Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 300219
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1019 PM EDT MON SEP 29 2014

LATEST UPDATE...
UPDATE

.SYNOPSIS...
ISSUED AT 309 PM EDT MON SEP 29 2014

A COLD FRONT WILL COME THROUGH THE AREA TONIGHT AND BRING SHOWERS
AND MAYBE A RUMBLE OF THUNDER OR TWO.  THE RAIN WILL MOVE OUT OF THE
REGION LATE TONIGHT.  TUESDAY AND WEDNESDAY ARE EXPECTED TO BE
DRY...ALTHOUGH COOLER.  HIGHS ON TUESDAY WILL ONLY BE 55 TO 60...AND
IN THE 60S ON WEDNESDAY.

A GOOD CHANCE FOR A SOAKING RAIN SHOULD MOVE IN THURSDAY AFTERNOON
INTO FRIDAY.  TEMPERATURES ARE EXPECTED TO BE IN THE 70S THURSDAY...
BUT THEN COOL DOWN TO 60 TO 65 INTO THE WEEKEND.

&&

.UPDATE...
ISSUED AT 1017 PM EDT MON SEP 29 2014

DROPPED THUNDER FROM THE FORECAST AND TIMED THE STEADY RAINS ALONG
THE FRONT THROUGH THE SOUTHERN HALF OF THE FORECAST AREA
OVERNIGHT. ADDED DRIZZLE ACROSS THE CENTRAL AND NORTHERN ZONES
BASED ON OBS AND EXPECTATION THAT LOW STRATUS WITH SOME
CONVERGENCE/LIFT WILL PERSIST BEHIND THE FRONT OVERNIGHT.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 309 PM EDT MON SEP 29 2014

A COLD FRONT WAS ALREADY SAGGING SOUTH INTO THE NORTHERN CWA THIS
AFTERNOON.  MUCH OF THE PCPN WITH THE FRONT WILL BE POST FRONTAL
THIS EVENING...WITH THE RAIN TAPERING OFF OVERNIGHT.  THE FRONT WILL
BE ACCOMPANIED BY A DEEPENING SHORT WAVE ALONG WITH THE LEFT EXIT
REGION OF THE UPPER JET.  SO BELIEVE THE SHOWERS AND PERHAPS A FEW
THUNDERSTORMS WILL SURVIVE ACROSS THE ENTIRE CWA AND WILL MAINTAIN
THE LIKELY POPS.  HOWEVER TRENDED THE RAIN OUT QUICKER LATE
TONIGHT...ESPECIALLY NW...AS THE UPPER WAVE TAKES THE PCPN TO OUR
EAST BY DAYBREAK.

TUESDAY WILL BE MOSTLY CLOUDY AND MUCH COOLER.  AFTER A WEEK OF
HIGHS IN THE 70S...WE WILL ONLY SEE 55 TO 60 ON TUESDAY.  THERE
COULD BE A FEW LIGHT SHOWERS OR SPRINKLES OVER THE NORTHERN CWA AS
THE UPPER WAVE CLOSES OFF INTO AN UPPER LOW OVER LAKE HURON...BUT
THESE SHOULD NOT AMOUNT TO MUCH.  WE WILL LIKELY HANG ON TO THE
CLOUDS TUESDAY NIGHT AS THE UPPER LOW MOVES SE TOWARD ERIE PA.

EXPECT CLEARING WEDNESDAY MORNING AS SHORT WAVE RIDGING MOVES ACROSS
THE CWA.  TEMPS SHOULD BE ABOUT 10 DEGREES WARMER WITH THE ADDED
SUNSHINE.

ANOTHER COLD FRONT WILL BE MOVING INTO THE UPPER MIDWEST WEDNESDAY
NIGHT.  KEPT LOW CHANCE POPS OVER THE NW CWA AS INITIALLY THE FRONT
WILL BATTLE DRY LOW LEVELS.  RAISED MIN TEMPS AS CLOUDS BLANKET THE
AREA AGAIN OVERNIGHT.

.LONG TERM...(THURSDAY THROUGH MONDAY)
ISSUED AT 309 PM EDT MON SEP 29 2014

THERE IS QUIET A DRAMATIC CHANGE IN OUR WEATHER PATTERN HEADING THIS
WAY FOR LATE THIS WEEK THROUGH THE WEEKEND. THE PERSISTENT WARM
WEATHER WITH NO PRECIPITATION PATTERN WE HAVE BEEN IN FOR OVER A
WEEK WILL SOON BE HISTORY. A STRONG COLD FRONT WILL BRING SHOWERS
AND THUNDERSTORMS INTO OUR AREA THURSDAY INTO EARLY FRIDAY. THEN
MUCH COOLER WEATHER WITH PERIODIC LAKE EFFECT RAIN SHOWERS SHOULD
CONTINUE THROUGH THE WEEKEND.

