Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 190006
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
806 PM EDT MON AUG 18 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 345 PM EDT MON AUG 18 2014

THE REGION IS HEADING INTO A WETTER PATTERN THE NEXT WEEK WITH THE
FIRST CHANCES FOR RAINFALL COMING UP TONIGHT INTO TUESDAY. ANOTHER
TIME FRAME OF PERIODS OF SHOWERS AND STORMS WILL COME FROM THURSDAY
THROUGH SUNDAY WITH A FRONTAL BOUNDARY NEAR THE AREA. SHOWERS AND
STORMS WILL BECOME MORE NUMEROUS LATE TONIGHT AND ESPECIALLY ON
TUESDAY AS AN AREA OF LOW PRESSURE MOVES INTO THE GREAT LAKES. A
GRADUAL WARMING TREND WILL BE SEEN THROUGH THE WEEK AND INTO NEXT
WEEKEND. HIGHS AROUND 80 AT THE START OF THE WEEK WILL WARM TO THE
MIDDLE 80S BY NEXT WEEKEND.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 345 PM EDT MON AUG 18 2014

MAIN FOCUS IN THE SHORT TERM IS ON THE CHANCES FOR SHOWERS/STORMS
TONIGHT INTO TUESDAY. PRECIPITATION WILL BE DRIVEN BY AN TROUGH
DIGGING INTO THE GREAT LAKES REGION FROM THE NORTHERN PLAINS.
MOISTURE SURGES INTO REGION THIS EVENING WITH THE HRRR TRYING TO
FLOAT CONVECTION FROM WISCONSIN OVER LAKE MICHIGAN IN THE 00Z-06Z
TIME FRAME. THINKING OUR BEST CHANCES FOR PRECIP THOUGH WILL BE
OVERNIGHT INTO TUESDAY WHEN ALL OF THE SHORT TERM MODELS FOCUS A LLJ
ON THE AREA. NOT EXPECTING SEVERE WEATHER GIVEN THE TIMING OF THE
PRECIP AND THE FACT THAT INSTABILITY WILL LIKELY BE LIMITED SOMEWHAT
BY OVERNIGHT PRECIP. 0-6KM SHEAR IS SUB 30 KNOTS BOTH TONIGHT AND
TUESDAY FOR THE MOST PART AS WELL. SOME LOCALLY HEAVY RAIN IS
POSSIBLE.

SHOWERS AND STORMS WILL BECOME MORE SCATTERED TUESDAY NIGHT THROUGH
WEDNESDAY AS THE SYSTEM FILLS OVERHEAD. PLENTY OF MOISTURE LINGERS
HOWEVER SO SCATTERED SHOWERS AND A FEW STORMS WILL REMAIN POSSIBLE
BOTH PERIODS. WEDNESDAY NIGHT KEPT THE DRY FORECAST GOING AS SURFACE
RIDGING BEGINS TO TAKE OVER AND THE UPPER LOW SLIDES SLIGHTLY OFF TO
THE EAST.

.LONG TERM...(THURSDAY THROUGH MONDAY)
ISSUED AT 345 PM EDT MON AUG 18 2014

IT LOOKS TO BE A RATHER ACTIVE EXTENDED PERIOD. THE MAIN FOCUS WILL
BE ON OPPORTUNITIES FOR SHOWERS AND STORMS THURSDAY THROUGH SUNDAY
NIGHT. BY 12Z THURSDAY...A ULJ CORE WILL BE MOVING ACROSS THE LOWER
PENINSULA AS UPPER LEVEL RIDGING BUILDINGS IN. IN CONCERT WITH THIS
WILL BE A FAIRLY STRONG H850 TEMP GRADIENT (6-8C) MOVING INTO SW
LOWER MICHIGAN AND INCREASING MID LEVEL MOISTURE. LIGHT EASTERLY
WIND CONV AT THE SFC (AS SHOWN BY THE ECMWF) MAY HELP ENHANCE
CONVECTIVE DEVELOPMENT PARTICULARLY ACROSS THE LAKESHORE REGION AND
GENERALLY ALONG AND WEST OF US 131 FOR THURSDAY EVENING INTO FRIDAY.

WHILE MODEL QPF IS NOT HIGH...INCREASING PW VALUES TO 2" OR SO ON
FRIDAY IS A CAUSE FOR CONCERN WITH ANY STORMS THAT DO DEVELOP.
LOCALLY HEAVY DOWNPOURS WOULD BE A POSSIBILITY THURSDAY NIGHT AND
FRIDAY ON THE WING OF WARM AIR ADVECTION. IF H500 HEIGHTS CONTINUE
TO BUILD STRONG ENOUGH BY SATURDAY (LIKE THE ECMWF SHOWS) THEN
PERHAPS WE WILL BE STABLE ENOUGH TO MITIGATE ANY SIGNIFICANT
CONVECTION. ON SATURDAY...GFS BUFKIT SOUNDINGS INDICATE SIGNIFICANT
SFC BASED CAPE UPWARDS OF 2000 J/KG AND LI VALUES OF -4 TO -6 BUT
WEAK SHEAR AND WEAK MID LEVEL LAPSE RATES. ECMWF WOULD SUGGEST A
LACK OF TRIGGER AND MORE STABLE CONDITIONS. OUR POP GRIDS ARE
CURRENTLY MIDDLE OF THE ROAD CHC CATEGORY FOR SATURDAY...REFLECTING
A LACK OF MODEL BULLISHNESS ON PRECIP.

