Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 271519
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
919 AM MDT WED AUG 27 2014

.UPDATE...
ISSUED AT 919 AM MDT WED AUG 27 2014

SHOWERS WILL CONTINUE TO LIFT NORTH ACROSS LARIMER AND BOULDER
COUNTIES THIS MORNING AS A WAVE SLOWLY MOVES NORTHEAST INTO WYOMING.
WATER VAPOR IMAGERY SHOWING SOME DRIER JUST UPSTREAM AND WILL MOVE
OVER THE AREA LATE THIS MORNING AND INTO THIS AFTERNOON. THIS MID
AND UPPER LEVEL DRYING IS EXPECTED TO PRODUCE SOME PARTIAL CLEARING.
SEEING AN AREA OF LIFT OVER THE FOUR CORNERS ASSOCIATED WITH A JET.
THIS IS EXPECTED TO MOVE OVER THE AREA LATER TODAY AND HELP TRIGGER
THUNDERSTORMS.

THE PARTIAL CLEARING WILL HELP TEMPERATURES CLIMB INTO THE 70S.
DEPENDING ON HOW HIGH TEMPERATURES GET...CAPES MAY REACH AS HIGH AS
1500 J/KG OVER THE EASTERN PLAINS. SHEAR WILL BE A LITTLE BETTER
TODAY...SO THE THREAT FOR A FEW SEVERE STORMS IS A LITTLE HIGHER.
BEST CHANCE WILL BE OVER THE EASTERN PLAINS WHERE THE BEST
INSTABILITY AND MOISTURE WILL RESIDE. HAIL TO AROUND ONE INCH IN
DIAMETER AND WIND GUSTS TO 60 MPH WILL BE POSSIBLE. MODELS ARE
SHOWING CONVERGE ALONG AN INVERTED TROUGH OVER THE EASTERN PLAINS.
THIS MAY HELP TRIGGER STORMS. ALSO COULD SEE A BRIEF TORNADO OR TWO
WITH THE STORMS ALONG THIS AREA OF CONVERGENCE.

WILL UPDATED THE FORECAST TO MATCH UP TO THE CURRENT TRENDS. WILL
ALSO MENTION THE THREAT OF SEVERE WEATHER IN THE HWO.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 335 AM MDT WED AUG 27 2014

THE UPPER LOW IS NOW IN WESTERN UTAH WITH SHORTWAVE TROUGHS
ROTATING AROUND IT. THERE IS ONE SHORTWAVE FROM NORTHWEST COLORADO
TO SOUTH CENTRAL COLORADO THAT IS ROTATING NORTHWARD. A LINE OF
SHOWERS AHEAD OF THAT TROUGH ARE POISED TO MOVE BACK ACROSS OUR
HIGH COUNTRY. ANOTHER WEAK TROUGH APPEARED ON SATELLITE TO BE
LIFTING NORTH ACROSS EASTERN COLORADO...AND WEAK SHOWERS OVER
NORTHEAST COLORADO ARE SLOWLY LIFTING NORTHWARD.

AS THE UPPER LOW MOVES EAST...FLOW ALOFT IS FORECAST TO CHANGE
FROM SOUTHERLY TO SOUTHWESTERLY OR EVEN WEST SOUTHWESTERLY. THIS
WILL RESULT IN DOWNSLOPE FLOW THIS MORNING WITH DRYER CONDITIONS.
DIV Q MAPS SHOW GOOD LIFT OVER NORTHERN COLORADO THIS
AFTERNOON...BUT GOOD SUBSIDENCE OVER SOUTHERN COLORADO.

WE EXPECT A RELATIVELY DRY MORNING ON THE PLAINS...WITH SHOWERS IN
THE MOUNTAINS. THIS AFTERNOON THUNDERSTORMS WILL SPREAD TO THE
PLAINS...FIRST ALONG THE WYOMING BORDER...THEN OVER MOST OF
EASTERN COLORADO BY EVENING.

