Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 230848
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
248 AM MDT THU JUL 23 2015

.SHORT TERM...THURSDAY THROUGH SATURDAY NIGHT

LIKE THE PREVIOUS COUPLE OF DAYS...WE CONTINUE TO HAVE A COUPLE OF
SHOWERS AROUND THE AREA BUT THEY ARE LIGHT AND SHOULD BE OVER FOR
THE MOST PART BY DAYBREAK. AND LIKE YESTERDAY...THERE WILL ONCE
AGAIN BE A SCATTERING OF SHOWERS AND THUNDERSTORMS AROUND THE AREA.
THE DIFFERENCE TODAY IS THAT THE STORMS WILL BE CONCENTRATED ACROSS
NORTHERN AND WESTERN AREAS WITH MAINLY DRY CONDITIONS ACROSS
SOUTHEASTERN PORTIONS OF THE COUNTY WARNING AREA. THERE IS THE
GREATER CHANCE OF STRONGER STORMS AS WELL WITH THE CONVECTION
GETTING SOME UPPER LEVEL SUPPORT FROM THE LEFT FRONT QUADRANT OF A
JET STREAK. IN ADDITION A SHORTWAVE APPROACHING THE AREA WILL ADD
SOME FORCING. AS FOR THE FLASH FLOOD WATCH...WE HAVE SOME DOUBTS
WITH PRECIPITABLE WATER VALUES NOT REALLY HIGH BUT WITH THE STRONGER
STORM POTENTIAL WE WILL LEAVE IT UP FOR NOW. MEANWHILE...ACROSS
SOUTHERN AREAS...IT WILL BE QUITE A BLUSTERY DAY WITH THE
TIGHTENING PRESSURE GRADIENT. THIS WILL BE ESPECIALLY SO ACROSS
THE SOUTHWESTERN CORRIDOR FROM ROCK SPRINGS TO CASPER. THIS COULD
RAISE THE FIRE DANGER IN SOME AREAS. FOR MORE ON THAT...SEE THE
FIRE WEATHER PORTION OF THE DISCUSSION. AND LIKE WEDNESDAY
NIGHT...CONVECTION SHOULD SLOWLY WANE ACROSS THE AREA THROUGH THE
EVENING AND INTO THE OVERNIGHT HOURS.

AS FOR FRIDAY...IT LOOKS LIKE WE WILL BEGIN A SLOW DECREASE IN THE
COVERAGE OF CONVECTION AND SOMEWHAT DRIER AIR WORKS ITS WAY INTO THE
AREA. THERE WILL STILL BE ENOUGH JET SUPPORT FOR A FEW THUNDERSTORMS
THOUGH...WITH FAIRLY SIMILAR LOCATIONS HAVING THE CHANCE OF STORMS.
AS FOR FIRE DANGER...RELATIVE HUMIDITY WILL BE A BIT LESS BUT WINDS
WILL BE A BIT LIGHTER AS WELL. AGAIN...LOOK AT THE FIRE WEATHER
DISCUSSION FOR MORE DETAIL. ON SATURDAY...WITH HIGHER HEIGHTS AND
EVEN DRIER AIR BUILDING ACROSS THE AREA...ANY CONVECTION WOULD BE
RESTRICTED TO THE NORTHERN MOUNTAINS. TEMPERATURES WILL BE FAIRLY
CLOSE TO SEASONAL NORMALS WITH 80S TO AROUND 90 IN THE BASINS AND
60S AND 70S ACROSS THE MOUNTAINS.

