Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 120730
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
330 AM EDT SAT APR 12 2014

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

.SYNOPSIS...
ISSUED AT 330 AM EDT SAT APR 12 2014

AFTER A DRY MORNING THIS MORNING...A WET PERIOD IS IN STORE FOR THE
AREA FOR THE REMAINDER OF THE WEEKEND AND INTO THE DAY ON MONDAY.
WAVES OF RAIN AND THUNDERSTORMS WILL MOVE ACROSS THE AREA BEGINNING
THIS AFTERNOON...AND CONTINUE INTO MONDAY MORNING. HEAVY AMOUNTS OF
RAINFALL ARE LIKELY...WITH THE HEAVIEST RAIN EXPECTED NORTH OF THE
I-96 CORRIDOR. FLOODING IS VERY POSSIBLE ACROSS THE NORTHERN HALF OF
THE AREA. WARM AIR CAN BE EXPECTED THIS WEEKEND FOR A GOOD PORTION
OF THE AREA.

THE HEAVY RAINS WILL TRANSITION OVER TO LIGHT SNOW ON MONDAY AND
MONDAY NIGHT AS MUCH COLDER AIR MOVES IN. LIGHT SNOW ACCUMULATIONS
WILL BE POSSIBLE.

&&

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 330 AM EDT SAT APR 12 2014

MAIN CONCERNS IN THE SHORT TERM HAVE TO DO WITH THE HEAVY RAIN
POTENTIAL AND CONVECTION THREATS THROUGH THE PERIOD. WE HAVE
MAINTAINED THE FLOOD WATCH AS IS WITH GOOD RUN TO RUN CONTINUITY IN
THE MODELS. VERY LITTLE IN THE WAY OF CHANGES HAVE BEEN MADE TO THE
FCST.

THE QUIETEST PERIOD OF THE SHORT TERM WILL BE THE FIRST FEW HOURS OF
THE FCST THIS MORNING. A SMALL AREA OF HIGH PRESSURE IS CURRENTLY
MOVING EAST ACROSS THE CWFA EARLY THIS MORNING. LURKING TO OUR SW
HOWEVER IS A DEVELOPING WARM FRONT FROM NEAR CHICAGO AND BACK TO THE
WEST. THIS WARM FRONT WILL MAKE A MOVE INTO THE AREA AFTER 12Z THIS
MORNING AS LOW PRESSURE ACROSS THE PLAINS MOVES TOWARD THE AREA. WE
EXPECT A QUICK WARMUP THIS MORNING...ESPECIALLY ACROSS THE SRN HALF
OF THE CWFA...ALONG WITH WINDS PICKING UP FROM THE SOUTH.

WE ARE EXPECTING SHOWERS AND STORMS TO MOVE INTO THE NW PORTION OF
THE CWFA DURING THE AFTERNOON HOURS TODAY. THE WARM FRONT WILL
INITIALLY REMAIN DRY THIS MORNING IN OUR AREA. WE EXPECT IT TO
BECOME MORE ACTIVE THIS AFTERNOON AS THE LLJ FEEDING SHOWERS AND
STORMS ACROSS SE SOUTH DAKOTA AT 07Z THIS MORNING WILL TRANSLATE
EAST INTO THE AREA TOWARD 18Z THIS AFTERNOON. WE EXPECT THE BEST
COVERAGE OF RAIN TO OCCUR ALONG AND NORTH OF THE WARM FRONT WHICH
WILL BE NEAR I-96 THIS AFTERNOON. WE EXPECT ANY CONVECTION TO BE
MAINLY ELEVATED IN NATURE BEING NORTH OF THE FRONT. FCST SOUNDINGS
INDICATE RATHER THIN CAPE. SEVERE THREAT DOES NOT LOOK REALLY
GOOD...SOME MICROBURSTS WILL BE POSSIBLE WITH SOME DRY AIR IN THE
LOWER LEVELS INITIALLY.

WE WILL SEE THE AFTERNOON CONVECTION MOVE E/NE OF THE AREA BY THIS
EVENING...ONLY TO BE REPLACED BY ANOTHER LLJ WHICH WILL FIRE MORE
SHOWERS AND STORMS FOR THE TONIGHT PERIOD. AGAIN...WE ARE THINKING
THAT MOST OF THE PCPN WILL BE ALONG AND NORTH OF THE FRONT WHICH
WILL BE ACROSS THE NRN COUNTIES ONCE AGAIN. ONCE THE SECOND LLJ
MOVES EAST BY SUN MORNING...WE SHOULD SEE RESIDUAL PCPN SWING SE
THROUGH THE AREA AND DIMINISH IN COVERAGE FOR A SHORT TIME SUN
MORNING. THE FRONT MAY DRIFT A LITTLE FURTHER SE BRIEFLY.

THE PERIOD OF HEAVIEST RAIN STILL LOOKS TO COME BEGINNING SUN
AFTERNOON AND LAST THROUGH AROUND DAYBREAK ON MON. THIS IS WHEN THE
MAIN SFC LOW LIFTS OUT FROM THE SW AND MOVES ACROSS SOUTH
CENTRAL/SOUTHEAST LOWER. A 60 KNOT LLJ WILL RIDE OUT AHEAD OF THIS
LOW AND BRING COPIOUS AMOUNTS OF MOISTURE INTO THE AREA AND OVER THE
FRONT. THUNDER WILL REMAIN LIKELY UNTIL THIS LLJ PASSES EAST OF THE
AREA ON MON MORNING. COLDER AIR WILL THEN WRAP IN FROM THE NW DURING
THE DAY ON MON. THERE LOOKS TO BE A SHORT PERIOD OF SNOW ACROSS THE
NW HALF OF THE CWFA BEFORE THE PCPN ENDS MON AFTERNOON.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 330 AM EDT SAT APR 12 2014

STILL CANT RULE OUT THE POSSIBILITY OF A COUPLE INCHES OF WET SNOW
MONDAY NIGHT ON THE BACK SIDE OF THIS SYSTEM. THE PREVIOUS RUN OF
THE ECMWF... AND NOW THE LATEST RUN OF THE NAM... SHOW A QUARTER
INCH OR MORE OF QPF IN THE COLD AIR AND SUGGEST SOME ACCUMULATIONS
COULD OCCUR ESPECIALLY FROM GRR TO THE SOUTH AND EAST.

