Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 171748
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
148 PM EDT SUN MAY 17 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 315 AM EDT SUN MAY 17 2015

A WARM FRONT WILL LIFT NORTH TODAY PUTTING SOUTHERN LOWER MICHIGAN
IN AN INCREASINGLY WARM AND HUMID AIRMASS. AN ISOLATED SHOWER OR
STORM IS POSSIBLE TODAY WITH A MUCH BETTER CHANCE FOR SHOWERS AND
THUNDERSTORMS LATE THIS AFTERNOON AND EVENING. A STRONG COLD
FRONT WILL MOVE THROUGH MONDAY BRINGING A CONTINUED CHANCE FOR A
SHOWER OR THUNDERSTORM. MUCH COOLER WEATHER WILL MOVE IN TUESDAY
THROUGH MIDWEEK.

&&

.UPDATE...
ISSUED AT 1129 AM EDT SUN MAY 17 2015

I CURRENTLY REMAIN UNIMPRESSED ON THE CHANCE OF SEVERE STORMS
LATE THIS AFTERNOON AND THIS EVENING. THE RAP AND NAM FROM THE
LATEST MODEL RUNS HAVE TO CORE OF THE LOW LEVEL JET GOING OVER
NORTHERN LAKE MICHIGAN INTO THE UPPER PENINSULA BETWEEN 4 PM AND
MIDNIGHT. THAT PUTS SOUTHWEST MICHIGAN IN THE SPEED DIVERGENCE
AREA OF THE LOW LEVEL JET (NOT GOOD FOR SEVERE STORMS). THE UPPER
DIVERGENCE FROM THE UPPER LEVEL JET CORE IS OVER THE LOW LEVEL
JET MAX (NORTHERN WISCONSIN) THIS AFTERNOON AND EVENING...NOT
OVER SOUTHWEST MICHIGAN. THE DEEP LAYER SHEAR GREATER THAN 35
KNOTS IS MOSTLY WEST OF US-131 AND NORTH OF MKG THIS AFTERNOON AND
EVENING...REALLY IT IS OVER WISCONSIN (40 TO 60 KNOTS). THE SPC
ENSEMBLE 09Z HAS THE 30 TO 40 PERCENT CHANCE FOR SEVERE STORMS
OVER WISCONSIN THIS AFTERNOON AND EVENING...MEANWHILE A 10 PERCENT
AREA DOES GET INTO WESTERN LOWER MICHIGAN WEST OF US-131 FROM 4 PM
TILL 8 PM. ALL OF THIS TELL ME THE RISK FOR SEVERE STORMS OVER
SOUTHWEST MICHIGAN WOULD BE VERY LOW. STILL IT IS NOT ZERO SO WE
WILL HAVE TO WATCH AS CONDITIONS DEVELOP THIS AFTERNOON AND
EVENING.

OVERALL OUR BEST CHANCE FOR THUNDERSTORMS IS THIS EVENING. I HAVE
NOT SIGNIFICANTLY CHANGED OUR FORECAST IN THAT WAY.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 315 AM EDT SUN MAY 17 2015

OUR PRIMARY SHORT TERM FCST CHALLENGE IS TO DETERMINE
PROBABILITIES FOR CONVECTION TODAY THROUGH MONDAY.

THE AIRMASS OVER OUR FCST AREA WILL BECOME INCREASINGLY WARM AND
HUMID TODAY AS A WARM FRONT GRADUALLY MOVES NORTH OF OUR AREA.
THERE IS JUST A SMALL CHANCE OF AN ISOLATED SHOWER OR THUNDERSTORM
BUT MOST OF OUR AREA WILL STAY DRY THIS MORNING THROUGH MOST OF
THE AFTERNOON.

