Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 021741
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
141 PM EDT SUN AUG 2 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 318 AM EDT SUN AUG 2 2015

SEVERE THUNDERSTORMS ARE LOOKING MORE LIKELY FOR THIS EVENING
WITH THE PRIMARY HAZARD BEING DAMAGING WIND GUSTS. ADDITIONAL
THREATS INCLUDE SOME LARGE HAIL AND ALSO LOCALLY HEAVY RAINFALL.
COOLER AND DRIER CONDITIONS WILL MOVE IN FOR MONDAY AND TUESDAY
WITH PERHAPS SOME RAIN RETURNING TO THE AREA FOR THURSDAY.

&&

.UPDATE...
ISSUED AT 1110 AM EDT SUN AUG 2 2015

OUR CHALLENGE FOR THE DAY IS OBVIOUSLY DEALING WITH CONVECTIVE
TRENDS...AND THE THREAT FOR SEVERE WEATHER THROUGH THIS EVENING.

PLENTY OF AREAS OF CONVECTION ACROSS THE REGION THIS MORNING...
MAINLY ACROSS NE WISCONSIN AND NRN MICHIGAN. THESE AREAS ARE
PRETTY MUCH ON THE NRN PERIPHERY OF THE 40 KNOT LLJ THAT IS IN
PLACE. WE ARE EXPECTING AT THIS TIME THAT MOST OF THE CONVECTION
THROUGH THIS AFTERNOON WILL REMAIN NORTH OF A PENTWATER TO MT.
PLEASANT LINE. WE CAN NOT RULE OUT SEVERE WEATHER UP THERE WITH
THE LOW LEVEL JET CORE OVERHEAD. HOWEVER THOSE STORMS ARE SOMEWHAT
ELEVATED...SO WIDESPREAD SEVERE WEATHER IS NOT EXPECTED THROUGH
MID AFTERNOON.

WE ARE STILL EXPECTING THAT CONVECTION WILL EVOLVE INTO A SQUALL
LINE VERY LATE THIS AFTERNOON UP NORTH...TO EARLY THIS EVENING. WE
EXPECT THAT THE COLD FRONT AND A SHORT WAVE COMING DOWN FROM NRN
MN AND THE WRN U.P. WILL HELP TO CONSOLIDATE THE CONVECTION INTO A
SQUALL LINE AS IT DROPS SE. SEVERE WX WILL BE POSSIBLE UP
NORTH...BUT THE BIGGER CONCERN WILL BE FURTHER SOUTH WHERE PLENTY
OF DESTABILIZATION IS TAKING PLACE WITH THE SUN OUT.

ML CAPES ARE ALREADY RUNNING 2000-2500 J/KG IN THE SUNNY AREAS
WITH MU CAPES OVER 3000. THIS WILL ONLY GET WORSE DURING THE DAY.
A LITTLE OF THE INSTABILITY WILL LIKELY BE LOST AFTER PEAK
HEATING. WE WILL KEEP MUCH OF IT THOUGH...AND CONTINUE TO ADVECT
MORE INSTABILITY IN ALOFT WITH THE LLJ FEEDING IT IN THROUGH 00Z.

WIND SHEAR CONTINUES TO LOOK FAVORABLE WITH THE LOW LEVEL JET
HELPING 0-3KM SHEAR VALUES. THE STRONG LOW LEVEL JET AROUND WILL
BE AVAILABLE TO BE TAPPED WITH THE STORMS...AND THE LOWEST LEVELS
OF THE PROFILE WILL NOT STABILIZE MUCH. THIS WILL ALLOW DAMAGING
WINDS TO BE A REAL THREAT. THE STRONG LOW LEVEL SHEAR WILL ALSO BE
CONDUCIVE FOR ISOLATED TORNADOES ALONG THE LINE.

TIME FRAME FOR THE STRONGEST STORMS LOOKS TO BE AFTER ABOUT 6 PM
ACROSS THE NW...AROUND 10 PM FOR THE GRR AREA...AND THE STORMS
SHOULD MOVE OUT OF JACKSON AFTER MIDNIGHT.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 318 AM EDT SUN AUG 2 2015

VERY GOOD OPPORTUNITY FOR SOME SEVERE WEATHER TODAY ESPECIALLY
AFTER 21Z...STARTING IN OUR NW COUNTIES. PRIOR TO THIS...A MORNING
THUNDERSTORM IS POSSIBLE FROM LUDINGTON TO CLARE...AND A FEW
STORMS MAY FIRE THIS AFTERNOON THOUGH MORE WIDESPREAD ACTIVITY
HOLDS OFF UNTIL 21Z AND BEYOND. DAMAGING WINDS WILL BE OUR PRIMARY
CONCERN THOUGH THE ENVIRONMENT WILL SUPPORT A FEW ROTATING CELLS
WITH AN ISOLATED TORNADO POSSIBLE ACROSS SW LOWER MI.

