Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 200017
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
817 PM EDT SUN APR 19 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 258 PM EDT SUN APR 19 2015

A MAJOR CHANGE IN THE OVERALL WEATHER PATTERN IS ABOUT TO BEGIN. A
STRONG AND DEEPENING LOW PRESSURE SYSTEM WILL TRACK NORTHWARD
THROUGH WESTERN LOWER MICHIGAN TONIGHT BRINGING RAIN THAT MAY BE
HEAVY AT TIMES EARLY TONIGHT. AFTER THE SYSTEM MOVES NORTH OF THE
AREA LATER TONIGHT THE RAIN WILL DIMINISH TO SHOWERS BUT IT WILL
BE BREEZY. THEN SHOWERS AND BREEZY CONDITIONS WILL CONTINUE INTO
TUESDAY. BY TUESDAY NIGHT IT WILL GET COLD ENOUGH FOR SNOW TO MIX
WITH THE RAIN. THAT WILL CONTINUE INTO THURSDAY. IT WILL BE MUCH
COOLER THROUGH THIS ENTIRE PERIOD WITH HIGHS TUESDAY THROUGH
THURSDAY IN THE 40S AND LOWS NEAR FREEZING.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 258 PM EDT SUN APR 19 2015

THE PRIMARY ISSUE IS THE RAIN TONIGHT...THEN WINDY AND SHOWERS
MONDAY INTO TUESDAY. THERE IS A GOOD CHANCE OF MEASURABLE SNOW
OVER NORTHERN SECTIONS TUESDAY NIGHT.

THE DEEPENING STORM SYSTEM WILL TRACK THROUGH WESTERN LOWER
MICHIGAN TONIGHT BRINGING A PERIOD OF MODERATE TO HEAVY RAIN THAT
WILL LAST AROUND 6 HOURS IN ANY ONE PLACE. IT WILL BE BREEZY AT
FIRST BUT WINDS WILL DIMINISH TOWARD MIDNIGHT AS THE SURFACE LOW
MOVES THROUGH THE AREA.

THE RAIN EVENT TONIGHT REMAINS WELL SUPPORTED BY ALL THE MODELS.
THERE IS SOME ISSUE AS TO WHERE THE HEAVIEST RAIN WILL ACTUALLY
FALL BUT ALL AREAS GET AT LEAST A THIRD OF AN INCH AND MOST AREAS
SHOULD GET MORE THAN A HALF INCH OF RAIN TONIGHT. THIS IS ALL THE
RESULT OF UPPER WAVE THAT GOES NEGATIVE TILT OVER SOUTHWEST
MICHIGAN TONIGHT. THAT CAUSES THE SURFACE LOW TO TRACK NORTHWARD
AND DEEPEN RAPIDLY. ALSO THIS RESULTS IN A STRONG LOW LEVEL JET
(60 KNOTS)... STRONG 1000 TO 850 MOISTURE CONVERGENCE AIMED AT
SOUTHWEST LOWER MICHIGAN THIS EVENING AND CONDENSATION PRESSURE
DEFICITS NEAR ZERO MB THIS EVENING. THERE IS ALSO 40 KNOT OF WIND
PERPENDICULAR TO THE ISOTROPIC SURFACES EARLY TONIGHT... AND WE
CAN ALL ADD TO THAT PRECIPITATION WATER VALUES (1.4") NEAR 2
STANDARD DEVIATIONS FROM NORMAL AND MIXING RATIOS RISING TO NEAR 8
G/KG FROM UNDER 2 G/KG THIS MORNING. THERE IS ALSO A ZONE OF
STRONG MID-LEVEL FGEN JUST AHEAD OF THE SYSTEM AS IT MOVES THROUGH
SOUTHWEST MICHIGAN TONIGHT. BOTTOM LINE... IT WOULD BE HARD TO
IMAGINE WE WILL NOT GET RAIN OVERNIGHT.

ONCE THE LOW PASSES US THE SIGNIFICANT RAINFALL WILL END. HOWEVER
THE SECONDARY COLD FRONT AND TRAILING NORTHERN STREAM WAVE WILL
BRING ANOTHER PERIOD OF SHOWERS TO THE AREA MIDDAY MONDAY INTO
EARLY EVENING. THAT BRINGS IN THE TRULY COLDER AIR.

MONDAY NIGHT WE MAY SEE A BREAK IN THE SHOWERS EARLY ON BUT THEN
THE WRAP AROUND MOISTURE MOVES IN AND WE SEE SHOWERS THAT MAY MIX
WITH AN CHANGE TO SNOW SHOWERS BY TUESDAY NIGHT. BY THE WAY THE
SPC SOUNDING CLIMATOLOGY PAGE SHOWS THE COLDEST 850 TEMPERATURE
FOR THE DTX SOUNDING TO BE -12C ON THE 22ND. THE ECWMF SHOWS -9.8C
AT 2 PM WEDNESDAY NEAR GRR. TO SAY THE LEAST...IT WILL GET COLDER
THIS COMING WEEK!

