Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 290414
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1114 PM CDT THU AUG 28 2014

UPDATED AVIATION PORTION FOR 06Z TAF ISSUANCE

.SHORT TERM...TONIGHT AND FRIDAY
ISSUED AT 412 PM CDT THU AUG 28 2014

CHANCES FOR HEAVY RAINFALL AND POTENTIAL FOR FLOODING ARE THE
MAIN CONCERNS IN THE SHORT TERM.

RADAR MOSAIC LAPSE RATE SHOWED SHOWERS AND THUNDERSTORMS MOVING
OUT OF THE PLAINS AND DECREASING IN INTENSITY AND COVERAGE AS THEY
APPROACHED THE FORECAST AREA TODAY. KGRB RADAR AND SURFACE
OBSERVATIONS INDICATED SOME LIGHT SHOWERS IN WOOD COUNTY AT 21Z.
MODELS ALL HAD MEASURABLE RAINFALL IN THE AREA TONIGHT AS A WEAK
MID LEVEL SHORT WAVE PASSES ACROSS THE STATE AHEAD OF A CENTRAL
PLAINS TROUGH. MAJOR DIFFERENCES IN PWATS ON THE 12Z SOUNDINGS
FROM 0.77 INCH AT GRB TO 1.41 INCHES AT MPX AND 1.85 INCHES AT
DVN. EASTERLY SURFACE FLOW WAS KEEPING RELATIVELY DRIER AIR IN THE
AREA...WITH DEW POINTS MAINLY IN THE 50S. MOISTURE WILL REACH AND
THEN SPREAD ACROSS THE AREA TONIGHT.

THE SHORT WAVE ENERGY...AN 850MB JET AND WARM FRONT MOVING ACROSS
THE STATE TONIGHT...AND SOME UPPER LEVEL DIVERGENCE ASSOCIATED WITH
THE RIGHT ENTRANCE REGION OF A 300MB JET MAX WILL PROVIDE THE LIFT
FOR SHOWERS TONIGHT. BUFKIT TIME/HEIGHT SECTIONS SHOWED LITTLE
INSTABILITY OVERNIGHT TONIGHT...SO DOWNPLAYED THUNDER AND WENT
MAINLY WITH SHOWERS THROUGH 12Z. THE 12Z NAM AND ECMWF HAD AN AXIS
OF HIGHER QPF TONIGHT THAT EXTENDED ACROSS NORTH CENTRAL WISCONSIN
WHILE THE 12Z GFS HAD IT MORE TO THE NORTHWEST AND OUTSIDE THE
FORECAST AREA.

HAVE SHOWERS AND THUNDERSTORMS GOING ON FRIDAY...THOUGH THERE
COULD BE A LULL IN THE ACTIVITY LATE MORNING/EARLY AFTERNOON AS
SOME RELATIVELY DRIER AIR WORKS ITS WAY INTO SOUTHERN WISCONSIN.
THE UPPER JET SUPPORT LOOKS BETTER ON FRIDAY AS THE MID LEVEL
TROUGH APPROACHES AND BUFKIT WAS SHOWING CAPES IN EXCESS OF
1000J/KG IN CENTRAL AND EAST CENTRAL WISCONSIN. SPC HAD A SEE
TEXT...5 PERCENT CHANCE FOR SEVERE...FOR MOST OF THE AREA ON DAY 2
AND THIS SEEMS REASONABLE. THE NAM AND EC SHOWED THE AXIS OF
HIGHEST QPF ACROSS NORTHERN WISCONSIN WHILE THE GFS WAS FARTHER
NORTH...IN FAR NORTHERN WISCONSIN AND UPPER MICHIGAN.

THOUGH HEAVY RAINFALL IS LIKELY AT TIMES...RAINFALL TOTALS
THROUGH 00Z SATURDAY SHOULD NOT POSE MUCH OF A FLOODING RISK BUT
COULD SET THE STAGE FOR FLOODING IN SUBSEQUENT PERIODS IF MORE
HEAVY RAIN FALLS.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY
ISSUED AT 412 PM CDT THU AUG 28 2014

HEAVY RAINFALL POTENTIAL FOR FRIDAY NIGHT AND SATURDAY...AND PCPN
TRENDS WITH A FRONTAL PASSAGE SUNDAY NIGHT AND MONDAY...WILL BE
THE MAIN FCST CONCERNS.

HAVE DETAILED THE PCPN TRENDS...HEAVY RAINFALL THREAT AND FLOODING
POTENTIAL FOR FRIDAY NIGHT AND SATURDAY IN THE HYDROLOGY SECTION.
ANY LINGERING SHOWERS AND STORMS SHOULD PULL OUT OF FAR NE WI
EARLY SATURDAY EVENING...WITH DRY CONDITIONS EXPECTED FOR THE
REST OF SATURDAY NIGHT AND SUNDAY.

