Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 241924
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
324 PM EDT SUN APR 24 2016

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

.SYNOPSIS...
ISSUED AT 229 PM EDT SUN APR 24 2016

A LOW PRESSURE SYSTEM CENTERED OVER SOUTH DAKOTA WILL TRACK EAST
TONIGHT AND THROUGH MICHIGAN MONDAY INTO MONDAY NIGHT. SOUTHERLY
WINDS AHEAD OF THIS SYSTEM WILL DRAW UP AN UNSEASONABLY MILD AND
MOIST AIRMASS. THIS WILL LEAD TO AN INCREASING RISK FOR SHOWERS
AND THUNDERSTORMS...ESPECIALLY LATER MONDAY INTO MONDAY NIGHT.
SOME OF THE STORMS COULD BE STRONG WITH THE RAIN HEAVY AT TIMES. A
COOLER AIRMASS WILL FILTER IN FROM THE NORTH ON TUESDAY AS AN AREA
OF HIGH PRESSURE STRENGTHENS OVER ONTARIO.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 229 PM EDT SUN APR 24 2016

THE MAIN CHALLENGES DEAL WITH THE POTENTIAL FOR SEVERE WEATHER
MONDAY INTO MONDAY NIGHT ALONG WITH THE TIMING OF THE
PRECIPITATION.

MODELS VARY ON THE THE AMOUNT OF INSTABILITY THAT DEVELOPS ON
MONDAY ALONG THE WITH THE TIMING OF THE PRECIPITATION. THE NAM
FEATURES ABUNDANT INSTABILITY MONDAY AFTERNOON THROUGH MONDAY
EVENING. THAT COUPLED WITH STRENGTHENING DEEP LAYERED SHEAR AND
INCREASING HELICITY...ESPECIALLY MONDAY EVENING WOULD EASILY SUPPORT
SEVERE WEATHER. HOWEVER THE NAM SEEMS TO BE AN OUTLIER WITH THE
GFS AND HIGH RES EURO FAVORING MUCH LESS IN THE WAY OF
INSTABILITY. THESE TWO MODELS BRING THE STRONGER SHEAR IN WHILE
THE INSTABILITY IS DECREASING MONDAY EVENING. THE MESOSCALE
MODELS GENERALLY SHOW LITTLE IN THE WAY OF CONVECTION ON
MONDAY...UNTIL AFTER 21Z WHEN SOME STORMS START TO DEVELOP. THE
MESOSCALE MODELS SHOW THE BEST POTENTIAL FOR STORMS AND STRONGER
SHEAR MONDAY EVENING...AFTER 00Z ALSO WHEN THE INSTABILITY IS
DECREASING. IT APPEARS A WINDOW OF INCREASED SEVERE WEATHER
POTENTIAL MAY DEVELOP LATER MONDAY AFTERNOON AS THE INSTABILITY
IS MAXIMIZED AND THE SHEAR WILL BE ON THE INCREASE. THIS RISK IS
MARGINAL AT THIS TIME. I ENDED UP FEATURING ONLY A LOW RISK FOR
STORMS THROUGH MONDAY MORNING...THEN INCREASED THE POTENTIAL AS WE
GO THROUGH THE EVENING. WILL NEED TO MONITOR TRENDS CLOSELY.

AROUND 06Z TUE THE BEST INSTABILITY WILL BE SHIFTING SOUTH OF THE
CWA. WILL DIMINISH THE THUNDERSTORM POTENTIAL THROUGH THE LATE
NIGHT PERIOD. A FEW LINGERING SHOWERS COULD EXIST ON TUESDAY WITH
A SURFACE TROUGH OVER THE REGION.

WITH TEMPERATURES FALLING INTO THE 30S AND LIGHT WINDS TUESDAY
NIGHT...WILL NEED TO MONITOR THE FROST/FREEZE RISK.

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 229 PM EDT SUN APR 24 2016

WEDNESDAY NIGHT THROUGH THURSDAY AND SATURDAY THROUGH SUNDAY LOOK
WET ACROSS SOUTHWEST LOWER MICHIGAN.