MOST HI RES MODELS PAINT A SIMILAR PICTURE FOR OUR AREA THIS
EVENING...WITH AN IMPRESSIVE SQUALL LINE EXPECTED ALONG THE COLD
FRONT AS IT MOVES INTO THE CWA FROM AS EARLY AS 21Z OR 22Z NEAR
LUDINGTON AND PROGRESSING SE INTO THE REMAINDER OF THE CWA FROM 00Z-
04Z. DEEP LAYER SHEAR HAS ONLY LOOKED BETTER AND BETTER WITH THIS
EVENT...NOW FORECAST TO BE 40-50 KNOTS ESPECIALLY FOR OUR CENTRAL
AND NORTHERN COUNTIES. THE LLJ ALSO LOOKS IMPRESSIVE...AROUND 50
KNOTS RIGHT OVER US AROUND 00Z.

WITH MOST OF THE AREA STAYING DRY THROUGH THE MORNING AND EARLY
AFTERNOON HOURS...WE WILL BE IN A WELL MIXED ENVIRONMENT WITH HIGHS
SURGING INTO THE UPPER 80S TO NEAR 90 (ESPECIALLY FROM GRR TO LAN
AND SOUTH) AND SYNOPTIC WIND GUSTS OF 30-35 MPH EXPECTED. SB CAPE
READINGS WILL LIKELY REACH 3000 J/KG OR HIGHER THIS
AFTERNOON/EVENING (THE NSSL WRF IS SHOWING 4000+ J/KG...YIKES).
COMBINED WITH 0-1KM HELICITY READINGS OF 200-300 M2/S2 AHEAD OF
THE FRONT...OUR REGION WILL NOT ONLY BE FAVORED FOR WIDESPREAD
DAMAGING WIND GUSTS/BOWING LINE SEGMENTS BUT ALSO AN ISOLATED
TORNADO OR TWO NOT OUT OF THE QUESTION EITHER ALONG OR JUST AHEAD
OF THE SQUALL LINE. LARGE HAIL IS ALSO POSSIBLE WITH ABUNDANT CAPE
IN THE ICE GROWTH ZONE...AND WOULD BE MORE OF A CONCERN IF
COINCIDENT WITH STRONG WIND GUSTS WITHIN THE SQUALL LINE.

LOOKING AT THE NCAR HI RES ENSEMBLE FORECASTS...NUMEROUS SIGNS POINT
TO SEVERE WEATHER. ONE ITEM OF NOTE IS THE PROBABILITY OF 0-1 KM SRH
EXCEEDING 300 M2/S2. BETWEEN 21Z-00Z...THE ENSEMBLE MEAN PROB PLOT
IS SHOWING 60%-80% FROM MKG/BIV TO GRR/AZO. WHILE THE MAIN SQUALL
LINE MAY BE NORTH OF THESE LOCATIONS AT THAT POINT...WILL NEED TO
WATCH FOR ANY ISOLATED CELLS THAT TRY TO POP AHEAD OF THE LINE AS
WELL GIVEN THESE VERY HIGH SRH VALUES.

WITH THE LLJ SOLIDLY 50 KNOTS...IT WILL NOT BE DIFFICULT FOR THESE
WINDS TO MIX DOWN WITHIN THE SQUALL LINE. THE CONVECTIVE MODE OF THE
HI RES MODEL SIM Z PLOTS (IE. NAMDNG...NSSL WRF...AND THE
EXPERIMENTAL HRRR) SUGGESTS BOWING LINE SEGMENTS ARE POSSIBLE ALONG
THE SQUALL LINE. INTERESTINGLY...THE WRF ARW/NMM ARE CONSIDERABLY
LESS OPTIMISTIC WITH WIDESPREAD CONVECTION ACROSS OUR CWA...AND MORE
FOCUSED ON NORTHERN IL. THIS SCENARIO SEEMS LESS LIKELY GIVEN THE
STRONG FORCING...MOISTURE ADVECTION...AND INSTABILITY FEATURED ALL
ALONG THE FRONT TONIGHT.

