Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 220257
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1057 PM EDT THU AUG 21 2014

LATEST UPDATE...
UPDATE

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

VERY WARM AND HUMID CONDITIONS WILL PREVAIL FOR THE NEXT SEVERAL
DAYS. WIDESPREAD SHOWERS AND THUNDERSTORMS ARE EXPECTED TONIGHT BUT
ONLY ISOLATED SHOWERS AND STORMS ARE EXPECTED FROM FRIDAY THROUGH
THE WEEKEND.

&&

.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 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 649 PM EDT THU AUG 21 2014

IT WOULD SEEM THE THREAT FOR SIGNIFICANT RAINFALL HAS SHIFTED WELL
SOUTH OF THE GRR TAF SITES TONIGHT. EVEN SO THE FRONTAL BOUNDARY
BEING SOUTH OF MICHIGAN AND WITH A SHALLOW LAYER OF COLD AIR (LOW
LEVEL EAST FLOW) TO ABOUT 4000 FT AGL (RAP MODEL SOUNDINGS FROM
21Z RUN) THERE WILL BE OVERRUNNING OF THE WARM MOIST AIR TO THE
SOUTH OF THE BOUNDARY OVER THIS SHALLOW COLD LAYER. THAT SHOULD
LEAD TO A LOW LAYER OF STRATUS AND EVEN FOG. AS A RESULT IN HAVE
ALL TAF SITES BECOMING IFR IN STRATUS AND FOG BY 09Z OR SO. IT IS
QUESTIONABLE IF THIS WILL MIX OUT FRIDAY. THE MODELS SUGGEST THIS
SHALLOW BOUNDARY WILL MIX OUT BY EARLY AFTERNOON SO I LIFT THE
CIGS BUT DO NOT BE SURPRISED IF THE LOW CLOUDS HANG IN ALL DAY.


&&

.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...MEADE
SHORT TERM...MEADE
LONG TERM...NJJ
AVIATION...WDM
HYDROLOGY...MEADE
MARINE...MEADE





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