Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 051614
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1214 PM EDT SAT SEP 5 2015

LATEST UPDATE...
HYDRO

.SYNOPSIS...
ISSUED AT 308 AM EDT SAT SEP 5 2015

A WARM FRONT WILL LIFT NORTHWARD THROUGH THE REGION TODAY LEADING
TO SOME SHOWERS AND THUNDERSTORMS. HIGH PRESSURE CONTROLS OUR
WEATHER ON SUNDAY WHICH SHOULD END UP A MOSTLY DRY AND VERY WARM
DAY. THE CHANCES FOR SHOWERS AND THUNDERSTORMS WILL INCREASE AS WE
GO THROUGH LABOR DAY AND INTO TUESDAY AS A SLOW MOVING COLD FRONT
NEARS FROM THE WEST. THE TEMPERATURES WILL STILL END UP WELL ABOVE
NORMAL EARLY NEXT WEEK.

&&

.UPDATE...
ISSUED AT 1039 AM EDT SAT SEP 5 2015

WE HAVE UPDATED TO FCST THIS MORNING TO EXTEND THE DENSE FOG
ADVISORY UNTIL NOON UP NORTH. WE HAVE ALSO INCREASED THE
SHOWER/STORM CHCS DOWN SOUTH WITH PLENTY OF COVERAGE ALREADY IN
PLACE DOWN THERE.

THE FOG UP NORTH HAS BEEN SLOW TO DISSIPATE THIS MORNING WITH MANY
LOCATIONS STILL AT 1/4SM OR LESS LEADING UP TO THE INITIAL
EXPIRATION TIME OF 10 AM THIS MORNING. WITH A LACK OF WIND TO MIX
THINGS UP AND PLENTY OF STRATUS IN PLACE...IT WILL TAKE A LITTLE
LONGER THAN PREVIOUSLY EXPECTED TO MIX IT OUT. WE GAVE IT UNTIL
NOON FOR MORE OF A BUFFER. WE WILL CANCEL IT EARLY IF ALL SITES
COME UP SOONER.

PLENTY OF SHOWERS AND STORMS ACROSS THE SOUTH THIS MORNING. THE
PESKY WEAK UPPER LOW THAT HAS BEEN MEANDERING ACROSS THE STATE THE
PAST COUPLE OF DAYS IS OVER LAKE MICHIGAN EARLY THIS MORNING. IT
NOW LOOKS LIKE IT IS MAKING A MOVE TO THE EAST...AND FIRING PLENTY
OF SHOWERS/STORMS AHEAD OF IT WITH THE MOIST AIR MASS IN PLACE.

IT APPEARS THIS WILL CONTINUE EAST THROUGH THE DAY AND PUSH THE
MORE WIDESPREAD COVERAGE EAST BY LATER THIS AFTERNOON. WE CAN NOT
RULE OUT A POP UP SHOWER/STORM WITH THE UPPER LOW STILL NEARBY.
WEAK SHEAR AND LIMITED INSTABILITY WILL KEEP THINGS GENERALLY
TAME. HEAVY DOWNPOURS WOULD BE THE GREATEST THREAT WITH THE SLOW
MOVEMENT.

&&

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 308 AM EDT SAT SEP 5 2015

DENSE FOG HAS BEEN INCREASING OVER THE PAST FEW HOURS AND NOW
COVERS MUCH OF THE REGION. HRRR RUC SUGGESTS THE FOG WILL PERSIST
THROUGH DAYBREAK. WILL GO WITH AN ADVISORY AND CARRY IT UNTIL MID
MORNING. WE MAY SEE GRADUAL IMPROVEMENT IN THE VISIBILITIES FROM
SOUTH TO NORTH BEFORE DAYBREAK AS THE ELEVATED WARM FRONT MOVES
IN.

THE ATMOSPHERE WILL BE UNSTABLE THROUGH THE DAY. SOME LIFT ARRIVES
WITH THE ELEVATED WARM FRONT MOVING IN THIS MORNING FROM THE
SOUTH. THEREFORE WILL KEEP THE MENTION OF SHOWERS AND
THUNDERSTORMS IN THE FORECAST. LITTLE OR NO FORCING IS AROUND
TONIGHT INTO SUNDAY. WILL KEEP IT DRY FOR NOW. THE ATMOSPHERE
BECOMES RATHER UNSTABLE ON SUNDAY...SO WILL NEED TO MONITOR THIS
CLOSELY. SUNDAY SHOULD BE ONE OF THE WARMEST DAYS OF THE SEASON AS
THE LOW LEVEL THERMAL RIDGE ADVECTS IN FROM THE SOUTHWEST.

