Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 171957
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
257 PM CDT WED SEP 17 2014

FORECAST DISCUSSION FOR ROUTINE AFTERNOON FORECAST ISSUANCE

.SHORT TERM...TONIGHT AND THURSDAY
ISSUED AT 256 PM CDT WED SEP 17 2014

THE LATEST RUC ANALYSIS AND SATELLITE/RADAR IMAGERY SHOW A SHORTWAVE
TROUGH MOVING SOUTHEAST OVER THE UPPER PENINSULA AND A STRONG COLD
FRONT DROPPING SOUTH OVER THE UPPER PENINSULA OF MICHIGAN.
SCATTERED SHOWERS OVER LAKE SUPERIOR ARE EXITING THE REGION AHEAD OF
THE SHORTWAVE.  BUT THERE IS A FAIRLY WIDESPREAD AREA OF LOW STRATUS
BEHIND THE FRONT...THOUGH STARTING TO SEE SOME BREAKS IN THE
OVERCAST OCCUR OVER NORTHERN MINNESOTA AND LAKE SUPERIOR.  NORTHEAST
WINDS ARE ALSO QUITE GUSTY RIGHT BEHIND THE FRONT COINCIDENT WITH
MODEST PRESSURE RISES...AND SOME GUSTS ARE REACHING 30 KTS OVER
SOUTHERN LAKE SUPERIOR.  A CANADIAN SURFACE HIGH IS BUILDING
SOUTHEAST BEHIND THE FRONT AND USHERING IN ANOTHER COLD POLAR
AIRMASS WITH SOME SNOW BEING REPORTED JUST NORTH OF LAKE SUPERIOR.
AS THE FRONT DROPS SOUTH...SMALL PRECIP CHANCES...FROST/FREEZE
HEADLINES...AND WIND GUSTS ARE THE MAIN FORECAST CONCERNS.

TONIGHT...THE BACKDOOR COLD FRONT WILL CONTINUE TO SLIDE SOUTH
ACROSS CENTRAL AND NORTHEAST WISCONSIN DURING THE EVENING
HOURS...BEFORE SETTLING OVER SOUTHERN WISCONSIN OVERNIGHT.
MID-LEVEL MOISTURE WILL BE EXITING WITH THE SHORTWAVE THIS
AFTERNOON...SO NOT ANTICIPATING ANY SHOWERS WITH THE FRONT.  BUT DO
EXPECT A BAND OF LOW CLOUDS TO ACCOMPANY THE FRONT...ALONG WITH A
WIND SHIFT TO THE NORTHEAST.  WITH THE WIND SHIFT...WINDS COULD
BECOME QUITE GUSTY OVER NORTHEAST WISCONSIN...AS TRAJECTORIES WILL
BE FAVORABLE FOR FUNNELING DOWN THE BAY OF GREEN BAY.  SOME GUSTS TO
30 MPH ARE POSSIBLE.  SOME LOW STRATUS WILL LIKELY LINGER OVER
CENTRAL AND EAST-CENTRAL WISCONSIN THROUGH THE NIGHT...BUT
SUBSIDENCE WILL LIKELY LEAD TO CLEARING OVER N-C WISCONSIN
OVERNIGHT.  AS WINDS DIMINISH...THE LEADING GUIDANCE SHOWS LOW TEMPS
FALLING INTO THE UPPER 20S TO MID 30S OVER N-C WISCONSIN.  WILL
HOIST A FROST ADVISORY FOR THAT REGION.  GREATER CLOUD COVER AND
WIND SPEEDS SHOULD KEEP AREAS SAFE FROM THE FROST FURTHER SOUTH AND
EAST.

