Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 221755
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
155 PM EDT TUE JUL 22 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 325 AM EDT TUE JUL 22 2014

IT WILL BE VERY WARM AND QUITE HUMID TODAY. A COLD FRONT WILL
BRING SCATTERED SHOWERS AND THUNDERSTORMS LATE THIS AFTERNOON
AND TONIGHT. A SIGNIFICANTLY COOLER AND DRIER AIR MASS WILL
MOVE IN BEHIND THAT FRONT FOR MID TO LATE WEEK.

&&

.UPDATE...
ISSUED AT 1115 AM EDT TUE JUL 22 2014

NO MAJOR CHANGES TO THE GOING FCST FOR TODAY AND TONIGHT. OUR MAIN
FOCUS IS ON CONVECTIVE POTENTIAL AND SEVERE THREAT FOR LATE THIS
AFTERNOON INTO THE EARLY OVERNIGHT HOURS.

QUIET WEATHER ACROSS THE ENTIRE CWFA THIS MORNING...AND THIS IS
EXPECTED TO CONTINUE INTO MID AFTERNOON. BAND OF CLOUDS LEFT OVER
FROM CONVECTION OUT WEST LAST NIGHT IS MOVING INTO THE NW CORNER
OF THE CWFA. THIS IS MAINLY MID LEVEL CLOUD COVER PER THE RADAR
AND SFC OBS. NOT MUCH INSTABILITY HAS DEVELOPED YET OVERHEAD.

WE CONTINUE TO EXPECT THAT THE NW CORNER OF THE CWFA WILL SEE A
DECENT CHC OF CONVECTION AFTER AROUND 21Z OR SO...AND THEN SPREAD
SOUTH AND EAST THROUGH THE AREA THEREAFTER. THE MAIN INSTABILITY
AXIS IS IMMEDIATELY AHEAD OF THE SFC FRONT LOCATED FROM THE WRN
U.P. TO NE IA AS OF 15Z THIS MORNING. THIS WILL SHIFT INTO OUR
AREA AS THE LLJ/MAIN MOISTURE TRANSPORT SLIDES IN LATER THIS
AFTERNOON AND THIS EVENING. WE WILL SEE SOME DIURNAL INSTABILITY
DEVELOP OVERHEAD BEFORE THAT TIME...HOWEVER IT WILL REMAIN
GREATLY CAPPED THROUGH MID AFTERNOON.

MODEL CONSENSUS SHOWS THAT THE WRN AREAS OF THE CWFA SHOULD SEE
1500-2000 J/KG OF ML AND MU CAPE NOSE INTO THE AREA BY 00Z AND
SHIFT SOUTH OF THE AREA BY 06Z VIA AN ELEVATED MIXED LAYER. THE BETTER
INSTABILITY IS DEFINITELY WEST OF THE AREA...AND THE BETTER
DYNAMICS REMAIN NORTH OF THE AREA. WE DO SEE A SHORT WAVE ACROSS
SD THAT APPROACHES THIS EVENING AND WILL LIKELY HELP TO SUPPORT
CONVECTION OVER THE AREA.

WE BELIEVE THAT THE SEVERE THREAT REMAINS POSSIBLE ACROSS THE
AREA...ESPECIALLY ACROSS THE WRN HALF OF THE CWFA SIMILAR TO THE
THINKING OF SPC PER THE SWODY1 OUTLOOK. DEEP LAYER SHEAR HAS
TRENDED MORE FAVORABLE DURING THE EXPECTED TIME OF CONVECTION
PEAKING AT AROUND 30-35 KNOTS...HIGHEST WEST WHERE THE BEST
INSTABILITY WILL BE OVER THE AREA. LOW LEVEL INVERSION HEIGHTS ARE NOT
EXPECTED TO BE ALL THAT HIGH...SO A WIND THREAT WILL BE POSSIBLE
WITH 40 KNOTS IN THE MID LEVELS AND A 30+ KNOT LLJ PRESENT DURING
THE TIME OF CONVECTION. LARGE HAIL WILL BE POSSIBLE WITH FAIRLY
THICK CAPE IN THE -10C TO -30C LAYER. WE ALSO AGREE WITH SPC ABOUT
THE POSSIBILITY OF A TORNADO WITH 0-1KM SHEAR OF 20-25 KNOTS AND
0-1KM HELICITY VALUES 150+ M2/S2.

&&

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 325 AM EDT TUE JUL 22 2014

OUR PRIMARY SHORT TERM FCST CHALLENGE IS TO DETERMINE
CONVECTIVE/SEVERE WX POTENTIAL THIS AFTERNOON THROUGH TONIGHT.

IT WILL BE HOT AND HUMID TODAY WITH SOME SUN AND STRONG SSW FLOW
WAA HELPING TO BOOST MAX TEMPS INTO THE 85 TO 90 DEGREE RANGE THIS
AFTERNOON WITH DEW POINTS REACHING THE MID TO UPPER 60S. WE EXPECT
SEVERE CONVECTION OVER MN AND EXTREME NW WI EARLY THIS MORNING TO
TRACK ACROSS FAR NORTHERN WI AND THE U.P. THIS MORNING. HOWEVER THAT
ACTIVITY WILL STAY WELL TO THE NW OF OUR FCST AREA.