REGARDING THIS MORNING...A FEW THUNDERSTORMS OVER CENTRAL WISCONSIN
WILL TRY TO MOVE INTO THE LAKE SHORE REGION FROM PENTWATER TO THE
NORTH BETWEEN 10Z-12Z. THEY ARE NOT EXPECTED TO BE SEVERE IF THEY
MAKE IT TO THE LAKE SHORE...BUT I SUPPOSE THERE IS A LOW RISK FOR
SOME HAIL. RESIDUAL CLOUDINESS FROM THIS ACTIVITY MAY DELAY
DESTABILIZATION SOMEWHAT FOR OUR CENTRAL AND NORTHERN
COUNTIES...BUT STILL THINKING THAT THE ATMOSPHERE WILL RECOVER BY
THE AFTERNOON WITH DEEPER MIXING OCCURRING.

MONDAY AND TUESDAY WILL LARGELY STAY DRY OUTSIDE OF A FEW POP UP
AFTERNOON SHOWERS. COOLER READINGS IN THE MID 70S ARE EXPECTED.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 318 AM EDT SUN AUG 2 2015

TEMPERATURES WILL BE SEASONABLY COOL THROUGH THE LONG RANGE FORECAST
PERIOD AND AVERAGE AROUND 5 TO 10 DEGREES BELOW NORMAL FOR THIS TIME
OF YEAR WITH MAX TEMPS IN THE 70S AND MIN TEMPS MAINLY IN THE 50S. A
SFC HIGH PRESSURE RIDGE WILL BRING FAIR WX TUESDAY NIGHT AND
WEDNESDAY.

OVERALL MEDIUM RANGE GUIDANCE TRENDS INCLUDING THE 00Z ECMWF SHOW
INCREASING POTENTIAL FOR RAIN TO MAKE IT INTO OUR FCST AREA THURSDAY
THROUGH THURSDAY NIGHT TO THE NORTH OF A LOW PRESSURE SYSTEM THAT
WILL PASS JUST SOUTH OF LWR MI. RAISED POPS THURSDAY TO ACCOUNT FOR
THIS. BEYOND THAT FAIR AND TRANQUIL WX IS ANTICIPATED FRIDAY THROUGH
NEXT WEEKEND AS A HIGH PRESSURE RIDGE CENTERED OVER JAMES BAY CANADA
TAKES HOLD OF OUR WX PATTERN.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 140 PM EDT SUN AUG 2 2015

LITTLE CHANGE TO THE PREVIOUS FORECAST. STILL EXPECT STRONG
CONVECTIVE GUSTS FROM THE NORTHWEST WITH THE LINE OF STORMS MOVING
INTO THE AREA TONIGHT. BEHIND THIS LINE...WINDS MAY BRIEFLY RETURNTO
SOUTHWESTERLY IN DIRECTION AND POSSIBLY EVEN SOUTHEAST. THIS
SHOULD BE FOLLOWED BY A SHIFT TO THE NORTHWEST BEHIND THE ACTUAL
COLD FRONT AROUND OR SHORTLY AFTER 06Z.

&&

.MARINE...
ISSUED AT 318 AM EDT SUN AUG 2 2015

ROUGH CHOP ON THE LAKE TODAY WITH IMPRESSIVE WINDS EXPECTED FOR
THE BEGINNING OF AUGUST...POSSIBLY REACHING 30 KNOTS. WAVES WILL
LIKELY REACH 3 TO 6 FEET WITH SOME OVER 6 FEET POSSIBLE. A SQUALL
LINE OF THUNDERSTORMS THIS EVENING WILL POSE A HIGH RISK TO
MARINERS...WITH STRONG WIND GUSTS SHIFTING FROM THE SW TO NW AS IT
MOVES THROUGH. LIGHTNING WILL ALSO BE A THREAT.


&&

.HYDROLOGY...
ISSUED AT 255 PM EDT SAT AUG 1 2015

LOCALLY HEAVY RAINFALL ON SUNDAY WILL BE THE MAIN HYDRO CONCERN OVER
THE NEXT WEEK. GIVEN THE RECENT DRY WEATHER... BASIN AVERAGE QPF OF
A HALF TO AROUND AN INCH SHOULD BE EASILY HANDLED BY THE LARGER
RIVER SYSTEMS. POTENTIAL EXISTS FOR MINOR HEAVY RAIN IMPACTS
INCLUDING ROAD PONDING AND RISES OF SMALLER CREEKS AND RIVERS...
PRIMARILY IF THUNDERSTORMS TEND TO PERSIST OVER A GIVEN AREA.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...BEACH HAZARDS STATEMENT THROUGH MONDAY MORNING FOR MIZ037-043-
     050-056-064-071.

LM...SMALL CRAFT ADVISORY UNTIL 8 AM EDT MONDAY FOR LMZ844>849.

&&

$$

UPDATE...NJJ
SYNOPSIS...HOVING
SHORT TERM...HOVING
LONG TERM...LAURENS
AVIATION...TJT
HYDROLOGY...CAS
MARINE...HOVING


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