FXUS65 KRIW 010937
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
237 AM MST TUE DEC 1 2009
.SHORT TERM...TODAY THROUGH THURSDAY NIGHT
COLD FRONT MOVING RAPIDLY SOUTH THROUGH MONTANA THIS MORNING AND
WILL BE IN NORTHERN WYOMING SHORTLY AFTER 12Z. UPPER TROUGH DIGGING
SOUTH AND EAST OVER EASTERN BC...ALBERTA AND SASKATCHEWAN. TWO
JETS WITH THIS SYSTEM. THE FIRST OVER SOUTHERN ALB/SASK WITH A BIT
OF A BAROCLINIC LEAF UNDER THE RIGHT ENTRANCE REGION. THE SECOND
JET IS CYCLONICALLY CURVED AND IS DIGGING SOUTH ALONG THE EASTERN BC
BORDER. THIS SECOND JET WILL BE THE MAIN PLAYER FOR TODAYS WEATHER
OVER WESTERN AND CENTRAL WYOMING. VERY COLD AIR ASSOCIATED WITH
THIS SYSTEM AND A BIT SNOW AS WELL. 00Z RAOB NEAR EDMONTON WAS -17C
AT H7 AND -36C AT H5.
THE TROUGH WILL CONTINUE TO DIG SOUTH INTO THE NORTHERN ROCKIES
TODAY AND INTO THE NORTHERN PLAINS STATES OF THE CONUS. THE JET
OVER BC WILL DIG SOUTH ALONG THE WESTERN SLOPES OF THE ROCKIES AND
INTO WESTERN WYOMING BY MID DAY AND INTO COLORADO BY LATE THIS
EVENING. THIS JET WILL PROVIDE DECENT LFQ DYNAMICS FOR THE AREA
TODAY AND INTO THE EVENING. THE JET OVER ALB/SASK WILL MOVE SOUTH
AND EAST INTO THE DAKOTAS TODAY NOT PROVIDING MUCH FOR OUR AREA.
THE SURFACE FRONT WILL CONTINUE ITS SOUTHWARD PUSH INTO NORTHERN
WYOMING AFTER 12Z...MOVING INTO THE CENTRAL AROUND 18Z...THEN
SWEETWATER COUNTY BY LATE AFTERNOON. THE SNOW WILL FOLLOW AN HOUR
OR TWO AFTER THE INITIAL FRONTAL PUSH. SHOULD SEE A QUICK 4 TO 6
HOURS OF LIGHT TO LOCALLY MODERATE SNOWFALL. EXPECT SUB-ADVISORY
AMOUNTS WITH 1 TO 3 INCHES IN THE LOWER ELEVATIONS EAST OF THE
DIVIDE AND SWEETWATER COUNTY...WITH AS MUCH AS 5 INCHES IN THE
ABSAROKAS AND BIGHORN MOUNTAINS. WILL ALSO SEE TEMPERATURES PLUMMET
RAPIDLY BEHIND THE FRONT INTO THE 20S AND POSSIBLY SOME UPPER
TEENS. H7 TEMPERATURES TO -20C OVER EASTERN WYOMING WILL MOVE IN BY
THIS EVENING. WITH SOME CLEARING TONIGHT AND A FRESH SNOW
COVER...WILL SEE MINIMUM TEMPERATURES IN THE SINGLE DIGITS...TO
SINGLE DIGITS BELOW ZERO. SOME AREAS IN THE WEST COULD SEE LOWS IN
THE TEENS BELOW ZERO. IT REMAINS COLD THROUGH THURSDAY WITH HIGHS
IN THE TEENS TO LOWER 20S. OVERNIGHT LOWS THURSDAY COULD BE EVEN
COLDER IN SPOTS. A WAVE ROTATES AROUND THE LOW THROUGH EASTERN
WYOMING WEDNESDAY AFTERNOON THROUGH THURSDAY MORNING. THIS WILL
BRING LOW CLOUDS AND THE CHANCE OF LIGHT SNOW TO EASTERN PORTION OF
THE CWA. THE CLOUDS COULD HELP MODERATE SOME OVERNIGHT LOWS
THURSDAY MORNING...BUT WILL STILL BE QUITE COLD REGARDLESS.
SHORTWAVE RIDGE BUILDS IN THURSDAY AFTERNOON AND NIGHT WITH WARMING
ALOFT. EXPECT ANOTHER VERY COLD NIGHT...THOUGH TEMPERATURES
MODERATING IN THE MOUNTAINS.
.LONG TERM...FRIDAY THROUGH TUESDAY
MEDIUM RANGE PERIOD CONTINUES TO BE A CHALLENGE ONCE AGAIN TONIGHT.
