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000
FXUS63 KGRR 211930
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
315 PM EDT TUE MAY 21 2013

LATEST UPDATE...
AFTERNOON PACKAGE

.SYNOPSIS...
ISSUED AT 315 PM EDT TUE MAY 21 2013

AN AREA OF LOW PRESSURE WILL DEVELOP OVER SOUTHEAST MISSOURI THIS
EVENING AND MOVE THROUGH CENTRAL MICHIGAN ON WEDNESDAY. THE
DEVELOPING LOW CENTER WILL BRING SOAKING RAINS AND A FEW STRONG
THUNDERSTORMS TO THE AREA LATE TONIGHT AND WEDNESDAY.  MUCH COOLER
AIR AND SHOWERS WILL WRAP IN FROM THE NORTHWEST AS THE LOW DEPARTS
ON THURSDAY.  CANADIAN HIGH PRESSURE WILL BUILD OVER THE REGION
THURSDAY NIGHT AND PROVIDE COOL AND DRY WEATHER THROUGH THE HOLIDAY
WEEKEND. THERE WILL ALSO BE A GOOD CHANCE OF A SCATTERED FROST ON
BOTH FRIDAY AND SATURDAY MORNING.

&&

.SHORT TERM...(TONIGHT THROUGH THURSDAY NIGHT)
ISSUED AT 315 PM EDT TUE MAY 21 2013

THREATS ARE THREE FOLD NEXT FEW DAYS WITH ISOLATED STRONG/SEVERE
STORMS THIS EVENING...HEAVY RAIN AND POSSIBLE LOCAL FLOOD POTENTIAL
ON WEDNESDAY... AND THEN MUCH COOLER AIR WITH A LATE SEASON FROST
THREAT BOTH FRI AND SAT MORNING...

LIKE RECENT HRRR GUIDANCE INDICATING ISOL TO SCATTERED TSTORM
COVERAGE SOUTH AND EAST OF KBEH...KY70...KMOP LINE THIS EVENING.
OVERALL COVERAGE AND POTENTIAL FOR ORGANIZATION WILL BE SUPPRESSED
BY MODEST SHORTWAVE RIDGING AND UPPER CONVERGENCE. INITIAL FOCUS IS
AN AXIS OF 1000 J/KG MUCAPE STRETCHING FROM KGRR TOWARDS THE THUMB.
THAT COMBINED WITH 35KTS BULK 0-6KM SHEAR WILL LIKELY GIVE RISE TO
SOME STRONG AND POSSIBLY SEVERE PULSE TYPE STORMS.

HEAVY RAIN THREAT ON WEDNESDAY WITH SFC CYCLOGENESIS AND MID LEVEL
FRONTOGENESIS AS NICE SHORTWAVE MOVES NORTHEASTWARD FROM MO/AR THIS
EVENING CROSSING THE REGION WED.  BOTH ECMWF AND GFS AS WELL AS SOME
OF THE SHORTER TERM MESO GUIDANCE ALL INDICATE A 75 WIDE 1-2 INCH
BAND OF RAIN ORIENTED SSW TO NNE ON WEDNESDAY. THE MOISTURE AND
DYNAMICS ARE CERTAINLY IN POSITION TO SUPPORT THE RAINFALL...IT IS
JUST WHERE THE AXIS OF THE HEAVIER RAINFALL WILL BE.  AT THIS POINT
FEEL THE BEST BET WOULD BE JUST ABOUT ON A KAZO...KGRR...KMOP LINE
WITH KMKG ABOUT AS FAR WEST AS IT MIGHT BE AND KLAN AS FAR EAST.

WRAP AROUND MOISTURE AND MUCH COOLER AIR MOVE IN BY THURSDAY AS
UPPER LOW OVER MN OPENS AND SWINGS EASTWARD THROUGH THE REGION.  H85
TEMPS DROP TO NEAR ZERO BY THU EVENING WITH MUCH DRIER SFC DEWPOINT
DRIVING INTO THE REGION AS UPSTREAM CANADIAN SFC HIGH BUILD
OVERHEAD. FEEL PREETY CONFIDENT ABOUT FROST POTENTIAL FRI AND SAT
MORNING...ESPECIALLY UP NORTH AND IN SHELTERED LOW LYING AREAS
EVERYWHERE. NOT SURE WHICH MORNING WILL BE THE COLDER...FRI HAS THE
COLDER OVERALL AIRMASS BUT BOUNDARY LAYER WINDS WILL INHIBIT
RADIATIONAL COOLING.
&&

.LONG TERM...(FRIDAY THROUGH TUESDAY)
ISSUED AT 315 PM EDT TUE MAY 21 2013

THE LONG TERM PORTION OF THE FCST PERIOD LOOKS RATHER QUIET FOR
LOWER MICHIGAN. THE UPPER AIR PATTERN WILL TAKE ON SOME OF THE
CHARACTERISTICS OF AN OMEGA BLOCK. THIS OCCURS AS THE TROUGH/LOW
MOVING THROUGH MID WEEK HELPS TO ESTABLISH AN UPPER LOW ACROSS THE
NE U.S. AND THE CANADIAN MARITIMES. AN UPPER LOW WILL BECOME
ESTABLISHED ACROSS THE WRN U.S. COAST...WITH A RIDGE HOLDING ON IN
THE CENTRAL PORTION OF THE COUNTRY.

