Area Forecast Discussion
Issued by NWS Riverton, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS65 KRIW 271800
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1200 PM MDT MON JUL 27 2015

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

AN INTERESTING 24 HOURS IN STORE FOR THE STATE OF WYOMING AS A LARGE
AND STRONGLY FORCED TROUGH DIGS TO OUR WEST AND EVENTUALLY CLOSES
OFF AND STACKS OVER EASTERN MONTANA BY LATE THIS EVENING.

THERE WILL BE A NUMBER OF HAZARDS ASSOCIATED WITH THIS SYSTEM...THE
MOST WIDESPREAD IMPACT WILL BE ON FIRE WEATHER AS SOUTHWEST FLOW
INCREASES AHEAD OF THE SYSTEM AND THEN ACCELERATES AS THE LOW CLOSES
OFF TO THE NORTH WITH WIDESPREAD WINDS IN EXCESS OF 35 MPH THIS
AFTERNOON AND EVENING. IN ADDITION...RELATIVE HUMIDITY WILL BE IN
THE SINGLE DIGITS IN MANY AREAS EAST OF THE DIVIDE TODAY...WITH THE
LOWEST RELATIVE HUMIDITIES EXPECTED IN SWEETWATER COUNTY...WHERE WE
ALREADY HAVE A WILDFIRE...AND IN FREMONT...NATRONA AND SOUTHERN
JOHNSON COUNTIES. IN ADDITION...IT WILL BE UNSTABLE THIS AFTERNOON.
STORMS FORMED IN AREAS THOUGHT TO BE TOO DRY YESTERDAY...WHICH
KICKED OFF SOME DRY THUNDERSTORMS IN SWEETWATER COUNTY. THERE COULD
ALSO BE ENOUGH MID LEVEL MOISTURE THIS AFTERNOON FOR AN ISOLATED DRY
THUNDERSTORM...BUT AT THE VERY LEAST IT WILL BE DRY AND UNSTABLE
ENOUGH FOR A HIGH HAINES INDEX...WHICH MEANS THAT ANY LARGE FIRES
THAT MAY DEVELOP COULD BECOME PLUME DOMINATED.

FINALLY...A COLD FRONT WILL RAKE ACROSS THE STATE IN THE AFTERNOON.
FOR ABOUT HALF OF THE FORECAST AREA...THIS FRONT WILL BE DRY WHICH
MEANS A SUDDEN WIND SHIFT AND ERRATIC FIRE BEHAVIOR FOR MOST AREAS
SOUTH AND WEST OF THE BRIDGER/OWL CREEK RANGES.

SEVERE THUNDERSTORMS ARE POSSIBLE TO THE NORTH ALONG THE FRONT AS IT
DIPS SOUTH THIS AFTERNOON. THERE IS SIGNIFICANT BULK SHEAR IN EXCESS
OF 40KT THAT COULD ENCOURAGE LARGE HAIL...PWAT VALUES IN EXCESS OF
AN INCH INDICATING PLENTY OF FUEL FOR STRONGER STORMS WITH FLASH
FLOODING A POSSIBILITY IN MORE PRONE AREAS...AND PLENTY OF DOWNWARD
MOMENTUM ASSOCIATED WITH THE SWIFT MID LEVEL FLOW WILL ENCOURAGE
DAMAGING WIND GUSTS AND PERHAPS A TORNADO. THERE COULD ALSO BE A FEW
MORE ORGANIZED STORMS ACROSS THE WESTERN MOUNTAINS BUT THE POTENTIAL
FOR SEVERE THUNDERSTORMS IS LESS THAN IN THE BIGHORN BASIN AND
JOHNSON COUNTY.

