MESOSCALE PRECIPITATION DISCUSSION 0279
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1018 PM EDT SAT JUN 09 2018

AREAS AFFECTED...ERN IA...NWRN IL...SWRN WI...FAR SERN MN

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

VALID 100217Z - 100800Z

SUMMARY...CLUSTERS OF THUNDERSTORMS APPEAR LIKELY TO SPREAD FROM
NORTHEAST IOWA INTO SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS
TONIGHT...WITH A THREAT OF FLASH FLOODING. IN THE STRONGER AND
MORE PERSISTENT THUNDERSTORMS...RAIN RATES MAY OCCASIONALLY PEAK
IN THE 2-3 IN/HR RANGE WITH LOCALIZED TOTALS EXCEEDING 4 INCHES.

DISCUSSION...A LARGE CONVECTIVE CLUSTER CONTINUED TO MAKE GRADUAL
PROGRESS TO THE EAST SOUTHEAST AHEAD OF A PROMINENT MCV AND +PV
ANOMALY OVER SOUTH-CENTRAL MINNESOTA. THE MORE VIGOROUS UPDRAFTS
(INDICATED BY HIGHER REFLECTIVITY, COOLER CLOUD TOPS, AND HIGHER
AMOUNTS OF TOTAL LIGHTNING) HAVE BEEN GRADUALLY OCCURRING FURTHER
SOUTH AS CONVECTION BUILDS INTO THE RESERVOIR OF STRONG
INSTABILITY SITUATED TO THE SOUTH AND SOUTHWEST ACROSS MUCH OF
IOWA. THIS GRADUAL PROCESS SHOULD CONTINUE OVER THE NEXT SEVERAL
HOURS AND THE HEAVIEST RAIN RATES ARE LIKELY TO BE CONTAINED
WITHIN THE STRONGEST CONVECTIVE CLUSTERS.

KDMX AND KDVN RADAR VWPS SHOW A SLOW VEERING OF THE 925-850MB
LAYER WINDS IN THE PAST COUPLE HOURS...WHICH IS PROJECTED BY THE
RAP TO CONTINUE. BY 05Z...THE RAP SHOWS BROAD AND MOIST LOW-LEVEL
INFLOW FROM THE WSW ACROSS MUCH OF SOUTHERN AND CENTRAL IOWA...AND
THE NOSE OF THIS LOW-LEVEL INFLOW NEAR A SURFACE QUASI-STATIONARY
FRONT STRETCHING FROM NEAR WATERLOO IA TO NEAR STERLING IL. THE
MOST PROGRESSIVE PORTIONS OF THE CURRENT CONVECTIVE CLUSTER ARE
CURRENTLY IN SOUTHWEST WISCONSIN AND ARE INCREASINGLY ENCOUNTERING
A MORE STABLE AIR MASS AS THEY PUSH TO THE EAST. THE PROCESS OF
THE NORTHERN-MOST LINE SEGMENTS PUSHING EAST AND DECAYING MAY
EVENTUALLY ORIENT THE MORE VIGOROUS CONVECTION ALONG AN AXIS
ROUGHLY PARALLEL TO THE CURRENT STATIONARY FRONT AND LOW-LEVEL
INSTABILITY GRADIENT. GIVEN THE INCREASINGLY SMALL ANGLE OF THE
LOW-LEVEL INFLOW RELATIVE TO THAT CONVECTIVE ORIENTATION...THE
POTENTIAL FOR TRAINING CONVECTION SHOULD INCREASE THIS
EVENING...WITH THE GREATEST THREAT ALONG AND JUST NORTH OF THE
INTERSTATE 80 CORRIDOR.

THIS CONVECTION SHOULD BE TAPPING INTO AN ENVIRONMENT WITH STRONG
INSTABILITY (MLCAPE AROUND 1500-2000 J/KG) AND DEEP MOISTURE
(PWATS AROUND 1.7 INCHES) WHICH WILL BE SUPPORTIVE OF VERY HEAVY
RAINFALL. RAIN RATES IN THE STRONGER AND LARGER CONVECTIVE
CLUSTERS SHOULD PEAK IN THE 2-3 IN/HR RANGE...AND GIVEN THE
POTENTIAL FOR TRAINING SOME LOCALIZED RAINFALL TOTALS IN EXCESS OF
4 INCHES APPEAR LIKELY. THIS SHOULD LEAD TO AREAS OF FLASH
FLOODING INTO THE LATE EVENING AND EARLY OVERNIGHT HOURS. IF
STRONG CONVECTION CAN GET ANCHORED ALONG THE FRONT IN A PARTICULAR
AREA FOR A FEW HOURS...MORE SIGNIFICANT FLASH FLOODING WOULD BE
POSSIBLE.

FURTHER NORTH...MODELS INDICATE THAT THE WARM CONVEYOR BELT SHOULD
ASCEND NORTH OF THE SURFACE FRONT AND QUICKLY BEND BACK TO THE
WEST-NORTHWEST TOWARD THE MCV (WITH A RELATIVELY DEEP CIRCULATION)
OVER SC MN. THIS SHOULD SUSTAIN A RIBBON OF FOCUSED LOW-MID LEVEL
MOISTURE TRANSPORT COINCIDENT WITH RELATIVELY HIGH PWATS FURTHER
NORTH...FROM THE EASTERN MN-IA BORDER REGION INTO SOUTHWEST
WISCONSIN. INSTABILITY IS UNLIKELY TO SUBSTANTIALLY GROW IN THESE
AREAS...BUT AT LEAST SEVERAL HUNDRED J/KG OF MUCAPE SHOULD BE
MAINTAINED. MODELS SHOW RAIN BEING SUSTAINED IN THIS REGION WITH
SOME SHALLOW CONVECTION EVEN INITIATING OVERNIGHT...AND BEING
CHANNELED OVER A NARROW CORRIDOR IN THE WARM CONVEYOR BELT. GIVEN
THE HEAVY RAIN THAT HAS ALREADY OCCURRED IN PORTIONS OF THIS
REGION...SOME FLOODING CANNOT BE RULED OUT...BUT WOULD HAVE TO
ORIGINATE FROM LONGER-DURATION RAINFALL.

LAMERS

ATTN...WFO...ARX...DMX...DVN...ILX...LOT...MKX...MPX...

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

LAT...LON   44049124 43558971 42768859 41748862 40948969
            41109100 41609229 42469351 43879308