Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 241820
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1120 AM MST SAT JAN 24 2015

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

A SWATH OF MID AND HIGH CLOUDS SHOWING UP ON SATELLITE ASSOCIATED
WITH ANOTHER SHORT WAVE MOVING THROUGH THE REGION. THERE ARE ALSO
SOME RETURNS ON THE BILLINGS RADAR BEGINNING TO SHOW AT THIS EARLY
HOUR THOUGH IT APPEARS AS THOUGH NOT MUCH IS REACHING THE SURFACE AS
DEWPOINTS ARE STILL IN THE TEENS AND 20S. THIS AREA OF CLOUD COVER
IS ACTUALLY SEVERAL HOURS AHEAD OF SCHEDULE...SO WAS GENEROUS WITH
THE COVERAGE OF POPS THIS MORNING EVEN THOUGH NOT MUCH PRECIPITATION
IS EXPECTED OUT OF THIS SYSTEM...ESPECIALLY THIS FAR AHEAD OF THE
JET SUPPORT. OVERALL...FLOW WILL BE OUT OF THE NORTHWEST TODAY AS
HIGH PRESSURE REMAINS TO OUR WEST AND TROUGHING TO OUR EAST. THERE
WILL BE A SHOT AT SOME MORE PRECIPITATION TODAY...ESPECIALLY ACROSS
THE NORTHERN MOUNTAINS AND IN THE NORTHERN BIGHORN BASIN AND JOHNSON
COUNTY. THERE IS SOME MODEST LIFT ASSOCIATED WITH A JET OVERHEAD IN
ADDITION TO SOME ISENTROPIC UPGLIDE...THOUGH THE SIGNATURE IS NOT
LOOKING AS PRONOUNCED IN RECENT MODEL RUNS...KEPT ISOLATED SHOWERS
ACROSS THE NORTH AS THAT SHOULD COVER THE EXTENT OF THE
PRECIPITATION FROM THIS WAVE.

THERE IS SOME CONCERN OF A BRIEF WIND EVENT AROUND BUFFALO AND
PINEY CREEK AS FLOW ALIGNS TO THAT SWEET SPOT FOR THIS AREA...A FEW
WIND GUSTS COULD EXCEED 55MPH TODAY...700MB FLOW REMAINS STRONGER TO
THE NORTH AND EAST AND THE AREA OF CONCERN REMAINS IN A LESS FAVORED
POSITION FOR THE DOWNWARD FORCING NEEDED FOR A DAMAGING WIND
EVENT...NONETHELESS IT WILL BE A VERY WINDY DAY AROUND NORTHERN
JOHNSON COUNTY AND WE WILL CONTINUE TO WATCH FOR ANY LAST MINUTE
PATTERN CHANGES THAT WOULD REQUIRE A HIGH WIND WARNING FOR THE
BUFFALO AREA. OTHERWISE...LEE SIDE TROUGHING HOLDS AT THE SURFACE WITH
DECENT MIXING OF MILD MID LEVEL TEMPERATURES EXPECTED DURING THE DAY
TODAY. MANY LOCATIONS EAST OF THE DIVIDE WILL BE VERY MILD WITH MANY
AREAS TOPPING OUT INTO THE MID TO UPPER 40S.

HEIGHTS WILL STEADILY RISE ON SUNDAY AND MONDAY AS THE HIGH PRESSURE
CENTERED TO OUR WEST MIGRATES EAST. AS A RESULT...THINGS BEGIN TO
CLEAR OUT ON SUNDAY AND A WARMING TREND BEGINS. IT WILL BRING IN
SOME VERY MILD AIR FOR THIS TIME OF YEAR...RISING TO AROUND +7C AT
H7 BY MONDAY...WHICH IS NEAR RECORD TERRITORY FOR THIS TIME OF
YEAR...ABOUT 15 DEGREES ABOVE NORMAL...AT THE SURFACE THIS WILL
TRANSLATE TO TEMPERATURES WELL INTO THE 50S DURING THE
DAY...ESPECIALLY IN AREAS THAT NO LONGER HAVE A SNOW PACK AND IN
AREAS WHERE THERE WILL BE AN AFTERNOON BREEZE.

.LONG TERM...TUESDAY THROUGH SATURDAY...

SYNOPSIS...ANOTHER UNSEASONABLY MILD AND DRY DAY WILL PREVAIL EAST
OF THE DIVIDE ON TUESDAY. A STORM SYSTEM LIFTING NORTHEAST ACROSS
THE GREAT BASIN WILL SPREAD SOME RAIN AND SNOW SHOWERS ACROSS THE
SOUTHWEST DURING THE DAY. THIS SYSTEM WILL TURN EAST ACROSS
WYOMING TUESDAY NIGHT SPREADING CHANCES OF RAIN AND SNOW SHOWERS
ACROSS MOST AREAS THROUGH WEDNESDAY MORNING. A DRIER NORTHWEST
FLOW WILL PREVAIL BEHIND THIS SYSTEM WEDNESDAY NIGHT AND THURSDAY
ALONG WITH COOLER...BUT STILL NEAR OR SLIGHTLY ABOVE NORMAL
TEMPERATURES.


