Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 220211
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
811 PM MDT SUN SEP 21 2014

.UPDATE...
ISSUED AT 811 PM MDT SUN SEP 21 2014

MAIN AREA OF RAIN WITH A COUPLE EMBEDDED THUNDERSTORMS WAS
SHIFTING FROM THE SOUTHERN FOOTHILLS RIGHT ACROSS THE DENVER METRO
AREA. THE ISOLATED STORMS HAVE BEEN PRODUCING LOCALLY HEAVY RAIN
IN EXCESS OF 1 INCH DUE TO THE VERY SLOW MOVEMENT...BUT MOST
AREAS OF RAIN HAVE BEEN MUCH LIGHTER WITH AMOUNTS AT OR LESS THAN
A THIRD OF AN INCH. HAVE UPDATED THE LATEST FORECASTS FOR FURTHER
REFINEMENT OF EVENING POPS...HIGHER DENVER METRO AREA AND LOWER
FARTHER NORTH AND EAST. SHORTER RANGE GUIDANCE ALSO SUGGESTING
ANOTHER ROUND OF SHOWERS TOWARD MONDAY MORNING BUT PERSISTENT LIFT
COULD MEAN SHOWERS/ISOLATED STORMS PRETTY MUCH ANY TIME FROM NOW
THROUGH MONDAY.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 301 PM MDT SUN SEP 21 2014

UPPER LEVEL LOW OVER NEVADA WILL SLOWLY MOVE NORTHEAST TONIGHT AND
MONDAY. SCATTERED SHOWERS AND ISOLATED SHOWERS ARE EXPECTED TO
SPREAD FROM THE HIGH COUNTRY ONTO THE FRONT LATE THIS AFTERNOON AND
EARLY THIS EVENING. PRECIPITABLE WATER VALUES ARE AROUND AN INCH
ALONG THE FRONT RANGE. THIS COMBINED WITH SLOW MOVING SHOWERS AND
STORMS COULD PRODUCE LOCALLY HEAVY RAIN...MAINLY OVER THE HIGHER
TERRAIN WHERE THE GREATEST INSTABILITY WILL BE. SHOWERS WILL
DECREASE OVERNIGHT...BUT DUE TO THE MOISTURE AND WEAK QG
LIFT...STILL COULD SEE A FEW SHOWERS. WILL KEEP LOW POPS IN THE
FORECAST THROUGH THE NIGHT AND INTO MONDAY MORNING.

QG LIFT WILL REMAIN OVER COLORADO MONDAY AS THE UPPER LEVEL LOW
MOVES ACROSS WYOMING. CAPES WILL BE UP TO 1000 J/KG AND PRECIPITABLE
WATER VALUES WILL LINGER AROUND AN INCH. THE QG LIFT COMBINED WITH
THE INSTABILITY AND MOISTURE IS EXPECTED TO PRODUCE SCATTERED
SHOWERS AND THUNDERSTORMS MONDAY AFTERNOON. COULD SEE A COUPLE OF
STORMS REACH SEVERE LIMITS...WITH LARGE HAIL AND STRONG WINDS.
TEMPERATURES WILL BE SLIGHTLY WARMER MONDAY WITH HIGHS IN THE MID TO
UPPER 70S.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 301 PM MDT SUN SEP 21 2014

ANOMALOUS HEIGHT FALLS ARE PROGGED OVER THE EASTERN PACIFIC
THROUGH MIDWEEK...RESULTING IN RIDGE BUILDING OVER THE HEART OF
THE COUNTRY. BEFORE THE RIDGE BUILDS OVER COLORADO...THE CLOSED
UPPER LOW SPINNING OVER THE CENTRAL WEST COAST ATTM IS FORECAST TO
OPEN UP AND TRACK EAST-NORTHEASTWARD ACROSS ERN WY BY 00Z/TUESDAY.
QG VERTICAL VELOCITY FIELDS INDICATE WEAK DEEP LAYER ASCENT OVER
ERN COLORADO DURING THE EVENING HOURS ON MONDAY...COINCIDENT WITH
A NORTH-SOUTH BAND OF 750-1500 J/KG OF SFC BASED CAPE ALONG A
RATHER SHARP BNDRY LAYER WIND SHEAR AXIS. NAM...GFS...ECMWF AND
SREF ALL SHOW THIS AXIS OF LIFT AND INSTABILITY SHIFTING SLOWLY
EWRD ACROSS THE NORTHEAST PLAINS DURING THE EVENING HOURS.
SCATTERED POPS ON THE PLAINS AND ISOLATED TO SCATTERED POPS IN THE
HIGH COUNTRY ARE CALLED FOR MONDAY EVENING. ISOLATED STORMS ON THE
FAR NORTHEAST PLAINS MAY PRODUCE BRIEF HEAVY RAIN...GUSTY WINDS
AND POSSIBLY SOME SMALL HAIL. MEANWHILE...THINGS DRY OUT AND
STABILIZE OVER MTNS AND HIGH VALLEYS WITH WEST-NORTHWESTERLY FLOW
IN THE WAKE OF THE TROUGH.

