Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 012056
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
356 PM CDT SAT AUG 1 2015

FORECAST DISCUSSION FOR ROUTINE AFTERNOON FORECAST ISSUANCE

.SHORT TERM...TONIGHT AND SUNDAY
ISSUED AT 356 PM CDT SAT AUG 1 2015

AFTER A RATHER TRANQUIL EVENING...FORECAST QUICKLY GETS
INTERESTING AS NORTHWESTERLY FLOW REGIME BRINGS SHORTWAVE IMPULSES
SOUTHEAST TOWARD THE WESTERN GREAT LAKES OVERNIGHT...FOLLOWED BY
PRIMARY SHORTWAVE TROUGH AND ASSOCIATED COLD FRONT SUNDAY
AFTERNOON INTO EARLY SUNDAY EVENING.

SURFACE ANALYSIS LATE THIS AFTERNOON INDICATED DEVELOPING SURFACE
LOW PRESSURE OVER THE DAKOTAS WITH A DEVELOPING WARM FRONT
EXTENDING SOUTHEAST ACROSS SOUTHERN MINNESOTA INTO NORTHERN IOWA.
RATHER PRONOUNCED MOISTURE GRADIENT ACROSS SOUTHWEST WISCONSIN.
DEEP MIXING ACROSS CENTRAL WISCONSIN ALLOWED SURFACE DEWPOINT TO
FALL INTO THE MID 40S WEST OF THE FOX VALLEY...WHILE SURFACE
DEWPOINTS ACROSS IOWA HAVE BEEN STEADILY CLIMBING TO AROUND 70F.

WATER VAPOR IMAGERY SHOWS DISTINCT SHORTWAVE IMPULSE MOVING ESE
ACROSS SOUTHERN NORTHERN DAKOTA INTO EASTERN SOUTH DAKOTA WITH
MODEST CONVECTION ONGOING MOST OF THE DAY OVER NORTHEAST
NEBRASKA. FURTHER TO THE NORTH OVER CENTRAL AND SOUTHERN
MINNESOTA...NEAR LEADING EDGE OF STEEPER MID-LEVEL LAPSE RATES
...MID-LEVEL AC HAS BEEN DEVELOPING AND SPREADING EASTWARD ACROSS
THE NORTHERN MISSISSIPPI RIVER VALLEY. SHORT RANGE MODEL GUIDANCE
FOR THE NEXT 12 TO 15 HOURS CONTINUES TO STRUGGLE ON HOW
CONVECTION WILL EVOLVE THIS EVENING UPSTREAM OVER PARTS OF
MINNESOTA AND IOWA. OVERALL CONSENSUS OF THE GUIDANCE SUGGESTS
SCATTERED TO BROKEN CONVECTION SHOULD DEVELOP AHEAD OF
AFOREMENTIONED SHORTWAVE IMPULSE OVER CENTRAL OR SOUTHERN
MINNESOTA THEN PUSH EAST OR SOUTHEAST INTO CENTRAL WISCONSIN AFTER
MIDNIGHT. 12Z NAM AND GFS HAD THE GENERAL IDEA ON THIS EVOLUTION.
HOWEVER...SOME OF THE HIGHER RESOLUTION WRF RUNS HAVE BEEN
INSISTENT ON DEVELOPING CONVECTION A BIT FURTHER NORTH ACROSS
NORTH CENTRAL MINNESOTA...THEN MOVING IT EAST SOUTHEAST ACROSS THE
NORTHERN HALF OF THE FORECAST AREA BETWEEN ABOUT 08Z AND 12Z
SUNDAY MORNING. GIVEN THE UNCERTAINTY ON THE LOCATION OF PRIMARY
CONVECTIVE DEVELOPMENT OVERNIGHT...CONTINUED A BROAD BRUSH HIGH-
END CHANCE POPS ACROSS THE ENTIRE FORECAST AREA AFTER MIDNIGHT. IT
STILL APPEARS THAT THE STRONGEST CONVECTIVE ACTIVITY SHOULD REMAIN
WEST OF THE FORECAST AREA OVER SOUTHERN MINNESOTA...IN THE
VICINITY OF THE STEEPER MID-LEVEL LAPSE RATES...STRONGER LOW-LEVEL
SOUTHWESTERLY WAA AND DEEPER MOISTURE. BY 12Z-14Z SUNDAY MORNING
THE CONVECTION SHOULD BE EXITING THE EASTERN PORTION OF THE
FORECAST AREA AS THE 850 MB WINDS VEER WESTERLY IN THE WAKE OF THE
INITIAL SHORTWAVE IMPULSE.

