Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 051804
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1204 PM MDT TUE MAY 5 2015

.UPDATE...
ISSUED AT 1204 PM MDT TUE MAY 5 2015

ONLY MINOR CHANGES TO THE FORECAST AT THIS TIME. MAIN AREA OF RAIN
WILL LIFT NORTH ACROSS THE AREA THIS AFTERNOON...DECREASING FROM
SOUTH TO NORTH THIS EVENING. FOR THE MOST PART A STEADY LIGHT TO
MODERATE RAIN IS EXPECTED...BUT THERE WILL LIKELY BE SOME DEEPER
CONVECTION IN AREAS OF SMALL SCALE CONVERGENCE. ONE SUCH AREA
APPEARS TO BE DEVELOPING FROM KIOWA COUNTY TOWARDS LIMON THAT
COULD HEAD TOWARD DENVER OR AREAS JUST NORTH OF DENVER IN THE LATE
AFTERNOON AND EVENING. THERE COULD BE ANOTHER ORGANIZED AREA THAT
DEVELOPS ON THE SOUTH EDGE OF THE RAIN BAND FOR THIS EVENING. WE
MAY ALSO NEED TO WATCH A WIND SHIFT LINE CURRENTLY FROM DENVER TO
LOVELAND...THIS COULD WIND UP BEING A FOCUS RATHER THAN THE
FOOTHILLS...OR LEAD TO STORMS FORMING THERE AND TRACKING NORTHWEST
INTO THE BOULDER/LARIMER FOOTHILLS. CELL MOTIONS LOOK TO BE
TOWARD THE NORTH TO NORTHWEST AT 15-20 MPH SO THE MAIN ISSUE WOULD
BE ANY ORGANIZATION THAT LEADS TO TRAINING ALONG A LINE. WITH
PRECIPITABLE WATER AROUND 0.8 INCH AND A 5000 FOOT DEEP MOIST
LAYER...IT IS A FAVORABLE ENVIRONMENT FOR HEAVY RAIN PRODUCTION
DESPITE THE LIKELY LACK OF STRONG UPDRAFTS OR MUCH SYNOPTIC SCALE
LIFT. THINK THE THREAT IS MAINLY HEAVIER RAIN ON THE 2-4 HOUR TIME
SCALE FROM TRAINING...RATHER THAN INTENSE SHORTER BURSTS. WITH THE
ANTECEDENT RAINFALL SOME PLACES COULD HAVE SOME MINOR FLOODING
WITH AN INCH OF RAIN. WILL LEAVE THE FLASH FLOOD WATCH ALONE.

ADJUSTED POPS UP A BIT MORE...BUT REDUCED THE OVERALL QPF A LITTLE
AS THE OVERALL RAIN DOES NOT LOOK QUITE AS HEAVY AS FORECAST.

SOME WEAK SHOWERS MAY LINGER LATER TONIGHT...BUT EXPECT THE MAIN
AREA OF RAIN TO LIFT NORTH OF OUR AREA BY MIDNIGHT.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 432 AM MDT TUE MAY 5 2015

