Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 040807
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
307 AM CDT MON MAY 4 2015

FORECAST DISCUSSION FOR ROUTINE MORNING FORECAST ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND TUESDAY
ISSUED AT 306 AM CDT MON MAY 4 2015

A SLOWLY SHRINKING STRATIFORM RAIN IN THE WAKE OF A COLD FRONT
WILL CONTINUE TO SLIDE EASTWARD OVER EAST CENTRAL WISCONSIN EARLY
THIS MORNING. ONLY ISSUE IS HOW LONG TO HANG ONTO MORNING PCPN
OVER AREAS SOUTHEAST OF LINE FROM OSH TO MTW THIS MORNING AS A
WEAK MESO VORT CENTER TRACKS OVER. PERHAPS ONLY MTW COUNTY THROUGH
7 AM.

HIGH PRESSURE BUILDING INTO THE REGION TODAY WILL BRING DRIER AIR
AND DECREASING CLOUDS FROM THE NORTH. WARM START THIS MORNING
FOLLOWED WITH SOME CLEARING SKIES SHOULD ALLOW TEMPERATURES TO
RISE INTO THE LOWER 70S OVER THE USUAL WARM SPOTS TODAY...AND
STILL SLIGHTLY ABOVE SEASONAL NORMAL TEMPERATURES ELSEWHERE.
COOL EASTERLY FLOW OFF LAKE MICHIGAN THE ONLY EXCEPTION.

THE PRIMARY FORECAST ISSUE LATER TODAY AS WELL AS THROUGH TUESDAY
DEALS WITH THE LOCATION OF THE COLD FRONT OR FRONTAL BOUNDARY AND
RATE OF NORTHWARD RETURN OF THIS BOUNDARY. RUN TO RUN PROGS HAVE
NOT BEEN CONSISTENT WITH THE TRACKING OF THIS FRONT AS OF
LATE...BUT CONSENSUS EARLY THIS MORNING IS A LATER ARRIVAL OF ANY
PRECIPITATION ON TUESDAY. MID TO HIGH LEVEL CLOUDS WERE NOTED OVER
SOUTH DAKOTA AND NORTH OF A DEVELOPING WAVE OVER NEBRASKA WHICH IS
PROGGED TO TRACK ALONG THE FRONT TONIGHT. SOME OF THESE CLOUDS MAY
DRIFT BACK INTO CENTRAL AND EAST CENTRAL WISCONSIN LATER TODAY AND
INTO TONIGHT. LATEST MODELS ARE GOOD AGREEMENT WITH KEEPING THIS
PRECIPITATION ASSOCIATED WITH THIS WAVE SOUTH OF THE AREA TOWARD
THE BOUNDARY TONIGHT. PROBLEM INCREASES ON TUESDAY WITH THE RATE
OF RETURN OF THE BOUNDARY AND ANY INCREASING PCPN CHANCES FROM THE
SOUTH. THE BOUNDARY MAY HOLD UP DUE TO THE PASSING WAVE LATE
TONIGHT INTO TUESDAY. WILL REDUCE BUT CONTINUE WITH A CHANCE OF
SHOWERS ON TUESDAY FOR AREAS SOUTH OF HIGHWAY 10...AND GO DRY
NORTH. ALSO REMOVED TSRA MENTION FOR TUESDAY DUE TO THE LOWER PCPN
CHANCES AND FORECAST SOUNDINGS FAIRLY STABLE. COOLER BUT STILL
SEASONABLE TEMPERATURES EXPECTED FOR TUESDAY WITH THE INCREASING
CLOUDS. THE WARMEST TEMPERATURES LIKELY ACROSS THE NORTH WITH MORE
SUNSHINE.

.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY
ISSUED AT 306 AM CDT MON MAY 4 2015

MEAN FLOW IS PROGGED TO BECOME AMPLIFIED AND BLOCKY THRU THE END
OF THE WEEK WITH A BROAD UPR TROF OVER THE WRN CONUS AND AN UPR
RDG OVER THE ERN CONUS. THIS SET-UP WOULD BRING A SW FLOW TO THE
CNTRL CONUS WITH ABOVE NORMAL TEMPS AND SEVERAL OPPORTUNITIES FOR
PCPN. MAIN FCST CHALLENGE MAY END UP TRYING TO FIND A PERIOD IN
THE EXTENDED FCST WHERE NO PCPN WL FALL AS AN ACTIVE STRETCH OF
WEATHER IS ANTICIIPATED.

MODELS CONT TO STRUGGLE WITH HOW FAST TO LIFT THE WRMFNT INTO TUE
NGT WHICH WL OBVIOUSLY HAVE AN IMPACT ON POPS ACROSS NE WI. THE
00Z GFS AND GEM HAVE REALLY BACKED OFF ON BOTH POPS AND QPF...
WHILE THE ECMWF AND ESPECIALLY THE NAM CONT TO BRING MEDIUM CHC
POPS TO MOST OF THE AREA. EXPECT THE WRMFNT TO LIFT NORTH IN
RESPONSE TO A PROMINENT SHORTWAVE TROF PULLING NE OUT OF THE SW
CONUS. DUE TO MODEL INCONSISTENCY WITH THE WRMFNT...PREFER TO USE
A MODEL COMPROMISE WHICH WOULD ESSENTIALLY DELAY ANY PCPN IN THE
NORTH TIL AFTER MIDNGT AND MAINTAIN THE HIGHEST CHC POPS OVER
CNTRL WI. MIN TEMPS TO RANGE FROM THE LWR TO MID 40S NORTH/ALONG
THE LAKE...MID TO UPR 40S SOUTH.

