Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 050730
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
328 AM EDT TUE MAY 5 2015

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

.SYNOPSIS...
ISSUED AT 328 AM EDT TUE MAY 5 2015

A WEAK COLD FRONT NEAR THE MICHIGAN INDIANA BORDER WILL BE A FOCUS
FOR SHOWERS AND EMBEDDED THUNDERSTORMS TODAY. THE COOLER AIR IN
COMBINATION WITH THE SHOWERS WILL HELP KEEP TEMPERATURES IN THE 50S
TODAY...NEARLY 20 DEGREES COLDER THAN MONDAY. TEMPERATURES WILL
QUICKLY CLIMB INTO THE 70S WEDNESDAY AND 80S THURSDAY AS THE FRONT
MOVES NORTH AGAIN. SHOWERS AND THUNDERSTORMS ARE POSSIBLE FRIDAY
THROUGH NEXT TUESDAY.

&&

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 328 AM EDT TUE MAY 5 2015

FORECAST CONCERNS DEAL WITH PCPN CHANCES THROUGH THE PERIOD.

A WEAK COLD FRONT PASSED THROUGH THE CWA A FEW HOURS AGO AND IS
LOCATED JUST SOUTH OF I-94. DEWPOINTS DROPPED FROM THE MID 50S TO
THE MID 30S BUT TEMPS DIDN`T DROP MUCH. RADAR SHOWS A LARGE AREA OF
SHOWERS WITH EMBEDDED STORMS MOVING NORTHEAST TOWARD LOWER MICHIGAN.
IT/S BEEN MAKING SLOW BUT STEADY PROGRESS OVERNIGHT AND SHOULD ENTER
THE SW CWA AROUND 10Z. A MINOR SHORT WAVE MOVING EAST FROM IOWA
SEEMS TO BE THE CATALYST FOR THE PCPN. ADDITIONALLY THE H8 THERMAL
BOUNDARY IS PROGD TO SET UP NEAR I-94 TODAY. MOSTLY THOUGH A STRONG
H3/H8 DIV/CONV COUPLET TRACKS FROM SE IOWA ACROSS LOWER MICHIGAN
TODAY AND IS THE REASON THE MODELS CRANK OUT AN INCH OF RAIN.
STRONG ISENTROPIC LIFT DEVELOPS EARLY THIS MORNING AND THAT WILL
LEAD TO RAIN THIS MORNING AND SOME THUNDER POSSIBLE TOO WITH THETA-E
DECREASING WITH HEIGHT SOUTH OF I-96. SHOWERS WILL DECREASE TONIGHT
BUT ARE STILL POSSIBLE DUE TO THE BOUNDARY REMAINING OVER THE SRN
CWA. BY WEDNESDAY NIGHT THE BOUNDARY LIFTS NORTH AND THE PCPN SHOULD
GO WITH IT. THAT WILL LEAD TO MUCH WARMER AIR THURSDAY WITH HIGHS IN
THE 80S.

.LONG TERM...(THURSDAY NIGHT THROUGH MONDAY)
ISSUED AT 328 AM EDT TUE MAY 5 2015

THERE IS LITTLE QUESTION THE BEGINNING OF THIS PERIOD WILL BE WARMER
THAN NORMAL. IT ALSO SEEMS LIKELY WE WILL BE SEEING SOME
THUNDERSTORM ACTIVITY OVER THE WEEKEND INTO EARLY NEXT WEEK. THE
MAIN ISSUE WITH THIS FORECAST IS JUST HOW FAST THE COLD AIR COME
BACK IN?

OUR CURRENT UPPER AIR PATTERN SHOWS A VERY LARGE SPLIT IN THE UPPER
LEVEL FLOW. THE SUBTROPICAL JET IS WEST TO EAST OVER MEXICO INTO THE
GULF OF MEXICO AND THAT REMAINS LARGELY UNCHANGED UNTIL THIS COMING
WEEKEND. MEANWHILE THE NORTHERN BRANCH OF THE POLAR JET IS CURRENTLY
JUST NORTH OF THE CANADIAN BOARDER BUT IT LIFTS WELL NORTH OVER
CENTRAL AND EASTERN CANADA TO HUDSON BAY BY LATE IN THE WEEK. THAT
LIFTING NORTH IS THE RESULT DOWN STREAM RIDGE BUILDING AS THE UPPER
LOW...CURRENTLY OFF THE COAST OF SOUTHERN BRITISH COLUMBIA AND THE
STATE OF WASHINGTON GETS PUSHED SOUTHEAST INTO THE SOUTHWEST UNITED
STATES BY AN EVEN STRONGER SYSTEM CURRENTLY OVER THE ALEUTIAN
ISLANDS.

