Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 211929
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
329 PM EDT THU MAY 21 2015

LATEST UPDATE...
SYNOPSIS/SHORT TERM/LONG TERM/MARINE

.SYNOPSIS...
ISSUED AT 329 PM EDT THU MAY 21 2015

SCATTERED RAIN SHOWERS WILL MOVE SOUTH THROUGH THE AREA WITH A COLD
FRONT. BEHIND THIS FRONT...HIGH TEMPERATURES FRIDAY WILL BE AROUND
60...WHICH IS ABOUT 10 DEGREES BELOW NORMAL THIS TIME OF YEAR.

PATCHY FROST IS POSSIBLE OVER PARTS OF CENTRAL LOWER MICHIGAN FRIDAY
MORNING. THERE IS EVEN BETTER POTENTIAL FOR FROST SATURDAY MORNING.
RAIN CHANCES RETURN SUNDAY AFTERNOON WITH A WARMER AND WETTER
PATTERN LASTING WELL INTO NEXT WEEK.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY NIGHT)
ISSUED AT 329 PM EDT THU MAY 21 2015

SCATTERED SHOWERS ARE POSSIBLE THIS EVENING. COOLER THAN NORMAL
TEMPERATURES WILL PERSIST THROUGH FRIDAY NIGHT. FROST FORMATION IS
POSSIBLE TONIGHT MAINLY ACROSS CENTRAL LOWER MICHIGAN. WIDESPREAD
AREAS OF FROST ARE MORE LIKELY LATE FRIDAY NIGHT INTO SATURDAY
MORNING.

A WEAK COLD FRONT WILL DROP SOUTH THROUGH LOWER MICHIGAN THIS
EVENING AS AN UPPER LEVEL SHORTWAVE PROPAGATES OVER THE LOWER GREAT
LAKES REGION. MOISTURE IS CONFINED TO THE MID LEVELS WITH CLOUD
BASES AROUND 9K FEET. SFC DEWPOINTS ARE ONLY IN THE 30S TO LOWER
40S. ALL THIS SHOULD RESULT IN ISOLATED TO SCATTERED LIGHT RAIN
SHOWERS...CONFIRMED BY THE LAST SEVERAL RUNS OF THE RAP AND HRRR. A
SIMILAR AIRMASS YESTERDAY EVENING RESULTED IN A RAIN/SLEET MIX
MAINLY IN THE CHICAGO AREA. BUT PRECIP THIS EVENING WILL LIKELY NOT
BE HEAVY ENOUGH TO CAUSE SIGNIFICANT WET-BULBING.

MID-LEVEL CLOUDS WILL START TO CLEAR OUT FROM NORTH TO SOUTH LATE
TONIGHT AND WINDS WILL SUBSIDE AS THEY VEER NORTHERLY BEHIND THE SFC
FRONT. THIS SHOULD ALLOW DECENT RADIATIONAL COOLING CONDITIONS TO
SET UP AFTER MIDNIGHT. FROST WILL BE POSSIBLE ACROSS CENTRAL LOWER
MICHIGAN.

ANOTHER COOL DAY IS EXPECTED ON FRIDAY WITH NORTHWEST FLOW AT THE
SURFACE. BUT PLENTY OF SUNSHINE IS EXPECTED AS A SURFACE HIGH BUILDS
IN. UPPER RIDGING WILL CONTINUE TO BUILD IN THROUGH SATURDAY NIGHT
AS THE SFC HIGH SLIDES OFF TO THE SOUTHEAST. FAIR WEATHER IS
EXPECTED FRIDAY NIGHT THROUGH SATURDAY NIGHT...BUT THIS SHOULD ALLOW
GOOD FROST CONDITIONS TO SET UP FRIDAY NIGHT INTO SATURDAY MORNING.
WITH CLEAR SKIES AND LIGHT WINDS...LOWS WILL LIKELY DROP INTO THE
LOW TO MID 30S ACROSS MUCH OF THE FORECAST AREA. SOUTHWEST RETURN
FLOW FINALLY SETS UP SATURDAY...ALONG WITH PLENTY OF SUNSHINE AND
HIGHS IN THE LOWER 70S.

.LONG TERM...(SUNDAY THROUGH THURSDAY)
ISSUED AT 329 PM EDT THU MAY 21 2015

THE MAIN STORY IN THE LONG TERM PERIOD IS THAT WE WILL FINALLY SEE
WARMER TEMPERATURES AS THE PERSISTENT HUDSON BAY UPPER LOW RETREATS
AND WE GET INTO DEEP SOUTHWEST FLOW. HIGHS IN THE 70S ARE LIKELY
AWAY FROM LK MI... WITH PERHAPS 80 DEGREES AND NOTICEABLY MORE HUMID
FROM MONDAY ON.

