000
FXUS65 KRIW 171721
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1121 AM MDT MON JUN 17 2013

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

A MID LEVEL SHORT WAVE COMBINED WITH MOIST UPSLOPE FLOW AT THE
SURFACE AS WELL AS STEEP MID LEVEL LAPSE RATES ALL COMBINED TO
SUSTAIN CONVECTION ALONG THE I25 CORRIDOR OVERNIGHT...THESE STORMS
HAD VERY SLOW STEERING FLOW AS WELL...WHICH INCREASED THE FLOOD
THREAT AROUND MIDWEST. A URBAN AND SMALL STREAM FLOOD ADVISORY WAS
ISSUED THROUGH THE EARLY MORNING HOURS...WITH THE MAIN CONCERN BEING
SALT CREEK.

THIS DISTURBANCE MOVES ON THROUGH BY MID MORNING INTO THE PLAINS.
THE NEXT ONE ARRIVES THIS AFTERNOON. IT WILL AGAIN COMBINE WITH
CONTINUED MOIST UPSLOPE FLOW AT THE SURFACE...TAKING 40 DEGREE
DEWPOINTS ALL THE WAY TO THE CONTINENTAL DIVIDE WITH DEW POINTS
APPROACHING 50 DEGREES IN NATRONA AND JOHNSON COUNTIES AGAIN. BEST
SHEAR...MOISTURE AND INSTABILITY WILL BE FROM THE NORTHERN PORTION
OF THE BIG HORN BASIN INCLUDING THE CODY AREA...THEN INTO NATRONA
AND JOHNSON COUNTIES...AND PERHAPS INTO EASTERN FREMONT COUNTY. THE
CAP WILL BE MUCH EASIER TO BREAK TODAY...SO CONVECTION IS EXPECTED
TO START EARLIER AND WILL BE MORE WIDESPREAD. EVEN THOUGH MOISTURE
AND INSTABILITY LOOK PRETTY GOOD FOR THIS AFTERNOON IT WILL BE
DIFFICULT TO SUSTAIN AN UPDRAFT FOR LONG WEST OF THE I25
CORRIDOR...THE BEST CAPE AND DEEP SHEAR WILL BE AROUND CASPER AND
MIDWEST...WHERE HAIL WILL BE THE PRIMARY THREAT WITH THE STRONGER
STORMS. FURTHER SOUTH AND WEST...STRONG DOWNDRAFT POTENTIAL WILL
EXIST AS THE STRONGER STORMS COLLAPSE AND SEND OUT POTENTIALLY
SEVERE OUTFLOWS INTO THE DRY BOUNDARY LAYER.

AN UPPER LEVEL TROUGH OFF THE PACNW COAST FINALLY MAKES SOME
PROGRESS INLAND MONDAY NIGHT INTO TUESDAY...WORKING TO BREAK DOWN
THE RIDGE ACROSS THE CENTRAL ROCKIES. LOW LEVEL UPSLOPE FLOW
INCREASES AHEAD OF THIS SYSTEM...MAINTAINING THE MOISTURE FEED EAST
OF THE DIVIDE AND INCREASING THE EFFECTIVE SHEAR NEEDED TO MAINTAIN
AN UPDRAFT. STEEP MID LEVEL LAPSE RATES AGAIN COMBINE WITH THE
FAVORABLE SURFACE FLOW AND AN UPPER LEVEL DISTURBANCE...AND MUCH
STRONGER SURFACE BASED INSTABILITY...TO AGAIN INCREASE THE
THUNDERSTORM THREAT ACROSS THE REGION...WITH A FEW OF THESE STORMS
POSSIBLY BECOMING SEVERE LATE IN THE AFTERNOON. THESE INGREDIENTS
COME TOGETHER MOST FAVORABLY AGAIN EAST OF THE DIVIDE ALONG THE I25
CORRIDOR...WITH A SECONDARY FOCUS EXPECTED IN THE BIGHORN BASIN.

SOUTHWEST FLOW INCREASES AHEAD OF THE PACNW TROUGH AS IT MOVES
FURTHER INLAND. VERY HOT DRY AIR WILL OVERSPREAD THE REGION WITH
FREQUENT GUSTS OVER 25 MPH EXPECTED FOR WEDNESDAY...THERE WILL BE
VERY LITTLE CHANCE OF A THUNDERSTORM IN AIR THIS DRY. NORMALLY THIS
SETUP WOULD RAISE FIRE WEATHER CONCERNS IF WE WERE FURTHER PAST
GREEN UP AND SURFACE VEGETATION WAS MORE RECEPTIVE TO FIRE. A COLD
FRONT ASSOCIATED WITH THE UPPER LOW FINALLY MOVES INTO THE WEST LATE
ON WEDNESDAY...COOLING THE AIRMASS AND PROVIDING GOOD RH RECOVERY IN
THE WESTERN MOUNTAINS...RH RECOVERY EAST OF THE DIVIDE WILL LIKELY
BE VERY POOR AHEAD OF THE FRONT.

