FXUS65 KPUB 281132
AFDPUB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PUEBLO CO
432 AM MST SAT NOV 28 2009
.SHORT TERM...
(TODAY AND TONIGHT)
UPPER LOW OVER CENTRAL CALIFORNIA IS CONTINUING TO DROP
SOUTHEASTWARD EARLY THIS MORNING WITH AREA OF LIGHT PCPN EXTENDING
ACROSS WRN NV/CEN AND SRN CA. MEANWHILE...NRN STREAM TROF CONTINUES
TO MOVE ACROSS THE NRN U.S. ROCKIES WITH SOME WEAKER PCPN ECHOES
ACROSS PORTIONS OF SRN MT/NW WY. STARTING TO SEE SOME NORTHERLY
WINDS SPREAD INTO NRN SECTIONS OF THE SE PLAINS AS LEE TROF KICKS
EASTWARD...BUT STRONGEST PRESSURE RISES IN MSAS FIELDS ARE STILL
BACK IN CENTRAL WY ASSOCIATED WITH THE TRUE FRONTAL BOUNDARY. THIS
FRONT IS EXPECTED TO DROP THROUGH SOUTHEAST COLORADO DURING THE LATE
MORNING/EARLY AFTERNOON...AND BE POSITIONED ACROSS NE NM/NRN TX
PANHANDLE BY 21Z. THUS...A FAIRLY SIGNIFICANT COOL DOWN IS EXPECTED
TODAY OVER YESTERDAY...THOUGH MAX TEMPS WILL STILL BE SLIGHTLY ABOVE
CLIMO.
MAIN CONCERN WILL BE ONSET AND MAGNITUDE OF SNOWFALL ACROSS SOUTHERN
MOUNTAINS BEGINNING LATE THIS AFTERNOON AND TONIGHT. WHILE MODELS
ARE IN FAIRLY GOOD AGREEMENT WITH THE LARGE SCALE FEATURES...THEY
ARE STILL OSCILLATING THE SMALLER SCALE FEATURES AND PCPN MAXES
AROUND WITH EACH RUN. THE CLOSED LOW IS PROGGED TO DROP INTO NW OLD
MEXICO...NRN BAJA PENINSULA AND EXTREME SOUTHWEST AZ BY 12Z TONIGHT
WITH NRN STREAM TROF SWEEPING INTO THE NRN PLANS BY 06Z TONIGHT.
00Z NAM WAS CONSIDERABLY DRIER ACROSS THE FCST AREA DURING THE
OVERNIGHT HOURS...WHILE 03Z SREF...00Z GFS...AND 00Z ECMWF START TO
RAMP UP SNOWFALL ACROSS THE SOUTHWEST MTS DURING THE EVENING HOURS.
THE 00Z RUNS...GFS WAS THE HEAVIEST WITH QPF...SUGGESTING WINTER
WEATHER ADVSY AMOUNTS ACROSS ZONE 68 AND POSSIBLY THE SRN SANGRES
AS WELL. HOWEVER...06Z RUNS HAVE FLIPPED WITH NAM12 NOW INDICATING
SNOWFALL AMOUNTS OF 4 TO 8 INCHES ACROSS THE EASTERN SAN JUANS
TONIGHT WHILE GFS IS SHOWING MORE ON THE ORDER OF 2 TO 4 INCHES BY
12Z WITH ADDITIONAL SNOWFALL EXPECTED ON SUNDAY. GIVEN THAT BEST
DYNAMICS STAYS WELL TO THE SOUTH...06Z NAM SEEMS OVERDONE AS DOES
00Z GFS. WILL LEAN FORECAST TOWARDS A BLEND OF SREF AND 06Z GFS
FOR NOW. GIVEN THIS IS A HOLIDAY WEEKEND WITH TRAVEL
CONCERNS...HAVE OPTED TO PROACTIVELY ISSUE A WINTER WEATHER
ADVISORY FOR ZONE 68 STARTING TONIGHT. NOT MUCH OROGRAPHIC FORCING
FOR THIS EVENT...THOUGH THERE IS SOME FAIRLY DEEP EASTERLY FLOW
AROUND 10-15 KTS WHICH MAY PROVIDE SOME UPSLOPE ALONG THE LOWER
EASTERN SLOPES OF THE EASTERN SAN JUANS TONIGHT. AND WHILE LAPSE
RATES NOT TERRIBLY UNSTABLE...THEY ARE SATURATED THROUGH THE -12
TO -18C DENDRITIC GROWTH ZONE...WHICH WOULD SUPPORT SOME MODERATE
ACCUMULATIONS.
AS A REINFORCING COLD SURGE BEHIND THE FRONT DROPS THROUGH THE
SOUTHEAST PLAINS TONIGHT...LOWER LAYERS START TO SATURATE AFTER 06Z
WITH THE POSSIBILITY OF LIGHT SNOW DEVELOPING ACROSS THE EASTERN
MTS/ADJACENT I-25 CORRIDOR TOWARDS MORNING. AT THIS POINT MOST
ACCUMS WILL STAY SOUTH OF HIGHWAY 50...WITH A DUSTING OF SNOW
POSSIBLE ACROSS PIKES PEAK REGION/PALMER DIVIDE. STILL TOO MUCH
UNCERTAINTY REGARDING SNOW AMOUNTS FOR THE EASTERN SLOPES OF THE
SANGRES DE CRISTO MTS...SO NO HIGHLIGHTS PLANNED AT THIS TIME. WILL
LET DAY SHIFT TAKE A LOOK AT NEW 12Z RUNS FOR THIS AREA. -KT
.LONG TERM...
