Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 201604
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1004 AM MDT WED MAY 20 2015

.UPDATE...
ISSUED AT 1004 AM MDT WED MAY 20 2015

MOST DRIZZLE HAS ENDED ACROSS THE AREA WITH LOW CLOUDS STARTING TO
RAISE A LITTLE. TEMPERATURES ARE SLIGHTLY COOLER THAN FORECAST AT
THIS TIME...UPDATED HOURLY TEMP FORECASTS TO ACCOUNT FOR THIS.
WITH SOME BREAKS IN THE CLOUDS EXPECTED...WILL NOT ADJUST MAX
TEMPS FOR TODAY JUST YET...BUT MAY NEED TO BE LOWERED.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 258 AM MDT WED MAY 20 2015

A MOIST EASTERLY FLOW AROUND A SURFACE HIGH OVER THE NORTHERN
PLAINS WILL CONTINUE TO BRING LOW CLOUDS...DRIZZLE AND PATCHY FOG
THROUGH MID MORNING. FOG AND DRIZZLE WILL END AND CLOUDS WILL LIFT
DUE TO SURFACE HEATING. THE EASTERLY FLOW WILL LINGER THROUGH THE
DAY AND MAKE IT DIFFICULT FOR THE CLOUDS TO BURN OFF. WILL KEEP
MOSTLY CLOUDY SKIES IN THE FORECAST THROUGH THE DAY. THIS WILL
KEEP TEMPERATURES COOL WITH HIGHS STRUGGLING TO REACH 50 DEGREES.

AIRMASS OVER THE MOUNTAINS BECOMES SLIGHTLY UNSTABLE. CAPES STAY
BELOW 500 J/KG. WEAK UP SLOPE FLOW ALONG WITH BEING UNDER THE
FAVORABLE PART OF THE JET COULD TRIGGER A FEW SHOWERS OR
THUNDERSTORMS ALONG WITH THE INSTABILITY OVER THE MOUNTAINS.
APPEARS THE LOWER ELEVATIONS WILL BE TOO STABLE FOR STORMS SO
WILL KEEP THE MENTION OF THUNDERSTORMS CONFINED TO THE HIGHER
TERRAIN AND PALMER DIVIDE FOR THIS AFTERNOON AND EVENING. RAINFALL
WILL BE ON THE LIGHT SIDE WITH MOST LOCATIONS RECEIVING LESS THAN
A TENTH INCH. MOST MODELS INDICATING THE BEST CHANCE FOR
PRECIPITATION BEING THIS EVENING OVER THE SOUTHERN
FOOTHILLS...PALMER DIVIDE AND PARK COUNTY.


.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 258 AM MDT WED MAY 20 2015

AN ANOMALOUSLY DEEP LONGWAVE TROUGH OVER THE WEST COAST IS
PROGGED TO SLOWLY MOVE INLAND ACROSS THE GREAT BASIN AND DESERT
SOUTHWEST DURING THE NEXT FEW DAYS. AND AS THE UPPER TROUGH
MIGRATES EAST...UNUSUALLY STRONG PACIFIC AND SUBTROPICAL JETS FOR
THIS TIME OF YEAR CONVERGING NEAR THE BOTTOM OF THIS TROUGH WILL
CONTINUE TO TRANSPORT MOIST SUBTROPICAL AIR UP OVER THE SWRN U.S..
THE 00Z MODEL RUN SHOWS A MID-LEVEL SHORTWAVE TROUGH/VORT LOBE
RACING UP THE FRONT SIDE OF THE MAIN TROUGH OVER ARIZONA LATE
WEDNESDAY NIGHT AND REACHING NORTHEAST COLORADO BY THURSDAY NIGHT.
NAM...GFS...ECMWF...CANADIAN MODELS ALL INDICATE AN INFLUX OF
LOW-LEVEL MOISTURE EAST OF THE MTNS WITH 10-20KT SELY FLOW DURING
THE DAY THURSDAY IN ADVANCE OF THE UPPER AIR DISTURBANCE. THE
ECMWF SHOWS A SFC LOW AND AN ASSOCIATED VORTICITY CONVERGENCE
BOUNDARY FORMING JUST EAST-SOUTHEAST OF THE DENVER METRO AREA
LATE THURSDAY AFTERNOON AS THE TAIL END OF AN 80KT JET PASSES
OVERHEAD. NAM SHOWS SFC BASED CAPES IN THE 200-500 J/KG RANGE IN
THE VICINITY OF THIS FEATURE. HOWEVER WITH INCREASING CLOUD COVER
THROUGH THE DAY...T-STORM CHANCES ON THE PLAINS SHOULD BE LOW.
MORE LIKE SCATTERED RAIN SHOWERS BY MID TO LATE AFTERNOON. WHEREAS
IN THE HIGH COUNTRY...STEEPER LAPSE RATES...INCREASING MOISTURE
AND LIFT GENERATED BY THE APPROACHING SHORTWAVE SHOULD RESULT IN
SCATTERED SHOWERS AND T-STORMS AS EARLY AS MID-AFTERNOON. MODELS
SHOW THE AMBIENT AIRMASS CONTINUING TO MOISTEN THURSDAY NIGHT
ESPLY EAST OF THE CONTINENTAL DIVIDE. HOWEVER...MODELS DO NOT
INDICATE AS MUCH UPSLOPE FLOW OR THETA-E AS WERE PRESENT DURING
THE HEAVY PRECIP EVENT OBSERVED THIS PAST MONDAY NIGHT AND
TUESDAY. 12-HOUR FCST QPF AMOUNTS VARY QUITE A BIT FROM MODEL TO
MODEL...ANYWHERE FROM A COUPLE TENTHS OF AN INCH TO 0.90 INCH ON
THE PLAINS...AND IN THE HIGH COUNTRY FROM A FEW TENTHS OF AN INCH
TO AROUND 1.40 INCHES OVERNIGHT. WETBULB ZERO REMAINS RELATIVELY
HIGH WITH THIS SYSTEM...ROUGHLY UP AROUND 9500-10,000 FT ASL. SO
ANY NEW SNOW ACCUMULATION SHOULD REMAIN CONFINED TO THE HIGHER MTN
SLOPES AND PASSES WHERE ANYWHERE FROM 2-5 INCHES OF WET SNOW COULD
PILE UP BY FRIDAY MORNING.

