Area Forecast Discussion
Issued by NWS Grand Rapids, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KGRR 041407
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1007 AM EDT FRI SEP 4 2015

LATEST UPDATE...
UPDATE

.SYNOPSIS...
ISSUED AT 307 AM EDT FRI SEP 4 2015

A WEAK AREA OF LOW PRESSURE WILL REMAIN OVER LOWER MICHIGAN
THROUGH TODAY. THIS SYSTEM WILL GENERATE A FEW SHOWERS AND PERHAPS
A THUNDERSTORM. THE VERY WARM AIRMASS RETURNS FOR SATURDAY.
ACCOMPANYING THE ARRIVAL OF THIS WARM AIR COULD BE SOME
THUNDERSTORMS. HIGH PRESSURE CONTROLS THE WEATHER FOR SUNDAY AND
THAT SHOULD BE ONE OF THE WARMER DAYS OF SEASON. A COLD FRONT
NEARS FOR LABOR DAY WHICH COULD LEAD TO SOME AFTERNOON
THUNDERSTORMS WITH THE VERY WARM AIRMASS CONTINUING.

&&

.UPDATE...
ISSUED AT 1007 AM EDT FRI SEP 4 2015

CANCELLED DENSE FOG ADVISORY BASED ON OBSERVATIONS IN THAT AREA
SHOWING VISIBILITIES CLIMBING TO ABOVE A MILE. AS MENTIONED
EARLIER...WIDESPREAD CEILINGS OF LOW CLOUDS AND THEIR ASSOCIATED
ABSORPTION AND DOWN-WELLING OF LONGWAVE RADIATION HELPED TO
MITIGATE THE FOG.

ALSO REDUCED RAIN CHANCES BASED ON CURRENT RADAR AND SATELLITE
TRENDS. CONVECTION ALLOWING GUIDANCE SUGGESTS SCATTERED DIURNALLY
FORCED SHOWERS WILL DEVELOP THIS AFTERNOON MAINLY NORTHEAST OF
THE AREA IN A WARM FRONTAL ZONE ASSOCIATED WITH A WEAK SURFACE
LOW OVER CENTRAL MICHIGAN DRIFTING NORTH TODAY.

&&

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 307 AM EDT FRI SEP 4 2015

FOG HAS BEEN A CHALLENGE THIS MORNING. WE DEVELOPED SOME THICK FOG
DURING THE EVENING...BUT THE THICKER MID TO UPPER LEVEL CLOUDS
HAVE CAUSED THE FOG TO THIN OUT SOMEWHAT. I CHECKED WITH MANY OF
OUR CENTRAL COUNTIES...ALONG WITH LOOKING AT WEBCAMS...AND IT
APPEARS THAT GRATIOT AND MONTCALM ARE SEEING SOME DENSE FOG. I
WILL FEATURE A DENSE FOG ADVISORY FOR THESE COUNTIES. IF CLEARING
DOES DEVELOP ELSEWHERE WE MAY NEED TO EXPAND THE HEADLINE...BUT
FOR NOW IT LOOKS LIKE STRATUS IT TAKING OVER.

AS FOR THE RAIN POTENTIAL...WITH THE MID TO UPPER FLOW BEING
CYCLONIC AND THE AIRMASS STILL VERY MOIST...WE SHOULD SEE SHOWERS
AROUND TODAY AND INTO TONIGHT. INSTABILITY DEVELOPS THIS AFTERNOON
SO I FEATURED A FEW THUNDERSTORMS AS WELL. AS FOR
TONIGHT...INITIALLY WAS THINKING ONLY SHOWERS BUT MODELS ARE
SHOWING ELEVATED INSTABILITY ARRIVING FROM THE SOUTH. THUS I WILL
MENTION THUNDER INTO SATURDAY.

NOT SURE WE WILL STAY DRY ON SUNDAY. THE ATMOSPHERE DOES BECOME
UNSTABLE IN THE AFTERNOON. NO SIGNIFICANT FORCING. WE MAY NEED TO
MONITOR FOR POSSIBLE CONVECTION IF A LAKE BREEZE CAN DEVELOP. WILL
KEEP IT DRY FOR NOW.

VERY WARM TEMPERATURES ARE EXPECTED BOTH SATURDAY AND SUNDAY.
HIGHS SHOULD TOP MID 80S AT MOST LOCATIONS AS 925 MB TEMPERATURES
REACH INTO THE MID 20 DEG C LEVEL.  SOME 90S ARE POSSIBLE.

.LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY)
ISSUED AT 307 AM EDT FRI SEP 4 2015

PRIMARY CONCERN IS WITH THUNDERSTORM POTENTIAL MONDAY AFTERNOON INTO
WEDNESDAY. THE BEST CHANCE FOR RAINFALL APPEARS TO BE TUESDAY AND
TUESDAY NIGHT WITH SOME LOCATIONS LIKELY GETTING AN INCH OR TWO OF
RAINFALL. I WOULD NOT BE SURPRISED TO SEE A FEW STRONGER STORMS ON
TUESDAY.

