Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 231709
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1209 PM CDT MON MAR 23 2015

UPDATED AVIATION PORTION FOR 18Z TAF ISSUANCE

.SYNOPSIS...
ISSUED AT 340 AM CDT MON MAR 23 2015

SEASONABLY COOL TEMPERATURES THIS WEEK WITH A WINTRY MIX OF
PRECIPITATION TUESDAY NIGHT AND WEDNESDAY.

SOMEWHAT DIFFUSE BAND OF LOW-AMPLITUDE WESTERLIES ACRS THE CONUS
WL UNDERGO CONSOLIDATION AND AMPLIFICATION DURING THE WEEK...AS
PACIFIC SHRTWV AND ASSOCIATED CYCLONE PROGRESSES ACRS THE COUNTRY.
THE AMPLIFICATION PHASE SHOULD PEAK EARLY NEXT WEEKEND...WITH A
RIDGE IN THE W AND A TROF IN THE E.

TEMPERATURES WILL START OUT BELOW NORMAL...MODERATE SOME IN
ADVANCE OF THE PACIFIC WV...THEN DROP BACK AGAIN DURING THE LATTER
PART OF THE WORK WEEK AS ANOTHER SWD PUSH OF COLD AIR OCCURS IN
THE WAKE OF THE DEPARTING CYCLONE. PCPN AMNTS ARE LIKELY TO END UP
NR NORMAL...MAINLY DUE TO THE MID-WEEK SYSTEM.
&&

.SHORT TERM...TODAY...TONIGHT...AND TUESDAY
ISSUED AT 340 AM CDT MON MAR 23 2015

COMPACT BUT POTENT SNOW PRODUCING SYSTEM SLIDING SE THROUGH THE
BAROCLINIC ZONE ON THE SW FLANK OF THE COLD AIR MASS ACRS THE RGN
WL PASS MAINLY S OF THE AREA. LIGHT SNOWS WL CLIP THE SW CORNER OF
THE FCST AREA EARLY THIS MORNING...BEFORE SHIFTG OFF TO THE SE.
FINAL POPS WL BE ISSUANCE-TIME DECISION.

COMPACT CLOSED UPR SYSTEM...THE REMNANTS OF FAIRLY STG PAC
SHRTWV...HAVE CROSSED THE BROAD RIDGE TO THE W AND WERE NOW MOVG
ESE FM THE SRN LAKE WINNIPEG RGN. SYSTEM STILL PRETTY IMPRESSIVE
LOOKING ON STLT IMAGERY...AND WAS PRODUCING CLDS AND SOME SHSN
EARLY THIS MORNING. MODELS UNANIMOUS IN SHOWING FEATURE WEAKENING
AND PRETTY MUCH WIPING OUT AS IT SHIFTS TOWARD NRN WI TDA/THIS
EVENING. IT/S RUNNING INTO CONFLUENT FLOW DOWNSTREAM...SO
WEAKENING IS REASONABLE. BUT GIVEN IT/S CURRENT APPEARANCE ON STLT
IMAGERY...SOMEWHAT SKEPTICAL ALL THE CLDS WL DISSIPATE BEFORE
REACHING THE AREA. OPTED TO BRING A PERIOD OF PARTLY CLOUDY
CONDITIONS ACRS THE N IN THE SKYCON GRIDS. WL COUNT ON DRY AIR AT
LOW-LEVELS TO SUBLIMATING ANY SNOW THAT WOULD BE FALLING FM THE
MID-DECK...SO LEFT FLURRIES OUT OF THE FCST.

QUIET WX WITH MORNING SUNSHINE THEN INCRG HIGH CLDS IS EXPECTED
TUE AS PLAINS STORM SYSTEM STARTS TO EDGE CLOSER TO THE AREA.

.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY
ISSUED AT 340 AM CDT MON MAR 23 2015

MAIN FORECAST CONCERNS WILL BE DEALING WITH P-TYPES AND AMOUNTS
TUESDAY NIGHT AND WEDNESDAY...CHANCES FOR PRECIP LATE IN THE
PERIOD...AND TEMPS.

