Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 230428
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
928 PM MST SAT NOV 22 2014

.UPDATE...
ISSUED AT 923 PM MST SAT NOV 22 2014

00Z MODEL RUN COMING IN NOW. WILL NEED TO UPDATE PRECIP CHANGES
AND ADD SNOW ACCUMULATION TO PORTION OF THE HIGH PLAINS FOR LATER
TONIGHT AND SUNDAY MORNING. COLD AIR SURGING SOUTHWARD THRU
EASTERN WYOMING AT THE MOMENT WILL COUPLE WITH LARGE SCALE LIFT
GENERATED BY THE PASSING MID-LEVEL TROUGH. ALL THIS POINTS TO
SEVERAL HOURS OF LIGHT TO POSSIBLY MODERATE SNOWFALL ON THE
PLAINS...ROUGHLY SOUTH OF A BOULDER TO AKRON LINE. AREAS NORTH OF
THIS LINE MAY SEE A FEW HOURS OF LIGHT SNOWFALL NOT TOO LONG
AFTER MIDNIGHT WITH THE COLD AIR SPILLING DOWN FROM WYOMING. WILL
INCREASE WIND SPEEDS AS WELL FOLLOWING PASSAGE OF THE COLD FRONT.
BUT ITS FARTHER SOUTH WHERE MODELS INDICATE THE GREATER QPF/SNOW
ACCUMS. NAM AND MESOSCALE MODELS ARE NOW INDICATING A BAND OF 1-3
INCH SNOW ACCUMULATION ACRS DOUGLAS AND ELBERT COUNTIES..WITH 1-2
INCH AMTS ON THE SOUTH SIDE OF THE METRO AREA AND SRN PORTIONS OF
WASHINGTON AND NORTHERN PORTIONS OF LINCOLN COUNTIES. 09Z-15Z
APPEARS TO BE THE PRIME TIME FOR THIS SNOWFALL. THEREFORE WILL
RAISE POPS TO AT LEAST 70 PCT IN THESE AREAS DURING THE LATE NIGHT
AND EARLY MORNING HOURS. MOST OF THE SNOW WILL COLLECT ON GRASSY
SFCS...BUT WITH TEMPERATURES FALLING BELOW FREEZING NEAR DAWN...
ACCUMULATION ON ROADWAYS...ESPLY ON THE PALMER DIVIDE IS A GOOD
BET.

MEANWHILE...CURRENT FORECAST IS PRETTY MUCH ON TRACK FOR THE HIGH
COUNTRY. SNOWFALL SO FAR THIS EVENING HAS BEEN INTERMITTENT...WITH
THE BULK OF THIS INITIAL WAVE OF SNOWFALL UP ALONG THE
CONTINENTAL DIVIDE AND OVER THE HIGH MTN PASSES. ONCE THE 700-500
MB TROUGH AXIS CROSSES THE MTNS NOT LONG AFTER MIDNIGHT...SHOULD
SEE SNOWFALL RATES JUMPING UP WITH ONSET OF COLD AIR ADVECTION AND
STRONGER WEST-NORTHWEST FLOW ALOFT.

UPDATE ISSUED AT 517 PM MST SAT NOV 22 2014

AFTER AN INITIAL BLAST OF SNOW IN THE MOUNTAINS THERE HAS BEEN
SOME RAPID DIMINISHMENT OF PRECIP GIVEN LACK OF ECHOES NOW ON 88D
IMAGERY. EXPECT SNOW TO REDEVELOP AGAIN DURING THE EARLY EVENING
HOUR AS RADAR AND OBSERVATIONS SHOW HEAVIER PRECIP OVER WESTERN
COLORADO. WITH CONTINUED STRONG SURFACE GRADIENT SOME GUSTY WINDS
HAVE SURFACED OVER PORTIONS OF THE URBAN CORRIDOR.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 329 PM MST SAT NOV 22 2014

