Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 250546
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
146 AM EDT SAT JUL 25 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 330 PM EDT FRI JUL 24 2015

AN APPROACHING WEAKENING COLD FRONT WILL CAUSE SCATTERED SHOWERS
AND THUNDERSTORMS TO DEVELOP VERY LATE TONIGHT THROUGH SATURDAY.
WIDESPREAD RAIN IS NOT ANTICIPATED AND MOST OF THIS TIME PERIOD
WILL BE DRY AND VERY WARM. HOT AND INCREASINGLY HUMID WEATHER WILL
DEVELOP SUNDAY THROUGH THE MIDDLE OF NEXT WEEK WITH INCREASING
POTENTIAL FOR SOME THUNDERSTORMS TOWARD THE MIDDLE OF NEXT WEEK.

&&

.UPDATE...
ISSUED AT 1029 PM EDT FRI JUL 24 2015

UPSTREAM TRENDS SUGGEST IT MAY TAKE UNTIL AFTER 5 OR 6 AM FOR
ANY SHOWERS TO GET IN HERE... AND THE THUNDER RISK LOOKS RATHER
LIMITED UNTIL AFTER 11 AM SATURDAY BASED ON LATEST RAP MU CAPE
PROGS. HAVE ADJUSTED POP/WX/SKY GRIDS TO ACCOUNT FOR LATEST
TRENDS AND SHORT RANGE GUIDANCE.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 330 PM EDT FRI JUL 24 2015

PRIMARY SHORT TERM FCST CONCERNS INVOLVE ASSESSMENT OF CONVECTIVE
POTENTIAL VERY LATE TONIGHT THROUGH SATURDAY AFTERNOON.

A WEAKENING COLD FRONT WILL CAUSE SCATTERED SHOWERS AND A FEW
THUNDERSTORMS TO DEVELOP NEAR TO NW OF A LINE FROM KGRR TO KMOP
BETWEEN 06Z AND 12Z SATURDAY AS SUGGESTED BY 12Z NSSL WRF
GUIDANCE. THE STORMS WILL DEVELOP IN AN AXIS OF INCREASING
ELEVATED INSTABILITY AND WITH LOW LEVEL MOISTURE POOLING ALONG AND
AHEAD OF THE FRONT.

SEVERE WX IS NOT ANTICIPATED LATE TONIGHT DUE TO LACK OF DEEP LAYER
SHEAR... WEAK INSTABILITY AND WEAK FORCING FROM THE FRONT. SCATTERED
SHOWERS AND STORMS WILL REDEVELOP ALONG AND JUST AHEAD OF THE FRONT
SATURDAY AS INSTABILITY INCREASES WITH DAYTIME HEATING.

CANNOT ENTIRELY RULE OUT A FEW STRONG TO ISOLATED MARGINALLY SEVERE
STORMS MAINLY OVER OUR SE FCST AREA SATURDAY NEAR TO SE OF KGRR.
OVERALL THOUGH LACK OF STRONGER FORCING... RELATIVELY WEAK
INSTABILITY AND FAIRLY WEAK DEEP LAYER SHEAR ARE ALL MITIGATING
FACTORS. INSTABILITY WILL ALSO LIKELY BE LIMITED SOMEWHAT BY MORNING
CLOUDS AND SCATTERED SHOWERS AND STORMS.

FAIR WX WILL RETURN SATURDAY NIGHT THROUGH SUNDAY AS ANOTHER HIGH
PRESSURE RIDGE BUILDS IN. THERE IS JUST A SMALL CHANCE OF SHOWER
OR THUNDERSTORM LATE SUNDAY NIGHT OVER OUR SW FCST AREA BUT A
CONSENSUS OF SHORTER TO MEDIUM RANGE GUIDANCE SUGGESTS THAT MOST
IF NOT ALL PCPN SUNDAY NIGHT WILL STAY SW TO SOUTH OF OUR FCST AREA.

