Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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072
FXUS63 KGRR 181145
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
745 AM EDT MON MAY 18 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 330 AM EDT MON MAY 18 2015

A STRONG COLD FRONT WILL MOVE THROUGH THIS AFTERNOON WITH MUCH
COOLER WEATHER TO FOLLOW FOR TONIGHT THROUGH MIDWEEK. THERE IS
POTENTIAL FOR SCATTERED SHOWERS AND STORMS TO DEVELOP ALONG AND
JUST AHEAD OF THE FRONT SOUTHEAST OF GRAND RAPIDS THIS AFTERNOON
AND EARLY EVENING. THERE IS POTENTIAL FOR FROST FORMATION LATE
TUESDAY NIGHT THROUGH THE EARLY MORNING HOURS WEDNESDAY WHEN
TEMPERATURES WILL FALL INTO THE 30S. TEMPERATURES WILL UNDERGO A
GRADUAL MODERATING TREND LATE THIS WEEK INTO THE WEEKEND.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 330 AM EDT MON MAY 18 2015

OUR PRIMARY SHORT TERM FCST CHALLENGE IS TO DETERMINE POTENTIAL
FOR SHOWERS AND STORMS ALONG AND JUST AHEAD OF THE COLD FRONT
TODAY. WE ALSO NEED TO EVALUATE POTENTIAL FOR FROST TUESDAY NIGHT.

ALTHOUGH THE PROBABILITIES ARE LOW THERE IS SOME POTENTIAL FOR A
BROKEN LINE OF SHOWERS AND STORMS TO DEVELOP FROM MID AFTN THROUGH
EARLY EVE EAST/SE OF KGRR ALONG AND JUST AHEAD OF THE COLD FRONT.
THIS WOULD BE DUE TO STRONG FORCING FROM THE FRONT COINCIDENT WITH
MAX INSTABILITY FROM DAYTIME HEATING AS HIGH TEMPS REACHING THE
LOWER 80S AHEAD OF THE FRONT IN CONJUNCTION WITH SB CAPE VALUES
REACHING AT LEAST 1000-1500 J/KG.

THIS NOTION IS SUPPORTED BY 00Z 4KM WRF-NMM SIM Z GUIDANCE BUT NOT
AS MUCH BY THE 00Z NSSL WRF. THE RELATIVELY GREATER CHANCE FOR
SHOWERS AND STORMS STILL LOOKS TO BE FURTHER SE OF OUR FCST AREA
AS SUGGESTED BY A CONSENSUS OF 00Z SHORT RANGE MODEL GUIDANCE.

IT WILL TURN BREEZY AND MUCH COOLER TONIGHT THROUGH TUESDAY WITH
MAX TEMPS TUESDAY ONLY REACHING THE 50S. PARTIAL CLEARING IN
CONJUNCTION WITH CALM WINDS WILL SET UP DECENT RADIATIONAL COOLING
CONDITIONS TUESDAY NIGHT AS THE HIGH PRESSURE RIDGE BUILDS IN.

A CONSENSUS OF LATEST 00Z NUMERICAL GUIDANCE AND MODEL TRENDS
SUGGESTS POTENTIAL FOR AREAS OF FROST TO DEVELOP ACROSS ROUGHLY
THE NORTHERN HALF OF OUR FCST AREA DURING THE EARLY MORNING HOURS
WEDNESDAY. HOWEVER THE EXTENT OF CLEARING IS UNCERTAIN AS SOME
STRATOCU COULD LINGER WELL INTO THE EVENING HOURS.

POTENTIAL FOR FROST IS LESS NEAR TO SOUTH OF I-96. POTENTIAL FOR
FROST IS ALSO CONTINGENT ON EXTENT OF CLEARING AS 00Z GUIDANCE
TIME HEIGHT RH X SECTIONS SHOW POTENTIAL FOR A FAIR AMOUNT OF MID
TO HIGH LEVEL CLOUD COVER TO MOVE IN FROM THE WEST AFTER MIDNIGHT
ESPECIALLY ACROSS OUR SOUTHERN FCST AREA IN ADDITION TO THE
POTENTIAL EVENING LINGERING STRATOCU.

THE COOL WX WILL CONTINUE ON WEDNESDAY WITH A FAIR AMOUNT OF CLOUD
COVER IN PLACE AFTER A COOL START TO THE DAY AND WEAK CAA.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 330 AM EDT MON MAY 18 2015

THE MID TO LATE WEEK PERIOD WILL CONTINUE TO BE COOLER AND DRIER
THAN NORMAL... FOLLOWED BY A WARMING TREND WITH INCREASING RAIN
CHANCES OVER THE LATTER HALF OF THE HOLIDAY WEEKEND. THE UPPER LEVEL
PATTERN WILL FEATURE NORTHWEST FLOW THURSDAY THROUGH SATURDAY...
TRANSITIONING TO SOUTHWEST FLOW ALOFT BY SUNDAY.

