Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 251923
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
323 PM EDT SAT JUL 25 2015

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

.SYNOPSIS...
ISSUED AT 323 PM EDT SAT JUL 25 2015

HOT AND DRY WEATHER WILL PREVAIL INTO NEXT WEEK WITH HIGHS IN THE
UPPER 80S. THE NEXT CHANCE FOR SHOWERS AND THUNDERSTORMS ARRIVES
WEDNESDAY. THIS WILL BE FOLLOWED BY A RETURN TO DRY CONDITIONS AND
SLIGHTLY COOLER TEMPERATURES WITH HIGHS IN THE LOWER 80S.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 323 PM EDT SAT JUL 25 2015

STILL EXPECT SHOWERS AND THUNDERSTORMS TO BE LIMITED TO OUR FAR
SOUTHEASTERN ZONES THIS AFTERNOON AND EVENING AS STABILIZING
MARINE AIR HAS OVERSPREAD MUCH OF THE REMAINING AREA. GIVEN
MODERATE INSTABILITY /MLCAPE 1500 J PER KG/ AND SURFACE
CONVERGENCE ALONG THE PREFRONTAL TROUGH IN THIS AREA...WILL NEED
TO MONITOR FOR STRONG STORMS.

AFTER PRECIPITATION EXITS THE AREA THIS EVENING...MAIN FORECAST
CONCERN IS MAXIMUM TEMPERATURES. WENT NEAR OR ABOVE GUIDANCE WITH
WIDESPREAD UPPER 80S EXPECTED BOTH SUNDAY AND MONDAY AFTERNOONS.
DURING THIS TIME...AN UPSTREAM UPPER RIDGE GRADUALLY AMPLIFIES AND
APPROACHES THE FORECAST AREA WHICH IS CONDUCIVE TO MID-LEVEL
SUBSIDENCE AND SURFACE ANTICYCLOGENESIS. THIS PATTERN MAKES DRY
CONDITIONS AND LIMITED CLOUDS HIGHLY PROBABLE.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 323 PM EDT SAT JUL 25 2015

THE FOCUS FOR THIS FORECAST IS CONVECTION WITH THE PASSAGE OF A
RATHER STRONG (FOR THIS TIME OF YEAR) COLD FRONT IN THE WEDNESDAY
TIME FRAME. BEYOND THAT THE THEME OF OVERALL COOL SUMMER FOR
SOUTHWEST MICHIGAN WILL CONTINUE AS A LONGWAVE TROUGH RE-
ESTABLISHES ITSELF OVER THE EASTERN CONUS AND ADJACENT SOUTHERN
CANADA.

OVERALL THE MODELS ARE IN GOOD AGREEMENT THROUGH MOST OF THIS COMING
WEEK... WELL AT LEAST THROUGH THURSDAY ANYWAY. BEYOND THAT THERE ARE
ISSUES WITH THE NEXT SHORTWAVE RIDGE/TROUGH MOVING IN FROM THE
PACIFIC INTO THE CONUS. IT SHOULD BE NOTED THAT THE OPERATIONAL GFS
IS AT ODDS WITH ITS OWN ENSEMBLE MEAN BEYOND THURSDAY. THE ENSEMBLE
MEAN OF THE GFS IS IN AGREEMENT WITH OPERATIONAL ECMWF SO I AM GOING
WITH THAT IDEA.

THE BIG PICTURE IS THE LONGWAVE RIDGE ...WHICH IS CURRENTLY OVER THE
CENTRAL CONUS RETROGRADES TO THE WESTERN CONUS BY THE MIDDLE OF NEXT
WEEK.  THIS HAPPENS AS A SERIES OF STRONG PACIFIC SYSTEMS TRACK EAST
FROM THE EASTERN NORTH PACIFIC OCEAN INTO THE SOUTHERN CANADA AND
THE NORTHERN CONUS. IT IS THE LEAD SHORTWAVE..WHICH IS CURRENTLY A
CLOSED UPPER LOW AND SURFACE SYSTEM OVER THE GULF OF ALASKA. THIS
SYSTEM TRACKS OVER THE UPPER RIDGE IN THE TUESDAY TIME FRAME TO HELP
DIG THE EASTERN TROUGH ONCE AGAIN. IT IS THIS DIGGING INTO THE
EASTERN TROUGH OF THAT SYSTEM THAT BRING SOUTHWEST MICHIGAN THE
CONVECTION ON WEDNESDAY.

SO...HOW STRONG WILL THE CONVECTION BE? ONCE AGAIN... AS IT HAS BEEN
MORE TIMES THAN I WANT TO COUNT THIS SUMMER...THE JUXTAPOSITION OF
THE UPPER LEVEL JET...THE LOW LEVEL JET AND THE TIME OF DAY THIS ALL
HAPPENS IS VERY MUCH NOT OPTIMAL FOR SIGNIFICANT THUNDERSTORMS.
THE PRIMARY UPPER LEVEL JET ON BOTH THE ECMWF AND GFS GO WELL TO
THE NORTH AND WEST OF MICHIGAN AND AS A RESULT WE DO NOT GET A
GOOD LOW LEVEL JET TO AID THE CAUSE OF A SIGNIFICANT THUNDERSTORM
EVENT. LIKELY THERE WILL BE SOME THUNDERSTORMS WITH THE FRONT BUT
THIS LIKELY WILL NOT BRING RAIN TO ALL AREAS AND EVEN THOSE PLACES
THAT DO GET RAIN...LIKELY WILL NOT SEE ALL THAT MUCH (SYSTEM
MOVING THROUGH TO FAST).