WHERE OUR FORECAST UNCERTAINLY COMES IN IS WHAT HAPPENS TO
THAT CLOSED UPPER LOW OVER THE SOUTHWESTERN UNITED STATES OVER THE
WEEKEND. JUST HOW QUICKLY DOES IT GET BOOTED OUT INTO THE CENTRAL
PLAINS? THIS TURNS OUT TO BE VERY COMPLEX ISSUE AS THERE ARE
INTERACTIONS WITH SOUTHERN STREAM JET BUT MORE IMPORTANTLY THAT
SECOND SYSTEM THAT WAS OVER THE ALEUTIAN ISLANDS. JUST HOW QUICKLY
THE SOUTHWEST UNITED STATES SYSTEM GETS BOOTED OUT OF THE
SOUTHWESTERN UNITED STATES AND HOW MUCH IS MERGES WITH A NORTHERN
STREAM WAVE ONCE IS DOES WILL RESULT IN MAJOR ADJUSTMENT TO OUR
FORECAST FOR SOUTHWEST MICHIGAN FROM SAT THROUGH MONDAY AND ACTUALLY
WELL BEYOND THAT. SEEMS NO MATTER WHAT IT WILL NOT COME OUT IN ONE
BIG STORM BUT A SERIES OF SHORTWAVE WAVES. THAT MEANS A PROLONGED
PERIOD OF ROUNDS OF THUNDERSTORMS.

FOR NOW I AM GOING WITH THE IDEA THAT THE UPPER LOW BEING BOOTED OUT
WILL HOLD ON TO ITS OWN CIRCULATION LONGER. THIS FAVORS THE ECMWF
FORECAST WHICH WOULD KEEP US IN THE WARM AIR LONGER. EITHER WAY WE
CONTINUE TO SEE ROUNDS OF CONVECTION INTO MONDAY SINCE THE MAIN
UPPER TROUGH REMAINS WEST OF MICHIGAN INTO THE MIDDLE OF NEXT WEEK.
THE COLD AIR ISSUE I BROUGHT UP INITIALLY IS MORE OF A MIDDLE OF
NEXT WEEK ISSUE.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1224 AM EDT TUE MAY 5 2015

MODELS HAVE SHIFTED TOWARDS MORE IN THE WAY OF RAIN AND LOWER
CLOUDS AS WE HEAD INTO THE DAY ON TUESDAY. MUCH OF THE REST OF THE
NIGHT SHOULD CONTINUE TO BE VFR AND RAIN FREE. AS WE HEAD TOWARDS
12Z...SHOWERS AND A FEW EMBEDDED THUNDERSTORMS WILL BE ENCROACHING
ON KMKG AND KAZO. PERIODS OF SHOWERS AND A FEW STORMS ARE EXPECTED
ON TUESDAY WITH CEILINGS AND VISIBILITIES TRENDING DOWNWARD. IT
APPEARS WE WILL BE TRENDING TOWARD IFR AS WE WILL BE LOCATED JUST
NORTH OF A WARM FRONT IN EASTERLY WINDS.

BOTTOM LINE...DETERIORATING AVIATION CONDITIONS BEGINNING AROUND
DAYBREAK TUESDAY LASTING RIGHT INTO TUESDAY EVENING. CEILINGS WILL
BE TRENDING TO IFR IN ALL AREAS TUESDAY MORNING.


&&

.MARINE...
ISSUED AT 328 AM EDT TUE MAY 5 2015

OUTSIDE OF THUNDERSTORMS...NORTHEAST WINDS WILL BE IN THE 5 TO 15
KNOT RANGE.

&&

.HYDROLOGY...
ISSUED AT 1137 AM EDT MON MAY 4 2015

THE FOCUS WILL BE ON THE ADDITIONAL BOUTS OF RAINFALL POSSIBLE IN
THE WEEK AHEAD.

WHILE THE PATTERN STILL LOOKS ACTIVE IT IS NOT PROMISING THAT WE
WILL SEE ANY WIDESPREAD HEAVY RAIN. BENEFICIAL AMOUNTS SHOULD
AVERAGE OUT TO A QUARTER INCH OR SO WITH EACH EPISODE THROUGH THE
WORK WEEK. THAT MAY LEAD TO DECENT TOTALS IN THE GRAND SCHEME BUT
NOTHING THAT PUTS RIVERS OVER THEIR BANKS.

THE NEXT CHANCE OF RAIN COMES WHEN THE STALLING FRONT TO OUR SOUTH
RETURNS AS A WARM FRONT TUESDAY AND INTO EARLY WEDNESDAY. EVEN
THIS LOOKS TO COME IN A PIECE-WISE FASHION...ONCE LATE TONIGHT AND
AGAIN LATE TUESDAY INTO EARLY WEDNESDAY. THE BEST CHANCE AT RAIN
THEN ENTERS THE PICTURE LATE IN THE WEEK AND INTO NEXT WEEKEND WITH
AN APPROACHING SYSTEM. THIS IS WHEN WE COULD PICK UP OUR HIGHEST
TOTALS...PENDING THE NORTHERN EXTENT OF THE WARM FRONT OUT AHEAD
OF THE SYSTEM. SEVEN DAY TOTALS ON THE ORDER OF AN INCH TO AROUND
AN INCH AND A HALF KEEP CONCERNS LOW AS IT IS RECEIVED IN CHUNKS
WITH SEVERAL HOURS OF DRY TIME BETWEEN. LOCALIZED HEAVIER RAINFALL
CANNOT BE RULED OUT...BUT DURATION AND COVERAGE IS NOT LOOKING
EXTENSIVE AT THIS POINT.

&&

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

$$

SYNOPSIS...04
SHORT TERM...04
LONG TERM...MJS
AVIATION...DUKE
HYDROLOGY...JAM
MARINE...04









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