WINDS HAVE BEEN THE DIFFICULT ELEMENT TODAY...AS KBJC WENT
SOUTHWESTERLY...WINDS DIED ABRUPTLY. AFTER CONSISTENT
SOUTHWESTERLY WINDS...KDEN JUST WENT TO NORTHWESTERLY. ALSO THE
HIGH WINDS HAVE NOT BEEN QUITE AS PREVALENT AS EARLIER
THOUGHT...THE BRISK AND GUSTY WEST SOUTH WEST WINDS ARE CONFINED
TO MAINLY THE CONTINENTAL DIVIDE. WE WILL SEE SOME EXPANSION OF
THE WIND FIELD TONIGHT...THEN WINDS WILL TRANSITION TO WESTERLY
AND NORTHWESTERLY BEHIND THE FRONT TONIGHT. EXPECT THE FRONT TO
SWEEP ACROSS NORTHEAST COLORADO BETWEEN 05Z AND 10Z TONIGHT. GUSTY
NORTHWEST WINDS WILL SPREAD ACROSS THE AREA SUNDAY AFTERNOON.

SNOW IS JUST BEGINNING IN ZONE 31 AS LEAD EDGE OF PRECIPITATION
ARRIVES. EXPECT SNOW TO BECOME WIDESPREAD ACROSS THE MOUNTAINS AND
HIGH VALLEYS THIS EVENING AND CONTINUE OVERNIGHT INTO SUNDAY. WE
EXPECT A LULL IN SNOW ACTIVITY SUNDAY MORNING...THEN ANOTHER
TROUGH WILL BRING MORE SNOW TO THE AREA LATER SUNDAY.

ON THE PLAINS...THERE IS A HINT IN THE MODELS THAT SOME MEASURABLE
PRECIPITATION WILL REACH THE GROUND. THE PREVIOUS SHIFT SHOWED
SCATTERED POPS OVER THE PALMER DIVIDE LATE TONIGHT WITH AND BEHIND
THE FRONT. HAVE KEPT THAT AND EXPANDED A SLIGHT CHANCE OF
PRECIPITATION OF THE NORTHEAST PLAINS. ISOLATED SHOWERS ARE
POSSIBLE MAINLY OVER THE PALMER DIVIDE DURING THE DAY SUNDAY.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 329 PM MST SAT NOV 22 2014

WIDESPREAD OROGRAPHIC SNOW WITH STRONG WINDS WILL CONTINUE IN THE
MOUNTAINS SUNDAY INTO MONDAY. THE MOISTURE WILL BE A BIT SHALLOWER
WITH A BREAK IN THE QG LIFT ON SUNDAY...BUT THE STRONGER WINDS MAY
OFFSET THIS. THEN ANOTHER EMBEDDED SHORTWAVE WILL INCREASE THE
LIFT ON MONDAY. WITH ALL THE WIND IT STILL LOOKS APPROPRIATE TO
CARRY THE WARNINGS AND ADVISORIES THROUGH THIS PERIOD THOUGH THE
SNOWFALL MAY BE LIGHTER. MEANWHILE THERE WILL BE STRONG WINDS ON
THE EAST SLOPES...BUT IT LOOKS LIKE ONLY A SMALL HIGH WIND THREAT
THROUGH MONDAY AS THE WINDS WILL BE A RESULT OF MIXING THE STRONG
WINDS IN THE 500-700 MB LAYER DOWNWARD. TAIL END OF THE SUNDAY
SHORTWAVE AND ANOTHER LATE MONDAY WILL BRING A SLIGHT CHANCE OF
LIGHT SHOWERS TO THE PLAINS.

STRONG WARMING AND DRYING ALOFT MONDAY NIGHT INTO TUESDAY MORNING SHOULD
BRING A SIGNIFICANT DECREASE TO THE MOUNTAIN SNOW. IT WILL ALSO
ESTABLISH A GOOD WIND AND TEMPERATURE PROFILE FOR AN AMPLIFIED
MOUNTAIN WAVE. THIS PERIOD LOOKS LIKE A BETTER THREAT FOR HIGH
WINDS ON THE EAST SLOPES OF THE FRONT RANGE AS THERE IS STILL LOTS
OF WIND ALOFT TO WORK WITH. MOISTURE RETURNS IN THE WARMER AIRMASS
DURING THE DAY TUESDAY...SO CLOUDINESS SHOULD INCREASE AGAIN ALONG
WITH SOME LIGHT MOUNTAIN SNOW.

