MESOSCALE PRECIPITATION DISCUSSION 0869
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1035 PM EDT FRI OCT 06 2017

AREAS AFFECTED...NE KANSAS...SE NEBRASKA...NW MISSOURI...IOWA

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

VALID 070231Z - 070700Z

SUMMARY...FLASH FLOODING WILL BE POSSIBLE ACROSS PORTIONS OF THE
CORN BELT NEAR AND AHEAD OF A DEVELOPING LOW PRESSURE SYSTEM.
CONVECTIVE BANDS WITH RAIN RATES OF 1-2 IN/HR HAVE BEEN OBSERVED
AND SHOULD PERSIST FOR THE NEXT SEVERAL HOURS.

DISCUSSION...REGIONAL RADARS AND IR SATELLITE IMAGERY SHOW A BAND
OF CONVECTION EXTENDING ALONG A FRONT...FROM AS FAR SOUTHWEST AS
THE TEXAS PANHANDLE INTO EASTERN IOWA. THE INFLECTION POINT WAS IN
NORTHEAST KANSAS NEAR A DEVELOPING SURFACE LOW. TO THE NORTHEAST
OF THAT...THE FRONT WAS ROUGHLY STATIONARY...AND CELL MOTIONS WERE
MORE PARALLEL TO THE BOUNDARY (VERSUS MORE PROGRESSIVE AND
FORWARD-PROPAGATING STORMS TO THE SOUTHWEST OF THE SURFACE LOW).
THIS IS EXPECTED TO CONTINUE FOR THE NEXT SEVERAL HOURS AS THE
SURFACE LOW CONSOLIDATES AND DEVELOPS TO THE NORTHEAST INTO
WESTERN IOWA. INCREASING LOW-LEVEL DEFORMATION AHEAD OF THE
STRENGTHENING CYCLONE WILL COINCIDE WITH THE RIGHT ENTRANCE REGION
OF A 100+ KNOT UPPER LEVEL JET STREAK AND PROVIDE FAVORABLE LARGE
SCALE SUPPORT FOR ASCENT THROUGH AROUND 06-07Z. AFTER THAT
POINT...THE JET STREAK BEGINS TO LIFT NORTH...INSTABILITY
WANES...AND THE LOW-LEVEL CYCLONE BECOMES INCREASINGLY DETACHED
FROM THE DEEPER MOISTURE PLUME FURTHER TO THE EAST.

CONSIDERING ALL OF THAT...THERE APPEARS TO BE A WINDOW OF 4-5
HOURS IN WHICH TRAINING CONVECTION WITH LOCALIZED HEAVY RAINFALL
WILL BE LIKELY...AND FLASH FLOODING WILL BE
POSSIBLE...PARTICULARLY IF THAT OCCURS OVER AREAS THAT PREVIOUSLY
RECEIVED HEAVY RAINFALL. ONE SUCH AREA IS IN SOUTHWEST
IOWA...WHERE KOAX RADAR RAINFALL ESTIMATES ARE ON THE ORDER OF 2-4
INCHES OVER THE PAST 36 HOURS...AND FLASH FLOOD GUIDANCE IS LOWER.
ONE MESOSCALE FEATURE THAT MAY AID IN FOCUSING CONVECTION IS AN
MCV...NOTED IN A SUBTLE SPIN IN RADAR REFLECTIVITY AND BROAD
CIRCULATION ON MID-LEVEL RADAR VELOCITIES NEAR THE KS-NE BORDER.
ENHANCED LOW-MID LEVEL MOISTURE FLUX AND ASCENT JUST AHEAD OF THIS
MAY PROMOTE A BRIEF 1-3 HOUR WINDOW OF MORE FOCUSED HEAVY RAIN
POTENTIAL FROM ABOUT 15N MANHATTAN KS TO NEAR CRESTON IA. THIS
DOES HAPPEN TO ALSO COINCIDE WITH THE REGION OF LOWER FLASH-FLOOD
GUIDANCE...SO IT COULD BE A FAVORED AREA FOR FLASH FLOODING TO
OCCUR IF THE MESOSCALE DETAILS ALIGN CORRECTLY.

LAMERS

ATTN...WFO...ARX...DMX...DVN...EAX...FSD...OAX...TOP...

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

LAT...LON   43309338 43299234 42909173 42249168 41359242
            40449360 39889428 39239493 38759540 38489577
            38599644 38709696 39039741 39489745 40179725
            41189671 42149583 42809471