FXUS65 KBOU 221101
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
400 AM MST TUE DEC 22 2009

.SHORT TERM...WATER VAPOR LOOP SHOWS THE UPPER LEVEL LOW CARVING 
ITSELF SOUTHWARD ACROSS WASHINGTON AND OREGON EARLY THIS MORNING.  
THIS LOW IS STILL ON TRACK TO MOVE SOUTH/SOUTHEAST TO NEAR LAS VEGAS 
BY THIS EVENING...AND THEN BEGIN TO MOVE MORE EASTWARD LATER TONIGHT 
ACROSS ARIZONA AND NEW MEXICO.  IT SHOULD BE NOTED THERE HAS BEEN A 
SLIGHT NORTHWARD SHIFT IN THE OVERALL TRACK DURING THE PAST 24 
HOURS.  THE BEST LIFT WITH THIS STORM ARRIVES LATE THIS AFTERNOON 
AND EVENING...WITH SNOW BREAKING OUT IN THE MOUNTAINS THIS AFTERNOON 
AND THE COLUMN FINALLY SATURATING ON THE PLAINS DURING THE EVENING 
HOURS.  THE Q-G VERTICAL MOTION FIELDS SHOW A BIT MORE LIFT AS A 
RESULT OF THE SLIGHTLY NORTHWARD TRACK AND BETTER VERTICAL MOTION 
THROUGH THE DENDRITIC GROWTH LAYER...SO WE WILL BE INCREASING SNOW 
AMOUNTS ANOTHER INCH OR TWO FOR TONIGHT.  THE Q-G DERIVED 
PRECIPITATION SHOWS ABOUT 0.30 INCH OF WATER AFTER THE COLUMN 
SATURATES...WHICH SHOULD TRANSLATE TO A GOOD 2-4 INCHES AND PROBABLY 
A LITTLE MORE THAN THAT AGAINST THE FRONT RANGE WHERE THE WEAK 
UPSLOPE AROUND 10 KNOTS HELPS OUT.  SEE NO REASON TO MAKE ANY 
SIGNIFICANT CHANGES TO ONGOING HIGHLIGHTS... JUST MOVED UP BEGINNING 
TIME TO 5 PM AND ADDED PARK COUNTY TO THE ADVISORY IN THE HIGH 
COUNTRY.  WE WILL STILL HAVE TO MONITOR THE TRACK CAREFULLY...AS ANY 
MORE OF A NORTHWARD SHIFT COULD LEAD TO HEAVIER SNOWFALL AND A NEED 
FOR WARNINGS ALONG THE FRONT RANGE.

.LONG TERM...IT SEEMS LIKE THE MODELS ARE GOING TO KEEP PITCHING 
SLIGHTLY DIFFERENT SOLUTIONS WITH EACH MODEL RUN...ALL RESULTING IN 
THE SAME CONCLUSION THAT A PERIOD OF SNOWFALL ACROSS THE FORECAST 
AREA WILL BE FOLLOWED BY INCREASING NORTH WINDS AS THE MAIN STORM 
CENTER MATURES OVER THE CENTRAL PLAINS.  QPF FORECASTS FROM THE 
MODELS CONTINUE TO BE MODEST...SO IT APPEARS THAT ONLY ADVISORY-LIKE 
AMOUNTS WILL FALL OVER A 24-36 HOUR PERIOD BEGINNING THIS EVENING.  
NORTHERLY WINDS ON THE EASTERN PLAINS ARE EXPECTED TO BEGIN 
INCREASING LATE WEDNESDAY NIGHT OR THURSDAY MORNING.  THE WINTER 
STORM WARNING FOR THE EASTERN TIER OF OUR COUNTIES IS TO HIGHLIGHT 
THE TRAVEL DIFFICULTIES THAT WILL BE DEVELOPING DUE TO THE BLOWING 
AND DRIFTING SNOW.  THE OTHER MAIN STORY FOR THE LATTER HALF OF THE 
WEEK IS GOING TO BE THE COLD TEMPERATURES AS THE MERCURY DROPS TO 
THE LOWER SINGLE DIGITS FOR UP TO A FEW MORNINGS...INCLUDING 
CHRISTMAS.  

PREVIOUS FORECAST PACKAGE HAD THE SYSTEM PRETTY WELL COVERED WITH 
ADVISORIES AND WARNINGS ALREADY IN PLACE.  WITH NO INDICATIONS OF 
ANY MAJOR CHANGES FROM THE MODELS...DID NOT MAKE ANY CHANGES EXCEPT 
ADJUSTING SOME TEMPERATURES ON THURSDAY.

&&

.AVIATION...CLOUDS WILL GRADUALLY LOWER THIS AFTERNOON WITH ILS 
LANDING CONDITIONS LIKELY DEVELOPING IN THE 23Z-02Z PERIOD.  SNOW 
SHOULD COMMENCE SHORTLY THEREAFTER WITH IFR CONDITIONS AND 
PREVAILING VISIBILITIES LOWERING TO AROUND 1 MILE AND CEILINGS 
DROPPING BELOW 1000 FEET IN THE 03Z-07Z PERIOD.  SNOW SHOULD BE 
HEAVIEST AND FAIRLY STEADY FROM 06Z-18Z WEDNESDAY...THEN SOME 
DECREASE POSSIBLE WEDNESDAY AFTERNOON.  ACCUMULATIONS BY DAYBREAK 
WEDNESDAY SHOULD RANGE FROM 2-4 INCHES...WITH ANOTHER 1-3 INCHES 
DURING THE DAY WEDNESDAY.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...WINTER STORM WARNING FOR THE 
     FAR EASTERN PLAINS TONIGHT THROUGH THURSDAY...ZONES 46..48>51.
   WINTER WEATHER ADVISORY FOR THE MOUNTAINS...FOOTHILLS...FRONT
     RANGE URBAN CORRIDOR...AND REST OF THE EASTERN PLAINS TONIGHT
     THROUGH WEDNESDAY NIGHT...ZONES 33>45..AND 47.

$$

BARJENBRUCH/KDRBY