Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 220933
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
333 AM MDT FRI MAY 22 2015

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 300 AM MDT FRI MAY 22 2015

WATER VAPOR IMAGERY SHOWING UPPER LOW AND BACK EDGE OF TROF
LIFTING NORTH AND NORTHEAST ACROSS FAR SOUTHERN COLORADO WITH BIT
OF SWIRL OVER SOUTHEAST COLORADO. PRECIP HAS SURE TAKEN ITS TIME
GETTING HERE BUT RADAR FINALLY SHOWING AN INCREASE IN LIGHT RAIN
SHOWERS OVER THE PLAINS. APPEARS HEAVIEST RAINFALL WILL BE OVER
THE FAR EASTERN PLAINS AND FURTHER WEST OVER THE WEST SLOPE. GIVEN
THE LOW LEVEL SOUTHEAST FLOW PRECIP HAS WEAKENED SOME AS IT COMES
OFF THE PALMER DIVIDE. THERE WILL BE CONTINUE WEAK QG ASCENT AS
THE TROF MOVES OVER NORTHERN COLORADO THAN WEAK TO NEUTRAL
DECENT BY AFTERNOON. PRECIP RATES WITH THE DEVELOPING SHOWERS HAS
BEEN VERY LIGHT...GENERALLY AROUND .04"/HOUR. OVERALL QPF FROM
MODELS HAS ALSO DECREASED TODAY WITH OVERALL AMOUNTS GENERALLY
AROUND A TENTH TO A HALF INCH ON THE PLAINS...HIGHEST OVER THE FAR
NORTHEAST. SHOWERS GRADUALLY DECREASING FROM SOUTH TO NORTH AFTER
MID MORNING. WILL MAKE SOME ADJUSTMENTS TO CURRENT FORECAST BASED
ON RECENT TRENDS.

WILL KEEP THE WINTER WEATHER ADVISORY FOR THE MOUNTAINS UNTIL 6 AM
AS LOOKS LIKE MOST LOCATIONS OVER SUMMIT AND PARK COUNTY ARE NOW
GETTING LIGHT SNOW. AMOUNTS MAY BE A BIT HIGH SO WILL TAPER DOWN A
BIT THROUGH THIS MORNING.

AS FOR THIS AFTERNOON/EVENING THERE LOOKS TO BE SOME CLEARING AND
HEATING INITIALLY OVER THE PALMER DIVIDE WHICH WOULD HELP THE
INSTABILITY CAUSE FOR THUNDERSTORMS TODAY. SURFACE BASED CAPES
RANGE FROM 700 TO 1000J/KG FROM DENVER SOUTH AND SOUTHEASTWARD
THIS AFTERNOON AND EVENING. WITH SURFACE LOW OVER SOUTHEAST
COLORADO APPEARS SO SORT OF CONVERGENCE BOUNDARY WILL DEVELOP OVER
DOUGLAS AND ELBERT COUNTIES WHERE BOTH RAP/HRRR SEEM TO FOCUS
STORM DEVELOPMENT TODAY. GIVEN CAPE AND SHEAR ALOFT COULD BE A FEW
SEVERE STORMS WITH LARGE HAIL THE MAIN IMPACT. WOULD EXPECT LOWER
POPS AND LESS INSTABILITY FURTHER NORTH AND EAST ON THE PLAINS
WITH LESS HEATING AND INSTABILITY. FORECAST SOUNDINGS INDICATE
STRATUS AND PATCHY FOG AGAIN LATER TONIGHT WITH SHALLOW UPSLOPE
FLOW ON THE PLAINS. STILL COULD BE SOME LINGERING SHOWERS PAST
MIDNIGHT ON THE PLAINS GIVEN CONTINUED WEAK ASCENT FROM THE NEXT
APPROACHING CLOSED LOW.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 300 AM MDT FRI MAY 22 2015

SYNOPTICALLY...A LARGE SCALE BLOCKING PATTERN OVER THE ERN
PACIFIC/WRN CONUS WILL CONTINUE TO DOMINATE OUR WEATHER OVER THE
NEXT SEVERAL DAYS. THE ANOMALOUSLY DEEP UPPER TROUGH WITH ITS
CLOSED LOW SPINNING OVER CNTRL CALIFORNIA AT THE PRESENT TIME IS
STILL FORECAST TO MIGRATE SLOWLY EASTWARD OVER THE NEXT 48 HOURS.
MODEL CONSENSUS PLACES THE 500 MB LOW OVER SRN UTAH BY EARLY
SATURDAY MORNING. FYI...EARLIER GFS RUNS SHOWED THIS TROUGH
OPENING UP AS IT ACCELERATED NORTHEASTWARD ACRS WYOMING DURING THE
DAY SATURDAY. IT NO LONGER INDICATES THAT...AT LEAST NOT UNTIL
SUNDAY.

