Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 281021
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
421 AM MDT MON JUL 28 2014

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 420 AM MDT MON JUL 28 2014

TODAY IS SHAPING UP TO BE SIMILAR TO YESTERDAY. OVERALL WEATHER
PATTERN HAS CHANGED VERY LITTLE WITH LIGHT NORTHWEST FLOW ALOFT ON
PERIPHERY OF UPPER RIDGE TO OUR EAST. AT THE LOW LEVELS...SURFACE
HIGH PRESSURE OVER THE NORTHERN PLAINS STATES AND WEAK TROUGH
EXTENDING FROM THE FRONT RANGE NORTHWARD INTO SOUTHERN WYOMING
WILL KEEP MOIST LOW LEVEL SOUTHEAST FLOW IN PLACE. A WEAK DENVER
CYCLONE THIS MORNING IS EXPECTED TO GRADUALLY ERODE...BUT
DEPENDING ON POSSIBLE STRATUS DEVELOPMENT IT COULD HOLD THROUGH
THE DAY AS ANY DIFFERENTIAL HEATING WOULD ENHANCE CYCLONE.
PRECIPITABLE WATER VALUES HAVE INCREASED TO AROUND 1.1 TO 1.25
INCHES ON THE PLAINS...BUT MOST SHORT RANGE MODELS SUGGEST SOME
MID LEVEL DRYING COMING INTO FROM THE NORTHWEST LATER TODAY. AS A
RESULT...PW VALUES BY AFTERNOON SHOULD BE SIMILAR TO THOSE SEEN
YESTERDAY. CAPE VALUES WILL BE SLIGHTLY HIGHER AS SURFACE
DEWPOINTS IN THE MID/UPPER 50S AND HIGHS IN THE MID 80S WOULD
YIELD CAPES OF 1000-1500 J/KG. WITH LACK OF SHEAR AND SKINNY CAPE
PROFILE...SEVERE THREAT WOULD BE LOW BUT LOCALLY HEAVY RAINFALL
IS EXPECTED FROM STORMS...SEE HYDRO SECTION BELOW. ALSO CONCERNED
THAT CAP MAY BE A LITTLE STRONGER WITH SLIGHT WARMING ALOFT...SO
NOT ENTIRELY SURE WE WILL SEE WIDESPREAD CONVECTION ON THE PLAINS.
HIGHEST PROBABILITY CERTAIINLY ALONG THE FRONT RANGE
MOUNTAINS/FOOTHILLS/PARK COUNTY AREA WHERE CAP WILL BE BROKEN.

FOR TONIGHT...SHOWERS AND STORMS WILL LIKELY CONTINUE THROUGH A
GOOD CHUNK OF THE EVENING BEFORE DECREASING AS MOIST AIRMASS
SLOWLY GETS WORKED OVER. A FEW SHOWERS/STORMS COULD ACTUALLY
LINGER THROUGH THE NIGHT WITH LOW/MID LEVEL FLOW TURNING WEAK
UPSLOPE LATE AND WEAK Q-G FORCING REMAINS OVERHEAD.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 420 AM MDT MON JUL 28 2014

INCREASING CONCERN ABOUT HEAVY RAINFALL THREAT FOR LATE TUESDAY
INTO EARLY WEDNESDAY MORNING. THERE HAS BEEN SOME FLIP FLOPPING
BETWEEN THE MODELS ON THE POSITION OF THE SYNOPTIC SCALE
FORCING...WITH SOME MODELS FOCUSED FROM LARIMER AND BOULDER
COUNTIES ACROSS NORTHEASTERN COLORADO AND OTHERS FROM OUR SOUTHERN
FOOTHILLS INTO SOUTHEASTERN COLORADO. BUT THERE IS PRETTY GOOD
AGREEMENT ON A WIDE SWATH OF 1 TO 3 INCH RAIN AMOUNTS IN ABOUT AN
18 HOUR PERIOD. BIGGEST CONCERN HOWEVER IS THE POTENTIAL FOR
HEAVIER RAINFALL AMOUNTS PRODUCED BY TERRAIN FOCUS...CONVECTION ON
STATIONARY BOUNDARIES...OR TRAINING WITHIN THE LARGER RAIN BAND.
WIND AND THERMODYNAMIC PROFILES LOOK TUESDAY EVENING LOOK REALLY
FAVORABLE FOR STATIONARY HEAVY RAIN PRODUCING STORMS. DEEP MEAN
WIND IS LIGHT AND PERHAPS A LITTLE EASTERLY...WITH STRONGER LOW
LEVEL EASTERLIES AT THE SURFACE. THIS IS FAVORABLE FOR BOTH BACK
BUILDING STORMS AND TERRAIN ANCHORING ON THE FOOTHILLS. IF
CONVECTION GETS ORGANIZED ALONG THE FOOTHILLS THIS COULD PRODUCE
A STATIONARY BOUNDARY PRODUCING REPEATED CONVECTION MOVING FROM
THE BASE OF THE FOOTHILLS OR FURTHER EAST UP ACROSS THE FOOTHILLS.
PRECIPITABLE WATER IS NOT EXTREME BUT IS QUITE SUFFICIENT FOR
HEAVY RAIN RATES...PROBABLY AROUND 1.25 INCHES. SAME STORY FOR
CAPE...DEEP SKINNY CAPE AROUND 500 J/KG...MAYBE AS MUCH AS 1000
J/KG WITH SOME OF THE EARLY CONVECTION. WARM CLOUD DEPTH IS ABOUT
AS GREAT AS WE GET...UP TO AROUND 8000 FEET BY TUESDAY
EVENING...SO WARM RAIN PROCESSES WILL BOOST PRECIPITATION
EFFICIENCY ESPECIALLY IN A BROADLY SATURATED ENVIRONMENT. WOULD
NOT BE SURPRISED TO SEE SEVERAL AREAS WITH 1 TO 2 INCH PER HOUR
RAIN AMOUNTS THAT SUSTAIN FOR SEVERAL HOURS. A LITTLE EARLY FOR A
WATCH YET...THERE MAY BE MORE CLARITY ON THE POSITION AND TIMING
LATER TODAY...BUT WE WILL BE HIGHLIGHTING THE THREAT IN OUR
PRODUCTS THIS MORNING.

