FXUS65 KPUB 282154
AFDPUB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PUEBLO CO
254 PM MST SAT NOV 28 2009
.SHORT TERM...
(TONIGHT AND SUNDAY)
CURRENTLY...UPPER LOW CONTINUES TO DROP SOUTH OVER CALIFORNIA...WITH
EXTENSIVE SWATH OF MID AND HIGH LEVEL CLOUDS OVER SOUTHERN COLORADO.
REGIONAL RADAR/SATELLITE LOOPS SHOW CONVECTION BREAKING OUT NEAR THE
4 CORNERS...WITH A FEW LIGHTNING STRIKES MOVING INTO EXTREME
SOUTHWEST PORTIONS OF THE STATE. INITIAL PRE-FRONTAL TROUGH/WIND
SHIFT HAS MOVED THROUGH ALL OF THE EASTERN PLAINS...THOUGH BULK OF
THE COLDER AIR MASS IS BEHIND THE TRUE COLD FRONT CURRENTLY DROPPING
SOUTH THROUGH THE ARKANSAS VALLEY AS OF 21Z. SLOWER ARRIVAL OF THE
COLD AIR MASS HAS LED TO SOME FAIRLY WARM TEMPS OVER THE FAR EASTERN
PLAINS...WITH THE LOWER ARKANSAS VALLEY CLIMBING INTO THE LOW 60S
AHEAD OF THE FRONT.
TONIGHT...UPPER LOW CONTINUES TO DROP SOUTH...REACHING NORTHERN
MEXICO BY 12Z SUNDAY MORNING. FLOW ALOFT OVER MOST OF COLORADO
BECOMES BROADLY DIFFLUENT OVERNIGHT...WITH NAM/GFS HINTING AT A WEAK
PIECE OF UPPER ENERGY EJECTING FROM THE LOW AND ROTATING NORTHWARD
TOWARD SOUTHWEST COLORADO BY EARLY SUNDAY MORNING. STILL APPEARS
BEST LOCATION FOR SIGNIFICANT SNOW ACCUMULATION WILL BE OVER THE
SOUTH FACING SLOPES OF THE SAN JUANS WHERE DYNAMIC AND OROGRAPHIC
LIFT IS MAXIMIZED. WOULD LIKE TO SEE STRONGER SOUTHWESTERLY MID
LEVEL FLOW FOR BIG SNOW AMOUNTS... BUT COULD SEE ACCUMULATIONS
APPROACHING 8 INCHES AT LOCATIONS LIKE WOLF CREEK PASS.
ELSEWHERE...FORCING FOR PRECIP IS PRETTY MINIMAL...WITH ONLY WEAK
UPSLOPE AND DIFFLUENCE CREATING LIFT. THUS TRIMMED BACK POPS
OVERNIGHT...ESPECIALLY NORTHERN SECTIONS WHERE LIFT IS WEAKEST. BEST
BET FOR ACCUMULATING SNOW OVERNIGHT OUTSIDE OF THE SAN JUANS WILL BE
OVER THE SOUTHERN SANGRES...SOUTH OF LA VETA PASS...WHERE A COUPLE
INCHES COULD FALL. FOR THE I-25 CORRIDOR...MAY NOT SEE MUCH MORE
THAN FLURRIES OR VERY LIGHT SNOW FROM MONUMENT HILL TO
WALSENBURG...WITH 18Z NAM SHOWING NO PRECIP AT KCOS AND KPUB THROUGH
THE NIGHT.
SUNDAY...UPPER LOW CONTINUES ITS SLOW DRIFT SOUTH INTO MEXICO...WITH
BEST LIFT SINKING SOUTH OF COLORADO DURING THE DAY. HIGHEST POPS
WILL OVER THE MOUNTAINS ALONG THE NM BORDER...WHERE 2 TO 4 INCHES OF
ADDITIONAL SNOW IS LIKELY OVER THE HIGHER PEAKS OF THE SAN JUANS AND
SANGRES. COULD SEE SOME ACCUMULATIONS ALONG THE RATON MESA AS
WELL...THOUGH AMOUNTS WILL ONLY BE IN THE 2 TO 4 INCH RANGE HERE AS
WELL. BEGAN TO TAPER BACK POPS NORTHERN SECTIONS...ESPECIALLY LATE
IN THE DAY...AND WILL NOTE THAT IF NAM VERIFIES...AREAS ALONG AND
NORTH OF THE ARKANSAS RIVER WILL SEE LITTLE IF ANY SNOWFALL. GIVEN
THE LACK OF STEADY PRECIP...SUSPECT MAX TEMPS WILL BE ON THE WARMER
SIDE OF GUIDANCE...SO NUDGED NUMBERS UP SLIGHTLY.