DURING THE REMAINDER OF THE MORNING AND PERHAPS INTO THE EARLY
AFTERNOON...THERE COULD BE A LULL IN THE ACTIVITY BEFORE PRIMARY
SHORTWAVE TROUGH AND COLD FRONT IMPINGE ON THE FORECAST AREA.
CONSENSUS OF THE MODEL GUIDANCE SUGGESTS SURFACE LOW PRESSURE TO
STRENGTHEN SOMEWHAT ON THE FRONTAL BOUNDARY SOMEWHERE OVER EASTERN
OR EASTCENTRAL WISCONSIN DURING THE AFTERNOON AS UPPER-LEVEL
TROUGH APPROACHES. RATHER IMPRESSIVE SOUTHERLY SURGE OF COOLER AND
DRIER AIR BY LATE IN THE AFTERNOON...WITH NOTABLE FRONTOGENTIC
FORCING ALONG AND AHEAD OF THE COLD FRONT FROM EAST-CENTRAL
WISCONSIN TO CENTRAL LOWER MICHIGAN. IF THE MORNING CONVECTION IS
RATHER LIMITED AND WE ARE ABLE TO DESTABILIZE DURING THE LATE
MORNING INTO THE EARLY AFTERNOON...CERTAINLY POTENTIAL FOR STRONG
TO SEVERE STORMS TO DEVELOP ALONG THE COLD FRONT BY MID-AFTERNOON.
THE OPERATIONAL NAM AND GFS AS WELL AS THE HIGHER RESOLUTION WRF
RUNS SUGGEST CONVECTION TO DEVELOP SOMEWHERE OVER EASTERN OR
NORTHEASTERN WISCONSIN BY 19-21Z AND THEN MOVE SE ACROSS THE FOX
VALLEY AND LAKE SHORE THEREAFTER. IF THE EARLIER MORNING
CONVECTION PERSISTS LATER INTO THE MORNING...RECOVERY WILL LIKELY
BE SLOWER WITH THE NEW CONVECTIVE DEVELOPMENT MORE LIKELY TO
DEVELOP OVER THE SOUTHERN FOX VALLEY. WILL HAVE TO WAIT AND SEE
HOW THINGS EVOLVE SUNDAY MORNING. PER SPC DAY2 OUTLOOK...IF STORMS
CAN GET GOING SUNDAY AFTERNOON...DEEP LAYER AND 0-3 SHEAR IN
CONCERT WITH ROBUST FRONTAL FORCING AND INSTABILITY COULD
GENERATE LINEAR MCS CAPABILITY OF DAMAGING WINDS OVER THE
SOUTHERN FOX VALLEY.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY
ISSUED AT 356 PM CDT SAT AUG 1 2015

UPPER LEVEL LOW WILL DRIFT FROM HUDSON/S BAY SUNDAY
NIGHT TO SOUTHERN QUEBEC WEDNESDAY. AS IT DOES SO IT WILL PRODUCE
A NORTHWEST CYCLONIC FLOW ACROSS NORTHERN GREAT LAKES AND BRING A
RETURN TO BELOW NORMAL TEMPERATURES.

ANY REMAINING SHOWER OR THUNDERSTORM ACTIVITY ASSOCIATED WITH THE
COLD FRONT MOVING ACROSS WISCONSIN SUNDAY AFTERNOON AND EVENING
SHOULD EXIT THE AREA BY MIDNIGHT OR SO. BREEZY...COOLER WEATHER
FOR MONDAY WITH A CHANCE OF A SHOWER IN THE NORTH DURING THE
AFTERNOON AND EVENING WITH COLD CYCLONIC UPPER FLOW AND SURFACE
HEATING. ANOTHER CHANCE FOR SHOWERS TUESDAY AS A SURFACE TROUGH
MOVES BY WITH SOME ADDITIONAL COOL AIR ALOFT.

WEDNESDAY SHOULD BE DRY AND PLEASANT.THURSDAY THROUGH FRIDAY
SHOULD BE MAINLY DRY THOUGH THE GFS SUGGESTS THAT WARM ADVECTION
AHEAD OF A SURFACE WAVE MOVING ACROSS THE MIDWEST COULD BRING
SHOWERS TO THE SOUTHWEST HALF OF OUR FORECAST AREA. KEPT IN A
CHANCE OF SHOWERS FOR THURSDAY AND FRIDAY BUT WOULD NOT BE
SURPRISED IF IT STAYS DRY.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1258 PM CDT SAT AUG 1 2015

VFR CONDITIONS WILL PREVAIL AT LEAST 06Z SUNDAY WITH MAINLY HIGH-
BASED CUMULUS ACROSS NORTHERN WISCONSIN AND SOME SCT MID-LEVEL
CLOUDS ACROSS THE SOUTH. STILL SOME OCCASIONAL GUSTY W TO NW
WINDS TO ABOUT 20KTS THIS AFTERNOON.

LOW PRESSURE SYSTEM DEVELOPING OVER THE NORTHERN PLAINS AND AN
APPROACHING WARM FRONT AFTER MIDNIGHT WILL BRING AN INCREASINGCHANCE
FOR SCATTERED SHOWERS AND THUNDERSTORMS. STILL A FAIR AMOUNT OF
UNCERTAINTY ON THE TIMING AND LOCATION OF ANY SCATTERED
THUNDERSTORM ACTIVITY. BEST GUESS AT THIS TIME IS THAT MOST LIKELY
AREA TO SEE SCATTERED ACTIVITY WOULD BE OVER CENTRAL AND NORTHERN
WISCONSIN AFTER ABOUT 08Z. DUE TO LOW CONFIDENCE IN THIS
REGARD...WILL NOT INCLUDE MENTION OF THUNDER IN 18Z TAF PACKAGE.

AFTER 18Z SUNDAY...COLD FRONT DROPPING SOUTHEAST ACROSS THE
FORECAST AREA...ALONG WITH DEVELOPING LOW PRESSURE OVER EASTERN
WISCONSIN SUNDAY AFTERNOON WILL BRING ANOTHER CHANCE OF PERHAPS
MORE WIDESPREAD AND VIGOROUS CONVECTION BY MID-AFTERNOON SUNDAY.
GREATEST LIKELIHOOD FOR THUNDERSTORM ACTIVITY SUNDAY AFTERNOON
WOULD BE GENERALLY SOUTHEAST OF A LINE FROM MNM TO AUW.

SOME LLWS IS PSBL AT RHI/AUW/CWA AFTER 04Z...THEN AROUND 08Z AT
ATW/GRB/MTW.
&&

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

$$

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


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