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000
FXUS63 KGRR 181643
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1243 PM EDT SAT MAY 18 2013

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 330 AM EDT SAT MAY 18 2013

FAIR AND MILD WEATHER IS ANTICIPATED THIS WEEKEND. A LOW PRESSURE
SYSTEM OVER THE UPPER MIDWEST WILL BRING A PERIOD OF UNSETTLED
WEATHER WITH OCCASIONAL ROUNDS OF RAIN AND THUNDERSTORMS FROM MONDAY
THROUGH WEDNESDAY. FAIR AND COOLER WEATHER IS EXPECTED LATE IN THE
WEEK.

&&

.UPDATE...
ISSUED AT 1100 AM EDT SAT MAY 18 2013

SATELLITE TRENDS SHOW THE CLOUD COVER DECREASING ACROSS THE REGION
AT THIS TIME. FORECAST SOUNDINGS KEEP THE ATMOSPHERIC RELATIVELY
HUMIDITY LOW THROUGH THE AFTERNOON. CI IN WRN WI FROM THOSE STORMS
COULD ARRIVE IN SOUTHWEST MI LATER IN THE DAY. FOR THE MOST PART
MUCH OF THE REGION WILL SEEN MOSTLY SUNNY SKIES.  AS A RESULT WILL
FEATURE MORE IN THE WAY OF SUNSHINE FOR THE REMAINDER OF THE
AFTERNOON. THE LAKE BREEZE AROUND SOUTH HAVEN COULD TOUCH OFF A
BRIEF RAIN SHOWER AS THERE IS SOME VERY THIN CAPE FOR LIFTED
AFTERNOON PARCELS. THIS POTENTIAL THOUGH IS SMALL.

&&

.SHORT TERM...(TODAY THROUGH MONDAY AFTERNOON)
ISSUED AT 330 AM EDT SAT MAY 18 2013

OUR PRIMARY SHORT TERM FCST CHALLENGE IS TO DETERMINE PROBABILITIES
FOR SHOWERS AND STORMS MAINLY FOR MONDAY.

FAIR AND MILD WX IS ANTICIPATED THROUGH THE WEEKEND WITH MAX TEMPS
WELL INTO THE 70S TO NEAR 80 DEGREES TODAY AND A FEW DEGREES WARMER
THAN THAT FOR SUNDAY.

THERE IS JUST SLIGHT CHC OF A SHOWER THIS AFTN SW OF KGRR WHERE SOME
INSTABILITY WILL DEVELOP. AN OVERALL CONSENSUS OF 00Z SHORT RANGE
GUIDANCE SUGGESTS PROBABILITIES FOR A SHOWER THERE WOULD BE REALLY
LOW.

THE WX PATTERN WILL BECOME MORE UNSETTLED AND ACTIVE BEGINNING
MONDAY... PARTICULARLY IN THE AFTERNOON. WE BOOSTED MAX TEMPS UP BY
SEVERAL DEGREES FOR MONDAY WITH THE EXPECTATION OF A FAIR AMOUNT OF
SUN AND SOUTHERLY FLOW WAA BY THEN.

THIS WILL LEAD TO INCREASING INSTABILITY WITH POTENTIAL FOR SB CAPES
TO REACH 2000-3000 J/KG MONDAY AFTERNOON AND AS THE UPPER RIDGE AXIS
SHIFTS EAST AND SOME PVA BEGINS TO MOVE IN FROM THE SW LATE IN THE
DAY. MOISTURE WILL ALSO BE ON THE INCREASE IN THE SOUTHERLY FLOW WAA
REGIME ALLOWING DEW POINT VALUES TO CLIMB INTO THE 60S. SO THE
THREAT FOR SHOWERS AND STORMS WILL BEGIN TO RAMP UP BEGINNING MONDAY
AFTERNOON.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 330 AM EDT SAT MAY 18 2013

LONG TERM PERIOD LOOKS TO BE A WET TIME FRAME...AS AN UPPER LOW IN
THE NORTHERN PLAINS SLOWLY WORKS INTO AND THROUGH THE REGION DURING
THIS TIME FRAME. IN FACT...YESTERDAY EVENING/S 7 DAY EXPERIMENTAL
PRECIPITATION PRODUCT FROM WPC WAS INDICATING 1 TO AROUND 2 INCHES
OF RAINFALL ACROSS THE SOUTHWEST QUARTER OF LOWER MI.