UPPER LEVEL RIDGING MAY FLATTEN LATER SUNDAY AND AN ASSOCIATED
COLD FRONT COULD ARRIVE BY SUNDAY NIGHT. THE TIMING OF THIS IS
ACTUALLY AGREED UPON BY THE GFS AND ECMWF (00Z-06Z MON)...WHEREAS
THE GEM CLEARS THE FRONT 24 HOURS EARLIER. CURRENTLY AM PREFERRING A
SLOWER BREAKDOWN OF THE H500 RIDGE AND THUS A SLOWER FROPA AS SHOWN
BY THE GFS AND ECMWF. THERE WILL LIKELY BE SUFFICIENT DEEP LAYER
SHEAR BY THAT TIME TO PROVIDE A MORE CONDUCIVE ENVIRONMENT TO
STRONGER STORMS.

IN TERMS OF TEMPS AND HUMIDITY...BOTH WILL BE GOING UP BY THE
WEEKEND. DEW POINTS SHOULD CLIMB TO AROUND 70 AND HIGHS IN THE MID
80S MAY BE CONSERVATIVE FOR SATURDAY AND SUNDAY DEPENDING ON MUCH
CLOUD COVER HANGS AROUND. WOULDN`T BE SURPRISED IF HIGHS NOTCH UP
SEVERAL DEGREES WARMER WITH H850 TEMPS OF 20C KNOCKING ON THE DOOR
SATURDAY EVENING. COOLER WEATHER MOVES IN FOR EARLY NEXT WEEK BEHIND
THE FRONT.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 805 PM EDT MON AUG 18 2014

VFR CONDITIONS ARE EXPECTED TO DETERIORATE TO MVFR AROUND 05Z OR
SO. AS OF THIS WRITING...THE LEADING EDGE OF A LINE SHOWERS AND
WEAKENING THUNDERSTORMS OVER CENTRAL WISCONSIN IS MAKING ITS WAY
ACROSS NORTHERN LAKE MICHIGAN. THESE STORMS ARE EXPECTED TO
CONTINUE TO COLLAPSE AS THEY MOVE ESE TOWARD KLDM.

HIGHER IMPACTS ARE EXPECTED AFTER ROUGHLY 10Z AND CONTINUING
THROUGH THE MORNING FOR ALL TAF SITES. MORE WIDESPREAD SHOWERS AND
STORMS WILL MOVE IN AND WINDS WILL INCREASE TO AROUND 10-12 KTS
OUT OF THE SOUTH. SCATTERED IFR CERTAINLY A POSSIBILITY UNDER
HEAVIER PRECIPITATION. CONFIDENCE IN IFR IS AVERAGE AND FUTURE
AMENDMENTS AND ISSUANCES MAY LOWER VSBYS/CIGS. CONDITIONS WILL
GRADUALLY IMPROVE AFTER 18Z TUESDAY.

&&

.MARINE...
ISSUED AT 345 PM EDT MON AUG 18 2014

MAIN IMPACT WEATHER FOR WINDS/WAVES WILL COME ON TUESDAY. SOUTH
WINDS WILL INCREASE TONIGHT INTO TUESDAY WITH WAVES BECOMING
BORDERLINE FOR BEACH HAZARDS FROM HOLLAND NORTHWARD UP THE SHORE.
EXPECTING WAVES TO PUSH INTO THE 2 TO 4 FOOT RANGE ON TUESDAY NORTH
OF HOLLAND OR SO. THE WINDS SLACKEN OFF AS WE HEAD INTO WEDNESDAY AS
THE GRADIENT BECOMES BAGGY...SO THE WAVES WILL SUBSIDE FOR MID WEEK.


&&

.HYDROLOGY...
ISSUED AT 139 PM EDT MON AUG 18 2014

RIVERS ARE RUNNING A LITTLE ABOVE NORMAL... BUT ARE STILL FAR BELOW
BANK FULL. PRECIPITATION THIS EVENING THROUGH WEDNESDAY IS EXPECTED
TO TOTAL AROUND HALF AN INCH. THIS SHOULD LEAD TO SLOW RISES ON AREA
RIVERS WITH PEAK LEVELS WELL BELOW FLOOD STAGE OCCURRING BY THE END
OF THE WEEK. LOCALLY HEAVY RAINFALL IS POSSIBLE AND COULD LEAD TO
BRIEFLY HIGHER FLOWS.

LOOKING AHEAD...IT APPEARS TO BE A RATHER ACTIVE SECOND HALF OF
AUGUST WHICH MAY HELP BRING MANY RIVERS TO ABOVE NORMAL FLOWS.
WITH AN UPPER LEVEL RIDGE DEVELOPING TO THE SOUTH OF THE GREAT
LAKES OVER THE NEXT WEEK OR SO...IT WILL PLACE MICHIGAN IN AN
ACTIVE WEATHER PATTERN WITH NUMEROUS OPPORTUNITIES FOR RAIN.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...NONE.
&&

$$

SYNOPSIS...DUKE
SHORT TERM...DUKE
LONG TERM...HOVING
AVIATION...EBW
HYDROLOGY...63
MARINE...DUKE






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