Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 291533
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1133 AM EDT FRI AUG 29 2014

LATEST UPDATE...
UPDATE/MARINE

.SYNOPSIS...
ISSUED AT 325 AM EDT FRI AUG 29 2014

SHOWERS AND A FEW THUNDERSTORMS ARE POSSIBLE TODAY AS A WARM FRONT
MOVES THROUGH THE AREA. MORE WIDESPREAD THUNDERSTORM ACTIVITY IS
EXPECTED SATURDAY AHEAD OF THE COLD FRONT...WHICH COMES THROUGH
EARLY SUNDAY MORNING. BEHIND THE COLD FRONT ON SUNDAY EXPECT
PARTIAL CLEARING BY AFTERNOON. THEN A STRONG COLD FRONT WILL BRING
THE RISK OF ADDI TONAL STORMS MONDAY.

&&

.UPDATE...
ISSUED AT 1130 AM EDT FRI AUG 29 2014

LOWERED TEMPERATURES SLIGHTLY AND ADDED A RISK FOR THUNDERSTORMS
THIS AFTERNOON. ELEVATED INSTABILITY MOVES IN FOR THE AFTERNOON.
ALSO RADAR SHOWS CONVECTION CROSSING THE LAKE. CLOUDS WILL LIKELY
LIMIT HIGH TEMPERATURES TODAY. WARMEST READINGS MAY BE LATER IN
THE AFTERNOON WHEN WE WILL POTENTIALLY SEE MORE SUN.


&&

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 325 AM EDT FRI AUG 29 2014

WE ARE TRACKING SHOWERS AND THUNDERSTORMS TODAY THROUGH SATURDAY
NIGHT. WHILE THERE COULD BE SOME SHOWERS AND ISOLATED THUNDERSTORMS
AROUND TODAY....IT WOULD SEEM OUR BEST POTENTIAL FOR WIDESPREAD
CONVECTION IS SATURDAY AS THE UPPER WAVE MOVES THROUGH.

THE BIG PICTURE FINDS A OPENING UP SOUTHERN STREAM CLOSED UPPER
LOW MOVING EAST AS IT SHEARS OUT AND MOVES OVER MICHIGAN DURING
THE DAY TIME SATURDAY. THE MODELS AS NEARLY ALWAYS WEAK THESE
FEATURE TO FAST SO I WOULD EXPECT STRONG DYNAMICS SATURDAY THEN
ANY OF THE MODELS CURRENTLY WOULD SUGGEST. IN ANY EVENT AS THIS
UPPER WAVE HEADS TOWARD MICHIGAN IT DISPLACES A SHORTWAVE RIDGE
CURRENTLY IN PLACE OVER MICHIGAN. THAT RESULTS IN A SURGE OF MID
LEVEL MOISTURE THAT SHOULD LEAD TO SOME SHOWER AND THUNDERSTORM
ACTIVITY OVER THE WESTERN AND NORTHER SECTIONS OF THE CWA TODAY.
THEN THE PASSAGE OF THE MAIN SYSTEM SATURDAY WILL BRING MORE
WIDESPREAD CONVECTION TO THE AREA.

LOOKING AT THE 1000/850 MOISTURE TRANSPORT VECTORS FROM THE
GFS...NAM AND ECMWF FOR TODAY THE STORY THEY TELL IS SIMILAR TO
WHAT THEY SHOWED YESTERDAY AND THE DAY BEFORE THAT. FOR THE MOST
PART THE BEST MOISTURE TRANSPORT WILL BE NORTH AND WEST OF THE GRR
CWA TODAY. THE LOW LEVEL JET AXIS IS WEST OF MICHIGAN EARLY THIS
MORNING AND IS MOSTLY OVER NORTHERN LOWER AND UPPER MICHIGAN THIS
AFTERNOON INTO TONIGHT. ALSO THE INSTABILITY IS RATHER LIMITED AND
WHAT THERE IS OF IT IS MOSTLY OVER WESTERN SECTIONS OF LOWER
MICHIGAN INTO THIS AFTERNOON. THE SHORTWAVE RIDGE AHEAD OF THE
UPPER WAVE HAS BROUGHT TO WARM OF AIR ABOVE 700 MB SO THAT
VERTICAL TOTALS ARE MARGINAL AT BEST FOR THUNDERSTORMS TODAY. WHAT
BRING THE SHOWERS TO THE AREA TODAY IS A SURGE OF MID LEVEL
MOISTURE AS THE PRECIPITABLE WATER SURGES FROM UNDER A SEVEN TENTS
OF AN INCH EARLY THIS MORNING TO ABOVE ONE AND THREE QUARTER
INCHES OVER MOST OF THE CWA BY NOON. THE FOCUS OF THIS WILL BE ON
THE WARM FRONT NEAR THE AXIS OF THE LOW LEVEL JET. THAT MEANS MOST
OF THE CONVECTION WILL BE NORTH AND WEST OF THE GRR CWA TODAY.

SATURDAY IS WHEN THE MAIN UPPER WAVE MOVES THROUGH THE AREA AND
THERE IS WORKABLE LOW LEVEL JET IN THE AREA AND SOME UPPER LEVEL
JET SUPPORT SO WE SHOULD HAVE WIDESPREAD SHOWERS AND A FEW NON
SEVERE THUNDERSTORMS (CAPE IS LIMITED AND DEEP LAYER SHEAR IS WEAK
TOO).

