Severe Thunderstorm Warning 20, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1048 AM EDT SAT JUN 2 2007

.UPDATED...
I LOWERED THE POP THIS AFTERNOON OVER ALL OF THE CWA TO CHC SINCE I
DO NOT SEE ANY REAL MECHANISM FOR THUNDERSTORM GENERATION OTHER THEN
THE LAKE BREEZE BOUNDARY INTRACTION. TRUE...THERE ARE DECENT CAPES
AND THE SURFACED BASED LI VALUES WILL BE NEGATIVE OVER JUST ABOUT
ALL OF THE CWA. EVEN SO...THE DNVA BEHIND THE EARLY MORNING
CONVECTION SHOULD SUPPRESS CONVECTION INTO MID AFTERNOON. MEANWHILE
SHORTWAVE ENERGY NEAR CHI AT 15Z MAY AID LAKE BREEZE CONVECTION NEAR
US-131 BY MID AFTERNOON.  DUE TO THE LAKE BREEZE INTERACTION WITH
THE SHORTWAVE THIS AFTERNOON I DO HAVE  LIKELY POP NEAR US-131 BY
MID AFTERNOON. THAT CONVECTION WILL LIKELY MOVE INLAND THIS EVENING
BEFORE WEAKENING WITH THE LOSS OF SOLAR ENERGY. THUS I KEEP THE
NUMEROUS WORDING EARLY EVENING HOURS FOR THUNDERSTORMS.

AS FOR SEVERE THUNDERSTORMS...CAPES ARE IMPRESSIVE BUT THE WIND
FIELD THROUGH MID LEVELS IN NOT CONDUCIVE TO SEVERE WEATHER.
FREEZING LEVELS ON TAMDAR AT 12-14Z ARE SLOPE UP FROM 12000 FT NEAR
JXN TO 1300 FT NEAR THE LAKE MICHIGAN SHORE. THE HIGH FREEZING
LEVELS AT FIRST GLANCE WOULD NOT SUPPORT HAIL. HOWEVER...MODEL
FORECAST SOUNDING SUGGEST PULSE LARGE HAIL IS NOT OUT OF THE
QUESTION SINCE BASED ON THE RUC MODEL SOUNDINGS THERE IS A FAIR
AMOUNT OF CAPE ABOVE THE -10C LEVEL. THE NAM IS MORE CONSERVATIVE.
THE BIG QUESTION IS WILL THE LOW LEVEL DEW POINTS LOWER THIS
AFTERNOON AS DEEPER MIXING OCCURS. IF SO ALL BETS OF OFF FOR ANY
SEVERE WEATHER OVER THE GRR CWA TODAY OR TONIGHT.

THE REST OF THE ZONE FORECAST SEEMS TO BE ON TRACK... SO THAT
REMAINS AS IS.

.PREVIOUS DISCUSSION...
WV IMAGERY THIS MORNING SHOWS THE UPPER LOW CONTINUING TO SPIN OVER
THE PLAINS STATES EARLY THIS MORNING. THE LOW IS CURRENTLY CENTERED
OVER THE ERN BORDER OF SOUTH DAKOTA AND NEBRASKA. AHEAD OF THE UPPER
LOW IS A NICE BELT OF DEEP SW FLOW WITH EMBEDDED SHORT WAVES RIDING
TO THE NE. OUR MAIN CONCERN IN THE SHORT TERM PORTION OF THE
FORECAST IS PCPN CHCS AND SEVERE POTENTIAL FROM TODAY RIGHT ON
THROUGH MON AS THE UPPER LOW MOVES TOWARD THE AREA THROUGH SUN AND
IS THEN RIGHT OVERHEAD LATE SUN INTO MON.

REMNANTS OF THE LINE OF CONVECTION THAT AFFECTED AREAS TO OUR WEST
OVER IA/IL/WI DURING THE DAY ON FRI...ARE CURRENTLY MOVING THROUGH
THE CWFA THIS MORNING. THE CONVECTION HAS DIMINISHED SIGNIFICANTLY...
HOWEVER DUE TO MESOSCALE EFFECTS AND AN INSTABILITY AXIS ALOFT...
SOME OF THE CONVECTION HAS MAINTAINED ITSELF AS IT MOVES NE. THIS
BATCH OF CONVECTION WILL MOVE EAST OF THE CWFA BY 12Z...LEAVING THE
AREA IN A RELATIVE VOID OF MOST PCPN TEMPORARILY. CLOUDS SHOULD BE
SOMEWHAT LIMITED THIS MORNING WITH DEBRIS FROM UPSTREAM CONVECTION
RESPONSIBLE MOST CLOUD COVER INITIALLY. BREAKS IN THE CLOUDS MAY
ALLOW FOR SOME FOG TO DEVELOP WITH THE HIGHER DEW POINTS IN
PLACE...ESPECIALLY AT LOCATIONS THAT HAVE SEEN SOME RAIN THIS
MORNING.