THERE IS THE THREAT OF STRONG TO SEVERE STORMS LATER THURSDAY INTO
EARLY FRIDAY MORNING BUT SINCE THE MODELS SEEM TO FAVOR THE
OVERNIGHT HOURS OF THURSDAY NIGHT INTO FRIDAY MORNING FOR BRINGING
THIS SYSTEM THROUGH...THE THREAT FOR SURFACE BASED CONVECTION SEEMS
MORE THAN LIMITED. EVEN SO BOTH THE GFS AND ECMWF SHOW A STRENGTHEN
LOW LEVEL JET AIMED AT LOWER MICHIGAN DURING THE EARLY MORNING HOURS
OF FRIDAY WHILE WE ARE IN THE RIGHT ENTRANCE REGION OF THE UPPER
JET. THE PRECIP TABLE WATER IS NEARLY 2 STANDARD DEVIATIONS FROM
NORMAL OR NEARLY 3 TIMES THE MEAN VALUE FOR EARLY OCTOBER. GIVEN
THERE IS SOME CAPE TO PLAY WITH... THE STRONG JET DYNAMICS AND
CONSIDERABLE MOISTURE ONE CAN NOT TOTALLY RULE OUT STRONG TO SEVERE
STORMS EVEN AT NIGHT IN EARLY OCTOBER. ONE THING FOR SURE WE WILL
SEE MORE THAN A HALF INCH OF RAIN FROM THIS EVENT.

AS FOR THE BIG PICTURE... MOST OF LAST WEEK THROUGH THIS WEEKEND THE
POLAR JET WAS NORTH OF 55 N OVER EASTERN CANADA. THE COMBINATION OF
A SYSTEM CURRENTLY TRACKING THROUGH CENTRAL ALASKA AND PACIFIC
SYSTEM OVER GULF OF ALASKA MERGE TUESDAY OVER SOUTHWEST CANADA AND
THE NORTHWEST CONUS. NORMALLY THE JET STREAK DOING THAT WOULD TRACK
THROUGH THE DIGGING TROUGH AND WE WOULD BE DONE WITH IT HOWEVER IN
THIS CASE WE SEE A SERIES OF PACIFIC SHORTWAVES CONTINUE TO TRACK
THROUGH THE WESTERN SIDE OF THE DIGGING UPPER TROUGH INTO THE
WEEKEND (I AM SIDING WITH THE MORE CONSISTENT ECMWF HERE). THE
RESULTS DEVELOP A CLOSED UPPER LOW THAT TRACKS SLOWLY ACROSS LOWER
MICHIGAN SATURDAY.  BECAUSE EVEN MORE ENERGY CONTINUES TO FEED INTO
THE WESTERN SIDE OF THE TROUGH...THE NORMAL QUICK PROGRESSION OF
THIS SYSTEM WILL NOT HAPPEN. WE WILL LIKELY REMAIN IN THE COLD AIR
THROUGH MONDAY (AS SHOWN BY THE CURRENT AND SEVERAL PREVIOUS RUNS OF
THE ECMWF).

I AM THINKING WHAT WE WILL SEE IS THE CONVECTION FROM THE COLD FRONT
WILL COME THROUGH EARLY FRIDAY MORNING. LIKELY THERE WILL BE A DRY
SLOT MID DAY FRIDAY... THEN PERIODIC LAKE EFFECT SHOWERS AIDED BY
THE COLD CORE UPPER LOW OVER LOWER MICHIGAN...WILL CONTINUE THROUGH
THE WEEKEND. THE CURRENT GRIDS DO NOT DO THIS SYSTEM JUSTICE.  I
BELIEVE OVER TIME WE WILL SEE BOTH THE HIGH AND LOW TEMPERATURES
FALL IN OUR GRIDS FOR SAT THROUGH MONDAY. LOWS WILL LIKELY BE IN THE
MID TO UPPER 30S WITH HIGHS UPPER 40S TO MID 50S MOST OF THE
WEEKEND. I DID NOT ADJUST THE GRIDS TO THIS JUST YET SO AS NOT TO
CAUSE TO BIG A CHANGE AT ANY ONE TIME.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 733 PM EDT MON SEP 29 2014

COLD FRONT WILL HAVE MVFR AND SOME AREAS OF IFR ALONG AND BEHIND
IT. SHOWERS SHOULD BE LIGHT THIS EVENING AND THUNDERSTORMS ARE
UNLIKELY. THE LOW CLOUDS WILL PERSIST INTO TUESDAY MORNING WITH
AREAS OF IFR POSSIBLE. WINDS WILL GO NORTH TONIGHT AND CONTINUE
AROUND 10 KNOTS TUESDAY.


&&

.MARINE...
ISSUED AT 309 PM EDT MON SEP 29 2014

TWEAKED THE SMALL CRAFT ADVISORY HEADLINES SLIGHTLY TO MATCH THE
MOVEMENT OF THE COLD FRONT.  NOW HAVE THE SCA FOR AREAS SOUTH OF
GRAND HAVEN STARING AT 10 PM.  NORTH WINDS BEHIND THE FRONT WILL BE
RATHER BRISK...PEAKING MID TO LATE EVENING.  THIS WILL BUILD WAVES
OF SIX FEET IN PLACES.  THE NORTH WINDS SLOWLY TAPER OFF TUESDAY AND
BECOMING NORTHEAST BY THE END OF THE DAY.  THE END TIME OF THE
ADVISORY...EARLY TOMORROW EVENING SHOULD WORK OUT FINE.


&&

.HYDROLOGY...
ISSUED AT 309 PM EDT MON SEP 29 2014

TONIGHT/S FRONT WILL BRING A BAND OF SHOWERS THAT WILL LAST 2 TO 4
HOURS AT ANY ONE LOCATION.  THIS WILL LIKELY PUT DOWN LESS THAN A
QUARTER INCH OF RAIN IN MOST AREAS.  NO HYDRO ISSUES ARE EXPECTED.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 8 PM EDT TUESDAY FOR LMZ844>849.

&&

$$

UPDATE...OSTUNO
SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...WDM
AVIATION...OSTUNO
HYDROLOGY...JK
MARINE...JK






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