WILL FEATURE AN INCREASING RISK FOR SHOWERS AND THUNDERSTORMS ON
LABOR DAY. MODELS VARY ON THE TIMING OF ANY PRECIPITATION. HOWEVER
GIVEN THE APPROACHING FRONT DURING THE AFTERNOON WILL ENCOUNTER AN
UNSTABLE AIRMASS...IS SEEMS THAT A RISK FOR THUNDERSTORMS WILL
EXIST. WILL HIGHLIGHT THE AFTERNOON FOR POSSIBLE THUNDERSTORMS.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 308 AM EDT SAT SEP 5 2015

MAIN FOCUS IS CURRENTLY ON THE THREAT FOR HEAVY RAINFALL MONDAY
NIGHT THROUGH TUESDAY NIGHT WITH SOME TRAINING THUNDERSTORMS
POSSIBLE IN ASSOCIATION WITH MAINLY UNIDIRECTIONAL WINDS IN THE
PROFILE...A VERY MOIST AIRMASS...AND A WARM FRONT LIFTING THROUGH
DURING THIS PERIOD. MANY AREAS NEAR AND NORTH OF I-96 ARE EXPECTED
TO RECEIVE ONE TO TWO INCHES OF RAIN BY WEDNESDAY MORNING WITH
HIGHER AMOUNTS QUITE POSSIBLE.

I BELIEVE THERE ARE SOME KEY INGREDIENTS COMING IN PLACE FOR LOCALLY
EXCESSIVE RAINFALL ACROSS WEST CENTRAL AND SOUTHWEST LOWER MI. AS
HAS BEEN MENTIONED MANY TIMES...A WEAK COLD FRONT WILL WASH OUT
ACROSS THE CWA MONDAY...WHICH WILL BECOME STATIONARY AND THEN LIFT
NORTH AS A WARM FRONT TUESDAY. JUST HOW FAR NORTH THIS BOUNDARY
LIFTS IS QUESTIONABLE GIVEN NUMEROUS AREAS OF CONVECTION THAT COULD
SUPPRESS THE FRONT SOUTHWARD. CURRENTLY FAVORING THE ECMWF WITH THIS
SYSTEM GIVEN A FEW DIFFERENT GYRATIONS NOTED WITH THE GFS RECENTLY
WITH HOW QUICK THE BOUNDARY WILL MOVE THROUGH.

DEEP LAYER RH (H1000-H500) ON TUESDAY COULD TOP 90% FOR A GOOD
PORTION OF THE CWA...ESPECIALLY FROM GRR TO THE NORTH. ALL OF THE
MODELS ARE ALSO SHOWING SOME H1000-H700 WIND CONVERGENCE. A 20 KT
LLJ AT 00Z TUES STRENGTHENS TO 30-35 KT BY 00Z WED. HIGHER UP...WE
WILL BE SQUARELY IN THE RIGHT ENTRANCE REGION OF A 100 KT JET STREAK
AS H500 POSITIVE VORTICITY ADVECTION MOVES INTO THE CWA DURING THE
MORNING AND AFTERNOON HOURS. NEAR THE SURFACE...THE WARM FRONT WILL
BE DRAPED ACROSS THE CWA NEAR GRR AT 12Z TUESDAY...POSSIBLY LIFTING
NORTH TOWARD ROUTE 10 BY 18Z. DEW POINT READINGS AROUND 70 COUPLED
WITH PW VALUES OF 2.00-2.25" STRONGLY SUGGEST ANY STORMS WOULD BE
CAPABLE OF HEAVY DOWNPOURS. IF THE NWP SOLUTIONS CONTINUE SUPPORTING
THESE DETAILS...COULD FORESEE A FLOOD THREAT FOR AREAS THAT GET THE
MOST PERSISTENT RAINS.

IN TERMS OF ANY SEVERE WEATHER THREAT...IT IS UNCLEAR AT THIS TIME.
ONGOING CONVECTION EARLY TUESDAY COULD HAMPER ANY DESTABILIZATION
DURING THE AFTERNOON. SFC BASED CAPE IS NOT MUCH MORE THAN 1000 J/KG
FOR THE AREA ON TUESDAY...THOUGH BULK SHEAR IS LOOKING MUCH BETTER
OFF THE ECMWF AT AROUND 35-40 KTS. IT IS ALSO SHOWING 100-150 M2/S2
OF 0-1 KM HELICITY COURTESY OF THE WARM FRONT NEARBY. NOT OUT OF THE
QUESTION THERE COULD BE SOME STRONGER STORMS CAPABLE OF GUSTY WINDS
AND SOME HAIL IF WE CAN DESTABILIZE SUFFICIENTLY.

