Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 050545
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
145 AM EDT SAT SEP 5 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 323 PM EDT FRI SEP 4 2015

A WEAK LOW PRESSURE AREA WILL HELP TRIGGER SHOWERS AND POSSIBLY A
THUNDERSTORM THIS EVENING INTO EARLY TONIGHT OVER NORTHERN LOWER
MICHIGAN AS IT DRIFTS NORTHWARD. BEHIND IT...WARM AND HUMID AIR WILL
RETURN FROM THE SOUTH WITH SLIGHT CHANCES FOR SHOWERS AND
THUNDERSTORMS. SUNDAY WILL BE HOT AND DRY WITH HIGHS NEAR 90. THIS
WILL BE FOLLOWED BY A WET PERIOD LASTING LABOR DAY THROUGH TUESDAY
AS A COLD FRONT PASSES. BEHIND THIS FRONT...THE LATTER HALF OF THE
WORK WEEK WILL FEATURE MUCH DRIER CONDITIONS AND HIGHS IN THE LOW TO
MID 70S.

&&

.UPDATE...
ISSUED AT 1049 PM EDT FRI SEP 4 2015

DID NOT MAKE BIG CHANGES TO THE FORECAST...BUT DID ADD AREAS OF
FOG WORDING VERSUS PATCHY AS WE SHOULD SEE FOG IN MANY AREAS.
MASON AND CHARLOTTE HAVE ALREADY HAD VISIBILITIES DIP TO AROUND 1
MILE. EXPECTING FOG TO BECOME MORE PREVALENT THROUGH THE NIGHT
GIVEN LIGHT WINDS AND A MOIST AIR MASS.

AS FOR PRECIP CHANCES...FEEL WE MAY SEE ISOLATED TO SCATTERED
SHOWERS AND STORMS DEVELOP NEAR AND ESPECIALLY SOUTH OF INTERSTATE
96. THE RAP13 MODEL AS WELL AS THE NAM ARE INDICATING A WEAK LLJ
DEVELOPING ALONG WITH SOME MODEST 850MB MOISTURE TRANSPORT. THE
SOUTHERN CWA WILL BE NEAR A WEAK 850MB WARM FRONTAL FEATURE THAT
CAN BE SEEN IN THE 850MB DEW POINT FIELDS. HAVE ISOLATED SHOWERS
POSSIBLE NORTH WITH ISOLATED SHOWERS AND STORMS TO THE SOUTH.
LATEST RUN OF THE HRRR HAS THE SHOWERS AND STORMS DEVELOPING
TOWARD INTERSTATE 94 AROUND DAYBREAK. OTHER CONVECTION ALLOWING
MODELS HAVE ACTIVITY DEVELOPING SOONER IN THE NIGHT. NOTHING
STRONG...BUT WE WILL BE KEEPING AN EYE ON THE RADAR OVERNIGHT.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 323 PM EDT FRI SEP 4 2015

CONTINUED TO TRIM RAIN CHANCES FOR THIS EVENING AND EARLY TONIGHT AS
LOW LEVEL FORCING CONTINUES WITH SURFACE LOW DRIFTING NORTH. SOME
CONVECTION ALLOWING MODELS SUGGEST SHOWERS AND THUNDERSTORMS WILL
DEVELOP OR SPREAD NORTH TOWARDS THE I-94 CORRIDOR SATURDAY
MORNING...POSSIBLY ASSOCIATED WITH REMNANTS OF THE ONGOING
CONVECTION ACROSS NORTHERN INDIANA. ALSO EXPECT AT LEAST PATCHY FOG
AGAIN SATURDAY MORNING...BUT THIS WILL AGAIN BE TRICKY GIVEN THE
POTENTIAL FOR LOW CLOUDS.

SUNDAY STILL LOOKS HOT WITH HIGHS NEAR 90. ALSO STILL EXPECT IT TO
BE DRY PER GFS FORECAST SOUNDINGS...BUT AS NOTED IN THE PREVIOUS
DISCUSSION...LAKE BREEZE SHOWERS OR STORMS ARE NOT OUT OF THE
QUESTION AND THIS WILL HAVE TO BE WATCHED.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 323 PM EDT FRI SEP 4 2015

WE WILL SEE A BIG PATTERN CHANGE IN THE EXTENDED AS UPPER RIDGING AT
THE BEGINNING OF THE PERIOD IS REPLACED BY UPPER TROUGHING BY THE
END. IN BETWEEN WE ARE DEALING WITH A SLOW MOVING FRONT THAT SHOULD
BRING PERIODS OF RAIN...POSSIBLY HEAVY...FROM LATE MONDAY INTO EARLY
WEDNESDAY.