THE WRMFNT SHOULD CONT TO LIFT NWD THRU THE REST OF WI ON WED AS
THE SHORTWAVE TROF MOVES INTO THE CNTRL PLAINS AND BEGINS TO
WEAKEN IN THE PROCESS. WL NEED TO CARRY CHC POPS IN THE FCST TIL
THE FNT CLEARS THE AREA WITH THE ACTIVITY BECOMING MORE ISOLATED
IN THE AFTERNOON FROM SOUTH TO NORTH. MAX TEMPS TO RANGE FROM THE
UPR 50S ALONG LAKE MI...TO THE MID 70S OVER THE WARMER LOCATIONS
OF CNTRL WI.

NE WI TO RESIDE IN THE WARM SECTOR WED NGT THRU THU WITH THE
WRMFNT WELL TO OUR NORTH AND THE WEAKENING SHORTWAVE TROF MOVING
NE THRU THE UPR MS VALLEY/NW SECTIONS OF THE GREAT LAKES. THERE
COULD BE A LULL IN THE PCPN CHCS (ESPECIALLY ERN WI) WED NGT INTO
THU MORNING AS THERE IS NO TRIGGER OR FOCUSING MECHANISM OTHER
THAN WEAK WAA. BY THU AFTERNOON...PROSPECTS FOR PCPN BEGIN TO
INCREASE ESPECIALLY OVER CNTRL WI AS WEAK FORCING FROM THE
SHORTWAVE TROF REACHES WI AND THE ATMOSPHERE BECOMES INCREASINGLY
UNSTABLE AS MAX TEMPS SOAR INTO THE UPR 70S/LWR 80S (COOLER
LAKESIDE) AND DEW POINTS APPROACH 60 DEGS. IF THE SHEAR WOULD BE
STRONGER...WE COULD BE LOOKING AT STRONGER/BORDELINE SVR STORMS.

AS THE REMAINS OF THE SHORTWAVE TROF SHIFTS INTO ONTARIO THU NGT...
A TRAILING CDFNT IS PROGGED TO PUSH EAST INTO THE WRN GREAT LAKES.
PROBLEM HERE IS THAT THE MODELS DIFFER WITHI THE TIMING OF THIS
FNT WITH THE ECMWF FASTER THAN THE GFS AND GEM. WHILE CHC POPS ARE
NECESSARY THU NGT AHEAD OF THE CDFNT...THE MAIN ISSUE IS ON FRI AS
THE ECMWF ALREADY DRYING THE FCST AREA OUT WHILE THE OTHER MODELS
ARE STILL SENDING THE FNT THRU WI. HAVE FOLLOWED THE MODEL
CONSENSUS FOR NOW AND KEPT CHC POPS IN THE FCST FOR BOTH THU NGT
AND FRI.

CHC OF SHWRS AND TSTMS MAY CARRY OVER THRU FRI NGT AS A SFC WAVE
MAY DEVELOP AND MOVE ALONG THE CDFNT AND LIFT NE THRU THE GREAT
LAKES. ONCE THIS FEATURE CLEARS THE REGION...THERE IS A POTENTIAL
OF SEEING A BRIEF PERIOD OF DRY WEATHER ON SAT AS NE WI TO RESIDE
BETWEEN SYSTEMS. TIMING OF ALL THIS IS STILL SUSPECT AT THIS TIME
AND CONFIDENCE IS RATHER LOW...THUS WL LEAVE A TOKEN SMALL POP IN
THE FCST FOR SAT AND HOPE TO SEE SOME CLARITY AMONG THE MODELS.

MAIN FOCUS FOR THE END OF THE WEEKEND WL BE THE MOVEMENT OF THE
WRN CONUS UPR TROF WHICH IS PROGGED TO LIFT NEWD TOWARD THE CNTRL
PLAINS. WOULD EXPECT THE CDFNT TO RETURN NORTH AS WRMFNT ON SUNDAY
AND BEGIN TO INCREASE THE POPS OVER WI ONCE AGAIN...ESPECIALLY
OVER THE SRN HALF OF THE STATE.
&&

.AVIATION...FOR 06Z TAF ISSUANCE
ISSUED AT 1143 PM CDT SUN MAY 3 2015

SHOWERS AND THUNDERSTORMS WILL DEPART LATE TONIGHT AHEAD
OF A COLD FRONT.  GUSTY WINDS TO 30 KTS AND SMALL HAIL WILL BE
POSSIBLE WITH ANY STORMS.  BEHIND THE FRONT...CANADIAN HIGH PRESSURE
WILL BUILD INTO THE REGION BRINGING AMPLE DRY AIR WITH IT.  AS A
RESULT...SHOULD SEE GOOD FLYING WEATHER FOR MUCH OF THE DAY TOMORROW.
&&

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

$$

SHORT TERM.....TDH
LONG TERM......KALLAS
AVIATION.......MPC






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