National Weather Service Forecast Discussion

000
FXUS65 KBOU 092210
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
300 PM MST TUE MAR 9 2010

.SHORT TERM...UPPER LEVEL LOW WILL SLOWLY WEAKEN OVER THE NEXT 24
HOURS AS IT SPINS OVER NEBRASKA. WILL STILL SEE WRAP AROUND SHOWERS
MOVE OVER THE EXTREME NORTHEAST CORNER OF COLORADO TONIGHT AND
WEDNESDAY. THESE SHOWERS WILL BE LIGHT...IF RAIN CHANGES OVER TO
SNOW...LITTLE IF ANY SNOW ACCUMULATION IS EXPECTED.

ANOTHER CLOSED LOW OVER NORTHERN ARIZONA WILL QUICKLY SWEEP ACROSS
NEW MEXICO TONIGHT AND END UP IN NORTHERN TEXAS AND OKLAHOMA BY
WEDNESDAY AFTERNOON. MODELS INDICATE THE LIFT ASSOCIATED WITH THIS
LOW WILL REMAIN SOUTH OF THE FORECAST AREA. HOWEVER...THE AIRMASS
HAS BECOME SLIGHTLY UNSTABLE THIS AFTERNOON AND EXPECT SCATTERED
SHOWERS OVER THE MOUNTAINS...FOOTHILLS AND FRONT RANGE. THIS WILL
LINGER THROUGH THE EVENING. ATMOSPHERE IS CAPPED AROUND 550MB SO
VERTICAL GROWTH WILL BE LIMITED. THIS PLUS A LARGE TEMPERATURES/DEW
POINT SPREAD WILL KEEP ANY PRECIPITATION LIGHT ALONG THE FRONT RANGE
AND ACROSS THE PLAINS. THE MOUNTAINS WILL RECEIVE A LITTLE MORE
MOISTURE THAN THE FRONT RANGE. IN ADDITION TO THE UNSTABLE
ATMOSPHERE...WEAK OROGRAPHIC LIFT WILL AID IN SNOW DEVELOPMENT. THE
NAM AND GFS SHOWING THE GREATEST PRECIPITATION FALLING IN THE
MOUNTAINS SOUTH OF I-70. AMOUNTS ARE ON THE LIGHT SIDE AND ONLY
EXPECT A FEW INCHES AT MOST.

.LONG TERM....WILL USE A BLEND OF THE NAM/GFS/ECMWF/CANADIAN GLOBAL
MODELS TO DERIVE A REASONABLY SOUND FORECAST...AT LEAST OUT THRU
SATURDAY. BEYOND THAT MODELS DIFFER QUITE A BIT AS TO THE POSITION
AND TRACK OF THE NEXT IN A SERIES OF UPPER AIR SYSTEMS PROGGED TO
PASS SOMEWHERE OVER THE ROCKY MTN REGION LATE IN THE WEEKEND. SO
MOST OF MY ATTENTION WILL BE SPENT ON THE DUAL UPPER LOW SYSTEM
GENERATING THE UNSETTLED WEATHER ACROSS THE FCST AREA WEDNESDAY
NIGHT AND THURSDAY. AS ONE SHORTWAVE EJECTS OUT FROM THE BOTTOM OF
THE MAIN UPPER TROUGH SITTING OVER THE ROCKY MTN REGION...A SECOND
SHORTWAVE DROPS INTO THE MEAN TROUGH FROM UTAH. ACCORDING TO MODELS
THE SECOND SYSTEMS PIVOT AROUND AN AXIS POINT NEAR GOODLAND
EVENTUALLY MERGING TOGETHER AS A STRONG VERTICALLY STACKED CYCLONE
OVER ERN KANSAS LATE ON THURSDAY. BEFORE THIS HAPPENS MODELS SHOW
THE OUTER EDGES OF THESE TWO SYSTEMS MERGING OVER EASTERN COLORADO
WEDNESDAY NIGHT. IT IS DURING PERIOD WHEN WE`LL LIKELY SEE THE BEST
FORCING AND DEEPEST MOISTURE OVER THE FCST AREA. HOWEVER THE DRIVING
MECHANISM APPEARS TO BE OROGRAPHIC LIFT UP ALONG THE FRONT RANGE
WHERE WE COULD SEE SEVERAL INCHES OF SNOW ACCUMULATION BY EARLY
THURSDAY MORNING. SNOW ACCUMULATION LESS LIKELY TO OCCUR ON THE
PLAINS...EXCEPT PERHAPS ON THE PALMER DIVIDE AND ALONG THE BASE OF
THE FOOTHILLS WHERE WE MAY SEE AN INCH OR TWO OF WET SNOW ACCUMULATE
BY MORNING. ALTHOUGH SHOULD SEE MOST IF NOT ALL OF THE SNOW ON THE
PLAINS MELTING SOON AFTER FALLING WITH RELATIVELY WARM GROUND
TEMPERATURES. CONDITIONS WILL BE SLOW TO IMPROVE DURING THE DAY
THURSDAY WITH GUSTY N-NWLY WINDS CONTINUING TO ADVECT COLD AIR
CLOUD COVER DROP THE BACK SIDE OF THE DEPARTING UPPER LOW. LOOKING
FOR HIGH TEMPERATURES ON THURSDAY SOME 12-15F BELOW NORMAL.