A S/W TROF AND ASSOCIATED COLD FRONT WILL MOVE THROUGH THE REGION
LATE SUNDAY NIGHT INTO MONDAY...AND PRODUCE ANOTHER SWATH OF
SIGNIFICANT PCPN. DEPENDING ON THE TIMING OF THE FRONT...AND
AMOUNT OF CLOUD COVER AND HEATING THAT OCCURS AHEAD OF IT...SEVERE
TSTMS MAY BE A CONCERN ON MONDAY. INCREASING DEEP LAYER SHEAR AND
MID-LEVEL WINDS WILL BE FAVORABLE...BUT INSTABILITY IS IN
QUESTION.

THE REST OF THE WORK WEEK DOES NOT LOOK AS ACTIVE...WITH A SMALL
CHANCE OF SHOWERS EXPECTED ON TUESDAY AS A S/W TROF MOVES THROUGH...
AND A CHANCE OF SHRA/TSRA TOWARD THURSDAY AS A WARM FRONT
APPROACHES,.
&&

.AVIATION...FOR 06Z TAF ISSUANCE
ISSUED AT 1113 PM CDT THU AUG 28 2014

SCATTERED SHOWERS WILL BECOME MORE NUMEROUS OVERNIGHT AS LOW LEVEL
JET CONTINUES TO ADVECT MOISTURE NORTHWARD FROM THE PLAINS. CIGS
SHOULD CONTINUE TO GRADUALLY LOWER TO MVFR AND IFR IN HEAVIER
SHOWER ACTIVITY. PRECIPITATION THUS FAR HAS BEEN LESS WIDESPREAD
AND WEAKER THAN PREVIOUSLY FORECAST. AS LOW LEVEL JET CONTINUES TO
STRENGTHEN...PRECIPITATION AREA WILL CONTINUE TO EXPAND AND
INCREASE IN INTENSITY SOMEWHAT RESULTING IN MORE WIDESPREAD
MODERATE RAIN AND IFR CIGS ESPECIALLY AT CENTRAL AND NORTHERN WISCONSIN
TAF SITES. BAND OF RAIN WILL CONTINUE TO PUSH NORTHEAST INTO
NORTHERN WISCONSIN AFTER 12Z FRIDAY.

MORE SHOWER AND THUNDERSTORM ACTIVITY IS THEN EXPECTED TO
REDEVELOP OVER MUCH OF THE FORECAST AREA FRIDAY AFTERNOON...AMOUNT
OF THUNDERSTORM ACTIVITY WILL DEPEND SOMEWHAT ON AMOUNT SUNSHINE
THAT CAN BE REALIZED DURING THE AFTERNOON. REGARDLESS...EXPECT
GENERALLY MVFR CIGS WITH AREAS OF IFR CIGS IN HEAVIER
PRECIPITATION.
&&

.HYDROLOGY...
ISSUED AT 412 PM CDT THU AUG 28 2014

LATEST FORECAST MODELS CONTINUE TO SHOW SEVERAL ROUNDS OF RAIN AND
TSTMS TONIGHT THROUGH SATURDAY. THE FIRST ROUND WILL ACCOMPANY AN
H8 WARM FRONT AND 30-40 KT LLJ TONIGHT INTO EARLY FRIDAY...ALONG
WITH THE RETURN OF A VERY MOIST AIR MASS (PWATS APPROACHING 2
INCHES). EXPECT SOME AREAS TO GET 1-2 INCHES OF RAIN WITH THIS
EPISODE. A DECREASE IN THE RAIN IS EXPECTED FRIDAY MORNING...BUT
ADDITIONAL CONVECTION SHOULD REDEVELOP FRIDAY AFTERNOON...AND MAY
BECOME ENHANCED OVER THE NW HALF OF THE CWA ON FRIDAY NIGHT AS AN
UPPER TROF AND SFC LOW APPROACH FROM THE WEST...AND A COUPLED
UPPER JET PULLS THROUGH. THE THREAT OF HEAVY RAINFALL SHOULD
SLOWLY SHIFT SE ON SATURDAY...IN ASSOCIATION WITH THE MOVMT OF
THE UPPER TROF AND SFC LOW. ADDITIONAL RAINFALL AMOUNTS OF 1-2
INCHES APPEAR LIKELY FRIDAY NIGHT INTO SATURDAY...WITH LOCAL
HIGHER AMOUNTS.

WILL CONTINUE WITH THE ESF THIS AFTERNOON. WILL NEED TO MONITOR
HOW TONIGHT`S EVENT UNFOLDS...THEN DETERMINE IF ANY OF THE
SUBSEQUENT HEAVY RAINFALL WILL OVERLAP AREAS THAT GET HIT TONIGHT.
THINK THE MAIN FLOODING THREAT WILL BE FRIDAY NIGHT...AND MAINLY
IN URBAN AREAS AND ON SMALLER STREAMS THAT ARE MORE PRONE TO FLASH
FLOODING.
&&

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

$$

SHORT TERM.....MG
LONG TERM......KIECKBUSCH
AVIATION.......ESB
HYDROLOGY......KIECKBUSCH





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