FOR THE REST OF THIS AFTERNOON AND EVENING DRY AND FAIR WX WILL
CONTINUE FOR THE VAST MAJORITY OF OUR AREA. HOWEVER AN ISOLATED
RAIN SHOWER OR TWO MAY DEVELOP FROM MID TO LATE AFTN THROUGH
EARLY EVE OVER OUR FAR EASTERN FCST AREA COINCIDENT WITH MAX
INSTABILITY FROM DAYTIME HEATING.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 330 PM EDT FRI JUL 24 2015

MODELS STILL ADVERTISING A STRONGER COLD FRONTAL PASSAGE FOR THE
MIDDLE OF NEXT WEEK.  BASED ON THE STRENGTH OF THE DEEP LAYER SHEAR
AND INSTABILITY THAT WILL BE PRESENT WHEN THE FRONT COMES
THROUGH...AND ELEVATED RISK FOR SEVERE WEATHER EXISTS.  BETTER THAN
40 KNOTS OF SHEAR ARE SHOWN.  WILL CONTINUE TO HIGHLIGHT THIS PERIOD
FOR STORMS...MAINLY TUE NIGHT INTO WED NIGHT.

CONTINUES TO LOOK WELL ABOVE NORMAL FOR TEMPERATURES GOING INTO WED.
850 MB TEMPS CLIMB INTO THE UPPER TEENS TO LOW 20S SUPPORT AT LEAST
MID 80S FOR HIGHS.  STRONG COLD AIR ADVECTION BEHIND THE FRONT
SUGGESTS A COOLER THAN NORMAL END OF THE WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 146 AM EDT SAT JUL 25 2015

THE BEGINNING AND END OF THE FCST PERIOD LOOKS QUIET...WITH A
SHORT PERIOD OF A FEW SHOWERS/STORMS ALONG WITH SOME MVFR POSSIBLE
FOR A FEW HOURS IN THE MIDDLE OF THE PERIOD.

CONDITIONS ARE STARTING OUT VFR...AND WILL TREND TOWARD POSSIBLE
MVFR JUST AFTER DAYBREAK AT KMKG AS THE FRONT AND A FEW SHOWERS
WILL ARRIVE. THIS BAND OF POSSIBLE SHOWERS AND LOWER CONDITIONS WILL
PUSH SE...AND COULD BECOME A FEW STORMS SOUTH AND EAST OF KGRR
THIS AFTERNOON. THE MODELS INDICATE THAT SRN AREAS WILL SEE LESS
OF A CHC OF MVFR CIGS.

WE EXPECT THE PCPN TO MOVE OUT BY 22Z AT ALL TERMINALS WITH KJXN
SEEING IT LAST THE LONGEST. CLOUDS WILL THEN CLEAR OUT SHORTLY
AND WINDS WILL SHIFT FROM SW TO NW AS THE FRONT MOVES THROUGH.

&&

.MARINE...
ISSUED AT 330 PM EDT FRI JUL 24 2015

WINDS AND WAVE HEIGHTS WILL BRIEFLY INCREASE LATE TONIGHT WITH
WAVE HEIGHTS POTENTIALLY REACHING 2 TO 4 FEET. HOWEVER CONDITIONS
SHOULD REMAIN BELOW SMALL CRAFT/BEACH HAZARDS CRITERIA. WAVE
HEIGHTS AND WIND SPEEDS THROUGH THE WEEKEND WILL BE LIGHT WITH
WAVE HEIGHTS MAINLY AOB 2 FT.


&&

.HYDROLOGY...
ISSUED AT 1156 AM EDT FRI JUL 24 2015

RIVER LEVELS ARE FALLING AND ARE WELL BELOW BANKFULL. WITH UNDER
AN INCH OF PRECIPITATION EXPECTED THROUGH THE WEEK... THESE
CONDITIONS SHOULD CONTINUE. LOCALLY HEAVY RAINFALL COULD LEAD TO
PONDING OF WATER... MAINLY SATURDAY OR WEDNESDAY.

&&

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

$$

UPDATE...MEADE
SYNOPSIS...LAURENS
SHORT TERM...LAURENS
LONG TERM...MJS
AVIATION...NJJ
HYDROLOGY...63
MARINE...LAURENS


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