Special Marine Warning 21, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
407 AM EDT WED AUG 22 2007

LATEST UPDATE...ALL SECTIONS EXCEPT AVIATION...

.SYNOPSIS...(407 AM EDT WED AUG 22 2007)
A STALLED OUT FRONTAL BOUNDARY IS LOCATED JUST SOUTH OF LOWER
MICHIGAN THIS MORNING. THIS FRONT IS EXPECTED TO REMAIN RATHER
ACTIVE AS WAVES OF LOW PRESSURE MOVE ALONG IT FROM THIS MORNING
RIGHT ON THROUGH THE DAY ON SATURDAY. PERIODIC ROUNDS OF SHOWERS AND
THUNDERSTORMS WILL REMAIN POSSIBLE ACROSS THE AREA FROM TODAY RIGHT
ON THROUGH THE DAY ON SATURDAY. SEVERE WEATHER WILL BE BE POSSIBLE
THROUGH THIS PERIOD...AS WILL HEAVY RAINFALL.

&&

.SHORT TERM... (407 AM EDT WED AUG 22 2007)
LATEST SFC ANALYSIS THIS MORNING AS OF 07Z HAS THE FRONTAL BOUNDARY
ROUGHLY ALONG A LINE FROM THE QUAD CITIES...TO JUST NORTH OF
KORD...TO NEAR KFWA...AND THEN TO KDAY. IMPRESSIVE MCS OVER WI
EARLIER IS NOW IN THE STAGE OF WEAKENING AS IT HEADS E/NE TOWARD
CENTRAL LAKE MICHIGAN. WE DO THINK THAT AT LEAST THE NW COUNTIES
WILL SEE RAIN FROM THIS DECAYING MCS IF NOT AREAS FURTHER SOUTH.
INSTABILITY IS DEFINITELY MORE IMPRESSIVE ACROSS THE LAKE OVER WI AS
THE LLJ IS MUCH BETTER OVER THERE. IT DOES LOOK LIKE ANOTHER LINE IS
ORGANIZING LIKELY NEAR THE SFC FRONT OVER NRN IL. WE WILL WAIT UNTIL
PRESS TIME TO DETERMINE PCPN CHC FOR THIS MORNING. THERE IS A BIT OF
ELEVATED INSTABILITY IN PLACE WITH ELEVATED LI/S FALLING DOWN TO -2
TO -4 BY 12Z THIS MORNING...THUS THUNDER REMAINS VERY POSSIBLE.
OBVIOUSLY THIS PCPN WILL HAVE AN IMPACT ON THE FRONTAL POSITION
THROUGH THE DAY. IT SEEMS LIKE THE FRONT MAY MAKE IT NO FURTHER
NORTH THAN I-96 IF THAT FAR. THIS ALONG WITH PCPN AND CLOUD DEBRIS
SHOULD HOLD TEMPS DOWN A BIT FOR A GOOD PORTION OF THE CWFA...AND WE
HAVE ONCE AGAIN UNDERCUT THE MAV GUIDANCE AS FAR AS TEMPS GO FOR THE
NRN TWO THIRDS OF THE CWFA.

ADDITIONAL WEAKER WAVES ALONG THE FRONT WILL BE POSSIBLE THROUGH THE
DAY TODAY. PLENTY OF MOISTURE IS AVAILABLE WITH PWATS IN THE 1.5 TO
2 INCH RANGE OVER THE REGION. SOUTH OF THE FRONT...MODELS ARE
INDICATING THAT OVER 2K J/KG OF SB CAPE WILL BE AVAILABLE WITH DEW
POINTS IN THE LOWER 70S AND TEMPS SOUTH OF THE FRONT WELL INTO THE
80S. BULK SHEAR DECREASES AS YOU HEAD SOUTH TO AROUND 25 TO 30
KTS...BUT THE GOOD DEAL OF INSTABILITY WITH MARGINAL SHEAR WILL
PRODUCE A SEVERE THREAT.

THE FRONT IS EXPECTED TO REMAIN IN THE AREA THROUGH A GOOD PORTION
OF THE NIGHT TONIGHT AND DURING THE DAY ON THU...UNTIL A FAIRLY
DECENT SHORT WAVE MOVES OUT OF THE PLAINS AND TOWARD THE GREAT
LAKES. THIS LOOKS TO BE THE BEST OPPORTUNITY FOR THE WARM FRONT TO
BE PUSHED NORTH THROUGH THE AREA. UNTIL THIS OCCURS...SHOWERS AND
STORMS WILL REMAIN POSSIBLE WITH THE BEST CHANCES JUST NORTH OF THE
FRONT. THE WARMEST DAY LOOKS TO BE ON THU AS MORE OF THE CWFA GETS
INTO THE WARM SECTOR.

