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000
FXUS63 KGRB 202007
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
307 PM CDT MON MAY 20 2013

FORECAST DISCUSSION FOR ROUTINE AFTERNOON FORECAST ISSUANCE

.SHORT TERM...TONIGHT AND TUESDAY
ISSUED AT 306 PM CDT MON MAY 20 2013

THE THREAT FOR SVR STORMS CONTS TO BE THE PRIMARY FOCUS OF THE
FCST FOR BOTH TNGT AND ON TUE.

THE 19Z MSAS SFC ANALYSIS SHOWED A STRONG AREA OF LOW PRES OVER
THE NE CORNER OF SD WITH A FRONTAL BOUNDARY EXTENDED EWD THRU
CNTRL WI. A CDFNT STRETCHED SWD FROM THE LOW THRU THE PLAINS. A
LOOK AT THE WATER VAPOR IMAGERY INDICATED AN MID-LEVEL AREA OF LOW
PRES OVER THE NRN PLAINS. TSTMS HAVE FIRED OVER IN LWR MI WHERE
BETTER INSTABILITY RESIDES AND SHWRS CONTINUED TO SPIN NWD OVER
WRN WI.

AN INITIAL SURGE OF DRIER AIR ALOFT WAS NOT HANDLED WELL BY THE
MDLS EARLIER TODAY...HOWEVER PREVAILING SW WINDS TO PUMP MORE
MOISTURE INTO WI LATER THIS AFTERNOON/EARLY EVENING AND HELP TO
LIFT CAPES INTO THE 1000-1500 J/KG RANGE. MODERATE TO STRONG 0-6KM
SHEAR REMAINS OVER THE REGION...THUS AS MOISTURE INCREASES AND A
TRIGGER ARRIVES (MID-LEVEL SPEED MAX)...EXPECT TO SEE CONVECTION
BLOSSOM TO OUR SOUTH AND OVERSPREAD NE WI LATER THIS EVENING. THE
TSTM ACTIVITY SHOULD BE LINE SEGMENTS WHICH COULD BRING SOME OF
THIS STRONGER WIND ALOFT DOWN TO THE SFC...THUS THE GREATEST SVR
THREAT WOULD BE DAMAGING WIND GUSTS. STORMS SHOULD WEAKEN A BIT
DURING THE OVRNGT HOURS AS INSTABILITY WEAKENS...BUT HAVE KEPT
SHWR/ISOLATED TSTM WORDING OVRNGT AS SHORTWAVE ENERGY TO STILL BE
MOVING THRU THE REGION.

THE UPR TROF TO OUR WEST IS FCST TO SLOWLY EDGE EAST ACROSS THE
PLAINS AND WEAKEN A BIT. MEANWHILE...THE SFC LOW TRACKS ACROSS THE
UPR MS VALLEY AND ALSO WEAKENS SOMEWHAT ON TUE. THE MAIN QUESTION
FOR TUE FOR NE WI IS HOW MANY CLOUDS WL STILL BE AROUND DURING THE
MORNING FROM OVRNGT CONVECTION? THE ATMOSPHERE SHOULD HAVE
STABILIZED BY THIS TIME AND WL HAVE TO WAIT FOR THE CLOUDS TO
BREAK UP TO PERMIT SUFFICIENT HEATING TO ALLOW DESTABILIZATION TO
TAKE PLACE. ANOTHER CONCERN WOULD BE THE ANTICIPATED MCS OVER THE
SRN PLAINS/MID-MS VALLEY WHICH COULD ROB SOME OF THE INCOMING GULF
MOISTURE. ONCE INSTABILITY OCCURS...MDLS SHOW ENUF SHEAR TO HELP
ORGANIZE THE NEXT ROUND OF STRONG TO SVR TSTMS FROM THE GREAT
LAKES SW TO THE OZARKS. SINCE THERE IS SOME DOUBT AS TO WHEN THE
NEW STORMS WOULD FIRE AND EXACTLY WHERE THEY WOULD FIRE...PREFER
TO FOCUS HIGHER POPS IN THE AFTERNOON.

.LONG TERM...TUESDAY NIGHT THROUGH MONDAY
ISSUED AT 306 PM CDT MON MAY 20 2013

THE LATEST GFS ENSEMBLE MEAN INDICATES THAT THE PESKY UPPER LOW
THATS CURRENTLY OVER THE CENTRAL PLAINS WILL SHIFT EAST ACROSS THE
AREA WEDNESDAY NIGHT BEFORE DEPARTING.  THEREAFTER...NW FLOW WILL
PREVAIL FOR SEVERAL DAYS...WHICH WILL LEAD TO QUIETER AND COOLER
CONDITIONS.  THE NEXT CHANCE OF PRECIP FOLLOWING THE UPPER LOW WILL
OCCUR DUE TO RETURN FLOW NEXT WEEKEND...WHICH MODELS OFFER DIFFERENT
SOLUTIONS.  AS IS USUAL...THE GFS IS MORE PROGRESSIVE IN ADVANCING
A WARM FRONT INTO THE REGION SATURDAY NIGHT INTO SUNDAY...WHICH THE
ECMWF PORTRAYS A STRONG HUDSON BAY HIGH KEEPING THE WARM FRONT TO
OUR SW.  THE ECMWF HAS SUPPORT FROM THE CANADIAN SO THINK A
COMPROMISE BETWEEN THE TWO SOLUTIONS IS IN ORDER.

