Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 210729
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
325 AM EDT THU AUG 21 2014

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

.SYNOPSIS...
ISSUED AT 325 AM EDT THU AUG 21 2014

A WARM FRONT WILL MOVE TOWARD SOUTHWEST LOWER MICHIGAN AND BRING
A FEW SHOWERS AND ISOLATED THUNDERSTORMS TODAY. NUMEROUS
THUNDERSTORMS ARE ANTICIPATED TONIGHT WITH POTENTIAL FOR HEAVY
RAINFALL AND LOCALIZED FLOODING AS WELL AS POTENTIAL FOR ISOLATED
DAMAGING WIND GUSTS. VERY WARM AND HUMID WEATHER IS EXPECTED FRIDAY
THROUGH THE WEEKEND. DRY WEATHER SHOULD PREVAIL THE MAJORITY OF THE
TIME FRIDAY THROUGH THE WEEKEND BUT A FEW SHOWERS AND STORMS COULD
DEVELOP AT JUST ABOUT ANY TIME.

&&

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 325 AM EDT THU AUG 21 2014

A WARM FRONT APPROACHING FROM THE SSW WILL TRIGGER DEVELOPMENT OF
A FEW SHOWERS AND THUNDERSTORMS TODAY. SCATTERED SHOWERS AND
ISOLATED STORMS ARE POSSIBLE EARLY THIS MORNING MAINLY NEAR THE
I-94 CORRIDOR FOLLOWED BY A LITTLE BETTER CHANCE OF SCATTERED
SHOWERS AND STORMS FURTHER NORTH THIS AFTERNOON POSSIBLY UP INTO
THE I-96 CORRIDOR.

THE STRONG WARM FRONT AND INCREASING LLJ AND 1000-850 MB MOISTURE
TRANSPORT WILL RESULT IN DEVELOPMENT OF MORE NUMEROUS SHOWERS AND
THUNDERSTORMS THIS EVENING AND OVERNIGHT. 00Z SHORT RANGE GUIDANCE
SOLUTIONS VARY WIDELY IN TERMS OF QPF PLACEMENT AND AMOUNTS. THE
00Z GFS DOES NOT HAVE VERY MUCH QPF OVER OUR FCST AREA AT ALL (A
QUARTER TO A HALF AN INCH). 00Z 4KM WRF NMM AND NSSL WRF SIM Z
GUIDANCE SUGGESTS THAT HEAVY CONVECTION TONIGHT WILL STAY JUST
SOUTH OF OUR AREA ACROSS IL/IN.

CONVERSELY THE 00Z NAM DOES SHOW POTENTIAL FOR SOME HEAVY RAINFALL
PARTICULARLY NEAR TO SOUTH OF I-96 AND THE ECMWF FOR SEVERAL RUNS
NOW HAS ALSO INDICATED POTENTIAL FOR HEAVY RAIN PARTICULARLY NEAR
TO SOUTH OF I-96. IN ADDITION ISOLATED DAMAGING WIND GUSTS ARE
POSSIBLE WITH CONVECTION TONIGHT.

WE WILL CONTINUE TO FAVOR THE ECMWF SOLUTION WHICH HAS BEEN MORE
CONSISTENT AND ALSO SEEMS MORE REASONABLE GIVEN THE SYNOPTIC SETUP
FEATURING FORCING FROM A STRONG WARM FRONT... LLJ AND A VERY
HUMID AIRMASS THAT WILL BE MOVING IN. PRECIPITABLE WATER VALUES ARE
EXPECTED TO REACH 2 TO 2.25 INCHES LATE THIS EVENING AND OVERNIGHT.

SO THERE IS POTENTIAL FOR HEAVY RAINFALL AND LOCALIZED FLOODING
TONIGHT. ALTHOUGH STRONGLY CONSIDERED... THERE IS NOT ENOUGH
CONFIDENCE AT THIS TIME TO HOIST A FLOOD WATCH FOR PORTIONS OF OUR
AREA GIVEN THE SIGNIFICANT SPREAD IN SHORT RANGE GUIDANCE QPF
AMOUNTS. THERE IS ALSO SOME UNCERTAINTY AS TO THE
STRENGTH/ORIENTATION OF THE LLJ.