A MID LEVEL SHORTWAVE APPROACHING FROM THE WEST WEDNESDAY NIGHT WILL
SHEAR OUT AS IT COMES INTO SRN LWR MI. HOWEVER THERE SHOULD BE
CONSIDERABLE MID CLOUDS WITH IT AND PERHAPS EVEN SOME LIGHT RAIN
SHOWERS OR SPRINKLES REACHING THE GROUND NEAR AND SOUTH OF I-94. THE
CLOUDS SHOULD MITIGATE THE FROST POTENTIAL WEDNESDAY NIGHT.

CURRENT EXPECTATION IS FOR PLEASANT WEATHER AND PLENTY OF SUNSHINE
THURSDAY THROUGH SATURDAY WITH SFC RIDGING DOMINATING. HIGHS WILL BE
IN THE 60S WITH CHILLY OVERNIGHT LOWS IN THE MID 30S TO MID 40S.
CANT RULE OUT SOME PATCHY FROST ON BOTH THURSDAY AND FRIDAY NIGHTS.

AS A WARM ADVECTION PATTERN DEVELOPS SATURDAY NIGHT AND SUNDAY WE
SHOULD SEE INCREASING CLOUDS WITH A CHANCE OF SHOWERS. THE SFC WARM
FRONT IS PROGGED TO CREEP NORTH INTO THE AREA ON SUNDAY LEADING TO A
RISK OF TSTMS BY THAT TIME.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 745 AM EDT MON MAY 18 2015

OTHER THAN SOME MVFR CIGS AROUND JXN THROUGH 13-14Z... VFR
CONDITIONS ARE EXPECTED TODAY AND TONIGHT. A FEW SCATTERED
RAIN SHOWERS MAY DEVELOP SOUTH AND EAST OF GRR THIS AFTERNOON AND
ALSO CANNOT RULE OUT A TSTM AROUND JXN. THIS ACTIVITY SHOULD EXIT
THE AREA BY 00Z TONIGHT. GUSTY SOUTHWEST SFC WINDS OF 15 TO 25 KTS
WILL DIMINISH TO AROUND 10 KTS TONIGHT. MVFR CIGS ARE EXPECTED TO
ARRIVE FROM THE NORTHWEST TOWARD 12Z TUESDAY AS MUCH COLDER AIR
POURS INTO THE REGION.

&&

.MARINE...
ISSUED AT 330 AM EDT MON MAY 18 2015

WE HAVE DECIDED TO HOIST A SMALL CRAFT ADVISORY FOR ALL OUR
NEARSHORE ZONES FROM LATE THIS AFTERNOON THROUGH TONIGHT. WINDS
WILL VEER TO THE WEST AND INCREASE TO 20 TO 25 KTS WITH HIGHER
GUSTS AFTER FROPA. THIS IN CONJUNCTION WITH STRONG CAA WILL RESULT
IN WAVE HEIGHTS REACHING SCA CRITERIA. FUTURE SHIFTS MAY NEED TO
POTENTIALLY EXTEND THE SCA INTO TUESDAY.


&&

.HYDROLOGY...
ISSUED AT 1210 AM EDT SUN MAY 17 2015

THE MAIN THREAT THROUGH THE NEXT 24 HOURS WILL BE THE POSSIBILITY
FOR LOCALIZED HEAVY RAINFALL.

A MAJORITY OF THE AREA STREAMS AND RIVERS ARE RUNNING WELL BELOW
ADVISORY LEVELS WITH A COUPLE OF SITES SLIGHTLY BELOW. SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO DEVELOP AND TRAVEL EAST OUT OF THE
UPPER MIDWEST THIS EVENING AND INTO TONIGHT. AREA AVERAGE
RAINFALL MAY RUN FROM A FEW TENTHS OF AN INCH UPWARDS OF A HALF
INCH. LOCALIZED HEAVY POCKETS WILL CREATE GREAT VARIATIONS IN
RAINFALL TOTALS IN SHORT DISTANCES. LOCATIONS THAT ARE AFFECTED BY
HEAVIER RAINFALL MAY EXPERIENCE LOCALIZED PONDING OR TEMPORARY
STREET FLOODING WITH SMALL CREEK AND STREAM FLUCTUATIONS
POSSIBLE. LARGER RIVERS ARE EXPECTED TO REMAIN BELOW ACTION
STAGE THROUGH THE PERIOD AS FEEDBACK TIMES WILL TAKE US INTO
DRIER WEATHER FOR THE UPCOMING WEEK.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 6 AM EDT
     TUESDAY FOR LMZ844>849.

&&

$$

SYNOPSIS...LAURENS
SHORT TERM...LAURENS
LONG TERM...MEADE
AVIATION...MEADE
HYDROLOGY...JAM
MARINE...LAURENS



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