Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 260156
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
956 PM EDT SAT APR 25 2015

...VALID 03Z SUN APR 26 2015 - 00Z MON APR 27 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...




...NORTHEAST COLORADO...

THE LARGE SCALE PATTERN BETWEEN SATURDAY EVENING AND MIDDAY SUNDAY
WOULD BE CAUSE FOR CONCERN IN THIS REGION IF MOISTURE AND
INSTABILITY WERE MORE SUMMER-LIKE. LOW LEVEL UPSLOPE FLOW WILL
STRENGTHEN WHILE UPPER FLOW REMAINS DIFLUENT AND BECOMES
INCREASINGLY MERIDIONAL TO THE NORTHEAST OF A DEVELOPING CLOSED
LOW. DEEP AND SUSTAINED ASCENT WILL LIKELY MAKE THE MOST OF MEAGER
INSTABILITY TO PRODUCE CONTINUAL SHOWERS/THUNDERSTORMS THROUGH
EARLY SUNDAY BEFORE EMPHASIS BEGINS TO SHIFT SOUTHWARD. CELL
MOTIONS WERE INITIALLY ERRATIC AND UPDRAFT WIDTH RATHER MARGINAL
OWING TO THE WEAK INSTABILITY. NAM FORECAST SOUNDINGS OVER
NORTHEAST COLORADO DO INDICATE GRADUAL SATURATION AT ALL
LEVELS...HOWEVER...WHILE THE SUSTAINED MID AND UPPER LEVEL ASCENT
MAINTAINS LAPSE RATES CAPABLE OF SUPPORTING CONVECTIVELY ENHANCED
RAIN RATES. HRRR RUNS BETWEEN 22-00Z CONTAINED A CONSISTENT SIGNAL
FOR LOCAL RAINFALL AMOUNTS APPROACHING OR EXCEEDING ONE INCH ON
SMALL SCALES ALONG THE FRONT RANGE AND OVER THE NORTHEAST PLAINS
OF COLORADO THROUGH 12Z. IF ENOUGH OF A COLD POOL WERE TO BECOME
ESTABLISHED IT COULD BECOME AN ANCHOR FOR ONGOING CONVECTION...AND
BOOST DURATION OF MODERATE RAIN OVER A GIVEN LOCATION. THE MAIN
LIMITING FACTORS FOR FLASH FLOODING THOUGH...ARE PW VALUES ONLY
NEARING 0.75 INCHES AT BEST...AND A SLOW BUT STEADY LESSENING OF
CAPE VALUES AS SEEN IN THE RAP AND HRRR. THERE IS A SLIM
POSSIBILITY THAT ONE OR TWO LOCATIONS COULD SEE RAINFALL EXCEEDING
THE 1.5 INCH IN 3 HOUR OR 2 INCH IN 6 HOUR FLASH FLOOD GUIDANCE.

BURKE
$$




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