Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 240959
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
359 AM MDT SUN MAY 24 2015

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 327 AM MDT SUN MAY 24 2015

WATER VAPOR IMAGERY SHOWING CLOSED UPPER LOW OVER WEST CENTRAL
COLORADO MOVING EVER SO SLOWLY TO THE EAST. MODELS FORECAST THE
LOW TO SLOWLY MOVE EAST AND NORTHEAST INTO EASTERN COLORADO
TONIGHT WITH MODERATE SOUTHERLY FLOW ACROSS THE FAR EASTERN
PLAINS. MAIN CONCERN TODAY WILL BE POTENTIAL FLASH FLOODING AGAIN
ON THE EASTERN PLAINS. CONTINUED SOUTHEAST LOW LEVEL FLOW WITH
SURFACE DEWPOINTS IN THE UPPER 40S AND LOWER 50S OVER FAR EASTERN
PLAINS. STORM MOTIONS EXPECTED TO BE SLOWER TODAY AND POTENTIAL
FOR ECHO TRAINING. GIVEN THE FLOODING OCCURRING IN PORTIONS OF
LOGAN COUNTY AND SIGNIFICANT RAINFALL...EXPECT MORE FLOODING
PROBLEMS AGAIN THIS AFTERNOON AND SUNDAY EVENING. SEVERE WEATHER
THREAT A BIT LOWER TODAY BUT STILL POTENTIAL FOR HAIL/HEAVY RAIN
WITH UPWARDS OF 1000J/KG OVER THE PLAINS WITH 50 DEWPOINTS. HAVE
OPTED TO GO FOR A FLASH FLOOD WATCH OVER THE FAR NORTHEAST PLAINS
THIS AFTERNOON AND TONIGHT. FURTHER WEST...AIRMASS IS SLIGHTLY
DRIER WITH DEWPOINTS MAINLY LOWER 40S. SEE HYDRO DISCUSSION BELOW
FOR MORE.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 327 AM MDT SUN MAY 24 2015

AXIS OF THE UPPER TROUGH IS FORECAST TO PASS OVER ERN COLORADO
MONDAY MORNING WITH THE 500 MB LOW CENTER OVER SERN WYOMING. MODELS
SHOW THE TROUGH OPENING UP AS IT SWINGS EAST-NORTHEASTWARD OVER THE
NORTH-CENTRAL GREAT PLAINS DURING THE DAY. FLOW ALOFT OVER THE
FORECAST AREA STILL REMAINS MOIST AND MARGINALLY UNSTABLE AT MID-
LEVELS FOR MUCH OF MONDAY. MEANWHILE AT THE SURFACE...MODELS SHOW A
WEAK COLD FRONT TRAILING FROM A SFC LOW SOMEWHERE OUT NEAR THE NERN
CORNER OF THE STATE EARLY MONDAY MORNING. THIS FRONT IS FCST TO
QUICKLY SWEEP SOUTH ACRS THE PLAINS IN THE DURING THE MORNING HRS.
BY AFTERNOON MODELS SHOW THE NLY LOW-LEVEL FLOW BEHIND THIS FRONT
TURNING INTO THE FRONT RANGE WHICH PROVIDES ADDITIONAL LIFT TO
GENERATE CLOUD COVER OVER THE AREA. ALTHOUGH MODELS DO NOT INDICATE
MUCH IN THE WAY OF QPF WITH THIS CLOUD DEVELOPMENT...MAINLY LIGHT
RAINFALL FROM LOW TOP CONVECTION OVER AND ALONG THE FRONT RANGE MTNS
DURING THE AFTERNOON. IN THE HIGH COUNTRY...SHOULD SEE SHOWERS AND
POSSIBLY A T-STORM OR TWO LINGERING THROUGHOUT THE DAY WITH THE SNOW
LEVEL LOWERING TO AROUND 9500 FT BY MID-AFTERNOON. MAY EVEN SEE AN
INCH OR TWO OF NEW SNOWFALL ON THE HIGH PASSES BEFORE SHOWERS TAPER
OFF IN THE EVENING AS DRIER AIR FILTERS IN FROM THE NORTHWEST.
TEMPERATURES ON MONDAY WILL REMAIN SEVERAL DEGREES BELOW AVERAGE
WITH 60S ON THE PLAINS AND UPR 40S/50S ACROSS THE HIGH COUNTRY.

AS THE UPPER TROUGH MOVES FARTHER AWAY FROM COLORADO...SHOULD SEE
THE PLAINS AIRMASS CONTINUE TO DRY AND WARM ON TUESDAY WITH THE
BNDRY LAYER FLOW DOWNSLOPING OFF THE FRONT RANGE AND CHEYENNE RIDGE.
THE HIGH COUNTRY WILL BE SLOWER TO DRY OUT AND WARM UP WITH A
CONTINUATION OF NWLY MID-LEVEL FLOW. SHOULD SEE LESS CLOUD COVER AND
NOTABLY LESS SHOWER ACTIVITY ON TUESDAY AS UP UPPER RIDGE BUILDS IN
FROM THE GREAT BASIN. EXPECT TO SEE A 2-4 DEG F RISE IN MAX TEMPS
WITH THE INCREASE IN SUNSHINE. MODELS SHOW THE UPPER RIDGE MOVING
EAST OF THE STATE AND THE FLOW ALOFT BECOMING SWLY ON WEDNESDAY AND
A WARMING SLY LOW-LEVEL FLOW ON THE PLAINS. WEDNESDAY APPEARS WARMER
THAN THE DAY BEFORE. HOWEVER MODELS SHOW A WEAK SHORTWAVE TROUGH
CARRIED ALONG BY SWLY FLOW ALOFT PASSING OVER THE FCST AREA BY THE
AFTERNOON WHICH MAY INCREASE IN THE LIKELIHOOD FOR SHOWERS AND T-
STORMS...PARTICULARLY OVER HIGHER ELEVATIONS AND ALONG THE WYOMING
BORDER. SEVERE WEATHER RISK APPEARS LOW...BUT CAN`T RULE A STRAY
HAIL AND/OR HIGH WIND T-STORM OR TWO MOVING NEWRD OFF THE FRONT
RANGE MID TO LATE AFTERNOON. COULD SEE CONVECTION LINGERING WELL
INTO THE EVENING AS ATMOSPHERIC MOISTURE AND MID-LEVEL INSTABILITY
GRADUALLY INCREASE IN ADVANCE OF THE NEXT UPPER TROUGH CARVING OUT
OVER THE EASTERN GREAT BASIN.

