Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 120401
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1201 AM EDT SAT JUL 12 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 249 PM EDT FRI JUL 11 2014

SOUTHWEST WINDS AROUND A HIGH PRESSURE SYSTEM TRACKING EASTWARD
THROUGH THE CENTRAL APPALACHIANS WILL DRAW A MOIST AIRMASS INTO
MICHIGAN THROUGH SATURDAY. WET WEATHER CAN BE EXPECTED FOR THE
FIRST HALF OF THE WEEKEND. A COLD FRONT WILL PUSH THE MOIST
AIRMASS EAST OF THE REGION BY SUNDAY MORNING. AS A RESULT THE AREA
WILL SEE DIMINISHING CHANCES FOR RAIN SUNDAY.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 249 PM EDT FRI JUL 11 2014

THE MAIN CHALLENGE IN THE SHORT TERM DEALS THE THE TIMING AND
STRENGTH OF THE STORMS THIS WEEKEND. OVERALL IT STILL LOOKS LIKE
LATER SATURDAY INTO SATURDAY NIGHT WILL BE THE FAVORED PERIOD FOR
THUNDERSTORMS.

ONE LOW LEVEL JET ARRIVES SATURDAY AFTERNOON. THIS SYSTEM DRAWS IN
THE VERY MOIST AIRMASS WITH PWAT VALUES CLIMBING OVER 2 INCHES.
WEAK INSTABILITY IS NOTED...SO A FEW STORMS ARE POSSIBLE...MAINLY
IN THE AFTERNOON. LOCALLY HEAVY RAIN LOOKS LIKE THE MAIN RISK
SATURDAY AFTERNOON. HOURLY AMOUNTS COULD TOP AN INCH PER HOUR IN
THE STRONGER STORMS.

A MORE WIDESPREAD CONVECTIVE EVENT LOOKS POSSIBLE SATURDAY NIGHT.
THE LOW LEVEL JET STRENGTHENS CREATES FAVORABLE MOISTURE FLUX
CONVERGENCE AIMED A SOUTHERN LOWER MI. AN INCREASED RISK FOR
EXCESSIVE RAIN AND DAMAGING WINDS APPEARS TO EXIST. SHEAR VALUES
ALSO BECOME SUPPORTIVE OF SEVERE WEATHER AS WELL. UPPER LEVEL
DIFFLUENCE IS NOTED AT THE TROP LEVEL. WILL KEEP THE HIGH POPS
GOING.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 249 PM EDT FRI JUL 11 2014

THE CHANCE OF SHOWERS AND THUNDERSTORMS WILL REMAIN IN THE FORECAST
MONDAY AS LOW PRESSURE MOVES THROUGH THE GREAT LAKES REGION. AN
UNSEASONABLY COOL AIRMASS WILL ADVECT IN BEHIND THAT SYSTEM
BEGINNING MONDAY NIGHT THROUGH TUESDAY WITH BRISK NORTH TO NW FLOW
CAA.

SHOWERS AND PERHAPS SOME THUNDERSTORMS ARE POSSIBLE DUE TO
INSTABILITY FROM DAYTIME HEATING AND WITH THE POOL OF COLD AIR
ALOFT UNDER THE UPPER LOW TUESDAY.

THE UPPER LEVEL TROUGH WILL REMAIN ENTRENCHED OVER THE GREAT LAKES
REGION THROUGH MIDWEEK RESULTING IN TEMPS THAT WILL CONTINUE TO
AVERAGE 10 TO 15 DEGREES BELOW NORMAL WEDNESDAY. TEMPS WILL BEGIN TO
MODERATE SLOWLY LATE NEXT WEEK AS THE UPPER TROUGH MOVES NE OF OUR
REGION.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1159 PM EDT FRI JUL 11 2014

VFR CONDITIONS WILL CONTINUE TONIGHT INTO AT LEAST EARLY
SATURDAY... WITH MVFR CIGS/VSBYS BECOMING MORE WIDESPREAD AFTER
18Z SATURDAY AND ESPECIALLY TOWARD 00Z SUNDAY AS SHOWERS BECOME
MORE NUMEROUS. A FEW THUNDERSTORMS CANNOT BE RULED OUT SATURDAY
AFTERNOON AND EARLY EVENING... BUT KEPT THE MAIN RISK OF THUNDER
OUT OF THE TAFS UNTIL AFTER 02-03Z SUNDAY WHEN THE LOW LEVEL JET
KICKS IN.

&&

.MARINE...
ISSUED AT 249 PM EDT FRI JUL 11 2014

WILL NEED TO MONITOR WINDS SATURDAY NIGHT WITH THE CONVECTION
ROLLING IN. MAY NEED SMALL CRAFT ADVISORIES. FOR NOW...LOOKS LIKE
VALUES REMAIN BELOW HEADLINE CRITERIA. WINDS AND WAVE WILL BE
HIGHER NEAR ANY STORMS.


&&

.HYDROLOGY...
ISSUED AT 249 PM EDT FRI JUL 11 2014

MAY NEED TO CONSIDER A FLASH FLOOD WATCH FOR SATURDAY AFTERNOON
THROUGH SUNDAY NIGHT. LOW LCLS...DEEP CAPE AND A DEEP WARM CLOUD
LAYER SUPPORT EFFICIENT RAINFALL PROCESS. LOCAL AMOUNTS WELL OVER
2 INCHES POSSIBLE...ESPECIALLY IF THE STORMS TRAIN. CORFIDI DO
BECOME SMALL SAT NIGHT. THE OVERALL RISK WILL DEPEND ON HOW THE
CONVECTION UNFOLDS.

&&

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

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...LAURENS
AVIATION...MEADE
HYDROLOGY...MJS
MARINE...MJS





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