(SUNDAY THROUGH FRIDAY)
...SNOW FOR THE SOUTHERN MOUNTAINS THROUGH SUNDAY...
UPPER LOW WILL BE TRANSVERSING ACROSS NORTHERN MEXICO ON SUNDAY
WHILE AN UPPER TROUGH WILL MOVE INTO THE CENTRAL PLAINS. SNOW WILL
BE ONGOING SUNDAY MORNING ACROSS THE WESTERN MOUNTAINS INTO THE
SANGRE DE CRISTO RANGE AND WILL SPREAD EASTWARD INTO THE LEE
SLOPES AND ADJACENT PLAINS THROUGH SUNDAY AFTERNOON. MODELS STILL
HAVING LITTLE RUN TO RUN CONSISTENCY ON THE AMOUNT OF SNOWFALL
THEY PRODUCE. NAM CONTINUES TO FLOP FROM RUN TO RUN...THE GFS
SEEMS TO BE OVERDOING QPF...AND SREF LOOKS TO BE THE MIDDLE OF THE
ROAD. FORCING IS NOT ALL THAT IMPRESSIVE AND CONFINED TO NEW
MEXICO AND WIND FLOW ALOFT DOES NOT SUPPORT OROGRAPHIC LIFT.
HOWEVER COLD TEMPERATURES ALOFT AND DIFFLUENCE IN THE UPPER LEVELS
LOOK TO AID IN PRODUCING ADVISORY CRITERIA SNOWFALL OVER THE
EASTERN SAN JUANS. ISSUING WINTER WEATHER ADVISORY FOR THE EASTERN
SAN JUAN THROUGH SUNDAY WITH 4 TO 9 INCHES OF SNOWFALL EXPECTED
IN THE HIGHER ELEVATIONS. THE OTHER AREA OF CONCERN WILL BE THE
CULEBRA RANGE OF THE SANGRE DE CRISTO MOUNTAINS WHERE ADVISORY
CRITERIA MAY BE MET. CONFIDENCE IS NOT AS HIGH AS FURTHER WEST SO
WILL HOLD OFF ON ISSUING HIGHLIGHTS FOR THAT AREA FOR NOW.
ELSEWHERE...MOUNTAIN LOCATIONS WILL SEE UP TO 6 INCHES WITH
GENERALLY LESS THAN AN INCH OVER THE LEE SLOPES AND ADJACENT PLAINS.
MODELS IN AGREEMENT WITH A FASTER END TO PRECIPITATION BY 06Z
MONDAY AS THE UPPER LOW MOVES INTO TEXAS AND TROUGH INTO THE
MISSOURI VALLEY. UPPER LEVEL RIDGE WILL WRAP AROUND THE UPPER LOW
OVER THE INTERMOUNTAIN WEST ON MONDAY AND TUESDAY. THIS WILL BRING
A WARM UP BOTH DAYS WITH HIGHS IN THE MID 50S OVER THE EASTERN PLAINS.
MODELS TRENDING TOWARDS A WARMER SOLUTION THROUGH THE EXTENDED
WITH AN UPPER TROUGH DROPPING INTO THE CENTRAL PART OF THE CONUS.
GFS CONTINUES TO BE THE OUTLIER WITH THE TROUGH REMAINING OVER THE
NORTHERN PLAINS. THE CANADIAN HAS COME INTO LINE WITH THE ECMWF
AND ENSEMBLE MEAN WITH THE TROUGH DROPPING INTO THE CENTRAL PLAINS
ON WEDNESDAY. COLD FRONT WILL DROP SOUTH OVER EASTERN COLORADO
WITH BRISK NORTHERLY WINDS AND MUCH COOLER AIR. BEGAN TO TREND
TEMPERATURES UPWARD WEDNESDAY AND THURSDAY AS THE COLDEST AIR IS
FORECAST TO REMAIN NORTHEAST OF THE FORECAST AREA. TEMPERATURES
WILL BE COOLER WITH HIGHS BOTH DAYS IN THE 30S TO LOW 40S OVER THE
EASTERN PLAINS. NOT MUCH IN THE WAY OF PRECIPITATION EXPECTED WITH
THIS TROUGH...HOWEVER MODELS HAVE BEEN PRODUCING LIGHT SNOW
WEDNESDAY INTO THURSDAY SO HAVE SLIGHT CHANCE POPS IN THE
FORECAST. UPPER TROUGH PUSHES EAST ON FRIDAY WITH RIDGING
DEVELOPING OVER THE WESTERN CONUS. MOZLEY
&&
.AVIATION...
VFR CONDITIONS EXPECT AT TAF SITES THROUGH TODAY. SNOW WILL SPREAD
INTO THE SOUTHWEST/CENTRAL MTS LATER THIS AFTERNOON...AND BECOME
MORE WIDESPREAD INTO THIS EVENING WHEN IFR TO LIFR CIGS WILL DEVELOP
ALONG AND WEST OF THE CONTDVD. MVFR CIGS EXPECTED TO MOVE INTO KALS
THIS EVENING...WITH POTENTIAL FOR BRIEF IFR CIGS AND -SN AFTER 09Z
AND CONTINUING INTO SUNDAY MORNING. ACROSS THE EASTERN
MTS/PLAINS...MVFR CIGS WILL DEVELOP LATE TONIGHT...POSSIBLY DROPPING
INTO THE IFR CATEGORY BY EARLY SUNDAY MORNING WITH SOME LIGHT
-SN/FLURRIES...ESPECIALLY SOUTH OF HIGHWAY 50 NEAR THE SOUTHEAST
MTS. -KT
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 5 PM MST
SUNDAY FOR COZ068.
&&
$$
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