Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 261713
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
113 PM EDT TUE MAY 26 2015

LATEST UPDATE...
HYDRO

.SYNOPSIS...
ISSUED AT 245 AM EDT TUE MAY 26 2015

THE SOUTHERLY FLOW OF WARM AND MOIST AIR WILL CONTINUE THROUGH
TODAY ACROSS THE REGION. A WAVE OF LOW PRESSURE WILL ARRIVE LATER
THIS AFTERNOON AND EVENING LIKELY TOUCHING OFF A ROUND OF
THUNDERSTORMS. A WESTERLY FLOW WILL DEVELOP WEDNESDAY SHIFTING THE
DEEPER MOISTURE EAST OF MICHIGAN. HIGH PRESSURE CONTROLS THE
WEATHER FOR THURSDAY HOWEVER BY THE END OF THE WEEK THE GULF
MOISTURE RETURNS WITH ADDITIONAL SHOWERS AND THUNDERSTORMS
EXPECTED.

&&

.UPDATE...
ISSUED AT 1118 AM EDT TUE MAY 26 2015

MADE A FEW MINOR ADJUSTMENTS TO POPS...BUT CURRENT FORECAST STILL
LOOKS ON TRACK. SATELLITE IMAGERY SHOW STRONG UPPER PV ANOMALY
OVER EASTERN IA MOVING NORTH AND THUNDERSTORMS OVER WI. BEST
UPPER FORCING WILL CONTINUE TO PUSH NORTH INTO WI. VERY LITTLE
LIGHTNING IS ASSOCIATED WITH LINE OF CONVECTION OVER ILLINOIS AND
SEVERAL CONVECTION ALLOWING MODELS SHOW THIS SYSTEM BECOMING
WEAKER AND MORE DIFFUSE AS IT APPROACHES MI. THIS MAKES SENSE AS
IT MOVES AWAY FROM BEST UPPER FORCING. HOWEVER...VISIBLE
SATELLITE SHOWS CLEARING UPSTREAM OVER INDIANA...SO DESTABILIZATION
AND A CONTINUED SEVERE THREAT ARE EXPECTED THIS AFTERNOON.

&&

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 245 AM EDT TUE MAY 26 2015

THE MAIN CHALLENGE IN THE SHORT TERM DEALS WITH THE COVERAGE AND
INTENSITY OF ANY THUNDERSTORMS TODAY AND TONIGHT.

THROUGH THE MORNING LITTLE IF ANY SHOWER OR THUNDERSTORM ACTIVITY
IS EXPECTED. NO REAL FORCING AND LACKING INSTABILITY ARE THE MAIN
LIMITING FACTORS. CONFIDENCE IS INCREASING THAT A MID AFTERNOON TO
EARLY EVENING THUNDERSTORM EVENT WILL OCCUR. DECENT INSTABILITY
WILL BE IN PLACE WITH FAVORABLE DEEP LAYER SHEAR. THE ARRIVAL OF
MID LEVEL SHORTWAVE IS EXPECTED TO TRIGGER THE STORMS. DAMAGING
WINDS SHOULD BE THE MAIN THREAT. BY EVENING THE STORMS SHOULD
PUSH NORTHEAST OF LANSING ROUGHLY AFTER 03Z.

LESS IN THE WAY OF STORM ACTIVITY IS EXPECTED ON WEDNESDAY.
HOWEVER WE DO DESTABILIZE INLAND AND THUS I KEPT THE STORM
POSSIBILITY GOING.

.LONG TERM...(THURSDAY NIGHT THROUGH MONDAY)
ISSUED AT 318 AM EDT TUE MAY 26 2015

STILL LOOKS LIKE A VERY GOOD CHANCE FOR RAIN AND THUNDERSTORMS
FOR FRIDAY AND SATURDAY. THE THREAT FOR SEVERE WEATHER APPEARS TO
REMAIN LOW AT THIS TIME. LOCALIZED HEAVY RAINFALL WOULD BE THE MAIN
THREAT.

DEEP SW FLOW WILL BE PRESENT ON FRIDAY AS A WEAK UPPER LEVEL
DISTURBANCE ACROSS THE S CENTRAL PLAINS TRIES TO PHASE WITH MAIN
H500 LONGWAVE TROUGH PATTERN ACROSS THE UPPER MIDWEST AND NORTHERN
GREAT LAKES. THIS EVOLUTION CONTINUES TO BE A POINT OF CONTENTION
BETWEEN THE GFS AND ECMWF...WITH THE GFS INSISTING THAT THE S PLAINS
DISTURBANCE HELPS DEVELOP A VORT MAX CUT OFF FROM THE MAIN STEERING
PATTERN ACROSS THE NORTHERN GREAT LAKES. THIS HAS A BEARING ON
WHETHER PRECIP LINGERS INTO SUNDAY AND BEYOND...OR NOT.