DISCUSSION...ECMWF HAS BEEN CONSISTENTLY SLOWER THAN GFS KICKING
BAJA UPPER LOW NE ACROSS THE GREAT BASIN...E ACROSS THE CENTRAL
ROCKIES TUESDAY AND WEDNESDAY.  THAT IS UNTIL THE LATEST RUNS WHERE
ECMWF NOW IS FASTER AND LESS FRAGMENTED SWINGING REMNANTS OF SYSTEM
ACROSS THE AREA TUESDAY NIGHT WHILE GFS IS NOW THE MORE FRAGMENTED
AND SLOWER MODEL...LAGGING MAIN COLD CORE BACK NEAR RENO 12Z
WEDNESDAY AND SHEARING OUT THIS SYSTEM ACROSS SOUTHERN WYOMING
WEDNESDAY NIGHT.  ECMWF SHOWS THE MOST OVERALL CONSISTENCY AND LESS
RADICAL CHANGES TO GOING FORECAST THROUGH THE PERIOD.  FORECAST
SPEEDS UP A TAD THE SPREADING OF RAIN AND SNOW SHOWERS INTO THE
SOUTHWEST ON TUESDAY WITH THE MAIN IMPACTS FROM THIS SYSTEM ON
TUESDAY NIGHT INTO WEDNESDAY MORNING.  THIS SYSTEM SHOULD WEAKEN
SIGNIFICANTLY AS IT MOVES INTO STRONG DOWNSTREAM RIDGE...SO
PRECIPITATION AMOUNTS SHOULD BE LIGHT AND COVERAGE SPOTTY WITH SNOW
LEVELS INITIALLY AROUND 8KFT AHEAD OF THE SYSTEM ACROSS THE WEST ON
TUESDAY...LOWERING TO 5-6KFT ACROSS THE AREA TUESDAY NIGHT.

ECMWF HAS THIS SYSTEM MOVING OUT INTO THE CENTRAL HIGH PLAINS BY 00Z
THURSDAY WITH CLIPPER IN NORTHERN STREAM RACING SE INTO THE NORTHERN
PLAINS.  THIS WILL PUT WYOMING IN NW CONFLUENT FLOW THROUGH THURSDAY
WITH SOME LINGERING SNOW SHOWERS OVER THE MOUNTAINS.  24 HOURS
AGO...GFS AND ECMWF WERE IN GOOD AGREEMENT ON DROPPING A SECOND
CLIPPER INTO THE NORTHERN PLAINS LATE FRIDAY.  LATEST GFS SHOWS A
SHARPER UPPER RIDGE ALONG THE WEST COAST AND DRIVES AN ARCTIC BLAST
DOWN THE EAST SLOPES OF THE ROCKIES DURING THE DAY FRIDAY.  ECMWF
CONTINUES TO KEEP THIS SYSTEM AND THE BULK OF THE ARCTIC AIRMASS TO
OUR EAST OVER THE NORTHERN/CENTRAL PLAINS.  CONFIDENCE IN AN ARCTIC
INTRUSION IS LOW AT THIS TIME WITH GFS AND ECMWF ENSEMBLE MEANS
SIDING WITH A BROADER RIDGE OVER THE WEST.

&&

.AVIATION.../18Z ISSUANCE/

A WEATHER SYSTEM WILL SPREAD SNOW ACROSS THE NORTHERN MOUNTAINS
THROUGH TONIGHT. EXPECT MOUNTAIN OBSCURATION AND MVFR TO IFR CONDITIONS.
SCATTERED AREAS OF LIGHT RAIN OR SNOW ARE POSSIBLE OVER THE LOWER
ELEVATIONS OF NORTHERN WY WITH LOCAL MVFR CONDITIONS. LIGHT RAIN
MAY GET CLOSE TO THE CASPER AIRPORT IN THE LATE AFTERNOON INTO THE
EVENING HOURS. EXPECT WINDY CONDITIONS AT KCPR AIRPORT TODAY AND
TONIGHT. A GUSTY WIND WILL DEVELOP OVER NORTHERN JOHNSON COUNTY
AFTER 17Z AND THIS WIND WILL CONTINUE THROUGH TONIGHT. THE KBYG
AIRPORT WILL LIKELY SEE WIND GUSTS OVER 40 KNOTS.

AT THE KJAC AIRPORT LIGHT SNOW WILL FALL AT TIMES THROUGH 12Z SUNDAY
WITH VFR TO MVFR CONDITIONS EXPECTED.

&&

.FIRE WEATHER...

HIGH PRESSURE LOOMS TO THE WEST WHILE ANOTHER WEAK SYSTEM RIPPLES
AROUND THE HIGH TODAY. IT WILL HAVE MINOR IMPACT ON THE AREA WITH
SOME INCREASING CLOUDS AND SOME BREEZES IN MOST AREAS...WITH STRONG
WINDS POSSIBLE IN THE BUFFALO AREA. THE MOUNTAINS MAY SEE SOME SNOW
WITH A VERY SMALL CHANCE OF A RAIN OR SNOW SHOWER IN THE LOW
ELEVATIONS OF NORTHERN CODY DISPATCH AND CASPER DISPATCH.
TEMPERATURES WILL BE MILD THROUGH THE PERIOD WITH A WARMING TREND
EXPECTED TO LAST INTO NEXT WEEK. WE STILL CAN NOT GET MIXING HEIGHTS
UP TOO MUCH...ESPECIALLY IN LESS WIND PRONE AREAS. HOWEVER THERE
WILL BE SOME HIGH END POOR TO FAIR SMOKE DISPERSAL POSSIBLE
TODAY...EVEN IN THE LESS WINDY AREAS.

&&

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

$$

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








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