FOR THE LATER PART OF THE FORECAST THERE IS STILL A FAIR AMOUNT OF
UNCERTAINTY. MODELS HAVE SETTLED ON A STRONG WESTERN U.S. RIDGE
WITH A JET AND RESULTING PRECIPITATION NORTH OF COLORADO. HOWEVER
THERE IS STILL A LOT OF DISAGREEMENT ON THE POSITION OF THIS...AND
THE FRONT WILL LIKELY SAG INTO COLORADO AT SOME POINT BUT MAYBE
NOT WITH FULL FORCE. THIS MORNINGS OPERATIONAL GFS AND ECMWF ARE
BOTH ON THE WARM EXTREME OF THE RANGE. HIGH TEMPERATURES FROM
ENSEMBLES FOR THURSDAY RANGE FROM THE 20S TO THE 60S...THOUGH MOST
ARE IN THE MIDDLE TO HIGHER END OF THE RANGE. FOR NOW THE MODEL
CONSENSUS IS AS GOOD AS WE CAN DO...WHICH SHOWS THE FRONT SAGGING
IN DURING THE DAY WITH HIGHS AROUND 40 IN THE NORTHEAST CORNER AND
AROUND 50 IN DENVER. THE RANGE COULD EASILY BE LARGER...SO MUCH
UNCERTAINTY. ODDS OF ANY SIGNIFICANT PRECIPITATION DO LOOK
SMALL...THOUGH THERE COULD BE SOME LIGHT SHOWERS NORTH OF THE
FRONT SO I DID LEAVE SOME LOW POPS IN THE NE CORNER WHERE THIS IS
MOST LIKELY. THE SAME BASIC ISSUES ARE PRESENT FOR FRIDAY AND
SATURDAY...THOUGH THERE WILL LIKELY BE A TREND BACK TOWARD ZONAL
FLOW AND PUSHING OUT ANY COLD AIR THAT DOES COME IN BY THE
WEEKEND. ADDED SOME LOW MOUNTAIN POPS SATURDAY FOR A POSSIBLE
APPROACHING SHORTWAVE IN THE SOUTHERN STREAM.

&&

.AVIATION...(FOR THE TAFS THROUGH 06Z SUNDAY EVENING)
ISSUED AT 923 PM MST SAT NOV 22 2014

BIGGEST CHANGE TO THE FORECAST NEXT 12 HOURS WILL INCLUDE ADDING
SNOWFALL AND POSSIBLE SNOW ACCUMULATION IN THE DENVER AREA FOR
LATE TONIGHT AND EARLY SUNDAY MORNING. A PASSING UPPER TROUGH AND
THE DEVELOPMENT OF MOIST NORTHEASTERLY UPSLOPE A COUPLE HOURS
AFTER THE PASSAGE OF A COLD FRONT AROUND 09Z SHOULD SET OFF
FEW HOURS OF LIGHT TO PERHAPS MODERATE SNOWFALL AT DENVER AREA
TERMINALS. PRIME TIME FOR THIS SNOWFALL IS FROM 09Z TO 15Z/
SUNDAY. KDEN AND KBJC COULD POSSIBLY SEE UP TO AN INCH OF SNOW
ACCUMULATION ON AIRPORT GROUNDS...WHILE KAPA COULD SEE AS MUCH OF
1-2 INCHES OF SNOW BY 15Z. IN ADDITION...LIGHT WEST-NORTHWEST
WINDS AT THE PRESENT TIME SHOULD ABRUPTLY SHIFT TO NORTH-NORTHWEST
AT 20-35KTS WITH FRONTAL PASSAGE AROUND 08Z...THEN A COUPLE HOURS
AFTER THAT SWITCH TO A NORTHEAST WIND AT 9-18KTS. SNOWFALL IS
EXPECTED TO END IN THE DENVER AREA BY 16Z. ANTICIPATE ILS APPROACH
CONDITIONS WITH IFR CIGS/VSBYS DURING THIS 4-5 HOUR PERIOD.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 5 PM MST MONDAY FOR COZ031-033-034.

WINTER WEATHER ADVISORY UNTIL 5 PM MST MONDAY FOR COZ030-032.

&&

$$

UPDATE...BAKER
SHORT TERM...RTG
LONG TERM...GIMMESTAD
AVIATION...BAKER


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