Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 281713
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1213 PM CDT SUN SEP 28 2014

UPDATED AVIATION PORTION FOR 18Z TAF ISSUANCE

.SYNOPSIS...
ISSUED AT 306 AM CDT SUN SEP 28 2014

ONE LAST DRY AND UNSEASONABLY WARM DAY TODAY...THEN SCATTERED
SHOWERS AND TURNING SHARPLY COOLER TOMORROW.

THE FLOW ENTERING NOAM IS SPLIT...WITH CLOSED UPR LOW IN THE SRN
STREAM ACRS THE INTERMOUNTAIN WEST. A NRN STREAM UPR LOW WAS BACK
TO THE NW OVER THE GULF OF AK. THE SPLIT CONSOLIDATES DOWNSTREAM...
INTO A BROAD BAND OF WESTERLIES ACRS CANADA. TO THE S...A LARGE
SPRAWLING UPR RIDGE DOMINATES THE CENTRAL AND ERN CONUS. PHASING
OF THE NRN AND SRN STREAMS OUT W WL CAUSE THE ERN CONUS RIDGE TO
CONSOLIDATE AND SHARPEN NWD THROUGH THE PLAINS THE NEXT COUPLE
DAYS...THEN SHIFT E AS THE RE-ENERGIZED WRN TROF HEADS ACRS THE
PLAINS DURING THE MIDDLE TO LATTER PART OF THE WORK WEEK. ITS
LIKELY THAT BY THE END OF THE PERIOD THE WE/LL HAVE A RIDGE IN
THE W AND A TROF IN ERN NOAM.

ONE MORE DRY AND UNSEASONABLY WARM DAY IS ON TAP FOR TDA AS UPR
RIDGE CONTS TO DOMINATE THE AREA. THEN THE WWD SHIFT/SHARPENING OF
THE RIDGE WL ALLOW A STG BACKDOOR COLD FRONT TO SURGE THROUGH THE
AREA MON...DROPPING TEMPS BACK TO AOB NORMAL...WHERE THEY WL REMAIN
AS THE UPR TROF APPROACHES AND THE CROSSES THE AREA. PCPN AMNTS
FOR THE PERIOD WL PROBABLY END UP AOA NORMAL...WITH THE BULK OF
THAT OCCURRING LATE IN THE PERIOD AS THE UPR TROF CROSSES THE RGN.
&&

.SHORT TERM...TODAY...TONIGHT...AND MONDAY
ISSUED AT 306 AM CDT SUN SEP 28 2014

SOME CI WL BE ACRS THE AREA TDA...BUT PROBABLY NOT ENOUGH TO
IMPACT TEMPS. WENT WITH MAX TEMPS VERY CLOSE TO YDA. A FEW OF THE
MODELS WERE GENERATING A LITTLE LGT PCPN OVER THE NE CORNER OF WI.
SCT SHRA AND EVEN SOME TSRA HAVE OCCURRED OUT TO OUR W THE PAST
FEW DAYS...NR THE CENTER OF A WK UPR LOW THAT WAS TRAPPED WITHIN
THE LARGE SCALE RIDGING. MODELS SUGGEST NEARLY AS MUCH INSTABILITY
ACRS THE C-NE WI TDA AS TOTAL-TOTALS RISE TO NR 50. BUT THE
PROBLEM IS FINDING A TRIGGER. LARGE SCALE QG FORCING FAVORS WK
SUBSIDENCE. THE MODELS GENERATING PCPN SEEM TO BE FOCUSING ON THE
INCREASED LOW-LEVEL CONVERGENCE NEAR THE DOUBLE LAKE BREEZE OVER
ERN UPPER MICHIGAN. BUT NOT SURE THAT WL BE ENOUGH...AND EVEN IF
IT IS...IT WL BE CENTERED NE OF THE FCST AREA. KEPT FCST
DRY...THOUGH DID ACKNOWLEDGE THE OUTSIDE POSSIBILITY OF PCPN BY
EDGING POPS UP TO 14 OVER THE FAR NE.

THE MAIN WX PRODUCER THE NEXT 24-48 HRS WL BE STG COLD FRONT
EXPECTED TO SURGE SWD/SWWD ACRS THE AREA. 20-25F 24-HR TEMPS DROPS
WERE OCCURRING WITH THE FRONT OVER ND AND SRN MB EARLY THIS
MORNING. A LITTLE DISAGREEMENT ON THE TIMING OF FROPA ON THE
MODELS...SO WENT WITH A COMPROMISE FOR THE FCST. THE FRONT SHOULD
BE STG ENOUGH TO PRODUCE A NOTICABLE DROP IN TEMPS WHEN IT GOES
THROUGH. EXPECT A PERIOD OF FAIRLY STG NE WINDS TO FOLLOW THE
FROPA IN E-C WI...ESP NEAR THE BAY. BACKDOOR FRONTS SUCH AS THIS
ARE NOT NORMALLY GOOD PCPN PRODUCERS. THIS ONE WL HAVE A SHRTWV
WITH SOME SIG QC FORCING AND FRONTOGENETIC FORCING FOLLOWING SWD
BEHIND IT. THE PCPN WL BE POST-FRONTAL AND ELEVATED INSTABILITY IS
RATHER POOR SO LEFT THUNDER OUT OF THE FCST. PCPN AMNTS WL
PROBABLY BE MODEST AS WELL. WENT WITH THE HIGHEST POPS...IN THE
LIKELY CATEGORY...ACRS THE FAR N/NE. CENTRAL WI WL BE FARTHER FM
THE STRONGEST FORCING...SO SHRA THERE WL PROBABY BE MORE SCT.
TEMPS WL HAVE A STG NON-DIURNAL TREND. THE N PROBABLY WON/T WARM
UP MUCH AT ALL. EXPECT MID-LATE MORNING MAXES OVER ALL BUT THE FAR
SRN PART OF THE FCST AREA...WITH MID-DAY HIGHS IN THE FAR S.

