Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 130102
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
902 PM EDT SAT JUL 12 2014

LATEST UPDATE...
MESOSCALE DISCUSSION

.MESOSCALE DISCUSSION...
ISSUED AT 902 PM EDT SAT JUL 12 2014

SHOWERS AND ISOLATED STORMS ARE ONGOING ACROSS THE CWFA...
ESPECIALLY ACROSS THE NRN COUNTIES WHERE THE INITIAL SURGE OF
MOISTURE TRANSPORT IS ONGOING ALOFT. ELSEWHERE...SHOWERS AND
STORMS ARE LESS CONCENTRATED FOR NOW.

FOR THE REMAINDER OF THE AREA...EYES ARE ON THE CONVECTION THAT IS
STARTING TO RAMP UP NEAR THE MISSISSIPPI RIVER. CONVECTION
CONTINUES TO FIRE THERE NEAR THE LFQ OF THE LLJ RAMPING UP THIS
EVENING AND WHERE ML/MU CAPE IS APPROACHING 3000 J/KG AND
EFFECTIVE SHEAR IS 40-50 KNOTS NEAR THE WARM SECTOR. WE ARE EXPECTING
THE LLJ TO NOSE IN HEAR BY 06Z...AND DEPART BY 12Z. FCST CAPE
VALUES ARE EXPECTED TO BE LESS HERE...ONLY UP TO AROUND 1000-1500 J/KG
OR SO NEAR I-94 WITH LESS NORTH FURTHER AWAY FROM THE WARM FRONT.

WE CONTINUE TO EXPECT DAMAGING WINDS TO BE THE MAIN THREAT WITH
THE STRONG LLJ IN PLACE RESULTING IN GOOD SHEAR VALUES. HEAVY RAIN
WILL ALSO BE A BIGGER THREAT WITH PWATS UP AND OVER 2.0 INCHES. WE
CONTINUE TO THINK THAT AN ISOLATED TORNADO WILL BE POSSIBLE WITH
THE WARM FRONT NOSING IN...RESULTING IN SOLID 0-1KM SHEAR VALUES
EXPECTED TO PEAK AROUND 30 KNOTS OR SO CENTERED AROUND 06Z NEAR
THE MI/IN BORDER.

&&

.SYNOPSIS...
ISSUED AT 231 PM EDT SAT JUL 12 2014

A COLD FRONT WILL PUSH THROUGH THE REGION LATE TONIGHT INTO SUNDAY
MORNING. THIS SYSTEM WILL TRIGGER THUNDERSTORMS. SOME OF THE
STORMS WILL CONTAIN HEAVY RAIN AND A FEW COULD TURN SEVERE. A
DRIER AIRMASS WILL FILTER IN FROM THE NORTHWEST ON SUNDAY. A COOL
CANADIAN AIRMASS ARRIVES FOR EARLY NEXT WEEK.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 231 PM EDT SAT JUL 12 2014

CHALLENGE IN THE SHORT TERM DEALS WITH THE SEVERE POTENTIAL
TONIGHT. LOOKS LIKE AN INCREASED POTENTIAL FOR SEVERE WEATHER WILL
EXIST.

THE FORCING FROM AN APPROACHING MID LEVEL WAVE COMBINES WITH THE
INSTABILITY AND A LOW LEVEL JET TO TRIGGER THUNDERSTORMS TONIGHT.
GOOD DIFFLUENCE WAS NOTED AT THE TROP.  THE MAIN TIMEFRAME LOOKS
TO BE 03Z TO 08Z. DAMAGING WINDS SEEMS LIKE THE MAIN THREAT WITH A
50 KNOT LOW LEVEL JET. GIVEN THE HIGH 0 TO 1 KM SHEAR...LOW LCL
AND LOW LEVEL CAPE...WOULD NOT RULE OUT A TORNADO AS WELL. THIS
RISK SEEMS HIGHEST AROUND INTERSTATE 94 GIVEN THE FORECASTED LOW
LEVEL JET LOCATION. HAZARDS WERE UPDATED IN THE HWO AND SOCIAL
MEDIA POSTS. HIGH POPS ALL ZONES. BY 09Z NORTHWEST COUNTIES SHOULD
SEE A DIMINISHING TREND TO THE PRECIPITATION.