A DRY SLOT AT MID-LEVELS ROUNDING THE FRONT SIDE OF THE TROUGH
SHOULD ALLOW FOR AT LEAST A FEW HOURS OF STG SOLAR HEATING SAT
MORNING TO QUICKLY DESTABILIZE AN ALREADY MOIST AND MARGINALLY
UNSTABLE BNDRY LAYER EAST OF THE MTNS. AS THE DAY PROGRESSES MOIST
SUBTROPICAL AIR CIRCULATING WITHIN THE TROUGH WILL PARTNER WITH AN
INFLUX OF LOW-LEVEL MOISTURE CARRIED NORTHWARD BY A STRENGTHENING
S-SELY BNDRY LAYER FLOW ON THE PLAINS. THE NAM...GFS...SREF AND
ECMWF ALL SHOW A THETA-E RIDGE SURGING UP OVER WELD AND LOGAN
COUNTIES BY EARLY AFTERNOON. THESE SAME MODELS ALSO SHOW A SFC LOW
FORMING IN THE VICINITY OF MORGAN COUNTY ABOUT MIDDAY AND A SHARP
DEFORMATION AXIS EXTENDING SOUTHWEST FROM THE SFC LOW TO THE
FOOTHILLS IN BOULDER COUNTY...AND EAST ACRS SRN PHILLIPS COUNTY.
AS MOISTURE ACCUMULATES ALONG THIS AXIS...FURTHER DESTABILIZATION
IS ANTICIPATED. NAM SHOWS SFC BASED CAPES ANYWHERE FROM 1900-2700
J/KG AND VIRTUALLY NO CONVECTIVE INHIBITION IN THE VICINITY OF THE
SFC LOW BY 21Z. IN ADDITION...MODELS SHOW NERN COLORADO UNDER THE
RIGHT ENTRANCE REGION OF A DEPARTING 90-100KT JET. ALL THIS SHOULD
RESULT IN A FEW HOURS OF ACTIVE SUPERCELL DEVELOPMENT...ANYWHERE
FROM ERN LARIMER...WELD...MORGAN...NRN WASHINGTON...LOGAN...SEDGWICK
AND PHILLIPS COUNTIES. LARGE HAIL WILL LIKELY BE THE PRINCIPLE
SEVERE WEATHER RISK BUT WITH RESPECTABLE HELICITY VALUES IN THE
VICINITY OF THE SFC LOW...CAN`T RULE OUT A BRIEF WEAK TORNADO OR
TWO. FARTHER SOUTH...SAY IN AND AROUND THE DENVER METRO AREA...
MOISTURE AND INSTABILITY PROFILES APPEAR LESS FAVORABLE FOR DEEP
CONVECTION DUE TO THE DRYING EFFECTS OF A GUSTY SLY WIND
DOWNSLOPING OFF THE PALMER DIVIDE. THOUGH SCATTERED POPS ARE
STILL WARRANTED LATE IN THE DAY. IN THE HIGH COUNTRY...COULD SEE
SCATTERED SHOWERS FORMING OVER THE HIGH RIDGES AS EARLY AS LATE
MORNING BEFORE EXPANDING IN COVERAGE TOGETHER WITH T-STORMS
THROUGH THE AFTERNOON AS THE UPPER TROUGH INCHES CLOSER. RAINFALL
AMOUNTS ARE NOT EXPECTED TO BE ALL THAT SIGNIFICANT DUE IN PART TO
FAST STORM MOTIONS. ANY SNOWFALL SHOULD REMAIN CONFINED TO
ELEVATIONS UP AROUND 11000 FT AT MIDDAY AND LOWERING TO AROUND
10000 FT BY EVENING. SATURDAY TEMPS LIKELY TO BE THE WARMEST
WE`VE SEEN IN A COUPLE WEEKS WITH MID/UPPER 60S AT LOWER
ELEVATIONS AND UPPER 40S/50S IN THE HIGH COUNTRY.

SATURDAY NIGHT AND SUNDAY...AIRMASS IS EXPECTED TO REMAIN RELATIVELY
MOIST AS THE UPPER TROUGH MAKES SLOW EASTWARD PROGRESS ACROSS THE
REGION. ALTHOUGH WIND SHEAR AND INSTABILITY SHOULD BE WEAKER AND
TEMPERATURES COOLER BY A FEW DEGS DUE TO COOLING ALOFT AND GREATER
CLOUD COVER. SO THE THREAT OF SEVERE WEATHER WILL BE MUCH
LOWER...BUT WILL CONTINUE THE FORECAST SCATTERED SHOWERS AND
THUNDERSTORMS. WITH LIGHTER PRECIP AMOUNTS ANTICIPATED...FURTHER
RUNOFF INTO AREA STREAMS AND RIVERS ALREADY RUNNING FAST AND HIGH
SHOULD BE MINOR.

