Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 290550
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
150 AM EDT WED JUL 29 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 320 PM EDT TUE JUL 28 2015

A COLD FRONT MOVING ACROSS WISCONSIN THIS AFTERNOON WILL MOVE OVER
LOWER MICHIGAN WEDNESDAY MORNING. SCATTERED SHOWERS AND PERHAPS A
THUNDERSTORM ARE POSSIBLE WITH THIS FRONTAL PASSAGE...BUT
SIGNIFICANT RAIN IS UNLIKELY. HIGHS WILL BE A COUPLE OF DEGREES
COOLER WEDNESDAY AND THURSDAY BUT REMAIN NEAR NORMAL.

&&

.SHORT TERM...(THIS EVENING THROUGH THURSDAY NIGHT)
ISSUED AT 320 PM EDT TUE JUL 28 2015

FORECAST CONCERNS DEAL WITH A COLD FRONTAL PASSAGE EARLY WEDNESDAY
AND THE PCPN ASSOCIATED WITH IT.

OVERALL...THIS SYSTEM DOESN`T IMPRESS ME. CONVECTION AHEAD OF THE
FRONT IN WISCONSIN HAS DIMINISHED QUITE A BIT THIS
AFTERNOON...PROBABLY DUE TO ITS MOVING INTO THE UPPER RIDGE THAT IS
OVER LOWER MICHIGAN ATTM.

THE CORE OF THE DYNAMICS WITH THIS SYSTEM ARE WELL NORTH IN WESTERN
ONTARIO AND THAT WILL RESULT IN NOT MUCH MORE THAN SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS WEDNESDAY. DESPITE SBCAPE AROUND 1200
J/KG...LI`S ARE NOT IMPRESSIVE AND THE CWA WILL BE IN THE RIGHT EXIT
REGION OF THE UPPER JET...ALSO NOT CONDUCIVE FOR STRONGER STORMS.
THERE ISN`T MUCH OF A LLJ EITHER. THE ONE THING THAT THE SYSTEM DOES
HAVE GOING FOR IT IS HIGH PRECIPITABLE WATER VALUES NEAR 2.35
INCHES. SO WE MAY HAVE A LOW TOPPED SHOWER SCENARIO WITH BURSTS OF
HEAVIER RAIN. PCPN SHOULD WIND DOWN BY AFTERNOON AFTER WHICH HIGH
PRESSURE WILL BUILD BACK INTO THE GREAT LAKES.

.LONG TERM...(FRIDAY THROUGH TUESDAY)
ISSUED AT 320 PM EDT TUE JUL 28 2015

I AM GOING TO CONTINUE TO SAY WHAT I HAVE BEEN SAYING...THE TREND IS
TOWARD COOLER AND WITH PERIODS OF SHOWERS (NOT SO MUCH THUNDERSTORMS
EITHER).

IT LOOKS VERY GOOD FOR A UNUSUALLY DEEP UPPER LOW TO DEVELOP AND
STALL OVER SOUTHERN HUDSON BAY. THIS IS A RATHER UNUSUAL WEATHER
PATTERN FOR LATE JULY OR EARLY AUGUST. THE NAERFS SHOWS THE RETURN
PERIOD OF SUCH AN EVENT (DEEP UPPER LOW OVER HUDSON BAY) TO BE ONE
DAY IN 10 YEARS. THE LARGE SCALE PATTERN FORECAST LOOKS GOOD AND CAN
BE RELIED ON... WHAT IS QUESTIONABLE IS THE DETAILED SURFACE WEATHER
WE WILL SEE FROM THIS UNUSUAL PATTERN. TYPICALLY THE MODELS DO NOT DO
WELL IN FORECASTING SUCH UNUSUAL PATTERNS. ONE CAN CLEARLY SEE THIS
IN HOW EACH MODEL RUN SEEMS TO HAVE A DIFFERENT SOLUTION THAN THE
RUN BEFORE. FROM MODEL TO MODEL THERE ARE SIGNIFICANT DIFFERENCES IN
THE TIMING OF THE SHORTWAVES AND THE STRENGTH OF THOSE SHORTWAVES
TOO.

