Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 291723
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1123 AM MDT FRI APR 29 2016

.UPDATE...
ISSUED AT 1120 AM MDT FRI APR 29 2016

MODIFICATIONS HAVE BEEN MADE TO SNOW AMOUNTS FOR TODAY AND
TONIGHT. BASICALLY...LOWERED AMOUNTS IN THE MTNS...ESPLY WEST OF
THE CONTINENTAL DIVIDE AND FOR THE FOOTHILLS...ESPLY NORTH OF
HIGHWAY 7. RAISED SNOW ACCUMS IN PARK COUNTY BASED ON RECENT
SPOTTER REPORT...AND ALSO RAISED SNOW AMTS ACRS THE SERN CORNER OF
THE CWA...IE ELBERT AND LINCOLN COUNTIES WHERE WX SPOTTERS AND
WX CAMS INDICATE 3-6 INCHES OF SNOW ON THE GROUND...CENTERED
AROUND LIMON AND HUGO. LASTLY...LOWERED SNOW AMOUNTS OVR NERN
PORTIONS OF THE I-25 CORRIDOR WHERE LITTLE TO NO SNOW HAS YET TO
PILE UP AND PCPN UP TO NOW HAS MAINLY BEEN RAIN OR DRIZZLE.

OVER THE NEXT SEVERAL HOURS...STILL ANTICIPATE A RAMP UP ON PRECIP
ACROSS NENR COLORADO WITH MEAN LAYER FLOW TURNING MORE EASTERLY AS
THE 500-400MB LOW CONTINUES TO TRACK EAST ALONG THE COLORADO/NEW
MEXICO BORDER. PINPOINTING SNOW AMOUNTS CONTINUE TO BE BIGGEST
CHALLENGE AS MODELS CONTINUE TO OFFER CONSIDERABLY DIFFER QPF
VALUES...ESPLY ON THE PLAINS. THE GFS BY FAR IS THE WETTEST OF
THE MODELS...AND IT HAS BEEN FOR THE PAST FEW DAYS. THE EC...SREF
AND HRRR QPF NUMBERS SEEM MORE REASONABLE BASED ON THE QG ASCENT...
INSTABILITY AND OROGRAPHIC LIFT PREDICTED BY THE MODEL BLEND.
THEREFORE WILL USE QPF ROUGHLY HALF OF THAT OFFERED BY THE GFS TO
REVISE SNOW AMOUNTS. LIQUID/SNOW RATIOS ON THE PLAINS BASED ON
FCST TEMPS IN THE 7.2 TO 9.4 TO 1 RANGE. HIGHER ELEVATIONS WHERE
TEMPS COLDER BY 4-8 DEGS...H2O TO SNOW RATIOS IN THE 12 TO 17 TO 1
RANGE.

NO CHANGES TO CURRENT WINTER WEATHER HIGHLIGHTS AT THIS TIME. IF
WE SEE MORE SNOW ACCUMULATION ON ROADWAYS ACRS ELBERT...LINCOLN
AND WASHINGTON COUNTIES...A WINTER WEATHER ADVISORY MAY BE
NECESSARY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 306 AM MDT FRI APR 29 2016

WATER VAPOR IMAGERY SHOWING ELONGATED UPPER LOW FROM EASTERN UTAH
TO NORTHWEST NEW MEXICO. PRECIPITATION HAS BEEN SLOW TO DEVELOP
ESPECIALLY NORTHERN SECTIONS OF THE CWA. THERE HAS BEEN A GENERAL
NORTHWARD SPREAD OF THE PRECIP WITH MAINLY SNOW FROM DENVER
SOUTHWARD. FURTHER NORTH TEMPERATURES ARE A BIT HIGHER SO LIGHT
RAIN AND DRIZZLE CONTINUE TO FALL FROM BOULDER NORTHWARD. EVEN
WITH THE HEAVIER PRECIP SHOWN ON RADAR...OBSERVATIONS SITES AT
DENVER ARE ONLY SHOWING LIGHT SNOW. PART OF THE PROBLEM IS THE
LIGHT SOUTHEAST FLOW WHICH IS DOWNSLOPING OVER THE FRONT RANGE SO
ONLY A VERY WEAK UPSLOPE COMPONENT. WE ALSO HAVE E A STRONG
SOUTHERLY MID LEVEL FLOW WHICH ALSO MAY BE LIMITING PRECIP. EVEN
NOW THERE APPEARS TO BE DRYING OR DIMINISHMENT OF PRECIP OVER THE
PALMER DIVIDE. LATEST HRRR PICKS UP ON THIS SO A LULL IN THE
PRECIP EARLY THIS AM BEFORE BECOMING WIDESPREAD AGAIN BY LATER BY
LATER THIS MORNING.

AS FOR THE WINTER HILITES...AM CONCERNED THAT WILL NOT BE ABLE TO
MAKE SNOWFALL CRITERIA IN THE MOUNTAINS AND FOOTHILLS. HAVE
LOWERED AMOUNTS....AND TOTAL VALUES LOOK NOW TO BE AROUND 4 TO 9
INCHES ALONG EAST5 SLOPES AND 4 TO 6 INCHES OVER THE PALMER
DIVIDE. THERE JUST DOES NOT SEEM TO BE ENOUGH STRONG UPSLOPE FLOW
DUE TO THE ELONGATED UPPER LOW AND NOT A NICE COMPACT SYSTEM. FOR
NOW WILL LEAVE THE HILITES AS THE BEST POTENTIAL IS STILL TO COME
FOR THIS AFTERNOON. DAY SHIFT MAY DECIDE TO CANCEL HILITES IF
THINGS DON`T COME TOGETHER. OVERALL...HEAVIEST QPF AMOUNTS WILL BE
OVER THE EASTERN PLAINS OF COLORADO WITH LESSER AMOUNTS FURTHER
WEST.

