Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 210258
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
858 PM MDT MON APR 20 2015

.UPDATE...
ISSUED AT 858 PM MDT MON APR 20 2015

INSTABILITY IS WANING WITH THE LOSS OF DAYTIME HEATING. ONLY
ISOLATED SHOWERS MAINLY SOUTH OF THE I-70 CORRIDOR WILL BE ENDING
IN THE NEXT HOUR OR TWO ON THE PLAINS AND TOWARD MIDNIGHT IN THE
HIGH COUNTRY AS WEAK SUBSIDENCE TAKES HOLD. SHOULD SEE A FAIR
AMOUNT OF CLEARING PER LATEST SATELLITE IMAGERY AND TRENDS SO WILL
LOWER OVERNIGHT LOW TEMPS A BIT. THIS MAY LEAD TO PATCHY FOG IN
HIGH MOUNTAIN VALLEYS WHERE LOW LEVEL MOISTURE IS TRAPPED AND
T/TD CROSSOVER TEMPS SHOULD BE MET IN THE NEXT FEW HOURS. WILL
KEEP THINGS MAINLY DRY AFTER MIDNIGHT THROUGH TOMORROW
MORNING...AND RESERVE NEXT SHOT OF PRECIP TIL TUESDAY AFTERNOON
WHEN AIRMASS SUFFICIENTLY DESTABILIZES AGAIN.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 400 PM MDT MON APR 20 2015

WEAK VORT LOBE/SHORTWAVE CARRIED ALONG BY MODERATE NORTHWEST FLOW
ALOFT NOW PASSING OVER SOUTH CENTRAL WY. CAN ROUGHLY SEE THIS
FEATURE ON WATER VAPOR SAT IMAGERY. BEGINNING TO SEE LOW TOP
CONVECTION DEVELOPING IN THE VICINITY OF THIS WAVE AS WELL AS OVER
THE FRONT RANGE MTNS/FOOTHILLS. THE FEW CELLS THAT HAVE MANAGED
TO DRIFT OFF THE FRONT RANGE THIS AFTERNOON HAVE QUICKLY
DISSIPATED/GLACIATED IN THE DRIER/MUCH MORE STABLE AIR ON THE
PLAINS. HOWEVER MAY SEE MORE OF THIS HIGH COUNTRY CONVECTION
HOLDING TOGETHER AS THEY DRIFT SEWRD OVER THE NEARBY PLAINS. DO
NOT SEE MUCH QPF IF ANY AT LOWER ELEVATIONS FROM THESE PASSING
SHOWERS. AIRMASS LOOKS TOO INHOSPITABLE FOR SHOWER FORMATION EAST
OF A CHEYENNE-TO-LIMON LINE...EVEN WITH PASSAGE OF THE UPPER AIR
DISTURBANCE. IN THE HIGH COUNTRY...SCATTERED SHOWER INITIATION
WELL UNDERWAY. SHOULD SEE COVERAGE INCREASE A BIT MORE NEXT
COUPLE OF HOURS. RAIN/SNOW LEVEL AT PRESENT TIME AROUND 8000-8500
FT MSL. WITH THE HEAVIER SHOWERS...COULD SEE RAIN/SNOW LINE LOWER
ANOTHER THOUSAND FEET. ANY SNOW ACCUMULATION IN THE MTNS SHOULD BE
MINOR...GENERALLY LESS THAN AN INCH OR TWO. BEST TIME FOR THIS
SHOWER ACTIVITY FROM 22Z THIS AFTERNOON THROUGH 04Z THIS EVENING.
ALTHOUGH ISOLATED HIGH COUNTRY SHOWERS COULD LINGER INTO THE WEE
HOURS OF THE MORNING. OVERNIGHT LOWS ABOUT THE SAME AS LAST NIGHT
WITH UPPER 20S AND 30S ON THE PLAINS...AND TEENS AND 20S IN THE
HIGH COUNTRY.

