Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 240349
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1049 PM CDT WED JUL 23 2014

UPDATED AVIATION PORTION FOR 06Z TAF ISSUANCE

.SHORT TERM...TONIGHT AND THURSDAY
ISSUED AT 252 PM CDT WED JUL 23 2014

MAIN CONCERNS DURING THIS PART OF THE FORECAST POTENTIAL FOR FOG
AND/OR FROST.

PLENTY OF CUMULUS DEVELOPED ACROSS WISCONSIN TODAY ONCE SURFACE
TEMPERATURES WARMED ENOUGH. THERE WERE ALSO SOME MID
CLOUDS...ASSOCIATED WITH A UPPER LEVEL SHORT WAVE...THAT WERE
MOVING ACROSS THE STATE. THE 12Z ECMWF AND 12Z GFS HAD SOME QPF IN
CENTRAL/NORTH CENTRAL WISCONSIN...BUT THE EC CONFINED IT TO THE
MORNING WHILE THE GFS HAD IT LASTING INTO THE EVENING. THE PREVIOUS
FORECAST WAS DRY FOR LATE THIS AFTERNOON AND THIS EVENING...THERE WERE
NO POPS IN GRIDS FROM ADJACENT OFFICES...AND THERE WAS NO STRONG
EVIDENCE THAT POPS NEEDED TO BE ADDED SO HAVE KEPT THE FORECAST DRY.

LOW CLOUDS SHOULD DISSIPATE WITH LOSS OF DAYTIME HEATING AND MID
CLOUDS WILL DEPART WITH THE SHORT WAVE. SURFACE HIGH PRESSURE
MOVING INTO THE STATE WILL RESULT IN A WEAK GRADIENT ACROSS THE
FORECAST AREA. CLEAR/MOSTLY CLEAR SKIES AND LIGHT/CALM WINDS
SHOULD ALLOW FOG TO DEVELOP. THERE WAS SOME PATCHY DENSE FOG IN
NORTH CENTRAL WISCONSIN THIS MORNING...SO HAVE GONE WITH PATCHY
DENSE FOG THERE AGAIN TONIGHT...AND PATCHY FOG ACROSS THE REST OF
THE AREA. 12Z GFS MOS HAS A LOW OF 33 AT LNL TONIGHT...BUT 12Z NAM
MOS HAD 39...AND DEW POINTS THERE RANGED FROM THE UPPER 40S TO
MIDDLE 50S AT 19Z...SO HAVE LEFT OUT ANY MENTION OF FROST NEAR THE
UPPER MICHIGAN BORDER OVERNIGHT.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY
ISSUED AT 252 PM CDT WED JUL 23 2014

STRONG ANTICYCLONE OVER THE SOUTHWESTERN CONUS AND ASSOCIATED
RIDGE AXIS EXTENDING NORTHWARD ACROSS THE WESTERN PLAINS INTO
CANADA EARLY IN THE EXTENDED...WILL BECOME UNDER ASSAULT BY VIGOROUS
SHORTWAVE ENERGY FORECAST TO UNDERCUT THE RIDGE ALONG THE
US/CANADA BORDER BY THE END OF THE WORK WEEK. AS THIS SHORTWAVE
PUSHES EAST TOWARD THE WESTERN GREAT LAKES AND BECOMES ENGULFED BY
UPPER VORTEX EAST OF HUDSON BAY OVER THE WEEKEND...UPPER RIDGE
WILL BECOME REESTABLISHED OVER THE WESTERN CONUS. THE NET RESULT
WILL LEAVE THE WESTERN GREAT LAKES UNDER THE INFLUENCE OF A RATHER
STRONG NORTHWESTERLY FLOW REGIME FOR THE FIRST HALF OF NEXT WEEK.

INITIAL PRECIPITATION CHANCES LATE IN THE WORK WEEK WILL BE
SOMEWHAT DEPENDENT OF WEAKER PIECES OF SHORTWAVE ENERGY FORECAST
TO BE EJECTED EASTWARD TOWARD THE WESTERN GREAT LAKES AS THE
VIGOROUS SHORTWAVE BEGINS TO IMPINGE ON THE UPSTREAM RIDGE AXIS.
THIS SCENARIO WOULD LEND TO LOWER FORECAST CONFIDENCE AS MODEL
GUIDANCE TYPICALLY SEEMS TO STRUGGLE WITH INTENSITY AND TIMING OF
THESE INITIAL DISTURBANCES. WOULD EXPECT BETTER CHANCE FOR MORE
WIDESPREAD ACTIVITY TO BE ASSOCIATED WITH PRIMARY SHORTWAVE AS IT
SWINGS EAST ACROSS THE FORECAST AREA SUNDAY INTO SUNDAY NIGHT.
TEMPERATURES SHOULD BE AT OR PERHAPS A FEW DEGREES ABOVE NORMAL
INTO THE FIRST HALF OF THE WEEKEND...THEN FALL BACK TO BELOW
NORMAL BY EARLY IN THE WORK WEEK. AT THE MOMENT IT WOULD APPEAR
THAT MONDAY WILL BE THE COOLEST DAY IN THE EXTENDED WITH HIGHS
POTENTIALLY IN THE 70 TO 75 DEGREE RANGE.