PLENTY OF AFTERNOON/EVENING INSTABILITY TO WORK WITH ON FRIDAY...BUT
WEAK DEEP LAYER SHEAR WILL MITIGATE ORGANIZED CONVECTION. ON THE
FLIP SIDE...WITH WEAKER FLOW NEAR THE SFC AND ALOFT AND
UNIDIRECTIONAL SHEAR...ANY STORMS THAT DO DEVELOP MAY NOT BE MOVING
VERY QUICKLY...SO LOCALIZED HEAVY RAINFALL IS POSSIBLE WITH PWAT
VALUES AROUND 1.5". AREAL QPF THROUGH SATURDAY MAY GENERALLY BE AN
INCH OR SO WITH THIS EVENT...BUT WELL OVER AN INCH IS POSSIBLE IN
HEAVIER STORMS.

MORE WIDESPREAD ACTIVITY MOVES IN FRIDAY NIGHT AND SATURDAY MORNING
AS A COLD FRONT APPROACHES. BETTER DEEP LAYER SHEAR EXISTS THEN AS
ONE WOULD EXPECT...BUT NOT COINCIDENT WITH APPRECIABLE INSTABILITY
AS CAA MOVES IN AND DEEP LAYER RH DIMINISHES BY LATE IN THE DAY
(UNLESS THE GFS VERIFIES...IN WHICH CASE WE REMAIN SATURATED IN THE
H1000-H500 LAYER THROUGH SUNDAY). THE ECMWF AND GEM INDICATE DRIER
AND COOLER CONDITIONS MOVING IN LATER SATURDAY...SO THAT IS THE MORE
LIKELY SCENARIO AT THIS TIME. SUNDAY LOOKS TO BE QUITE CHILLY WITH
HIGHS STRUGGLING TO REACH THE LOW 60S. TEMPS MUCH OF THE DAY MAY BE
IN THE 50S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 742 AM EDT TUE MAY 26 2015

CHALLENGING AVIATION FORECAST. LOW CLOUDS LIFTING IN FROM THE
SOUTH...WITH IFR SHOWING UP AROUND KJXN OVER TOWARD KLWA. IT
APPEARS THAT MOST SITES WILL SEE A PERIOD OF IFR THIS MORNING.
OUTSIDE OF THE IFR WE SHOULD SEE MVFR INTO THE EARLY AFTERNOON
HOURS. THUNDERSTORMS SHOULD THEN ARRIVE FOR THE EARLY TO MID
AFTERNOON HOURS. THIS IS SOMEWHAT SOONER THAN PREVIOUSLY THOUGHT.
WILL NEED TO MONITOR TRENDS. A BREAK IN THE LOW CLOUDS AND THUNDER
THIS EVENING...BUT LOW CLOUDS SHOULD WRAP BACK IN LATER TONIGHT
WITH MVFR OR LOWER CONDITIONS FORECASTED.

&&

.MARINE...
ISSUED AT 1118 AM EDT TUE MAY 26 2015

INCREASED WIND AND WAVE FORECAST SLIGHTLY...PARTICULARLY NORTH OF
MUSKEGON. AREA WEBCAMS AND SATELLITE IMAGERY SHOW FOG REMAINS AN
ISSUE NEAR AND NORTH OF MUSKEGON. HOWEVER SOME CLEARING IS SEEN
AND EXPECT MOST FOG TO BE GONE BY EVENING.

&&

.HYDROLOGY...
ISSUED AT 113 PM EDT TUE MAY 26 2015

RIVER LEVELS ARE LOW AND STABLE. EXPECTING 1/2 TO 3/4 OF AN INCH OF
PRECIPITATION THROUGH WEDNESDAY. THIS SHOULD LEAD TO SLOWLY
INCREASING RIVER LEVELS BY WEDNESDAY. EXPECTING NO OR MINOR/NUISANCE
FLOODING BY WEEKS END.

A POTENTIAL FOR MORE RAIN FRIDAY INTO SUNDAY (OVER AN INCH) MAY PUSH
SOME STREAMS AND RIVERS ABOVE BANKFULL BY NEXT WEEK... IF THESE
AMOUNTS ARE REALIZED.

&&

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

$$

UPDATE...TJT
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...HOVING
AVIATION...MJS
HYDROLOGY...63
MARINE...TJT



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