Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 311855
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1155 AM MST SUN JAN 31 2016

.UPDATE...
ISSUED AT 1155 AM MST SUN JAN 31 2016

WILL BE UPGRADING ALL WATCHES TO WINTER STORM WARNINGS...AS WELL
AS BACKING UP THE HIGHLIGHTS BY A FEW HOURS. WARNINGS HAVE BEEN
GROUPED TO ACCOUNT FOR THE SOUTH TO NORTH PROGRESSION OF THE
SNOW...SO NORTHERN SECTIONS OF THE WARNINGS MAY TAKE A COUPLE
HOURS TO SEE THE CRITERIA SNOWFALL.

UPDATE ISSUED AT 1054 AM MST SUN JAN 31 2016

CONTINUING TO SCOUR THROUGH UPDATED MODEL DATA AND TRYING TO NAIL
DOWN TIMING FOR THE UPCOMING STORM. SEEMS AS THOUGH THE MOUNTAINS
AND FOOTHILLS NEAR AND SOUTH OF THE I70 CORRIDOR WILL LIKELY
BEGIN TO SEE THE HEAVIER SNOW STARTING BY EARLY THIS EVENING WITH
SNOW TO SPREAD NORTHEAST FROM THERE. VIEWING 700 MB LEVEL
PARAMETERS...MOST MODELS INDICATING STRAIGHT SOUTHERLY FLOW
TONIGHT WITH WARM ADVECTION. THIS TENDS TO DOWNSLOPE AREAS NORTH
OF THE PALMER DIVIDE UP TO THE SOUTH PLATTE VALLEY...THOUGH FAVOR
AREAS TOWARDS THE CHEYENNE RIDGE. THEREFORE...COULD SEE AN INITIAL
BAND OF SNOW MARCH NORTH THIS EVENING TO BRING LIGHT TO MODERATE
SNOW BEFORE SNOW DECREASES OVER THE PALMER RIDGE TO SOUTH PLATTE
VALLEY AREAS THROUGH THE REST OF THE NIGHT. THEN...UPSLOPE FLOW
INCREASES IN THE MORNING AND 700 MB FLOW BEGINS VEERING
EASTERLY...THEN SNOW WILL INCREASE AGAIN THROUGH THE AFTERNOON
WITH MODERATE TO AT TIMES HEAVY SNOWFALL ALONG WITH STRENGTHENING
WINDS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 346 AM MST SUN JAN 31 2016

EXTENDED THE WINTER STORM WARNING FOR THE MOUNTAINS UNTIL 9AM.
RADAR INDICATES SNOW SHOULD LINGER AFTER SUNRISE. WEB CAMERAS
SHOWING HARSH DRIVING CONDITIONS IN THE MOUNTAINS AT THIS TIME
WITH SNOW COVERED ROADS AND LIMITED VISIBILITY. CONDITIONS WILL
BEGIN TO IMPROVE AROUND MID MORNING.

STRONG UPPER LEVEL LOW WILL MOVE ONTO THE WEST COAST THIS EVENING.
AHEAD OF IT...A STRONG JET WILL CONTINUE TO SINK SOUTH. HEAVY SNOW
ASSOCIATED WITH THIS JET WILL MOVE SOUTH OF THE AREA THIS MORNING.
IT WILL BE CLOSE ENOUGH THAT PERIODS OF LIGHT SNOW WILL BE POSSIBLE
FOR THE MOUNTAINS AROUND I-70. ADDITIONAL SNOWFALL TODAY WILL BE
LIGHT...UP TO 3 INCHES IN THE MOUNTAINS...MAINLY AROUND I-70 AND
SOUTH. NORTH OF THIS...AMOUNTS WILL BE LESS. THERE IS A CHANCE LIGHT
SNOW COULD MOVE OFF THE HIGHER TERRAIN AND ONTO THE FRONT RANGE. IF
THIS OCCURS ANY SNOWFALL WILL BE LESS THAN AN INCH.