AS ELUDED TO ABOVE...LATEST MODEL GUIDANCE SUGGESTS FIRST SHOT AT
MEASURABLE PRECIPITATION OVER WESTERN GREAT LAKES TO BE SOMETIME
LATE THURSDAY NIGHT INTO EARLY FRIDAY. MAJORITY OF MODEL GUIDANCE
INDICATES CONVECTIVE ACTIVITY TO BE FORCED PREDOMINANTLY BY
CONVERGENCE ASSOCIATED WITH STRENGTHENING NOCTURNAL LLJ LATE
THURSDAY NIGHT WITH MCS DEVELOPING NEAR NORTHERN EDGE OF EXTENSIVE
POOL OF STEEP MID-LEVEL LAPSE RATES SPREADING INTO EASTERN
NEBRASKA AND INTO SOUTHWEST MINNESOTA. GIVEN THIS SCENARIO...SEEMS
REASONABLE TO EXPECT THAT BULK OF CONVECTIVE ACTIVITY WOULD REMAIN
SOUTHWEST OF THE FORECAST AREA THROUGH AT LEAST 12Z FRIDAY AS IT
SLIDES SOUTHEAST ALONG 850 THERMAL GRADIENT. THUS...TAPERED POPS BACK
SLIGHTLY ON FRIDAY MORNING RETAINING JUST SLIGHT CHANCE POPS OVER
THE SOUTHWEST HALF OF THE FORECAST AREA AND KEEPING IT DRY
ELSEWHERE. IN FACT LATEST 12Z WRF NMM/ARW AND NAM ALL SUGGEST
ENTIRE FORECAST ARE WILL REMAIN DRY AS WELL THE SREF ENSEMBLE
MEAN.

FRIDAY AND FRIDAY NIGHT...STILL MUCH UNCERTAINTY AS WEAKENING
FRONTAL BOUNDARY MAKES A MOVE TOWARD THE FORECAST AREA. MUCH WILL
DEPEND ON HOW MUCH RESIDUAL CLOUD COVER WILL PERSIST OVER THE AREA
AS WELL AS TIMING OF WEAK IMPULSES WORKING EASTWARD WITHIN
FLATTENING UPPER RIDGE AXIS. GIVEN APPROACHING FRONTAL
BOUNDARY...CONTINUED WEAK WAA AND POOL OF STEEP MID-LEVEL LAPSE
RATES SPILLING INTO SOUTHWEST PORTION OF THE FORECAST
AREA...KEEPING LOW CHANCE POPS OVER MOST OF FORECAST AREA SEEMS
REASONABLE WITH HIGHER VALUES MORE TOWARD THE SOUTHWEST PORTION
OF THE AREA.

LOWERED POPS ON SATURDAY...RELYING PRIMARILY ON CONSENSUS MODEL
POPS...AS MAJORITY OF GUIDANCE NOW SUGGEST FRONTAL BOUNDARY TO
BECOME QUITE DIFFUSE...WITH WEAK CAA AND SOMEWHAT DRIER AIR
WORKING INTO THE FORECAST AREA FROM THE WEST. MOST SIGNIFICANT
CHANGE WAS OVER CENTRAL PORTIONS OF THE FORECAST AREA WHERE WENT
DRY LOOK IN COORDINATION WITH SURROUNDING OFFICES.

BY SUNDAY...PRIMARY UPPER TROUGH SETTLES OVER THE FORECAST AREA.
IT APPEARS DEEPER MOISTURE...INSTABILITY AND MOST VIGOROUS
CONVECTIVE ACTIVITY SHOULD REMAIN TO THE SOUTHEAST OF THE
FORECAST AREA. HOWEVER...COMBINATION OF SECONDARY COLD
FRONT...SURFACE CYCLONE DEVELOPMENT OCCURRING JUST TO OUR EAST AND
INCREASING COLD AIR ALOFT...SHOULD ALLOW FOR FAIRLY WIDE SPREAD
SHOWER AND PERHAPS SOME THUNDER PARTICULARLY SUNDAY AFTERNOON INTO
SUNDAY EVENING. PRIMARY TROUGH AXIS SHOULD SWING EAST OF THE
FORECAST AREA SUNDAY NIGHT INTO MONDAY MORNING WITH STRONG CAA
AND PLUMMETING 850 TEMPS. WITH STRONG CYCLONIC FLOW DOMINATING
THE AREA MONDAY...WOULD EXPECT TO SEE LOTS OF CLOUDS...BRISK NORTHERLY
BOUNDARY LAYER FLOW AND UNSEASONABLY COOL DAYTIME HIGHS.
&&

.AVIATION...FOR 06Z TAF ISSUANCE
ISSUED AT 1049 PM CDT WED JUL 23 2014

PARTLY CLOUDY SKIES AND LIGHT WINDS MAY PERMIT DENSE GROUND
FOG TO FORM IN SOME LOCATIONS LATE TONIGHT AND EARLY THURSDAY.
PLACES LIKE ARV/LNL/RHI/RRL/AIG WILL PROBABLY HAVE IFR FOG AFTER
09Z THROUGH AROUND 11Z OR 12Z BUT THERE MAY BE FOG AT OTHER PLACES
TOO. OTHER THAN THE FOG TONIGHT FLYING WEATHER WILL BE GREAT
THROUGH THURSDAY NIGHT WITH MAINLY CLEAR SKIES AND LIGHT WINDS.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....MG
LONG TERM......ESB
AVIATION.......RDM





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