TEMPERATURES WILL BE COOL AGAIN TODAY...NO CHANGES TO GOING
FORECAST FOR TEMPERATURES.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 335 AM MDT WED AUG 27 2014

UPPER-LEVEL SHORTWAVE TROUGH CONTINUES ITS SLOW EASTWARD
PROGRESS ACROSS COLORADO DURING THE DAY THURSDAY. NAM...ECMWF...
GFS AND UKMET ALL SHOW THE 700-500MB TROUGH AXIS LINING UP WITH
THE CONTINENTAL DIVIDE AROUND 12Z/THU...MEANING EASTERN COLORADO
STILL UNDER THE INFLUENCE OF A RELATIVELY WARM AND MOIST SOUTHWEST
FLOW ALOFT. ALTHOUGH THE MONSOON MOISTURE PLUME APPEARS TO HAVE
SHIFTED EAST OF THE STATE BY THEN. MEANWHILE...MODELS SHOW LOW-
LEVEL CYCLOGENESIS IN WRN NEBRASKA SPREADING DRIER BOUNDARY LAYER
AIR DOWN FROM WYOMING. BY LATE MORNING...FLOW ALOFT ALSO BECOMES
NWLY WITH PASSAGE OF THE 500MB TROUGH AXIS. THIS CAUSES TEMPERATURES
TO LEVEL OUT OR EVEN FALL A FEW DEGS PRIOR TO THE NOON HOUR.
MODELS SHOW PRECIP COVERAGE EXPANDING OVER THE NORTH-CENTRAL MTNS
DURING THE MORNING HOURS WITH INCREASING NORTH-NORTHWESTERLY FLOW
AND COLD AIR ADVECTION ON THE BACK SIDE OF THE TROUGH. NAM AND GFS
INDICATE 6-HR PRECIP AMTS IN THE NORTHERN MTNS IN THE TWO TO THREE
TENTHS OF AN INCH RANGE DURING THE MORNING...WITH ANOTHER COUPLE
TENTHS OF AN INCH DURING THE AFTERNOON. A COUPLE MODELS EVEN SHOW
SOME LIGHT SNOW ACCUMULATION ROUGHLY ABOVE TIMBERLINE BEFORE
MIDDAY. MODELS SHOW RAIN SHOWERS MOVING OFF THE FRONT RANGE AND
OVER THE NEARBY PLAINS DURING THE MORNING HOURS AND FARTHER OUT
OVER THE PLAINS LATER IN THE DAY. PRECIP AMOUNTS EXPECTED TO BE ON
THE LIGHT SIDE AT LOWER ELEVATIONS WITH THE BOUNDARY LAYER DRYING
OUT. DURING THE AFTERNOON...DEVELOPMENT OF GUSTY DOWNSLOPE WINDS
ALONG THE FRONT RANGE SHOULD HELP DRIVE TEMPERATURES UP AND RH
VALUES DOWN...BUT HIGH TEMPS STILL SEVERAL DEGS C BELOW AVERAGE
FOR THE DATE.

BY THURSDAY EVENING THE LAST OF THESE SHOWERS AND WEAK T-STORMS
SHOULD EXIT EASTERN PARTS OF THE FCST AREA AS DRY AND STABLE AIR
CONTINUES TO FEED IN FROM THE NORTHWEST. ON FRIDAY...WARMER
TEMPERATURES RETURN WITH STABLE NORTHWEST FLOW IN ADVANCE OF AN
UPPER-LEVEL RIDGE BUILDING OVER THE GREAT BASIN. LOOKING FOR
TEMPERATURES TO RETURN IN THE LOWER 80S ON THE PLAINS AND BACK TO
THE 60S AND LOWER 70S IN THE HIGH COUNTRY. LATE DAY HEATING AND
LINGERING MOISTURE MAY BE SUFFICIENT TO FUEL A FEW HIGH COUNTRY
THUNDERSHOWERS...WHILE LOWER ELEVATIONS SHOULD REMAIN DRY.