AS THE SHORT WAVE AND ASSOCIATED SFC LOW MOVE WELL NORTHEAST BY FRI
MORNING...THE FRONT WILL COME BACK TO THE SOUTH AND WILL LIKELY
CLEAR THE AREA BY 12Z FRI MORNING. THE BEST POTENTIAL FOR PCPN THU
NIGHT WILL BE NORTH OF THE AREA AS A STRONG LLJ FIRES CONVECTION
NEAR THE SFC LOW. POTENTIAL FOR CONVECTION OVER THE CWFA WILL REMAIN
AS THE COLD FRONT DROPS THROUGH. TIME OF DAY WILL NOT BE IN FAVOR OF
HIGH POPS WITH THE FRONT COMING THROUGH AT NIGHT. HOWEVER PLENTY OF
MOISTURE WILL BE IN PLACE...AND SFC BASED AND ELEVATED INSTABILITY
IS EXPECTED TO BE PRESENT. ADDITIONAL WAVES OF LOW PRESSURE ARE THEN
EXPECTED TO RIDE ALONG THE FRONT ON FRI...CONTINUING THE THREAT OF
PCPN.

&&

.LONG TERM... (407 AM EDT WED AUG 22 2007)
FINAL WAVE EXPECTED TO MOVE NE ALONG THE BAROCLINIC ZONE EITHER
FRIDAY NIGHT OR SATURDAY. ONCE THAT OCCURS THE ACTIVE FRONTAL
BOUNDARY SHOULD FINALLY PUSH SOUTHEAST OUT OF THE AREA. WILL CARRY
POPS BOTH FRIDAY NIGHT AND SATURDAY... ALTHOUGH ITS QUITE POSSIBLE
SATURDAY WILL END UP BEING DRY (ESPECIALLY IN THE NW CWFA) IF THE
GFS/S EARLIER TIMING IS CORRECT. QUIET WX WITH LESS HUMID CONDITIONS
EXPECTED TO RETURN FOR SUNDAY INTO EARLY NEXT WEEK AS A SFC HIGH
SLIDES EAST ACROSS THE REGION.

&&

.AVIATION...(155 AM EDT WED AUG 22 2007 )
FOG/STRATUS TRENDS ARE DIFFICULT TO NAIL DOWN TONIGHT. SOME SITES
HAVE LIFR CIGS WITH 1-2 MI VSBYS WHILE OTHERS HAVE VFR CIGS WITH 4-5
MI VSBYS. THE WARM FRONT STILL APPEARS TO BE SOUTH OF THE AREA...
BUT MAY BE TRYING TO BULGE NORTH ALONG THE LK MI SHORELINE. LOWEST
CIGS/VSBYS TONIGHT SHOULD BE IN THE EAST (NORTH OF THE BOUNDARY)
AROUND LAN AND JXN... WHILE MKG MAY HAVE BEST CONDITIONS. IN ANY
EVENT... DEW POINTS AOA 70 ARE SPREADING NORTH WHICH COULD PROMOTE
FOG/STRATUS DEVELOPMENT JUST ABOUT ANYWHERE.

CONVECTION RACING EAST THROUGH WI EXPECTED TO WEAKEN BY THE TIME IT
CROSSES LK MI... BUT STILL WORTHY OF VCTS FOR MKG TOWARD 12Z.
OTHERWISE LOOK FOR IMPROVING CIGS/VSBYS WED MRNG... WITH SCATTERED
CONVECTION PROBABLY INCREASING IN THE AFTERNOON AS INSTABILITY
INCREASES.

&&

.MARINE... (407 AM EDT WED AUG 22 2007)
AS THE WARM FRONT MOVES SLOWLY NORTH INTO THE AREA...WINDS WILL
SHIFT FROM SOUTHEAST NORTH OF THE FRONT TO SOUTH/SOUTHWEST SOUTH OF
IT. WINDS ARE EXPECTED TO GENERALLY STAY AT OR BELOW 15 KNOTS TODAY
AND TONIGHT. AS A MORE SUBSTANTIAL WAVE OF LOW PRESSURE MOVES INTO
THE AREA ON THURSDAY...WINDS WILL LIKELY INCREASE FROM THE SOUTH.

&&

.HYDROLOGY... (407 AM EDT WED AUG 22 2007)
USGS RIVER AND STREAM DATA INDICATES THAT ALMOST ALL DATA POINTS
REMAIN AT ABOVE TO MUCH ABOVE NORMAL. EVEN WITH THIS SAID...NO
PROBLEMS ARE BEING REPORTED AT THIS TIME...AND ALL GAGE DATA
INDICATES ALL RIVERS REMAIN BELOW ACTION STAGE. LATEST RIVER
FORECASTS FROM THE RFC FOR THE AREA KEEP ALL FORECAST POINTS BELOW
ACTIONS STAGE WITH A GENERAL 0.5 TO 1 INCH BASIN AVERAGE OVER THE
NEXT 24 HOURS. WE WILL HAVE TO CONTINUE TO MONITOR HEAVY RAINFALL
POTENTIAL AS IF WE GET A WHOLE LOT MORE PRECIPITATION...SOME
PROBLEMS WILL BEGIN TO OCCUR AS FAR AS HIGH RIVER LEVELS ARE
CONCERNED.

&&

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

&&

SYNOPSIS:   NJJ
SHORT TERM: NJJ
LONG TERM:  MEADE
AVIATION:   MEADE
MARINE:     NJJ
HYDROLOGY:  NJJ