FORECAST UNCERTAINTY IS NOT SO MUCH WITH THE TIMING OF THAT INITIAL
FRONT BUT WITH THE HANDLING OF A SECONDARY FRONT THAT FOLLOWS AS THE
UPPER TROUGH DEEPENS. THE SPLIT BETWEEN THE SOLUTIONS VARIES FROM A
MUCH QUICKER GFS SOLUTION THAT BRINGS IT IN WEDNESDAY NIGHT AND
THURSDAY TO THE EURO WHICH HOLDS IF OFF UNTIL FRIDAY. DECIDED TO GO
TOWARDS THE LATER SOLUTION...SO KEPT THURSDAY DRY FOR NOW.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 142 AM EDT SAT SEP 5 2015

AREAS OF FOG WILL LIKELY BE IN AND OUT OF THE TAF SITES THROUGH
12Z OR 13Z. ABRUPT CHANGES IN VIS/CIG CAN BE EXPECTED AS THE FOG
DEVELOPS MAINLY NORTH OF THE AZO/BTL TERMINALS WHERE MORE CLEARING
HAS OCCURRED. VCTS THREAT EXISTS THIS MORNING MAINLY FOR AZO/BTL
PER HIGH RES MODEL GUIDANCE AND RADAR COLLABORATION. DAYTIME POP-
UP STORMS ARE POSSIBLE JUST ABOUT ANYWHERE TODAY WITH THE THREAT
ENDING CLOSE TO DARK.

&&

.MARINE...
ISSUED AT 323 PM EDT FRI SEP 4 2015

WINDS AND WAVES EXPECTED TO STAY LOW THROUGH SATURDAY NIGHT WITH A
SLIGHT UPTICK SUNDAY AHEAD OF AN APPROACHING COLD FRONT. LABOR DAY
COULD FEATURE WAVES OF 3 OR MORE FEET NORTH OF MUSKEGON AS WINDS
FROM THE SOUTH PERSIST AND CONTINUE TO INCREASE.


&&

.HYDROLOGY...
ISSUED AT 1054 AM EDT FRI SEP 4 2015

NO CONCERNS EXIST IN THE NEAR TERM. QUESTIONS ARISE GOING INTO NEXT
WEEK AS A BOUNDARY DRAPES ITSELF SOMEWHERE THROUGH OR NEAR THE GREAT
LAKES REGION.

AREA RIVERS HAVE RESPONDED PRETTY WELL TO YESTERDAYS RAINFALL.
LOCALIZED TOTALS OF MORE THAN TWO INCHES RESULTED IN DECENT UPWARD
TRENDS AT A FEW FORECAST POINTS. MOST NOTABLE IS SYCAMORE CREEK AT
HOLT...WHICH HAS LEVELED OFF ABOUT A FOOT BELOW ADVISORY CRITERIA.
PROVIDED THAT ADDITIONAL RAINFALL IS LIMITED...HOLT SHOULD CONTINUE
ITS DOWNWARD TREND. OTHER SITES HAVE ALSO LEVELED OFF AND RESPONSES
HAVE BEEN MINOR.

RAINFALL THROUGH THE WEEKEND IS EXPECTED TO BE SCATTERED WITH
LOCALIZED HEAVY RAIN POSSIBLE IN OR AROUND THUNDERSTORMS. CONDITIONS
ARE NOT FAVORABLE FOR WIDESPREAD HEAVY RAIN. A PATTERN CHANGE WILL
TAKE PLACE NEXT WEEK AND ITS ASSOCIATED BOUNDARY LOOKS TO BE MOVING
SLOWLY. DIFFERENCES IN LONG RANGE MODELS PUT A CAP ON ANY HIGH
CONFIDENCE. HOWEVER...PWATS ARE 1.5-2.0 INCHES AND THE SLOW
PROGRESSION OF THE BOUNDARY COULD RESULT IN PRETTY DECENT RAINFALL
TOTALS MONDAY THROUGH WEDNESDAY. THE SETUP MAY SUGGEST MORE THAN AN
INCH...WITH AREAS EXCEEDING A COUPLE OF INCHES IF STORMS ARE SLOW
MOVERS. THIS WILL LIKELY BE THE FOCUS HYDRO-WISE OVER THE NEXT
FEW DAYS.

&&

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

$$

UPDATE...DUKE
SYNOPSIS...TJT
SHORT TERM...TJT
LONG TERM...OSTUNO
AVIATION...HOVING
HYDROLOGY...JAM
MARINE...TJT



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