OVER THE LABOR DAY WEEKEND...AN 80-100KT PACIFIC JET MOVING ONSHORE
IN THE PACIFIC NORTHWEST CARVES OUT A BROAD UPPER TROUGH OVER THE
NORTHWEST CONUS RESULTING IN MODERATE ZONAL FLOW ALOFT OVER
COLORADO. THE COMBINED EFFECTS OF COOLING ALOFT AND STRONG SOLAR
HEATING AHEAD OF THIS TROUGH ARE EXPECTED TO PRODUCE ISOLATED TO
WIDELY SCATTERED T-STORMS IN THE HIGH COUNTRY DURING THE AFTERNOON.
OTHERWISE DRY AND WARM CONDITIONS WILL PREVAIL AT LOWER ELEVATIONS.
FOR SUNDAY...MODELS SHOW A WEAK UPPER AIR DISTURBANCE AND A BATCH OF
MOISTURE ROUNDING THE BOTTOM OF THIS TROUGH. WITH THEIR PASSAGE
COULD SEE ANOTHER ROUND OF ISOLATED TO WIDELY SHOWERS AND T-STORMS
IN THE MTNS AND HIGH VALLEYS. ONE OR TWO LATE DAY STORMS MAY ALSO
MOVE OUT ONTO THE PLAINS...MAINLY UP ALONG THE WYOMING BORDER AS A
SFC COLD FRONT DROPS DOWN FROM WYOMING. THE BOUNDARY LAYER LOOK DRY.
SO THE CHANCE FOR MEASURABLE SHOULD REMAIN LOW AT LOWER ELEVATIONS.
GUSTY OUTFLOW WINDS MORE LIKELY THAN RAINFALL.

FOR LABOR DAY...PLAINS AIRMASS COOLS A FEW DEGS AND BECOMES MORE
HUMID WITH UPSLOPE POST-FRONTAL FLOW. AIRMASS LOOKS STRONGLY
CAPPED EAST OF THE MTNS WITH COOLER AIR IN PLACE. HOWEVER UPSLOPE
FLOW AND DAYTIME HEATING SHOULD BE ADEQUATE TO WARRANT MENTIONING
AT LEAST A SLIGHT CHANCE OF T-STORMS IN THE FRONT RANGE MTNS AND
FOOTHILLS. MODEL GUIDANCE INDICATES A 3-4C DROP IN TEMPERATURES
FROM THE DAY BEFORE...MAINLY EAST OF THE MTNS. LASTLY...TUESDAY
LOOKS SLIGHTLY COOLER WITH REINFORCEMENT OF UPSLOPE FLOW EAST OF
THE MTNS AS THE UPPER TROUGH PASSES TO OUR NORTH. HOWEVER PRECIP
CHANCES SHOULD REMAIN LOW.

&&

.AVIATION...(FOR THE TAFS THROUGH 18Z THURSDAY MORNING)
ISSUED AT 919 AM MDT WED AUG 27 2014

LIGHT WINDS WILL TURN NORTHERLY BY 1700Z IN THE DENVER AREA. SOME
DRIER AIR WILL RESULT IN PARTIAL CLEAR LATE THIS MORNING AND
AFTERNOON. THERE WILL BE A GOOD CHANCE FOR THUNDERSTORMS THIS
AFTERNOON AND EVENING WITH THE BEST TIME BEING 22Z TO 02Z.
HAIL...GUSTY WINDS AND HEAVY RAIN WILL ACCOMPANY THE STRONGER
STORMS. SHOWERS AND STORMS EXPECTED TO END BY 06Z. THERE WILL BE A
SLIGHT CHANCE FOR LOW CLOUDS LATE NIGHT AND EARLY THURSDAY
MORNING.

&&

.HYDROLOGY...
ISSUED AT 919 AM MDT WED AUG 27 2014

SCATTERED TO NUMEROUS STORMS ARE EXPECTED TO MOVE ACROSS THE AREA
THIS AFTERNOON AND EVENING. SOME THUNDERSTORMS WILL PRODUCE HEAVY
RAIN DUE TO GOOD INSTABILITY AND MOISTURE. STORMS ARE EXPECTED TO
PROGRESS NORTH AND EAST THROUGH THE LATE AFTERNOON AND EVENING.
THERE WILL BE A SLIGHT RISK FOR FLASH FLOODING WITH THE STRONGEST
STORMS. STORMS ARE EXPECTED PROGRESS ACROSS THE REGION AND NOT
REMAIN OVER THE SAME AREAS. DO NOT ANTICIPATE ON ISSUING A FLASH
FLOOD WATCH TODAY DUE TO THE STORM MOVEMENT AND SHORT DURATION OF
HEAVY RAIN.

&&

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

$$

UPDATE...MEIER
SHORT TERM...RTG
LONG TERM...BAKER
AVIATION...MEIER
HYDROLOGY...MEIER


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