TUESDAY NIGHT THROUGH THURSDAY...UPPER LOW OVER THE DAKOTAS WILL
FINALLY SHIFT EAST TUESDAY NIGHT AND WEDNESDAY.  BROAD SURFACE LOW
PRESSURE WILL MOVE EAST ACROSS WISCONSIN TUESDAY NIGHT BEFORE A
SECONDARY SURFACE LOW ORGANIZES OVER NORTHERN ILLINOIS.  SHOULD HAVE
ENOUGH SURFACE INSTABILITY AND FORCING FOR THE THREAT OF STORMS TO
CONTINUE THROUGH TUESDAY EVENING.  STORMS SHOULD DISSIPATE OVERNIGHT
ON TUESDAY...BUT SOME SHOWERS MAY CONTINUE OVER N-C WISCONSIN CLOSER
A STALLED OUT FRONT.  SHOWERS LOOK TO BE A DECENT BET ON WEDNESDAY AS THE
SURFACE LOW MOVES FROM NORTHERN ILLINOIS INTO LOWER MICHIGAN AND THE
UPPER LOW MOVES OVERHEAD.  OUT OF THE WARM SECTOR...TEMPS WILL BE
COOLING OFF INTO THE 60S WITH PLENTY OF CLOUDS AROUND.  WILL LOWER HIGHS A
TAD.  PRECIP WILL BE DIMINISHING FROM NW TO SE WEDNESDAY NIGHT AS
THE LOW HEADS TOWARDS THE EASTERN GREAT LAKES...AND A DRY HUDSON BAY
HIGH BUILDS OVER THE NORTHERN MISSISSIPPI VALLEY. THIS HIGH WILL
THEN RESIDE ACROSS THE AREA ON THURSDAY WITH HIGHS IN THE LOW TO MID
60S.

REST OF THE FORECAST...HUDSON BAY HIGH WILL CONTINUE TO BE PRESENT
ACROSS THE AREA ON FRIDAY WITH HIGHS NOT THAT DIFFERENT THAN ON
THURSDAY.  BY FRIDAY NIGHT AND SATURDAY...A BUILDING RIDGE OVER THE
CENTRAL PART OF THE CONTINENT WILL PUSH A WARM FRONT NORTH ACROSS
THE GREAT PLAINS.  SHOULD SEE A BAND OF PRECIP DEVELOP NORTH OF THE
BOUNDARY FROM THE NORTHERN PLAINS TO THE SOUTHWEST GREAT LAKES.  THE
HUDSON BAY HIGH PRESSURE WILL CONTINUE TO FUNNEL IN VERY DRY AIR
ACROSS WISCONSIN DURING THIS TIME...AND TEND TO THINK THAT THE DRY
AIR WILL WIN OUT FOR MUCH OF THE FORECAST AREA.  THINK PRECIP
CHANCES WILL IMPROVE OVER THE SECOND HALF OF THE WEEKEND AS THE
MID-LEVEL RIDGE MOVES EAST AND THE WARM FRONT LIFTS NORTH.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1243 PM CDT MON MAY 20 2013

AN INFLUX OF DRIER AIR EARLIER IN THE DAY HAS REALLY
SLOWED THE ONSET OF TSTM DEVELOPMENT OVER THE REGION SO FAR TODAY.
HAVE MAINTAINED VFR CONDITIONS THRU THIS AFTERNOON...BUT STILL
EXPECT TO SEE ANOTHER ROUND OF STORMS DEVELOP TO OUR SOUTH AS
MOISTURE/INSTABILITY FINALLY DO CLIMB AND A MID-LEVEL SPEED MAX
HELPS TO PROVIDE THE NECESSARY TRIGGER. INITIAL THOUGHTS ARE FOR
THESE TSTMS TO AFFECT THE NE WI TAF SITES ROUGHLY BETWEEN 02Z AND
06Z TUE AND THE POSSIBILITY OF SVR IS STILL THERE WITH DAMAGING
WIND GUSTS THE PRIMARY THREAT. MVFR CIGS/VSBYS WOULD ACCOMPANY
ANY OF THESE STORMS ALONG WITH HEAVY RAINFALL. SINCE BOTH THE SFC
LOW AND UPR LOW ARE STILL TO OUR WEST ON TUE...WE SHOULD SEE
ADDITIONAL SHWRS/TSTMS ESPECIALLY IN THE AFTERNOON AS THE
ATMOSPHERE RELOADS. IN THE MEANTIME...HAVE KEPT PRIMARILY VFR
CONDITIONS AROUND THRU TUE EXCEPT NEAR ANY STORMS.
&&

.MARINE...
ISSUED AT 306 PM CDT MON MAY 20 2013

NEXT ROUND OF SHOWERS AND STORMS SHOULD OCCUR EARLY THIS
EVENING AND LINGER INTO THE EARLY MORNING HOURS. THESE STORMS COULD
PRODUCE STRONG WINDS. MOIST AIR FLOWING OVER THE COLDER WATERS OF
THE BAY AND LAKE WILL RESULT IN FOG AT TIMES THROUGH TUESDAY
NIGHT. THE FOG WILL BE LOCALLY DENSE WITH VISIBILITIES BELOW ONE
MILE AT TIMES.
&&

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

$$

SHORT TERM.....AK
LONG TERM......MPC
AVIATION.......AK
MARINE.........AK