Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 182338
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
738 PM EDT SAT APR 18 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 322 PM EDT SAT APR 18 2015

TONIGHT WILL SEE INCREASING CLOUDS WITH LOWS FROM THE UPPER 30S TO
MID 40S. RAIN WILL OVERSPREAD THE AREA FROM SOUTH TO NORTH SUNDAY
AFTERNOON AND CONTINUE INTO SUNDAY EVENING BEFORE DIMINISHING TO SCATTERED
RAIN SHOWERS THAT WILL CONTINUE THROUGH MONDAY. IT WILL TURN MUCH
COOLER MONDAY WITH HIGHS ONLY AROUND 50. RAIN SHOWERS MAY MIX AT
TIME WITH SNOW SHOWERS TUESDAY NIGHT INTO THURSDAY AND IT WILL BE
MUCH COLDER THAN NORMAL WITH LOWS NEAR FREEZING AND HIGHS IN THE
40S.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 322 PM EDT SAT APR 18 2015

OUR PRIMARY ISSUE IS THE RAIN SUNDAY INTO SUNDAY NIGHT. THERE IS
LITTLE QUESTION ABOUT THIS EITHER. THE MODELS HAVE BEEN VERY
CONSISTENT WITH THIS SYSTEM FOR NEARLY A WEEK...EVEN THE TIMING
HAS NOT CHANGED ALL THAT MUCH OVER THE PAST FEW DAYS. IT WILL BE
BREEZY IN FRONT OF THE SYSTEM SUNDAY WITH WINDS GUSTING TO NEAR 30
MPH AT TIMES.

THIS IS A SOUTHERN STREAM SHORTWAVE THAT IS MERGING WITH AN
NORTHERN STREAM SYSTEM SO WE GET TO PERIODS OF RAIN FROM THIS
EVENT. THE FIRST AND MOST SIGNIFICANT IS FROM THE SOUTHERN
STREAM SHORTWAVE LIFTING NORTHWARD INTO LOWER MICHIGAN SUNDAY INTO
SUNDAY NIGHT. THEN WE HAVE THE TRAILING NORTHERN STREAM SHORTWAVE
COME THROUGH ON MONDAY WHICH BRINGS A PERIOD OF SHOWERS DURING THE
DAY TIME HOURS. IT IS THE NORTHERN STREAM WAVE THE BRINGS IN THE
REALLY COLD AIR.

THE SOUTHERN STREAM SYSTEM INCREASES THE MIXING RATIO FROM 1 G/KG
TO 8 G/KG IN 12 HOURS AND THE PRECIPITABLE  WATER SURGES FROM UNDER
A HALF INCH AROUND MIDNIGHT TO OVER ONE AND A QUARTER INCHES BY
SUNDAY EVENING. THERE IS A 60 KNOT LOW LEVEL JET AIMED AT
SOUTHWEST LOWER MICHIGAN LATE SUNDAY AFTERNOON AND THE 1000/850
MOISTURE TRANSPORT VECTORS ARE AIMED AT SOUTHWEST MICHIGAN SUNDAY
AFTERNOON INTO SUNDAY EVENING. WE ALSO SEE 40 KNOT OF WIND NEARLY
PERPENDICULAR TO THE ISOTROPIC SURFACES THROUGH 700 MB WITH THE
CONDENSATION PRESSURE DEFICITS NEAR ZERO OVER SOUTHWEST MICHIGAN
FROM LATE SUNDAY AFTERNOON INTO SUNDAY EVENING. WITH ALL OF THIS
THE INSTABILITY IS MARGINAL AT BEST SO I DO NOT SEE THUNDERSTORMS
AS MUCH OF AN ISSUE. STILL IT WILL RAIN... LIKELY BETWEEN .5
INCHES AND 1 INCH OVER MOST OF THE AREA BY MONDAY AFTERNOON.

