Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 250727
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
327 AM EDT MON MAY 25 2015

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

.SYNOPSIS...
ISSUED AT 247 AM EDT MON MAY 25 2015

A LARGE AREA OF HIGH PRESSURE SITUATED OFF THE MID ATLANTIC STATES
WILL CONTINUE TO DRAW UP A WARM AND INCREASINGLY MOIST AIRMASS
INTO THE GREAT LAKES REGION THROUGH TUESDAY. SEVERAL WAVES OF LOW
PRESSURE WILL TRACK NORTHEAST THROUGH THE WESTERN GREAT LAKES
REGION INTO WEDNESDAY SUPPORTING SHOWERS AND EVEN A FEW
THUNDERSTORMS AT TIMES FOR THE AREA. HIGH PRESSURE WILL TRACK
THROUGH ONTARIO THURSDAY AND COULD PROVIDE THE GREAT LAKES REGION
WITH MAINLY DRY WEATHER.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 247 AM EDT MON MAY 25 2015

THE MAIN CHALLENGE IN THE SHORT TERM DEALS WITH THE COVERAGE AND
INTENSITY OF ANY THUNDERSTORMS.

TO START THE UPSTREAM SHOWER AND THUNDERSTORM ACTIVITY HAS BEEN
WEAKENING. STILL WITH THE WARM AND MOIST AIR ADVECTION CONTINUING
AND A SHORT WAVE TO TRACK THROUGH THE REGION LATER THIS
MORNING...SHOWERS AND THUNDERSTORMS SHOULD REDEVELOP THIS AM. WITH
THE ATMOSPHERE DESTABILIZING LATER THIS MORNING...THAT COULD HELP
STRENGTHEN THE CONVECTION...ESPECIALLY TOWARD JACKSON AND LANSING.
SEVERE WEATHER RISK IS NOT ZERO...BUT AT THIS TIME THE LIMITED
INSTABILITY SUGGESTS THE SEVERE WEATHER RISK IS LIMITED TODAY.
WILL NEED TO MONITOR TRENDS CLOSELY. AS FOR THE WIND TODAY...IT
CONTINUES TO LOOK GUSTY. VALUES OVER 30 KNOTS POSSIBLE AS A LOW
LEVEL JET MIGRATES THROUGH AND MIXING INCREASES DURING THE DAY.

TONIGHT ELEVATED INSTABILITY ADVECTS IN FROM THE SOUTHWEST...SO A
RISK FOR STORMS. HOWEVER CURRENTLY THE REGION IS SHOWN TO BE IN
THE SPEED DIVERGENT REGION OF THE LOW LEVEL JET TO OUR
NORTH...WHICH WOULD ACT TO LIMIT THE LIFT. DECENT DEEP LAYER SHEAR
IS SHOWN. I WILL GENERALLY HOLD ONTO THE POTENTIAL FOR SHOWERS AND
THUNDERSTORMS TONIGHT.

TUESDAY INTO TUESDAY NIGHT LOOKS TO BE OUR BEST RISK FOR STRONGER
STORMS. A LOW LEVEL JET ARRIVES FROM THE SOUTH...DURING THE
AFTERNOON AND EVENING. THAT COUPLED WITH DECENT
INSTABILITY...SHEAR AND MID LEVEL HEIGHT FALLS SHOULD SUPPORT A
STRONGER ROUND OF CONVECTION. WILL MAINTAIN THE HIGHER POPS AND
MENTION A RISK FOR SEVERE WEATHER IN THE HAZARDOUS WEATHER
OUTLOOK.



.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 247 AM EDT MON MAY 25 2015

PRIMARY FOCUS IS ON THE CHANCE FOR THUNDERSTORMS FRIDAY AND
SATURDAY. GFS/ECWMF/GEM ALL SHOWING BAROCLINIC ZONE ACROSS THE UPPER
MIDWEST AT 12Z FRIDAY. ALOFT...ULJ DIVERGENCE MOVES INTO WI AND
LOWER MI BY 00Z SAT WITH A 30-35 KT LLJ INDICATED BY THE ECWMF.
HOWEVER...THE GFS HAS THE LLJ MUCH WEAKER THAN THAT AND PEELS IT OFF
TO THE EAST BY 06Z SAT. THE GEM HAS A CONSIDERABLY STRONGER LLJ AT
40-50 KNOTS AND THE MODEL QPF IS MUCH HIGHER THAN THE GFS AND ECMWF
(1"-2" FOR THE WESTERN CWA). REGARDLESS...MOIST SOUTHERLY FLOW AND
UPPER LEVEL SYNOPTIC SUPPORT SUGGEST AN INCREASED RISK FOR
THUNDERSTORMS FRIDAY NIGHT AND SATURDAY WITH PERHAPS THE HEAVIEST
PRECIPITATION FORMING ACROSS MN AND WI DURING THE DAY FRIDAY AND
WEAKENING A BIT AS IT PROPAGATES INTO SW LOWER MI.

WHILE SFC BASED CAPE WILL BE IN THE 1000-2000 J/KG RANGE ON FRIDAY
AND SFC COMPUTED LI VALUES SHOULD BE AROUND -5 OR -6...BULK SHEAR IS
EXPECTED TO BE ABOUT 20 KNOTS. THE BEST INSTABILITY WILL BE OFFSET
FROM THE TIMING OF UPPER LEVEL FORCING. SO...THIS DOES NOT LOOK TO
BE A SEVERE WEATHER SETUP...AND CONVECTIVE COVERAGE ON FRIDAY MAY BE
MORE ISOLATED/SCATTERED IN NATURE UNTIL THE COLD FRONT MOVES THROUGH
LATE FRIDAY NIGHT/SATURDAY MORNING.

