Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 231739
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
139 PM EDT SAT APR 23 2016

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 326 AM EDT SAT APR 23 2016

THE WEEKEND WILL START OFF DRY WITH NEAR NORMAL TEMPERATURES OF 55
TO 60 TODAY.  HOWEVER WE WILL BEGIN TO SEE RAIN MOVE INTO CENTRAL
LOWER MICHIGAN BY EARLY SUNDAY AND THIS WILL GRADUALLY MOVE INTO
SOUTHERN LOWER SUNDAY NIGHT AND MONDAY.  A FEW RUMBLES OF THUNDER
WILL ALSO BE POSSIBLE SUNDAY NIGHT AND A FEW STRONGER STORMS ARE
POSSIBLE BY MONDAY.

THE RAINS SHOULD COME TO AN END MONDAY NIGHT.  THEN ANOTHER CHANCE
OF RAIN APPEARS BY THURSDAY AND THURSDAY NIGHT.  DAYTIME
TEMPERATURES SHOULD LARGELY REMAIN IN THE 60S MUCH OF NEXT
WEEK...BUT IT SHOULD BE A BIT COOLER ON TUESDAY.

&&

.UPDATE...
ISSUED AT 732 AM EDT SAT APR 23 2016

I UPDATED THE SKY GRIDS TO SHOW MOSTLY CLEAR SKIES TODAY INTO
TONIGHT AS ALL OF THE LOW CLOUDS HAVE FINALLY EXITED THE AREA.
THERE IS A LITTLE FOG OVER THE NORTHEAST SECTIONS BUT THAT WILL BE
GONE WITHIN AN HOUR.

&&

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 326 AM EDT SAT APR 23 2016

QUIET WEATHER FOR THE NEXT 24 HOURS...THEN RAIN DEVELOPS SUNDAY OVER
CENTRAL LOWER THAT WILL GRADUALLY SAG SOUTH SUNDAY NIGHT AND MONDAY.

A SURFACE BOUNDARY WILL SET UP A BAROCLINIC ZONE OVER THE REGION AS
IT SLOWLY SAGS SOUTH THROUGH THE SHORT TERM.  IT WILL DROP ACROSS
CENTRAL LOWER SUNDAY MORNING AND STALL AS LOW PRESSURE BEGINS TO
RIDE ALONG IT OVER THE UPPER MIDWEST.  THEN THE MODELS DIFFER A BIT
INTO MONDAY AS TO HOW QUICKLY THE FRONT BEGINS TO DRIFT SOUTH AGAIN.
THIS WILL IMPACT WHETHER WE WILL SEE THE RISK OF STRONGER STORMS.

ALONG WITH THE SURFACE FRONT...THE RIGHT ENTRANCE REGION OF THE
UPPER JET WILL SIT OVER NORTHERN/CENTRAL LOWER FROM SUNDAY MORNING
UNTIL LATE SUNDAY NIGHT.  THE COMBINATION OF OVER RUNNING ACROSS THE
SURFACE BOUNDARY/BAROCLINIC ZONE AND UPPER DIVERGENCE FROM THE JET
COULD PRODUCE OCCASIONAL HEAVY RAINS ACROSS CENTRAL LOWER.  HOWEVER
THE HEAVIEST RAINS COULD REMAIN FARTHER NORTH.  WE WILL STILL HAVE
TO WATCH THIS FOR HYDRO PURPOSES AS NORTHERN LOWER RAINS STILL END
UP IN THE MUSKEGON BASIN.

SOUTHERN LOWER MAY ESCAPE MOST OF THE RAIN SUNDAY AS THE FRONT
STALLS...THIS AREA REMAINS IN THE WARM SECTOR WITH LESS LIFT
AVAILABLE. HOWEVER THE BETTER CHANCES OF RAIN ARRIVE HERE LATE
SUNDAY NIGHT INTO MONDAY.

TRICKY FORECAST FOR MONDAY AS THE MODELS HANDLE THE FRONT
DIFFERENTLY.  IT SEEMS TO MAKE SENSE FOR THE FRONT TO REMAIN FAIRLY
STATIONARY GIVEN DAYTIME THERMODYNAMICS...BUT THE LOW PRESSURE TO
THE WEST APPEARS TO MOVE ESE WHICH MAY HELP TO ALSO HELP SAG THE
FRONT SOUTH A BIT.  EITHER WAY THE SOUTH STANDS A BETTER CHANCE OF
RAIN AS THE LOW PRESSURE NEARS.  HOWEVER THIS WILL MAKE A DIFFERENCE
IN SEVERE STORM POTENTIAL AND ALSO MAX TEMPS.  BETTER INSTABILITY
WOULD BUILD IF THE FRONT REMAINS ACROSS CENTRAL LOWER MUCH OF THE
DAY. AND AT THIS POINT IT APPEARS AREAS SOUTH OF I-96 COULD SEE
THESE STRONGER STORMS.  NOT SEEING A DECENT LOW LEVEL JET
HOWEVER...SO THE SEVERE THREAT APPEARS LOW AT THIS POINT.  HIGHS
WILL BE IN THE 50S NORTH...AND LOWER 70S SOUTH LARGELY DEPENDENT ON
THE FRONTAL POSITION.