ALL EYES WILL BE FOCUSED ON THE STORM SYSTEM FOR TUESDAY NIGHT
INTO WEDNESDAY MORNING. STILL A LOT OF UNANSWERED
QUESTIONS...WHICH MAKES FOR A DIFFICULT FORECAST. LAST COUPLE OF
MODELS RUNS HAVE TRENDED A LITTLE COLDER AT THE SURFACE...WHICH
INCREASES THE CONCERN FOR A FREEZING RAIN EVENT...AS A ELEVATED
WARM LAYER WILL BE LIKELY PRESENT BETWEEN 800MB AND 900MB...MAINLY
OVER CENTRAL AND EASTERN WI. MODELS DO HANDLE THIS LAYER SLIGHTLY
DIFFERENTLY...WHICH IS EXPECTED WITH A COMPLEX SYSTEM LIKE THIS.
NAM IS THE MOST AGGRESSIVE WITH THIS WARM LAYER...LEADING TO A
PERIOD OF FREEZING RAIN FOR ALL BUT FAR NORTHERN WI TUESDAY
EVENING AND TUESDAY NIGHT. GFS/GEM/ECMWF ARE SLIGHTLY COLDER
ALOFT...AND SHOW MAINLY ALL SNOW AS YOU MOVE NORTH OF A WAUSAU TO
MARINETTE LINE. 00Z ECMWF SHOWS ALL SNOW FOR NORTH-CENTRAL...WITH
A MIX CHANGING TO SNOW FALL ALL OF CENTRAL WI INTO THE FOX
VALLEY...THEN ENDING AS A MIX. THE 00Z GEM WOULD SUPPORT THIS
SCENARIO. THE GEM IS FARTHER NORTH WITH THE LOW...SO THIS SCENARIO
WOULD PLAY OUT...JUST SLIGHTLY FARTHER TO THE NORTH.

TEMPS AT THE SURFACE WILL ALSO BE A CONCERN...AS JUST A DEGREE OR
TWO WILL MAKE THE DIFFERENCE FROM ALL RAIN TO SIGNIFICANT FREEZING
RAIN. AN EAST/NE WIND IS NOW EXPECTED WHICH SHOULD HELP KEEP THE
COLDER AIR IN PLACE AT THE SURFACE...HOWEVER IF THE SURFACE LOW
TRACKS SLIGHTLY FARTHER NORTH (AS THE GEM SHOWS)...THE FOX VALLEY
AND LAKESHORE WILL SWITCH TO A SOUTHERLY WIND FOR A PERIOD EARLY
WEDNESDAY ELIMINATING THE THREAT FOR FREEZING RAIN. THIS SLIGHT
DIFFERENCE IN TRACK AND WINDS COULD BE THE DECIDING FACTOR ON HOW
MUCH SUB-FREEZING AIR WILL REMAIN IN PLACE. CONFIDENCE REMAINS
LOW ON HOW TEMPS BELOW 800MB WILL BEHAVE.

LOOKING AT THE BIGGER PICTURE...MODELS HAVE TRENDED SLIGHTLY
FASTER WITH THE SYSTEM AS A SECONDARY SHORTWAVE NOW LOOKS TO
HANG BACK OVER THE UPPER MIDWEST. SO ALTHOUGH THERE WILL BE
IMPRESSIVE LIFT/FORCING WITH THE LEAD SHORTWAVE...IT WON`T LAST
LONG AND THE PRECIP IS LIKELY TO SHUT OFF QUICKLY AS IT EXITS.
THIS STRONG LIFT...ALONG WITH STEEP MID-LEVEL LAPSE RATES...COULD
PLAY HAVOC WITH P-TYPES...AND FOCUS THE MAJORITY OF THE PRECIP
OVER ONE PORTION OF THE CWA...LEAVING OTHER AREAS MISSING OUT OF
THE HEAVIEST PRECIP. IT COULD ALSO PRODUCE SOME THUNDER AND
POSSIBLY SOME SLEET AND GRAUPEL.

SO PUTTING EVERYTHING TOGETHER...IMPRESSIVE DRY AIR IN THE LOWER
AND MIDDLE LEVELS TUESDAY AFTERNOON WILL QUICKLY SATURATE WITH
EVAPORATIVE COOLING DROPPING TEMPS TO THE WET BULB TEMP WHICH ARE
NEAR OR BELOW 0C. USING A BLEND OF MODEL TEMPS...THIS WILL LEAD TO
THE THE PRECIP STARTING OFF AS A MIX. THE MIX WILL CHANGE OVER THE
SNOW ACROSS NORTH-CENTRAL WI WHERE TEMPS ALOFT ARE THE COLDEST.
IT BECOMES MUCH TRICKIER AS YOU MOVE SOUTH...BUT A MIX OF
RAIN...SNOW (MORE SNOW NORTH) AND SOME FREEZING RAIN IS EXPECTED
FOR CENTRAL WI INTO NE WI. DID INCREASE ICE ACCUMULATIONS UP TO
0.10". MAINLY RAIN IS EXPECTED OVER THE SOUTHERN FOX VALLEY AND
SOUTH OF KEWAUNEE ON THE LAKESHORE. DUE TO ALL THE UNCERTAINTY
WITH P-TYPE AND WHERE THE HEAVIEST PRECIP WILL OCCUR...WILL HOLD
OFF ON ANY HEADLINES. HOWEVER...EXPECT AT LEAST WINTER WEATHER
ADVISORIES WILL BE NEEDED FOR PARTS OF THE AREA...ESPECIALLY SINCE
THIS WILL IMPACT THE MORNING COMMUTE. WILL CONTINUE TO HIGHLIGHT
THIS SYSTEM IN THE HWO AND ISSUE A SPS.

