Severe Thunderstorm Warning 50, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1210 PM EDT SUN JUL 18 2010

LATEST UPDATE...SHORT TERM...

.SYNOPSIS...(359 AM EDT SUN JUL 18 2010)
THERE WILL BE THE POTENTIAL FOR SEVERE THUNDERSTORMS TODAY AS LOW
PRESSURE AND A COLD FRONT CROSSES THE REGION.  MOST OF THE STORMS
WILL BE EAST OF THE AREA BY THIS EVENING.  THE NEXT CHANCE OF RAIN
WILL COMING MONDAY NIGHT AS THE COLD FRONT STALLS TO OUR SOUTH AND A
WAVE OF LOW PRESSURE TRACKS ALONG IT.  SEVERE POTENTIAL WITH THIS
SYSTEM APPEARS TO BE LOW...HOWEVER FAR SOUTHERN LOWER MICHIGAN COULD
SEE A SOAKING RAIN THAT COULD LAST INTO TUESDAY.

&&

.SHORT TERM...(1210 PM EDT SUN JUL 18 2010)
(TODAY THROUGH TUESDAY)
OBVIOUSLY WE ARE MONITORING THE THREAT FOR SEVERE WEATHER FOR THIS
AFTERNOON AND EVENING ACROSS THE AREA.

RADAR CURRENTLY INDICATES A LINE OF STRONGER STORMS TRYING TO
ORGANIZE A BIT ACROSS CENTRAL LAKE MICHIGAN. THIS LINE OF STORMS IS
VERY LIKELY AT THE LEADING EDGE OF THE 30-35 KNOT LLJ THAT IS
TRANSLATING TOWARD THE AREA. SPC MESO-ANALYSIS PAGE SHOWS THAT THIS
LINE HAS VERY LITTLE IF ANY LOW LEVEL CAPE ASSOCIATED WITH IT...THAT
IT IS AN ELEVATED BATCH OF STORMS. WE EXPECT THAT THIS LINE WILL
AFFECT AREAS NORTH OF I-96 OVER THE NEXT FEW HOURS...AND IS EXPECTED
TO PRODUCE SOME SMALL HAIL AND SOME POSSIBLE WIND GUSTS TO 40-50 MPH
IF SOME OF THE DOWNDRAFTS CAN PUNCH DOWN THROUGH THE INVERSION UP
THERE.

THEN THE MAIN FOCUS IS DOWN WHERE THE SFC/ML BASED CAPE IS EXPECTED
TO HAVE THE BEST CHANCE TO BUILD THIS AFTERNOON IF SOME CLEARING CAN
TAKE PLACE. SFC LOW CENTER ACROSS SRN WI AND NRN IL WILL BE MOVING
TO THE EAST THIS AFTERNOON. QUITE A BIT OF CONVECTIVE DEBRIS ACROSS
THE AREA FROM THE MCS THAT OCCURRED ACROSS MN AND WI LAST NIGHT.
THIS DEBRIS IS IN THE PROCESS OF DISSIPATING AND CLEARING IS ALSO
WORKING IN FROM THE WEST.

WE BELIEVE THAT TEMPS WILL QUICKLY RISE AS THE CLEARING BUILDS IN
AND 30 KNOT LLJ HELPS TO ADVECT IN THE WARMER AND HIGHER DEW POINTS
AHEAD OF THE SFC LOW. MODELS ARE PROGGING THAT ML CAPES ARE EXPECTED
TO BUILD TO OVER 2000 J/KG ALONG AND SOUTH OF I-96. THE BEST
INSTABILITY WILL BE SOUTH OF I-94 WHERE VERY LITTLE CLOUD COVER WAS
EXPERIENCED.

THERE ARE INDICATIONS ON THE VIS SATELLITE IMAGERY THAT THE LINE OF
ELEVATED STORMS COULD EXPAND SOUTHWEST INTO SRN WI AND THEN MOVE IN
LATER THIS AFTERNOON. WE WILL HAVE TO CONTINUE TO MONITOR HOW MUCH
WE CAN DESTABILIZE. IF WE CAN DESTABILIZE FAIRLY QUICKLY...WE
BELIEVE THAT SEVERE WILL BE LIKELY WITH THE MAIN THREAT STILL
EXPECTED TO BE DAMAGING WINDS. A DECENT AMOUNT OF CAPE IS EXPECTED
IN THE -10 TO -30C LAYER...SO LARGE HAIL WILL BE POSSIBLE. THE
PROXIMITY TO THE SFC LOW/WARM FRONT ALONG WITH SOME FAIR LOW LEVEL
SHEAR KEEPS A TORNADO POSSIBLE....HOWEVER SOMEWHAT HIGH LCL/S
/1500M/ MAY NEGATE THAT THREAT A BIT.

