MESOSCALE PRECIPITATION DISCUSSION 0268
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1032 PM EDT WED JUN 06 2018

AREAS AFFECTED...NEBRASKA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 070231Z - 070831Z

SUMMARY...SLOW-MOVING STORM CLUSTERS ARE LIKELY OVERNIGHT IN
NEBRASKA...AND IF THEY PERSIST LONG ENOUGH THEY MAY MERGE IN SOME
AREAS. THIS SHOULD CREATE LOCALIZED AREAS WITH PROLONGED HEAVY
RAINFALL AND THE POTENTIAL FOR FLASH FLOODING. RAIN RATES COULD
EXCEED 2 IN/HR.

DISCUSSION...REGIONAL RADARS SHOWED TWO PROMINENT STORM CLUSTERS
ON EITHER END OF NEBRASKA (WEST AND EAST) AND BOTH APPEARED TO
HAVE ESTABLISHED A COLD POOL. THE FIRST MCS WAS JUST BEGINNING TO
PUSH EAST FROM THE NEBRASKA PANHANDLE AND WAS SHOWING SIGNS OF
MORE FORWARD PROPAGATION WITH TEMPERATURES FALLING TO AROUND 60F
AND 1-HR PRESSURE RISES AS HIGH AS 5 MILLIBARS (KOGA). ANOTHER
SMALLER CONVECTIVE CLUSTER APPEARED TO BE ANCHORED NEARLY IN PLACE
FROM NEAR KBVN TO KOLU ON THE UPSHEAR FLANK OF A CONVECTIVE COLD
POOL. SUFACE TEMPERATURES WERE INTO THE 60S JUST TO THE
NORTHEAST...AND THE NEARLY STATIONARY POSITION OF THIS COLD POOL
WAS SUSTAINING (AND LEADING TO BACKBUILDING) OF CONVECTION NEAR
WHERE THE MOIST LOW-LEVEL INFLOW WAS INTERCEPTING IT. THE
BACKBUILDING PROCESS WAS SOMEWHAT SLOW...HOWEVER.

ALTHOUGH HI-RES MODELS ARE STRUGGLING IN THIS REGION...THE 18Z NAM
NEST SHOWED A SOMEWHAT REASONABLE SCENARIO WHERE A FORWARD
PROPAGATING MCS PUSHES EAST INTO CENTRAL NEBRASKA...FOCUSING ALONG
AND JUST SOUTH OF A STATIONARY FRONT...AND EVENTUALLY MEETS A
SLOWLY BACKBUILDING CONVECTIVE CLUSTER FURTHER EAST. IT SHOWED
LOCALIZED RAINFALL AS HIGH AS 4-6 INCHES WITH RAIN RATES PEAKING
ABOVE 2 IN/HR WHERE CONVECTION WAS MORE SUSTAINED. ALTHOUGH THE
SPECIFICS OUTLINED BY THE 18Z NAM NEST MAY NOT BE EXACTLY
CORRECT...IT DOES SEEM TO BE A MORE LIKELY EVOLUTION...WITH A
LARGE RESERVOIR OF HIGH CAPE VALUES ACROSS CENTRAL NEBRASKA. THE
LIMITING FACTOR WOULD BE RELATIVELY WEAK WIND SHEAR WHICH MAY NOT
FAVOR GREATER STORM ORGANIZATION WITH TIME...BUT THE STRONG
INSTABILITY MAY COMPENSATE FOR THIS.

GIVEN THE POTENTIAL FOR BACKBUILDING AND TRAINING CONVECTION TO
CONTINUE...AND RAIN RATES EXCEEDING 2 IN/HR...FLASH FLOODING SEEMS
POSSIBLE ACROSS PORTIONS OF NEBRASKA TO THE SOUTH AND SOUTHEAST OF
THE SAND HILL REGION.

LAMERS

ATTN...WFO...BOU...GID...GLD...LBF...OAX...

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

LAT...LON   42089906 41889725 41009672 40409733 40209986
            40330154 40850208 41340171 41850048