UNTIL THEN...A SURFACE RIDGE WILL KEEP THE REGION QUIET TODAY WITH
PERHAPS A FEW LIGHT SHOWERS REACHING AREAS NEAR LDM LATE TONIGHT.
SOME AREAS EAST OF U.S. 131 MAY SEE PATCHY FROST TONIGHT.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 326 AM EDT SAT APR 23 2016

THE PRIMARY ASPECT OF SOUTHWEST MICHIGAN WEATHER DURING THIS TIME
WILL BE PERIODS OF SHOWERS AND POSSIBLY THUNDERSTORMS. LOCALLY HEAVY
RAIN IS ALSO POSSIBLE. TEMPERATURES FOR THE MOST PART WILL BE NEAR
NORMAL. FROST AND FREEZING TEMPERATURES REMAIN POSSIBLE OVER
NORTHERN AREAS TUESDAY NIGHT INTO WEDNESDAY MORNING.

AS I HAVE CONTINUED TO WRITE ABOUT...THE LARGE BLOCKING UPPER
LEVEL HIGH HAS DEVELOPED SOUTH OF GREENLAND...AS FORECAST. THAT
DISPLACES THE UPPER LOW (POLAR VORTEX) NORTH OF HUDSON BAY
SOUTHEAST TO NEAR NEWFOUNDLAND BY TUESDAY. GIVEN THE LARGE AMOUNT
OF SNOW STILL ON THE GROUND (2 TO 4 FEET) OVER MOST OF EASTERN
CANADA NORTH OF 48N... THERE IS AN ABUNDANT AMOUNT OF COLD AIR
THERE TOO. MEANWHILE THE PACIFIC STORM TRACK REMAINS ACTIVE AND
WILL CONTINUE TO FEED SYSTEMS INTO THE WEST COAST THROUGH THE
WEEK. THESE STORMS HAVE TO TRACK UNDER THE UPPER LEVEL BLOCK OVER
EASTERN CANADA. SINCE THE SOUTHERN EDGE OF THE BLOCK IS THE
CANADIAN BORDER... THAT PUTS SOUTHWEST MICHIGAN IN THE PLACE TO
SEE SEVERAL SIGNIFICANT PRECIPITATION EVENTS.

THE FIRST EVENT WILL CLEAR THE AREA BY TUESDAY MORNING... THEN THE
NEXT SYSTEM COMES OUT OF THE SOUTHERN PLAINS INTO GREAT LAKES IN THE
WEDNESDAY TO THURSDAY TIME FRAME. THE THIRD SYSTEM REACHES THIS AREA
LATE NEXT WEEKEND (AROUND MAY 1ST).  GULF MOISTURE WILL STREAM NORTH
WITH EACH OF THESE SYSTEMS...SO... AS LONG AS WE GET INTO THE WARM
AIR THUNDERSTORMS... SOME POSSIBLY STRONG ARE POSSIBLE WITH EACH OF
THESE EVENTS.

AS FOR THE WED/THU SYSTEM THE ISSUE IS JUST HOW FAR NORTH THIS
SYSTEM ACTUALLY TRACKS. THE GFS IS FARTHER NORTH THAN THE ECMWF ON
THE 00Z RUN. MODEL TRENDS ARE SLOWER AND FARTHER WEST WITH EACH
RUN(BOTH THE ECMWF AND GFS) OVER THE PAST 2 DAYS. IF ANYTHING...
THIS SYSTEM WILL LIKELY BE SLOWER THAN WE ARE CURRENTLY FORECASTING.
THERE IS ALSO AN ISSUE AS TO HOW MUCH THE CANADIAN BLOCK WILL FORCE
THE SYSTEM FARTHER SOUTH... LIKE THE ECMWF SEEMS TO WANT TO DO.