00Z 4KM WRF-NMM SIM Z GUIDANCE AND THE NSSL WRF SUGGEST THAT
SHOWERS AND THUNDERSTORMS ARE LIKELY TO DEVELOP ACROSS OUR AREA
LATE THIS AFTERNOON THROUGH THE EVENING. CONVECTIVE DEVELOPMENT LATE
THIS AFTERNOON AND EARLY EVENING WILL BE AIDED BY WEAK TO MODERATE
INSTABILITY WITH POTENTIAL FOR SB CAPE VALUES TO REACH AROUND
1000-2000 J/KG.

SHOWERS AND STORMS LATE THIS EVENING WILL BE AIDED BY FORCING
FROM A 35 TO 40 KT LLJ AND STRONG 1000-850 MB MOISTURE TRANSPORT.
A FEW SHOWERS OR ISOLATED STORMS MAY LINGER VERY LATE TONIGHT BUT
THE MOST LIKELY TIME FRAME FOR CONVECTION SEEMS TO BE FROM AROUND
21Z THIS AFTERNOON THROUGH 06Z TONIGHT.

CONVECTIVE POTENTIAL FOR MONDAY IS LARGELY CONTINGENT ON EXACT
COLD FRONTAL TIMING. A CONSENSUS OF LATEST GUIDANCE SUGGESTS THAT
THE BETTER CHANCE FOR STORMS WILL LIKELY STAY SE OF OUR FCST
AREA... BUT THAT SOME SHOWERS AND STORMS MAY REDEVELOP MAINLY OVER
OUR SE FCST AREA PRIOR TO FROPA.

SHORT RANGE GUIDANCE CONTINUES TO SUGGEST SOME WEAK TO MODERATE
INSTABILITY WILL DEVELOP JUST AHEAD OF THE FRONT SO THIS WILL NEED
TO BE MONITORED SINCE FORCING FROM THE FRONT WILL BE STRONG.
HOWEVER IF FRONT MOVES THROUGH FASTER AS SUGGESTED BY THE 00Z GFS
THEN ALL OF OUR FCST AREA SHOULD STAY DRY MONDAY.

IT WILL TURN BREEZY BEHIND THE FRONT MONDAY NIGHT THROUGH TUESDAY
WITH STRONG NW FLOW CAA. MAX TEMPS TUESDAY WILL ONLY REACH THE
50S.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 315 AM EDT SUN MAY 17 2015

THREAT OF FROST EXISTS ON TUESDAY NIGHT AS COLD DRY AIR MASS SETTLES
INTO THE REGION FROM THE NORTH. HOWEVER THERE IS STILL SOME QUESTION
AS TO HOW QUICK THE SFC RIDGE BUILDS IN AND WHETHER OR NOT THE WINDS
DIE OFF. EXTENT OF CLEARING IS ALSO UNCERTAIN AT THIS TIME.

OTHERWISE A RATHER QUIET/UNEVENTFUL LONG TERM PERIOD EXPECTED WITH
SURFACE RIDGING AND RELATIVELY COOL DRY AIR MASS DOMINATING OUR
WEATHER. THIS PATTERN SHOULD RESULT IN A DECENT AMOUNT OF SUNSHINE
ALONG WITH LARGE DIURNAL TEMPERATURES SWINGS. EXPECT COOL NIGHTS AND
GENERALLY PLEASANT DAYS WITH LOW HUMIDITIES AND HIGHS MODERATING A
FEW DEGREES EACH DAY.

ONE THING TO WATCH HOWEVER IS THE POTENTIAL FOR CONSIDERABLE MID AND
HIGH CLOUDS AND EVEN SOME SPRINKLES ON WEDNESDAY RELATED TO A SYSTEM
PASSING BY JUST TO OUR SOUTH IN THE ZONAL FLOW. THEN...THE NORTHWEST
FLOW ALOFT ON THURSDAY AND FRIDAY COULD ALSO LEAD TO SOME BRIEF
PERIODS OF THICKER CLOUDS AND SPRINKLES AS WEAK FAST MOVING
SHORTWAVES OCCASIONALLY DROP THROUGH.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 148 PM EDT SUN MAY 17 2015

A MIX OF VFR AND MVFR CEILINGS WERE OVER THE REGION AS OF 17Z.
THIS IS EXPECTED TO TREND TO MORE VFR AS CEILINGS GRADUALLY LIFT
THIS AFTERNOON. FOR THE MOST PART VFR CONDITIONS WILL PREVAIL
THEREAFTER INTO MID DAY MONDAY.