SNOW WILL INCREASE TONIGHT AS THE PACIFIC STORM SYSTEM MOVES INLAND.
BY 12Z MONDAY MORNING...THE UPPER LEVEL LOW WILL BE OVER NORTHERN
ARIZONA AND THE SURFACE LOW OVER THE FOUR CORNERS. A SOUTH TO
SOUTHEAST LOW LEVEL FLOW WILL DEVELOP. THIS WILL FAVOR THE BEST SNOW
DEVELOPMENT OVER NORTHERN PART OF THE FRONT RANGE. STRONG QG ASCENT
AHEAD OF THE TROUGH WILL PRODUCE WIDESPREAD SNOW OVER THE MOUNTAINS
THIS EVENING. THE SNOW WILL THEN SPREAD EASTWARD OVERNIGHT. SNOWFALL
AMOUNTS WILL BE UP TO 3 INCHES ALONG THE FRONT RANGE WITH 2 TO 6
INCHES FOR THE MOUNTAINS AND HIGHER FOOTHILLS. GUSTY EASTERLY WINDS
WILL START TO DEVELOP TOWARDS 12Z AS THE SURFACE LOW MOVES OVER THE
FOUR CORNERS.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 346 AM MST SUN JAN 31 2016

THE STORM SYSTEM EXPECTED TO GENERATE WIDESPREAD SNOW AND GUSTY
WINDS ACROSS N-CENTRAL/NORTHEAST COLORADO NEXT COUPLE OF DAY IS
STILL WELL OFF THE CALIFORNIA COAST AT THIS HOUR. THIS WAVE BEING
CARRIED ALONG BY A POWERFUL 140+KT PACIFIC JET IS FORECAST TO
MOVE QUICKLY ONSHORE LATER TODAY AND ACROSS THE GREAT BASIN
TONIGHT WHERE IT DEEPENS AND BEGINS TO ASSUME A NEGATIVE TILT.
DETERMINISTIC AND ENSEMBLE GUIDANCE SHOW THIS FEATURE ADVANCING
ACROSS THE FOUR CORNERS REGION MONDAY MORNING WHERE SOME MODELS
SHOW IT ATTEMPTING TO CLOSE OFF A 700/500MB LOW. IR/WATER VAPOR
SATELLITE IMAGERY SHOW THIS WAVE WITHIN A NEARLY CONTINUOUS
ATMOSPHERIC RIVER EXTENDING WELL ACROSS THE N-CENTRAL PACIFIC. BY
MONDAY...MODELS WITH EXCEPTION OF THE CANADIAN GEM SHOW THIS NEG
TILT TROUGH AND ALL OF ITS MOISTURE AND ENERGY PROPAGATING ACROSS
COLORADO...AND FORMING A CLOSED 700/500MB LOW OVER/NEAR SERN CO
AROUND 00Z/TUESDAY. Q-G OMEGA AND POT TENDENCY FIELDS INDICATE
MAXIMUM LARGE SCALE ASCENT OVER ERN COLORADO/WESTERN KANSAS
CENTERED AROUND 00Z/TUESDAY WITH NORTHEASTERN COLORADO ON THE
NORTHERN FRINGE OF THE ASCENT MAXIMA. ALTHOUGH THE GFS REMAINS THE
OUTLIER AS IT SHOWS THE 700 MB LOW FARTHER NORTH AND THE BEST DEEP
LAYER Q-G ASCENT CENTERED OVER NERN COLORADO. THAT WOULD
CERTAINLY ACCOUNT FOR THE SIGNIFICANTLY HIGHER STORM TOTAL SNOW
AMOUNTS ACROSS ERN PORTIONS OF THE CWA. FOR INSTANCE...GFS
INDICATES A STORM TOTAL AS OF 18Z/TUESDAY CLOSE TO 22 INCHES AT
DENVER`S INTERNATIONAL AIRPORT...WHILE OTHER MODELS AND ENSEMBLE
GUIDANCE INDICATE AMOUNTS CLOSER TO A FOOT. ON THE FLIP SIDE...
EUROPEAN MODEL IS ON THE DRY SIDE OF THE MEAN WITH BARELY A HALF
FOOT OF SNOW AT DIA AT THE SAME TIME. CLOSER EXAMINATION OF
850-700 HEIGHT/WIND FIELDS REVEAL LEE TROUGHING AND A MUCH WEAKER
UPSLOPE COMPONENT ALONG THE EAST FACE OF THE FRONT RANGE LATE ON
MONDAY. THIS WOULD ACCOUNT FOR THE LOWER SNOW AMOUNTS WITHIN THE
I-25 CORRIDOR. ASIDE FROM THESE RELATIVELY SMALL SCALE DIFFERENCES
IN THE MODELS...THIS STORM SYSTEM SHOULD HAVE LITTLE PROBLEM
GENERATING SIGNIFICANT STORM TOTAL SNOW AMOUNTS FOR AREAS MAINLY
FROM THE CONTINENTAL DIVIDE EASTWARD. WHILE HEAVY SNOWFALL IS NOT
EXPECTED TO BE WIDESPREAD...ITS THE LONG DURATION OF SNOWFALL THAT
WILL BE LARGELY RESPONSIBLE FOR THE LARGE SNOW AMOUNTS. OTHER
POTENTIAL THREAT WITH THIS STORM WILL BE THE STRONG/GUSTY NORTH-
NORTHEAST WINDS THAT THE NAM AND GFS INDICATE ON THE PLAINS LATE
MONDAY NIGHT AND TUESDAY ON THE BACK SIDE OF THE DEPARTING UPPER
LOW. WIND GRIDS INDICATE 20-30KT WIND SPEEDS ROUGHLY EAST OF A
LINE FROM ERN WELD COUNTY TO ERN ELBERT COUNTY. STRONGEST WINDS
APPEAR CENTERED ON SRN WASHINGTON...ERN ELBERT AND LINCOLN
COUNTIES WHERE GUSTS COULD APPROACH BLIZZARD THRESHOLD SPEEDS FOR
A SHORT TIME. WILL NEED TO MONITOR THIS AND BE READY TO HOIST A
BLIZZARD WARNING IF NEED BE. OTHERWISE THE WINTER STORM WATCH WILL
REMAIN IN PLACE FOR NOW. STILL CONSIDERABLE BLOWING AND DRIFTING
SNOW OVER THE OPEN RANGELAND COULD MAKE FOR TREACHEROUS DRIVING
CONDITIONS SUCH AS ALONG I-70 AROUND AGATE...STRASBURG AND LIMON.