VERY WARM AND HUMID CONDITIONS ARE THEN EXPECTED FRIDAY THROUGH
SATURDAY. A SCATTERED SHOWER OR STORM COULD DEVELOP AT JUST ABOUT
ANY TIME BUT DRY WX SHOULD PREVAIL THE MAJORITY OF THE TIME. WITH
THE VERY HUMID AIRMASS IN PLACE SOME AREAS OF EARLY MORNING FOG
ARE ALSO POSSIBLE AND THIS WILL BE LARGELY CONTINGENT ON EXTENT OF
CLEARING NIGHTLY.

.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 325 AM EDT THU AUG 21 2014

STILL LOOKING AT THE GENERAL IDEA OF STRONG UPPER RIDGING SLOWLY
BREAKING DOWN BY THE END OF THE PERIOD...BUT IT IS STILL HARD TO PIN
DOWN THE DETAILS. RUN TO RUN CONSISTENCY STILL NOT GREAT FOR EARLY
NEXT WEEK SO THE TIMING OF THE MAIN PUSH OF STORMS COULD BE ANYTIME
FROM MONDAY NIGHT TO WEDNESDAY. WILL HAVE CHANCE POPS DURING THAT
TIME FRAME WITH THE HIGHEST ON WEDNESDAY WHEN IT APPEARS THE HEIGHT
FALLS ARE GREATEST AND THE SFC COLD FRONT ARRIVES.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1120 PM EDT WED AUG 20 2014

IT NOW APPEARS THE CONVECTION I WAS THINKING WOULD OCCUR DUE TO
THE EXIT REGION OF A DEPARTING UPPER JET CORE WILL LARGELY BE
JUST SOUTH OF OUR TAF SITES SO I EXPUNGED THE VCSH FROM THE TAFS
TONIGHT. WE WILL STILL HAVE TO MONITOR THIS AS IT IS STILL
POSSIBLE.

I ALSO EXPECT DUE TO THE LIGHT WINDS SOME FOG TO DEVELOP TOWARD
MORNING. I HAVE LAN WITH THE LOWEST CONDITIONS AS I EXPECT THE LOW
LEVEL FLOW TO BE FROM THE EAST SO MOISTURE OFF SAGINAW BAY AND
LAKE HURON WILL INCREASE THE FOG THREAT THERE.

LOOKS LIKE THE CONVECTION ON THE WARM FRONT TOMORROW NIGHT WILL
LARGELY BE AFTER 03Z BUT I STILL PUT THUNDERSTORMS IN ALL OF THE
TAF FORECASTS AFTER 03Z TO GIVE A GENERAL TREND.


&&

.MARINE...
ISSUED AT 325 AM EDT THU AUG 21 2014

MINIMAL WIND AND WAVE ACTION IS EXPECTED THE REST OF THIS WEEK
THROUGH THE WEEKEND. HOWEVER AREAS OF DENSE FOG WILL POSE A HAZARD
TO MARINERS DUE TO A VERY WARM AND HUMID AIRMASS OVERRUNNING
RELATIVELY COOL LAKE WATER.

&&

.HYDROLOGY...
ISSUED AT 341 PM EDT WED AUG 20 2014

EXCESSIVE RAINFALL IS POSSIBLE THURSDAY NIGHT WITH PWATS OF 2.2
INCHES AND AN APPROACHING WARM FRONT UNDER A BUILDING UPPER RIDGE.
THIS PATTERN SUPPORTS THE POSSIBILITY OF FLOODING/FLASH FLOODING
ACROSS PARTS OF THE UPR MIDWEST/SRN GRTLKS REGION INCLUDING SW LWR
MI. DEPENDING ON HOW THE STORMS SET UP AND PERSIST... AREAL FLOODING
IS POSSIBLE THURSDAY NIGHT FOLLOWED BY THE POTENTIAL FOR RIVER
FLOODING IN THE DAYS FOLLOWING. SOME UNCERTAINTY STILL EXISTS
HOWEVER IN LOW LEVEL JET BEHAVIOR AND PLACEMENT OF BEST QPF.

&&

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

$$

SYNOPSIS...LAURENS
SHORT TERM...LAURENS
LONG TERM...OSTUNO
AVIATION...WDM
HYDROLOGY...MEADE
MARINE...LAURENS






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