WEAK RIDGING WILL BE IN PLACE WEDNESDAY WHICH WILL LEAD TO SOME
SUNSHINE EARLY IN THE DAY BEFORE CLOUDS INCREASE DURING THE
AFTERNOON AS LOW PRESSURE MOVES EAST FROM THE MISSOURI VALLEY. RAIN
WILL DEVELOP AHEAD OF THE LOW WHICH IS PROGD TO MOVE JUST SOUTH OF
THE CWA. THE GFS IS HINTING THAT AS TEMPERATURES FALL INTO THE 30S
WEDNESDAY NIGHT THAT THERE COULD BE SOME WET SNOW THAT MIXES WITH
THE RAIN NORTH OF I-96. WE DIDN`T PUT THAT IN THE GRIDS YET BUT IT/S
SOMETHING TO KEEP IN MIND. SHOWERS WILL DIMINISH THURSDAY NIGHT
BEHIND THE LOW AND FRIDAY LOOKS QUIET WITH SOME SUNSHINE AS HIGH
PRESSURE BUILDS IN.

THE NEXT PLAINS LOW MOVES TOWARDS THE GREAT LAKES FRIDAY NIGHT AND
SHOULD PRODUCE SOME PCPN SATURDAY. THE ECMWF IS QUICKER THAN THE GFS
AND CMC AND THE PCPN MAY BE DELAYED UNTIL LATE IN THE DAY DUE TO DRY
NORTHEAST WINDS AHEAD OF IT. ONCE THE LOW MOVES IN THOUGH WE SHOULD
SEE SHOWERS FOR A DAY OR SO.

INSTABILITY THROUGH THE WEEK LOOKS WEAK ENOUGH THAT THUNDER ISN/T
EXPECTED. HIGHS SHOULD BE IN THE 55 TO 60 RANGE.


&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 129 PM EDT SUN APR 24 2016

VFR EXPECTED THROUGH THE PERIOD. A FRONTAL BOUNDARY WILL MOVE FROM
NORTHERN LOWER TO NEAR US-10 BY MONDAY MORNING. SCATTERED SHOWERS
NEAR THE BOUNDARY MAY AFFECT THE NORTHERN TAF SITES. HOWEVER THE
SOUTHERN TAF SITES ARE EXPECTED TO BE DRY.


&&

.MARINE...
ISSUED AT 229 PM EDT SUN APR 24 2016

SOUTHERLY WINDS WILL CAUSE SOME BUILDING WAVES OVER LAKE MICHIGAN
TONIGHT INTO TUESDAY. AT THIS TIME IT LOOKS LIKE THE WIND AND
WAVES WILL REMAIN BELOW ADVISORY CRITERIA. HOWEVER THUNDERSTORMS
COULD POSE A RISK TO MARINERS.

MONDAY NIGHT INTO TUESDAY THE WIND WILL SHIFT TO THE NORTH AS
COLDER AIR FILTERS IN. WILL NEED TO MONITOR THE POTENTIAL FOR
SMALL CRAFT CONDITIONS AS CURRENTLY PROJECTED WAVES MAY REACH 4
FEET AROUND LITTLE AND BIG SABLE POINTS.


&&

.HYDROLOGY...
ISSUED AT 1255 PM EDT SUN APR 24 2016

MOST OF THE RAINFALL OVER THE NEXT COUPLE OF DAYS IS EXPECTED MONDAY
AFTERNOON THROUGH MONDAY NIGHT. HEAVIER SHOWERS AND SOME STRONG
STORMS WILL BE CAPABLE OF PRODUCING LOCALLY HEAVY RAINFALL...
ESPECIALLY MONDAY EVENING AND MONDAY NIGHT. MOST BASINS WILL SEE
OVER A HALF INCH OF RAIN... WHILE STRONG THUNDERSTORMS AND TRAINING
OVER THE SAME AREAS COULD PRODUCE OVER AN INCH LOCALLY. EXPECT
PONDING OF WATER/LOCALIZED MINOR FLOODING IN POOR DRAINAGE AREAS IF
THIS OCCURS.

RIVER RISES ARE LIKELY... AND SOME RIVERS MAY RISE ABOVE BANKFULL
THIS WEEK. THE MAIN IMPACT WILL BE NUISANCE FLOODING NEAR RIVER
BANKS.

&&

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

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...04
AVIATION...04
HYDROLOGY...EBW
MARINE...MJS



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