.LONG TERM...MONDAY NIGHT THROUGH SATURDAY
ISSUED AT 306 AM CDT SUN SEP 28 2014

THE LATEST GFS ENSEMBLE MEAN INDICATES A SIGNIFICANT PATTERN CHANGE
WILL TAKE PLACE BY THE END OF THE UPCOMING WORK WEEK AS THE LARGE
WESTERN NOAM TROUGH MOVES INTO THE GREAT LAKES.  EARLY INDICATIONS
ARE THAT BELOW NORMAL HEIGHTS WILL THEN STICK AROUND INTO THE
FOLLOWING WEEK.  BOTH THE ECMWF AND GFS HAVE COME INTO MUCH BETTER
AGREEMENT AS THIS PATTERN CHANGE TAKES PLACE...AND A BLEND OF THESE
MODELS WILL WORK.

MONDAY NIGHT THROUGH TUESDAY NIGHT...THE COLD FRONT WILL BE MOVING
SOUTH OVER SOUTHERN WISCONSIN EARLY IN THE EVENING AND INTO NORTHERN
ILLINOIS LATER IN THE NIGHT.  THOUGH WILL STILL HAVE MID-LEVEL FGEN
BEHIND THE FRONT...THE ADDITIONAL SUPPORT FROM THE SHORTWAVE SHOULD
CREATE THE BEST CHANCE OF RAIN OVER EAST-CENTRAL WISCONSIN EARLY
MONDAY EVENING...AND LESSER CHANCES FARTHER WEST.
MEANWHILE...INCOMING DRY AIR FROM A CANADIAN HIGH WILL PUSH SOUTH
ACROSS NORTH-CENTRAL WISCONSIN AND POSSIBLY CENTRAL AND
EAST-CENTRAL...THOUGH UNCERTAINTY WITH THE CLEARING IS HIGH DUE TO
THE POSSIBILITY OF LAKE CLOUDS BECOMING TRAPPED BENEATH THE LOWERING
INVERSION.  THIS COULD ALSO IMPACT FROST POTENTIAL OVER N-C
WISCONSIN.  HIGH PRESSURE WILL BE OVER THE AREA ON TUESDAY AS THE
FRONT STALLS FROM CENTRAL MINNESOTA TO NORTHERN ILLINOIS.  THE
FORECAST STILL LOOKS DRY BUT SIGNIFICANTLY COOLER OVER CENTRAL AND
NORTHEAST WISCONSIN.  WILL DROP HIGHS A GOOD 3 TO 5 DEGREES.  THE
FRONT STARTS TO RETURN NORTH OVER THE NORTHERN MISSISSIPPI VALLEY
TUESDAY NIGHT WITH A BAND OF RAIN REMAINING TO OUR WEST.  A COOL
NIGHT WITH CLOUDS ARRIVING LATE.  LOWS MAINLY IN THE 40S.

REST OF THE FORECAST...THE BAND OF SHOWERS AND POSSIBLY A FEW
THUNDERSTORMS WILL MAKE A LITTLE PROGRESS TO THE EAST BUT WILL RUN
OUT OF STEAM AS THEY RUN INTO DRIER AND MORE STABLE AIR CLOSER TO
THE CANADIAN HIGH ON WEDNESDAY.  WILL KEEP A CHANCE ACROSS CENTRAL
AND NORTH-CENTRAL WISCONSIN.  CHANCES FOR RAIN IMPROVE WEDNESDAY
NIGHT AND THURSDAY WHEN HEIGHT FALLS ARRIVE AHEAD OF THE DEEP
WESTERN NOAM TROUGH.  THE GFS NOW SHOWS A SIGNIFICANT RAIN EVENT
THURSDAY NIGHT INTO FRIDAY AS INTENSIFYING LOW PRESSURE CROSSES THE
REGION...BUT THE 00Z RUN OF THE ECMWF BACKED OFF ITS STRONG LOW SCENARIO.
SOME SHOWERS WILL LIKELY STICK AROUND ON FRIDAY UNDERNEATH THE UPPER
TROUGH.  THEN TURNING COOLER AND DRIER FOR SATURDAY.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1212 PM CDT SUN SEP 28 2014

VFR CONDITIONS TO PREVAIL INTO THE MID-EVENING HOURS BEFORE PATCHY
FOG DEVELOPS ONCE AGAIN AND SENDS VSBYS DOWN MAINLY IN THE MVFR
RANGE. THERE IS POTENTIAL ONCE AGAIN FOR THE RHI TAF SITE TO
BRIEFLY DIP TO LIFR RANGE BEFORE CLOUDS BEGIN TO ARRIVE AHEAD OF A
STRONG CDFNT. THIS FNT IS FCST TO DROP INTO NRN WI LATE TNGT AND
THEN SWEEP SWD THRU THE REST OF NE WI MON MORNING. A SHARP WIND
SHIFT TO THE NORTH IS EXPECTED BEHIND THE FNT WITH A CHC OF SHWRS
THRU THE DAY. CIGS WL ALSO DROP INTO THE IFR/MVFR RANGE BEHIND THE
FNT. NRN WI MAY SEE CIGS BEGIN TO RISE LATER MON AFTERNOON AS
DRIER AIR BEGINS TO PUSH INTO THE REGION.
&&

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

$$

SYNOPSIS.......SKOWRONSKI
SHORT TERM.....SKOWRONSKI
LONG TERM......MPC
AVIATION.......AK





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