THURSDAY...PLENTY OF LOW LEVEL MOISTURE WILL LINGER BEHIND THE FRONT
OVER CENTRAL AND EAST-CENTRAL WISCONSIN IN THE MORNING...WHICH WILL
GRADUALLY RETURN NORTHWARD DURING THE AFTERNOON.
THEREFORE...ANTICIPATE SCT TO BKN CLOUDS TO EXPAND WITH HEATING OF
THE DAY.  WITH THE CLOUD COVER AND SHALLOW COLD AIRMASS...HIGHS WILL
RANGE FROM THE MIDDLE 50S TO LOWER 60S.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY
ISSUED AT 256 PM CDT WED SEP 17 2014

ZONAL FLOW OVER THE NORTHERN CONUS LATE THIS WEEK WILL QUICKLY
TRANSITION TO MORE HIGHLY AMPLIFIED PATTERN...CHARACTERIZED BY DEEP
TROUGH OVER THE GREAT LAKES AND RIDGE OVER WESTERN CANADA...BY EARLY
NEXT WEEK. FORECAST CHALLENGE EARLY IN THE EXTENDED WILL BE CENTERED
AROUND TIMING AND INTENSITY OF INITIAL SHORTWAVE IMPULSES EMBEDDED
WITHIN ZONAL FLOW FRIDAY INTO SATURDAY. THEREAFTER GREAT LAKES
WILL BE DOMINATED NORTHWESTERLY UPPER-LEVEL FLOW AND BROAD HIGH
PRESSURE DURING THE FIRST HALF OF NEXT WEEK. BEST OPPORTUNITY FOR
SUBSTANTIAL RAINFALL WILL BE EARLY IN THE PERIOD FOLLOWED BY
MAINLY DRY CONDITIONS AT LEAST THROUGH THE MIDDLE OF NEXT WEEK.
TEMPERATURES WILL START OUT ABOVE NORMAL FRIDAY AND SATURDAY...THEN
FALL BACK TO WELL BELOW NORMAL TOWARD THE MIDDLE PART OF NEXT
WEEK...WITH CHILLY NIGHTS AND POTENTIAL FOR AREAS OF FROST ACROSS
PARTS OF CENTRAL AND NORTHERN WISCONSIN.

INITIAL FORECAST CHALLENGE WILL BE TIMING OF SHOWER AND SCATTERED
THUNDERSTORMS ACTIVITY FRIDAY AFTERNOON AND EVENING WITH
APPROACHING SHORTWAVE IMPULSE...IN CONCERT WITH INCREASING LOW-
LEVEL WAA IN WAKE OF DEPARTING HIGH PRESSURE. WARM ADVECTION
BECOMES QUITE ROBUST BY 00Z SATURDAY AS 850 MB SOUTHWESTERLY WINDS
APPROACH 40 KTS. APPEARS MAJORITY OF LATEST MODEL GUIDANCE ARE A
BIT SLOWER ON INITIAL SHORTWAVE IMPULSE THUS HAVE TRIMMED BACK POPS
ACROSS THE EASTERN HALF OF THE FORECAST AREA IN THE 12Z TO 18Z
TIME FRAME FOR FRIDAY. APPEARS BEST FORCING WILL BE OVER NORTHERN
PORTION OF THE FORECAST AREA LATE FRIDAY AFTERNOON INTO FRIDAY
AND HAVE ADJUSTED POPS ACCORDINGLY. ON FRIDAY NIGHT...THE FORECAST
AREA SHOULD BE BECOME INCREASINGLY UNDER THE INFLUENCE OF THE RRQ
OF AN UPPER LEVEL JET THUS EXPECT GENERAL INCREASE IN ORGANIZED SCALE
SYNOPTIC SCALE LIFT AND DESTABILIZATION AHEAD OF SURFACE COLD
FRONT MOVING INTO CENTRAL MINNESOTA BY 06Z. ALTHOUGH STILL MODEL
DIFFERENCES IN LOCATION OF HEAVIEST QPF OVERNIGHT...ALL GUIDANCE
SUGGEST AN OVERALL INCREASE IN COVERAGE OF SHOWER AND THUNDERSTORM
ACTIVITY.