BEYOND THIS PERIOD...LOOKING AT A PATTERN CHANGE FOR THE SECOND HALF
OF THE WEEK AND THE WEEKEND IN PARTICULAR. TROPICAL STORM IGNACIO
WILL GET SWEPT UP IN MID LEVEL FLOW OVER THE GULF OF ALASKA.
FOLLOWING THE ECMWF H500 HEIGHT FIELD...THIS HELPS DIG A TROUGH INTO
THE GREAT LAKES FOR FRIDAY AND SATURDAY...WITH CHILLY TEMPS AND
SCATTERED SHOWERS EXPECTED BY SATURDAY WITH HIGHS STRUGGLING INTO
THE 60S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 730 AM EDT SAT SEP 5 2015

SCATTERED THUNDERSTORMS THIS MORNING WILL IMPACT SOME OF THE TAF
SITES AS A WARM FRONT PUSHES NORTH. WIDESPREAD DENSE FOG WILL
LIFT SLOWLY NORTH AND DISSIPATE THIS MORNING. GENERALLY VFR
WEATHER THEN SETS UP IN AN UNSTABLE AIRMASS. SO WILL MAINTAIN A
RISK FOR THUNDERSTORMS...AS VCTS. TONIGHT THE RISK FOR
THUNDERSTORMS LOWERS...BUT WE MAY SEE FOG REFORMING ONCE AGAIN.


&&

.MARINE...
ISSUED AT 308 AM EDT SAT SEP 5 2015

WINDS AND WAVES INCREASE SUNDAY INTO SUNDAY NIGHT AS THE WARM AIR
ADVECTION STRENGTHS AHEAD OF THE APPROACHING COLD FRONT. WILL NEED
TO MONITOR LITTLE AND BIG SABLE POINTS FOR A POSSIBLE SMALL CRAFT
ADVISORY AND ASSOCIATED BEACH HAZARDS. RIGHT NOW I HAVE WAVES
INCREASING TO 2 TO 4 FEET.


&&

.HYDROLOGY...
ISSUED AT 1214 AM EDT SAT SEP 5 2015

LOCALIZED HEAVY RAINFALL HAS FALLEN OVER SOUTHERN PORTIONS OF THE
FORECAST AREA THIS MORNING. RADAR ESTIMATES SHOW MOST OF THE
RAINFALL ALONG AND SOUTH OF I-96 WITH SPOTTY ESTIMATES POSSIBLY
EXCEEDING ONE INCH. THOUGH THIS IS NOT AN IMMEDIATE PLAYER IN ANY
RIVER FLOODING IT COULD PLAY A ROLE IN NEXT WEEKS RAINFALL
POTENTIAL.

A BRIEF DRY PERIOD LATE TONIGHT THROUGH THE EARLY HALF OF MONDAY
WILL HELP IN ALLOWING RUNOFF TO MAKE ITS WAY DOWN STREAMS AND
RIVERS. THIS MAY BE BENEFICIAL IN THE EVENT THAT THE LATE MONDAY
THROUGH WEDNESDAY TIMEFRAME BRINGS HEAVY RAIN. THOUGH QUESTIONS
STILL EXIST IN PLACEMENT...IT IS BECOMING MORE EVIDENT THAT
MOISTURE FLOWS IN THIS DIRECTION AS PWATS APPROACH 2.0 INCHES.
THIS COUPLED WITH THE SLOW MOVEMENT OF THE FRONTAL BOUNDARY MAY
AID IN ROUNDS OF HEAVY RAINFALL ALONG THE BOUNDARY THROUGH
PORTIONS OF THE FORECAST AREA. WHILE EVERYONE HAS THE THE
POTENTIAL TO SEE SOME DECENT RAINFALL...SOME LOCATIONS MAY EASILY
ACCUMULATE AN INCH OR MORE IN OR AROUND THUNDERSTORMS. ANY
PREVIOUS RAINFALL FROM TODAY COULD HAVE DEPOSITED ENOUGH MOISTURE
TO SOUTHERN SECTIONS... ALLOCATING ADDITIONAL RAINFALL MORE SO TO
RUNOFF THAN TO GROUND WATER. SO THE PLACEMENT OF THE HEAVY RAIN
NEXT WEEK IS SOMETHING TO WATCH.

&&

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

$$

UPDATE...NJJ
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...HOVING
AVIATION...MJS
HYDROLOGY...JAM
MARINE...MJS


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