A WARM FRONTAL BOUNDARY WILL BE NEARBY OR DRAPED ACROSS THE FORECAST
AREA FOR MUCH OF THE MONDAY NIGHT THROUGH WEDNESDAY TIME FRAME.
DURING THIS TIME WE HAVE LIKELY CHANCES (60/70 PCT) FOR
SHOWERS/STORMS FOR MOST OF THE FORECAST AREA.

A DEEP SOUTHERLY FLOW WILL BE IN PLACE EMANATING FROM THE GULF
COAST...WHICH IS SOMETHING WE HAVE LACKED THIS MONTH. PRECIPITABLE
WATER VALUES WILL BE ON THE ORDER OF AN INCH TO AN INCH AND A HALF
INTO MID WEEK.

DIFFICULT TO NAIL DOWN ANY SPECIFIC SEVERE THREAT TIME FRAMES...BUT
MONDAY AFTERNOON AND EVENING AND AGAIN ON WEDNESDAY MAY BE TIMES TO
WATCH. HEATING TO AID IN INSTABILITY WILL BE THE DIFFICULT VARIABLE
TO PINPOINT GIVEN THE AMOUNT OF CLOUDS AND PRECIP AROUND. IF WE CAN
HEAT DURING THE DAYLIGHT HOURS THOUGH INSTABILITY SHOULD BUILD
READILY.

LATE IN THE WEEK THE LOW WILL SLIDE EAST FINALLY AND HIGH PRESSURE
WILL BEGIN TO BUILD IN FROM THE NORTH. HAVE A DRY FORECAST TOWARD
WEEKS END.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1241 PM EDT SAT MAY 18 2013

VFR CIGS EXPECTED THROUGH THE PERIOD. HOWEVER AS DEWPOINTS
INCREASE LATE TONIGHT WE MAY SEE SOME FOG DEVELOP WITH VSBYS
FALLING TO 4-5SM BR PRIOR TO SUNRISE.

&&

.MARINE...
ISSUED AT 1100 AM EDT SAT MAY 18 2013

WINDS AND WAVES WILL REMAIN LOW GIVEN THE WEAK PRESSURE GRADIENT
AND GENERAL OFFSHORE COMPONENT TO THE WIND INTO SUNDAY


&&

.FIRE WEATHER...
ISSUED AT 330 AM EDT SAT MAY 18 2013

FIRE WEATHER CONCERNS ARE FAIRLY MINIMAL DUE TO INCREASING DEW POINT
VALUES AND RELATIVE HUMIDITY VALUES THIS WEEKEND AND FAIRLY LOW WIND
SPEEDS MAINLY UNDER 15 MPH. SEVERAL ROUNDS OF RAIN AND STORMS ARE
EXPECTED MONDAY THROUGH WEDNESDAY.

&&

.HYDROLOGY...
ISSUED AT 330 AM EDT SAT MAY 18 2013

SEVERAL ROUNDS OF SHOWERS AND STORMS ARE EXPECTED MONDAY THROUGH
WEDNESDAY WITH TOTAL RAINFALL AMOUNTS ON AVERAGE IN THAT TIME FRAME
OF AROUND AN INCH TO INCH AND A HALF POSSIBLE WITH LOCALLY HIGHER
AMOUNTS WITH HEAVIER STORMS.

&&

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

$$

UPDATE...MJS
SYNOPSIS...LAURENS
SHORT TERM...LAURENS
LONG TERM...DUKE
AVIATION...93
FIRE WEATHER...LAURENS
HYDROLOGY...LAURENS
MARINE...MJS