ON THURSDAY...MODELS SHOW THIS NEXT UPPER TROUGH DEEPENING SOME AS
IT CHUGS ACROSS COLORADO OVER THE 36-48 HOURS...DEPENDING ON WHICH
MODEL YOU LOOK AT. ALL MODELS INDICATE COOLER TEMPERATURES...GREATER
CLOUD COVER AND AN ELEVATED CHANCE FOR MEASURABLE PRECIP. STILL IN
THE WARM SECTION OF THIS TROUGH PRECIP WILL MOST LIKELY COME FROM
UPRIGHT CONVECTION/T-STORMS. SO LOCALLY HEAVY RAINFALL WILL BE
POSSIBLE BASED ON THE ELEVATED PRECIPITABLE WATER VALUES GIVEN BY
THE MODELS. FRIDAY LOOKS EVEN WETTER AND PERHAPS SEVERAL DEGS COOLER
WITH A MOIST NELY UPSLOPE FLOW DVLPG EAST OF THE MTNS BENEATH THE
UPPER TROUGH. GFS IS THE WETTEST OF THE MODELS AS IT INDICATES WELL
OVER AN INCH OF QPF OVER AND ALONG THE FRONT RANGE BY LATE THAT
EVENING. EUROPEAN AND CANADIAN MODELS LOOK MUCH DRIER AS THEY ONLY
INDICATE 24-HR RAIN TOTALS WELL UNDER AN INCH AND A MORE PROGRESSIVE
UPPER TROUGH.

EVEN BY SATURDAY...GFS STILL SHOW RELATIVELY COOL AND WET CONDITIONS
ACRS THE CWA WITH UPSLOPE EAST OF THE MTNS AND THE UPPER TROUGH
STILL OVERHEAD. THE ECMWF INDICATES A DRIER AND SLIGHTLY WARMER DAY
WITH THE UPPER TROUGH SHIFTING EAST OF THE STATE. AS USUAL WILL USE
A BLEND OF THE TWO MODELS FOR DERIVE A FCST FOR FRIDAY AND SATURDAY.

&&

.AVIATION...(FOR THE TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 327 AM MDT SUN MAY 24 2015

NO FOG SHOWING UP YET ON THE FRONT RANGE BUT TEMP/DEWPOINT SPREADS
ARE ONLY 1-3 DEGREES WITH MAINLY CLEAR SKIES. THERE IS SOME LIGHT
DRAINAGE WINDS SO THIS MAYBE HELPING TO KEEP FOG FROM FORMING.
STILL AS WE GET CLOSER TO DAYBREAK...EXPECT LIGHT/VRBL WINDS WITH
STILL FOG POTENTIAL FROM 11-15Z. EXPECT ANOTHER ROUND OF
THUNDERSTORMS TODAY AS THE STRONG UPPER LOW REMAINS JUST TO THE
WEST OF FRONT RANGE. STORMS ENDING LATER THIS EVENING AS LOW
GRADUALLY MOVES EAST OF TERMINALS.

&&

.HYDROLOGY...
ISSUED AT 327 AM MDT SUN MAY 24 2015

STILL HIGH CONCERNS FOR MORE FLOODING ON THE NORTHEAST PLAINS THIS
AFTERNOON AND EVENING. SIGNIFICANT RAIN FELL YESTERDAY OVER THE PLAINS...
ESPECIALLY LOGAN COUNTY WHERE FLOODING CONTINUES OVERNIGHT OVER
PORTIONS OF STERLING. MODEL QPF SHOWING POTENTIAL FOR ANOTHER .50
TO 1.5" INCHES OF RAIN AGAIN BY LATER TNT WHILE MOISTURE LEVELS
REMAIN HIGH AND STORM MOTIONS SLOWER TODAY. WILL ISSUE ANOTHER
FLASH FLOOD WATCH FOR AFT/EVENING FROM LINCOLN COUNTY NORTHWARD
THROUGH MORGAN AND EXTENDING THROUGH FAR NE PLAINS. SOME DRYING
FURTHER WEST OVER THE FRONT RANGE AS PW VALUES HAVE DROPPED AROUND
A QUARTER INCH IN PAST 24 HOURS WHILE DEWPOINTS HAVE DROPPED INTO
THE UPPER 30S.

FLOOD WARNINGS CONTINUE ALONG THE CACHE LA POUDRE AND SOUTH PLATTE
RIVERS AT LEAST THROUGH TUESDAY. SOUTH PLATTE RIVER CONTINUES TO
RISE FROM SATURDAY`S RAINS FURTHER WEST AT DENVER AND HENDERSON
WILL STILL MONITOR THESE AREAS FOR POSSIBLE FLOODING IN THE NEXT
SEVERAL DAYS ESPECIALLY IF STRONGER STORMS SEND LEVELS RISING
AGAIN.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM NOON MDT TODAY THROUGH THIS EVENING FOR
COZ042-044>046-048>051.

&&

$$

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


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