THE OTHER ISSUE IS FROST AND FREEZING TEMPERATURES.... BETWEEN THE
SYSTEM ON MONDAY/TUE AND WED/THU WE GET SURFACE HIGH PRESSURE TO
MOVE IN. THIS IS CANADIAN POLAR AIR AND SKIES WILL LIKELY CLEAR
TUESDAY NIGHT INTO WEDNESDAY MORNING. WITH A SLOWER STORM TRACK...
THE MID AND HIGH CLOUDS FROM THE NEXT SYSTEM WOULD NOT HAVE GOTTEN
HERE YET. SO THAT DOES SET THE STAGE FOR FROST/FREEZE ISSUES (MOSTLY
NORTH OF I-96). WE WILL HAVE TO SEE HOW THIS PLAYS OUT.

SO THE BOTTOM LINE IS WET WEATHER IS LIKELY LATER WEDNESDAY INTO
THURSDAY WITH THUNDERSTORMS POSSIBLE SOUTH. FROST AND FREEZING
TEMPERATURES ARE POSSIBLE WEDNESDAY MORNING.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 139 PM EDT SAT APR 23 2016

HIGH PROBABILITY FOR VFR CONDITIONS AT ALL TERMINALS THROUGH THE
PERIOD. AS NOTED IN THE PREVIOUS DISCUSSION...A LAKE BREEZE HAS
SHIFTED WINDS TO THE SOUTHWEST AT THE MKG TERMINAL. BY THIS
EVENING MKG WILL EMULATE THE OTHER TERMINALS WITH LIGHT NORTHEAST
WINDS GRADUALLY VEERING TO THE SOUTHEAST OVERNIGHT.

RAIN WILL SPREAD SOUTH ACROSS THE AREA SUNDAY AFTERNOON AND
EVENING BEYOND THE VALID TIME OF THIS TAF PACKAGE.

&&

.MARINE...
ISSUED AT 326 AM EDT SAT APR 23 2016

WILL ALLOW THE SMALL CRAFT TO EXPIRE WITH THIS ISSUANCE.  SOUTHERLY
FLOW WILL PRODUCE ROUGH CONDITIONS NEAR THE POINTS SUNDAY AFTERNOON
AND WE COULD REACH BORDERLINE SMALL CRAFT CONDITIONS.  THIS COULD
HAPPEN AGAIN MONDAY AFTERNOON AFTER THE FRONT SAGS SOUTH OF THE
POINTS AND NORTHERLY FLOW TAKES OVER.  BOTH OF THESE PERIODS MAY NOT
NEED AN ADVISORY...BUT CONDITIONS WILL BE SOMEWHAT ROUGH.


&&

.HYDROLOGY...
ISSUED AT 1242 PM EDT SAT APR 23 2016

MINOR FLOODING IS POSSIBLE MONDAY AND MONDAY NIGHT. UNTIL THEN...
ONLY LIGHT RAIN IS EXPECTED ACROSS THE MUSKEGON RIVER BASIN ON
SUNDAY.

A RISK FOR HEAVY RAINFALL EXISTS MONDAY AND MONDAY NIGHT AS A QUASI-
STATIONARY BOUNDARY PUSHES SOUTH THROUGH LOWER MICHIGAN. GIVEN THE
PRESENCE OF MODEST INSTABILITY... THUNDERSTORMS ARE POSSIBLE. A WARM
CLOUD DEPTH OF ABOUT 10 KFT AND FAIRLY SATURATED SOUNDING SUGGEST
ANY STORMS WILL BE EFFICIENT RAIN PRODUCERS. VERTICAL UNIDIRECTIONAL
FLOW ORIENTED PARALLEL TO THE SURFACE BOUNDARY MAY RESULT IN
TRAINING OF MODERATE TO HEAVY SHOWERS OVER THE SAME AREAS FOR A FEW
HOURS MONDAY AFTERNOON THROUGH MONDAY NIGHT.

1 TO 2 INCHES OF RAIN IS POSSIBLE THROUGH MONDAY NIGHT. TUESDAY AND
WEDNESDAY LOOK FAIRLY DRY... WITH RAIN CHANCES RETURNING WEDNESDAY
NIGHT. MINOR AREAL FLOODING IS POSSIBLE MONDAY EVENING AND MONDAY
NIGHT... ESPECIALLY WITH HEAVIER RAINFALL THAT PERSISTS OVER
URBAN/POOR DRAINAGE AREAS. WE WILL LIKELY SEE SOME RIVERS RISE BACK
ABOVE BANKFULL NEXT WEEK.

&&

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

$$

UPDATE...WDM
SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...WDM
AVIATION...TJT
HYDROLOGY...EBW
MARINE...JK



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