AFTER ANY FOG DISSIPATES...SOME SUN WILL HELP WARM TEMPS BACK INTO
THE 80S ACROSS MOST OF THE CWFA. SUN WILL BE SOMEWHAT LIMITED AFTER
THE MORNING AS ADDITIONAL DEBRIS CLOUD COVER FROM CONVECTION SW OF
THE AREA WILL STREAM INTO THE AREA. ADDITIONAL WAVES THAT CAN BE
SEEN FROM LOWER MICHIGAN BACK DOWN INTO THE MO AREA WILL TEND TO
MOVE TOWARD THE AREA THIS MORNING. HOW MUCH WE DESTABILIZE OBVIOUSLY
HAS TO DO WITH HOW MUCH SUN WE CAN GET...AND THIS DEPENDS ON THE
TIMING OVER UPSTREAM SHORT WAVES. ASSUMING WE CAN GET A FAIR AMOUNT
OF SUN THIS MORNING...MODIFIED FCST SOUNDINGS FOR THIS AFTERNOON
WITH TEMPS IN THE MID 80S AND DEW POINTS IN THE LOW TO MID 60S WOULD
SUPPORT SB CAPES AROUND 2000 J/KG AND SB LI/S AROUND -5. WITH SHORT
WAVES EXPECTED TO BEGIN MOVING ACROSS THE AREA LATER TODAY AS THE
UPPER LOW APPROACHES THE AREA...THIS SUPPORTS A BETTER THREAT OF
CONVECTION THAN WHAT HAS BEEN PRESENT THE PAST FEW DAYS. DEEP LAYER
SHEAR ON A SYNOPTIC SCALE IS NOT VERY IMPRESSIVE FOR MOST OF THE DAY
AS MID LEVEL WINDS ARE ONLY 25 TO 30 KTS GIVING SHEAR VALUES OF
20 KTS OR SO. DEEP LAYER SHEAR DOES INCREASE LATE FROM THE NW AS THE
MID LEVEL JET MOVES IN. ALSO IF ANY CONVECTIVELY INDUCED VORT MOVES
IN...THERE WOULD BE SOME GOOD LOCALIZED SHEAR PRESENT. POTENTIAL
INSTABILITY COULD MAKE UP FOR THIS AND PRODUCE A WIND AND HAIL
THREAT...ESPECIALLY LATER AS THE SHEAR INCREASES. WE HAVE INCREASED
THE POPS IN THE AFTERNOON AND EVENING HOURS TO THE LIKELY/NUMEROUS
CATEGORY.

WITH THE LOSS OF DIURNAL INSTABILITY...THE THREAT OF WIDESPREAD
STORMS AND SEVERE WEATHER WILL DIMINISH BY THE OVERNIGHT HOURS. THE
THREAT OF SHOWERS AND STORMS WILL REMAIN THOUGH WITH THE AREA
REMAINING PRONE TO SHORT WAVES RIDING NE ALONG THE MID LEVEL FLOW.
WE HAVE TRENDED POPS LOWER FOR THE SECOND HALF OF THE NIGHT TONIGHT.

THE UPPER LOW WILL THEN FINALLY MOVE NEARBY DURING THE COURSE OF THE
DAY ON SUN ALONG WITH THE ASSOCIATED SFC FRONT. A FEW PEEKS OF SUN
WILL BE POSSIBLE SUN MORNING...BUT WITH THE COLD POOL ALOFT MOVING
OVERHEAD AND PLENTY OF LOW LEVEL MOISTURE...BREAKS IN THE CLOUDS
WILL FILL IN AND SHOWERS AND STORMS WILL BEGIN DEVELOPING.
INSTABILITY WILL NOT BE AS FAVORABLE AS SFC TEMPS WILL ONLY RISE
INTO THE 70S. HOWEVER DEW POINTS STILL IN THE 50S AND LOWER 60S WILL
ACT WITH COLD POOL ALOFT TO PROVIDE AROUND 1000 J/KG OF SB CAPE AND
LI/S AROUND -3. DEEP LAYER SHEAR WILL BE MUCH BETTER WITH THE MID
LEVEL JET MOVING OVERHEAD DURING THE DAY. SEVERE HAIL WILL BE
POSSIBLE DUE TO FREEZING LEVELS OF ONLY AROUND 9K TO 10K FEET...AND
SOME DOWNBURSTS WILL BE POSSIBLE WITH THE BETTER ORGANIZED STORMS.

