Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 261735
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
135 PM EDT TUE AUG 26 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 325 AM EDT TUE AUG 26 2014

WARM AND HUMID CONDITIONS WILL CONTINUE TODAY WITH A CHANCE OF
SHOWERS AND THUNDERSTORMS. THE BEST CHANCE OF THUNDERSTORMS WILL
COME LATE THIS MORNING AND AFTERNOON NEAR TO SOUTHEAST OF A LINE
FROM HOLLAND TO LANSING. A COOLER AND DRIER AIRMASS WILL MOVE IN
TONIGHT THROUGH THURSDAY. HOWEVER IT WILL TURN WARMER AND MORE
HUMID VERY LATE IN THE WEEK INTO NEXT WEEKEND WITH SCATTERED
SHOWERS AND THUNDERSTORMS.

&&

.UPDATE...
ISSUED AT 1054 AM EDT TUE AUG 26 2014

BUMPED UP POPS AND QPF ACROSS THE SOUTHERN ZONES AS CLUSTER OF
SHOWERS AND THUNDERSTORMS NOW ACROSS NORTHERN ILLINOIS AND
SOUTHERN LAKE MICHIGAN IS EXPECTED TO CONTINUE EAST AND MOVE
ACROSS AREAS SOUTH OF I-96 NEXT FEW HOURS. SIMILAR TO YESTERDAY
THE SEVERE THREAT IS LIMITED BY LACK OF DEEP LAYER SHEAR BUT
INSTABILITY WILL BE ENOUGH TO KEEP THE THREAT FOR STRONG
UPDRAFTS/DOWNDRAFTS AND SOME SMALL HAIL.

&&

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 325 AM EDT TUE AUG 26 2014

PRIMARY SHORT TERM FORECAST CONCERNS INVOLVE DETERMINING
CONVECTIVE POTENTIAL TODAY.

THE COLD FRONT WILL MOVE THROUGH OUR FCST AREA FROM NW TO SE THIS
MORNING AND AFTERNOON. SCATTERED SHOWERS AND THUNDERSTORMS WILL
DEVELOP ALONG AND JUST AHEAD OF THE FRONT MAINLY THIS AFTERNOON.
GIVEN THE FRONTAL TIMING THE BEST CHANCE FOR SCATTERED SHOWERS AND
STORMS WILL COME LATE THIS MORNING AND AFTERNOON OVER OUR SE FCST
AREA NEAR TO MAINLY JUST SE OF KGRR OVER TOWARD LAN... BTL... AND
JXN. THIS IS WHERE THERE IS POTENTIAL FOR SB CAPE VALUES TO REACH
2500-3000 J/KG BY EARLY AFTERNOON AS SUGGESTED BY 00Z NAM/GFS
GUIDANCE.

THE SEVERE WX THREAT TODAY IS FAIRLY LOW IN SPITE OF THE
POTENTIALLY MODERATE TO STRONG INSTABILITY MAINLY BECAUSE OF WEAK
DEEP LAYER SHEAR AND LACK OF STRONGER FORCING FROM THE FRONT. EVEN
SO CANNOT RULE OUT ISOLATE SEVERE STORMS OVER OUR SE FCST AREA
THIS AFTERNOON GIVEN POTENTIAL FOR STRONG INSTABILITY JUST AHEAD
OF THE FRONT.

A COOLER AND DRIER AIRMASS WILL ADVECT IN BEHIND THE FRONT TONIGHT
THROUGH MIDWEEK. HAVE TRENDED THE FORECAST DRY FOR TONIGHT AFTER
FROPA WITH DRY WX ANTICIPATED WEDNESDAY THROUGH THURSDAY AS A HIGH
PRESSURE RIDGE BUILDS IN. PCPN TIED TO THE NEXT SYSTEM APPROACHING
FROM THE WEST SHOULD HOLD OFF UNTIL THURSDAY NIGHT.

.LONG TERM...(THURSDAY NIGHT THROUGH MONDAY)
ISSUED AT 325 AM EDT TUE AUG 26 2014

OVERALL MODEL CONTINUITY IS FAIRLY GOOD TONIGHT BETWEEN THE GFS AND
THE ECMWF. THERE IS SOME DIVERGENCE IS SOLUTIONS OUT ON SUNDAY AND
MONDAY THOUGH. HAVE OPTED TO CONTINUE TO FOLLOW THE ECMWF HAS IT HAS
HAD MUCH BETTER RUN TO RUN CONSISTENCY LATELY. ALSO THE GFS HAS BEEN
CONVERGING TOWARDS ITS SOLUTIONS. FORECAST CONFIDENCE IS ONLY MEDIUM
THOUGH GIVEN THE DISPARITY BETWEEN THE MODELS.

THE LONG TERM STILL LOOKS LIKE A WET PERIOD AS A SURFACE BOUNDARY
WILL BE OSCILLATING THROUGH THE AREA ALMOST THE ENTIRE TIME. A WARM
FRONT SURGES NORTH THURSDAY NIGHT INTO FRIDAY...WITH THE ASSOCIATED
COOL FRONT STALLING OUT OVER THE AREA SATURDAY INTO SUNDAY. THE
ECMWF THEN PIVOTS A LOW THROUGH THE SOUTHERN GREAT LAKES INTO
MONDAY. HAVE MAINLY CHANCE POPS RIGHT THROUGH THE LONG TERM PERIOD
FOR SHOWERS AND STORMS. HEAVY RAINS ARE A DEFINITE POTENTIAL GIVEN
THE REPEATED ROUNDS OF CONVECTION. WPC QPF FOR THE LONG TERM IS ON
THE ORDER OF 1 TO 2 INCHES.

TEMPERATURES THROUGH THE PERIOD SHOULD BE SEASONABLE...IN THE UPPER
70S TO NEAR 80 ON MOST DAYS FOR HIGHS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 133 PM EDT TUE AUG 26 2014

AN AREA OF SHOWERS AND THUNDERSTORMS IS MOVING EAST ACROSS
SOUTHERN LOWER MICHIGAN. THESE STORMS WILL MOVE ACROSS THE TAF
SITES THROUGH 20Z...AFTER WHICH CONDITIONS SHOULD RETURN TO VFR.
CIGS/VSBYS WILL FALL TO IFR/MVFR DURING STORMS.

&&

.MARINE...
ISSUED AT 325 AM EDT TUE AUG 26 2014

WINDS AND WAVES WILL BE RELATIVELY LIGHT TODAY THROUGH MIDWEEK.
HOWEVER PATCHY FOG WILL POSE A HAZARD TO MARINERS TODAY BEFORE A
DRIER AIRMASS MOVES IN TONIGHT THROUGH MIDWEEK.


&&

.HYDROLOGY...
ISSUED AT 1101 PM EDT MON AUG 25 2014

A FEW THUNDERSTORMS COULD REDEVELOP OVERNIGHT...AND THUNDERSTORMS
ARE ALSO POSSIBLE ON TUESDAY PRIMARILY EAST OF US-131. THESE
STORMS WILL REMAIN ISOLATED TO SCATTERED IN NATURE AND WIDESPREAD
HYDRO IMPACTS ARE NOT EXPECTED. STORMS COULD PRODUCE LOCALLY HEAVY
RAINFALL. DRIER AIR MOVES IN LATE TUESDAY INTO WEDNESDAY.

&&

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

$$

UPDATE...OSTUNO
SYNOPSIS...LAURENS
SHORT TERM...LAURENS
LONG TERM...DUKE
AVIATION...93
HYDROLOGY...EBW
MARINE...LAURENS





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