FXUS65 KRIW 062229
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
329 PM MST SUN DEC 6 2009

SHORT TERM...TONIGHT THROUGH WEDNESDAY
UPDATED TO REMOVE ALL HIGHLIGHTS AS SN0W AND WINDS
HAVE DECREASED ENOUGH ALLOW THEM TO BE CANCELLED
A LITTLE EARLY.

NICE BAROCLINIC LEAF ROTATED SLOWLY NWD TODAY WITH
WIDESPREAD LIGHT TO OCCASIONAL MODERATE SNOW TODAY IN OUR CNTRL
ZONES AND EARLIER IN THE SWRN ZONES. SNOW WAS ONLY TEMPERED BY
UNFAVORABLE TEMPERATURE PROFILE FOR MAX DENDRITIC SNOW GROWTH.
OTHERWISE...A MAJOR SNOWSTORM WOULD HAVE BEEN UNDERWAY. EVEN WITH
THE FRIGID PROFILE...LANDER PICKED UP 5 TO 6 WITH 3 TO 5.5 INCHES
AROUND CASPER. THE I80 CORRIDOR WAS VERY WINDY TODAY WITH
CONSIDERABLE BLOWING SNOW...ESPECIALLY IN THE ERN SECTIONS WITH
GENERALLY LIGHT SNOW. JEFFREY CITY ALSO REPORTED UP TO 4 INCHES.
EVEN THE SOUTH HALF OF RIVERTON REPORTED A COUPLE INCHES OF SNOW
THIS MORNING WHEN A BAND OF HEAVIER SNOW PARKED OUT FOR 4 HOURS.
THE WEAKENING UPPER TROUGH AND ASSOCIATED COOL CLOUD TOPS SHOULD
LIFT GRADUALLY NWD THROUGH THE EVENING WITH JUST UPSLOPE LOW
CLOUDS REMAINING BEHIND. RAISED POPS THROUGH THE EVENING IN OUR
ERN ZONES BECAUSE EVEN THOUGH SNOW WILL BE LIGHT OR VERY LIGHT IT
WILL BE SNOWING. BITTER COLD NIGHT IN STORE WITH ONLY CLOUD COVER
HOLDING IN MANY AREAS STOPPING IT FROM BEING EVEN WORSE. SHOULD
SEE 5 TO 15 BELOW EAST OF THE DIVIDE AND 10 TO 20 BELOW IN THE
WEST WITH EVEN COLDER TEMPS IN YELLOWSTONE. NEXT TROUGH IS ALREADY
DEVELOPING OVER THE PACNW AND IS EXPECTED TO DIG TOWARDS THE
4-CORNERS ON MONDAY NIGHT. ISENTROPIC UPGLIDE DEVELOPS IN THE
SOUTH LATER TONIGHT AND MONDAY MORNING FOR THE FIRST SHOT AND THEN
AGAIN LATER MONDAY NIGHT AND TUESDAY WITH THE TROUGH PASSAGE.
UPPER LOW FAR ENOUGH SOUTH SO WE GET SOME FORCING FROM THE NRN
PORTION OF THE TROUGH AS IT MOVES SE ACROSS THE AREA. QG
FRONTOGENESIS SPREADS IN THE WRN LATE TONIGHT AND ACROSS THE ERN
ZONES DURING THE DAY MONDAY. THE NEXT SHOT OF FORCING WILL HIT
MAINLY THE SERN ZONES LATER MONDAY NIGHT AND TUESDAY. DEPENDING ON
THE DETAILS SNOW AMOUNTS IN THE FAVORED SERN ZONES WILL BE NEAR OR
SLIGHTLY BELOW ADVISORY AMOUNTS. AIRMASS WILL CONTINUE BITTER COLD
WITH ANOTHER REINFORCING SHOT ON TUESDAY. NO BREAK IN SITE FOR THE
SHORT TERM WITH TEMPS STRUGGLING INTO THE SINGLE DIGITS TO LOWER
TEENS AT BEST THROUGH WEDNESDAY WITH FRIGID OVERNIGHT LOWS. LOWS
WILL BE TRICKY TUESDAY NIGHT IN THE ERN ZONES WHEN FLOW IS
EXPECTED TO REVERSE AND BECOME SW. LOWS COULD BE IN THE EVENING
AND THEN STABILIZE OR RISE SLIGHTLY LATE IN AREAS LIKE CASPER AND
SW TO THE REST OF THE WIND CORRIDOR IN THE RED DESERT.