HOWEVER WE EXPECT A FEW SHOWERS AND TSTORMS TO DEVELOP OVER OUR
FAR NW FCST AREA BY LATE AFTN AS THE COLD FRONT MOVES INTO THAT
AREA. THE COLD FRONT WILL THEN MOVE QUICKLY ACROSS THE REST OF OUR
FCST AREA DURING THE MID TO LATE EVENING HOURS BRINGING SCATTERED
SHOWERS AND STORMS.

ISOLATED STRONG TO MARGINALLY SEVERE STORMS ARE POSSIBLE MAINLY
EARLY TO MID EVENING COINCIDENT WITH PEAK OR NEAR PEAK INSTABILITY
WITH POTENTIAL FOR SB/ML CAPE VALUES TO BRIEFLY REACH UP TO AS
HIGH AS 2000 J/KG FOR A SMALL PORTION OF OUR SOUTHWESTERN FCST
AREA. SHORT RANGE GUIDANCE HAS ALSO TRENDED FASTER WITH FRONTAL
TIMING THE PAST 24 HRS WHICH IS ALSO POTENTIALLY MORE FAVORABLE
FOR A FEW STRONGER STORMS. THE MOST LIKELY TIME FRAME FOR
CONVECTION IS FROM AROUND 23Z THIS EVENING THROUGH 05Z WEDNESDAY
AS SUGGESTED BY 00Z 4KM NSSL WRF AND LATEST HRRR SIM Z GUIDANCE.

HOWEVER IT IS NOTED THAT 0-6 KM BULK SHEAR IS WEAK AND MAINLY ONLY
AROUND 20-25 KTS OFF LATEST SREF GUIDANCE... ALTHOUGH VERY BRIEFLY
HIGHER VALUES ARE NOTED OVER OUR FAR NW FCST AREA. UPPER LEVEL
SUPPORT FOR MORE ORGANIZED CONVECTIVE DEVELOPMENT PASSES BY WELL
NORTH OF OUR FCST AREA. INSTABILITY IS FCST TO DIMINISH RATHER
QUICKLY FROM MID TO LATE EVENING. SO THE OVERALL THREAT FOR SEVERE
WX LATE THIS AFTERNOON THROUGH THE LATE EVENING HOURS IS RATHER
LOW/MARGINAL.

IT WILL BE BREEZY AND MUCH COOLER/DRIER WEDNESDAY WITH MAX TEMPS
ONLY REACHING THE 70S. SKIES WILL CLEAR WEDNESDAY NIGHT AS HIGH
PRESSURE BUILDS IN FROM THE NW. HIGH PRESSURE WILL PRODUCE MOSTLY
SUNNY SKIES THURSDAY WITH MAX TEMPS IN THE MID TO UPPER 70S.

.LONG TERM...(THURSDAY NIGHT THROUGH MONDAY)
ISSUED AT 325 AM EDT TUE JUL 22 2014

THE MAIN CHALLENGE WITH THE LONG TERM FORECAST IS THE SHOWER AND
TSTM POTENTIAL OVER THE COMING WEEKEND. GUIDANCE CONTINUES TO
SUGGEST THAT THE PRIMARY CORRIDOR OF HEAVIER MCS ACTIVITY WILL BE
SOUTHWEST/SOUTH OF MICHIGAN FRIDAY THROUGH SUNDAY... FROM ERN IOWA
TO INDIANA.  HOWEVER WE MAY STILL BE IMPACTED BY THE NRN PERIPHERY
OF THESE CONVECTIVE COMPLEXES WITH PERIODS OF SHOWERS AND SCATTERED
TSTMS...AIDED BY WEAK SHORTWAVES IN THE FAST W/NW FLOW ALOFT.

A RATHER POTENT LOOKING SHORTWAVE IS PROGGED TO DROP DOWN FROM THE
NORTHWEST SUNDAY NIGHT AND MONDAY... AND THE GFS/ECMWF ARE IN GOOD
AGREEMENT ON THIS FEATURE. BEST POPS WILL EXIST DURING THIS
PERIOD... FOLLOWED BY HIGH CONFIDENCE BELOW NORMAL TEMPERATURES
BEHIND THIS SYSTEM FOR MOST OF NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 154 PM EDT TUE JUL 22 2014

VFR CONDITIONS IN PLACE AREA WIDE AT 18Z...WHICH WILL CONTINUE
THROUGH THE REMAINDER OF THE AFTERNOON. THE FOCUS IS ON THE
EXTENT OF THUNDERSTORM DEVELOPMENT THIS EVENING. ESSENTIALLY
EXPECTING SCATTERED THUNDERSTORMS TO DEVELOP AND SINK SOUTH THROUGH
THE TAF SITES BETWEEN 22Z AND 06Z. BEST CHANCE FOR STORMS WILL BE
AT KMKG...KGRR AND KAZO...WITH SLIGHTLY LESSER CHANCES INLAND. AT
THIS POINT NOT CONFIDENT ENOUGH TO GO PREVAILING STORMS AT ANY
GIVEN LOCATION SO USED VCTS WORDING THROUGH THE EVENING TIME
FRAME. SOME STORMS MAY CONTAIN STRONG GUSTY WINDS IN EXCESS OF 35
KNOTS.

