Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 172327
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
727 PM EDT WED SEP 17 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 324 PM EDT WED SEP 17 2014

A COLD FRONT WILL MOVE SOUTH FROM CANADA TONIGHT. WE/LL SEE THE
CLOUDS INCREASE AS THE FRONT APPROACHES AND THERE COULD ALSO BE A
BRIEF PERIOD OF DRIZZLE TOWARD MORNING. SKIES WILL BECOME MOSTLY
SUNNY THURSDAY AS HIGH PRESSURE BUILDS OVER LOWER MICHIGAN. CLEAR
SKIES AND LIGHT WINDS WILL RESULT IN CHILLY TEMPERATURES THURSDAY
NIGHT AND FROST MAY BE POSSIBLE NORTHEAST OF GRAND RAPIDS.

RAIN IS EXPECTED FRIDAY NIGHT AND EARLY SATURDAY BUT TEMPERATURES
WILL WARM INTO THE MID TO PERHAPS UPPER 70S SATURDAY.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY NIGHT)
ISSUED AT 324 PM EDT WED SEP 17 2014

FORECAST CONCERNS DEAL WITH FROST POTENTIAL THURSDAY NIGHT AND RAIN
CHANCES FRIDAY NIGHT.

A COLD FRONT MOVING SOUTH FROM CANADA TONIGHT WILL SET THE STAGE FOR
A CHILLY THURSDAY NIGHT. HIGH PRESSURE WILL QUICKLY BUILD IN BEHIND
THE FRONT AND CLEAR OUT THE CLOUDS. LIGHT WINDS WILL ALLOW TEMPS TO
FALL THURSDAY NIGHT INTO THE MID 30S NORTHEAST OF GRAND RAPIDS.
ADDED SOME FROST TO THE GRIDS AND WENT A DEGREE OR TWO BELOW
GUIDANCE. THERE IS SOME CONCERN THAT THE HIGH WILL MOVE EAST QUICK
ENOUGH TO ALLOW LIGHT SOUTH WINDS TO DEVELOP BEFORE SUNRISE FRIDAY
MORNING...SO WE HELD OFF ON A FROST ADVISORY AT THIS POINT.

LOW PRESSURE MOVING EAST FROM THE PLAINS LATE FRIDAY WILL PUSH A
WARM FRONT NORTH THROUGH THE CWA. MOISTURE TRANSPORT VECTORS
LENGTHEN QUITE A BIT FRIDAY NIGHT...ESPECIALLY AFTER 06Z WHEN PWATS
CLIMB TO AROUND 1.7 INCHES OVER THE NW CWA. LOCALLY HEAVY RAINFALL
SEEMS POSSIBLE AFTER MIDNIGHT FRIDAY NIGHT NW OF A GRAND HAVEN TO
CLARE LINE. TSRA CHANCES ARE HIGHER AFTER MIDNIGHT THAN BEFORE DUE
TO GROWING ELEVATED INSTABILITY. INCREASED POPS TO LIKELY DURING
THIS TIME FRAME.

IN THE MEANTIME...THE FRONT THAT MOVES SOUTH TONIGHT WILL BRING SOME
CLOUDS WITH IT. BUFKIT DATA SHOWED SOME LIFT IN THE CLOUD LAYER FOR
A SHORT TIME FROM AROUND 09-13Z...SO SOME -DZ MAY BE POSSIBLE.

.LONG TERM...(SATURDAY THROUGH WEDNESDAY)
ISSUED AT 324 PM EDT WED SEP 17 2014

SOMEWHAT TRICKY HIGH TEMPERATURE FCST ON SATURDAY DUE TO LOW
CONFIDENCE IN EXTENT OF CLOUDS AND CONVECTION. BEHAVIOR OF THE LOW
LEVEL JET IS STILL UNCLEAR. THE HIGHEST POTENTIAL FOR SHOWERS/TSTMS
WOULD APPEAR TO BE NORTH AND WEST OF GRR CLOSER TO THE APPROACHING
SFC COLD FRONT. WILL HAVE HIGHS IN THE LOW TO MID 70S ACROSS THIS
AREA WHICH IS ALSO WHERE THE STRONG LOW LEVEL SOUTHWEST FLOW OFF
LAKE MICHIGAN WILL BE OCCURRING. SOUTH AND EAST OF GRR HOWEVER HIGHS
MAY REACH 80 ON SATURDAY AWAY FROM THE LAKE INFLUENCE IF CLOUDS AND
CONVECTION ARE NOT PARTICULARLY WIDESPREAD.

THE COLD FRONTAL PASSAGE IS STILL ON TRACK FOR SATURDAY NIGHT WITH
GRADUAL COLD ADVECTION FOLLOWING IN ITS WAKE SUNDAY AND MONDAY. THE
COLD ADVECTION BEHIND THE FRONT MAY SUPPORT SOME SCATTERED RAIN
SHOWERS ALTHOUGH SFC RIDGING/ANTICYCLONIC FLOW IS RATHER QUICK TO
BUILD INTO THE REGION ON MONDAY. THIS IS A LIMITING FACTOR FOR LAKE
EFFECT/ENHANCED RAIN SHOWERS IN THE COLDER AIR.