PROLONGED WARM ADVECTION PATTERN WITH A FLOW OFF THE GULF AND A
QUASI STATIONARY FRONTAL BOUNDARY WILL LIKELY LEAD TO ROUNDS OF
SHOWERS AND POSSIBLE TSTMS. HOWEVER THE TIMING/LOCATION/DURATION OF
CONVECTIVE EPISODES AND DAILY POSITION OF THE SFC FRONT IS LOW
CONFIDENCE AT THIS TIME.  CURRENTLY WE HAVE THE HIGHEST POPS ON
SUNDAY NIGHT AND MONDAY WHICH IS WHEN THE SFC WARM FRONT IS LIFTING
NORTH THROUGH THE AREA.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 153 PM EDT THU MAY 21 2015

VFR WEATHER WILL CONTINUE THE NEXT 24 HOURS. THE AREA OF CLOUDS
CURRENTLY OVERHEAD WITH BASES AT OR ABOVE 12,000 FT WILL MOVE OUT
THIS AFTERNOON... AND WILL BE FOLLOWED BY A NARROW BAND OF CLOUDS
DROPPING DOWN FROM THE NORTH THIS EVENING. THESE CLOUDS WILL HAVE
BASES BETWEEN 6000 AND 10,000 FT AND MAY PRODUCE A FEW LIGHT
RAIN SHOWERS OR SPRINKLES BUT NO REDUCTIONS TO VSBYS. CLEAR SKIES
WILL FOLLOW BEHIND THIS BAND OF CLOUDS FOR LATER NIGHT AND FRIDAY
MORNING. A PERIOD OF GUSTY WEST WINDS IS EXPECTED THROUGH 00Z
BEFORE DIMINISHING AND TURNING NORTHERLY LATER TONIGHT.


&&

.MARINE...
ISSUED AT 329 PM EDT THU MAY 21 2015

BREEZY WESTERLY WINDS WILL CONTINUE THIS AFTERNOON WITH WAVES IN
THE 1 TO 3 FOOT RANGE. SCATTERED LIGHT SHOWERS WILL BE POSSIBLE
LATE THIS AFTERNOON AND EVENING. WINDS ARE EXPECTED TO SUBSIDE
AND VEER NORTHERLY BEHIND A WEAK COLD FRONT OVERNIGHT. WAVES WILL
BE 1 TO 2 FEET. NORTHERLY WINDS OF 5 TO 10 KNOTS ON FRIDAY WITH
WAVES AROUND 1 FOOT. FRIDAY WILL FEATURE PLENTY OF SUNSHINE BUT
STILL COOLER THAN NORMAL TEMPS. WINDS WILL TURN SOUTHWESTERLY ON
SATURDAY IN THE 5 TO 15 KNOT RANGE WITH WAVES AROUND 1 FOOT.

&&

.HYDROLOGY...
ISSUED AT 1240 PM EDT THU MAY 21 2015

NO CONCERNS THROUGH THE WEEKEND. PRECIPITATION THAT COULD AFFECT
MAINSTEM RIVERS IS NOT EXPECTED UNTIL LATE SUNDAY...WHICH MARKS THE
START OF A WETTER PATTERN LASTING WELL INTO THE COMING WORK WEEK.
NATIONAL GUIDANCE ADVERTISES UNIFORM RAINFALL TOTALS OF 1-1.5
INCHES ACROSS THE AREA THROUGH THURSDAY MORNING. GIVEN THAT BASE
FLOWS ARE NEAR OR BELOW NORMAL AND THAT RAIN SHOULD BE SPREAD OUT
OVER TIME...WE EXPECT FAIRLY GENTLE RISES WILL BE UNDERWAY BY THE
MIDDLE OF NEXT WEEK.

THAT SAID...FORECASTING CONVECTIVE RAINFALL THIS FAR OUT IS
HIGHLY UNCERTAIN SO THERE STILL REMAINS A FAIRLY WIDE RANGE OF
POSSIBILITIES FOR RAINFALL AND RIVER RESPONSES AT THIS POINT.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...FROST ADVISORY FROM 3 AM TO 9 AM EDT FRIDAY FOR MIZ037>040-
     043>046.

LM...NONE.
&&

$$

SYNOPSIS...TJT
SHORT TERM...EBW
LONG TERM...MEADE
AVIATION...MEADE
HYDROLOGY...TJT
MARINE...EBW


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