OVERNIGHT...THE THREAT EXISTS FOR A MVFR CLOUD DECK TO SETTLE INTO
THE TAF SITES ON NORTHERLY WINDS BEHIND A COLD FRONT. AT THIS
POINT USED SCATTERED WORDING AT 1500FT TO CONVEY THE CHANCE OF
THIS DECK DEVELOPING. A CHANCE AT SOME MVFR FOG FOR A TIME
OVERNIGHT AS WELL WITH HIGH DEW POINT AIR IN PLACE. SKIES SHOULD
GRADUALLY CLEAR/SCATTER OUT ON WEDNESDAY AS DRIER AIR WORKS IN
FROM THE NORTH. SOME MODELS INDICATE A MVFR DECK HOLDING ON ACROSS
MUCH OF THE AREA THOUGH THROUGH WEDNESDAY MORNING.

&&

.MARINE...
ISSUED AT 1145 AM EDT TUE JUL 22 2014

BEACH HAZARDS EVENT UNDERWAY AND GOING DOWN AS EXPECTED THUS FAR.
THE LUDINGTON BUOY IS CURRENTLY SHOWING 4.6 FOOT WAVES AND THE
WEBCAM THERE IS SHOWING SOME PRETTY BIG WAVES AT TIMES SMACKING
THE SOUTH BREAKWALL. HOFFMASTER STATE PARK HAD 4 FOOTERS IN THEIR
MORNING BEACH OB. IN LOOKING AT THE GRAND HAVEN WEBCAM FEELING OK
WHERE WE HAVE THE BREAK IN THE SMALL CRAFT ADVISORY AND BEACH
HAZARDS STATEMENT...WHICH IS JUST NORTH OF GRAND HAVEN. THE NORTHERN
PORTIONS OF THE OTTAWA ZONE (GRAND HAVEN) WILL BE BORDERLINE THIS
AFTERNOON WITH WAVES HOVERING AROUND THE 2-4 FOOT RANGE.

HAVE OPTED TO JUMP INTO THE NORTH FLOW PORTION OF THE EVENT NOW AS
WELL. HAVE EXTENDED THE NORTHERN HALF OF THE MARINE PRODUCTS
SCA/BHS THROUGH TOMORROW EVENING. IN THE SOUTH HALF HAVE THEM
STARTING UP AT 06Z TONIGHT AND LASTING THROUGH WEDNESDAY NIGHT AS
THE FLOW COMES AROUND TO THE NORTH.

IN TERMS OF BEACH IMPACT TODAY/S EVENT IN THE NORTH HALF OF THE
MARINE AREA MAY BE THE HIGHER THREAT GIVEN THE WARM TEMPS...AND
THEREFORE A LARGER BEACH POPULATION. TOMORROW/S WAVES WILL BE
BIGGER BUT THE IMPACT MAY BE MITIGATED BY COOLER BEACH
TEMPERATURES...RESULTING IN LESS FOLKS ON THE BEACH AND IN THE
WATER.


&&

.HYDROLOGY...
ISSUED AT 334 PM EDT MON JUL 21 2014

WIDESPREAD SIGNIFICANT RAINFALL LOOKS UNLIKELY TUESDAY NIGHT AND
WEDNESDAY. GENERALLY WE ARE EXPECTING A QUARTER TO THREE QUARTERS
OF AN INCH OF RAINFALL WITH HIGHER AMOUNTS POSSIBLE IN HEAVIER
THUNDERSTORMS. NOT ALL LOCATIONS ARE EXPECTED TO RECEIVE RAINFALL
WITH THIS COLD FRONT. WITH A FAIRLY QUICK MOVING LINE OF CONVECTION
ALONG THE FRONT...FLOODING IS A GREATLY MITIGATED THREAT. RIVERS
HAVE BEEN FALLING STEADILY AND ASIDE FROM A TEMPORARY BUMP IN SOME
LEVELS ON WEDNESDAY THIS TREND SHOULD CONTINUE FOR THE REST OF THE
WEEK.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...BEACH HAZARDS STATEMENT FROM LATE TONIGHT THROUGH THURSDAY
     MORNING FOR MIZ056-064-071.

     BEACH HAZARDS STATEMENT THROUGH LATE WEDNESDAY NIGHT FOR MIZ037-
     043-050.

LM...SMALL CRAFT ADVISORY UNTIL 2 AM EDT THURSDAY FOR LMZ847>849.

     SMALL CRAFT ADVISORY FROM 2 AM WEDNESDAY TO 8 AM EDT THURSDAY
     FOR LMZ844>846.

&&

$$

UPDATE...NJJ
SYNOPSIS...LAURENS
SHORT TERM...LAURENS
LONG TERM...MEADE
AVIATION...DUKE
HYDROLOGY...HOVING
MARINE...DUKE





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