SATURDAY A BIT MORE UNCERTAIN AS STILL A FAIR AMOUNT OF MODEL
SPREAD ON TIMING OF COLD FRONT ACROSS THE FORECAST AREA. ECMWF
FASTER THAN MOST OF THE OTHER GUIDANCE. OPTED TO LEAN MORE TOWARD
A BLEND OF THE SREF MEAN AND ECMWF WHICH SUGGEST A SOMEWHAT FASTER
PROGRESSION. ADJUSTED POPS ACCORDINGLY WITH LIKELY POPS IN THE
MORNING AND TAPERED TOWARD CHANCE DURING THE AFTERNOON. GIVEN
THIS SCENARIO APPEARS ANY DEEP CONVECTION THAT CAN DEVELOP ALONG
THE COLD FRONT DURING THE AFTERNOON WILL MOST LIKELY OCCUR OVER
THE SOUTHEAST HALF OF THE STATE. IF ECMWF IS CORRECT...SATURDAY
AFTERNOON COULD BE MAINLY DRY. IF ENOUGH CLEARING CAN OCCUR
DAYTIME TEMPS SHOULD BE ABLE TO RESPOND AND RISE WELL INTO THE 70S
AS 850 TEMPS REALLY DO NOT FALL MUCH BEHIND THE COLD FRONT
INITIALLY.

ON SATURDAY NIGHT PRONOUNCED LFQ OF UPPER JET THEN PUSHES INTO
THE AREA WITH PRIMARY SHORTWAVE TROUGH CONTINUING TO DEEPEN OVER
THE AREA. WOULD EXPECT TO SEE SHOWER ACTIVITY INCREASE OVERNIGHT
SATURDAY ESPECIALLY ACROSS THE NORTH. UPPER TROUGH AXIS WILL
PERSIST OVER THE AREA ON SUNDAY WITH CAA CONTINUING. SCENARIO
FAVORABLE FOR AFTERNOON DIURNAL SHOWER ACTIVITY TO DEVELOP OVER
THE NORTHERN PORTION OF THE FORECAST AREA. LEFT SMALL POPS IN FOR
SUNDAY TO ACCOUNT FOR THIS.

HIGH PRESSURE FINALLY BUILDS IN SUNDAY NIGHT AND MONDAY BRINGING A
STRETCH OF DRIER WEATHER INTO AT LEAST MIDWEEK. EXPECT TEMPS TO BE
BELOW NORMAL THROUGH THE FIRST HALF OF THE WEEK WITH POTENTIAL FOR
SOME EARLY MORNING FROST OR FREEZE ESPECIALLY ON TUESDAY MORNING.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1133 AM CDT WED SEP 17 2014

A BACKDOOR COLD FRONT WILL DROP SOUTH ACROSS THE REGION
LATE THIS AFTERNOON AND EVENING. MOISTURE IS LACKING SO EXPECT ONLY
CLOUDS AS THE FRONT GOES BY. PLENTY OF MVFR CIGS BEHIND THE
FRONT...AND THINK THESE CIGS WILL MAKE IT INTO THE NORTH-CENTRAL AND
CENTRAL WISCONSIN TAF SITES.  SOME CLEARING IS LIKELY ACROSS
NORTH-CENTRAL WISCONSIN LATE...WHICH WILL RESULT IN A FROST OR
FREEZE. SKIES WILL BECOME MOSTLY CLOUDY ONCE AGAIN THURSDAY
MORNING OVER N-C WISCONSIN WITH MVFR CIGS...BUT PARTLY SUNNY
FARTHER EAST.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
FROST ADVISORY FROM 1 AM TO 8 AM CDT THURSDAY FOR WIZ010>013-018-
019.

FREEZE WARNING FROM 1 AM TO 8 AM CDT THURSDAY FOR WIZ005.
&&

$$

SHORT TERM.....MPC
LONG TERM......ESB
AVIATION.......MPC





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