Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 241804
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
204 PM EDT SUN MAY 24 2015

LATEST UPDATE...
HYDRO

.SYNOPSIS...
ISSUED AT 315 AM EDT SUN MAY 24 2015

A WARM FRONT WILL LIFT NORTHWARD THROUGH LOWER MICHIGAN TODAY AND
TONIGHT. SHOWERS WILL BE ON THE INCREASE AS THIS SYSTEM TRACKS
THROUGH AND THERE COULD EVEN BE A FEW STORMS ESPECIALLY TONIGHT.
MEMORIAL DAY IS LOOKING WARM AND WINDY WITH SOME SHOWERS AND
STORMS AROUND...MAINLY EARLY. UNSETTLED WEATHER WILL CONTINUE
THROUGH TUESDAY AS THE FRONT REMAINS SITUATED IN MICHIGAN.

&&

.UPDATE...
ISSUED AT 1150 AM EDT SUN MAY 24 2015

INCREASED POPS FOR LATER TODAY...ESPECIALLY OVER THE NW CWA.

AS OF 1530Z WE HAVE A FEW SPRINKLES AROUND COMING FROM A MIDDLE
LEVEL DECK OF CLOUDS. WE ARE IN THE PROCESS OF MOISTENING THE
LAYER AND FEEL WE WILL BE SEEING A FAIRLY WIDESPREAD AREA OF RAIN
SHOWERS OVER THE NW PRIOR TO 00Z SO INCREASED TO LIKELY POPS
THERE.

ELSEWHERE THE MOIST DEPTH APPEARS TO OCCUR A BIT SLOWER...SO
MAINLY EXPECTED SCATTERED SHOWERS. THESE SHOULD BE MORE COMMON
AFTER ABOUT 19Z IN THE SW CWA...AND 21-22Z IN THE EASTERN CWA.

KEPT THE MENTION OF THUNDER CONFINED TO THE I-94 CORRIDOR OF
COUNTIES AS WEAK SURFACE BASED INSTABILITY IS INDICATED TOWARD
EVENING.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 315 AM EDT SUN MAY 24 2015

THE MAIN CHALLENGE DEALS WITH THE COVERAGE AND AMOUNT OF SHOWERS
AND THUNDERSTORMS THROUGH THE PERIOD.

TO START...I BACKED OFF ON THE POPS MAINLY TODAY AND LATER
MEMORIAL DAY. THE LATEST MODEL DATA AND RADAR TRENDS SHOW WHAT
UPSTREAM SHOWER ACTIVITY WILL LIKELY WEAKEN AS IT MOVES INTO LOWER
MICHIGAN LATER THIS MORNING INTO THIS AFTERNOON. SO POPS WERE
LOWERED TODAY. AFTER 22Z SOME INSTABILITY TRIES TO MOVE INTO THE
SOUTH HAVEN REGION...SO I DID MAINTAIN A LOW RISK FOR THUNDER
THEN.

ON MEMORIAL DAY MOST MODELS ARE SHOWING A SHORTWAVE TRACKING
THROUGH BY EARLY AFTERNOON. IF THIS HAPPENS WE WILL SEE MORNING
SHOWERS AND STORMS FOLLOWED BY A CONSIDERABLE DECREASE IN THE
ACTIVITY FOR THE AFTERNOON. I DID LOWER POPS FOR WESTERN LOCATIONS
FOR THE AFTERNOON BASED ON THIS MODEL TREND. IT WILL LIKELY END UP
WINDY DURING THE AFTERNOON AS A LOW LEVEL JET COMBINES WITH BETTER
MIXING TO SUPPORT STRONGER GUSTS.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 315 AM EDT SUN MAY 24 2015

TWO MAIN OPPORTUNITIES FOR RAINFALL WILL BE CENTERED ON TUESDAY
NIGHT AND THEN AGAIN FOR FRIDAY AND SATURDAY. OUTSIDE OF THESE
PERIODS...LITTLE RAINFALL IS EXPECTED WITH PREDOMINANTLY DRY WEATHER
LIKELY.

CURRENT WV ANALYSIS WITH RAP40 H850-H300 MEAN HEIGHTS OVERLAID
REVEALS A WELL DEFINED UPPER LEVEL SHORTWAVE ACROSS SOUTHERN
CALIFORNIA...WHICH IS THE FEATURE OF INTEREST FOR TUESDAY NIGHT.
THIS IMPULSE IS FORECAST TO PHASE WITH DEEPER UPPER LEVEL TROUGHING
ACROSS THE NORTHERN PLAINS...WHICH WILL BE IN THE PROCESS OF
WEAKENING. THE GFS IS SLOWEST WITH THIS PHASING COMPARED WITH THE
ECMWF AND GEM...AND HENCE LINGERS PRECIPITATION FURTHER INTO
WEDNESDAY MORNING. ALL THE MODELS DO BRING SOME PRECIP INTO SW LOWER
MI HOWEVER...SO A WIDE AREA OF LIKELY POPS IS BEING CARRIED. SOME
INSTABILITY IS PRESENT VIA BUFKIT SOUNDINGS...SO THUNDERSTORMS WILL
BE POSSIBLE THOUGH SHOWERS MAY BE MORE THE GENERAL RULE.

WEDNESDAY WILL LARGELY BE DRY OUTSIDE OF A FEW SCATTERED SHOWERS OR
STORMS...MAINLY DUE TO A WEAK FRONTAL BOUNDARY SLATED TO MOVE
THROUGH BETWEEN 12Z AND 18Z. ONCE THAT PASSES...THINGS SHOULD DRY
OUT. THURSDAY LOOKS WARM AND PLEASANT WITH DRY CONDITIONS OUTSIDE OF
VERY ISOLATED SHOWERS OR T-STORMS TOWARD EXTREME SOUTHERN MI.