CONCERN TODAY SURROUNDS POTENTIAL FOR HEAVY RAINFALL AND FLOODING.
LAST NIGHTS SHOWERS AND STORMS WERE VERY EFFICIENT AND SOME WARM
RAIN PROCESSES WERE NOTED ALONG THE FRONT RANGE FOOTHILLS. A SMALL
AREA IN NORTH CENTRAL BOULDER COUNTY RECORDED 1.3 TO 2.8 INCHES OF
RAIN IN LOW TOPPED CONVECTION...AND LOCALIZED AMOUNTS OVER 1 INCH
IN CENTRAL JEFFERSON COUNTY FOOTHILLS WITH NO LIGHTNING. WARM
CLOUD DEPTH WAS AS DEEP AS 5000-5500 FEET...AND SAME EXPECTED FOR
TODAY. THERE IS AN UPSLOPE EAST/SOUTHEAST COMPONENT MOST OF THE
DAY...AND AS SOON AS DEEPER MOISTURE ARRIVES WITH APPROACH OF
UPPER LEVEL TROUGH AND AT LEAST WEAK Q-G LIFT SHOULD SEE SHOWERS
BREAK OUT IN EARNEST WITH A FEW EMBEDDED THUNDERSTORMS. SHOWERS
WERE ALREADY INCREASING IN SOUTHEAST COLORADO...AND THESE SHOULD
REACH PALMER DIVIDE BY MID MORNING AND DENVER/I-25 CORRIDOR LATE
MORNING. ONE FACTOR THAT COULD LIMIT RAINFALL AMOUNTS WOULD BE
CONVECTIVE CLUSTERS AHEAD OF UPPER TROUGH. A COUPLE OF THESE
ALREADY NOTED IN WEST TEXAS AND SOUTHEAST NEW MEXICO. THOSE COULD
KEEP THREAT OF HEAVIER RAINFALL ON THE EASTERN COLORADO PLAINS
INTO WESTERN KANSAS. SHOWERS AND A FEW THUNDERSTORMS WILL TAPER
OFF OVERNIGHT ALONG THE FRONT RANGE...BUT MAY CONTINUE OVER THE
FAR NORTHEAST CORNER AND THE MOUNTAINS AS WEST/NORTHWEST FLOW
DEVELOPS BEHIND THE TROUGH. FINALLY...CANT RULE OUT AN ISOLATED
TORNADO THREAT WITH INCREASING LOW LEVEL WIND SHEAR AND DENVER
CYCLONE...BUT UPDRAFTS WILL BE QUITE WEAK WITH LIMITED CAPE LESS
THAN 500 J/KG.  WITH REGARD TO FLASH FLOOD WATCH...SEE FURTHER
METEOROLOGICAL DISCUSSION IN HYRDO SECTION BELOW.

IN THE MOUNTAINS...WET BULB ZERO LEVELS SUGGEST SNOW LEVELS
AVERAGING 10500-12000 FEET TODAY...LOWERING ABOUT A THOUSAND FEET
BEHIND TROUGH AXIS TONIGHT. SEVERAL INCHES OF SNOW EXPECTED OVER
THE HIGHER PEAKS ABOVE MOST ROADS...SO NO ADVISORIES AT THIS TIME.

AREAS OF FOG AND DRIZZLE WILL PERSIST THROUGH AT LEAST MID
MORNING WITH MOIST EASTERLY FLOW. THEN DEEPER SHOWER DEVELOPMENT
AND MIXING SHOULD ERODE FOG TOWARD LATE MORNING.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 432 AM MDT TUE MAY 5 2015

THE ABNORMALLY WET WEATHER PATTERN STILL LOOKS LIKE IT WILL EXTEND
INTO THE WEEKEND. AFTER TONIGHTS NEGATIVELY TILTED UPPER TROUGH
MOVES OUT ONTO THE NORTHERN PLAINS...COLORADO WILL REMAIN UNDER
WEAK SOUTHWESTERLY FLOW ALOFT WHICH WILL BE OPEN TO THE FURTHER
INTRUSION OF MOISTURE FROM THE GULF OF MEXICO. AS THE MOIST
AIRMASS REMAINS IN PLACE...DAYTIME HEATING WILL BE MORE THAN
SUFFICIENT TO GENERATE ADDITIONAL ROUNDS OF SHOWERS EACH DAY.
MEDIUM RANGE MODELS SHOW THE 700 MB SPECIFIC HUMIDITY LEVELS
RISING TO A JUICY 6 G/KG AT TIMES. MODEL SOUNDINGS SHOW MODEST
CAPE VALUES AROUND 500 J/KG ON WEDNESDAY AND THEN ALMOST 1000 J/KG
ON THURSDAY. LOW LEVEL WINDS WILL BE OUT OF THE EAST AND
SOUTHEAST...HELPING TO HOLD MOISTURE NEAR THE FOOTHILLS. ALL OF
THE INGREDIENTS APPEAR TO BE IN PLACE FOR MORE RAIN ACROSS THE
FORECAST AREA EACH DAY THROUGH FRIDAY.

