Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 201837
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1137 AM MST THU NOV 20 2014

.UPDATE...
ISSUED AT 1135 AM MST THU NOV 20 2014

HIGH CLOUDS ARE SPREADING IN FROM THE SOUTHWEST A BIT MORE SLOWLY
THAN EXPECTED...MADE SOME MINOR ADJUSTMENTS FOR SLOWER INCREASE IN
CLOUDS AND ABOUT 3 DEGREES WARMER THIS AFTERNOON.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 340 AM MST THU NOV 20 2014

CURRENT SATELLITE IMAGERY SHOWING CLOUDS OVER SOUTHEASTERN
PORTIONS OF THE CWA...ESPECIALLY PARK COUNTY DUE TO SOME MID LEVEL
MOISTURE AND A SURFACE LEE TROUGH ALONG THE FOOTHILLS. FOR THE
REMAINDER OF THE PLAINS UPPER LEVEL THIN CIRRUS WILL ALLOW FOR
COOLER OVERNIGHT TEMPERATURES SO DROPPED LOWS A FEW DEGREES. CLOUDS
WILL THIN OUT BY MORNING AND MOVE NORTH THROUGH THE CWA AS THE
NEXT TROUGH MAKES IT WAY INTO WESTERN COLORADO. ALL MODELS MINUS
THE GFS KEEP THIS SYSTEM DRY WITH JUST SOME MID LEVEL MOISTURE.
THIS WILL KEEP MOSTLY CLOUDY CONDITIONS OVER THE MOUNTAINS TODAY
WITH PARTLY CLOUDY TURNING TO MOSTLY CLOUDY OVER THE PLAINS THIS
EVENING. HIGH TEMPERATURES FOR THURSDAY WILL REMAIN CLOSE TO
SEASONAL NORMALS.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 340 AM MST THU NOV 20 2014

MAIN FORECAST IMPACTS WILL SURROUND STRONG WEST/NORTHWEST FLOW
DEVELOPING ACROSS THE STATE BY THIS WEEKEND. THIS WILL BRING
INCREASING WIND AND PERSISTENT OROGRAPHIC MOUNTAIN SNOWFALL.

UNTIL THEN...FRIDAY WILL FEATURE MILD TEMPERATURES WITH READINGS
LIKELY REACHING OR JUST EXCEEDING THE 50F DEGREE MARK ON THE
PLAINS. THERE IS SLIGHT WARMING ALOFT...BUT STILL A FEW CLOUDS TO
CONTEND WITH AFFECTING HIGH TEMPS. WHILE THE DAY SHOULD START OFF
GENERALLY SUNNY...HIGH LEVEL CLOUDS ARE EXPECTED TO THICKEN
THROUGH THE DAY AS NEXT BATCH OF UPPER LEVEL MOISTURE REACHES THE
FORECAST AREA. WINDS WILL REMAIN LIGHT AS BOTH FLOW ALOFT AND
PRESSURE GRADIENT REMAIN QUITE WEAK AS UPPER LEVEL TROUGH MOVES
ACROSS THE DESERT SOUTHWEST.

