Snow Advisory 8, NWS Denver/Boulder, CO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
301 AM MDT TUE OCT 17 2006

.SHORT TERM DISCUSSION...THE UPPER LEVEL TROUGH WILL MOVE ACROSS THE
AREA LATER THIS AFTN THRU TONIGHT.  BOTH GFS AND WRF CONTINUE TO
SHOW MDT TO STG QG ASCENT OVER THE AREA FROM MIDDAY INTO TONIGHT.
CROSS-SECTIONS SHOW DECENT MOISTURE HOWEVER 700 MB WINDS ARE FCST TO
BE FROM THE SSW THRU TONIGHT WHICH IS NOT GOOD FOR OROGRAPHICS IN
THE NRN MTNS.  HOPEFULLY FAVORABLE LAPSE RATES AND DECENT QG ASCENT
WILL OFFSET POOR OROGRAPHICS AND ALLOW FOR SOME HEAVIER SNOW TO
OCCUR THIS AFTN INTO THE EVENING HOURS IN THE MTNS.  MEANWHILE OVER
LOWER ELEVATIONS SFC LOW WILL DEVELOP OVER SERN CO AS COLD FRONT
MOVES INTO NERN CO THRU THE MORNING HOURS.  THIS SHOULD ALLOW FOR
INCREASING UPSLOPE FLOW BY AFTN INTO THE EVENING HOURS AND COMBINED
WITH FAVORABLE QG ASCENT SHOULD ALLOW FOR THE DEVELOPMENT OF
WIDESPREAD PCPN.  BEST TIME FOR HEAVY SNOW IN THE FOOTHILLS APPEARS
TO BE FROM 21Z TO 06Z SO MAY REACH WARNING CRITERIA IN A FEW SPOTS
THUS WILL UPGRADE WATCH TO WARNING.  OVER NERN CO SOUNDINGS SHOW
TEMPS BECOMING COLD ENOUGH FOR RAIN TO CHANGE TO SNOW BY EARLY
EVENING WITH SOME ACCUMULATIONS POSSIBLE.  MAY NEED A SNOW ADVISORY
FOR THE PALMER DIVIDE WHERE AMOUNTS COULD LOCALLY EXCEED 6 INCHES OR
SO.  ELSEWHERE BELIEVE WARM GROUND TEMPS WILL KEEP ACCUMULATIONS
CONFINED MOSTLY TO GRASSY AREAS WITH AMOUNTS IN THE 2 TO 4 INCH
RANGE.

.LONG TERM DISCUSSION...MODELS HAVE THE UPPER TROUGH AXIS PUSHING
ACROSS THE FORECAST THROUGH THE DAY WEDNESDAY.  WEDNESDAY NIGHT AND
THURSDAY THE FLOW ALOFT IS NORTHWESTERLY.  BY THURSDAY NIGHT INTO
FRIDAY IT BECOMES MORE ZONAL.  THE QG VERTICAL VELOCITY FIELDS HAVE
VERY WEAK UPWARD MOTION IN FRONT OF THE AXIS WEDNESDAY MORNING.  BY
AFTERNOON...WEAK DOWNWARD MOTION IS PROGGED.  IT GETS A BIT STRONGER
WEDNESDAY NIGHT...THEN WEAKER DOWNWARD FORCING CONTINUES THROUGH
THURSDAY AND THURSDAY NIGHT.  THE LOW LEVEL WIND FIELDS SHOW THE
BOUNDARY LAYER UPSLOPE FLOW OVER THE PLAINS/FOOTHILLS TO BE GONE BY
WEDNESDAY MORNING.  THEN FOR THE REST OF THE PERIODS...THE FLOW IS
RATHER WEAK AND DOWNSLOPING WELL INTO FRIDAY.  FOR MOISTURE...BOTH
MODELS HAVE IT DECREASING THROUGH THE DAY WEDNESDAY...THE NAM A BIT
SLOWLY.  MOISTURE LINGERS IN THE HIGH MOUNTAINS WITH WEDNESDAY
NIGHT.  BY THURSDAY AFTERNOON... MOISTURE AGAIN IS ON THE INCREASE
OVER THE MOUNTAINS...WITH SOME MID AND UPPER LEVEL CLOUDS EXPECTED
FOR THE PLAINS THROUGH THE DAY THURSDAY.  MOISTURE CONTINUES TO
INCREASE IN THE MOUNTAINS THURSDAY NIGHT.  OVERALL WILL CEASE POPS
ON THE PLANES NO LATER THEN MID DAY WEDNESDAY WITH THE MOISTURE
...UPSLOPE...AND UPPER TROUGH PASSAGE IN MIND.  OROGRAPHIC
ENHANCEMENT IS OK ON WEDNESDAY FOR THE MOUNTAINS ...BUT THE MOISTURE
IS ON THE DECREASE AND THE SYNOPTIC SCALE ENERGY WONT HELP
EITHER.   WILL MAKE MINOR ADJUSTMENTS...BUT KEEP LIKELYS FOR SOME
OF THE DAY WEDNESDAY.  AFTER EARLY WEDNESDAY...NO POPS FOR THE
PLAINS UNTIL FRIDAY NIGHT.  WILL KEEP POPS GOING IN THE MOUNTAINS
WEDNESDAY NIGHT WELL INTO THE EXTENDED PERIOD...WITH MOISTURE AND
OROGRAPHICS IN MIND. HOWEVER NOTHING GREAT WILL ALL THE WARMING
EXPECTED AT LEAST THROUGH FRIDAY.

FOR THE LATER DAYS...FRIDAY THROUGH MONDAY...THE MEDIUM RANGE MODELS
SHOW ANOTHER PIECE OF ENERGY FROM THE MEAN TROUGH COVERING NORTH
AMERICA TO MOVE INTO THE FORECAST AREA STARTING LATER FRIDAY
CONTINUING INTO SATURDAY.  WILL MAKE A FEW ADJUSTMENT FOR FRIDAY AND
FRIDAY NIGHT...OTHERWISE WONT TOUCH SATURDAY THROUGH MONDAY. THE
LATER DAYS.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...HEAVY SNOW WARNING MOUNTAINS...
  ZONES 31..33..34 THROUGH 12Z WED.  WINTER STORM WARNING THIS
AFTERNOON AND TONIGHT FOOTHILLS...ZONES 35 AND 36.

&&

RPK/RJK

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