.LONG TERM...SUNDAY THROUGH THURSDAY

MEDIUM RANGE MODELS ARE IN GOOD AGREEMENT WITH THE FORECAST AREA
IN A MAINLY DRY AND HOT SOUTHWEST FLOW SUNDAY AHEAD OF A TROUGH
DIGGING INTO THE PACIFIC NORTHWEST. THIS TROUGH OVER THE PACIFIC
NORTHWEST IS PROGGED TO PUSH INTO THE INTERMOUNTAIN WEST SUNDAY
NIGHT AND THEN ACROSS THE NORTHERN ROCKIES MONDAY. THE ASSOCIATED
COLD FRONT IS EXPECTED TO PUSH ACROSS THE AREA LATE SUNDAY NIGHT
INTO THE DAY MONDAY. MODELS ARE SHOWING THE BEST MOISTURE/DYNAMICS
WITH THIS SYSTEM WILL BE NORTH ACROSS MONTANA. WILL HAVE SLIGHT
POPS CONFINED ACROSS THE NORTHWEST AND/OR NORTH SUNDAY NIGHT AND
MONDAY. SOME OF THESE STORMS COULD BE ON THE STRONG SIDE
MONDAY BUT INSTABILITY PARAMETERS ARE PROGGED TO BE MINIMAL AT
THIS TIME. ELEVATED TO EXTREME FIRE WEATHER CONDITIONS WILL BE
PROBABLY BE THE MAIN ISSUE. THANKFULLY ONLY A COUPLE OF FIRE
WEATHER ZONES HAVE CRITICAL FUELS...DUE TO A WET LATE SPRING/EARLY
SUMMER.

MODELS ARE SHOWING A DRY...COOL ENOUGH AIR MASS PUSHING INTO THE
WEST MONDAY NIGHT...THAT THE FAR WESTERN VALLEYS COULD SEE A LIGHT
FREEZE TUESDAY MORNING.

GLOBAL SHOW A DRY WESTERLY FLOW OVER THE AREA TUESDAY THROUGH
THURSDAY. THE 00Z GFS IS SHOWING THE MEAN RH BETWEEN 850MB AND
500MB ONLY BETWEEN 10 AND 30 PERCENT DURING THAT TIME FRAME. THUS
THE MAIN CONCERN WOULD PRIMARILY BE FIRE WEATHER AS RH SHOULD BE
LOW/VERY LOW...BUT WINDS WILL BE LIGHTER THAN WHAT OCCURS SUNDAY
AND MONDAY.

&&

.AVIATION.../12Z ISSUANCE/

AN UPPER LEVEL DISTURBANCE AND MOST OF ITS SHOWERS WILL LIFT NORTH
INTO MONTANA BY 12Z LEAVING ISOLATED SHOWERS AND PATCHY FOG ACROSS
THE WEST THROUGH 15Z.

SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP VCNTY AND NORTH OF
A KAFO-KBYG LINE THIS AFTERNOON WITH A DRY WESTERLY FLOW PREVAILING
SOUTH OF THIS LINE.  THUNDERSTORMS WILL BE MOST NUMEROUS AGAIN
ACROSS THE NW OR VCNTY AND WEST OF A KCOD-KJAC LINE WHERE BRIEF MVFR
CONDITIONS AND HIGHER MTN OBSCURATIONS WILL OCCUR IN THE AFTERNOON
AND EVENING.  STORMS WILL BE MORE HIGH-BASED AND ISOLATED ACROSS
THEN NORTHERN BASINS WITH THE MAIN HAZARD OF MICROBURST WINDS 40KTS
OR GREATER. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE LIKELY
TO LINGER WEST OF THE DIVIDE OVERNIGHT THURSDAY.&&

.FIRE WEATHER...

EXPECT A FAIRLY SIMILAR COVERAGE OF SHOWERS AND THUNDERSTORMS ACROSS
NORTHERN AND WESTERN WYOMING TODAY WITH SOME LOCALLY HEAVY RAIN
POSSIBLE. MEANWHILE...EXPECT DRY WEATHER IN SOUTHERN AND EASTERN
PORTIONS OF THE AREA. A TIGHTENING PRESSURE GRADIENT WILL BRING
GUSTY WEST TO SOUTHWEST WINDS FOR THIS AREA...ESPECIALLY FROM ROCK
SPRINGS TO CASPER WITH RELATIVE HUMIDITY FALLING INTO THE MIDDLE
TEENS AT TIMES. ALTHOUGH RED FLAG CONDITIONS ARE NOT
EXPECTED...THERE COULD BE A COUPLE OF HOURS OF NEAR CRITICAL FIRE
CONDITIONS IN THE AFTERNOON. EXPECT SIMILAR CONDITIONS FOR FRIDAY
WITH LOWER HUMIDITY BUT SOMEWHAT LESS WIND ACROSS THE SOUTHWESTERN
WIND CORRIDOR.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM NOON MDT TODAY THROUGH THIS EVENING FOR
WYZ001-002-012-013-023>026.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...WM
AVIATION...AEM
FIRE WEATHER...HATTINGS



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