Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 021757
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
157 PM EDT WED SEP 2 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 306 AM EDT WED SEP 2 2015

HIGH PRESSURE OVER THE LOWER OHIO VALLEY WILL CONTINUE TO DRAW AND
UNSEASONABLY WARM AIRMASS INTO THE GREAT LAKES REGION INTO
THURSDAY. A WEAK COLD FRONT WILL DROP DOWN FROM ONTARIO THURSDAY
INTO FRIDAY. AS A RESULT SHOWERS AND THUNDERSTORMS WILL INCREASE
ACROSS THE REGION LATER TONIGHT AND INTO THURSDAY.

&&

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 306 AM EDT WED SEP 2 2015

SOME CONCERN THAT WE COULD SEE MORE WIDESPREAD SHOWER AND
THUNDERSTORM ACTIVITY LATER TONIGHT INTO THURSDAY. A MID LEVEL
SHORTWAVE MOVES IN FROM THE WEST NORTHWEST TONIGHT INTO THURSDAY.
AT THE SURFACE A BACKDOOR COLD FRONT DROPS DOWN. THE ATMOSPHERE IS
UNSTABLE AND REMAINS THAT WAY THROUGH THE PASSAGE OF THESE
FEATURES. GIVEN THE SHOWERS THAT POPPED UP RECENTLY TELLS ME THAT
THERE IS NOT MUCH HOLDING BACK THE CONVECTION IN THIS UNSEASONABLY
WARM AIRMASS. SO I RAISED POPS AND QPF FOR TONIGHT INTO THURSDAY.

WILL NEED TO MONITOR TEMPERATURE FORECASTS AS WELL. IF WE DO END
UP WITH A CONVECTIVE COMPLEX LATE TONIGHT INTO THURSDAY...OUR VERY
WARM TEMPERATURE FORECAST FOR THURSDAY COULD TOO HIGH.

.LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY)
ISSUED AT 306 AM EDT WED SEP 2 2015

A CONSENSUS OF LATEST MEDIUM RANGE GUIDANCE CONTINUES TO SUGGEST
THAT VERY WARM AND HUMID WEATHER WILL CONTINUE THROUGH THE HOLIDAY
WEEKEND. MAX TEMPS DAILY WILL REACH THE 85 TO 90 DEGREE RANGE WITH
MIN TEMPS IN THE 60S. HUMIDITY LEVELS WILL REMAIN HIGH WITH DEW
POINT VALUES WELL INTO THE 60S TO AROUND 70 DEGREES.

MAINLY DRY WX IS ANTICIPATED FRIDAY NIGHT THROUGH SUNDAY WITH THE
UPPER LEVEL RIDGE IN PLACE. HOWEVER ISOLATED SHOWERS AND NON SEVERE
STORMS ARE POSSIBLE FROM TIME TO TIME AS SEVERAL WEAK UPPER LEVEL
DISTURBANCES MOVE THROUGH. THIS IN CONJUNCTION WITH SOME INSTABILITY
AND FORCING FROM MESOSCALE BOUNDARIES SUCH AS LAKE BREEZE
CONVERGENCE MAY BE SUFFICIENT ENOUGH TO CAUSE DEVELOPMENT OF
ISOLATED SHOWERS OR STORMS.

A COLD FRONT WILL BRING A RELATIVELY BETTER CHANCE FOR MORE
ORGANIZED SHOWERS AND STORMS LATE MONDAY THROUGH MONDAY NIGHT INTO
TUESDAY. HOWEVER THERE IS STILL SOME UNCERTAINTY AS TO TIMING AND
STRENGTH OF THAT FRONT. A SOMEWHAT COOLER AND LESS HUMID AIRMASS
SHOULD FINALLY MOVE IN FOR THE MIDDLE OF NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 157 PM EDT WED SEP 2 2015

THE RISK OF SHOWERS AND TSTMS THIS AFTERNOON AND EVENING WILL BE
PRIMARILY NORTH AND EAST OF THE TERMINALS IN SW AND SC LWR MI.
EXPECT VFR CONDITIONS WITH A SCATTERED TO BROKEN CUMULUS DECK WITH
BASES AROUND 4000-5000 FT.

THE CHANCE OF SHOWERS AND TSTMS OVER SW LWR MI IS EXPECTED TO
INCREASE FROM NORTHWEST TO SOUTHEAST LATE TONIGHT AND THURSDAY.
WILL HAVE CONVECTION DEVELOPING 06Z-09Z AT MKG/GRR/AZO/BTL WHERE
CHANCES ARE HIGHEST... BUT WILL HOLD OFF AT LAN AND JXN UNTIL
AFTER DAYBREAK THURSDAY (STILL SOME FOG AT THESE SITES THOUGH).

WILL FCST PREDOMINATELY MVFR CONDITIONS IN THE SHOWERS AND
TSTMS... BUT IF STORMS PERSIST AND HEAVY RAIN
DEVELOPS... CONDITIONS COULD SETTLE INTO IFR FOR A TIME LATE
TONIGHT AND THURSDAY AT SOME OF THE TAF SITE.


&&

.MARINE...
ISSUED AT 306 AM EDT WED SEP 2 2015

WINDS AND WAVES WILL REMAIN ON THE LOW SIDE DUE TO THE WEAK
PRESSURE GRADIENT THAT WILL BE IN PLACE. AN OFFSHORE FLOW DEVELOPS
ON THE BACKSIDE OF THE BACKDOOR COLD FRONT BY FRIDAY. THIS WILL
ACT TO KEEP THE WAVES LOW FOR OUR NEARSHORE WATERS. FOG COULD
BECOME AN ISSUE...AND LOCALLY HIGHER WINDS COULD ACCOMPANY THE
THUNDERSTORMS.


&&

.HYDROLOGY...
ISSUED AT 1147 AM EDT WED SEP 2 2015

CONFIDENCE IS INCREASING THAT OUR AREA WILL SEE AT LEAST SCATTERED
THUNDERSTORMS THURSDAY... OR PERHAPS A MORE EXPANSIVE CLUSTER. A
SLOW MOVING THUNDERSTORM OVER THE CITY OF MASON PRODUCED RAINFALL
RATES OF OVER 1 INCH PER HALF HOUR WEDNESDAY MORNING. WHILE BRIEF
HEAVY RAINFALL IS NOT MUCH OF A CONCERN IN MOST LOCATIONS... SOME
STORMS MAY PERSIST LOCALLY AND PRODUCE MORE SIGNIFICANT RAINFALL
TOTALS. THIS MAY CAUSE SOME FLOODING ISSUES IN URBAN AND POOR
DRAINAGE AREAS.

&&

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

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...LAURENS
AVIATION...MEADE
HYDROLOGY...CAS
MARINE...MJS



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