ON TUESDAY...CONDITIONS GRADUALLY IMPROVE THROUGH THE DAY AND INTO
THE NIGHT AS THE UPPER LOW TRACKS NEWRD ACROSS THE CNTRL GREAT
PLAINS. COLD ADVECTION AND MODERATE NWLY FLOW ON THE BACK SIDE OF
THIS TROUGH SHOULD CONTINUE TO PRODUCE LIGHT/MODERATE SNOWFALL IN
THE HIGH COUNTRY WITH ANOTHER 2-4 INCHES AS A RULE BY EVENING. THIS
SAME NORTHWEST FLOW WILL HELP TO DRY OUT OF THE PLAINS AIRMASS
PUTTING AN END TO MOST SNOWFALL BY EVENING. TEMPERATURES ON TUESDAY
ARE PROGGED TO BE COLDEST OF THE WEEK.

LOOKING AHEAD...PERSISTENT NORTHWEST FLOW ALOFT WILL KEEP A CHANCE
OF SNOW IN THE MOUNTAINS WITH THE OCCASIONAL PASSING SHORT WAVE.
THE PLAINS SHOULD REMAIN MAINLY DRY AFTER TUESDAY WITH A DOWNSLOPE
FLOW COMPONENT. TEMPERATURE GUIDANCE INDICATES GRADUAL WARMING FOR
THE REMAINDER OF THE WEEK...THOUGH READINGS SHOULD STAY BELOW
AVERAGE.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1054 AM MST SUN JAN 31 2016

CEILINGS OF 1000 TO 3000 FEET WILL BE IMPROVING TO 3000 TO 6000
FEET...ESPECIALLY OVER THE NORTHERN AREAS. WINDS WILL REMAIN
LIGHT TODAY AND OUT OF A NORTHEAST TO SOUTHEAST DIRECTION.

CEILINGS WILL LOWER TONIGHT AND SNOW WILL FORM. MODELS SEEM TO
WANT TO HINT AT AN INITIAL WAVE OF SNOW...ONLY TO DECREASE AS
DOWNSLOPING EFFECTS OFF THE PALMER DIVIDE OCCUR BETWEEN 06-12Z.
CEILINGS WILL FALL TO 1000 TO 3000 FEET. VISIBILITY MAY FALL TO A
MILE IN SNOW... ESPECIALLY TOWARDS 12Z MONDAY THEN FALL EVEN
FURTHER BY 18Z WITH HEAVIER SNOW FORECAST AS WELL AS INCREASING
NORTHEASTERLY WINDS TO PERHAPS PRODUCE BLOWING SNOW. SNOWFALL
THROUGH 12Z MONDAY IS EXPECTED TO BE LESS THAN 3 INCHES IN THE
DENVER AREA...WITH ANOTHER 2 TO 4 INCHES THROUGH 18Z.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO NOON MST TUESDAY
FOR COZ042-044-048>051.

WINTER STORM WARNING FROM 5 PM THIS AFTERNOON TO NOON MST
TUESDAY FOR COZ033>037.

WINTER STORM WARNING FROM 8 PM THIS EVENING TO NOON MST TUESDAY
FOR COZ038>041-043-045>047.

&&

$$

UPDATE...KRIEDERMAN
SHORT TERM...MEIER
LONG TERM...BAKER
AVIATION...KRIEDERMAN


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