ONCE THE MAIN SLUG OF MOISTURE PUSHES THROUGH WEDNESDAY
MORNING... MODELS HAVE HAVE MOST OF AREA DRYING OUT (AT LEAST
PARTIALLY)...WITH ONLY A CHANCE AT SOME RAIN/SNOW SHOWERS. WILL
BACK OFF ON POPS IN THE AFTERNOON...ESPECIALLY OVER THE SOUTH. THE
CHANCE FOR RAIN AND SNOW SHOWERS WILL CONTINUE INTO WEDNESDAY
NIGHT...AS ANOTHER PIECE OF SHORTWAVE ENERGY AND WEAK SURFACE LOW
PRESSURE PUSHES ACROSS THEA AREA. AN INTERESTING NEW IDEA IN THE
MODELS IS TO DEVELOP A SURFACE LOW OVER NORTHERN INDIANA. IF THIS
SHIFTS A LITTLE TO THE NORTH...EASTERN WI COULD HAVE TO CONTEND
WITH SOME ACCUMULATING SNOW. STRONG COLD AIR ADVECTION WILL BEGIN
AS THESE SYSTEMS PUSH EAST OF THE AREA OVERNIGHT INTO THURSDAY
MORNING. COLD AIR ALOFT...MOIST/CYCLONIC FLOW WILL DOMINATE ON
THURSDAY INTO THURSDAY NIGHT...WITH RAIN/SNOW SHOWERS POSSIBLE AS
A BROAD UPPER TROUGH SWINGS ACROSS THE GREAT LAKES. DRIER AIR
WORKS INTO THE AREA LATE THURSDAY AND INTO FRIDAY...WITH DRY
CONDITIONS EXPECTED. FRIDAY LOOKS TO BE THE COLDEST DAY...AS 850MB
TEMPS DROP BETWEEN -15C AND -19C. LOCATIONS OVER THE NORTH WON`T
MAKE IT OUT OF THE 20S...WHILE THE REST OF THE AREA WILL STRUGGLE
TO CLIMB INTO THE LOW 30S.

THE COLD AIR MASS WILL PUSH EAST OF THE REGION THIS WEEKEND...AS
WARM AIR ADVECTION SPREADS IN FROM THE PLAINS AHEAD OF THE NEXT
WEATHER SYSTEM CROSSING CANADA. THIS WILL ALLOW TEMPS TO MODERATE
AT LEAST CLOSER TO NORMAL. QUESTIONS ON WHEN AND HOW MUCH THINGS
WILL WARM UP STILL NEED TO BE SORTED OUT THOUGH. A SHORTWAVE
TROUGH IS SCHEDULED TO MOVE OVER THE NORTHERN GREAT LAKES SATURDAY
NIGHT INTO SUNDAY...BRINGING THE CHANCE FOR RAIN AND SNOW TO THE
AREA. ANOTHER PUSH OF COLD AIR ARRIVES BEHIND THE SYSTEM SUNDAY
NIGHT INTO MONDAY.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1208 PM CDT MON MAR 23 2015

VFR CONDITIONS THROUGH THE TAF FORECAST WITH PERIODS OF MID AND HIGH
CLOUDS THROUGH THE EVENING...THEN CLEARING OUT OVERNIGHT. AS A HEADS
UP...HEAVY PRECIP IS POSSIBLE TUESDAY NIGHT WITH SEVERAL INCHES OF
SNOW POSSIBLE.  THE MOST LIKELY SCENARIO IS FOR THIS SNOW TO FALL
NORTH AND WEST OF THE FOX VALLEY...A WINTRY MIX OF
SNOW/SLEET/FREEZING RAIN OVER THE FOX VALLEY AND POINTS EAST.
&&

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

$$

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





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