FXUS65 KRIW 060940
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
240 AM MST SUN DEC 6 2009
.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
TIGHTENING OF CIRCULATION AROUND CLOSED LOW OVER EXTREME NORTHERN
UTAH BECOMING APPARENT ON IR SATELLITE IMAGERY EARLY THIS MORNING.
COLDER CLOUD TOPS WITH BAROCLINIC LEAF-LIKE STRUCTURE ALSO
DEVELOPING OVER CENTRAL UTAH. THE COLDER CLOUD TOPS AND LEAF LIKE
STRUCTURE INDICATING THAT NUMERICAL PREDICTION MODELS ON TRACK
WITH THE SLIGHT DEEPENING OF THE UPPER LEVEL CLOSED LOW OVER
NORTHERN UTAH DURING THE EARLY MORNING HOURS. 00Z GLOBAL MODEL SUITE
IN GOOD AGREEMENT GRADUALLY SHEARING APART THE CLOSED LOW OVER
NORTHERN UT/SRN ID AFTER SUNRISE AS ANOTHER CLOSED LOW OVER
WESTERN WASHINGTON DIGS SOUTHWARD INTO WESTERN OREGON. UPPER LEVEL
DIFLUENCE WITH SHALLOW ISENTROPIC UPGLIDE WILL CONTINUE OVER
CENTRAL AND WESTERN WYOMING THROUGH THE DAY WITH THE H6-H3 FLOW
GRADUALLY VEERING. KEPT WINTER WEATHER ADVISORIES GOING THROUGH
THE DAY WITH AT LEAST LIGHT TO MODERATE SNOW DEVELOPING EARLY THIS
MORNING AND CONTINUING OFF AND ON THROUGH THE DAY. CURRENT
THINKING IS THAT A LITTLE ICE FROM MID AND HIGHER CLOUDS ROTATING
UP FROM UTAH WILL FALL INTO THE LOWER STRATUS/UP-SLOPE CLOUDS WILL
BEGIN THE SEEDER-FEEDER PROCESS. STRONG NORTHEAST TO SOUTHWEST PRESSURE
GRADIENT WILL CONTINUE TO REMAIN OVER THE REGION TODAY AND TONIGHT SO
PLENTY OF BLOWING AND DRIFTING SNOW ADDING TO THE TRAVEL/OUTDOOR
ENTHUSIAST IMPACT. MAIN AREA OF UPPER LEVEL LIFT AND ASSOCIATED
CLOUDS EXPECTED TO TRANSITION WESTWARD LATE THIS AFTERNOON AND
EARLY EVENING AS THE WESTERN OREGON LOW BECOMES THE DOMINATE
CIRCULATION IN THE LONG- WAVE TROUGH. ARCTIC AIRMASS BECOMES FULLY
ENTRENCHED OVER THE CWA THIS MORNING WITH WIDESPREAD BITTERLY COLD
-20C TO -25C H7 AIR OVER THE AREA. MANY LOCATIONS WILL BE HARD
PRESSED TO GET OUT OF THE SINGLE DIGITS AND WITH BRISK NORTH TO
NORTHEAST WIND...IT WILL FEEL MUCH COLDER. BITTERLY COLD NIGHT IN-
STORE FOR MOST AREAS TONIGHT. ESPECIALLY FOR LOCATIONS THAT
EXPERIENCE AN HOUR OR TWO OF PARTIALLY CLEAR SKY.
LATEST OPERATIONAL AND ENSEMBLE MODEL SOLUTIONS FARTHER SOUTH WITH THE
175KT JET STREAK ASSOCIATED WITH THE POLAR AND SUBTROPICAL JET
STREAMS MERGING MONDAY NIGHT AND TUESDAY. BEGAN TREND TO LOWER
SNOW CHANCES FOR NORTHERN AND CENTRAL AREAS MONDAY NIGHT AND TUESDAY AS A
RESULT OF THE MORE SOUTHERN TRACK.
.LONG TERM...WEDNESDAY 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...
SNOW AND LOW CLOUDS WILL IMPACT MOST OF CENTRAL AND SOUTHERN WY
TODAY WITH MVFR TO LIFR CONDITIONS OCCURRING THROUGH 00Z MON.
IN NORTHERN WY ONLY SCATTERED AREAS OF LIGHT SNOW AND LOW CLOUDS
WILL OCCUR WITH VFR TO MVFR CONDITIONS THROUGH 00Z MON. MOUNTAIN
OBSCURATION WILL BE WIDESPREAD OVER WY TODAY. VFR CONDITIONS WILL
OCCUR AROUND THE KJAC AIRPORT ALL DAY WITH SNOW SHOWERS IN THE
SURROUNDING MOUNTAINS. A NORTHEAST WIND OF 20 TO 30 KNOTS WITH GUSTS
TO 35 KNOTS WILL IMPACT SOUTHERN WY TODAY...INCLUDING THE KRKS
AIRPORT...THROUGH 00Z MON. AFTER 00Z MON...VFR TO MVFR CONDITIONS
WILL OCCUR OVER CENTRAL AND SOUTHERN WY WITH SCATTERED AREAS OF
LIGHT SNOW AND LOW CLOUDS. NORTHERN WY WILL SEE VFR CONDITIONS AFTER
00Z MON.
&&
.FIRE WEATHER...
BITTERLY COLD CONDITIONS WITH LIGHT TO MODERATE SNOW ACCUMULATIONS ARE
EXPECTED TODAY AND MONDAY. WIDESPREAD NORTHEAST WIND OF 10 TO 20
MPH WITH GUSTS TO 30 MPH WILL CONTINUE THROUGHOUT MOST OF THE
DISTRICT THROUGH MONDAY NIGHT. AREAS OF BLOWING AND DRIFTING SNOW
ARE EXPECTED THROUGH THE BEGINNING OF THE WORK WEEK...ESPECIALLY
OVER SWEETWATER COUNTY AND THE SOUTH PASS AREA.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR WYZ014-
015-017>020-022-027>030.
&&
$$
SHORT TERM...CHURCH
LONG TERM...WM
AVIATION...AR
FIRE WEATHER...CHURCH