THE UPPER LOW IS PROGGED TO CONSOLIDATE A BIT BETTER BY LATER
THIS AFTERNOON OVER SOUTHEAST COLORADO WHICH LOOKS TO SHOW THE
BEST POTENTIAL FOR PRECIP UNDER THE STRONGEST QG ASCENT.
TEMPERATURES WILL HOVER IN THE LOWER TO MID 30S TODAY AND GIVEN
HIGH SUN ANGLES...MOST OF THE SNOW WILL MELT ON PAVEMENT SURFACES
BUT STILL SOME LIGHT ACCUMULATIONS ON GRASSY SURFACE. LOOK FOR
GRADUAL IMPROVEMENT LATER THIS EVENING AND OVERNIGHT AS THE UPPER
LOW MOVES INTO CENTRAL KANSAS BY LATER TONIGHT. THERE WILL STILL
BE A FAIR AMOUNT OF WRAP AROUND PRECIP OVER FAR NORTHEAST PLAINS.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 306 AM MDT FRI APR 29 2016

ON SATURDAY...THE UPPER LOW WILL BE MOVING INTO SOUTHWESTERN
NEBRASKA WITH MOISTURE WRAPPING AROUND THE SYSTEM AND MOVING
ACROSS THE NORTHEAST PLAINS. HIGHEST POPS WILL BE NORTH AND EAST
OF DENVER...WITH THE BEST CHC OF ACCUMULATING SNOWFALL...ALBEIT
LIGHT...IN THE MORNING. AS THE SYSTEM CONTINUES TO TRACK TO THE
NORTHEAST SATURDAY AFTN/EVNG...THE MDLS SHOW WEAK DOWNWARD QG
OVER THE CWA. NAM12 SPATIAL CROSS SECTIONS MAINTAIN A WEAK ELY
FLOW BLO 700 MB SATURDAY NIGHT...BUT MUCH DRIER ALOFT. BEST CHC OF
PCPN WILL BE IN AND NEAR THE FRONT RANGE FOOTHILLS SATURDAY NIGHT
INTO SUNDAY MORNING. WITH THE DRIER AIR ALOFT...COULD SEE PATCHY
FREEZING DRIZZLE DEVELOP SO WILL THROW A LITTLE BIT OF THAT INTO
THE GRIDS. SUNDAY AFTERNOON INTO MONDAY MORNING...ANOTHER CLOSED
PACIFIC SYSTEM AROUND THE FOUR CORNERS REGION AT 18Z SUNDAY IS
PROGGED TO OPEN UP AND MOVE INTO NEBRASKA BY 18Z MONDAY. THIS
SYSTEM IS FAIRLY WEAK...BUT IT DOES HAVE SOME QG ASCENT IN THE MID
LEVELS AND DOES DEEPEN THE MOISTURE ALONG THE FRONT RANGE.
THEREFORE COULD SEE ANOTHER CHANCE OF PCPN...ESPECIALLY FROM THE
URBAN CORRIDOR WESTWARD. TEMPERATURES WILL MODIFY FURTHER ON
TUESDAY BUT AN INTERESTING FEATURE DOES SHOW UP ON THE ECMWF. A
LOW PRESSURE SYSTEM OVER SERN MT/WRN NORTH DAKOTA AROUND 18Z
MONDAY IS PROGGED SLIDE NORTHEAST TO SOUTHWEST AROUND AN OMEGA
RIDGE SITTING OVER THE NRN ROCKIES...AND INTO NWRN CO BY 18Z
TUESDAY. THIS COULD BRING A CHC OF PCPN TO THE REGION TUESDAY
AFTN/EVNG. THE GFS ON THE OTHER HAND SHOWS NO SUCH FEATURE...SO
MAINLY CHC POPS MAINLY OVER THE HIGHER TERRAIN AT THAT TIME. TREND
FOR DRIER AND WARMER STILL ON TRACK FOR THE REST OF THE WEEK WITH
AN UPPER LEVEL RIDGE THE PREVAILING FEATURE FOR WEDNESDAY AND
THURSDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1120 AM MDT FRI APR 29 2016

ILS CIGS AND VSBYS ANTICIPATED AT DENVER AREA AIRPORTS THROUGH AT
LEAST 22Z THIS AFTERNOON. VSBY REDUCTIONS WILL BE A COMBINATION OF
SNOW AND FOG. WITH THE CORE OF THIS STORM SYSTEM PREDICTED TO
PASS TO OUR EAST AROUND MID-AFTERNOON TODAY...SHOULD SEE THE
MOIST UPSLOPE FLOW GRADUALLY WEAKENING AND BECOMING MORE
NORTHERLY IN DIRECTION. THIS SHOULD RESULT IN A REDUCTION IN
SNOWFALL RATES AND A SLIGHT IMPROVEMENT IN CIG HEIGHTS AND VSBYS
AT KBJC AND KDEN. NOT SO AT KAPA WHERE ILS CONDITIONS ARE LIKELY
TO PERSIST UNTIL AT LEAST 02Z-03Z THIS EVENING. SHOULD THEN SEE
GRADUAL IMPROVEMENT AT ALL DENVER AREA TERMINALS AFTER MIDNIGHT
WITH THIS STORM MOVING AWAY FROM THE FRONT RANGE.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL MIDNIGHT MDT TONIGHT FOR COZ041.

WINTER STORM WARNING UNTIL MIDNIGHT MDT TONIGHT FOR COZ033>037.

&&

$$

UPDATE...BAKER
SHORT TERM...ENTREKIN
LONG TERM...COOPER
AVIATION...BAKER



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