Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 210208
AFDBOU

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

.UPDATE...
ISSUED AT 808 PM MDT WED AUG 20 2014

ISOLATED TO SCATTERED STORMS HAVE FORMED AND ARE MOVING ACROSS
NORTHEAST COLORADO. EXPECT MOST OF THE CONVECTION TO END BY
MIDNIGHT AS THE AIRMASS STABILIZES. OVER THE FAR NORTHEAST
CORNER...A FEW WEAK SHOWERS AND STORMS WILL BE POSSIBLE INTO THE
EARLY MORNING HOURS. ADJUSTED THE FORECAST TO MATCH UP WITH
CURRENT TRENDS.

&&

.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 06Z THURSDAY EVENING)
ISSUED AT 808 PM MDT WED AUG 20 2014

AN ISOLATED SHOWER OF THUNDERSTORM WILL REMAIN POSSIBLE THROUGH
05Z. WINDS WILL CONTINUE TO VARY DUE TO OUTFLOWS FROM NEAR BY
STORMS. EVENTUALLY WINDS WILL SETTLE AT A NORMAL SOUTHERLY
DIRECTION...LIKELY AROUND 06Z. THERE WILL BE ANOTHER CHANCE FOR
SHORT LIVED THUNDERSTORMS THURSDAY AFTERNOON AND EVENING. OUTFLOWS
FROM THE STORMS WILL LIKELY CAUSE A FEW WIND SHIFTS LATE IN THE
DAY.

&&

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

$$

UPDATE...MEIER
SHORT TERM...ET
LONG TERM...GIMMESTAD
AVIATION...MEIER



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