FRONT DRAPED
ROUGHLY ALONG THE BORDER BETWEEN WY AND MT AND A MINOR TROF LAYING
JUST TO THE SOUTH. HIGH P ACROSS THE SWRN FA.

THIS AFTERNOON AND TONIGHT...ISOLATED TO WIDELY SCATTERED SHOWERS
AND THUNDER ACROSS THE WESTERN MOUNTAIN AND TO A LESSER EXTENT OVR
THE NRN FA INCLUDING THE BIGHORN BASIN. UPR LV SWRLY FLOW WITH
EMBEDDED SW TROF MOVING NEAR OR OVR NWRN WY W/ MODEST BUT DECREASING
MID LVL MOISTURE ACROSS THE NWRN HALF OF THE STATE...HIGHEST
MOISTURE OVR NERN WY. GENERALLY WIDELY SCATTERED STORMS
AROUND...MAINLY OVR THE W/NW AND NRN FA. SOUNDINGS SHOW LONG SKINNY
RELATIVELY LOW CAPE IN THIS AREA WITH MODEST SHEAR UP TO 30 KTS THRU
6 KM. 35 TO 45 KT DOWNDRAFTS WITH AN ISOLATED BORDERLINE SVR
DOWNDRAFT POSSIBLE. SMALL HAIL ALSO POSSIBLE ON AN ISOLATED
BASIS...MAINLY WITH A STRONGER STORM OVR THE WEST THIS AFTERNOON.
BRIEF HEAVY RAIN MAKERS MOST LIKELY ACROSS THE NRN BIGHORN BASIN
LATE AFTERNOON TO EARLY EVENING...NRN JOHNSON COUNTY THIS EVENING.
STORMS WILL BE TRUCKING ALONG TO THE ENE AT AROUND 30 KTS.
OTHERWISE...GUSTY W TO SW WINDS ACROSS THE S/SERN ZONES THIS
AFTERNOON WILL BE ON THE DECREASE EARLY THIS EVENING.
BORDERLINE...RH AND LENGTH OF TIME...RED FLAG CONDITIONS...OVR FIRE
WX ZONE 280 LATER THIS AFTERNOON SHOULD DECREASE QUICKLY THIS
EVENING. WILL DROP THE FFW THIS AFTERNOON ACROSS THE WEST AS DRYING
IS CURRENTLY OCCURRING AND PWS ARE DROPPING.

FRIDAY...UPR RIDGING BEGINNING WITH DECREASING MOISTURE THROUGHOUT
THE ATMOSPHERE ACROSS THE FA. MAINLY ISOLATED TO OCCASIONAL WIDELY
SCATTERED STORMS OVR THE NW AND NRN ZONES. AGAIN...HIGH BASED...LOW
CAPE AND HIGH SHEAR WITH GUSTY WINDS AS THE MAIN THREAT.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

SHOWERS TO CONTINUE ACROSS NORTHWESTERN WYOMING THROUGH SATURDAY.
MODEL MOISTURE PEGS YELLOWSTONE AS ITS PRIMARY AREA TO
TARGET...WITH ACTIVITY WANING FINALLY LATE SUNDAY. GENERAL
SOUTHWEST FLOW CONTINUE SUNDAY AFTERNOON...WITH SOME GUSTY WIND
POSSIBLE.

AN APPROACHING TROUGH OF LOW PRESSURE WILL ADVANCE TOWARDS WYOMING
SUNDAY NIGHT...WITH ACTIVITY REACHING INTO NORTHWESTERN WYOMING BY
MONDAY MORNING. THIS SYSTEM MAY PUSH A WEAK COLD FRONT THROUGH THE
FORECAST AREA...THOUGH THE MAIN AREA OF LOW PRESSURE WILL BEGIN TO
LIFT NORTH ONCE IT HITS THE WYOMING-IDAHO-MONTANA BORDER.
AGAIN...YELLOWSTONE LOOKS TO BE THE FAVORED LOCATION FOR ANY
EXPECTED PRECIPITATION.

WITH THE DEPARTURE OF THIS WAVE OF LOW PRESSURE...THE EXPECTATION
REMAINS FOR A BUILDING AREA OF HIGH PRESSURE OVER THE
INTERMOUNTAIN WEST. DRY CONDITIONS EXPECTED THROUGH THE REMAINDER
OF THE FORECAST PERIOD...WITH WARMING TEMPERATURES EXPECTED.

&&

.AVIATION.../06Z ISSUANCE/

ISOLATED SHOWERS OVER THE NORTH THROUGH 11Z...NORTH OF A LINE FROM
KJAC TO KBYG. THEN NEW SHOWERS AND STORMS WILL DEVELOP OVER
NORTHWEST WY AFTER 19Z AND MOVE NORTHEAST INTO FAR NORTH WY AFTER
21Z. MOST OF THE ACTIVITY WILL BE ALONG AND NORTH OF A LINE FROM
AFTON TO KAYCEE. THE SHOWERS AND STORMS WILL OCCUR THROUGH 03Z WITH
LINGERING SHOWERS AFTER 03Z. VFR CONDITIONS WILL PREVAIL OVER THE
REGION. LOCAL MVFR CONDITIONS MAY OCCUR IN STORMS THAT PRODUCE
LOCALLY HEAVY RAIN REDUCING VISIBILITY. WIND GUSTS TO 30 KNOTS WILL
ALSO BE POSSIBLE WITH SHOWERS AND STORMS. THE NORTHWEST MOUNTAINS
AND THE BIGHORN MOUNTAINS WILL BE PARTIALLY OBSCURED AT TIMES DURING
THE LATE AFTERNOON AND EVENING HOURS.

&&

.FIRE WEATHER...

FUELS CRITICAL ACROSS ZONES 280 AND 281. NEAR RED FLAG CONDITIONS
FOR A FEW HOURS TODAY ACROSS ZONE 280...NATRONA COUNTY...AS BOTH
WINDS AND MINIMUM RH VALUES GET CLOSE TO CRITICAL. HOWEVER...AT THE
MOMENT IT APPEAR THAT CRITICAL LEVELS WILL EITHER NOT BE MET OR WILL
BE TOO SHORT-LIVED. ELSEWHERE...FIRE DANGER WILL BE SOMEWHAT ENHANCED
AS A WARM AND RELATIVELY DRY ATMOSPHERE CONTINUES AND WINDS BECOME
GUSTY AT TIMES OUT OF THE SOUTHWEST TO WEST...OR NEAR ISOLATED TO
WIDELY SCATTERED THUNDERSTORMS ACROSS THE WEST AND NORTH. A SMALL
POTENTIAL FOR FIRE STARTS WILL EXIST DUE TO LIGHTNING STRIKES ACROSS
THOSE AREAS WHERE THUNDERSTORMS ARE PRESENT. FRIDAY...SIMILAR
CONDITIONS WILL EXIST OVER THE SAME LOCATIONS AS TODAY...BUT WITH
SLIGHTLY LESS GUSTY WINDS OVER ZONE 280...AND SMALLER CHANCES FOR
THUNDER ACROSS THE NORTHWEST AND NORTHERN FORECAST AREA.

&&

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

&&

$$

SHORT TERM...BRAUN
LONG TERM...BRANHAM
AVIATION...AR
FIRE WEATHER...BRAUN


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