MEMORIAL DAY THROUGH WEDNESDAY WILL FEATURE SHOWERS AND T-STORMS
DURING THE AFTERNOON AND EVENING HOURS THE PRODUCT OF DAYTIME
HEATING AND PLENTY OF RESIDUAL MOISTURE. MODELS ALSO SHOW A SERIES
OF WEAK DISTURBANCES IN WESTERLY FLOW ALOFT PASSING OVER THE AREA.
STILL TOO EARLY TO KNOW WITH ANY CERTAINTY HOW THESE SYSTEMS WILL
INFLUENCE THIS DAILY CYCLE OF CONVECTION. BY THURSDAY...GFS
INDICATES A SHIFT TO DRIER AND WARMER CONDITIONS ACROSS THE
REGION UNDER A RIDGE OF HIGH PRESSURE. WHEREAS THE ECMWF SHOWS YET
ANOTHER SHORTWAVE TROUGH BRINGING CLOUDS...COOLER TEMPS AND
SHOWERY PRECIP TO THE FCST AREA. FOR NOW WON`T STRAY TOO FAR OFF
FROM A BLEND OF THE GUIDANCE. FOR INSTANCE...NOT ALL THAT
CONFIDENT WE`LL SEE UPPER 70S/LOWER 80S AT LOWER ELEVATIONS AS
THE GFS IS INDICATING LATE IN THE PERIOD. WILL KEEP TEMPS NEAR
SEASONAL NORMS FOR NOW.

&&

.AVIATION...(FOR THE TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 300 AM MDT FRI MAY 22 2015

SHOWERS BECOMING A BIT MORE ORGANIZED AND NUMEROUS AS UPPER TROF
APPROACHES TERMINALS. LIGHT RAIN SHOWERS WILL CONTINUE THROUGH MID
MORNING AND THEN A BREAK WITH PARTIAL CLEARING WITH SUBSIDENCE
BEHIND TROF. THE SOUTHEAST LOW LEVEL FLOW HAS ALSO KEPT CEILINGS
FROM GETTING TO LOW SO GENERALLY MVFR AND ILS APPROACHES THROUGH
15Z OR SO. SOME HEATING THIS AFTERNOON WILL LEAD TO SCATTERED
SHOWERS AND THUNDERSTORMS LATER THIS AFTERNOON. BEST CHANCE FOR
STINGER STORMS LOOKS TO BE EAST AND SOUTH OF LOCAL TERMINALS.
COULD BE A RETURN STRATUS NIGHT AGAIN WITH LINGERING LOW LEVEL
MOISTURE AND WEAK EASTERLY FLOW.

&&

.HYDROLOGY...
ISSUED AT 300 AM MDT FRI MAY 22 2015

CURRENT SYSTEM ONLY PRODUCING LIGHT RAIN SHOWERS AND DON`T EXPECT
RAINFALL RATES MUCH ABOVE A TENTH OF AN INCH PER HOUR. THIS WILL
HAVE LITTLE OR MINIMAL EFFECT ON RIVERS AND STREAMS THIS MORNING.
BETTER INSTABILITY WILL RESULT IN SCATTERED THUNDERSTORMS THIS
AFTERNOON AND EVENING. COULD BE SOME BRIEF HEAVY RAIN AND HAIL
WITH STORMS AS PW VALUES ARE AROUND 3/4 OF AN INCH. THIS COULD
RESULT IN LOCALIZED HIGHER STREAM LEVELS AND MINOR FLOODING IN
LOCATIONS UNDER A PASSING STORM.

SOUTH PLATTE RIVER LEVELS STILL INCREASING ACROSS MORGAN COUNTY
AND EXPECT A CONTINUED SLOW RISE IN RIVER LEVELS TODAY WHERE RIVER
LEVELS WILL BE AROUND FLOOD STAGE THIS MORNING AT WELDONA. THE
SOUTH PLATTE RIVER AT KERSEY AND THE CACHE LA POUDRE RIVER AT
GREELEY WILL REMAIN IN FLOOD STAGE TODAY.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 AM MDT EARLY THIS MORNING FOR
COZ034.

&&

$$

SHORT TERM...ENTREKIN
LONG TERM...BAKER
AVIATION...ENTREKIN
HYDROLOGY...ENTREKIN


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