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

MEDIUM RANGE MODELS ARE IN GOOD AGREEMENT WITH DEEP NORTHWEST FLOW
OVER THE AREA WEDNESDAY AND THURSDAY. THIS WILL RESULT IN A
CONTINUATION OF THE COLD WEATHER. MAINLY DRY WEATHER IS
EXPECTED IN THIS NORTHWEST FLOW...WITH PERHAPS SOME LIGHT SNOW SHOWERS
AFFECTING THE NORTHWEST AND NORTHERN MTS...AND PERHAPS ADJACENT
LOWER ELEVATIONS. FRIDAY INTO NEXT WEEKEND...MEDIUM RANGE MODELS
ARE SHOWING A MOIST WESTERLY FLOW AFFECTING THE REGION...WITH A
SHORTWAVE TROUGH IN THE FLOW APPROACHING THE AREA LATE IN THE
WEEKEND. THE 00Z ECMWF IS DRIER THAN THE 00Z GFS IN THIS FLOW
UNTIL SATURDAY NIGHT AND SUNDAY. THUS...HAVE BROAD BRUSHED LOW
POPS FRIDAY THROUGH SUNDAY...WITH AN EMPHASIS ACROSS THE WEST
DURING THIS TIMEFRAME DUE TO THE UNCERTAINTY. TEMPERATURES ARE
EXPECTED TO WARM UP A BIT FRIDAY THROUGH SUNDAY TO NEAR SEASONAL
LEVELS...AS 700MB TEMPS WARM TO -5 TO -10 DEG CELSIUS. HOWEVER...INVERSION
TRAPPED...SNOW COVERED BASINS WILL BE SLOWER TO WARM UP. HAVE GONE
BELOW MEX MOS GUIDANCE ESPECIALLY IN THESE AREAS.

AVIATION...
PERIODS OF MVFR AND IFR CONDITIONS WILL CONTINUE ACROSS MUCH OF THE 
AREA TODAY AS WIDESPREAD LIGHT SNOWFALL CONTINUES THROUGH 06Z THIS 
EVENING. INCREASED WIND WILL ALSO REMAIN PRESENT OVER THE WIND 
CORRIDOR WITH 20G30KT POSSIBLE...CREATING BLOWING SNOW AT THE 
AIRPORTS...WHICH COULD LOWER CONDITIONS TO THE LIFR CATEGORY. A 
BRIEF REPRIEVE IN SNOWFALL IS EXPECTED BETWEEN 06Z AND 12Z. AFTER 
12Z...ANOTHER PUSH OF MOISTURE WILL MOVE INTO THE AREA BRINGING 
ADDITIONAL SNOWFALL TO SOUTHERN...CENTRAL AND EASTERN WYOMING. THIS 
WILL BEING ANOTHER ROUND OF MVFR TO IFR CONDITIONS TO 
KRKS...KLND...KRIW AND KCPR.

FIRE WEATHER...
BITTER COLD AIRMASS WILL CONTINUE THE NEXT SEVERAL DAYS WITH AREAS
OF LIGHT SNOWFALL AND GUSTY NORTHEAST WIND.

&&

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

&&

$$

SHORT TERM...SKRBAC
LONG TERM...WM
AVIATION...BRANHAM
FIRE WEATHER...SKRBAC