MESOSCALE PRECIPITATION DISCUSSION 0329
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
941 PM EDT WED AUG 27 2014
 
AREAS AFFECTED...NORTHEAST CO, NORTHWEST KS, SOUTHERN & EASTERN NE 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 280140Z - 280740Z
 
SUMMARY...THUNDERSTORMS HAVE BEEN AMASSING ACROSS NORTHEAST CO,
SOUTHERN NE, AND NORTHERN KS.  WITH A STRONG SIGNAL FOR HEAVY
RAINFALL SEEN WITHIN THE MESOSCALE QPF GUIDANCE, FLASH FLOODING IS
LIKELY TO CONTINUE OVERNIGHT.

DISCUSSION...A MESOSCALE FRONTAL WAVE ACROSS NORTHEAST CO AHEAD OF
A DEEP CYCLONE PROGRESSING THROUGH THE WEST HAS BEEN MOVING 15-20
KTS TO THE SOUTHEAST OVER THE PAST SEVERAL HOURS.  WITHIN THE WARM
ADVECTION REGIME TO ITS EAST, THUNDERSTORMS WITH HEAVY RAINFALL
HAVE BEEN THE RULE ACROSS NORTHERN KS AND PORTIONS OF SOUTHERN AND
WESTERN NE.  PRECIPITABLE WATER VALUES OF 1.5-2" ARE FORECAST TO
REMAIN ACROSS THE REGION -- PER RECENT RAP RUNS -- WHICH ARE OVER
2.5 SIGMAS ABOVE AVERAGE, OR NEAR THE 99TH PERCENTILE FOR LATE
AUGUST.  AREA SOUNDINGS ARE QUITE MOIST, WITH WET BULB ZEROES IN
THE 11000-13000 FT RANGE -- WARM RAIN PROCESSES WILL LIKELY BE AT
PLAY.  VAD WIND PROFILES SHOW 25-30 KTS OF 850 HPA INFLOW INTO THE
REGION TOWARDS POTENTIAL CLOUD BASES.  MUCAPE VALUES OF 1000-2000
J/KG EXIST, WITH HIGHER VALUES ACROSS NORTHEAST KS WHERE
CONVECTION HAS BEEN MINIMAL THUS FAR.

OUTFLOW BOUNDARY COLLISIONS ARE COMPLICATING THE FORECAST, WITH A
LARGE OUTFLOW BOUNDARY COLLISION IMMINENT ACROSS NORTHEAST CO NEAR
THE SYSTEM'S TROWAL.  TO THE EAST, THE FORECAST IS FOR 850 HPA
INFLOW TO INCREASE TO THE 40+ KT RANGE PER RECENT RAP GUIDANCE,
WITH THE AREA OF 25+ KT INFLOW BROADENING INTO AND OVER THE
FRONTAL ZONE WHICH SHOULD LEAD TO A LENGTHENING CONVECTIVE BAND
ACROSS PORTIONS OF KS AND NE.  THIS COULD CONTINUE THE RECENT
TREND OF CELL BACKBUILDING AND TRAINING.  INCREASING CIN NEAR THE
BOUNDARY OVERNIGHT SHOULD LEAD TO INCREASINGLY ELEVATED
CONVECTION, WHICH IS WELL-ADVERTISED BY THE MESOSCALE QPF
GUIDANCE.  HOURLY RAINFALL RATES UP TO 2.5" ARE EXPECTED -- WITH
EVEN HIGHER TOTALS POSSIBLE WHERE OUTFLOW BOUNDARIES COLLIDE.  THE
MESOSCALE QPF GUIDANCE IS UNANIMOUS IS FORECASTING LOCAL AMOUNTS
OF 4-6" WITHIN A SHORT PERIOD OF TIME ACROSS PORTIONS OF
SOUTH-CENTRAL AND EASTERN NE -- A STRONG SIGNAL FOR HEAVY
RAINFALL.  CONSIDERING THIS SIGNAL IN THE GUIDANCE, FLASH FLOODING
IS CONSIDERED LIKELY OUTSIDE THE NE SAND HILLS, AND POSSIBLE OVER
THE SAND HILLS THEMSELVES.

ROTH

ATTN...WFO...OAX...TOP...ICT...GID...LBF...DDC...GLD...BOU...
CYS...

ATTN...RFC...ABRFC...MBRFC...

LAT...LON   40469613 39309801 38390002 38550146 38750221 39100360
            39480412 40060412 40660367 41470141 42229829 41959646
            40469613