WEDNESDAY WILL LIKELY BE FAIRLY PLACID AFTER THE MAIN RAIN AREA
EXITS. ECMWF IS SLOWER TO DO THAT...KEEPING SOME SIGNIFICANT RAIN
INTO THE MORNING. WILL LEAVE SOME SUBSTANTIAL POPS...BUT THINK THE
MAIN EVENT WILL BE OVER BEFORE WEDNESDAY MORNING.

FOR THE REST OF THE PERIOD...SOME TEMPERATURE RECOVERY BUT LOW
LEVELS REMAIN RELATIVELY COOL AS THE NNW FLOW CONTINUES. PROBABLY
SOME MINOR RIPPLES IN THE FLOW THAT WILL MODULATE CONVECTIVE
ACTIVITY...BUT OVERALL PROBABLY SCATTERED OVER THE MOUNTAINS AND
ISOLATED LATE DAY STORMS WITH MARGINAL TEMPERATURES ON THE
PLAINS.

&&

.AVIATION...(FOR THE TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 420 AM MDT MON JUL 28 2014

ANOTHER TOUGH CALL ON POSSIBLE STRATUS DEVELOPMENT THIS MORNING.
DENVER CYCLONE IS QUITE WEAK AT THIS TIME AND SOME MID/HIGH LVEL
CLOUDINESS WAS KEEPING BOUNDARY LAYER SLIGHTLY WARMER. THIS COULD
PREVENT LOW CLOUDS OR STRATUS FROM BECOMING WIDESPREAD THIS
MORNING. AT THIS TIME...PROBABILITY OF A STRATUS DECK/LIGHT FOG
NEAR 50-60%. WILL CONTINUE TO MONITOR AS DECK USUALLY DEVELOPS
12Z-13Z. OTHER CONCERN WILL BE THUNDERSTORM POTENTIAL. AT THIS
TIME THREAT IS HIGH ENOUGH TO WARRANT TEMPO TSRA IN TAFS 22Z-02Z
BUT COULD LINGER AS LATE AS 04Z-05Z LIKE LAST EVENING. VISIBILITIY
RESTRICTION DOWN TO 1-2SM AND CEILINGS AT OR BELOW 3000 FT AGL
IN/NEAR STORM CORES. OTHERWISE VFR CONDITIONS WILL PREVAIL.

&&

.HYDROLOGY...
ISSUED AT 420 AM MDT MON JUL 28 2014

TODAY WILL FEATURE A SIMILAR SETUP TO YESTERDAY. PRECIPITABLE
WATER VALUES EXPECTED TO RANGE FROM 1.0 TO 1.25 INCHES FROM THE
FOOTHILLS ONTO THE NEARBY ADJACENT PLAINS...AND WARM CLOUD DEPTH
SHOWN TO BE NEAR 5000 FT. LOCALLY HEAVY RAINFALL WILL OCCUR THIS
AFTERNOON AND EVENING...STRONGER STORMS WOULD PRODUCE 1 INCH IN
20-30 MINUTES. COLD POOL INTERACTION WITH INFLOW AND VERY WEAK
FLOW ALOFT WOULD LIKELY RESULT IN VERY SLOW MOVING STORMS TODAY SO
ISOLATED STRONGEST STORMS WOULD PRODUCE 2 INCHES IN AN HOUR.
FLASH FLOOD PRONE AREAS SUCH AS BURN SCARS AND URBAN AREAS COULD
SEE FLOODING ISSUES FROM THE ISOLATED STRONGEST STORMS.

FLASH FLOOD RISK IS LOOKING HIGH FOR TUESDAY AFTERNOON AND TUESDAY
NIGHT. TOO EARLY TO PICK THE FOCUS...THOUGH AREAS IN AND NEAR THE
FOOTHILLS ARE MOST LIKELY. A WIDESPREAD INCH OF RAIN IS EXPECTED
WITH LOCALIZED AMOUNTS OF SEVERAL INCHES POSSIBLE WHERE SLOW
MOVING THUNDERSTORMS WITH ONE TO TWO INCH PER HOUR RAINFALL RATES DEVELOP.
HEAVY RAIN MAY BE WIDESPREAD ENOUGH TO PRODUCE FLOODING ON LARGER
CREEKS AND THE SOUTH PLATTE RIVER.

FOR LATER IN THE WEEK AND THE WEEKEND THERE WILL STILL BE SOME
RISK OF HEAVY RAINFALL...BUT THE FLOOD RISK WILL BE LOWER DUE TO
SOME DRYING AND REDUCED THUNDERSTORM ACTIVITY.

&&

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

$$

SHORT TERM...BARJENBRUCH
LONG TERM...GIMMESTAD
AVIATION...BARJENBRUCH
HYDROLOGY...BARJENBRUCH/GIMMESTAD


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