GFS AND UKMET IS ON THE FAST END OF THE GUIDANCE AND MAINTAINS
JUST ONE RIDGE INSTEAD OF THE GEM/ECMWF WHICH SHOW TWO RIDGES TO
START THIS PERIOD...ONE OVER THE ROCKIES AND THE OTHER OFF THE
COAST. I STILL THINK THE GFS...AND NOW UKMET...EVOLUTION LOOKS
MORE REALISTIC THAN THE DUAL RIDGES THAT THE OTHER MODELS CONTINUE
TO SHOW. PATTERN IS NO DOUBT CHAOTIC WITH RAPID CHANGES AND
POTENTIAL EL NINO PATTERN SETTING UP LATER IN THE PERIOD OR
BEYOND. GENERALLY TOOK A COMPROMISE APPROACH BETWEEN THE GFS AND
ECMWF WHICH WITH TIME COULD BE SOLVED TO PROVIDE SOMEWHAT SIMILAR
WEATHER... ALBEIT FROM DIFFERENT PATTERNS. WITH THAT SAID...SLOWED
DOWN THE BIG CHANGE TO LATER SATURDAY INTO SATURDAY NIGHT WITH
NEXT ARCTIC BLAST AND POTENTIAL OVERRUNNING PATTERN THAT CONTINUES
THROUGH AT LEAST MONDAY. AS LONG AS THE ARCTIC AIR DOES BECOME
ENTRENCHED EAST OF THE DIVIDE THEN WE SHOULD HAVE A DECENT SHOT OF
SNOW DURING THIS PERIOD. THE WEST SHOULD ALSO SEE SNOW IN THE
MODERATELY STRONG W TO SW FLOW. DYNAMICS OVERRUNNING THE COLD DOME
COULD BE QUITE IMPRESSIVE AT TIMES AND WE'LL JUST HAVE TO SEE IF
IT ALL COMES TOGETHER OR ONLY PARTIALLY GETS IT ACT TOGETHER. H7
TEMPS DROP TO -20C OR LESS SATURDAY NIGHT THROUGH MONDAY ON THE
GFS WITH WARMING ON THE EURO BY MONDAY MORNING. IF THIS MUCH
ARCTIC AIR DOES BECOME ENTRENCHED FOR A FEW DAYS...IT WILL
DEFINITELY FEEL LIKE DECEMBER FOR A FEW DAYS AND WITH POTENTIAL
FRESH SNOW COVER FROM OUR SHORT TERM SYSTEM WE COULD HAVE OUR
FIRST BITTER COLD DAYS AND FRIGID NIGHTS. DROPPED TEMPS QUITE A
BIT MORE AND LATER SHIFTS CAN ADJUST AS WE GET CLOSER. COULD SEE
HIGHS ONLY STRUGGLING INTO THE SINGLE DIGITS AND TEENS SUNDAY AND
MONDAY WITH LOWS IN THE SINGLE DIGITS AT BEST...IF ITS SNOWING AND
BELOW ZERO IF IT CLEARS AND WELL BELOW ZERO IN THE WESTERN BASINS
AND VALLEYS.
&&
.AVIATION...
A COLD FRONT WILL MOVE INTO NORTHERN WY AROUND 12Z. THIS FRONT WILL
MOVE SOUTH DURING THE DAY. THE FRONT WILL LIE ALONG FROM KJAC TO
NEAR KRKS AT 00Z WED. LIGHT SNOW AND MVFR TO IFR CONDITIONS WILL
DEVELOP BEHIND THE FRONT IN NORTHERN WY THIS MORNING. THE SNOW AND
MVFR TO IFR CONDITIONS WILL SPREAD INTO CENTRAL WY AROUND 21Z.
EXPECT THESE CONDITIONS TO SPREAD SOUTHWEST TO KRKS BY 05Z WED. WEST
OF THE DIVIDE SCATTERED SNOW SHOWERS WILL OCCUR DURING THE AFTERNOON
AND EVENING HOURS WITH LOCAL MVFR CONDITIONS FROM KJAC TO KPNA.
A GUSTY NORTH WIND OF 15 TO 25 KNOTS WILL OCCUR WITH THE FRONTAL
PASSAGE AND CONTINUE FOR A FEW HOURS AFTER THAT...THEN DIMINISHING.
AFTER 00Z WED IN NORTHERN WY...THE SNOW IS FORECAST TO END WITH VFR
TO MVFR CEILINGS OCCURRING.
&&
.FIRE WEATHER...
A STRONG COLD FRONT WILL MOVE THROUGH THE STATE TODAY BRINGING LIGHT
SNOW...STIFF NORTH TO NORTHEAST WINDS AND VERY COLD TEMPERATURES.
SNOWFALL WILL BE MAINLY EAST OF THE DIVIDE AND SWEETWATER COUNTY.
COULD SEE SOME SNOW IN THE WESTERN MOUNTAINS THOUGH. SNOWFALL OF 1
TO 3 INCHES IS EXPECTED WITH UP TO 5 INCHES IN THE BIGHORNS AND
ABSAROKAS. TEMPERATURES BEHIND THE FRONT WILL DIP INTO THE 20S AND
EVEN SOME TEENS. OVERNIGHT LOWS WEDNESDAY AND THURSDAY MORNINGS
WILL BE IN THE SINGLE DIGITS TO SINGLE DIGITS BELOW ZERO...WITH SOME
TEENS BELOW ZERO IN THE WEST AND MOUNTAINS.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
SHORT TERM...TWB
LONG TERM...SKRBAC
AVIATION...AR
FIRE WEATHER...TWB
