Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 220338
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1138 PM EDT THU AUG 21 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 1105 PM EDT THU AUG 21 2014

A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE TONIGHT BUT MANY
AREAS WILL STAY DRY. AREAS OF FOG ARE LIKELY THROUGH MID MORNING
WHICH COULD IMPACT THE MORNING COMMUTE. MUCH OF THE WEEKEND WILL
BE DRY AND GRADUALLY WARMING UP. THE WARMEST DAY LOOKS TO BE
MONDAY WHEN 90 DEGREES WILL BE POSSIBLE.

&&

.UPDATE...
ISSUED AT 1057 PM EDT THU AUG 21 2014

WILL BE ADDING AREAS OF FOG TO THE FORECAST THRU 13Z. METAR TRENDS
ARE ALREADY HEADING IN THAT DIRECTION AND WITH HIGH DEW
POINTS...LIGHT WINDS...AND A STABLE LAYER AT ABOUT 5K FEET
BUFFERING THE 10-15 KNOT WIND SPEEDS...WILL SEE AREAS OF FOG
DEVELOP. SCT CLOUDS ARE PRESENT ACROSS WI...LK MI...AND SW LOWER
MI...SO VARIABLE CONDITIONS ARE POSSIBLE.

HAVE NOT CHANGED POPS TONIGHT...WHICH WERE REDUCED TO CHC BY THE
DAY SHIFT. THIS STILL LOOKS REASONABLE AS A FEW SHOWERS DID POP
NEAR LAN ON THE BACK EDGE OF THE DEPARTING MCV. KGRR BV DID
SUGGEST THAT THE WARM FRONT LIFTED THRU GRR AS A BOUNDARY APPEARED
TO BE MOVING NORTH ON RADAR AND WINDS TURNED LIGHT OUT OF THE
SOUTH. REGARDLESS...IT MAY NOT MATTER THAT WE HAVE THE BOUNDARY IN
THE AREA TONIGHT AS THE LLJ DYNAMICS SHIFT SOUTH WITH TIME. WE
WOULD NEED STORM GENESIS TO BE ACROSS CENTRAL WISCONSIN BY THIS
POINT BUT NO SIGNS OF THAT OCCURRING AND A CONSENSUS OF NWP
GUIDANCE KEEPS US FAIRLY INACTIVE OVERNIGHT.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY NIGHT)
ISSUED AT 330 PM EDT THU AUG 21 2014

CONFIDENCE IS STILL TOO LOW TO ISSUE A FLOOD WATCH FOR TONIGHT.
LATEST MODEL GUIDANCE TRENDS ARE TO SHIFT THE AXIS OF HEAVIEST RAIN
TONIGHT A BIT FARTHER SOUTH.

PREVIOUS GUIDANCE HAD BEEN FOCUSING THE BEST QPF FROM MILWAUKEE TO
KALAMAZOO... BUT NOW IT LOOKS MORE LIKE CHICAGO TO SOUTH BEND. THIS
MAKES SENSE BASED ON THE LOW LEVEL JET PROGS WHICH SHOW A SOUTHWEST
FLOW AIMED TOWARD SW LWR MI THIS EVENING BUT THEN INDICATE IT
VEERING WESTERLY OVERNIGHT. THE SEVERE WEATHER THREAT HAS SHIFTED A
TAD FARTHER SOUTH AS WELL TO THE CHICAGO TO SOUTH BEND CORRIDOR
WHERE BEST INSTABILITY AND WARM FRONT WILL BE.

HOWEVER BASED ON INCONSISTENT MODEL QPF AND LLJ SOLUTIONS FOR
TONIGHT OVER THE LAST FEW RUNS... STILL CANT TOTALLY RULE OUT
LOCALLY HEAVY RAIN/FLOODING OVER THE SW CWFA CORNER OF THE CWFA
TONIGHT. ALSO OF CONCERN IS THE PRESENCE OF RIGHT ENTRANCE REGION
LIFT RELATED TO NW TO SE ORIENTED JETLET OVER LK HURON.

IN THE SHORT TERM... INCREASED POPS CONSIDERABLY FOR THE REST OF
TODAY AS WIDESPREAD RAIN FROM DECAYING WI MCS MOVES EAST.

.LONG TERM...(SUNDAY THROUGH THURSDAY)
ISSUED AT 330 PM EDT THU AUG 21 2014

THE LONG TERM PORTION OF THE FCST LOOKS TO BE RATHER WARM THROUGH A
GOOD PORTION OF THE PERIOD AND FAIRLY UNSETTLED WITH CHCS OF PCPN
EACH DAY THROUGH THE PERIOD.

