FXUS65 KPUB 022234
AFDPUB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PUEBLO CO
334 PM MST WED DEC 2 2009

.SHORT TERM...
(TONIGHT AND THURSDAY)

CURRENTLY...THE UPPER TROUGH WAS DROPPING DOWN INTO THE NORTHERN 
PLAINS OF THE US WED...PRODUCING OCNL SNOW ALL ALONG THE I25 
CORRIDOR AND VERY COLD TEMPS. TEMPS ALONG THE EASTERN SLOPES OF THE 
EASTERN MTS...AND THE ADJACENT PLAINS...HAVE HOVERED TODAY RIGHT 
AROUND 20-25F...WHILE THE FAR EASTERN PLAINS HAVE WARMED TO AROUND 
30F. WINDS HAVE SHIFTED TO AN EASTERLY DIRECTION ACROSS THE 
SLV...AND AS OF 3 PM CLOUD COVER WAS STARTING TO DEVELOP THERE...BUT 
NO SNOW YET.

TONIGHT AND TOMORROW...UPPER TROUGH CONTINUES SAGGING SOUTHWARD FOR 
THE NEXT 24 HRS...WITH THE LLVL FLOW SHIFTING TO A MORE UPSLOPE 
DIRECTION THIS EVENING. 12Z AND 18Z MODEL RUNS CONTINUED THE ONGOING 
TREND OF THE UPSLOPE SHIFT...COUPLED WITH VERY COLD AIR STEADILY 
STREAMING INTO THE CWA. H7 TEMPS OF -17 TO -19C INDICATE A FAVORABLE 
REGIME FOR EFFICIENT FLUFFY SNOW PRODUCTION. IN ADDITION...NAM AND 
GFS MODELS INDICATE A H5 VORT MAX OVER THE AREA...FURTHER AIDING IN 
THE SNOWFALL. THEREFORE...NOT A LOT OF CHANGE NEEDED TO THE ONGOING 
FORECAST GRIDS FOR THE SHORT TERM. UPSLOPE FLOW SHOULD KEEP MAJORITY 
OF THE SNOWFALL PINNED TO THE E MTS AND I25 CORRIDOR...WITH THE BEST 
AREA BEING THE E SLOPES OF THE WETS AND THE POCKET FORMED BY THE S 
SANGRES AND THE RATON RIDGE. INHERITED A SNOW ADV FOR THAT AREA 
LASTING UNTIL 00Z TOMORROW...AND THIS LOOKS REASONABLE. ONLY CONCERN 
WILL BE WHETHER THE SNOW MAKING PROCESS BECOMES TOO 
EFFICIENT...PUSHING AMOUNTS INTO WARNING CRITERIA. ONE OTHER 
THING...LATEST NUMERICAL GUIDANCE CAME IN EVEN COLDER FOR MAX TEMPS 
FOR TOMORROW...SO LOWERED TEMPS A DEG OR TWO AT SOME SPOTS. MOORE

.LONG TERM...
(THURSDAY NIGHT THROUGH NEXT WEDNESDAY)

SNOW FADES AWAY FAIRLY QUICKLY THURSDAY NIGHT AS LOW LEVEL FLOW
LOSES ITS UPSLOPE COMPONENT AND BEST DYNAMIC LIFT SHIFTS SOUTH.
MOST LOCATIONS WILL BE FAIRLY COLD BY FRIDAY MORNING...WITH BELOW
ZERO READINGS WIDESPREAD OVER THE MOUNTAINS AND HIGH VALLEYS. VERY
WEAK LEE TROUGH DEVELOPS BY LATE FRIDAY AFTERNOON...WITH SOME
MODEST 700 MB WARM ADVECTION DEVELOPING AS UPPER TROUGH MOVES AWAY
FROM THE AREA. SHOULD THUS SEE WARMER TEMPS ALL AREAS...THOUGH
WITH RATHER LIGHT FLOW LIMITING MIXING...MOST LOCATIONS WILL
REMAIN AT OR BELOW FREEZING THROUGH THE DAY. INCREASING WLY FLOW
FRI NIGHT WILL HELP KEEP TEMPS SLIGHTLY WARMER...ESPECIALLY
FAVORED EASTERN MOUNTAIN SLOPES. NICE WARM-UP IN STORE FOR
SATURDAY...AS DOWNSLOPE FLOW STRENGTHENS AHEAD OF NORTHWESTERN
U.S. UPPER TROUGH. SHOULD SEE 40S REAPPEAR OVER MUCH OF THE
EASTERN PLAINS...WITH MOUNTAIN MAX TEMPS REACHING THE 30S AT MANY
LOCATIONS.