ALL OF THIS MOVES OUT SATURDAY NIGHT AND SUNDAY FINES US WITH
SHORT WAVER RIDING. SO I EXPECT CLEARING TO OCCUR DURING THE DAY
SUNDAY AS DRY AIR MOVES IN FROM THE NORTHWEST.

.LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY) ISSUED AT 325 AM
EDT FRI AUG 29 2014

THE MAIN WEATHER IN THE LONG TERM WILL BE FOCUSED ON THE CONVECTION
CHCS EARLY ON IN THE PERIOD WITH A SYSTEM THAT WILL BE MOVING
THROUGH THE AREA. THE AREA WILL SEE A BREAK IN THE WEATHER FOR SUN
NIGHT IN THE WAKE OF THE DEPARTING SYSTEM FROM SAT/SAT NIGHT...AND
WELL OUT AHEAD OF THE SYSTEM POISED TO MOVE THROUGH THE AREA ON MON.

THE BREAK WILL BE A SHORT ONE AS THE STORM CHCS WILL BE INCREASING
ON MON MORNING AND LASTING INTO MON EVENING. SHORT WAVE ENERGY
EXPECTED TO COME ONSHORE ACROSS OREGON ON SAT WILL TRAVERSE THE
COUNTRY OVER THE HOLIDAY WEEKEND AND WILL BE LIFTING INTO ONTARIO BY
MON AFTERNOON. THE SHORT WAVE REMAINS MAINLY NORTH OF THE AREA.
HOWEVER THE ASSOCIATED LLJ AND STRONG MOISTURE TRANSPORT DOES MOVE
RIGHT INTO THE AREA MON. WE ENVISION A RESIDUAL LINE OF SHOWERS/
STORMS COMING INTO THE AREA FROM THE WEST ON MON...AND STRENGTHENING
AS IT ENCOUNTERS AN INCREASINGLY UNSTABLE AIR MASS WITH DIURNAL
HEATING THAT TAKES PLACE.

WE CAN NOT RULE SOME OF THE STORMS BECOMING SEVERE MON. DEEP LAYER
SHEAR WILL BE ON THE INCREASE WITH THE UPPER JET NEARBY. LI/S ARE
EXPECTED TO DROP DOWN AROUND -6C WITH CAPES APPROACHING OVER 1500
J/KG. THE LLJ OVERHEAD WILL INCREASE THE 0-3 KM SHEAR WHICH WILL
HELP THE CAUSE. THE LIMITATIONS OF POSSIBLE SEVERE WEATHER WOULD BE
LIMITED INSTABILITY IF NOT MUCH HEATING CAN TAKE PLACE...AND NOT
IDEAL UPPER JET DYNAMICS OVERHEAD.

MOST OF THE REST OF THE WEEK SHOULD BE RATHER QUIET AND SEASONABLE
FOR THE AREA. SOME RESIDUAL CHCS OF PCPN WILL HOLD ON TUE UNTIL THE
SECONDARY SHORT WAVE MOVES THROUGH. AFTER THAT...WE GET INTO A
NEARLY ZONAL FLOW WITH LOWER MICHIGAN JUST DOWNSTREAM OF SOME
RIDGING.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 740 AM EDT FRI AUG 29 2014

ALL OF THE HIGH RESOLUTION MODELS (HRRR 09Z AND RAP 10Z) SHOW THE
AREA OF SCATTERED SHOWERS OVER LAKE MICHIGAN BECOMING A SOLID AREA
OF SHOWERS WITH EMBEDDED HEAVER RAIN SHOWERS (INSTABILITY QUESTIONABLE
FOR THUNDERSTORMS). THE AREA OF SHOWERS WILL IMPACT THE TAF SITES
FROM AROUND 15Z TILL AROUND 21Z BEFORE DISSIPATING.

I ALSO ADDED MVFR CIGS AFTER 07Z IN THE WESTERN TAF SITES TO
REFLECT INCREASED LOW LEVEL MOISTURE ADVECTION AS THE UPPER
SHORTWAVE GETS CLOSER TO LOWER MICHIGAN. SO EXPECT MVFR VSBY/CIGS
IN SHOWERS AT MOST OF THE TAR SITES FROM 15Z TILL 19Z....THEN
BECOMING VFR.


&&

.MARINE...
ISSUED AT 1130 AM EDT FRI AUG 29 2014

KEPT THE HAZARDS GOING. SOUTHEAST WINDS BECOME MORE SOUTHERLY AND
INCREASE. THIS SHOULD RESULT IN WAVES POTENTIALLY CLIMBING ABOVE 4 FT.

&&

.HYDROLOGY...
ISSUED AT 328 PM EDT THU AUG 28 2014

THE HEAVY RAIN THREAT APPEARS TO BE LIMITED TO THE MUSKEGON AND
PERE MARQUETTE BASINS AS AN INCH OF QPF CAN BE EXPECTED THERE BY
SUNDAY MORNING...WHICH WOULD RESULT IN RISES BY EARLY NEXT WEEK.
MUCH LESS RAIN IS EXPECTED IN THE GRAND AND KALAMAZOO RIVER
BASINS.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...BEACH HAZARDS STATEMENT FROM 8 PM EDT THIS EVENING THROUGH
     SATURDAY EVENING FOR MIZ037-043-050-056-064-071.

LM...SMALL CRAFT ADVISORY UNTIL 11 PM EDT SATURDAY FOR LMZ848-849.

     SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 11 PM EDT
     SATURDAY FOR LMZ844>847.

&&

$$

UPDATE...MJS
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...NJJ
AVIATION...WDM
HYDROLOGY...OSTUNO
MARINE...MJS






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