Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 251639
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1239 PM EDT MON MAY 25 2015

LATEST UPDATE...
HYDRO

.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 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 624 AM EDT MON MAY 25 2015

SHOWERS WILL BE ON THE INCREASE THIS MORNING...HOWEVER ANY SUB VFR
CONDITIONS ARE EXPECTED TO REMAIN LIMITED AS THE LOW LEVEL
MOISTURE IS GENERALLY LACKING. A FEW THUNDERSTORMS COULD DEVELOP
LATER THIS MORNING OR THIS AFTERNOON. I INCLUDED VCTS GENERALLY
EAST OF KBTL TO ACCOUNT FOR THIS POTENTIAL. THERE WILL BE A TIGHT
PRESSURE GRADIENT TODAY. THIS WILL LEAD TO GUSTY WINDS WITH 25
KNOTS LIKELY AT ALL TAF SITES.

THE WIND WILL SETTLE DOWN THIS EVENING. A MAINLY DRY NIGHT IS
FORECASTED. LATER AT NIGHT WE WILL NEED TO MONITOR THE POTENTIAL
FOR ADDITIONAL STORMS TO DEVELOP. INCREASING LOW LEVEL MOISTURE
WILL SUPPORT SOME DEVELOPING MVFR CLOUDS.

&&

.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 1239 PM EDT MON MAY 25 2015

THE HYDROLOGIC SERVICE AREA HAS EXPERIENCED GENERALLY LESS THAN A
HALF INCH OF PRECIPITATION WITH THE CURRENT SYSTEM. RIVER LEVELS ARE
LOW AND STABLE. EXPECTING ANOTHER 1/2 TO 3/4 OF AN INCH OF
PRECIPITATION TONIGHT THROUGH WEDNESDAY. THIS SHOULD LEAD TO SLOWLY
INCREASING RIVER LEVELS BY MID WEEK. EXPECTING NO OR MINOR/NUISANCE
FLOODING BY WEEKS END.

A POTENTIAL FOR MORE RAIN FRIDAY INTO SUNDAY (OVER AN INCH) MAY PUSH
SOME STREAMS AND RIVERS ABOVE BANKFULL BY NEXT WEEK... IF THESE
AMOUNTS ARE REALIZED.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...BEACH HAZARDS STATEMENT THROUGH LATE TONIGHT FOR MIZ056-064-071.

     BEACH HAZARDS STATEMENT THROUGH TUESDAY MORNING FOR MIZ037-043-
     050.

LM...SMALL CRAFT ADVISORY UNTIL 8 AM EDT TUESDAY FOR LMZ847>849.

     SMALL CRAFT ADVISORY UNTIL 1 AM EDT TUESDAY FOR LMZ844>846.

&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...MJS
AVIATION...MJS
HYDROLOGY...63
MARINE...MJS



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