ON FRIDAY...THIS WEATHER DISTURBANCE LIFTS OUT ALLOWING FOR MORE
SUNSHINE AND A 2-3 DEG C WARM-UP WITH A SOUTH-SOUTHWESTERLY FLOW IN
PLACE. WHILE THE OVERALL AIRMASS APPEARS DRIER ON FRIDAY...DAYTIME
HEATING AND WET SOIL CONDITIONS SHOULD HAVE LITTLE PROBLEM SUPPORTING
ISOLATED TO SCATTERED SHOWERS/T-STORMS BY MID TO LATE AFTERNOON
OVER THE MTNS AND ADJACENT PLAINS. ADDITIONAL RAIN AMOUNTS THIS GO
ROUND SHOULD BE ON THE LIGHT SIDE.

FRIDAY NIGHT-SATURDAY...THE MAIN UPPER TROUGH CONTINUES ITS INLAND
MARCH...BUT MODELS DIFFER REGARDING THE SPEED AND DIRECTION OF THE
TROUGH AND 500 MB LOW. THE GFS WEAKENS THE TROUGH AND QUICKLY LIFTS
ITS NORTHEASTWARD ACROSS THE NRN ROCKIES ON SATURDAY WHICH PLACES
NORTHEAST COLORADO UNDER A RELATIVELY DRY SOUTHWEST FLOW ALOFT AND
A DRIER DOWNSLOPE FLOW OFF THE FRONT RANGE. THE ECMWF SHOWS THE
TROUGH WITH ITS CLOSED LOW TAKING A MORE EASTERLY PATH ACROSS
UTAH ON SATURDAY AND THEN OPENING IT UP AS IT PASSES OVER COLORADO
ON SUNDAY. THE CANADIAN MODEL DRIVES THE UPPER TROUGH AND 500 MB
LOW SOUTHEASTWARD OVER THE LOWER DESERTS WHERE THE UPPER LOW
WOBBLES AROUND THROUGH SUNDAY BEFORE TRACKING EAST AND STAYING
WELL SOUTH OF COLORADO ON MONDAY. THAT SAID...AIRMASS OVER NERN
COLORADO APPEARS TO REMAIN RELATIVELY MOIST AND UNSTABLE SATURDAY
THROUGH MONDAY...ENOUGH TO WARRANT MENTIONING A CHANCE OF SHOWERS
AND A SLIGHT CHANCE OF T- STORMS EACH DAY. TUESDAY LOOKS DRIER AND
SLIGHTLY WARMER...ALTHOUGH THE GFS SHOWS ANOTHER WEATHER
DISTURBANCE SWINGING ACROSS WYOMING AND NORTHERN COLORADO BRINGING
ANOTHER ROUND OF LATE DAY SHOWERS AND T-STORMS FOR PORTIONS OF THE
FORECAST AREA.

&&

.AVIATION...(FOR THE TAFS THROUGH 18Z THURSDAY MORNING)
ISSUED AT 1004 AM MDT WED MAY 20 2015

LOW CLOUDS AND FOG HAVE BEEN SLOWLY RISING...WITH FOG ONLY
AFFECTING AIRPORTS OVER THE SOUTHERN METRO AREAS. EXPECT CEILINGS
TO RISE TO 2000 TO 4000 FEET AFTER 18Z. A WEAK SYSTEM WILL BRING
SCATTERED SHOWERS LATE THIS AFTERNOON AND TONIGHT. CEILINGS WILL
LOWER TONIGHT INTO THE 500 TO 2000 FOOT RANGE. WINDS WILL BE EAST
TO NORTHEAST TODAY AND TURN SOUTHEASTERLY TONIGHT.

&&

.HYDROLOGY...
ISSUED AT 258 AM MDT WED MAY 20 2015

ADDITIONAL RAINFALL TODAY AND TONIGHT WILL BE LIGHT AND IS NOT
EXPECTED TO CAUSE ANY ADDITIONAL FLOODING ISSUES. THE CACHE LA
POUDRE AT GREELEY AND THE SOUTH PLATTE RIVER FROM KERSEY TO
WELDONA ARE EXPECTED TO JUST REACH FLOOD STAGE. A FLOOD WARNING
REMAINS IN EFFECT FOR THIS. RIVER LEVELS ARE EXPECTED TO BE LESS
THAN THE WHAT OCCURRED LAST WEEK.

&&

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

$$

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



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