Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 030005
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
705 PM CDT TUE SEP 2 2014

UPDATED AVIATION PORTION FOR 00Z TAF ISSUANCE

.SYNOPSIS...
ISSUED AT 213 PM CDT TUE SEP 2 2014

A COUPLE ROUNDS OF THUNDERSTORMS TOMORROW NIGHT AND THURSDAY...
SOME OF WHICH COULD BE SEVERE.

LATE SUMMER/EARLY AUTUMN UPPER PATTERN IN PLACE ACRS NOAM.
SUBTROPICAL RIDGE STILL DOMINATING THE SRN CONUS...WITH A STG AND
ENERGETIC BAND OF WESTERLIES ACRS THE NRN U.S. AND SRN CANADA.
THOUGH THE MEAN FLOW WL HAVE MODEST AMPLITUDE THROUGH THE
PERIOD...A SERIES OF SHRTWVS OF VARIOUS SIZES AND INTENSITIES WL
BE MIGRATING THROUGH THE PATTERN.

THE MAIN PCPN CHCS WL BE EARLY IN THE PERIOD AND AGAIN LATE...WITH
GENERALLY DRY WX LIKELY IN BETWEEN. BUT THOSE TWO EVENTS WL
PROBABLY PRODUCE ENOUGH RAIN TO RESULT IN AOA NORMAL PCPN FOR THE
PERIOD. TEMPS...AND HUMIDITIES...WL REMAIN AOA NORMAL LEVELS THE
NEXT COUPLE DAYS...THEN WL DROP BACK CLOSER TO NORMAL FOR THE
WEEKEND AND EARLY NEXT WEEK.
&&

.SHORT TERM...TONIGHT AND WEDNESDAY
ISSUED AT 213 PM CDT TUE SEP 2 2014

WHILE ONE SHORT WAVE DEPARTS TO THE EAST THIS AFTERNOON ANOTHER
ONE IS APPROACHING THE GREAT LAKES REGION THIS EVENING. MODELS IN
AGREEMENT WITH KEEPING THIS SECOND PIECE OF ENERGY NORTH IN
RESPONSE TO BUILDING UPPER HEIGHTS...SO WILL CONTINUE WITH A DRY
FORECAST TONIGHT INTO THE START OF WEDNESDAY.

ADDED AN ISOLATED SHOWER MENTION FOR THE REST OF THE AFTERNOON
OVER CENTRAL WISCONSIN DUE TO SOME ISOLATED CONVECTION ALONG A
SUBTLE WEST TO EAST SURFACE BOUNDARY FROM AROUND MFI TO JUST NORTH
OF GRB. UPPER HEIGHTS SHOULD BE INCREASING BUT A MODIFIED SOUNDING
PRODUCING AROUND 800 CAPES.

OTHERWISE ONLY WEATHER ELEMENT OF CONCERN FOR TONIGHT IS THE
USUAL PATCHY FOG OVER THE MAIN STEM RIVER BASINS INCLUDING THE
WOLF RIVER AND WISCONSIN RIVER BASINS.

ON WEDNESDAY...AFTER SOME MORNING SUN...CLOUDS WILL BE ON THE
INCREASE FROM SOUTHWEST OT NORTHEAST AS A WARM FRONT LIFTS
NORTHWARD TO SOUTHERN MINNESOTA TO SOUTHWEST WISCONSIN LATE IN THE
DAY. BRUNT OF THE CONVECTION ARRIVES AFTER WEDNESDAY AFTERNOON
HOWEVER WILL START RAMPING UP POPS FOR THE LATER AFTERNOON HOURS
WITH THE WAA WORKING OVER THE NORTHWEST THIRD OF THE STATE AND RRQ
REGION OF THE UPPER JET BEGINS TO BRUSH OVER THE NORTH HALF OF
THE STATE.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY
ISSUED AT 213 PM CDT TUE SEP 2 2014

MAIN FOCUS IS ASSESSING SVR POTENTIAL WED NGT AND THU/THU EVE.
FOR WED NGT...CONVECTION SHOULD INITIALLY FIRE W OF THE AREA AND
THEN MV/EXPAND INTO THE FCST AREA AS LLJ STRENGTHENS TO ARND 50
KTS AND AND VEERS TO BECOME DIRECTED INTO THE AREA. HIGH POPS ARE
IN ORDER...AND GIVEN THE MOISTURE TRANSPORT...HEAVY RAIN IS
POSSIBLE AND THERE COULD EVEN BE A FLOODING THREAT.