EVEN IF WE DO NOT SEE MUCH IN THE WAY OF SNOW ACCUMULATION MONDAY
NIGHT... THE TUESDAY MORNING COMMUTE COULD STILL BE IMPACTED BY
SLICK ROADS AS TEMPERATURES PLUNGE DOWN INTO THE MID 20S CAUSING ANY
RESIDUAL MOISTURE TO FREEZE UP. THIS MAY LEAD TO PATCHES OF BLACK
ICE.

HIGH PRESSURE BUILDING IN ON TUESDAY SHOULD END ANY LINGERING SNOW
SHOWERS BY AFTERNOON... FOLLOWED BY A VERY COLD NIGHT TUESDAY NIGHT
WITH LOWS AROUND 20. THE MID TO LATE WEEK PERIOD WILL FEATURE
RELATIVELY QUIET WEATHER WITH TEMPERATURES MODERATING BACK TO CLOSER
TO NORMAL VALUES.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1153 PM EDT FRI APR 11 2014

LITTLE CHANGE IN MY THINKING TO THE AVIATION FORECAST. FOR THE
MOST PART VFR CONDITIONS SHOULD PREVAIL THROUGH SATURDAY EVENING.
THE MAIN PUSH OF RAIN THIS WEEKEND AT THE TAF SITES SHOULD REALLY
BE LATER SUNDAY INTO SUNDAY NIGHT.

MEANWHILE...FOR TONIGHT INTO SATURDAY MORNING DEPARTING SURFACE HIGH
PRESSURE WILL KEEP SKIES CLEAR BELOW 12000 FT AGL. THE COMBINATION
OF JET ENTRANCE REGION DYNAMICS AND THE PUSH OF A WARM FRONT WILL
BRING THE RISK OF THUNDERSTORMS TO OUR WESTERN TAF SITES BY MID
AFTERNOON. EVEN SO...IT SEEMS THE BEST CHANCE FOR THESE STORMS
WILL ACTUALLY BE NORTH OF OUR TAF SITES. I PUT VCTS FOR TO COVER
THAT THREAT FOR NOW. WE WILL MONITOR FOR THUNDERSTORMS SATURDAY
AFTERNOON TO ADD THE DETAILS FOR THEM.

&&

.HYDROLOGY...
ISSUED AT 337 PM EDT FRI APR 11 2014

HAVE OPTED TO ISSUE A FLOOD WATCH FOR ESSENTIALLY THE NORTHWEST HALF
OF THE FORECAST AREA...OR FROM ALLEGAN...KENT...IONIA AND GRATIOT
COUNTIES NORTHWARD. CONFIDENCE IS INCREASING IN A HEAVY RAIN EVENT
AT LEAST ACROSS THE NORTHWEST WEST HALF OF THE CWA. THE HEAVIEST
RAIN WILL LIKELY FALL ACROSS CENTRAL LOWER MICHIGAN...BUT THERE IS
STILL SOME ZEROING IN THAT WILL LIKELY OCCUR OVER THE COURSE OF THE
NEXT FEW SHIFTS. DECIDED THERE WAS ENOUGH CONFIDENCE TO GO WITH A
WATCH GIVEN MULTIPLE RUNS FROM MULTIPLE MODELS INDICATING 2 PLUS
INCHES OF RAIN ACROSS OUR NORTHERN CWA...WITH THE POSSIBILITY OF
LOCALLY 4 INCHES.

SETUP FOR HEAVY RAIN INCLUDES A STATIONARY BOUNDARY THAT LOOKS TO
SET UP ACROSS THE CWA WITH WAVES OF LOW PRESSURE AND UPPER LEVEL
DISTURBANCES RUNNING ALONG IT. THIS WILL BE OUR FIRST EVENT OF THE
YEAR THAT WILL LIKELY CONTAIN EMBEDDED THUNDERSTORMS AS WELL.
PRECIPITABLE WATER VALUES ARE ON THE ORDER OF 1.3 INCHES NEAR THE
FRONTAL ZONE WHICH IS RUNNING NEAR THE 99TH PERCENTILE. EXPECTING
REPEATED ROUNDS OF SHOWERS AND EMBEDDED STORMS FROM SATURDAY
AFTERNOON RIGHT INTO MONDAY. THE HEAVIEST MAY FALL SUNDAY AFTERNOON
INTO SUNDAY NIGHT AS THE MAIN UPPER DISTURBANCE MOVES THROUGH THE
AREA.

ANTECEDENT CONDITIONS ARE RIPE FOR FLOODING WITH GROUND MOISTURE
BEING HIGH WHICH WILL LEAD TO EFFICIENT RUN OFF. EARLIER RAINS AND
SNOWMELT HAVE AREA RIVERS RUNNING ABOVE NORMAL FOR THIS TIME OF
YEAR.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...FLOOD WATCH FROM 2 PM EDT THIS AFTERNOON THROUGH MONDAY MORNING
     FOR MIZ037>040-043>046-050>052-056>058-064.

LM...NONE.
&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MEADE
AVIATION...WDM
HYDROLOGY...DUKE





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