Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 190332
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1132 PM EDT FRI JUL 18 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 259 PM EDT FRI JUL 18 2014

HIGH PRESSURE WILL MOSTLY DOMINATE THE WEATHER ACROSS THE GREAT
LAKES REGION THROUGH THE WEEKEND. ACROSS SOUTHEAST LOWER MI
HOWEVER...A WEAKENING AREA OF LOW PRESSURE WILL TRACK THROUGH THAT
REGION...LEADING TO SOME SHOWERS ON SATURDAY. MODERATING
TEMPERATURES ARE PREDICTED INTO NEXT WEEK. A COLD FRONT WILL PUSH
THROUGH THE REGION MID WEEK LEADING TO A AROUND OF THUNDERSTORMS.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 259 PM EDT FRI JUL 18 2014

THE MAIN CHALLENGE IN THE SHORT TERM DEALS WITH THE POTENTIAL FOR
SOME SHOWERS ON SATURDAY. MODELS ARE SHOWING A WEAKENING MID LEVEL
SHORTWAVE LIFTING OUT OF THE LOWER MS VALLEY TONIGHT AND CROSSING
SOUTHEAST LOWER MI. AT THE SURFACE A WEAK INVERTED TROUGH WILL BE
IN PLACE. AS A RESULT TO POTENTIAL FOR SOME SHOWERS IS THERE.
SOUNDINGS DO SHOW WEAK CAPE UP TO AROUND THE FREEZING LEVEL FOR
JACKSON. I WILL ADD A LOW RISK FOR SHOWERS MAINLY FOR THE REGION
AROUND JACKSON SATURDAY. THERE IS A POTENTIAL FOR THEM TO ARRIVE
LATE TONIGHT...JUST NOT CONFIDENT ENOUGH TO ADD THAT TO THE
DRY FORECAST.

I DID BUMP UP THE CLOUD COVER FOR TONIGHT AND SATURDAY...MAINLY
FOR EASTERN ZONES. THIS INCLUDES LANSING TO JACKSON TO BATTLE
CREEK. THIS WILL LIKELY IMPACT TEMPERATURES AS WELL. SO THE VALUES
WERE LOWERED A COUPLE OF DEGREES WHERE THE CLOUDS WILL BE THE
THICKEST ON SATURDAY.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 259 PM EDT FRI JUL 18 2014

WE CONTINUE TO FOCUS ON THE MIDWEEK PERIOD FOR THE POSSIBILITY OF
MORE ACTIVE WEATHER ACROSS THE GREAT LAKES REGION...WITH ONE OR MORE
COMPLEXES OF THUNDERSTORMS POTENTIALLY IMPACTING SW LOWER MI FROM
TUESDAY NIGHT INTO LATE WEDNESDAY OR EARLY THURSDAY.

THERE IS A BIT MORE CONFIDENCE REGARDING THE RISK FOR THUNDERSTORMS
FOR MID WEEK...ALTHOUGH IT IS TOUGH TO PIN DOWN TOO MANY SPECIFICS
YET. FIRST...THE 12Z GFS...GEM...AND ECMWF AGREE ON A VERY STRONG
UPPER LEVEL RIDGE DEVELOPING ACROSS THE SOUTH CENTRAL ROCKIES BY
TUESDAY...WITH 500 MB HEIGHTS REACHING 600 DM IN THAT REGION. THIS
IN TURN FORCES A DIGGING SHORTWAVE TROUGH ACROSS THE UPPER MIDWEST
ON TUESDAY AS OUR 500 MB HEIGHTS BEGIN DIMINISHING AND PVA
OVERSPREADS THE REGION. MODELS DO SHOW A LLJ DEVELOPING...THOUGH
RATHER MODEST AT 30 KTS OR SO ON TUESDAY AND WEDNESDAY.
NEVERTHELESS...THIS TYPE OF SYNOPTIC SETUP NEEDS TO BE MONITORED FOR
POTENTIAL RIDGE RIDER MCS ACTIVITY.

AS WAS SEEN WITH THE MODEL RUNS FROM 12Z YESTERDAY AND LAST NIGHT`S
00Z RUNS...THE ECMWF HAS A DIFFERENT APPROACH THAN THE GFS AND GEM.
IT TAKES THE SHORTWAVE TROUGH AND DEVELOPS IT INTO AN UPPER LEVEL
LOW THAT SLOWS DOWN ACROSS THE GREAT LAKES...BRINGING A MORE
EXTENDED PERIOD OF RAINFALL TO THE REGION. WOULD PREFER TO SEE
TRENDS IN THE GFS AND GEM (PLUS ADDITIONAL ECMWF RUNS) BEFORE
TOTALLY BUYING INTO THIS SOLUTION. GENERAL AGREEMENT EXISTS BETWEEN
THE GFS AND GEM REGARDING STRENGTH AND TIMING OF THE SHORTWAVE
TROUGH AND GENERAL EVOLUTION OF THE LLJ SUCH THAT CONVECTION WOULD
STRENGTHEN ACROSS MN AND WI DURING THE DAY TUESDAY AND PROPAGATE
OVER LK MI LATE TUES NIGHT AND EARLY WED.

