Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 211155
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
655 AM CDT MON APR 21 2014

UPDATED AVIATION PORTION FOR 12Z TAF ISSUANCE
AND NEW INFORMATION ADDED TO UPDATE SECTION

.UPDATE...
ISSUED AT 645 AM CDT MON APR 21 2014

DENSE FOG HAS BECOME MORE WIDESPREAD IN THE PAST COUPLE HOURS...
ESPECIALLY OVER NC/C WI. HAVE INCREASED THE FOG COVERAGE THE IN
THE GRIDS/ZFP...AND ENHANCED THE WORDING IN THE SPECIAL WEATHER
STATEMENT. NO HEADLINES EXPECTED...AS CONDITIONS SHOULD IMPROVE IN
A COUPLE HOURS.
&&

.SHORT TERM...TODAY...TONIGHT...AND TUESDAY
ISSUED AT 401 AM CDT MON APR 21 2014

FCST CONCERNS INCLUDE PCPN TRENDS AND THE THREAT OF TSTMS TODAY...
AND TEMPERATURES THROUGH THE PERIOD.

A COLD FRONT WAS SWEEPING ACROSS MN EARLY THIS MORNING...AND A WARM
FRONT WAS SITUATED JUST SOUTH OF GRB CWA. LIGHT NORTHEAST WINDS
AND ABUNDANT LOW-LEVEL MOISTURE NORTH OF THE WARM FRONT WAS LEADING
TO FOG DEVELOPMENT...WITH PATCHY DENSE FOG REPORTED. ALTHOUGH MUCH
DRIER AIR WAS SITUATED OVER FAR NORTHERN WI...BREAKS IN THE CLOUDS
WERE ALSO ALLOWING FOG TO FORM THERE. SHOWERS WERE ONGOING OVER
PARTS OF C/EC WI...DUE TO THE PROXIMITY OF THE WARM FRONT. MORE
NUMEROUS SHOWERS AND TSTMS HAD FORMED OVER SE MN AND NORTHERN IA...
DUE TO AN APPROACHING SFC LOW AND A WEAK S/W TROF.

FOG IS EXPECTED TO MIX OUT BY MID-LATE MORNING. PLAN TO ISSUE A
SPECIAL WEATHER STATEMENT TO HIGHLIGHT POTENTIAL IMPACTS ON THE
MORNING COMMUTE. SHOWERS AND TSTMS WILL GRADUALLY INCREASE ACROSS
THE REGION TODAY AS THE SFC LOW AND COLD FRONT APPROACH...AND THE
RRQ OF AN UPPER LEVEL JET MOVES INTO WI. INSTABILITY WILL INCREASE
AHEAD OF THE FRONT...WITH CAPE OF 500-1000 J/KG AND LI`S -2 TO -4
AFFECTING THE SW HALF OF THE CWA THIS AFTERNOON. IN ADDITION...
PRECIPITABLE WATER VALUES OF 1.00-1.25 INCHES WILL RESIDE OVER
C/EC WI DURING THE DAY. GIVEN THE DEGREE OF INSTABILITY/MOISTURE...
SUSPECT THAT THE STRONGER TSTMS WILL PRODUCE SMALL HAIL AND HEAVY
RAINFALL. WILL NEED TO MONITOR CONVECTIVE TRENDS EARLY THIS
MORNING...AND DECIDE IF QPF AMOUNTS NEED TO BE INCREASED. PCPN
WILL QUICKLY TAPER OFF AFTER THE COLD FRONT MOVES THROUGH THIS
AFTERNOON. ALTHOUGH CLOUD COVER WILL BE EXTENSIVE TODAY...S-SW
WINDS AHEAD OF THE FRONT SHOULD BOOST TEMPS INTO THE 60S.

THE FRONTAL PCPN WILL SHIFT EAST OF THE REGION EARLY THIS EVENING...
BUT STRONG CAA AND NW WINDS MAY LEAD TO SCT LAKE-EFFECT FLURRIES
OR LIGHT SNOW SHOWERS OVER NC WI OVERNIGHT. TEMPERATURES SHOULD
DROP INTO THE 30S.

A PARTLY CLOUDY...COOLER AND BLUSTERY DAY IS ANTICIPATED ON TUESDAY...
WITH HIGHS IN THE UPPER 40S AND 50S. NW WINDS WILL GUST TO 25 MPH.

.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY
ISSUED AT 401 AM CDT MON APR 21 2014

THE ECMWF AND GFS REMAIN IN VERY GOOD AGREEMENT THROUGH 12Z
FRIDAY...AND THEN THE GFS BECOMES SLOWER IN EXITING A DEEP UPPER
LEVEL TROUGH FROM THE WESTERN GREAT LAKES.  THIS MIGHT BE DUE TO THE
GENERATION OF A MORE AMPLIFIED PATTERN UPSTREAM OF THIS DEEP UPPER
LOW...AND CONSEQUENTLY...FORWARD MOTION OF LARGE SCALE FEATURES IS
SLOWED.  PREFER THE ECMWF/GFS ENSEMBLE BLEND FOR LATER PERIODS.

TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...HIGH PRESSURE WILL BE IN
CONTROL ACROSS THE REGION TUESDAY NIGHT...WHICH SHOULD ALLOW FOR
MOSTLY CLEAR AND COOL CONDITIONS.  HIGH CLOUDS MAY INCREASE FROM THE
WEST LATE...BUT WILL STICK WITH MOSTLY CLEAR SKIES.  THAT SURFACE
HIGH SHIFTS EAST OF THE REGION ON WEDNESDAY AS LOW PRESSURE AND A
WARM FRONT MOVE EAST ACROSS THE CENTRAL PLAINS.  MODELS REMAIN
AGGRESSIVE IN PUSHING LIGHT RAIN INTO THE SOUTHWEST HALF OF THE
FORECAST AREA WEDNESDAY AFTERNOON...AS A RESULT OF MID-LEVEL FGEN
ALONG THE THETAE GRADIENT.  THE LOW LEVEL THERMAL GRADIENT WILL
REMAIN WELL WEST OF THE REGION OVER THE NORTHERN MISSISSIPPI VALLEY
AND WILL HAVE EAST WINDS OUT OF THE DEPARTING HIGH.  REMAIN
SKEPTICAL THAT PRECIP WILL ARRIVE SO QUICKLY...BUT WILL KEEP THE
CHANCE GOING OVER CENTRAL WISCONSIN.  BETTER CHANCES WILL ARRIVE
WEDNESDAY NIGHT WHEN BETTER RETURN FLOW/ISENTROPIC ASCENT/FGEN
PUSHES INTO THE AREA.  WILL INCREASE POPS WEDNESDAY
NIGHT...ESPECIALLY OVER WESTERN SECTIONS OF THE FORECAST AREA.  WILL
DROP HIGHS A COUPLE DEGREES DUE TO CLOUD COVER AND EAST WINDS ON WEDNESDAY.

REST OF THE FORECAST...LOW PRESSURE WILL SHIFT NORTHEAST INTO
WESTERN WESTERN WISCONSIN BY THURSDAY AFTERNOON.  AHEAD OF THE
LOW...40+ KNOTS OF 850MB FLOW WILL BE RIDING OVER THE THERMAL
GRADIENT IN A REGION OF STRONG FORCING AHEAD OF A DYNAMIC
SHORTWAVE.  DESPITE THE GREAT DYNAMICS...850-700MB THETAE LAPSE
RATES ARE POSITIVE AND ELEVATED CAPES ARE UNDER 50 J/KG...INDICATIVE
OF WEAK ELEVATED INSTABILITY.  ADDITIONALLY...SURFACE FLOW WILL BE
OFF LAKE MICHIGAN SO SURFACE TEMPS WILL STRUGGLE TO RISE.  THERE
SHOULD BE SOME THUNDERSTORMS WITH THE GREAT DYNAMICS...BUT ANY
SEVERE THREAT LOOKS REALLY MARGINAL AT THIS TIME.  THE BEST CHANCE
OF ANY SIGNIFICANT THUNDERSTORM ACTIVITY MAY OCCUR RIGHT AHEAD OF
THE OCCLUDED FRONT AND WITHIN THE DRY SLOT LATE THURSDAY AFTERNOON
INTO THE EARLY EVENING.  ONCE THE FRONT EXITS...COMMA HEAD PRECIP
WILL WRAP BACK AROUND INTO THE NORTHWEST HALF OF THE FORECAST AREA
THURSDAY NIGHT INTO FRIDAY.  COLDER AIR WILL BE ARRIVING BY THIS
SAME TIME...BUT NOT COLD ENOUGH FOR SNOW.  THEN COOL AND DRY NEXT
WEEKEND UNDER THE INFLUENCE OF A HUDSON BAY HIGH.  MORE PRECIP IS
THEN POSSIBLE BY LATE NEXT WEEKEND.
&&

.AVIATION...FOR 12Z TAF ISSUANCE
ISSUED AT 645 AM CDT MON APR 21 2014

AREAS OF DENSE FOG WILL IMPACT THE RHI/AUW/CWA/GRB TAF SITES
THROUGH 13Z-14Z...FOLLOWED BY IMPROVING CONDITIONS. SHOWERS AND
SCATTERED TSTMS WILL DEVELOP ALONG AND AHEAD OF A COLD FRONT
TODAY...ALONG WITH MVFR/IFR CONDITIONS. THE PCPN WILL END
AFTER THE FRONT MOVES THROUGH...AND GUSTY NW WINDS WILL DEVELOP.
CLEARING SKIES WILL ARRIVE LATER THIS AFTERNOON AND EVENING.
&&

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

$$

UPDATE.........KIECKBUSCH
SHORT TERM.....KIECKBUSCH
LONG TERM......MPC
AVIATION.......KIECKBUSCH






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