BEYOND THAT THE COLD AIR MOVES BACK IN AND THERE MAY BE COLD AIR
INSTABILITY SHOWERS THURSDAY OVER OUR NORTHEAST CWA. I DID NOT PLAY
THIS TO BIG JUST YET BUT IT WILL HAVE TO BE WATCHED. ONE OTHER THING
TO NOTE... THE GFS HAS ALL SUMMER HAD A WARM BIAS ON THE
TEMPERATURES BEHIND THESE COLD FRONTS. MORE THAN LIKELY IT WILL
BE COOLER THAN WE ARE CURRENTLY FORECASTING THURSDAY AND FRIDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 156 PM EDT SAT JUL 25 2015

GENERALLY MVFR CIGS PREVAIL AHEAD OF THE SECONDARY COLD FRONT
(WHICH IS CURRENTLY NEAR ROUTE 10) . IT IS THAT SECONDARY COLD
FRONT THAT IS BOTH THE FOCUS FOR DEVELOPING SHOWERS AND CLEARING
OF THE LOW CLOUDS BEHIND IT. ALSO THE WEST WIND LAKE SHADOW IS
CLEARING ALL CLOUDS WEST OF US-31. I USED THE HRRR LOW 925 TO 850
MB RH AS A GUIDE TO CLEAR OUT THE LOW CLOUDS AND ALSO HELP DECIDE
JUST WHERE TO HAVE THE VCSH IN THE TAFS.

FOR THE MOST PART THE MVFR CIGS SHOULD MIX OUT TO VFR CIGS BY 21Z
AT ALL TAF SITES...THAT IS JUST FROM DAY TIME MIXING AND NOT
RELATED TO THE FRONTAL PASSAGE. THE ACTUAL CLEARING OF THE CLOUDS
WILL BE BEHIND THE SECONDARY COLD FRONT THAT SHOULD OCCUR IN THE
00Z TO 03Z TIME FRAME. MKG SHOULD CLEAR SOON DUE TO THE LAKE
SHADOW MOVING INLAND.

THE CONVECTION AHEAD OF THE SECONDARY COLD FRONT WILL LARGELY STAY
EAST OF THE TAF SITES. THIS IS TYPICAL FOR WHAT HAPPENS WITH WEST
WINDS AT LOW LEVELS AT THIS TIME OF YEAR. I DID HOWEVER PUT VCSH
AT LAN AND JXN TAF SITES JUST IN CASE SHOWERS MAKE IT A TOUCH
FARTHER WEST.

BUFKIT TIME SECTIONS AND THE NAMDNG5 FORECAST DO SUGGEST THERE
COULD BE FROM FOG AT THE EASTERN TAF SITES DUE TO LIGHT WINDS
...CLEAR SKIES BUT MY CONFIDENCE  WAS NOT HIGH GIVEN THERE IS
COLD ADVECTION GOING ON (HELP MIXING OUT THE FOG). LATE TAF
FORECAST MAY HAVE TO ADD FOG FOR THE EASTERN TAF SITES TONIGHT.

&&

.MARINE...
ISSUED AT 323 PM EDT SAT JUL 25 2015

NO CONCERNS IN THE SHORT TERM. VERY LIGHT WINDS OVERALL
SHOULD SHOULD BE DOMINATED BY LAKE/LAND BREEZES AT THE LAKESHORE
WITH ONSHORE WINDS DURING THE DAY AND OFFSHORE WINDS OVERNIGHT.

&&

.HYDROLOGY...
ISSUED AT 1137 AM EDT SAT JUL 25 2015

NO FLOODING CONCERNS EXIST THROUGH THE NEXT SEVERAL DAYS.

RECENT DRY CONDITIONS AND LITTLE EXPECTED RAINFALL HAS RESULTED
IN FALLING RIVER LEVELS. A FEW SCATTERED STORMS ARE EXPECTED TODAY
WITH VERY LOCALIZED HEAVY RAINFALL POSSIBLE. HOWEVER...THIS MAY BE
BRIEF WITH THE LACK OF ANY WIDESPREAD MOISTURE.

ALL RIVERS ARE WELL WITHIN BANKS AND THE STEADY OR FALLING TREND
WILL LIKELY CONTINUE THROUGH THE NEXT FEW DAYS. WARM AND HUMID
CONDITIONS WILL LACK MUCH IN THE WAY OF RAINFALL. A MID WEEK COLD
FRONT WILL HELP TO INCREASE RAIN CHANCES...BUT EVEN THESE TOTALS
SHOULD WILL BE RELATIVELY LIGHT IN REGARDS TO ANY HIGHLIGHTING AND
HYDRO ISSUES.

&&

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

$$

SYNOPSIS...TJT
SHORT TERM...TJT
LONG TERM...WDM
AVIATION...WDM
HYDROLOGY...JAM
MARINE...TJT



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