Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 270720
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
320 AM EDT WED AUG 27 2014

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

.SYNOPSIS...
ISSUED AT 320 AM EDT WED AUG 27 2014

QUIET WEATHER WITH COOLER TEMPERATURES AND LOWER HUMIDITY IS
EXPECTED TODAY THROUGH TOMORROW. RAIN AND THUNDERSTORM CHANCES
RETURN THURSDAY NIGHT AND PERSIST THROUGH SATURDAY NIGHT. HIGH
TEMPERATURES WILL BE IN THE 70S AND 80S.

&&

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 320 AM EDT WED AUG 27 2014

MAIN WEATHER IMPACTS IN THE SHORT TERM ARRIVE THURSDAY NIGHT IN
THE FORM OF SHOWERS AND THUNDERSTORMS. THE CHANCE FOR
SHOWERS/STORMS EXTENDS THROUGH THE DAY ON FRIDAY AND INTO THE
WEEKEND.

MODELS AGREE ON A DEEP UPPER TROUGH EJECTING INTO THE GREAT PLAINS
THURSDAY NIGHT WITH UPPER RIDGING AND WESTERLY FLOW ALOFT OVER THE
GREAT LAKES. AT 850 MB...WINDS TURN SOUTHWESTERLY AND WAA
COMMENCES THU NIGHT WITH ISENTROPIC ASCENT. PRECIPITABLE WATER
RAMPS UP ABOVE 1.5 INCHES THURSDAY NIGHT. THERE IS THE POTENTIAL FOR
STORMS AND WIDESPREAD RAINFALL THURSDAY NIGHT INTO FRIDAY. THERE IS
SOME UNCERTAINTY ABOUT WHERE THE HEAVIEST WARM FRONTAL RAINS SET UP.
00Z ECMWF AND GFS SUGGEST NORTHWEST CWA HAS THE BEST CHANCE...WHERE
THE BETTER LOW LEVEL JET DYNAMICS AND MOISTURE TRANSPORT ARE
LOCATED.

UNTIL THEN...QUIET WEATHER IS EXPECTED TODAY AND TOMORROW. SKIES
WILL BE PARTLY TO MOSTLY CLOUDY TODAY DUE TO A SHORTWAVE TROUGH
AND ASSOCIATED PV MAX SLIDING EAST FROM THE UPPER MIDWEST. SKIES
WILL BEGIN TO CLEAR OUT THIS EVENING ALLOWING TEMPS TO DROP INTO
THE 40S/LOWER 50S TONIGHT. HIGHS TODAY AND TOMORROW WILL BE IN THE
70S.

.LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY)
ISSUED AT 320 AM EDT WED AUG 27 2014

THIS LOOKS LIKE A VERY WET WEATHER PATTERN FOR SOUTHWEST MICHIGAN
FRIDAY NIGHT INTO SATURDAY NIGHT THEN AGAIN MONDAY AFTERNOON INTO
TUESDAY.

LARGELY THE MODELS AGREE ON THE OVERALL UPPER AIR PATTERN AND
CONTINUITY WHILE NOT EXCELLENT IS DECENT. WHAT IS HAPPENING IS WE
HAVE A CLOSED UPPER LOW OVER NEVADA AT 00Z WEDNESDAY WITH A NORTHERN
STREAM TROUGH OVER WESTERN CANADA. BOTH OF THESE SYSTEMS IN TANDEM
HEAD EAST INTO THE GREAT LAKES FRIDAY INTO SATURDAY.  HELPING TO
MOVE THINGS ALONG IS A MUCH STRONGER SYSTEM NOW HEADING INTO WESTERN
ALASKA AND THE BERING SEA. THAT SYSTEM REACHES OUR AREA EARLY NEXT
WEEK AND SHOULD BRING STRONG DYNAMICS WITH A GOOD RETURN FLOW OFF
THE GULF OF MEXICO.