THERE ARE DIFFERENCES IN THE TIMING OF THIS SYSTEM WITH THE 00Z
GUIDANCE...WITH THE ECMWF NOW THE QUICKEST TO EXIT THE BOUNDARY
TUESDAY NIGHT. MODELS GENERALLY AGREE THAT A COLD FRONT WILL WASH
OUT ACROSS THE REGION MONDAY. SOME SCATTERED SHOWERS AND STORMS WILL
BE POSSIBLE MONDAY AFTERNOON AND EVENING AS THIS OCCURS. THE
BOUNDARY LIFTS THROUGH AS A WARM FRONT TUESDAY AS THE RIGHT ENTRANCE
REGION OF THE UPPER LEVEL JET CORE MOVES OVERHEAD. WITH UL DIV...A
MID LEVEL VORT LOBE MOVING THROUGH BETWEEN 18Z-00Z...AND THE SFC
BOUNDARY IN THE AREA THERE COULD BE SOME STRONGER STORMS. THE LLJ
HOLDS UP AT 30-35 KTS SO THERE MAY BE AT LEAST MODEST SHEAR DOWN
LOW.

MODEL QPF INDICATES POCKETS OF HEAVIER RAIN ARE POSSIBLE TUESDAY
INTO EARLY WEDNESDAY. THE ECMWF SWEEPS THE FRONT THROUGH QUICKER
THAN THE GFS AND GEM...WHICH ARE ALMOST IN LOCK STEP AND LINGER SOME
HEAVIER RAINS ACROSS THE SOUTHERN CWA WELL INTO WEDNESDAY AFTERNOON
AND EVENING. GFS PW VALUES ARE QUITE HIGH TUESDAY NIGHT AND
WEDNESDAY...APPROACHING 2.00" FROM I-96 TO THE SOUTH. ANY
SHOWERS/STORMS IN THIS ENVIRONMENT WOULD BE HEAVY RAIN PRODUCERS
WITH IMPRESSIVE HOURLY RAINFALL RATES.

COOLER AND DRIER WEATHER SETTLES IN FOR THE SECOND HALF OF THE WEEK.
THERE MAY BE SOME SYNOPTIC SCALE INFLUENCE FOR THE GREAT LAKES
REGION LATE IN THE WEEK WITH TROPICAL STORM IGNACIO EXPECTED TO GET
ABSORBED IN UPPER LEVEL ENERGY ACROSS ALASKA...WHICH MAY DEEPEN
LONGWAVE TROUGHING OVER THE GREAT LAKES BY THE END OF THE WEEK. COOL
AND PERHAPS SHOWERY CONDITIONS ARE POSSIBLE BY FRIDAY AND SATURDAY
AS THIS OCCURS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 719 AM EDT FRI SEP 4 2015

IFR AND LOWER CONDITIONS WILL PREVAIL FOR A FEW HOURS THIS
MORNING. THE TREND SUPPORTS DIMINISHING THESE LOW CONDITIONS
SOONER AS THE FOG/STATUS IS NOT QUITE AS LOW AS FORECASTED
EARLIER. THE ATMOSPHERE BECOMES UNSTABLE THIS AFTERNOON...SO SOME
THUNDERSTORMS COULD DEVELOP. FOG COULD REDEVELOP THIS EVENING.
LATER AT NIGHT AROUND KAZO AND KBTL WE COULD SEE A FEW STORMS
DEVELOP AS THE WARMER AIRMASS STARTS TO RETURN.


&&

.MARINE...
ISSUED AT 307 AM EDT FRI SEP 4 2015

RELATIVELY WEAK PRESSURE GRADIENT INTO SATURDAY WILL ACT TO KEEP
THE WINDS AND WAVES DOWN. SOME INCREASE IN THE WIND SHOULD OCCUR
ON SUNDAY AND INTO MONDAY AS A COLD FRONT NEARS FROM THE WEST
CAUSING THE PRESSURE GRADIENT TO WEAKEN. WAVE WILL BUILD
SLIGHTLY BUT HAZARDOUS CONDITIONS SHOULD STILL BE LIMITED.


&&

.HYDROLOGY...
ISSUED AT 1110 AM EDT THU SEP 3 2015

NO IMMEDIATE CONCERNS TO BE AWARE OF TODAY REGARDING RIVER
FLOODING.

HEAVY RAINFALL ASSOCIATED WITH THUNDERSTORM ACTIVITY WILL QUICKLY
PASS THROUGH THE AREA THIS MORNING AND THROUGH EARLY AFTERNOON.
PONDING MAY OCCUR ON ROADWAYS AND LOW LYING AREAS IN AND AROUND
THE HEAVIER RAINFALL. MUCH OF THE HEAVIER ACTIVITY WILL VACATE
THE REGION BY MID AFTERNOON.

THE NEXT 7 DAYS REMAINS ACTIVE AND INCLUDES MULTIPLE CHANCES FOR
RAIN. 7 DAY AREA AVERAGE RAINFALL OF ONE TO TWO INCHES IS POSSIBLE
WITH LOCALLY HIGHER AMOUNTS IN THE VICINITY OF THUNDERSTORMS.
RECENT DRY WEATHER AND LOW RIVER LEVELS...COUPLED WITH THE
PIECEWISE FASHION OF THE RAINFALL...SHOULD ALLOW FOR THE GROUND TO
SOAK UP MUCH OF THE ONSET OF MOISTURE. RUNOFF THEREAFTER IS
LIKELY TO BE HANDLED WELL BY RIVERS...AS THEY HAVE PLENTY OF ROOM
TO TAKE ON ADDITIONAL WATER.

&&

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

$$

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


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.