Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 290438
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1238 AM EDT MON SEP 29 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 325 PM EDT SUN SEP 28 2014

HIGH PRESSURE WILL CONTINUE TO BRING FAIR AND MILD WEATHER THROUGH
MIDDAY MONDAY. A COLD FRONT WILL MOVE SOUTH ACROSS SOUTHERN LOWER
MICHIGAN MONDAY AFTERNOON AND EVENING AND BRING POTENTIAL FOR A
FEW LIGHT RAIN SHOWERS. COOLER AIR WILL BRIEFLY FILTER IN BEHIND
THE FRONT FOR TUESDAY. TEMPERATURES WILL MODERATE WEDNESDAY AND
THURSDAY BEFORE A STRONG COLD FRONT MOVES THROUGH THURSDAY NIGHT AND
BRINGS POTENTIAL FOR SHOWERS AND STORMS. A SIGNIFICANTLY COOLER
AIRMASS WILL MOVE IN FRIDAY THROUGH THE WEEKEND.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 325 PM EDT SUN SEP 28 2014

FAIR WX WILL CONTINUE THROUGH MIDDAY MONDAY WITH A HIGH PRESSURE
RIDGE STILL IN CONTROL OF THE WX PATTERN. PARTLY CLOUDY TO MOSTLY
CLEAR SKIES TONIGHT AND CALM WINDS WILL BE CONDUCIVE FOR THE
FORMATION OF PATCHY FOG ONCE AGAIN DURING THE EARLY MORNING HOURS
MONDAY.

A COLD FRONT DROPPING DOWN FROM THE NORTH WILL BRING CLOUDS AND A
FEW SHOWERS AS EARLY AS MONDAY AFTERNOON NORTH OF I-96. THE BETTER
CHANCE FOR SCATTERED LIGHT RAIN SHOWERS ACROSS MOST OF OUR FCST
AREA WILL COME MONDAY EVENING. MOISTURE WITH THIS SYSTEM IS
FAIRLY LIMITED AND RAINFALL AMOUNTS OF UNDER TWO TENTHS OF AN INCH
ARE ANTICIPATED.

WE TWEAKED THE MAX TEMP FCST DOWN A COUPLE OF DEGREES ON AVERAGE
FOR TUESDAY SINCE A CONSENSUS OF SHORT RANGE GUIDANCE SHOWS
POTENTIAL FOR EXTENSIVE LOW CLOUD COVER BEHIND THE FRONT AND WEAK
NORTH TO NE FLOW COOL AIR ADVECTION. THEREFORE MAX TEMPS WILL LIKELY
STRUGGLE TO REACH THE UPPER 50S TO LOWER 60S.

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 325 PM EDT SUN SEP 28 2014

LITTLE QUESTION WE ARE IN FOR A BIG CHANGE IN THE WEATHER STARTING
THURSDAY. THERE IS EVEN A SEVERE WEATHER THREAT FOR THURSDAY
AFTERNOON INTO THE EVENING. ONCE THAT COLD FRONT COMES THROUGH...
YOU WILL KNOW IT IS FALL IN WEST MICHIGAN. THIS SHOULD BE THE
COLDEST AIR OF THE SEASON TO DATE. EXPECT LAKE EFFECT SHOWERS FRIDAY
INTO SATURDAY.

