Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 070722
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
313 AM EDT THU MAY 7 2015

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

.SYNOPSIS...
ISSUED AT 312 AM EDT THU MAY 7 2015

HIGH PRESSURE OVER THE EASTERN US WILL GIVE US ANOTHER MOSTLY
SUNNY DAY WITH MILD TEMPERATURES. SHOWERS AND THUNDERSTORMS ARE
IN THE FORECAST LATE TONIGHT THROUGH MUCH OF THE WEEKEND.

&&

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 312 AM EDT THU MAY 7 2015

FORECAST CONCERNS DEAL WITH CONVECTIVE TRENDS THROUGH THE PERIOD.

LATEST IR LOOP SHOWS HIGH CLOUDS OVER LOWER MICHIGAN. QUITE A BIT
OF CONVECTION WAS NOTED OVER THE PLAINS WHICH IS WHERE IT WILL
STAY TODAY. HOWEVER, IT WILL EVENTUALLY MAKE IT INTO LOWER
MICHIGAN.

LOW PRESSURE IN THE PLAINS WILL MOVE EAST LATER TONIGHT AND DRAG A
COLD FRONT TO NEAR THE UPPER MISSISSIPPI VALLEY BY MIDNIGHT. THIS
POSITION WILL FOCUS STORMS OVER EASTERN MN/WESTERN WISCONSIN. AS
THE FRONT CONTINUES SLOWLY MOVING EAST...SOME OF THOSE STORMS WILL
MAKE IT TO LOWER MICHIGAN AFTER MIDNIGHT. AS THE FRONT SAGS INTO
WESTERN LOWER...SMALL AREAS OF LOW PRESSURE WILL MOVE NE ALONG THE
FRONT FROM THE SRN PLAINS. THESE WAVES OF LOW PRESSURE WILL BOTH
SLOW THE PROGRESSION OF THE COLD FRONT AND ALSO ENHANCE THE
RAINFALL POTENTIAL FRIDAY THROUGH SATURDAY.

TODAY WILL BE MOSTLY SUNNY AND MILD AS HIGH PRESSURE OVER THE EAST
COAST WILL CONTROL WEATHER OVER THE GREAT LAKES.

.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 312 AM EDT THU MAY 7 2015

WARMER THAN NORMAL TEMPERATURES WITH PERIODS OF SHOWERS AND
THUNDERSTORMS ARE EXPECTED THROUGH MONDAY WITH THE GREATEST THREAT
FOR STRONG STORMS BEING MONDAY. THEN IT WILL TURN COOLER BUT RAIN
SHOWERS WILL CONTINUE INTO WEDNESDAY.

THE THREAT FOR STRONG THUNDERSTORMS ON MONDAY IS LOOKING A LITTLE
MORE LIKELY FROM THE LASTED MODEL RUN. IT NOW SEEMS THE ECMWF AND
GFS ARE IN BETTER AGREEMENT AS TO HOW FAR NORTH THE SYSTEM ON MONDAY
GETS. IT NOW APPEARS THE CLOSED UPPER LOW THAT GETS EJECTED FROM THE
SOUTHWESTERN UNITED STATES BY THE NEXT UPSTREAM PACIFIC SYSTEM OVER
THE WEEKEND WILL IN FACT MERGE WITH THE NORTHERN STREAM SYSTEM IN
THE MONDAY TIME FRAME. THAT FAVORS A STRONGER SURFACE SYSTEM THAT
WOULD TRACK FARTHER NORTH. THIS WOULD ALSO PUT SOUTHWEST MICHIGAN IN
THE PRIME LOCATION FOR STRONGER STORMS MONDAY AFTERNOON AS WE WOULD
BE IN THE WARM SECTOR OF THE SYSTEM DURING MAX HEATING. ADDED TO
THAT IT WOULD SEEM BOTH THE GFS AND ECMWF 07/00Z RUNS SHOW SOUTHWEST
MICHIGAN IN THE RIGHT ENTRANCE REGION OF 80 KNOT 300 MB JET SEGEMENT
LATE MONDAY AFTERNOON. ADD TO THAT THE 50 KNOT LOW LEVEL JET OVER
CENTRAL LOWER MICHIGAN AND 18Z AND 40 TO 50 KNOTS OF DEEP LAYER
SHEAR...DEEP MOISTURE AND IT WOULD SEEM MORE THAN REASONABLE WE
COULD BE LOOKING AT A SIGNIFICANT THUNDERSTORM EVENT.

AFTER THAT WITH THE MERGER OF THE NORTHERN AND SOUTHERN STREAM
SYSTEMS WE SEE A LARGE CLOSED UPPER LOW OVER THE GREAT LAKES INTO
WEDNESDAY. THAT BRINGS DOWN COLDER AIR...850 TEMPS BELOW ZERO... AND
WITH INSTABILITY SHOWERS THAT MAY LINGER INTO TUESDAY EVENING. SOME
CLEARING MAY FOLLOW WEDNESDAY AS A NORTHERN STREAM SHORTWAVE BOOTS
THIS SYSTEM OUT OF THE WAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1148 PM EDT WED MAY 6 2015

SOME LIGHT FOG WILL BRING MVFR CONDITIONS OVERNIGHT WITH THE
POSSIBILITY OF SOME PATCHY DENSE FOG AND IFR CONDITIONS BETWEEN
09Z AND 12Z...MOSTLY AT AZO. THE FOG SHOULD DISSIPATE BY 13Z AND
VFR IS EXPECTED THROUGH THURSDAY AFTERNOON. WINDS WILL BE BLO 10
KNOTS UNTIL ABOUT 15Z WHEN SOUTH WINDS WILL INCREASE TO AROUND 10
TO 15 KNOTS WITH GUSTS NEAR 20 KNOTS AT TIMES...DIMINISHING BLO 10
KNOTS AGAIN THURSDAY EVENING.


&&

.MARINE...
ISSUED AT 312 AM EDT THU MAY 7 2015

NO MARINE HAZARDS TODAY.

&&

.HYDROLOGY...
ISSUED AT 312 AM EDT THU MAY 7 2015

SHOWERS AND THUNDERSTORMS HAVE THE POTENTIAL OF PRODUCING A HALF
INCH OF RAIN THROUGH SATURDAY. LOCALLY HIGHER AMOUNTS ARE ALSO
POSSIBLE.

&&

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

$$

SYNOPSIS...04
SHORT TERM...04
LONG TERM...WDM
AVIATION...OSTUNO
HYDROLOGY...04
MARINE...04



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