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 258 PM EDT SUN APR 19 2015

UNSEASONABLY COLD WEATHER IS ANTICIPATED WEDNESDAY AND THURSDAY WITH
DEEP CYCLONIC FLOW AND COLD AIR ADVECTION WITH THE UPPER LEVEL LOW
STILL IN PLACE OVER THE NORTHERN GREAT LAKES REGION. SCATTERED RAIN
SHOWERS WILL CONTINUE AND MAY BE MIXED AT TIMES WITH WET SNOW FLAKES
ESPECIALLY OVER RELATIVELY HIGHER ELEVATIONS OF OUR NORTHERN FCST
AREA.

TEMPERATURES SHOULD MODERATE SLIGHTLY FRIDAY THROUGH THE WEEKEND BUT
WILL STILL AVERAGE SEVERAL DEGREES BELOW NORMAL. THIS AS A SFC RIDGE
BUILDS IN AND AS THE UPPER LEVEL LOW MOVES MUCH FURTHER EAST TO THE
NEW ENGLAND REGION BY THEN. THE RIDGE WILL BRING FAIR AND SEASONABLY
COOL WEATHER FRIDAY THROUGH SUNDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 817 PM EDT SUN APR 19 2015

AVIATION CONDITIONS WILL CONTINUE TO DETERIORATE THIS EVENING WITH
MVFR AND IFR WEATHER DEVELOPING. BY MIDNIGHT OR A LITTLE BIT
AFTER...ALL SITES SHOULD HAVE IFR CEILINGS. THE STEADIER RAIN WILL
CONTINUE THROUGH ABOUT 100AM...THEN BECOME MORE SCATTERED
OVERNIGHT. THE LOW CEILINGS WILL PERSIST RIGHT INTO THE MORNING
HOURS OF MONDAY...WITH IFR AND LIFR CEILINGS PREVALENT INTO MID
MORNING. CONDITIONS SHOULD BEGIN TO IMPROVE MONDAY AFTERNOON AS
THE IFR CEILINGS TRY TO LIFT TO MVFR.

IT WILL BE BREEZY OUT OF THE EAST THIS EVENING AND THEN TURNING
WINDY MONDAY AFTERNOON FROM THE SOUTHWEST BEHIND A COLD FRONT.


&&

.MARINE...
ISSUED AT 258 PM EDT SUN APR 19 2015

I EXTENDED THE SCA THROUGH TUESDAY AFTERNOON FOR THE ALL THE ZONES
FROM WHITEHALL SOUTH ( NORTH OF THERE WINDS WILL NOT BE AS STRONG
OVERNIGHT). AFTER THE SURFACE LOW MOVES NORTH OF MUSKEGON WINDS WILL
INCREASE TO 30 KNOTS FROM THE SOUTHWEST THEN I EXPECT 15 TO 25
KNOT WINDS MONDAY INTO TUESDAY. AS THE COLD AIR COMES IN WAVES
WILL BUILD SO WE WILL LIKELY NEED A SCA FOR THE NORTHERN TWO ZONE
GROUPS MONDAY NIGHT AND TUESDAY.


&&

.HYDROLOGY...
ISSUED AT 1114 AM EDT SUN APR 19 2015

PERIODS OF RAIN ARE EXPECTED TO DEVELOP LATE THIS AFTERNOON AND
AFFECT THE AREA OVER THE NEXT COUPLE OF DAYS. THE LIGHTER VARIETY OF
PRECIPITATION MAY EXTENT INTO MIDWEEK. THOUGH WE WILL SEE A DECENT SOIL
SOAKING IT SHOULD NOT BE SUBSTANTIAL ENOUGH TO CREATE FLOODING
CONCERNS. GRADUAL BUT MINOR RISES ARE LIKELY...SUSPECTING THAT
THIS WOULD STAY WITHIN BANKS FOR MOST LOCATIONS. I WOULD NOT RULE
OUT A COUPLE OF SITES FLIRTING WITH ADVISORY STAGE AS WE GO INTO
TUESDAY...ESPECIALLY IF ANY MODERATE RAINFALL IS MORE PERSISTENT
WITH THE FIRST COUPLE OF ROUNDS OF MOISTURE. OTHERWISE...AREA
RIVERS ARE WELL BEHAVED THROUGH THE PERIOD.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 6 PM EDT TUESDAY FOR LMZ844>847.

&&

$$

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






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