Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 061945
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
ISSUED BY NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
345 PM EDT WED MAY 6 2015

LATEST UPDATE...
SYNOPSIS...SHORT TERM...LONG TERM...MARINE...HYDROLOGY

.SYNOPSIS...
ISSUED AT 345 PM EDT WED MAY 6 2015

WARMER WEATHER IS EXPECTED THURSDAY...AS HIGHS REACH THE LOWER 80S.
THE BEST CHANCE OF THUNDERSTORMS OVER THE NEXT FEW DAYS IS FRIDAY
WHEN A COLD FRONT APPROACHES. SHOWERS AND THUNDERSTORMS WILL REMAIN
IN THE FORECAST INTO EARLY NEXT WEEK.

&&

.SHORT TERM...(THIS EVENING AND TONIGHT)
ISSUED AT 345 PM EDT WED MAY 6 2015

A GROWING BOUNDARY LAYER THIS AFTERNOON HAS LED TO RISING CEILING
HEIGHTS AND DISSIPATION OF LOW CLOUD ACROSS SOUTHERN MICHIGAN. THUS
FAR...SURFACE DEWPOINTS HAVE BEEN HOLDING ON IN THE UPPER 50S ACROSS
MOST OF THE AREA WHICH IS FAIRLY IMPRESSIVE GIVEN THE BACKGROUND
EASTERLY FLOW TRAJECTORY. AN ANTICYCLONIC GYRE IS EXPECTED TO LIFT
NORTHEASTWARD INTO SOUTHWESTERN LOWER MICHIGAN THEN ROLL EASTWARD.
MODELED RH/EQUIVALENT POTENTIAL TEMPERATURES SUGGESTS A PERIOD OF
DEEP DRY AIR ADVECTION OVERNIGHT COINCIDING WITH THIS ANTICYCLONIC
FEATURE. AS A RESULT...NOT EXPECTING ANYWHERE NEAR THE SAME SETUP
FOR TONIGHT AS LAST NIGHT AS SKIES ARE EXPECTED TO CLEAR OUT. ALL
INDICATIONS ARE FOR A FAVORABLE RADIATIVE COOLING ENVIRONMENT. NAM
IS FAIRLY BULLISH WITH NEAR SURFACE PROFILE INDICATIVE OF FOG.
SURFACE PRESSURE GRADIENT WILL PREVENT WINDS FROM DOING FLAT CALM.
WILL MAINTAIN INHERITED MENTION OF PATCHY FOG IN THE PUBLIC FORECAST
FOR TOMORROW MORNING BUT DENSE FOG IS NOT EXPECTED AT THIS TIME.

&&

.LONG TERM...(THURSDAY THROUGH NEXT WEDNESDAY)
ISSUED AT 345 PM EDT WED MAY 6 2015

ACTIVE WEATHER PATTERN SETTING UP FROM THE BEGINNING OF THE WEEKEND
THROUGH MONDAY AS A DEEP TROUGH OVER THE SW CONUS AND RIDGE OVER THE
EASTERN CONUS...AND INTO THE GREAT LAKES...ALIGNS A FRONTAL BOUNDARY
ACROSS THE REGION. THE UPPER LOW WILL EJECT SEVERAL SHORTWAVES
THROUGH THE SW FLOW WHICH WILL RIDE ALONG THE FRONT BRINGING
ENHANCED PERIODS OF SHOWERS AND TSTORMS TO THE AREA THIS WEEKEND.
TIMING THESE WAVES ALONG WITH FRONTAL TIMING WILL BE THE MAIN
CHALLENGE WHEN CONSIDERING POTENTIAL FOR STRONG THUNDERSTORMS.

TO WRAP UP THE WORK WEEK THE MAIN STORY WILL BE WARMTH AS HIGH
TEMPERATURES REACH 80+ DEGREES BOTH THURSDAY AND FRIDAY. BY THE
START OF THE DAY THURSDAY...THE 900-950MB LAYER WILL BE APPROACHING
20C WHILE TEMPS AT 850MB WILL BE RESPECTABLY IN THE LOW TEENS. THE
MID/UPPER LEVEL RIDGE AXIS WILL LIFT UP AND THROUGH LOWER MI
ALLOWING THE WARM SECTOR INTO THE REGION. THIS AS THE FRONT LOSES
DEFINITION WITH DEEP MIXING COMMENCING. THIS COMBINED WITH A GOOD
DEAL OF MAY SUNSHINE SHOULD ALLOW TEMPS TO EARLY REACH 80 DEGREES.
WE WILL NOT BE WITHOUT MOISTURE AS SFC DEWPOINTS START OFF IN THE
MID 50S...BUT THERE WILL BE NO FORCING MECHANISM TO REALIZE THAT
MOISTURE. BEST LL DYNAMICS WILL RESIDE TO THE WEST CLOSER TO THE
APPROACHING COLD FRONT.

