Littleton, CO Area Forecast Discussion Issued by NWS
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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