MESOSCALE PRECIPITATION DISCUSSION 0811
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1131 PM EDT THU SEP 14 2017

AREAS AFFECTED...NORTH-CENTRAL AND NORTHEAST MINNESOTA

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

VALID 150330Z - 150830Z

SUMMARY...ELEVATED THUNDERSTORMS MAY TRAIN SUFFICIENTLY OVER
LOCALIZED AREAS TO LEAD TO FLASH FLOODING THROUGH 09Z OR 4AM CDT.
THE STORMS IN GENERAL SHOULD DRIFT OR BUILD TO THE SOUTH OR
SOUTHWEST INTO A MORE UNSTABLE AIR MASS.

DISCUSSION...A BAND OF ELEVATED CONVECTION HAS DEVELOPED IN A
WSW-ENE ORIENTED FASHION NEAR THE IRON RANGE OF THE MINNESOTA
ARROWHEAD AND JUST NORTH OF THE BRAINERD LAKES REGION. AS OF
03Z...THE HEAVIEST RAINFALL HAD OCCURRED IMMEDIATELY SOUTH OF
EVELETH MN PER KDLH DUAL POL AND MRMS ESTIMATES...ON THE ORDER OF
3-5 INCHES. A SPOTTER REPORT OF 5 INCHES IN THE SAME AREA CONFIRMS
THESE ESTIMATES AS ACCURATELY DEPICTING ONGOING RATES AND STORM
TOTAL RAINFALL.

THE CONVECTION WAS OCCURRING NORTH OF A SURFACE FRONT/TROUGH...AND
APPEARED TO BE ROOTED AROUND 850MB AS IT COINCIDED WITH AN 850MB
FRONTOGENESIS MAXIMUM. THE BAND OF CONVECTION AS A WHOLE WAS
EXHIBITING A SLIGHT SOUTHWARD DRIFT WITH TIME...WHICH IS NOT
CAPTURED WELL BY CURRENT HI-RES MODEL GUIDANCE. IN
GENERAL...HI-RES MODELS WANT TO LIFT THE CONVECTION TO THE NORTH
AND DIMINISH IT WHICH SEEMS IN CONFLICT WITH THE MESOSCALE SETUP.
STORMS ARE CURRENTLY SITUATED ON THE NOSE OF AN 850MB MOISTURE
TRANSPORT MAXIMUM AND THE HIGHEST INSTABILITY IS SOUTH AND
SOUTHWEST OF A COMPOSITE OUTFLOW BOUNDARY AND LAKE-ENHANCED FRONT.
FROM A PATTERN RECOGNITION STANDPOINT...ONE WOULD EXPECT THE
STORMS TO SHOW A GRADUAL PROPAGATION INTO THE REGION OF HIGHER
INSTABILITY...AND THAT IS EXACTLY WHAT THEY ARE DOING.

THEREFORE...THE ONGOING CONVECTION MAY PROVE MORE RESILIENT THAN
HI-RES GUIDANCE WOULD SUGGEST. HOWEVER...BOTH RAP AND GLOBAL MODEL
GUIDANCE SHOWS A CONTINUED DIMINISHING TREND OF INSTABILITY
(MUCAPE AS WELL AS CAPE FOR LOWER-LEVEL PARCELS) AND THE MAGNITUDE
OF LOW-LEVEL MOISTURE TRANSPORT. THIS SHOULD LEAD TO A WANING OF
CONVECTION CLOSER TO DAYBREAK.

UNTIL THAT OCCURS...CONVECTION CONTINUES TO BE FAVORABLY ORIENTED
(ROUGHLY PARALLEL) RELATIVE TO THE MEAN FLOW TO ENABLE TRAINING
CELLS AND RAIN RATES PEAKING IN THE 1-2 IN/HR RANGE. THE AREA OF
GREATEST CONCERN WOULD BE CENTRAL OR SOUTH-CENTRAL ST. LOUIS
COUNTY JUST SOUTH OF THE IRON RANGE COMMUNITIES WHERE THE HEAVIEST
RAIN HAS ALREADY FALLEN. RADAR SHOWS CONTINUED CELL GROWTH
UPSTREAM SO ADDITIONAL RAINFALL APPEARS LIKELY...AND THIS COULD
LEAD TO ADDITIONAL FLOODING OR EXACERBATE ONGOING FLOODING. THIS
AREA OF CONCERN ALSO POSSIBLY EXTENDS WSW/SW TOWARD GRAND RAPIDS
AND NORTHERN AITKIN COUNTY AS THE AXIS OF CONVECTION TENDS TO
DRIFT AND BUILD IN THAT DIRECTION OVER TIME.

LAMERS

ATTN...WFO...DLH...

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

LAT...LON   48029068 47849003 47489047 47029109 46689206
            46459349 46539469 47259445 47779314