FORECAST SOUNDINGS FOR SUNDAY AFTERNOON INTO SUNDAY NIGHT SHOULD A
LIMITED RISK FOR PRECIPITATION. WITH MOST LOCATIONS TO REMAIN
DRY...I LOWERED POPS.

THE UPPER LOW PIVOTS THROUGH THE REGION ON MONDAY. THIS WILL ACT
TO KEEP IT COOL WITH A RISK FOR A THUNDERSTORM...ESPECIALLY IN THE
AFTERNOON.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 231 PM EDT SAT JUL 12 2014

THE LONG TERM PERIOD WILL SEE A STEADY MODERATING TREND AS THE DEEP
UPPER TROUGH MOVES SLOWLY EASTWARD. VERY COLD H5 TEMPS NEAR -19C
WILL RESULT IN UNSTABLE CONDITIONS. THIS TIME OF YEAR THAT USUALLY
MEANS PM STORMS WITH SMALL HAIL. TRENDED CLOUD COVER UPWARD DURING
THE AFTERNOON TUESDAY OVER INLAND AREAS. INCLUDED A THUNDER MENTION
TUESDAY AFTERNOON AND WEDNESDAY AFTERNOON. BY THURSDAY THE UPPER LOW
WILL BE EAST OF THE CWA AND THE PCPN THREAT WILL BE GREATLY
DIMINISHED. A VERY CHILLY DAY IS EXPECTED TUESDAY WITH HIGHS IN THE
MID 60S. HOWEVER...BY THE WEEKEND TEMPS WILL BE BACK TO AROUND 80.
THE LAST HALF OF THE PERIOD LOOKS DRY AS SFC HIGH PRESSURE WILL
DEVELOP OVER LOWER MICHIGAN.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 757 PM EDT SAT JUL 12 2014

MVFR CONDITIONS ARE EXPECTED TO BECOME MORE WIDESPREAD THIS
EVENING AS RAIN CONTINUES TO INCREASE IN COVERAGE. TSTM POTENTIAL
WILL INCREASE SIGNIFICANTLY BETWEEN 02Z AND 04Z... LASTING 2-4
HOURS AT MOST LOCATIONS. POTENTIAL EXISTS FOR SOME STRONG TO SVR
STORMS WITH TORRENTIAL DOWNPOURS... ESPECIALLY ALONG THE I-94
CORRIDOR. THIS COULD LEAD TO AREAS OF IFR/LIFR VSBYS AS WELL AS A
BRIEF WIND GUST OVER 30KTS.

IFR CIGS WILL PROBABLY BECOME COMMON FOR A FEW HOURS LATE TONIGHT
BEHIND THE DEPARTING RAIN BEFORE CONDITIONS IMPROVE TO VFR BY MID
TO LATE MORNING SUNDAY. SFC WINDS WILL INCREASE OUT OF THE WEST TO
12-22 KTS FOR SUNDAY AFTERNOON.


&&

.MARINE...
ISSUED AT 231 PM EDT SAT JUL 12 2014

OVERALL CONDITIONS ARE EXPECTED TO REMAIN BELOW CRITERIA FOR
HEADLINES. CONVECTION COULD LEAD TO BRIEF PERIOD OF STRONGER WINDS
AND HIGHER WAVES.


&&

.HYDROLOGY...
ISSUED AT 231 PM EDT SAT JUL 12 2014

AT THIS TIME NO WATCH FOR FLOODING. THE THOUGHT IS THAT THE STORMS
WILL TRACK STEADILY EAST...ROUGHLY 03Z TO 08Z. MOST LOCATIONS WILL
SEE A STORM THAT LASTS FOR AN HOUR OR PERHAPS TWO. GENERALLY AN
INCH OF RAIN WILL ACCOMPANY THE STORMS...BUT LOCAL AMOUNTS COULD
TOP 2 INCHES. URBAN AND POOR DRAINAGE FLOODING APPEARS TO BE THE
MAIN RISK FROM THESE STORMS. PWAT VALUES OVER 2 INCHES AND GOOD
FORCING SUPPORT MOST LOCATIONS SEEING THESE HEAVY DOWNPOURS.

&&

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

$$

MESOSCALE...NJJ
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...93
AVIATION...MEADE
HYDROLOGY...MJS
MARINE...MJS





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