IT WILL BE QUITE COOL BEHIND THE FRONT FOR JULY...WITH H7 TEMPS
PROJECTED TO DIP TO -2C IN THE WESTERN MOUNTAINS...INCLUDING
YELLOWSTONE...WHICH WOULD TRANSLATE TO A SNOW LEVEL OF
7500FT...LUCKILY MOST OF THE PRECIPITATION WILL BE OVER AND DONE BY
THE TIME TEMPERATURES BOTTOM OUT TUESDAY MORNING...BUT THERE COULD
REALISTICALLY BE SOME SNOW ABOVE 9000FT IN THE PARK TONIGHT.

SPEAKING OF COLD...THERE COULD BE SOME TEMPERATURES BELOW FREEZING
ACROSS THE WEST ON TUESDAY MORNING...INCLUDING AREAS OF THE UPPER
WIND RIVER BASIN...YELLOWSTONE...JACKSON VALLEY...AND STAR VALLEY.
OTHERWISE IT WILL BE FAIRLY MILD ON TUESDAY WITH HIGHS IN THE 70S
ACROSS MOST OF THE AREA WITH LOW HUMIDITY...ESPECIALLY ACROSS THE
SOUTH. WINDS WILL BE QUITE A BIT CALMER AS WELL. WEDNESDAY WILL ALSO
BE DRY BUT SEVERAL DEGREES WARMER.

.LONG TERM...THURSDAY THROUGH MONDAY

SYNOPSIS...UPPER LEVEL HIGH PRESSURE WILL BUILD OVER THE FOUR
CORNERS AREA THURSDAY AND PERSIST THROUGH THE EXTENDED PERIOD.
DRY CONDITIONS WITH A RETURN TO ABOVE NORMAL TEMPERATURES WILL
PREVAIL THURSDAY AND FRIDAY. SOME MOISTURE WILL BEGIN TO WRAP
AROUND THE PERIPHERY OF THE FOUR CORNERS HIGH OVER THE WEEKEND
BRINGING SLIGHT CHANCES OF THUNDERSTORMS ACROSS THE NORTH.

DISCUSSION...MEDIUM RANGE MODELS HAVE TRENDED TOWARD A MORE
DOMINANT UPPER HIGH SETTLING INTO THE FOUR CORNERS REGION LATE IN
THE WEEK...AND HIGHER OVERALL HEIGHTS ACROSS WYOMING. A VERY DRY
AIRMASS WILL REMAIN OVER THE AREA THURSDAY AND FRIDAY...SO FIRE
WEATHER CONDITIONS WILL REMAIN ELEVATED...THOUGH WINDS SHOULD BE
GENERALLY LIGHT.

A SHALLOW COLD FRONT WILL PUSH INTO NORTHERN WYOMING ON
SATURDAY...COMBINED WITH SOME MID AND HIGH LEVEL MONSOONAL
MOISTURE BEGINNING TO WRAP AROUND THE NORTH SIDE OF THE FOUR
CORNERS HIGH. ISOLATED HIGH-BASED THUNDERSTORMS WILL BE MAINLY
CONFINED ALONG FAVORED MOUNTAIN/VALLEY BREEZE BOUNDARIES NEAR THE
MOUNTAINS IN THE NORTH ON SATURDAY. RETURN SE FLOW AROUND SFC HIGH
PRESSURE OVER THE PLAINS MAY BRING BETTER LOW LEVEL MOISTURE
ACROSS NORTH AND EASTERN WYOMING ON SUNDAY AND MONDAY...WHILE MID
AND HIGH LEVEL MOISTURE FLOW FROM THE GREAT BASIN ACROSS THE WEST
AND NORTH. THIS WILL BRING A FEW HIGH-BASED THUNDERSTORMS ACROSS
THE WESTERN MOUNTAINS BY MONDAY WHILE SOME STRONGER STORMS WILL BE
POSSIBLE ACROSS MAINLY JOHNSON COUNTY IN WHAT WILL BE THE
BEGINNINGS OF LATE NIGHT MCS ACTIVITY FURTHER EAST OVER THE HIGH
PLAINS. HIGHS THROUGH THE PERIOD WILL BE MAINLY IN THE UPPER 80S
TO MID 90S ACROSS THE CENTRAL BASINS WITH MOSTLY 80S IN THE
WESTERN VALLEYS.