SO HERE IS MY PROBLEM...THE FIRST SYSTEM IS A SHEARING OUT
BAROTROPIC UPPER LOW. THESE TEND TO BE OPENED UP BY THE MODELS TOO
QUICKLY AND MORE THAN LIKELY THIS SYSTEM WILL BE STRONGER FRIDAY
INTO SATURDAY THAN ANY OF THE MODELS SHOW IT TO BE. EVEN SO BOTH THE
ECMWF (12Z AND 00Z PLUS THE GFS 12Z-18Z AND 00Z) ALL SHOW THE
1000/850 MOISTURE TRANSPORT VECTORS AIMED AT SOUTHWEST MICHIGAN
FRIDAY INTO SUNDAY MORNING. THE PRECIPITABLE WATER VALUES ARE AROUND
1.8 INCHES WHICH IS NEARLY 2 STANDARD DEVIATION FROM NORMAL. THE LOW
LEVEL JET IS FOCUSED OVER CENTRAL AND NORTHERN LOWER FRIDAY INTO
EARLY SATURDAY BUT IS AIMED AT SOUTHERN CWA SATURDAY NIGHT...WITH
THE GFS SHOWING 35 TO 40 KNOTS AT 06Z SUN OVER SE LOWER MICHIGAN.
ADD TO THIS THE CIPS ANALOGS NEARLY ALL OF THE 18 ANALOGS FOR THE
FRIDAY INTO INTO SATURDAY NIGHT TIME FRAME RESULT IN 1 TO 3 INCH+
QPF VALUES. I COULD SEE LOCALLY WELL OVER THAT AMOUNT BY SUNDAY
MORNING.

WHAT I AM THINKING IS WE WILL HAVE TWO PERIODS OF SIGNIFICANT
RAINFALL... FRIDAY NIGHT WITH THE LEAD WAVE THEN SATURDAY NIGHT WITH
THE MAIN UPPER WAVE TRACKING THROUGH THE AREA. THIS ONE SHOULD BE
THE WETTEST.

ONCE THAT IS ALL DONE WE WAIT FOR THE NEXT SYSTEM FROM ALASKA. THAT
WILL MOVE INTO OUR AREA STARTING MONDAY WITH THE BEST DYNAMICS
TUESDAY. THIS COULD BE A SEVERE WEATHER AND HEAVY RAIN EVENT.
GIVE THE ALL THE RAIN POSSIBLE OVER THE WEEKEND THEN AGAIN LATER
MONDAY INTO TUESDAY WE MAY BEGIN TO HAVE HYDRO ISSUES.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1157 PM EDT TUE AUG 26 2014

A FEW MVFR CIGS WERE STILL IMPACTING THE I-94 CORRIDOR AT MIDNIGHT
ALTHOUGH THIS AREA APPEARS TO BE MOVING SLOWLY SOUTH AND SHOULD
CLEAR OUT BY 2 AM. HOWEVER EVEN AFTER THIS AREA OF STRATUS
DEPARTS... ADDITIONAL MVFR TO IFR STRATUS AND FOG IS EXPECTED TO
DEVELOP SOUTH AND EAST OF GRR AFTER 5 AM OR SO. MORNING
FOG/STRATUS SHOULD BE GONE BY 10-11 AM WEDNESDAY FOLLOWED BY VFR
CONDITIONS FOR THE REST OF THE DAY.


&&

.MARINE...
ISSUED AT 320 AM EDT WED AUG 27 2014

WINDS WILL GENERALLY BE OUT OF THE NORTH IN THE 5-15 KT RANGE
TODAY. WAVES WILL REMAIN AROUND 1 FOOT. WINDS AND WAVES ARE
EXPECTED TO RAMP UP FRIDAY INTO THE WEEKEND.

&&

.HYDROLOGY...
ISSUED AT 328 PM EDT TUE AUG 26 2014

A WARM FRONT COULD BRING THUNDERSTORMS WITH HEAVY RAIN BY FRIDAY.
WET WEATHER COULD CONTINUE INTO SUNDAY AS LOW PRESSURE MOVES
THOUGH.

&&

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

$$

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








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