MESOSCALE PRECIPITATION DISCUSSION 0854
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
611 PM EDT MON OCT 02 2017

AREAS AFFECTED...SRN AND ERN MINNESOTA...NW WISCONSIN

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 022210Z - 030400Z

SUMMARY...FLASH FLOODING WILL BECOME INCREASINGLY LIKELY THIS
EVENING AS STORMS CONTINUE TO TRAIN OVER THE SAME AREAS IN
SOUTHERN AND EASTERN MINNESOTA...AND FAR NORTHWEST WISCONSIN.

DISCUSSION...SHOWERS AND THUNDERSTORMS HAVE ALREADY BEEN
DEVELOPING OVER THE PAST SEVERAL HOURS ACROSS PORTIONS OF
MINNESOTA...GENERALLY TO THE NORTHWEST OF A STRENGTHENING
STATIONARY FRONT. CONVECTION HAS GENERALLY BEEN LOOSELY ORGANIZED
WITH A BROAD FRONTAL ZONE STILL TAKING SHAPE. MODEL FORECASTS SHOW
THE FRONT BECOMING MUCH MORE SHARPLY DEFINED AROUND 00Z WITH AN
INCREASING FRONTOGENETIC CIRCULATION. THIS IS LIKELY DUE TO THE
EXPECTED INCREASE IN THE SOUTHERLY LLJ FEEDING INTO THE OUTLINED
AREA...AS WELL AS A RESPONSE TO A STRONG LOBE OF +PV EJECTING OUT
OF COLORADO INTO THE PLAINS THIS EVENING. ALL THINGS
CONSIDERED...THE LARGE SCALE FORCING WILL BE RAMPING UP
CONSIDERABLY IN THE NEXT FEW HOURS.

HI-RES MODEL FORECASTS ARE UNANIMOUS IN SHOWING A PROMINENT
CONVECTIVE BAND DEVELOPING BY 03-04Z IN RESPONSE TO THE INCREASED
AND MORE FOCUSED FORCING...AND STRETCHING FROM SOUTHWEST MINNESOTA
NEWD TOWARD THE TWIN CITIES AND TWIN PORTS. THIS CONVECTIVE BAND
IS EXPECTED TO BE ROUGHLY ALIGNED WITH THE MEAN FLOW VECTORS
(WITHIN 10 DEGREES OR SO)...WHICH SHOULD LEAD TO EXTENDED PERIODS
OF TRAINING ECHOES IN SOME LOCATIONS. THE STRUCTURE OF THE FORCING
RELATIVE TO THE MEAN FLOW WOULD SUPPORT A FLASH FLOOD THREAT IN
GENERAL...HOWEVER THE ATMOSPHERIC MOISTURE CONTENT AND LOW-LEVEL
MOISTURE FLUX WILL BE ANOMALOUSLY HIGH AS WELL. FOR A THREE WEEK
PERIOD CENTERED ON TODAY...MODEL FORECAST PWATS AND INTEGRATED
VAPOR TRANSPORT RISE TO THE 99TH PERCENTILE IN THE 00-06Z TIME
FRAME ACROSS THE OUTLINED DISCUSSION PERIOD.

CONSIDERING THESE FACTORS...FLASH FLOODING APPEARS LIKELY ACROSS
PORTIONS OF MINNESOTA AND NORTHWEST WISCONSIN. HI-RES MODELS
INDICATE HOURLY RAIN RATES PEAKING UP TO 2 IN/HR AND GIVEN THE
ENVIRONMENT...THAT SEEMS REASONABLE. THE MOST IMMEDIATE CONCERN
MAY BE FROM NEAR WORTHINGTON MN...TO NEAR NEW ULM MN...TO THE
NORTHWEST SIDE OF THE TWIN CITIES METRO AREA...WHICH HAS RECEIVED
THE HEAVIEST RAINFALL THUS FAR FROM THE INITIAL BURST OF
CONVECTION. HOWEVER...THE THREAT OF FLASH FLOODING SHOULD EXPAND
TO A LARGER AREA AS SPATIAL COVERAGE OF CONVECTION INCREASES AND
BECOMES MORE CONTINUOUS.

LAMERS

ATTN...WFO...DLH...FSD...MPX...MQT...

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

LAT...LON   48169030 48128983 47948941 47358942 46938969
            46618993 46079067 45709112 45299167 44839233
            44379298 43959349 43659409 43549451 43539472
            43529549 43779618 43929632 44259632 44909579
            45519510 46119434 46709359 47369253 47879124