Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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000
FXUS65 KBOU 202103
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
303 PM MDT WED AUG 20 2014

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 158 PM MDT WED AUG 20 2014

MIDLEVEL QUASIGEOSTROPHIC SUBSIDENCE /FROM RAP ANALYSES/ AND
STABILITY /ACARS DATA/ IS KIND OF KEEPING CONVECTION AT BAY AS OF
20Z. THERE ARE A FEW ECHOES ON THE RADAR BUT THEY ARE RATHER WEAK
AND SHORT-LIVED AT THIS TIME. THERE IS ALSO A VERY LOCALIZED AREA
OF DOWNSLOPE FLOW OVER BOULDER COUNTY WHICH HAS LOWERED DEWPOINTS
AND GPS-MEASURED PRECIPITABLE WATER VALUES THERE AND PRETTY MUCH
SQUELCHED THE CONVECTION ALTOGETHER. THE HRRR HAS BEEN A BIT
OVERZEALOUS WITH CONVECTION THAT IS SUPPOSED TO BE ONGOING AT THIS
TIME AND INSISTS ON GENERATING QUITE A BIT OF ACTIVITY INTO THE
EVENING HOURS OF THE PLAINS. THE GFS QPF FIELDS SUGGEST THE SAME
THING WITH THE NAM AND ECMWF SEEMING A BIT MORE IN TOUCH WITH
REALITY. IT SEEMS PRUDENT TO HOLD ONTO LOW POPS IN ALL AREAS THIS
EVENING.  TOMORROW DOES NOT APPEAR TO BE MUCH DIFFERENT THAN
TODAY. QUASIGEOSTROPHIC FORECAST DIAGNOSTICS CONTINUE TO FORECAST
SUBSIDENCE AND MODEL SOUNDINGS HAVE THE MIDLEVEL INSTABILITY LIKE
TODAY. CONSEQUENTLY NOT EXPECTING ANY MORE CONVECTION THAT WHAT
IS AROUND TODAY WITH THE PLAINS PERHAPS NOT SEEING ANYTHING.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 158 PM MDT WED AUG 20 2014

PRETTY GOOD MODEL AGREEMENT THROUGH THIS PERIOD...SHORTWAVES LIFT
OUT OF THE MEAN TROUGH OVER THE WEST PASSING OVER COLORADO ON
FRIDAY AND SUNDAY. A BIT MORE DISCREPANCY BY THE MIDDLE OF NEXT
WEEK WITH THE PROSPECTS FOR THE TROUGH SHIFTING EAST...OR JUST
ANOTHER SHORTWAVE MOVING AROUND IT.

FOR THE FRIDAY WAVE...WE WILL BE FIGHTING THE SAME ISSUES WE HAVE
HAD WITH SEVERAL OF THESE MOISTURE SURGES. WARM ADVECTION ALOFT
WILL LIMIT INSTABILITY WHILE THE LOW LEVELS DO NOT MOISTEN
MUCH...AND BY THE TIME THE BEST LIFT ARRIVES THERE IS EVEN A
LITTLE COOLING AT THE SURFACE. STILL EXPECTING INCREASED SHOWER
COVERAGE BUT MAINLY DUE TO LIFT IN THE ELEVATED MOIST LAYER. THIS
CURRENTLY APPEARS TO BE PLAYED WELL WITH SCATTERED SHOWERS AND
STORMS MAINLY FRIDAY AFTERNOON AND EVENING. I DID ADD A BIT MORE
SHOWER ACTIVITY THURSDAY NIGHT AS SOME MODEL RUNS SHOW SOME
CONVECTION MOVING OFF THE SOUTHERN COLORADO MOUNTAINS AND
PERSISTING OVERNIGHT. ALSO SLOWED DOWN THE END OF THE SHOWERS
EARLY SATURDAY IN LINE WITH MODEL TRENDS.

FOR THE WEEKEND...DRIER AIR SHOULD TAKE AWAY THE INSTABILITY SO
EXPECTING FAIRLY QUIET DAYS...STILL A LITTLE DIURNAL CONVECTION
AND SOME LIFT FROM THE SECOND WAVE SUNDAY SHOULD HELP...BUT A
RATHER UNFAVORABLE ENVIRONMENT.

FOR EARLY NEXT WEEK...THERE APPEARS TO BE A WEAK FRONT DROPPING
DOWN THE PLAINS IN THE MONDAY/TUESDAY TIME PERIOD RELATED TO SOME
DEEPENING OF THE UPSTREAM TROUGH. THIS COULD BRING INCREASED LOW
LEVEL MOISTURE...BUT ALSO SOME LOW LEVEL COOLING. SO ONCE AGAIN A
TRADEOFF THAT RESULTS IN SOME INCREASED COVERAGE...BUT NOT
NECESSARILY A LOT OF RAIN. THERE COULD BE AN OPTIMAL TIME ON
TUESDAY OR WEDNESDAY IF THE TROUGH AXIS DOES SHIFT EASTWARD WHERE
THERE IS A COMBINATION OF LIFT AND INSTABILITY. GFS WOULD SUGGEST
DRYING BEHIND THE TROUGH BY WEDNESDAY...WHILE THE ECMWF HOLDING
THE LONGWAVE TROUGH WEST OF US WOULD INDICATE NO COOLING ALOFT.
SO OVERALL MINOR VARIATIONS ON AN ENVIRONMENT WHICH IS ONLY
SLIGHTLY UNSTABLE IN THE AFTERNOONS...BUT IN THE MOIST PERIODS
COULD ALLOW SOME WEAK CONVECTION WHENEVER THERE IS FORCING. BLEND
OF THE MODEL CONSENSUS WITH THE PREVIOUS FORECAST LOOKS GOOD...I
DID RAISE POPS A LITTLE ON TUESDAY AND WEDNESDAY ON THE PLAINS IN
LINE WITH OUR NEIGHBORING OFFICES...WITH GREATER MOISTURE OUT
THERE THAT SEEMS REASONABLE.

&&

.AVIATION...(FOR THE TAFS THROUGH 00Z THURSDAY LATE AFTERNOON)
ISSUED AT 158 PM MDT WED AUG 20 2014

IF PRESENT CONDITIONS CONTINUE IT LOOKS LIKE KAPA WOULD HAVE THE
BEST /ALBEIT SMALL/ CHANCE OF SEEING SOME THUNDER THIS EVENING.
THE 19Z HRRR MODEL IS STILL INSISTING ON CREATING A LOT OF
THUNDERSTORM ACTIVITY WHICH IS LOOKING LESS AND LESS LIKELY AT
THIS POINT. THUS KBJC AND KDEN MAY MAKE IT THROUGH THE EVENING
WITHOUT ANY THUNDER. KBJC SHOULD SEE DOWNSLOPE FLOW/DRAINAGE WINDS
THROUGH TONIGHT WITH SPEEDS IN THE 8-15KT RANGE. KAPA AND KDEN
WILL HAVE LIGHTER WINDS THROUGHOUT THE PERIOD WITH DRAINAGE FLOW
KICKING IN AFTER DARK.

&&

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

&&

$$

SHORT TERM...ET
LONG TERM...GIMMESTAD
AVIATION...ET



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