&&

.AVIATION.../18Z ISSUANCE/
A STRONG COLD FRONT IS PUSHING INTO THE WEST AND WILL PLOW THROUGH
AREAS EAST OF THE DIVIDE LATER THIS AFTERNOON. ISOLATED TO SCATTERED
-TSRA WILL DEVELOP ALONG THE FRONT MAINLY VCNTY AND NORTH OF A KJAC-
KWRL-KBYG LINE IN THE AFTERNOON AND EVENING. SFC SW WINDS AT
20-35KTS WILL PRECEDE THE FRONT WITH THE STRONGER WINDS FROM VCNTY
KRKS-KCPR AND ALONG THE EAST SLOPES FROM VCNTY KTHP-KLND.
LLWS IN ADDITION TO CONVECTIVE WIND SHEAR MAY BE ENCOUNTERED
BEHIND THE COLD FRONT VCNTY KCOD-KBYG IN THE AFTERNOON WITH A
PREVAILING NORTHERLY SFC WIND AND SW WINDS 20-30KTS AT RIDGETOP
LEVEL. SFC WEST WINDS AT 20-30KTS WILL FOLLOW THE COLD FRONT
ACROSS CENTRAL AND SOUTHERN WYOMING. WINDS WILL GRADUALLY DIMINISH
OVERNIGHT. THE NORTHERN ABSAROKA AND BIGHORN RANGES WILL LIKELY
REMAIN FQTLY OBSCURED WITH SCT -SHRA/-SHSN MONDAY NIGHT INTO
TUESDAY MORNING.

&&

.FIRE WEATHER...

...RED FLAG WARNING FOR ZONES 280 281 283 285 AND 300 THROUGH 10PM
TONIGHT...

JUST ABOUT EVERY ELEMENT WORTHY OF A RED FLAG WARNING WILL BE
PRESENT TODAY FROM WIDESPREAD STRONG WIND OVER 35 MPH ACROSS THE
AREA WITH GUSTS AROUND 50 MPH POSSIBLE IN THE MORE EXPOSED AND WIND
PRONE AREAS...TO LOW HUMIDITY...TO DRY THUNDERSTORMS AND A DRY COLD
FRONT. AREAS EXPECTED TO BE MOST AFFECTED WILL BE CASPER
DISPATCH...SOUTHERN CODY DISPATCH...AND RAWLINS DISPATCH AS THEY
WILL HAVE THE MOST TIME AHEAD OF THE COLD FRONT IN THE HOT AND DRY
SOUTHWEST FLOW. MOST OF THE WET THUNDERSTORM ACTIVITY WILL BE IN
TETON DISPATCH WITH SEVERE THUNDERSTORMS POSSIBLE IN NORTHERN CASPER
AND CODY DISPATCH WITH HAZARDS THAT RANGE FROM LARGE HAIL TO A
TORNADO...WITH DAMAGING DOWNBURST WINDS THE MOST LIKELY HAZARD. IT
WILL BE QUITE A BIT CALMER AND COOLER BEHIND THE FRONT FOR TUESDAY
BUT IT WILL REMAIN DRY...ESPECIALLY ACROSS THE SOUTHERN THIRD OF THE
STATE...WINDS WILL CALMER BUT A FEW GUSTS TO 25 MPH CANNOT BE RULED
OUT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL 10 PM MDT THIS EVENING FOR WYZ280-281-285-
300.

RED FLAG WARNING FROM 10 AM THIS MORNING TO 10 PM MDT THIS
EVENING FOR WYZ283.

&&

$$

SHORT TERM...ALLEN
LONG TERM...AEM
AVIATION...AEM/LIPSON
FIRE WEATHER...ALLEN


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.