MESOSCALE PRECIPITATION DISCUSSION 0374
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
355 PM EDT THU JUN 28 2018

AREAS AFFECTED...NORTHERN MN

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

VALID 282000Z - 290200Z

SUMMARY...CONVECTION TRAINING IN ENVIRONMENT WITH DEEPENING
MOISTURE ALONG A FRONTAL BOUNDARY COULD POSE A FLASH FLOOD THREAT
INTO THE EARLY EVENING.

DISCUSSION...THE GOES-16 CLEAN IR LOOP SHOWED AN EXPANDING AREA OF
COOLING TOPS ACROSS A PORTION OF NORTHERN MN THIS AFTERNOON. THE
SCATTERED CONVECTION WAS DEVELOPING IN AN AREA OF 1000-2000 J/KG
OF MUCAPE NEAR AND NORTH OF A FRONTAL BOUNDARY EXTENDING FROM EAST
CENTRAL ND INTO NORTHERN WI...AHEAD OF SHORT WAVE ENERGY IN A
QUASI ZONAL MID LEVEL FLOW.

THE CONVECTION WAS FORMING ON THE NORTHERN EDGE OF A PRECIPITABLE
WATER GRADIENT OVER CENTRAL AND NORTHERN MN...WITH THE MOST RECENT
RAP ANALYSIS SHOWING VALUES APPROACHING 1.50 INCHES NEAR THE
FRONT. IN THIS ENVIRONMENT...THE KDLH RADAR SHOWED HOURLY RAINFALL
RATES BETWEEN 1.50 AND 2.00 INCHES OVER NORTHERN AITKIN COUNTY.
HOWEVER...BASED ON THE KDLH HCA PRODUCT... THE RADAR PRESENTATION
AND STEEP LAPSE RATES NOTED ON RAP MODEL SOUNDING HERE... IT IS
LIKELY THAT THERE IS SOME HAIL CONTAMINATION OF THE HOURLY
RAINFALL RATES. THAT HAVING BEEN SAID...WFO DLH REPORTED SOME OF
THE CONVECTION PRODUCED RAINFALL AMOUNTS BETWEEN 1.50 AND 3.00
INCHES IN LESS 30 MINUTES.

THE 12Z WRF-ARW APPEARED TO HAVE THE BEST HANDLE ON THE PLACEMENT
OF THE CONVECTION (THE MOST RECENT HRRR WAS TOO FAR SOUTH... AND
THE MOST RECENT EXPERIMENTAL HRRR DID NOT HAVE MUCH CONVECTION
WHERE IT IS OCCURRING). THIS MODEL SHOWED A GENERAL INCREASE IN
THE CONVECTIVE COVERAGE ALONG THE FRONT THROUGH 29/00Z...AND AS
THE 850-300 MB MEAN FLOW BECOMES BETTER ALIGNED WITH THE
PROPAGATION VECTORS...THE THREAT FOR FLASH FLOODING INCREASES.

THE 12Z WRF-ARW SHOWED LOCAL 2.00-3.00 INCH RAINFALL AMOUNTS WHERE
THE CONVECTION TRAINING NEAR THE FRONT...AND BASED ON THE
INFORMATION SUPPLIED BY WFO DLH...THESE AMOUNTS SEEM PLAUSIBLE.
THREE HOUR FLASH FLOOD GUIDANCE VALUES ARE GENERALLY ABOVE 2.00
INCHES ALONG THE FRONT...SO THIS COULD BE A LIMITING FACTOR FOR
FLASH FLOODING. BASED ON THE MOISTURE IN PLACE...AND HOURLY
RAINFALL RATES ON RADAR AND IN REPORTS...FLASH FLOODING IS
CONSIDERED POSSIBLE INTO EARLY EVENING.

HAYES

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

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

LAT...LON   48179607 48109333 47249157 46779257 47119522
            47459655