WHILE THERE HAS BEEN SOME MINOR ADJUSTMENTS TO TIMING AND UPPER WAVE
DEVELOPMENT WITH THIS SYSTEM THURSDAY INTO FRIDAY THE MODELS HAVE
BEEN FORECASTING THIS SYSTEM FOR OVER A WEEK NOW (USING THE 360 HOUR
GFS LAST WEEK). WHAT SEEMS TO BE HAPPENING IS A SYSTEM  OVER
WESTERN ALASKA MERGES WITH A SYSTEM OVER THE GULF OF ALASKA IN THE
TUESDAY TIME FRAME. THE UPPER JET IS BEHIND THE SYSTEM SO THIS
SHOULD HELP TO SLOW IT DOWN AND DEEPEN IT.  ONE OTHER THING TO ADD
TO THE MIX IS THERE IS A RECURVING PACIFIC TROPICAL STORM...KAMMURI.
SO SINCE WE KNOW THAT NEARLY ALWAYS LEADS TO MUCH COOLER WEATHER IN
ABOUT A WEEK... ALL OF THIS ADDS UP NICELY. THE PRIMARY COLD FRONT
COMES THROUGH THURSDAY EVENING THEN THE COLD AIR FOLLOWS INTO THE
WEEKEND. THE MODELS ALL LIKE A CLOSED OFF UPPER LOW OVER THE GREAT
LAKES BY SATURDAY. THAT WILL ALLOW LAKE EFFECT SHOWERS TO CONTINUE
FROM FRIDAY INTO SATURDAY.

THE SEVERE WEATHER THREAT COMES FROM THE COMBO DECENT LOW LEVEL JET
PHASING WITH THE ENTRANCE REGION OF THE UPPER JET (LATE THURSDAY).
THERE IS ALSO WORKABLE INSTABILITY TOO. AS ALWAYS TIMING WILL BE OUR
ISSUE TO WATCH FOR THIS SORT OF EVENT.

ONCE THE FRONT IS THROUGH WE GET INTO DEEP CYCLONIC FLOW FRIDAY INTO
SATURDAY. GIVEN THE DEVELOPMENT AN UPPER LEVEL CLOSE COLD CORE LOW
SATURDAY... LITTLE QUESTION IN MY MIND THERE WILL BE SHOWERS NEAR
AND WEST OF US-131 FRIDAY INTO SATURDAY SO I INCREASED POPS AS MUCH
AS I DARED TOO THIS FAR OUT IN TIME.

SO BOTTOM LINE.... SHOWERS AND THUNDERSTORMS THURSDAY AND WARM...
THEN MUCH COLDER...WINDY PERIODS OF SHOWERS INTO EARLY SUNDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1236 AM EDT MON SEP 29 2014

FOG IS EXPECTED TO CONTINUE TO DEVELOP AGAIN OVERNIGHT. SEEMS TO
BE MORE OF AN ISSUE AT THE WRN TAF SITES TONIGHT VS THE EASTERN
TAF SITES. LOOKING FOR SOME IFR AGAIN AND VSBYS BOUNCING BETWEEN
VFR AND IFR. FOG SHOULD LIFT AFTER 12Z.

&&

.MARINE...
ISSUED AT 325 PM EDT SUN SEP 28 2014

WIND SPEEDS WILL REMAIN LIGHT WITH MINIMAL WAVE ACTION THROUGH
MIDDAY MONDAY WITH HIGH PRESSURE STILL IN CONTROL OF THE WEATHER
PATTERN. HOWEVER A COLD FRONT WILL MOVE THROUGH MONDAY AFTERNOON
AND EVENING AND WAVE HEIGHTS WILL RAMP UP TO 3 TO 6 FEET BEHIND
THAT FRONT MONDAY NIGHT.


&&

.HYDROLOGY...
ISSUED AT 325 PM EDT SUN SEP 28 2014

DRY WEATHER WILL CONTINUE THROUGH MIDDAY MONDAY. A COLD FRONT WILL
BRING A FEW SHOWERS AS EARLY AS MONDAY AFTERNOON AND MAINLY FOR
MONDAY EVENING. BASIN AVERAGE RAINFALL AMOUNTS WILL BE LIGHT AT
UNDER A QUARTER OF AN INCH. THEREFORE THERE ARE NO HYDRO CONCERNS.

&&

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

$$

SYNOPSIS...LAURENS
SHORT TERM...LAURENS
LONG TERM...WDM
AVIATION...93
HYDROLOGY...LAURENS
MARINE...LAURENS





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