ON TUESDAY...CWA REMAINS UNDER NORTHWEST FLOW ALOFT WITH A
SHORTWAVE UPPER RIDGE FORMING TO OUR WEST. DAY SHOULD START OUT
DRY...EVEN FOR THE HIGH COUNTRY...AIDED BY DRY N-NWLY LOW-LEVEL
FLOW AT THE SFC. THROUGH THE DAY...MODELS SHOW BOUNDARY LAYER
WINDS ALONG THE FRONT RANGE TURNING ANTICYCLONICALLY INTO THE
FOOTHILLS...BUT REMAINING NWLY ACROSS THE NERN CORNER OF THE CWA.
THIS UPSLOPE FLOW POOLS LOW-LEVEL MOISTURE UP AGAINST THE FRONT
RANGE IN THE AFTERNOON AND WITH DAY TIME HEATING GENERATES SFC
BASED CAPES IN THE 100-400 J/KG RANGE IN AND NEAR THE FOOTHILLS.
THEREFORE WILL GO WITH SCATTERED POPS IN THE FRONT RANGE
MTNS/FTHLS IN THE AFTERNOON AND ISOLATED POPS WITHIN THE I-25
URBAN CORRIDOR. WILL INCLUDE A SLIGHT CHANCE OF THUNDER. FARTHER
OUT ON THE PLAINS...ENVIRONMENT LOOKS TO DRY AND STABLE FOR ANY
SHOWER GROWTH. HIGHS ON TUESDAY 10-12 DEG F WARMER THAN TODAY.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 400 PM MDT MON APR 20 2015

FOR TUESDAY NIGHT...COLORADO REMAINS UNDER NORTHWEST FLOW ALOFT
WITH UPSTREAM RIDGING OVER THE NORTHERN ROCKIES. THERE IS JUST
ENOUGH MOISTURE AND INSTABILITY FOR ISOLATED LATE DAY SHOWERS BUT
MOST OF THIS LOOKS TO REMAIN ANCHORED OVER MOUNTAINS...ADJ PLAINS
AND PALMER DIVIDE. THE RIDGE AXIS ALOFT SHIFTS OVER COLORADO BY
LATE WEDNESDAY...WHILE SURFACE HIGH PRESSURE MOVES INTO THE
CENTRAL PLAINS FOLLOWING A WEAK FRONTAL SURGE TUESDAY EVENING.
THIS WILL RESULT IN A RETURN...SOUTHEAST LOW LEVEL FLOW AND
POTENTIAL FOR DENVER CYCLONE AND CONVERGENCE BOUNDARY SETUP WEDNESDAY
AFTERNOON. SURFACE BASED CAPES DO INCREASE TO 500-1000J/KG OVER
THE URBAN CORRIDOR SO A BIT BETTER CHANCE FOR STRONGER STORMS
DEVELOPING. WILL HAVE SOME HIGHER POPS IN THIS PERIOD.

BIGGER CHANGE APPEARS IN STORE FOR COLORADO ON LATE THURSDAY AND
FRIDAY AS NEXT SYSTEM BEGINS TO MOVE OFF THE SOUTHERN CA COAST
AND MOVES INLAND. THERE ARE SOME TIMING DIFFERENCES AS THE GFS IS
THE MOST PROGRESSIVE AS IT MOVES THE UPPER LOW INTO COLORADO BY
FRIDAY WHILE EUROPEAN SOLUTION STILL HAS THE LOW OVER ARIZONA
EARLY FRIDAY MORNING. THE GEM IS THE MIDDLE OF THE ROAD SOLUTION.
WILL HAVE THE HIGHEST POPS IN THIS LATE THURSDAY AND FRIDAY TIME
PERIOD WITH BEST QG ASCENT AND MOISTURE OVER COLORADO. HAVE
TRENDED POPS UPWARDS A BIT DURING THESE PERIODS.

THE WEEKEND LOOKS TO BE A LITTLE WARMER AND DRIER BUT THERE WILL
BE A WEAKER UPPER LEVEL TROF WHICH MOVES IN BEHIND THE UPPER LOW
LATE SATURDAY/EARLY SUNDAY. STILL A THREAT FOR SHOWERS AND
THUNDERSTORMS EXIST IN THIS SETUP. MORE PRONOUNCED DRYING FOR
MONDAY AND INTO EARLY NEXT WEEK AS THE HIGH PRESSURE RIDGE ALOFT
AMPLIFIES OVER THE GREAT BASIN.

&&

.AVIATION...(FOR THE TAFS THROUGH 06Z WEDNESDAY)
ISSUED AT 858 PM MDT MON APR 20 2015

VFR CONDITIONS WILL PERSIST WITH ONLY SCATTERED MID/UPPER LEVEL
CLOUDS THROUGH 18Z TUESDAY. THEN SHOULD SEE MID LEVEL CLOUD DECK
AROUND 8000-10000 FT AGL DEVELOP WITH CONVECTIVE ENHANCEMENT IN
THE AFTERNOON. ONLY ISOLATED 10 PERCENT COVERAGE SHOWER/THUNDER
POSSIBLE 21Z TUESDAY-03Z WEDNESDAY. LIGHT AND FAIRLY NORMAL
DIURNAL WIND PATTERNS EXPECTED.

&&

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

$$

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


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