GFS BUFKIT SOUNDINGS FOR GRR INDICATE SFC BASED CAPE > 1000 J/KG AND
LI`S OF -4 TO -6 TUES AFTERNOON RIGHT ON THRU WED EVENING. THIS IS
ALSO IN CONJUNCTION WITH SOME RATHER STEEP MID LEVEL LAPSE RATES OF
-8C TO -9C ESPECIALLY TUES NIGHT AND WEDNESDAY. IT WOULD BE
PREMATURE TO SUGGEST A SEVERE WEATHER THREAT AT THIS POINT...BUT
SOME LARGE HAIL AND PERHAPS GUSTY WINDS WOULD BE POSSIBLE IF STORMS
DEVELOP. PW VALUES OF 1.75-2.00" COULD BE REALIZED IN CONCERT WITH
RISING DEW POINTS AROUND 70F. THIS SUGGESTS ANY STORMS COULD BE
ACCOMPANIED BY RATHER EFFICIENT RAINFALL. AS WE HAVE SEEN SO FAR
THIS YEAR...SOME STORMS HAVE GENERATED 1-2"/HR RATES WITH PW VALUES
THIS HIGH.

THUNDERSTORMS MAY LINGER INTO WEDNESDAY NIGHT OR EARLY
THURSDAY...AND WILL AT LEAST GIVE A NOD TO THE ECMWF RUNS BY KEEPING
30-40 POPS IN FOR WEDNESDAY NIGHT/EARLY THURS AM. IT APPEARS OUR
MOST LIKELY TIMEFRAME FOR STORMS WOULD BE LATE TUESDAY NIGHT AND
THROUGHOUT WEDNESDAY...BUT UNTIL BETTER MODEL AGREEMENT IS IN PLACE
WE ARE GOING FOR 40-50 POPS FOR THIS PARTICULAR PERIOD.

TUESDAY WILL BE THE WARMEST DAY OF THE WEEK WITH HIGHS IN THE UPPER
80S AWAY FROM THE LAKE. THIS IS EXPECTED TO BE OUR WARMEST DAY SINCE
JUNE 1 FOR MANY LOCATIONS. WITH DEW POINTS AROUND 70F...HEAT INDEX
READINGS AROUND 90F WILL LIKELY OCCUR...WHICH MAY FEEL HOT RELATIVE
TO OUR COOLER THAN NORMAL JULY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1132 PM EDT FRI JUL 18 2014

VFR CONDITIONS SHOULD PREVAIL ACROSS THE TAF SITES THROUGH SATURDAY
NIGHT. FOR THE TAF SITES WEST OF US-69 JUST SOME CIRRUS CLOUDS
TONIGHT AND A FEW CUMULUS CLOUDS SATURDAY. WINDS WILL BE LIGHT
FROM THE SOUTHEAST MOSTLY. MKG WILL SEE THE LAKE BREEZE SHIFT THE
WIND TO SOUTHWEST BY EARLY AFTERNOON.

FOR THE TAF SITES NEAR AND EAST OF US-69 THERE IS A CHANCE SHOWERS
SATURDAY AFTERNOON. THAT IS THE RESULT OF A SYSTEM PASSING TO THE
SOUTH AND EAST OF MICHIGAN SATURDAY. THE EXTREME NORTHWEST PART OF
THE PRECIPITATION SHIELD COULD BRING SOME SHOWERS TO THE JXN AND
MAYBE THE LAN TAF SITES DURING THE LATE MORNING INTO THE EARLY
AFTERNOON. I PUT VCSH FOR THOSE TAF SITES TO COVER THIS. EVEN IF
THERE ARE A FEW SHOWERS THERE FOR THE MOST PART CONDITIONS SHOULD
STAY VFR.

&&

.MARINE...
ISSUED AT 259 PM EDT FRI JUL 18 2014

THE WEAK PRESSURE GRADIENT WILL PERSIST THROUGH THE WEEKEND. THIS
WILL ACT TO KEEP THE WINDS UNDER 20 KNOTS AND WAVES TO A MINIMUM.


&&

.HYDROLOGY...
ISSUED AT 259 PM EDT FRI JUL 18 2014

LITTLE OR NO QPF INTO EARLY NEXT WEEK. THIS SUPPORTS FALLING RIVER
LEVELS.

&&

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

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...HOVING
AVIATION...WDM
HYDROLOGY...MJS
MARINE...MJS





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