.LONG TERM...
(SUNDAY NIGHT THROUGH SATURDAY)
SUNDAY NIGHT...THE UPPER LOW IS FORECAST TO DROP DOWN ACROSS SW AZ
DURING THE EVENING...WHILE THE NORTHERN TIER TROUGH AXIS ROTATES
ACROSS THE NE CORNER OF COLORADO. THERE IS A CONTINUED SLIGHT
CHANCE FOR SOME PCPN ACROSS THE CWA SUN NIGHT...BUT IT SEEMS TO
QUICKLY COME TO AN END BY MIDNIGHT. THEREFORE...TAPERED POPS BACK
AND REALLY CUT THEM MIDWAY THROUGH THE NIGHT. FAVORED AREAS OVER
THE EASTERN SAN JUANS MIGHT SEE AN ADDITIONAL INCH OF SNOW
ACCUMULATION.
MONDAY AND TUESDAY...MODELS AGREE ON TRACKING THE UPPER LOW WELL
SOUTH ACROSS THE SOUTHERN BORDERS OF AZ AND NM...KEEPING CO UNDER A
BROAD AREA OF HIGH PRESSURE AND DRY CONDITIONS. LATEST GFS RUN WANT
TO EDGE THE PCPN BAND BACK UP ACROSS THE SE CORNER OF THE STATE BY
TUE AFTN...BUT FOR NOW LEFT THE FORECAST AREA DRY UNTIL TUE NIGHT.
TUESDAY NIGHT THROUGH THURSDAY...AS THE SOUTHERN UPPER LOW TRACKS
ACROSS TEXAS TUE NIGHT AND OUT OF THE REGION...ANOTHER LARGER LOW
PRESSURE SYSTEM IS FORECAST TO DROP DOWN OUT OF CANADA AND ACROSS
THE UPPER MIDWEST. THERE ARE DIFFERENCES BETWEEN THE MODELS
THEMSELVES AND BETWEEN RUNS...BUT THERE HAVE BEEN HINTS OF A
SLIGHTLY MORE WESTERN POSITIONING OF LOBES OF ENERGY ROTATING AROUND
THE LOW BACK DOWN ACROSS THE EASTERN HALF OF THE STATE. BRISK N-NW
FLOW IS EXPECTED TO BE IN PLACE BEGINNING WED...AND FAVORED AREAS
FOR POSSIBLE PCPN WILL BE THE HIGHER TERRAIN...RAMPART RANGE AND THE
PALMER DIVIDE. ONGOING POP GRIDS MIGHT BE OVERDONE WITH THIS
EVENT...ESPECIALLY IF THE UPPER TROUGH TRACKS MORE EAST...BUT FOR
NOW THE FORECAST TREND IS REASONABLE AND WILL MAINTAIN.
FRIDAY AND SATURDAY...THE 12Z GFS RUN HAS ANOTHER LOW DROPPING OUT
OF CANADA AND DOWN ACROSS THE N ROCKIES ON FRI...BRINGING STRONG
WESTERLY FLOW TO COLORADO PRIOR TO A HEALTHY DOSE OF MT SNOW ON SAT.
THIS IS TOTALLY DIFFERENT FROM THE 00Z RUN LAST NIGHT...AND IS OUT
OF PHASE WITH WHAT THE ECMWF HAS AS A SOLUTION. THEREFORE CONFIDENCE
IS LOW AND WILL NOT MAKE ANY ADJUSTMENTS AT THIS TIME. MOORE
&&
.AVIATION...
EXPECT CLOUDS TO THICKEN AND LOWER OVERNIGHT ACROSS THE AREA...WITH
MOUNTAINS BECOMING OBSCURED BY CLOUDS AND SNOW SHOWERS AFTER 06Z.
MVFR TO IFR CONDITIONS ARE FORECAST FOR MOST MOUNTAIN LOCATIONS
FROM 06Z-18Z...WITH CONDITIONS IMPROVING TO VFR FROM NORTH TO
SOUTH AFTER 18Z. AT KCOS AND KPUB TAF SITES...COULD SEE SOME PATCH
MVFR CIGS IN THE 10-18Z TIME-FRAME DUE TO SNOW SHOWERS...WITH
CONDITIONS IMPROVING TO VFR AFTERWORDS. AT KALS...PATCHY MVFR CIGS
WILL DEVELOP AFTER 10Z...WITH A COUPLE PERIODS OF IFR CIGS/VIS DUE
TO SNOW SHOWERS POSSIBLE FROM 10Z-17Z.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 5 PM MST SUNDAY FOR COZ068.
&&
$$
10/27