ON FRIDAY...WARM AIR ABOVE THE INVERSION WILL QUICKLY MIX BACK DOWN
TO THE SFC ALLOWING RAPID ASCENTION BACK INTO THE 80S. THIS AIDED BY
DEEPER AND STRONGER SW FLOW BRINGING IN INCREASINGLY WARMER AND
MOISTER AIR TO SOUTHERN MI...WITH DEWPOINTS RISING INTO THE LOW 60S.
MOST OF THE AREA WILL SEE A SLIGHT UPTICK IN TEMPERATURES OVER
THURSDAY...BUT INCREASING CLOUD FIELD AND DEVELOPMENT OF SHOWERS AND
STORMS WILL LIMIT HIGH TEMPS IN THE AFTERNOON. AS MENTIONED
PREVIOUSLY...TIMING OF MID LEVEL SHORTWAVE ENERGY WILL BE IMPORTANT
FRIDAY AS TO HOW CONVECTION DEVELOPS AND EVOLVES.

EURO SHOWS A NICE BUMP IN THE CAPE FOR SATURDAY AFTERNOON THAT COULD
HELP PULL THE TRIGGER ON THUNDERSTORM DEVELOPMENT...PARTICULARLY
LATE MORNING THROUGH EVENING. HIGHER CAPE VALUES APPEAR TO SETTLE A
LITTLE FURTHER SOUTH ON SUNDAY...BUT THERE SHOULD STILL BE ENOUGH
ENERGY REMAINING OVER SOUTHERN MICHIGAN TO KEEP THE THUNDERSTORM
POTENTIAL IN THE MIX FOR SUNDAY. ON THE HEELS OF THE SLOW MOVING
WEEKEND COLD FRONT...A CUTOFF LOW EMERGES OUT OF THE DESERT
SOUTHWEST MONDAY. IF THIS PANS OUT...IT COULD KEEP SHOWER AND
THUNDERSTORM ACTIVITY ALIVE AND WELL IN THE FORECAST THROUGH
TUESDAY...AND POSSIBLY INTO WEDNESDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 101 PM EDT WED MAY 6 2015

LINGERING LOW CLOUDS AND FOG WILL CONTINUE TO RAPIDLY DIMINISH OVER
THE NEXT HOUR UNDER DAYTIME HEATING. STRONG HEATING WILL DEEPEN THE
BOUNDARY LAYER DURING THE AFTERNOON WHICH WILL HOLD BASES ASSOCIATED
WITH ANY DIURNALLY DRIVEN CLOUDS ABOVE 6K FT. GOOD RADIATIONAL
COOLING TONIGHT AND RESIDUAL SFC MOISTURE WILL POSE THE RISK FOR
SOME FOG DEVELOPMENT LATE. THE GRADIENT FLOW WILL BE A BIG LIMITING
FACTOR AND WILL ONLY WARRANT FCST VISIBILITIES INTO THE 2-5SM
RANGE...WITH THE POTENTIAL FOR MORE WIDESPREAD FOG OVER ERN LOWER MI
WHERE THE GRADIENT WILL BE MUCH WEAKER.

&&

.MARINE...
ISSUED AT 345 PM EDT WED MAY 6 2015

SOME FOG IS POSSIBLE OVER THE LAKE TONIGHT. OTHERWISE...WEAK
SOUTHEASTERLIES WILL VEER TO SOUTHERLY AND INCREASE IN SPEED
THURSDAY NIGHT INTO FRIDAY. EXPECTING WAVES TO REMAIN BELOW 4 FEET
IN THE NEARSHORE TIME WINDOW.

&&

.HYDROLOGY...
ISSUED AT 345 PM EDT TUE MAY 5 2015

ROUNDS OF SHOWERS THUNDERSTORMS ARE EXPECTED FRIDAY THROUGH MONDAY.
RIVERS AND STREAMS ARE WELL WITHIN BANKS...CONDITIONS WILL NEED
TOP BE MONITORED FOR POTENTIAL RISES DUE THE EXPECTED ACTIVITY.

&&

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

$$

SYNOPSIS...MANN
SHORT TERM...CB
LONG TERM...DK/DE
AVIATION...SC
HYDROLOGY...MANN
MARINE...MANN



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