MODEL DIFFERENCES EXIST REGARDING THE REMAINDER OF THE WEEKEND WITH
THE BOUNDARY HANGING UP SOUTH OF THE STATE. THE GFS BRINGS PRECIP
BACK IN SUNDAY AND MONDAY WITH THE ECMWF KEEPING MOST OF THE
ACTIVITY SOUTH OF OUR AREA.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 131 AM EDT MON MAY 25 2015

FOCUS CONTINUES TO BE ON STRONG S/SW WIND GUSTS FOR THE AFTERNOON
HOURS ESPECIALLY. MODELS CONTINUE TO INDICATE WIND GUSTS OF 25 TO
30 KNOTS WILL BE MIXED DOWN TO THE SFC AS THESE WINDS ARE NOT MORE
THAN 500 FT OFF THE GROUND. SHOULD THE CLOUDS CLEAR OUT SOON
ENOUGH THIS AFTERNOON...WIND GUSTS APPROACHING 40 KNOTS ARE NOT
OUT OF THE QUESTION. THESE WINDS WILL BE LOCATED ABOUT 2K FT OFF
THE GROUND AND THE POSSIBILITY EXISTS FOR SFC GUSTS TO BE THAT
HIGH IN THE 18Z-21Z TIME FRAME.

THE CIGS/VIS ASSOCIATED WITH ANY SHOWERS TODAY DO NOT LOOK TO BE
CATEGORIZED AS IFR...BUT WILL HAVE TO WATCH OUT FOR AFTERNOON
T-STORM DEVELOPMENT FROM BTL TO LAN AND JXN WHERE GREATER HEATING
COMBINED WITH INSTABILITY WILL BE PRESENT.


&&

.MARINE...
ISSUED AT 247 AM EDT MON MAY 25 2015

STABLE LAKE CONDITIONS MAY LIMIT WAVE HEIGHTS TODAY AND INTO
TONIGHT SOMEWHAT...BUT ENOUGH PRESSURE GRADIENT APPEARS TO EXIST
TO CREATE HAZARDOUS WAVES AND WINDS. WILL MAINTAIN THE CURRENT SET
OF HEADLINES. THE PRESSURE GRADIENT IS SHOWN TO WEAKEN ON
TUESDAY...SO THAT SHOULD ALLOW FOR DECREASING WINDS AND WAVES.


&&

.HYDROLOGY...
ISSUED AT 204 PM EDT SUN MAY 24 2015

THREE MAIN ROUNDS OF RAIN ARE FORECAST FOR SOUTHWEST LOWER MICHIGAN
THROUGH NEXT WEEKEND...THE FIRST OF WHICH IS ARRIVING NOW. RAINFALL
TOTALS OF UP TO HALF AN INCH ARE POSSIBLE ACROSS CENTRAL LOWER
MICHIGAN THROUGH MONDAY AFTERNOON...MAINLY OVER THE UPPER MUSKEGON
BASIN AND PERE MARQUETTE BASINS. MONDAY AFTERNOON THROUGH MONDAY
NIGHT LOOKS FAIRLY DRY. A SECOND ROUND OF SHOWERS AND A FEW STORMS
WILL BE POSSIBLE TUESDAY AFTERNOON THROUGH TUESDAY NIGHT.

THE BIGGEST HYDRO CONCERN COULD BE THE THIRD ROUND ON FRIDAY AND
SATURDAY. A MORE UNSTABLE AND INCREASINGLY HUMID AIRMASS WILL BE
MORE CONDUCIVE TO STRONGER THUNDERSTORMS CAPABLE OF HEAVY RAINFALL
FRIDAY INTO SATURDAY. THE ECMWF EPS...GEM...AND GFS AGREE THAT 2 TO
3 INCHES OF WIDESPREAD RAINFALL IS POSSIBLE THROUGH SUNDAY...WITH
HIGHER AMOUNTS POSSIBLE IN STRONG THUNDERSTORMS. RIVER RISES ARE
EXPECTED THIS WEEK AND ESPECIALLY NEXT WEEKEND. THE MAIN IMMEDIATE
THREAT WILL BE MINOR NUISANCE FLOODING MIDWEEK WITH THE POSSIBILITY
OF HEAVY RAINFALL TUESDAY AFTERNOON THROUGH TUESDAY NIGHT. THE
FLOODING RISK IS HIGHER NEXT WEEKEND...ESPECIALLY IN URBAN AREAS AND
ON SMALLER STREAMS.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...BEACH HAZARDS STATEMENT FROM 9 AM EDT THIS MORNING THROUGH LATE
     TONIGHT FOR MIZ056-064-071.

     BEACH HAZARDS STATEMENT FROM 9 AM EDT THIS MORNING THROUGH
     TUESDAY MORNING FOR MIZ037-043-050.

LM...SMALL CRAFT ADVISORY FROM 9 AM THIS MORNING TO 8 AM EDT TUESDAY
     FOR LMZ847>849.

     SMALL CRAFT ADVISORY FROM 9 AM THIS MORNING TO 1 AM EDT TUESDAY
     FOR LMZ844>846.

&&

$$

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


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