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000
FXUS63 KGRR 182316
AFDGRR

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

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 311 PM EDT SAT MAY 18 2013

LOW PRESSURE DEVELOPING IN COLORADO WILL TRACK SLOWLY EAST OVER
THE NEXT COUPLE OF DAYS. SOUTHEAST WINDS AHEAD OF THIS SYSTEM WILL
DRAW WARMER AND INCREASINGLY MOIST AIR INTO THE GREAT LAKES
REGION.  AS A RESULT NUMEROUS SHOWERS AND THUNDERSTORMS ARE FORECAST
TO ARRIVE BY MONDAY. THIS UNSETTLED WEATHER PATTERN WILL PERSIST
INTO THE MIDDLE PART OF THE WEEK.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 311 PM EDT SAT MAY 18 2013

THE MAIN CHALLENGE IN THE SHORT TERM DEALS WITH THUNDERSTORM
AND SEVERE WEATHER POTENTIAL ON MONDAY.

THE COMBINATION OF UPPER LEVEL DIVERGENCE...INCREASING DEEP LAYER
SHEAR...ARRIVAL OF GULF MOISTURE AND BUILDING CAPE SUPPORTS AN
INCREASED RISK FOR ORGANIZED CONVECTION MONDAY INTO MONDAY NIGHT.
MID LEVEL LAPSE RATES STEEPEN TO 7.5 TO 8 DEG C/KM.  A 20 TO 30
KNOT LOW LEVEL JET SETS UP JUST SOUTH OF THE MI BORDER MONDAY AND
STAYS THERE THROUGH MON NIGHT. THIS SHOULD FOCUS THE CONVECTION IN
LOWER MI THROUGH THAT PERIOD. THE SURFACE WARM FRONT WILL BE
LIFTING THROUGH AT THAT TIME WHICH WILL ALSO HELP TO PROVIDE A
FOCUS FOR THE CONVECTION. MODELS ARE IN DECENT AGREEMENT ON THIS
SCENARIO. SO WILL FEATURE NUMEROUS SHOWERS AND THUNDERSTORMS FOR
THIS PERIOD. I SUSPECT WE WILL SEE MORE THAN ON ROUND OF
CONVECTION IN THIS TIME FRAME. RAINFALL COULD BE HEAVY AND REPEAT
OVER THE SAME REGION GIVEN THE FRONTAL ZONE WILL BECOME NEARLY
PARALLEL TO THE MID TO UPPER LEVEL FLOW.

I CONSIDERED ADDING A SMALL CHANCE FOR A STORM SUNDAY AFTERNOON
CLOSER TO THE LAKESHORE. A LAKE BREEZE WILL TRY TO DEVELOP. WHILE
SOME INSTABILITY WILL BE PRESENT...THE MOISTURE IS STILL SOMEWHAT
LIMITED. THERE IS A WEAK CAP/WARM LAYER NOTED IN FORECAST
SOUNDINGS UP AROUND 650 MB AS WELL. SO WILL KEEP IT DRY. IT WILL
BE A WARM DAY WITH MOST LOCATIONS TOPPING OUT IN THE LOW TO MID
80S. I DID WARM TEMPERATURES UP ALONG THE SHORELINE AS THE FLOW
WILL FEATURE AN OFFSHORE COMPONENT TO START THE DAY.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 311 PM EDT SAT MAY 18 2013

AN ACTIVE WEATHER PATTERN WILL BE UNDERWAY TUESDAY AS A SLOW MOVING
LOW MIGRATES FROM THE PLAINS EASTWARD. A STATIONARY FRONT EXTENDING
EASTWARD FROM THE LOW WILL BE A FOCUS FOR SHOWERS AND THUNDERSTORMS
THROUGH WEDNESDAY. PWAT VALUES NEAR 1.75 INCHES SUGGESTS A HEAVY
RAIN POTENTIAL. MODELS CERTAINLY SHOW QUITE A BIT OF INSTABILITY
WITH LI/S NEAR -8C AND MLCAPE AROUND 2500 J/KG SHEAR VALUES IN THE
45-50KT RANGE POINT TOWARD A SVR POTENTIAL TOO. NO ONE TIME PERIOD
LOOKS MORE FAVORABLE THAN ANOTHER. OF COURSE AFTERNOON INSTABILITY
MAY BE KEY. HOWEVER WITH THE FRONT NEARBY...ELEVATED STORMS COULD BE
POSSIBLE TOO AND BE LESS INFLUENCED BY DAYTIME HEATING. THE LLJ
ISN/T ALL THAT IMPRESSIVE WITH THE SYSTEM BUT MOISTURE TRANSPORT
LOOKS ADEQUATE FOR STORM INITIATION.

AS THE LOW MOVES OVERHEAD WEDNESDAY NIGHT AND THURSDAY WE SHOULD SEE
THUNDERSTORM CHANCES DECREASE IN FAVOR OF SHOWERS. A DRYING TREND
WILL GREET THE BEGINNING OF THE MEMORIAL DAY WEEKEND RESULTING IN PT
CLDY SKIES WITH HIGHS IN THE MID 60S AND LOWS IN THE MID 40S.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 716 PM EDT SAT MAY 18 2013

SOME MVFR VISIBILITIES IN FOG MAY DEVELOP FOR ABOUT THREE TO SIX
HOURS TOWARD DAYBREAK SUNDAY. OTHERWISE...VFR CONDITIONS EXPECTED
THROUGH THE FORECAST PERIOD.

&&

.MARINE...
ISSUED AT 311 PM EDT SAT MAY 18 2013

WATER TEMPERATURES WILL BE ON THE RISE INTO EARLY NEXT. WHILE WE
HAVE OFFSHORE FLOW...IT IS NOT THAT STRONG. THE FLOW VEERS TO THE
SOUTH AND THE AIR TEMPERATURE WARMS. ALSO MOISTURE WILL BE ON THE INCREASE.
TYPICALLY IN THESE SETUPS WATER TEMPERATURES CLIMB RATHER QUICKLY. WILL
NEED TO MONITOR THE FOG SETUP AS SURFACE DEW POINTS WILL CLIMB INTO
THE 60S. THE STABLE COLDER WATER TEMPERATURES GENERALLY IN THE LOW 40S WILL
LIMIT THE WAVE DEVELOPMENT.


&&

.FIRE WEATHER...
ISSUED AT 311 PM EDT SAT MAY 18 2013
WARM AND DRY INTO SUNDAY. MOISTURE WILL BE ON THE INCREASE AND
THAT WILL KEEP HUMIDITY LEVELS UP. WIND VALUES WILL BE RELATIVELY
LIGHT DUE TO THE WEAKER PRESSURE GRADIENT.

&&

.HYDROLOGY...
ISSUED AT 311 PM EDT SAT MAY 18 2013

GULF MOISTURE WILL BE STREAMING INTO LOWER MICHIGAN THROUGH THE
MIDDLE PART OF THE WEEK. THIS WILL INCREASE THE RISK FOR HEAVIER
RAIN. THE MAIN TIME FRAME FOR POTENTIAL HEAVY RAIN WILL EXIST
BETWEEN MONDAY AND WEDNESDAY.

&&

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

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...93
AVIATION...MACZKO
FIRE WEATHER...MJS
HYDROLOGY...MJS
MARINE...MJS