WE SEE SOME DRY AIR MOVE IN MONDAY EVENING BUT GIVEN THE COLD
CONVECTION IS COULD SEE SOME SCATTERED SHOWERS CONTINUING
OVERNIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 322 PM EDT SAT APR 18 2015

IT WILL BE UNSEASONABLY COLD NEXT WEEK WITH SCATTERED RAIN AND MIXED
RAIN AND SNOW SHOWERS TUESDAY THROUGH THURSDAY WITH DEEP CYCLONIC
FLOW AND THE UPPER LEVEL LOW IN PLACE OVER THE NORTHERN GREAT LAKES
REGION. SOME LIGHT SNOW ACCUMULATIONS ARE EVEN POSSIBLE MAINLY
ACROSS RELATIVELY HIGHER ELEVATIONS OF OUR NORTHERN FORECAST AREA.

HIGH TEMPERATURES TUESDAY THROUGH THURSDAY WILL ONLY REACH THE 40S
WITH CONSIDERABLE CLOUD COVER AND COLD AIR ADVECTION. TEMPERATURES
MAY MODERATE SLIGHTLY FRIDAY AND SATURDAY AS THE UPPER LEVEL LOW
SHIFTS FURTHER EAST TO THE NEW ENGLAND REGION. MAX TEMPS BY FRIDAY
AND SATURDAY SHOULD REACH THE LOWER TO PERHAPS MIDDLE 50S WITH DRY
WX AS A SFC RIDGE BUILDS IN.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 738 PM EDT SAT APR 18 2015

MAIN CHANGE WITH THIS UPDATE IS TO TIME PRECIPITATION EARLIER.
VFR CONDITIONS ARE EXPECTED THROUGH 15Z SUNDAY FOR THE
AZO...BTL...JXN TERMINALS AND SLIGHTLY LATER AT MKG...GRR...LAN.
WE EXPECT WIND GUSTS TO DIMINISH AROUND SUNSET. PREDOMINANTLY
MVFR CIGS/VSBYS ANTICIPATED AREAWIDE AFTER 15-18Z WITH BRIEF IFR
POSSIBLE IN HEAVIER SHOWERS.

&&

.MARINE...
ISSUED AT 322 PM EDT SAT APR 18 2015

I ISSUED A SMALL CRAFT ADVISORY FOR ALL BUT OR NORTHERN MOST NEAR
SHORE SECTION DUE TO EAST WINDS OF 20 TO 25 KNOTS SUNDAY. DUE TO
THE OFF SHORE WIND... WAVE HEIGHTS WILL BE MINIMAL BUT GIVEN THE
STRONG WINDS I THROUGH IT BEST TO ISSUE THE ADVISORY EVEN SO.
SINCE THE SURFACE LOW MOVES INTO THE AREA SUNDAY NIGHT WINDS WILL
DIMINISH SO THE ADVISORY IS JUST FOR SUNDAY DURING THE DAY LIGHT
HOURS.


&&

.HYDROLOGY...
ISSUED AT 1126 AM EDT SAT APR 18 2015

A GOOD SOAKING RAINFALL IS STILL ON TRACK TO AFFECT THE ENTIRE AREA
BEGINNING SUNDAY. THE BULK OF THE MOISTURE WILL LIKELY FALL
BETWEEN SUNDAY AFTERNOON INTO MONDAY MORNING WITH SOME GUIDANCE
HINTING AT OVER AN INCH IN SPOTS. ADDITIONAL CHANCES FOR RAIN WILL
SPAN THROUGH THE MIDDLE OF THE WEEK BUT ARE NOT EXPECTED TO BE
QUITE AS ABUNDANT WITH MOISTURE.

RIVERS WILL MAINLY RESPOND IN THE MANNER OF MINOR RISES. THIS SHOULD
MOSTLY CONSIST OF WITHIN BANK RISES. I HAVE A LITTLE MORE CONFIDENCE
IN THINKING MAPLE RAPIDS COULD FLIRT WITH ADVISORY CRITERIA ONCE
AGAIN.
THIS IS PENDING THE AMOUNT OF RAINFALL RECEIVED THROUGH EARLY MONDAY.
OTHERWISE...WE ARE LOOKING PRETTY GOOD WITH THIS NOT BEING A
CONVECTIVE
MODE OF PRECIPITATION...NO REAL SURPRISES AT THIS POINT.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY FROM 6 AM TO 6 PM EDT SUNDAY FOR LMZ844>848.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...LAURENS
AVIATION...TJT
HYDROLOGY...JAM
MARINE...WDM






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