Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 182128
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
328 PM MDT SAT APR 18 2015

.SHORT TERM...TONIGHT THROUGH SUNDAY

AS THE UPPER LOW CONTINUES TO SPIN OVER COLORADO...IT WILL CONTINUE
TO WRAP SOME MORE MOISTURE AROUND THE LOW INTO EASTERN PORTIONS OF
THE FORECAST AREA THROUGH THE NIGHT. MOST OF THE RAIN WILL CONTINUE
TO FALL FROM THE BIGHORNS TO EASTERN FREMONT COUNTY TO ROCK SPRINGS
AND AREAS TO THE EAST. THERE WILL BE SOME LOWERING SNOW LEVELS AS A
COLD FRONT DROPS DOWN FROM THE NORTH EARLY THIS EVENING ALONG WITH A
SHORT WAVE DROPPING OUT OF CANADA. MOST AREAS WILL NOTICE GUSTY
NORTH WINDS AND COOLER TEMPERATURES ALONG WITH THE FRONT EARLY IN
THE PERIOD BUT THERE WILL BE A FEW SHOWERS AND STORMS OCCURRING WEST
OF THE MAIN CLOUD SHIELD FROM OUR RESIDENT LOW.

BY SUNDAY MORNING...THE BACK SIDE OF OUR KICKER TROUGH WILL BE OVER
THE AREA WITH A FEW GUSTY NORTHWEST WINDS CONTINUING ALONG WITH
COOLER TEMPERATURES BUT OVERALL IT WILL BE A DRIER DAY...ESPECIALLY
FOR CASPER AND THE I80 CORRIDOR. ANOTHER WEAK WAVE MOVES THROUGH
LATE ON SUNDAY...THIS COULD KICK OFF A FEW MORE SHOWERS IN THE
MOUNTAINS BUT OVERALL A MUCH QUIETER DAY.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SUNDAY NIGHT WILL FEATURE RESIDUAL RAIN/SNOW SHOWER ACTIVITY OVER
THE NORTHEAST FACING SLOPES EAST OF THE DIVIDE AS THE LAST OF THE
WRAP AROUND ISENTROPIC LIFT CIRCULATES AROUND THE PESKY LOW WHICH BY
THEN IS PROGGED TO BE NORTH OF MINNESOTA AFTER THE BULK OF THE
ENERGY SHIFTS TO THE NORTHERN STREAM. PESKY LOWS BY THE WAY ARE WHAT
WE DEPEND ON THIS TIME OF YEAR FOR MUCH OF OUR ANNUAL PRECIP. THEN
ON MONDAY ONLY SOME ISOLD SNOW SHOWER ACTIVITY IS EXPECTED ON THE
HIGHEST SLOPES OF THE WIND RVR/BIG HORNS AS A WEAK RIPPLE IN THE NW
FLOW CIRCULATING AROUND THE LOW WHICH BY THEN WILL BE OVER THE
HUDSON BAY AREA. ON TUESDAY THE RIDGE TO THE WEST WILL BUILD EAST
INTO THE AREA ALONG WITH MORE OF A CONFLUENT NW FLOW RESULTING IN
WARMER AND DRIER CONDITIONS. ON WEDNESDAY WE WILL SEE AN INCREASING
CHANCE OF RAIN/SNOW SHOWERS AND SOME T STORMS WEST OF THE DIVIDE AS
THE AIRMASS DESTABILIZES AHEAD OF A CLOSED LOW APPROACHING THE
MAINLAND OFF THE BC COAST. LIFTED INDICES ARE PROGGED TO BE CLOSE TO
-3 IN NW WY WED AFT. THURSDAY IS THE DAY THE GFS AND THE EURO REALLY
START TO DIVERGE WITH THE GFS KEEPING US UNDER A MORE OR LESS WEAK
WESTERLY FLOW WITH THE AFOREMENTIONED LOW OFF BC EJECTING A FAST
MOVING TROUGH ACROSS WY BY SATURDAY...WHERE AS THE EURO BUCKLES THE
RIDGE AND EJECTS THE SAME TROUGH IN THE FORM OF A CLOSED LOW ACROSS
MT AS IT ARCHES OVER THE AMPLIFIED RIDGE WITH AN INCREASINGLY
DIFLUENT SOUTHERLY FLOW DEVELOPING OUT AHEAD OF THE MAIN TROUGH OFF
THE PACIFIC. WITH THIS UNCERTAINTY...LEFT POPS ALONE DURING THE
LATTER PORTION OF THE WEEK KEEPING THE GENERAL TREND OF INCREASING
POPS ACROSS THE CWA. THE COLDEST AIR ASSOCIATED WITH THIS TROUGH
WILL REMAIN WELL TO OUR NORTH IN CANADA SO TEMPS WILL ONLY COOL A
LITTLE MAINLY FROM INCREASING CLOUD COVER AND PRECIP.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

SCT MVFR/IFR -SHRASN WILL FOLLOW BEHIND A COLD FRONT WITH MORE
NUMEROUS -SHSN OVER THE MOUNTAINS WITH MOUNTAINS BECOMING FREQUENTLY
OBSCURED THROUGH EARLY EVENING. DRIER AIR WILL WRAP INTO NORTHEAST
WYOMING TONIGHT...BUT AREAS OF MVFR/IFR CEILINGS ARE EXPECTED TO
BANK UP AGAINST THE EAST SLOPES OF THE DIVIDE...VICINITY KCOD-KLND.
AREAS OF FOG COULD DEVELOP AFTER 10Z TONIGHT. A FEW SHOWERS COULD
REDEVELOP AFTER 18Z SUNDAY...ESPECIALLY ON AND NEAR THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

SCT-NUMEROUS SHSN RESULTING IN FREQUENT MOUNTAIN OBSCURATIONS
THROUGH 04Z. THIS ACTIVITY IS EXPECTED TO BE MORE WIDELY SCT OVER
THE VALLEYS WITH -RASN POSSIBLE BRIEF MVFR/IFR CONDITIONS AT ALL
TERMINALS THROUGH THIS EVENING. MOST OF THIS ACTIVITY WILL SHIFT
ALONG AND EAST OF THE CONTINENTAL DIVIDE AFTER 06Z SUNDAY. BCFG WILL
BE POSSIBLE AFTER 10Z IN THE VALLEYS...ESPECIALLY WHERE -SHRA
DEVELOPS THIS EVENING. A FEW SHOWERS COULD REDEVELOP AFTER 18Z
SUNDAY...ESPECIALLY ON AND NEAR THE MOUNTAINS.

&&

.FIRE WEATHER...

THE COOL WET PATTERN WILL CONTINUE THROUGH THE WEEKEND WITH A GOOD
CHANCE OF WETTING RAIN THIS EVENING...ESPECIALLY ACROSS EASTERN
RAWLINS AND CASPER DISPATCH AREAS. IT WILL BE A BIT DRIER ON SUNDAY
BUT COOLER. THERE WILL BE A CHANCE FOR SHOWERS OFF AND ON THIS WEEK
BUT WITH A LOW CHANCE OF ANY WETTING RAIN UNTIL LATE IN THE WEEK
WHEN ANOTHER LARGE PACIFIC SYSTEM COULD BE MOVING IN AND STAYING FOR
A WHILE.

&&

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

$$

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





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