THE LOWEST THREAT OF RAIN LOOKS TO BE AT THE BEGINNING OF THE PERIOD
ON SUN. THIS IS WHEN THE UPPER RIDGE BUILDS OVERHEAD AS THE UPPER
LOW TAKES SHAPE ACROSS THE ROCKIES. THE CORE OF THE HOT AIR SHOULD
BE JUST WEST OF THE AREA...HOWEVER IT STILL LOOKS VERY WARM AND
HUMID ON SUN. FCST SOUNDINGS SHOW A FAIRLY SUBSTANTIAL CAP BETWEEN
5-10K FT THAT SHOULD KEEP MOST AREAS DRY. WE CAN NOT RULE OUT AN
ISOLATED STORM ALONG SOME SORT OF BOUNDARY LIKE A LAKE BREEZE WITH A
GOOD DEAL OF INSTABILITY PRESENT.

THE CHC OF SHOWERS AND STORMS WILL THEN INCREASE A BIT ON MON AND
REMAIN POSSIBLE THROUGH THE END OF THE PERIOD ON THU. THE ROCKIES
LOW WILL LIFT NE...REMAINING NORTH OF LAKE SUPERIOR. THIS WILL HELP
TO FLATTEN THE RIDGE OVER THE AREA...AND ALLOW THE COLD FRONT TO
SINK SOUTH INTO THE AREA BY TUE. THE WARMEST DAY LOOKS TO BE ON MON
WHERE 90 DEGREES WILL BE POSSIBLE. THE FRONT LOOKS TO STALL OUT OVER
THE SRN PORTION OF THE AREA ON TUE. THE MODELS ARE NOW SHOWING
ADDITIONAL ENERGY COMING IN FROM THE WEST MID WEEK HELPING TO KEEP
THE FRONT ACTIVE. THIS WILL KEEP THE CHC OF SHOWERS/STORMS IN FOR
THE AREA THROUGH THE END OF THE PERIOD. TEMPS WILL COOL A BIT WITH
THE LOWER HEIGHTS AND MORE PCPN POTENTIALLY AROUND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1138 PM EDT THU AUG 21 2014

THE MAIN ISSUE FOR EARLY FRIDAY MORNING IS FOG AND LOW CLOUDS. THE
RAP MODEL SHOWS EXTENSIVE LOW CLOUDS FORMING BETWEEN 06Z AND 09Z
ACROSS ALL OF THE TAF SITES AS SURFACE EAST WINDS ARE OVERRUN BY
SOUTH WINDS ABOVE 4000 FT ALG. THAT WILL BRING MORE MOIST AIR OVER
THE SHALLOW COLDER LAYER AND RESULT AN EXTENSIVE LAYER OF LOW
CLOUDS. THE QUESTION IS WILL THERE BE DENSE FOG? WHILE NOT OUT OF
THE QUESTION THE AREA OF MID CLOUDS OVERHEAD TONIGHT WITH THE
LIKELY HOOD OF LOW CLOUD DECK WOULD SEEM TO MITIGATE DENSE FOG...
STILL IFR FOG WOULD STILL BE POSSIBLE. SINCE THE LOW AND MID LEVEL
WINDS DO NOT BECOME IN SINK UNTIL MIDDAY THE LOW CLOUDS COULD LAST
INTO THE AFTERNOON. SOME CLEARING OF THE LOW CLOUDS SHOULD MOVE
FROM EAST TO WEST AS THE THINNER CLOUDS MIX OUT FIRST. I WOULD
EXPECT VFR CONDITIONS MOST OF THE TAF SITES BY 18Z TO 21Z.

&&

.MARINE...
ISSUED AT 330 PM EDT THU AUG 21 2014

MINIMAL WIND AND WAVE ACTION IS EXPECTED THE REST OF THIS WEEK
THROUGH THE WEEKEND. HOWEVER AREAS OF DENSE FOG WILL POSE A HAZARD
TO MARINERS DUE TO A VERY WARM AND HUMID AIRMASS OVERRUNNING
RELATIVELY COOL LAKE WATER.


&&

.HYDROLOGY...
ISSUED AT 330 PM EDT THU AUG 21 2014

GIVEN THE LATEST LOW LEVEL JET PROGS AND GUIDANCE PLACEMENT OF BEST
QPF MAINLY SOUTH OF MI... THE FLOOD THREAT SEEMS TO BE LOWER THAN
PREVIOUS THOUGHT. WILL NOT ISSUE A FLOOD WATCH BUT SOME AMOUNTS IN
EXCESS OF TWO INCHES CANNOT BE COMPLETELY RULED OUT SW OF GRR.

&&

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

$$

UPDATE...HOVING
SYNOPSIS...HOVING
SHORT TERM...MEADE
LONG TERM...NJJ
AVIATION...WDM
HYDROLOGY...MEADE
MARINE...MEADE





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