INSTABILITY AND MOISTURE WAS INCREASING ACROSS THE AREA AND
SHOWERS AND THUNDERSTORMS SHOULD BEGIN TO DEVELOP AFTER 20Z.
STORMS SHOULD REMAIN SCATTERED ACROSS THE AREA THROUGH ABOUT 09Z
TONIGHT WHEN DRIER AIR ARRIVES. A COLD FRONT WILL PASS THROUGH SW
MI MONDAY AFTERNOON BUT AT THIS POINT IS APPEAR IT WILL PASS
THROUGH MAINLY DRY AS THE DEEPEST MOISTURE RACES EAST...WELL AHEAD
OF IT. LEFT ANY MENTION OF SHOWERS/STORMS OUT OF THE TAFS AFTER
09Z.

SOUTHERLY WINDS WILL GUST TO AROUND 20 KNOTS THROUGH THIS
EVENING...THEN BECOMING SOUTHWEST LATE TONIGHT AT 10-15 KTS.

&&

.MARINE...
ISSUED AT 315 AM EDT SUN MAY 17 2015

WE HAVE EXTENDED THE MARINE DENSE FOG ADVISORY THROUGH TONIGHT
SINCE A VERY WARM AND HUMID AIRMASS WILL CONTINUE TO ADVECT IN
OVER RELATIVELY COLD LAKE WATERS AND RESULT IN AREAS OF DENSE FOG.
SOUTHERLY WINDS WILL INCREASE SOMEWHAT THIS AFTERNOON THROUGH
TONIGHT RESULTING IN GRADUALLY INCREASING WAVE HEIGHTS. HOWEVER
WINDS AND WAVE HEIGHTS WILL STAY BELOW SMALL CRAFT CRITERIA
THROUGH TONIGHT. THUNDERSTORMS WILL POSE A HAZARD TO MARINERS LATE
THIS AFTERNOON AND EVENING.


&&

.HYDROLOGY...
ISSUED AT 1210 AM EDT SUN MAY 17 2015

THE MAIN THREAT THROUGH THE NEXT 24 HOURS WILL BE THE POSSIBILITY
FOR LOCALIZED HEAVY RAINFALL.

A MAJORITY OF THE AREA STREAMS AND RIVERS ARE RUNNING WELL BELOW
ADVISORY LEVELS WITH A COUPLE OF SITES SLIGHTLY BELOW. SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO DEVELOP AND TRAVEL EAST OUT OF THE
UPPER MIDWEST THIS EVENING AND INTO TONIGHT. AREA AVERAGE
RAINFALL MAY RUN FROM A FEW TENTHS OF AN INCH UPWARDS OF A HALF
INCH. LOCALIZED HEAVY POCKETS WILL CREATE GREAT VARIATIONS IN
RAINFALL TOTALS IN SHORT DISTANCES. LOCATIONS THAT ARE AFFECTED BY
HEAVIER RAINFALL MAY EXPERIENCE LOCALIZED PONDING OR TEMPORARY
STREET FLOODING WITH SMALL CREEK AND STREAM FLUCTUATIONS
POSSIBLE. LARGER RIVERS ARE EXPECTED TO REMAIN BELOW ACTION
STAGE THROUGH THE PERIOD AS FEEDBACK TIMES WILL TAKE US INTO
DRIER WEATHER FOR THE UPCOMING WEEK.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...DENSE FOG ADVISORY UNTIL 8 AM EDT MONDAY FOR LMZ844>849.

&&

$$

UPDATE...WDM
SYNOPSIS...LAURENS
SHORT TERM...LAURENS
LONG TERM...MEADE
AVIATION...JK
HYDROLOGY...JAM
MARINE...LAURENS



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