FRIDAY AND SATURDAY...THE COOL AND UNSETTLED WEATHER MOVES OUT WITH
THE UPPER TROUGH THURSDAY NIGHT. IT NOW APPEARS WE/LL WAKE UP TO
MOSTLY CLEAR SKIES AND CHILLY TEMPS FRIDAY MORNING AS HEIGHTS RISE
WITH THE APPROACHING UPPER LEVEL RIDGE. TEMPS ON FRIDAY STILL 4-8F
BELOW AVERAGE...BUT BY SATURDAY LOOKING FOR MAX TEMPS AT OR SLIGHT
ABOVE AVERAGE WITH THE FCST AREA SQUARELY UNDER THE INFLUENCE OF THE
UPPER RIDGE.

BY SUNDAY...MODELS SHOW ANOTHER SHORTWAVE DIVING OUT OF THE PACIFIC
NORTHWEST. BUT THAT/S WHERE SIMILARITIES IN THE MODELS END. ONE
SHOWS THIS WAVE PASSING OVER SWRN COLORADO AS A WEAK OPEN WAVE
WHILE TWO OTHER MODELS SHOW THIS SYSTEM QUICKLY WINDING UP AS IT
PASSES OVER THE FOUR CORNERS REGION. ALL HINT AT AREAS OF LIGHT QPF
IN ERN COLORADO ON SUNDAY...BUT NOTHING CLEAR CUT. FOR NOW WILL
INTRODUCE LOW POPS...SLIGHTLY LOWER TEMPS AND MORE CLOUD COVER FOR
SUNDAY. BEYOND THAT STILL ANTICIPATE A RETURN TO DRIER AND MUCH
WARMER CONDITIONS NEXT WEEK.

&&

.AVIATION...NORTH WINDS OF 15 TO 30 KNOTS WILL TURN NORTHEASTERLY
LATE THIS AFTERNOON AND DECREASE BY 01Z. WINDS WILL BECOME LIGHT
OVERNIGHT AND BECOME NORTHERLY AGAIN BY LATE WEDNESDAY MORNING. A
DRY AND UNSTABLE AIRMASS IN PLACE WILL KEEP CEILINGS ABOVE 6000 FEET
THROUGH 03Z. CLOUDS WILL LOWER BUT GENERALLY REMAIN ABOVE 3000 FEET.
CEILINGS COULD DIP BELOW 3000 FEET FOR A SHORT TIME IF A RAIN OR
SNOW SHOWER PASSES OVER. ANY RAIN OR SNOWFALL WILL BE LIGHT. WILL
SEE A LULL IN SHOWERS FROM 09Z-18Z...THEY WILL THEN INCREASE
WEDNESDAY AFTERNOON AS THE AIRMASS BECOMES UNSTABLE AGAIN.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...NONE.

$$
MEIER/BAKER

NWS BOU Office Area Forecast Discussion