FAIRLY HIGH CONFIDENCE IN DRY WEATHER WITH MODERATING TEMPS TUESDAY
AND WEDNESDAY AS LARGE/SLOW MOVING SFC HIGH IMPACTS THE REGION.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 727 PM EDT WED SEP 17 2014

WE ARE WATCHING THE LOW CLOUDS MOVING SOUTH WITH COLD FRONT. AT
23Z THE FRONT WAS NEAR THE BIG MAC BRIDGE. THERE IS A BAND OF
MVFR/IFR CIGS JUST BEHIND THE FRONT OVER THE UPPER PENINSULA THAT
WILL FOLLOW THE FRONT SOUTH. THE SHORT STORY IS THAT I WOULD EXPECT
A PERIOD OF MVFR/IFR CIGS WITH AT THE I-96 TAF SITES IN THE 10Z TO
15Z TIME FRAME (AS SUGGESTED BY OUR PREVIOUS AVIATION AFD). I ALSO
AGREE THE LOW CLOUDS WILL MIX OUT DURING THE MID DAY HOURS
RESULTING IN LARGELY CLEAR SKIES BY 21Z OR SO.

HOWEVER THERE IS GLITCH. THE GLITCH IS LAKE MICHIGAN AND LAKE
HURON. BOTH THE NAM12 AND RAP13 AGREE THAT THE FRONT WILL SURGE
MORE QUICKLY SOUTH OVER BOTH LAKES THAN OVER THE INLAND SECTIONS
OF LOWER MICHIGAN. IN FACT THE NAM12 FORMS A MESO-LOW OVER LAKE
MICHIGAN...JUST WEST OF MKG AROUND 06Z THAT SLOWLY SINKS SOUTH
SOUTHWEST WITH THE FRONT. IT DISSIPATES AS IT REACHES JUST OFF
SHORE OF CHICAGO BY 18Z. THIS WILL SLOW DOWN THE PROGRESS OF THE
FRONT AND LOW CLOUDS WEST OF US-131 AND SOUTH OF I-96. AS SUGGESTED
BY OUR PREVIOUS AFD THE LAN TAF SITE HAS THE GREATEST RISK FOR IFR
CIGS/VSBY WITH THE AIR FLOW OFF SAGINAW BAY HELPING THE CAUSE. MKG
WOULD BE THE NEXT MOST LIKELY LOCATION TO GET THE LOW CLOUDS.
MEANWHILE THE AZO AND BTL TAF SITES ARE IN A LOCATION WHERE THE
MESO-LOW CIRCULATION COMBINED WITH THE TIMING OF THE FRONT WOULD
BE THE LEAST LIKELY TO HAVE ANY LOW CLOUD ISSUES THURSDAY. AS A
RESULT I KEPT THOSE TAF SITES LARGELY VFR ALL DAY (BRIEF MVFR F
AROUND SUNRISE AT AZO). JXN IS ON THE FENCE AS TO WHAT WILL HAPPEN
SO I KEPT THE IDEA FROM THE PREVIOUS TAF AND BROUGHT THE LOW
CLOUDS IN.



&&

.MARINE...
ISSUED AT 609 PM EDT WED SEP 17 2014

DECIDED TO ISSUE A SMALL CRAFT ADVISORY FOR THE POINTS REGION FOR
LATE TONIGHT INTO THURSDAY MORNING. NNE WINDS WILL BECOME RATHER
BRISK BEHIND THE COLD FRONT AND WILL KICK UP 3-5 FOOT WAVES. WINDS
TURN MORE NE AND LIGHTEN UP LATE THURSDAY MORNING WHEN WAVES SUBSIDE.

WAVES WILL INCREASE AGAIN LATE FRIDAY AS SOUTH FLOW DEVELOPS AHEAD
OF THE APPROACHING LOW. A SCA MAY BE NEEDED FRIDAY NIGHT/SATURDAY.


&&

.HYDROLOGY...
ISSUED AT 324 PM EDT WED SEP 17 2014

THE NEXT CHANCE OF RAIN WILL COME FRIDAY NIGHT AND EARLY SATURDAY AS
LOW PRESSURE MOVES EAST FROM THE NORTHERN PLAINS TOWARD THE GREAT
LAKES. MOISTURE TRANSPORT VECTORS INCREASE QUITE A BIT FRIDAY NIGHT
AS INSTABILITY ALSO RISES AFTER MIDNIGHT. WE COULD SEE SOME LOCALLY
HEAVY RAINFALL WITH SHOWERS AND THUNDERSTORMS...ESPECIALLY AFTER
MIDNIGHT.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY FROM 4 AM TO 10 AM EDT THURSDAY FOR LMZ848-
     849.

&&

$$

SYNOPSIS...93
SHORT TERM...93
LONG TERM...MEADE
AVIATION...WDM
HYDROLOGY...93
MARINE...JK





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