SVR THREAT WED NGT IS A LITTLE MORE DIFFICULT TO PIN DOWN. MID-LVL
LAPSE RATES ALSO EXPECTED TO STEEPEN AS STG WLY FLOW ALOFT BRINGS
ELEVATED MIXED LAYER EWD. MODELS PRETTY CONSISTENT IN SHOWING
MOISTURE AND INSTABILITY INCRG DURING THE NIGHT AS LOW-LEVEL SWLY
FLOW STRENGTHENS. BUT DEEP MOISTURE HAS BEEN SHOVED PRETTY FAR S
AS OF THIS AFTN...SO IT WL HAVE A WAY TO GO TO GET HERE...AND HAVE
TO WONDER IF WE/LL END UP WITH ENOUGH ELEVATED INSTABILITY TO GET
SVR STORMS.

ONE OF TWO KEY FACTORS AFFECTING THE SVR RISK THU WL BE WHETHER OR
NOT THERE IS SUFFICIENT RECOVERY AFTER THE WED NGT STORMS. WE/VE
HAD SIMILAR SCENARIOS THE PAST 2 MONDAYS AND NEVER GOT THE MORNING
CONVECTION TO END QUICKLY ENOUGH FOR THE ATM TO RECOVER FOR A
SECOND ROUND OF STORMS. WHAT APPEARS DIFFERENT THIS TIME...
HOWEVER...IS THAT WLY FLOW ALOFT SHOULD ADVECT VERY WARM TEMPS IN
THE 850-700 MB LAYER INTO THE AREA. THE RESULTING INCREASE IN
CONVECTIVE INHIBITION MAKES IT LIKELY THE LATE NIGHT/EARLY MORNING
STORMS WILL MOVE OUT OF THE AREA AND NOT IMMEDIATELY BE REPLACED
BY REDEVELOPMENT. THAT WOULD DEFINITELY INCREASE THE SVR RISK
LATER IN THE DAY.

HAVING THE STG CAPPING WL CUT BOTH WAYS HOWEVER...AS IT WL NEED TO
BE BROKEN/REMOVED BEFORE NEW STORMS CAN FIRE IN THE AFTN. THERE
APPEARS TO BE NO CLEAR-CUT MECHANISM IN PLACE TO GUARANTEE THE CAP
WL BE BROKEN. THE FCST AREA WL START TO COME UNDER THE INFLUENCE
OF THE RRQ OF UPR SPEED MAX...BUT BEST SUPPORT FM THAT WL STILL BE
TO OUR W. UPR HEIGHT FALLS FM TAIL OF SHRTWV LIFTG INTO CANADA WL
BRUSH THE AREA...BUT AREN/T PROGGED TO BE GREAT. THE NAM HAS NO
TROUBLE BREAKING THE CAP...BUT NAM-BASED BUFR FCST SOUNDINGS SEEM
TO ERODE THE WARM TEMPS ALOFT MUCH TOO QUICKLY/EASILY GIVEN THE
MODEST LARGE-SCALE FORCING.

THIS LOOKS LIKE ALMOST A CLASSIC CONDITIONAL SVR THREAT. IF
CONVECTION CAN BREACH THE CAP...THE STORMS THAT FORM WL QUICKLY
BECOME SVR...WITH THE POSSIBILITY OF A HIGHER-END SVR EVENT. CIPS
ANALOGS FROM THE PAST FEW MODEL RUNS INDICATE A CONSIDERABLE
POTENTIAL FOR SVR WX. IN FACT...TWO VERY HIGH-PROFILE LATE-SEASON
SVR EVENTS ARE AMONG THE TOP ANALOGS...THE LADYSMITH TORNADO OF
2002 AND THE BIG FLATS TORNADO OF 1994. BUT...THERE ARE ALSO
SEVERAL ANALOGS WHERE NOTHING AT ALL HAPPENED IN THE FCST AREA. IF
THE CAP HOLDS LONG ENOUGH TO DELAY STORMS UNTIL THE COLD FRONT
AND BETTER UPR SUPPORT ARRIVES MUCH LATER IN THE NGT...AFTER THE
ATM STABILIZES SOME...THE SVR RISK COULD BE MARGINAL. WL ATTEMPT
TO CONVEY THE CONDITIONAL NATURE OF THE THREAT IN THE HWO.

PCPN COULD LINGER INTO FRI AS THE FRONTAL ZONE CLEARS THE AREA.
THEN QUIET WX IS LIKELY FOR THE WEEKEND.

NO SIG CHGS NEED TO BROAD-BASED EXTENDED FCST INITIALIZATION
GRIDS.
&&

.AVIATION...FOR 00Z TAF ISSUANCE
ISSUED AT 644 PM CDT TUE SEP 2 2014

VFR CONDITIONS TO PREVAIL INTO WEDNESDAY...WITH THE EXCEPTION OF
PATCHY FOG OVER THE USUAL PLACES...ALONG/NEAR RIVER BASINS
OVERNIGHT. INCREASE IN HIGH/MID CLOUDS IN THE AFTERNOON AS
CONVECTION FORMS TO THE WEST. &&

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

$$

SYNOPSIS.......SKOWRONSKI
SHORT TERM.....TDH
LONG TERM......SKOWRONSKI
AVIATION.......TE





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