SEVERE STORMS SHOULD BE TO OUR EAST BY EARLY EVENING.  HOWEVER HAVE
KEPT LOW CHANCE POPS GOING FOR THE EARLY EVENING AS A FEW RANDOM
SHOWERS OR STORMS WILL BE POSSIBLE AS THE COLD FRONT EXITS.

THE FRONT HANGS UP TO OUR SOUTH AND THE MODELS INDICATE A WAVE OF
LOW PRESSURE MAY TRACK ALONG IT MONDAY NIGHT INTO TUESDAY.  SEVERE
POTENTIAL SHOULD BE MINIMAL IN THIS TIME FRAME...HOWEVER THERE WILL
BE THE POTENTIAL FOR HEAVY RAIN ACROSS THE SOUTHERN CWA.  THERE
STILL IS A FAIR AMOUNT OF DIFFERENCES IN THE MODELS ON HOW THIS
UNFOLDS.  SO HAVE MAINTAINED CHANCE POPS...HIGHEST IN THE SOUTH.

&&

.LONG TERM...(1007 AM EDT SUN JUL 18 2010)
(WEDNESDAY THROUGH SUNDAY)
LATEST MODEL RUNS FOR THE LONG TERM INDICATE LITTLE TO NO CHANGE IS
NEEDED FOR THE FCST. ZONAL FLOW IS EXPECTED TO HOLD IN ACROSS THE
NRN HALF OF THE COUNTRY. THIS ZONAL FLOW WILL CONTINUE TO INTERACT
WITH THE VERY WARM AND VERY MOIST CONDITIONS JUST SOUTH OF THE JET.
IT STILL APPEARS THAT THERE WILL BE NUMEROUS CHCS OF CONVECTION THIS
WEEK WITH THE NEARLY STATIONARY FRONTAL BOUNDARY EXPECTED TO SET UP
SHOP JUST SOUTH OF THE AREA. AS WAVES OF LOW PRESSURE MOVE ALONG
IT...THIS FRONT WILL TRY TO BULGE TO THE NORTH AND WILL SUPPORT THE
THREAT FOR CONVECTION.

WE DID TRY TO PIN DOWN A COUPLE OF OPPORTUNITIES WHERE THE THREAT
MAY BE A LITTLE LESS BEHIND A COUPLE OF STRONGER WAVES INDICATED BY
MULTIPLE MODELS. IT APPEARS THAT WED MAY HAVE A BETTER CHC OF BEING
A LITTLE DRIER THAN THE REST OF THE WORK WEEK AS A STRONGER WAVE
PUSHES THE FRONT A LITTLE FARTHER SOUTH. NEXT SUNDAY ALSO HAS THE
POTENTIAL OF BEING DRY AS ANOTHER STRONGER WAVE MOVES THROUGH ON SAT
AND PUSHES THE FRONT SOUTH IN ITS WAKE.

&&

.AVIATION...(717 AM EDT SUN JUL 18 2010)
VFR CONDITIONS THROUGH THIS MORNING EXCEPT FOR SOME 3 TO 5 MILE
VISIBILITIES IN HAZE OR LIGHT FOG AT AZO. THUNDERSTORMS SHOULD BE
MOVING INTO WESTERN LOWER MICHIGAN BY 18Z THEN SPREADING EAST AND
PERSISTING THROUGH THE AFTERNOON ALONG A SLOW MOVING COLD FRONT.
SOME AREAS OF MVFR AND ISOLATED IFR IN THE HEAVIER THUNDERSTORMS
THIS AFTERNOON. COVERAGE AND DURATION OF THE THUNDER IS HARD TO PIN
DOWN SO WILL KEEP THE VCTS IN THE FORECAST THOUGH THE AFTERNOON.

WINDS WILL BECOME GUSTY SUNDAY AFTERNOON. EXPECTING GUSTS TO AROUND
20 KNOTS. STRONG THUNDERSTORM WIND GUSTS ARE POSSIBLE WITH THE
THUNDERSTORMS... BUT TOO EARLY TO SAY IF ANY TAF SITES WILL BE
IMPACTED BY THIS THREAT.

THE SHOWERS WILL END AND WINDS WILL DROP OFF TO UNDER 10 KNOTS
TONIGHT. LIGHT FOG AND HAZE WILL AGAIN BECOME POSSIBLE TONIGHT AS
LOW LEVEL MOISTURE REMAINS BEHIND THE FRONT.