OVER THE WEEKEND IT LOOKS LIKE THE NEXT UPPER LEVEL CLOSED LOW
WILL TRAVERSE ACROSS THE STATE FROM THE DESERT SOUTHWEST. THIS
SHOULD DRAW UP ADDITIONAL MOISTURE AHEAD OF THE APPROACHING LOW
AND THEN GENERATE AREAS OF HEAVY RAIN AT TIMES ON SATURDAY AND
SUNDAY. 700 MB TEMPERATURES ARE FORECAST TO DROP TO THE -4 TO -8
DEGREE RANGE...SO THIS SHOULD BRING THE SNOW LEVELS
DOWN...ESPECIALLY SATURDAY NIGHT AND SUNDAY MORNING. THE HIGHER
FOOTHILLS COULD SEE ACCUMULATING SNOW WHICH WILL ALSO HELP OUT THE
HYDROLOGY SITUATION TEMPORARILY.

TEMPERATURES WILL COOLER THAN SEASONAL NORMALS THROUGH THE
FORECAST PERIOD...ESPECIALLY OVER THE WEEKEND. AND PROBABILITIES
OF PRECIPITATION WILL BE QUITE HIGH. THE HYDROLOGICAL SITUATION IS
GOING TO NEED TO BE MONITORED AS AREAS RECEIVE REPEATED RAINFALL
AND SOIL MOISTURE LEVELS BEGIN APPROACHING SATURATION. NEXT MONDAY
AND TUESDAY MAY BE THE BREAK WE ARE LOOKING FOR AS AN UPPER RIDGE
IS FINALLY FORECAST TO MOVE BACK OVER THE AREA...IF ONLY FOR A
COUPLE DAYS.

&&

.AVIATION...(FOR THE TAFS THROUGH 18Z WEDNESDAY MORNING)
ISSUED AT 1204 PM MDT TUE MAY 5 2015

MVFR CONDITIONS WILL PREVAIL THROUGH EARLY EVENING WITH LOCALIZED
LIFR IN AREAS OF HEAVIER RAIN. CONDITIONS WILL IMPROVE BETWEEN 03Z
AND 06Z WITH VFR CONDITIONS AFTER THAT. HIGHER CEILINGS MAY STILL
REQUIRE INSTRUMENT APPROACHES TO KDEN INTO WEDNESDAY MORNING.

&&

.HYDROLOGY...
ISSUED AT 1204 PM MDT TUE MAY 5 2015

PRECIPITABLE WATER HOLDING STEADY AT 0.75 INCH AND IT LOOKS LIKE
CONVECTION WILL BE LIMITED AS WE WILL BE IN THE CENTER OF THE RAIN
BAND THIS AFTERNOON. LOOKING AT A WIDESPREAD 0.25 TO 0.75 INCH
RAINFALL OVER THE NEXT 12 HOURS...A FEW SPOTS WITH TRAINING COULD
GET 1 TO 2 INCHES IN 2 TO 3 HOURS WHICH WOULD GIVE US FLOODING IF
IT IS IN THE MORE FLOOD PRONE LOCATIONS SUCH AS BURN AREAS...FLOOD
DAMAGED DRAINAGES...AND ELBERT COUNTY WHICH HAD HEAVY RAIN LAST
NIGHT.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH UNTIL 9 PM MDT THIS EVENING FOR COZ035-036-041-
046.

&&

$$

UPDATE...GIMMESTAD
SHORT TERM...BARJENBRUCH
LONG TERM...DANKERS
AVIATION...GIMMESTAD
HYDROLOGY...BARJENBRUCH



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