.LONG TERM...THURSDAY THROUGH MONDAY

MEDIUM RANGE GLOBAL MODELS HAVE TRENDED SLOWER OVERALL WITH THE MOVEMENT
OF THE UPPER LOW ACROSS THE NORTHERN ROCKIES INTO SOUTH CENTRAL
CANADA THURSDAY THROUGH SUNDAY. ECMWF SHOWS THE BEST RUN TO RUN
CONSISTENCY WITH THIS SLOWER TREND. REX BLOCK BRIEFLY FORMS OVER
THE CANADIAN/NORTHERN ROCKIES THURSDAY AND FRIDAY AS UPPER HIGH
SLIDES SOUTHEAST OUT OF ALASKA OVER UPPER LOW OVER NORTHERN
IDAHO/NW MONTANA. AS UPPER LOW DRIFTS FURTHER EAST...ECMWF SHOWS
UPPER RIDGE PHASING WITH UPPER HIGH ACROSS THE CENTRAL/NORTHERN
ROCKIES SUNDAY AND MONDAY.

COOLER TEMPERATURES WILL PREVAIL ACROSS THE NORTH AND WEST THURSDAY
AND FRIDAY BEHIND THE ASSOCIATED COLD FRONT...TEMPERATURES ACROSS
THE SOUTH AND CENTRAL ARE ONLY EXPECTED TO COOL OFF A FEW DEGREES
WITH VERY DRY AND BREEZY/WINDY CONDITIONS DEVELOPING IN THE
AFTERNOON. ISOLATED THUNDERSTORMS WILL BE CONFINED TO THE FAR
NORTH...MAINLY ACROSS THE NORTHERN BIGHORN RANGE INTO NE JOHNSON
COUNTY.  THIS OVERALL PATTERN WILL HOLD THOUGH SATURDAY.

SURFACE HIGH PRESSURE OVER THE NORTHERN PLAINS WILL BRING IN AN E-SE
FLOW AND BETTER MOISTURE/INSTABILITY...ISOLATED AFT/EVE
THUNDERSTORMS...ACROSS THE NORTH AND EAST SUNDAY AND MONDAY.  THE
SOUTH AND WEST ARE EXPECTED TO REMAIN DRY BUT WINDS WILL TREND
LIGHTER.


&&

.AVIATION.../18Z ISSUANCE/

A WEAK DISTURBANCE WILL MOVE THROUGH THE FORECAST AREA
TODAY...THOUGH SHOULD HAVE MINIMAL IMPACTS ON TERMINALS. THIS
DISTURBANCE WILL GENERATE SOME SHOWERS AND THUNDERSTORMS...
ESPECIALLY OVER THE WESTERN AND NORTHERN MOUNTAINS. A FEW SHOWERS
MAY MOVE INTO JOHNSON AND NATRONA COUNTIES THIS AFTERNOON...WITH
AN ISOLATED OPPORTUNITY FOR STORM DEVELOPMENT AROUND KCPR. SHOULD
STORMS DEVELOP...KCPR COULD SEE BRIEF PERIODS OF MVFR CONDITIONS.
OTHERWISE... TERMINALS ARE EXPECTED TO SEE VFR CONDITIONS THROUGH
THE FORECAST PERIOD. SHOWERS OVER THE MOUNTAINS TODAY COULD
GENERATE SOME INCREASED TURBULENCE FOR THE AVIATION PASSES.

&&

.FIRE WEATHER...

PERSISTENT UPPER LEVEL RIDGE WILL CONTINUE NEAR OUR FORECAST AREA
FOR THE NEXT FEW DAYS. A FEW UPPER LEVEL DISTURBANCES WILL RIDE
OVER/ALONG THE RIDGE AT TIMES PROVIDING CHANCES FOR CONVECTION EVERY
ONCE IN A WHILE...WITH THE MOST LIGHTNING ACTIVITY EXPECTED ON TUESDAY.
HOWEVER...MOST OF THE SHOWERS AND THUNDER WILL OCCUR ALONG AND EAST
OF THE DIVIDE...WITH THE WESTERN MOUNTAINS GETTING IN ON THE ACTION
EVERY ONCE IN A WHILE. OTHERWISE...WARM AND DRY CONDITIONS WILL
PERSIST ACROSS THE ENTIRE REGION...WITH THE WARMEST AND DRIEST
CONDITIONS EXPECTED TO REMAIN ACROSS RAWLINS DISPATCH...OCCASIONALLY
SPREADING FURTHER NORTH...ESPECIALLY ON WEDNESDAY AHEAD OF AN
APPROACHING COLD FRONT...FIRE POTENTIAL WILL LIKELY BE ENHANCED
DURING THIS PERIOD AS MINIMUM RHS DROP BELOW 10 PERCENT AND WINDS
WILL FREQUENTLY GUST OVER 25 MPH ACROSS MOST OF THE STATE.

&&

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

$$

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