&&

.MARINE...(359 AM EDT SUN JUL 18 2010)
THE LAKE WILL BECOME ROUGH THROUGH THE DAY AS 15 TO 20 KNOTS WINDS
ACCOMPANY THE APPROACHING WEATHER SYSTEM.  AT THIS POINT I AM NOT
THINKING WE WILL REACH SCA CRITERIA...HOWEVER CONDITIONS WILL BECOME
MORE SUITED FOR THE MORE SEASONED BOATER BY AFTERNOON.  WINDS WILL
PIVOT FROM SOUTH THIS MORNING TO WEST BY EVENING.

CONDITIONS ARE EXPECTED TO IMPROVE AFTER SUNSET THIS EVENING AS THE
STORM SYSTEM EXITS AND WINDS DIMINISH.  RATHER LIGHT WINDS AND LOW
WAVES ARE EXPECTED AFTER MIDNIGHT AND THIS WILL CONTINUE THROUGH
MONDAY NIGHT.

&&

.HYDROLOGY...(359 AM EDT SUN JUL 18 2010)
TODAY/S ROUND OF STORMS SHOULD BE FAIRLY FAST MOVERS OF AROUND 40
MPH WHICH SHOULD LIMIT ANY ONE AREA FROM RECEIVING HIGH RAINFALL
TOTALS.  MOST AREAS SHOULD SEE AROUND A HALF INCH OF RAIN...WITH
LOCALIZED AREAS PERHAPS SEEING AS MUCH AS AN INCH OF RAIN.  OVERALL
THE HYDRO THREAT APPEARS LOW.

ITS UNCLEAR HOW THE MONDAY NIGHT AND TUESDAY EVENT WILL UNFOLD.  BUT
THERE IS POTENTIAL FOR HEAVY RAINS ACROSS FAR SOUTHERN LOWER MI.  A
STATIONARY FRONT WILL LIE NEAR THE MI/IN BORDER AND WAVES OF HEAVY
RAIN WILL TRACK ALONG IT.  WHERE EXACTLY THIS SETS UP THOUGH IS THE
QUESTION.  PWAT VALUES CLIMB TO NEAR TWO INCHES LEADING TO THE
CONCERN.

&&

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

&&

SYNOPSIS:     JK
SHORT TERM:   JK/NJJ
LONG TERM:    NJJ
AVIATION:     OSTUNO
MARINE:       JK
HYDROLOGY:    JK

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
558 AM EDT SUN JUL 18 2010

LMZ844>849-MIZ037>040-043>046-050>052-056>059-064>067-071>074-191000-
ST JOSEPH TO SOUTH HAVEN MI-SOUTH HAVEN TO HOLLAND MI-
HOLLAND TO GRAND HAVEN MI-GRAND HAVEN TO WHITEHALL MI-
WHITEHALL TO PENTWATER MI-PENTWATER TO MANISTEE MI-MASON-LAKE-
OSCEOLA-CLARE-OCEANA-NEWAYGO-MECOSTA-ISABELLA-MUSKEGON-MONTCALM-
GRATIOT-OTTAWA-KENT-IONIA-CLINTON-ALLEGAN-BARRY-EATON-INGHAM-
VAN BUREN-KALAMAZOO-CALHOUN-JACKSON-
558 AM EDT SUN JUL 18 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST LOWER
MICHIGAN.

.DAY ONE...TODAY AND TONIGHT

THERE IS A SLIGHT RISK OF SEVERE WEATHER TODAY. THE PRIMARY THREAT
IS DAMAGING WINDS BUT LARGE HAIL AND AN ISOLATED TORNADO ARE
POSSIBLE. LOCALIZED FLOODING FROM HEAVY THUNDERSTORM RAINS ARE
POSSIBLE AS WELL. THIS AFTERNOON AND EVENING ARE THE MOST LIKELY
TIME FOR SEVERE WEATHER AND THE MOST LIKELY PLACE WILL BE SOUTH OF
INTERSTATE 96.

STORM MOTION WILL BE FROM WEST TO EAST AT ABOUT 40 MPH.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THUNDERSTORMS WITH HEAVY RAIN ARE POSSIBLE ON THURSDAY AND
THURSDAY NIGHT. STRONG THUNDERSTORMS ARE POSSIBLE ON SATURDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED THIS AFTERNOON OR EVENING.

OSTUNO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
343 PM EDT SUN JUL 18 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0330 PM     HEAVY RAIN       ALLENDALE               42.97N 85.95W
07/18/2010  M1.25 INCH       OTTAWA             MI   TRAINED SPOTTER

            RAINFALL TOTAL FROM THE PAST HOUR.

&&

MKALEMBK

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