THE POTENTIAL OF PCPN WILL THEN DIMINISH SOMEWHAT ON MON AS THE
UPPER LOW FINALLY OPENS UP INTO A WAVE AND THE BETTER MOISTURE MOVES
EAST OF THE AREA. A FEW INSTABILITY SHOWERS WILL BE POSSIBLE MON
AFTERNOON. THUNDER WILL REMAIN POSSIBLE AS THE COLD POOL ALOFT
REMAINS OVERHEAD AND LI/S REMAIN SLIGHTLY NEGATIVE. TEMPS ON MON
WILL LIKELY ONLY WARM INTO THE MID 60S TO LOWER 70S WITH THE THERMAL
TROUGH MOVING IN.

.LONG TERM...
MON THROUGH FRI...MID AND UPPER LEVEL CYCLONIC FLOW CONTINUES
THROUGH TUE WITH BUILDING HEIGHTS LATE ON TUE INTO THU AS WRN RIDGE
BUILD EWD. ON TUE LATEST GFS/ECMWF SHOWING WEAK S/W ENERGY MOVING
THROUGH TROF...SO THINKING IS FOR SCT SHOWER THREAT ESPECIALLY WITH
AFTN DIURNAL HEAT MAX. TEMPS WILL START OUT BELOW NORMAL AND TREND
UPWARDS TOWARDS THU.

BY THU EARLY AM WARM FRONT PUSHES INTO AREA WITH S/W ENERGY DIGGING
ESE AS IT TOPS RIDGE AXIS ALOFT.  THIS WOULD BE A GOOD SCENARIO FOR
EARLY MORNING MCS EVENT. BUMPED POPS A FEW PERCENT TO START A TREND
TOWARDS POTENTIAL EVENT.

.GRR WATCHES/WARNINGS/ADVISORIES...NONE

&&

NJJ COBB WDM

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1055 AM EDT SAT JUN 2 2007

LMZ844>849-MIZ037>040-043>046-050>052-056>059-064>067-071>074-030915-
ST JOSEPH TO SOUTH HAVEN-SOUTH HAVEN TO HOLLAND-
HOLLAND TO GRAND HAVEN-GRAND HAVEN TO WHITEHALL-
WHITEHALL TO PENTWATER-PENTWATER TO MANISTEE-MASON-LAKE-OSCEOLA-
CLARE-OCEANA-NEWAYGO-MECOSTA-ISABELLA-MUSKEGON-MONTCALM-GRATIOT-
OTTAWA-KENT-IONIA-CLINTON-ALLEGAN-BARRY-EATON-INGHAM-VAN BUREN-
KALAMAZOO-CALHOUN-JACKSON-
1055 AM EDT SAT JUN 2 2007

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

.DAY ONE...THIS AFTERNOON AND TONIGHT
SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP NEAR AND WEST OF
ROUTE 131 BY MID AFTERNOON. THOSE STORMS SHOULD THEN SPREAD INLAND
TOWARD LANSING AND MOUNT PLEASANT BY EARLY THIS EVENING. A FEW OF
THOSE THUNDERSTORMS MAY BECOME SEVERE FROM MID AFTERNOON INTO
EARLY THIS EVENING. THOSE ISOLATED STORMS WOULD PRODUCE DAMAGING
WIND GUSTS AND LARGE HAIL. ALL STORMS WILL PRODUCE BRIEF HEAVY
DOWNPOURS AND FREQUENT CLOUD TO GROUND LIGHTNING.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY
SHOWERS AND THUNDERSTORM ARE EXPECTED AGAIN ON SUNDAY...BUT ARE
NOT EXPECTED TO BE SEVERE AT THIS TIME. SCATTERED SHOWERS AND
THUNDERSTORMS ARE ALSO EXPECTED ON MON AND TUE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED SATURDAY AFTERNOON AND EVENING.

COBB WDM