LOWER MICHIGAN SHOULD END UP UNDER THE DRY PORTION DOWNSTREAM OF THE
RIDGE AS IT SITS ALMOST STATIONARY. COOL NW FLOW ALOFT WILL KEEP
HIGHS IN THE 60S FROM FRI AND LIKELY THROUGH SUN WITH H850 TEMPS
ROUGHLY FROM 3-5C. WE STILL ARE EXPECTING SOME FROST POTENTIAL UP
NORTH ON FRI NIGHT BEFORE THE AIR MASS MODERATES SOME FOR THE
REMAINDER OF THE WEEKEND.

A WEAK SHORT WAVE WILL PUSH THROUGH THE REGION LATE SUN AND SUN
NIGHT. RIGHT NOW IT SEEMS THAT THIS SHOULD MOVE THROUGH DRY AS THE
LONG WAVE RIDGE SHOULD OVERCOME THIS WEAK SHORT WAVE. ALSO THE AIR
MASS SHOULD BE FAIRLY DRY WITH THE RIDGE SITTING OVER THE AREA FOR A
FEW DAYS AND NO GOOD MOISTURE ADVECTION EXPECTED THROUGH SUN.

SOME SPORADIC MODEL RUNS HAD BEEN SHOWING A WARM FRONT APPROACHING
LATE SUN AND REMAINING THROUGH TUE. THIS WOULD HAVE BROUGHT SOME
RAIN CHCS TO THE AREA. IT APPEARS NOW THAT THE NW FLOW ALOFT SHOULD
KEEP THIS FRONT SW OF THE AREA UNTIL AT LEAST TUE BEFORE SOME LOW
CHCS OF SHOWERS/STORMS WOULD DEVELOP. TEMPS WILL WARM INTO THE 70S
BY TUE.
&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 137 PM EDT TUE MAY 21 2013

THE MAIN FOCUS OF THE 18Z FCSTS IS ONCE AGAIN CONVECTION TRENDS
OVER THE NEXT 24 HOURS.

THE AREA HAS BEEN SLOW TO HEAT UP SIGNIFICANTLY THIS MORNING DUE
TO THE RAIN EARLY THIS MORNING AND THE MID LEVEL CLOUD COVER THAT
HAS BEEN PLAGUING THE AREA. MORE BREAKS ARE OPENING UP...AND
INSTABILITY IS BUILDING. WE EXPECT JUST SPOTTY STORMS TO DEVELOP THIS
AFTERNOON ALONG AND INLAND OF THE LAKE BREEZE/LAKE SHADOW...MAINLY SE
OF A LINE FROM SOUTH HAVEN TO CADILLAC. SPOTTY MVFR CONDITIONS
SHOULD LIFT TO VFR EXCEPT DIRECTLY UNDER ANY STORMS THAT DEVELOP.

WE SHOULD SEE A BREAK IN CONVECTION THIS EVENING AND DURING THE
EARLY OVERNIGHT HOURS. WE WILL SEE THE CHCS OF RAIN INCREASE AFTER
08-10Z WED AS A WAVE OF LOW PRESSURE APPROACHES. THIS SHOULD BE
MAINLY SHOWERS/RAIN WITH ONLY A FEW EMBEDDED STORMS DOWN SOUTH.
THE STORM CHCS ARE LOW ENOUGH AT ANY ONE TERMINAL TO LEAVE OUT OF
THE FCST FOR NOW. WIDESPREAD MVFR CONDITIONS SHOULD ACCOMPANY THIS
PCPN WITH SOME LOCAL IFR NOT OUT OF THE QUESTION. THIS SHOULD HOLD
IN AT MOST LOCATIONS THROUGH 18Z BEFORE IT MOVES OUT AFTER 18Z WED.

&&

.MARINE...
ISSUED AT 315 PM EDT TUE MAY 21 2013

SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED ON THURSDAY AS COLDER AIR
WRAPS IN BEHIND DEPARTING LOW PRESSURE SYSTEM. HIGH PRESSURE WILL
BRING QUIET AND COOL CONDITIONS FOR MOST IF NOT ALL OF THE HOLIDAY
WEEKEND.

&&

.FIRE WEATHER...
ISSUED AT 315 PM EDT TUE MAY 21 2013

THE AREA WILL SEE PERIODS OF RAIN THROUGH THURSDAY.  OVER AN INCH OF
RAIN IS LIKELY KEEPING THE FIRE RISK LOW.

&&

.HYDROLOGY...
ISSUED AT 315 PM EDT TUE MAY 21 2013

PERIODS OF HEAVIER RAIN IS EXPECTED BY LATE TONIGHT AND SHOULD
LINGER UNTIL THURSDAY.  SOME TYPICAL LOCALIZED FLOODING IS POSSIBLE
BY WEDNESDAY AFTERNOON IN LOW LYING URBAN AND RURAL AREAS AND ON
SMALL STREAMS AND RIVERS.

&&

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

$$

SYNOPSIS...DKC
SHORT TERM...DKC
LONG TERM...NJJ
AVIATION...NJJ
FIRE WEATHER...DKC
HYDROLOGY...DKC
MARINE...DKC