UPPER PATTERN STILL LOOKS VERY COMPLEX/CHAOTIC OVER THE WESTERN
U.S. SUNDAY INTO THE MIDDLE OF NEXT WEEK...WITH SEVERAL PIECES OF
ENERGY ROTATING THROUGH THE UPPER TROUGH. FAIRLY CONFIDENT THAT
COLD AIR MASS WILL SURGE BACK SOUTH SUNDAY...WITH ARCTIC AIR
LOCKED IN EAST OF THE MOUNTAINS MONDAY/TUESDAY. WILL LIKELY SEE SOME
LIGHT SNOW OVER MUCH OF THE EASTERN MOUNTAINS AND PLAINS DUE TO
SHALLOW UPSLOPE AND WEAK WARM ADVECTION OVER THE COLD DOME. HAVE
LOWER CONFIDENCE IN TIMING OF PACIFIC MOISTURE AND EASTWARD
PROGRESSION OF THE WESTERN U.S. TROUGH...AS MODELS...ESPECIALLY
ECMWF...CONTINUE TO SHOW A GOOD DEAL OF RUN TO RUN VARIANCE. STILL
APPEARS CENTRAL AND SOUTHWEST MOUNTAINS WILL EVENTUALLY SEE A
PROLONGED/SIGNIFICANT SNOWFALL...WITH FIRST WAVE SUNDAY
NIGHT...THEN MAIN SYSTEM AND HEAVIER SNOW MONDAY NIGHT INTO
TUES...THOUGH TIMING OF HEAVIER SNOW COULD VARY 12-24 HOURS. DID
INCREASE POPS CONSIDERABLY ALONG THE CONTINENTAL DIVIDE FROM SUN
ONWARD.

OVER THE EASTERN MOUNTAINS AND PLAINS...FORCING FOR HEAVY
PRECIP IS LESS FAVORABLE AS MID LEVEL FLOW IS FAIRLY STRONG
WESTERLY...THOUGH ON AND OFF LIGHT SNOW WILL CONTINUE MON/TUE AS
PACIFIC MOISTURE OVERRUNS THE COLDER AIR MASS. STRONG WESTERLY
FLOW ALOFT CONTINUES WED...AND WITH ARCTIC AIR RETREATING EASTWARD
EXPECT WARMER AND DRIER CONDITIONS TO SPREAD ACROSS THE AREA BY
LATE WED AFTERNOON. --PETERSEN

&&

.AVIATION...MVFR TO IFR CONDITIONS EXPECTED AT KCOS AND KPUB OVER
THE NEXT 24 HRS AS SNOWFALL INCREASES LATER THIS EVENING AND
PERSISTS THRU THE NIGHT. MODELS INDICATE THAT EARLY TOMORROW
MORNING SNOW MIGHT WANE...BUT THEN KEEP IFR CONDITIONS IN PLACE
DUE TO FOG. SFC WINDS ARE EXPECTED TO REMAIN PREDOMINANTLY EAST.

KALS SHOULD REMAIN VFR FOR THE NEXT 24 HRS WITH SOME SNOW AND LOW 
CLOUDS JUST TO THE EAST OVER LA VETA PASS. CHANCES ARE SLIGHT...BUT 
IF LOW CLOUDS AND SNOW DOES DEVELOP IN THE KALS AREA IT SHOULD BE 
AFTER 12Z TOMORROW MORNING.

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 5 PM MST THURSDAY FOR COZ074-075-
079-080-087-088.

&&

$$

27/10