ON TUESDAY...TROUGH CONTINUES TO SLOWLY MOVE AWAY...BUT NOT BEFORE A
BUNDLE OF JET ENERGY...MOISTURE AND MID-LEVEL COLD ADVECTION SWEEPS
DOWN ITS BACK SIDE. ALL THIS SHOULD PRODUCE A FAIR AMOUNT OF CLOUD
COVER AND AT LEAST A FEW SHOWERS/T-STORMS MAINLY EAST OF THE MTNS
DURING THE LATE MORNING AND AFTERNOON HOURS. ANY PRECIP SHOULD BE
LIGHT AND SPOTTY WITH THE BOUNDARY LAYER CONTINUING TO DRY OUT. DO
NOT SEE MUCH IF ANY COOLING AT LOW LEVELS ON TUESDAY WITH MODEL TEMP
GUIDANCE INDICATING LOW/MID 80S ON THE PLAINS AND UPPER 50S TO LOWER
70S IN THE HIGH COUNTRY. FYI...AVERAGE HIGH FOR DENVER IS NOW 76.

WITH THE UPPER RIDGE BUILDING OVER THE ROCKY MTN REGION MIDWEEK...
DRY CONDITIONS SHOULD PREVAIL ACROSS COLORADO AS TEMPERATURES
CONTINUE TO CREEP UP. MODELS SPLIT BETWEEN WEDNESDAY AND THURSDAY AS
BEING THE WARMEST DAY OF THE WEEK. EITHER WAY...WE/RE LOOKING AT
HIGHS IN THE MID TO UPPER 80S AT LOWER ELEVATIONS AND A COMPARABLE
WARMUP FOR THE THE HIGH COUNTRY BOTH DAYS. SHOULD NOT SEE MUCH WIND
BENEATH THE UPPER RIDGE TO BLOW AWAY THE BEAUTIFUL AUTUMN FOLIAGE IN
THE HIGH COUNTRY.

BY FRIDAY AND SATURDAY...MEDIUM RANGE MODELS SHOW THE 589 UPPER
RIDGE MOVING OVER THE GREAT LAKES AND UPPER MISSISSIPPI RIVER VALLEY
AS A HIGH AMPLITUDE LONGWAVE TROUGH PLOWS INTO THE WEST COAST. DEEP
SOUTHWESTERLY FLOW AHEAD OF THE TROUGH IS FORECAST TO ADVECT MOIST
SUBTROPICAL AIR UP OVER DESERT SOUTHWEST THURSDAY NIGHT INTO
FRIDAY...AND EVENTUALLY UP OVER COLORADO LATE FRIDAY THROUGH
SATURDAY. MODELS ALSO SHOW A WEAK WAVE ACCOMPANYING THIS NORTHWARD
SURGE OF MOISTURE. ASSUMING THIS HOLDS TRUE...SHOULD SEE PRECIP
CHANCES INCREASING DURING THE WEEKEND WITH THE APPROACHING UPPER
TROUGH. HOWEVER A SWLY 700-400 MB FLOW WOULD FAVOR HIGHER PRECIP
CHANCES WEST OF THE CONTINENTAL DIVIDE DURING THIS PERIOD. UNTIL
WE GET A BETTER HANDLE ON THIS NEXT PACIFIC STORM SYSTEM...WILL
GO WITH A CHANCE OF PRECIP IN THE HIGH COUNTRY AND A SLIGHT
CHANCE OF SHOWERS/T-STORMS EAST OF THE DIVIDE LATE FRIDAY THROUGH
SUNDAY.

&&

.AVIATION...(FOR THE TAFS THROUGH 06Z MONDAY EVENING)
ISSUED AT 811 PM MDT SUN SEP 21 2014

MAIN BATCH OF SHOWERS/ISOLATED STORMS WILL CONTINUE TO AFFECT THE
FRONT RANGE AIRPORTS FROM NOW THROUGH 05Z-06Z BEFORE GRADUALLY
DISSIPATING. HOWEVER...COULD SEE MORE SHOWERS REDEVELOP INTO
MONDAY MORNING WITH WEAK AND PERSISTENT LIFT IN MOIST/SLIGHTLY
UNSTABLE AIRMASS. MOSTLY VFR CONDITIONS EXPECTED BUT CANT TOTALLY
RULE OUT LOWER CEILINGS DEVELOPING IN AREAS OF MORE PERSISTENT
SHOWERS AND WITH DENVER CYCLONE AROUND. THE DENVER CYCLONE WILL
ALSO MAKE WIND FORECAST CHALLENGING OVERNIGHT INTO MONDAY...BUT
SHOULD EVENTUALLY TURN MORE SOUTHERLY AT KDEN AND KAPA.

&&

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

$$

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


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