FOR FRIDAY AND SATURDAY...A BAROCLINIC ZONE LOOKS TO SET UP ACROSS
THE MIDWEST WITH MOIST SOUTHERLY FLOW AHEAD OF IT. THE GFS AND ECMWF
HAVE A RATHER LARGE AMOUNT OF SFC BASED CAPE INDICATED FOR FRIDAY
ACROSS OUR REGION (2000+ J/KG)...AND WITH AN INCREASINGLY HUMID
AIRMASS WITH PWATS OF 1.5-1.75" THERE COULD BE A FAIR AMOUNT OF
THUNDERSTORMS PRESENT WITH EITHER THE GFS OR ECMWF SOLUTIONS
VERIFYING. SOME HEAVIER RAINFALL WOULD CERTAINLY BE A POSSIBILITY AS
WELL.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY)
ISSUED AT 200 PM EDT SUN MAY 24 2015

SEVERAL POTENTIAL AVIATION HAZARDS DEVELOPING NEXT 24 HOURS...STRONG
SOUTH TO SOUTHWEST LOW LEVEL WINDS OF 40 TO 50 KTS ARE EXPECTED TO
DEVELOP AROUND 2 KFT ABOVE THE GROUND MONDAY MORNING. THERE MAY
INITIALLY BE SOME LOW LEVEL WIND SHEAR BETWEEN 09Z AND 14Z BEFORE
WINDS MIX TO THE SURFACE WITH 25 TO 30 KT WIND GUSTS. WINDS WILL
DIMINISH LATE MONDAY AFTERNOON INTO THE EVENING.

INCREASINLY WARM AND HUMID AIRMASS WILL INCREASE CHANCE OF IFR
CIGS/VIS MAINLY NEAR THE LAKESHORE MONDAY MORNING AND EVERYWHERE FOR
MONDAY NIGHT INTO TUESDAY. CURRENTLY THERE IS AN EXTENSIVE AREA OF
IFR / LIFR CIG AND VIS OVER WESTERN IL AND EASTERN IA...BUT FEEL
MOST OF THAT AREA WILL STAY WEST AND SPREAD NORTH OF A KMKG TO KMBS
LINE OVERNIGHT TONIGHT.

THERE WILL ALSO BE SOME SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
EARLY TUESDAY MORNING AND EAST OF A KRQB-KGRR-KAZO LINE FOR MONDAY
AFTERNOON. INSTABILITY IS LIMITED WITH THIS FIRST BATCH. THERE WILL
BE A BETTER CHANCE OF STRONG AND POSSIBLY SEVERE THUNDERSTORMS
TUESDAY.


&&

.MARINE...
ISSUED AT 315 AM EDT SUN MAY 24 2015

WE WILL LIKELY NEED SMALL CRAFT ADVISORIES MEMORIAL DAY. A
STRONGER PRESSURE GRADIENT SETS UP AND THE FETCH IS FAVORABLE FOR
BIGGER WAVES DESPITE THE STABLE LAKE CONDITIONS. ANY SWIMMING WILL
LIKELY BE HAZARDOUS AS WELL.

FOG WILL LIKELY INCREASE AS WELL AS GULF MOISTURE ADVECTS OVER THE
RELATIVELY COLD LAKE MI WATERS.


&&

.HYDROLOGY...
ISSUED AT 204 PM EDT SUN MAY 24 2015

THREE MAIN ROUNDS OF RAIN ARE FORECAST FOR SOUTHWEST LOWER MICHIGAN
THROUGH NEXT WEEKEND...THE FIRST OF WHICH IS ARRIVING NOW. RAINFALL
TOTALS OF UP TO HALF AN INCH ARE POSSIBLE ACROSS CENTRAL LOWER
MICHIGAN THROUGH MONDAY AFTERNOON...MAINLY OVER THE UPPER MUSKEGON
BASIN AND PERE MARQUETTE BASINS. MONDAY AFTERNOON THROUGH MONDAY
NIGHT LOOKS FAIRLY DRY. A SECOND ROUND OF SHOWERS AND A FEW STORMS
WILL BE POSSIBLE TUESDAY AFTERNOON THROUGH TUESDAY NIGHT.

THE BIGGEST HYDRO CONCERN COULD BE THE THIRD ROUND ON FRIDAY AND
SATURDAY. A MORE UNSTABLE AND INCREASINGLY HUMID AIRMASS WILL BE
MORE CONDUCIVE TO STRONGER THUNDERSTORMS CAPABLE OF HEAVY RAINFALL
FRIDAY INTO SATURDAY. THE ECMWF EPS...GEM...AND GFS AGREE THAT 2 TO
3 INCHES OF WIDESPREAD RAINFALL IS POSSIBLE THROUGH SUNDAY...WITH
HIGHER AMOUNTS POSSIBLE IN STRONG THUNDERSTORMS. RIVER RISES ARE
EXPECTED THIS WEEK AND ESPECIALLY NEXT WEEKEND. THE MAIN IMMEDIATE
THREAT WILL BE MINOR NUISANCE FLOODING MIDWEEK WITH THE POSSIBILITY
OF HEAVY RAINFALL TUESDAY AFTERNOON THROUGH TUESDAY NIGHT. THE
FLOODING RISK IS HIGHER NEXT WEEKEND...ESPECIALLY IN URBAN AREAS AND
ON SMALLER STREAMS.

&&

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

$$

UPDATE...JK
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...HOVING
AVIATION...COBB
HYDROLOGY...EBW
MARINE...MJS



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