I WOULD TOTALLY NOT RELY ON OUR FORECAST POPS FOR THIS WEEKEND. I
REALLY THINK THERE IS A CHANCE OF SHOWERS EACH DAY DEPENDING ON THE
TIMING OF THOSE SHORTWAVES AND THE STRENGTH THEREOF. WE HAVE THE
HIGHEST POPS SUNDAY INTO MONDAY... BUT THERE IS A SYSTEM COMING
THROUGH ON FRIDAY AND IT MAY WELL HAVE SHOWERS WITH IT. IN FACT I
WOULD EXPECT OUR POPS TO INCREASE SIGNIFICANTLY FOR FRIDAY OVER
TIME. SIMILARLY FOR SATURDAY TOO...BUT THAT COULD BE DELAYED UNTIL
SUNDAY... JUST DEPENDS ON THE TIMING OF THE SHORTWAVES.

ALSO LIKE I HAVE BEEN SAYING I THINK BY THE MIDDLE OF NEXT WEEK WE
WILL BE SEEING HIGHS IN THE 70S AND LOWS IN THE 50S. WITH AN UPPER
LOW THAT DEEP SO CLOSE TO US IT IS HARD TO IMAGINE SOME OF THAT COLD
AIR WOULD NOT FINALLY MAKE IT THIS FAR SOUTH. ACTUALLY THE LATEST
GFS AND ECMWF ARE NOW SHOWING THIS BUT THE 00Z RUN OF THE ECMWF DID
NOT SHOW THIS...WHILE THE 12Z RUN FROM YESTERDAY DID.

BOTTOM LINE THINK...COOLER WITH PERIODS OF SHOWERS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 149 AM EDT WED JUL 29 2015

OUR MAIN FOCUS WITH THE 06Z FCST IS THE POTENTIAL OF SHOWERS
AND/OR STORMS WITH A FRONT THAT WILL MOVE THROUGH TODAY.

WE HAVE ACCOUNTED FOR A COUPLE POP UP SHOWERS NEAR KMKG FOR THE
FIRST HOUR OF THE VALID FCST PERIOD. THESE WILL PRODUCE SOME LOCAL
MVFR IN RAIN ESPECIALLY SOUTH OF KMKG...BUT WILL MOVE OUT QUICKLY
AND WILL LIKELY NOT HIT THE OTHER SITES.

WE EXPECTED A SCT LINE OF SHOWERS TO FORM WEST OF THE AREA TOWARD
12Z AND THEN SHIFT EAST THROUGH THE MORNING. NOT SURE ALL OF THE
SITES WILL BE DIRECTLY HIT...SO WE HAVE USED A VCSH TO COVER THIS
POTENTIAL. IF A SITE GETS HIT BY A SHOWER...SOME MVFR OR EVEN
BRIEF IFR WILL BE POSSIBLE. SOME OF THE SHOWERS COULD BE STORMS
TOWARD KLAN AND KJXN THIS AFTERNOON BEFORE EVERYTHING MOVES OUT OF
THE AREA BY AROUND 22Z.

SOME GUSTY WINDS WILL BE POSSIBLE RIGHT BEHIND THE FRONT/SHOWERS.
THE WINDS WILL DIMINISH TOWARD SUNSET WITH CLEARING SKIES.

&&

.MARINE...
ISSUED AT 320 PM EDT TUE JUL 28 2015

AFTER THE COLD FRONT PASSES THROUGH WEDNESDAY WEST WINDS WILL BOOST
WAVE HEIGHTS TO AROUND 2 FEET. THUS NO HAZARDS IN THE SHORT TERM.


&&

.HYDROLOGY...
ISSUED AT 1250 PM EDT TUE JUL 28 2015

RIVER LEVELS ARE FALLING AND WELL BELOW BANKFULL. WITH UNDER A
HALF INCH OF PRECIPITATION EXPECTED INTO NEXT WEEK... THESE
CONDITIONS SHOULD CONTINUE.

&&

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

$$

SYNOPSIS...04
SHORT TERM...04
LONG TERM...WDM
AVIATION...NJJ
HYDROLOGY...63
MARINE...04


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