SATURDAY WILL BE A TRANSITION DAY. DOWNSLOPE WARMING IS EXPECTED
TO INCREASE AND WARM ADVECTION AHEAD OF FAST MOVING UPPER LEVEL
DISTURBANCE WILL BRING A RATHER MILD DAY TO THE FOOTHILLS AND
PLAINS. HIGH TEMPERATURES WILL BE CAPABLE OF REACHING 60F BUT
INCREASE IN CLOUDS COULD ONCE AGAIN OFFSET THAT A BIT. MEANWHILE...
IN THE MOUNTAINS...CLOUDS WILL INCREASE AND THICKEN THROUGH THE
AFTERNOON AS NOSE OF 150+ KT PACIFIC JET STREAM RACES ACROSS THE
GREAT BASIN. UPPER LEVEL DIVERGENCE ON THE NOSE OF THIS FEATURE
AND INCREASED PACIFIC MOISTURE PLUME SEEN IN THE 700-500 MB SPEC
HUMIDITY PROGS WILL REACH THE STATE BY AFTERNOON. AS A
RESULT...SNOW WILL LIKELY BEGIN TO DEVELOP DURING THE AFTERNOON
HOURS AND THEN INCREASE SATURDAY NIGHT. OROGRAPHIC FLOW IS
INITIALLY WEST/SOUTHWEST NEAR 250 DEGREES...BUT THEN TURNS MORE
WEST/NORTHWEST TOWARD 290 DEGREES SATURDAY NIGHT. COLD ADVECTION
OCCURS AS WELL SO INGREDIENTS ARE THERE FOR AN ACCUMULATING HIGH
COUNTRY SNOWFALL. THERE IS POTENTIAL FOR EVENTUAL WATCH/WARNING
CRITERIA SNOWFALL IF THE MOISTURE DEPTH CAN HOLD IN PLACE LONG
ENOUGH. SPEC HUMIDITY LEVELS REALLY DROP OFF WITH SUCH STRONG COLD
ADVECTION...BUT HIGH SNOW TO LIQUID RATIOS AND FAVORABLE
DENDRITIC GROWTH REGIME COULD STILL PRODUCE HEAVY ACCUMULATING
SNOWFALL INTO SUNDAY. WILL ADDRESS THIS POTENTIAL IN THE HAZARDOUS
WEATHER OUTLOOK. FOR FORECAST QPF AND SNOW GRIDS...GENERALLY
STARTED WITH BLENDED MODEL/LOCAL OROGRAPHIC SNOWFALL OUTPUT.

WE REMAIN IN RATHER STRONG NORTHWEST FLOW ALOFT THROUGH MONDAY AND
TUESDAY. THIS WILL KEEP GUSTY WINDS ACROSS MOST OF THE FORECAST
AREA AND COLDER THAN NORMAL TEMPERATURES. THE OROGRAPHIC SNOW
MACHINE WILL KEEP RUNNING IN THE MOUNTAINS WITH EMBEDDED SHORT
WAVES BRINGING PERIODS OF ACCUMULATING SNOWFALL.

THERE MAY BE A DECREASE IN MOUNTAIN SNOW BY TUESDAY IF WARM
ADVECTION OCCURS. IF THAT PATTERN DOES SET UP...THEN WE WILL ALSO
HAVE TO WATCH POTENTIAL FOR A DOWNSLOPE WIND EVENT BY TUESDAY
NIGHT OR WEDNESDAY. STILL A LONG WAYS OUT BUT SOMETHING TO MONITOR
OVER THE NEXT FEW DAYS AS FLOW ALOFT WILL REMAIN QUITE STRONG. AN
IMPORTANT NOTE IS THAT MODELS DIVERGE SIGNIFICANTLY BY THEN WITH
THE ECMWF SHOWING ANOTHER COLD FRONT AND STRONGER TROUGH MOVING
INTO THE REGION BY LATE WEDNESDAY. MEANWHILE...THE GFS AND MOST OF
ITS ENSEMBLES ARE FAR LESS PROGRESSIVE AND KEEP THE RIDGE OVER THE
WESTERN U.S. IN PLACE. GENERALLY...THE ECMWF/NAEFS SOLUTIONS WERE
FAVORED OVER THE GFS WHICH MAY HAVE IMPLICATIONS ON THE
THANKSGIVING DAY FORECAST FOR NORTHEAST COLORADO.

&&

.AVIATION...(FOR THE TAFS THROUGH 00Z FRIDAY LATE AFTERNOON)
ISSUED AT 1135 AM MST THU NOV 20 2014

VFR THROUGH FRIDAY WITH LIGHT WINDS.

&&

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

$$

UPDATE...GIMMESTAD
SHORT TERM...BOWEN
LONG TERM...BARJENBRUCH
AVIATION...GIMMESTAD


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