Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 051602
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1202 PM EDT TUE MAY 5 2015

LATEST UPDATE...
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 18Z TAFS THROUGH 18Z WEDNESDAY)
ISSUED AT 1200 PM EDT TUE MAY 5 2015

MVFR CONDITIONS WILL CONTINUE THIS AFTERNOON DUE TO LOW CLOUDS AND
LIGHT RAIN SHOWERS. CONDITIONS WILL GRADUALLY DETERIORATE TO IFR
THEN LIFR THIS EVENING AND OVERNIGHT AS CIGS LOWER ALONG WITH SOME
SCATTERED LINGERING LIGHT RAIN SHOWERS AND DRIZZLE AS WELL AS SOME
PATCHY FOG.

THIS WILL BE DUE TO A WARM FRONT DRAPED JUST TO THE SOUTH OF LWR MI.
IN FACT IFR/LIFT CONDITIONS DUE TO LOW CLOUDS AND PATCHY
DRIZZLE/PATCHY FOG WILL CONTINUE THROUGH MIDDAY WEDNESDAY. WINDS
WILL BE OUT OF THE EAST MAINLY AOB 10 KTS THIS AFTERNOON THROUGH 18Z
WED.


&&

.MARINE...
ISSUED AT 1158 AM EDT TUE MAY 5 2015

WINDS AND WAVES WILL REMAIN UNDER SMALL CRAFT ADVISORY CRITERIA
THROUGH THE NEXT FEW DAYS. WILL NEED TO MONITOR THE FOG RISK IN
THE COMING DAYS AS GULF MOISTURE STARTS TO ADVECT OVER THE COLD
LAKE MI WATERS.

&&

.HYDROLOGY...
ISSUED AT 1149 AM EDT TUE MAY 5 2015

TODAYS PRECIPITATION IS IN THE IMMEDIATE SCOPE OF ATTENTION WHILE
THE NEXT BIG CHALLENGE IS KEYING IN ON NEXT WEEKENDS RAIN
POTENTIAL. ANY RIVER CONCERNS WOULD BE IN THE LATE WEEK AND
WEEKEND TIMEFRAME.

PRECIPITATION MATERIALIZED FAIRLY WELL THIS MORNING WHICH IS
PROVIDING
SOME NEEDED RELIEF TO AREAS RECENTLY CONSIDERED ABNORMALLY DRY.
ADDITIONAL RAINFALL IS POSSIBLE THROUGH THE AFTERNOON WITH LOCALIZED
MODERATE TO HEAVY RAINFALL. LOCATIONS ALONG AND SOUTH OF I-94 HAVE
THE GREATEST CHANCE FOR SEEING CONVECTIVE TYPE RAINFALL...BUT LOWER
INSTABILITY WOULD LIMIT THE THREAT.

THE FORECAST GETS A BIT TRICKY GOING INTO LATE WEEK AND NEXT WEEKEND.
A SYSTEM WILL DEVELOP OUT OVER THE PLAINS AND IS EXPECTED TO
TRAVEL NORTH AND EAST. THE GULF OF MEXICO OPENS UP TO ALLOW FOR
ABUNDANT MOISTURE TO FEED NORTHWARD AS WELL. MEANWHILE...THE
SYSTEM OVER THE SOUTHEAST OFF THE CAROLINA COAST COULD PLAY A PART
IN HOW THE PATTERN RESPONDS. INLAND MOTION OF THE SOUTHEAST SYSTEM
COULD AID IN DRAPING A STATIONARY BOUNDARY THROUGH THE OHIO VALLEY
OR SOMEWHERE THROUGH THE MIDWEST. THE RESULT COULD VERY WELL END
UP BEING PERIODS OF RAINFALL...POSSIBLY HEAVY...SPANNING FROM
LATE FRIDAY ON THROUGH MONDAY. THIS IS SOMETHING THAT BARES
WATCHING AS WE HEAD INTO THURSDAY AND FRIDAY. IF THE SCENARIO WERE
TO PLAY OUT THE BIGGEST CONCERN WOULD THEN BECOME MULTIPLE ROUNDS
OF HEAVIER RAIN. THOUGH RIVERS AND STREAMS ARE WELL WITHIN
BANKS...FORECASTS WILL BE MONITORED FOR THIS POTENTIAL.

&&

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

$$

SYNOPSIS...04
SHORT TERM...04
LONG TERM...WDM
AVIATION...LAURENS
HYDROLOGY...JAM
MARINE...MJS






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