171
FXUS63 KGRB 300339
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1039 PM CDT SAT MAR 29 2025
UPDATED AVIATION PORTION FOR 06Z TAF ISSUANCE
UPDATE
ISSUED AT 853 PM CDT SAT MAR 29 2025
PRECIPITATION IS RAMPING UP QUICKLY THIS EVENING DUE TO INCREASING
(AND STRONG) MID-LEVEL FRONTOGENETIC FORCING AND WAA/ISENTROPIC
LIFT ALONG A TIGHT BAROCLINIC ZONE. ICING HAS BEEN FAIRLY MODEST
IN MOST AREAS TO THIS POINT, WITH A SOMEWHAT SURPRISING MAX OF
0.18 INCH OFF THE GRB ASOS, BUT EXPECT ICING TO RAMP UP ACROSS
NORTH CENTRAL AND NORTHEAST WI OVER THE NEXT FEW HOURS. THE
BIGGEST AND ONLY CHANGE TO THE HEADLINES WAS TO UPGRADE DOOR
COUNTY TO AN ICE STORM WARNING, AS SURFACE TEMPERATURES REMAINED
BELOW FREEZING IN THE FAR NORTH AND WEB CAMS APPEARED TO SHOW
ICING IN THE TREES AT NORTHPORT. ALSO CONSIDERED WHETHER WAUSHARA,
OUTAGAMIE AND BROWN COUNTIES SHOULD BE UPGRADED, BUT DECIDED THAT
EVEN THOUGH AMOUNTS COULD CREEP ABOVE A QUARTER INCH IN THE
NORTHERN PARTS OF EACH COUNTY, MOST OF EACH COUNTY WOULD PROBABLY
STAY BELOW CRITERIA AND WIDESPREAD SIGNIFICANT IMPACTS DID NOT
APPEAR IMMINENT. AS ALWAYS, HAD TO DRAW A LINE SOMEWHERE. ALSO
LOWERED ICE ACCUMS A LITTLE BIT OVER VILAS COUNTY, WHERE IT
APPEARED THAT SNOW AND SLEET MIGHT BECOME THE DOMINANT P-TYPE.
KEY MESSAGES
- A SIGNIFICANT ICE ACCUMULATION IS EXPECTED ACROSS CENTRAL,
NORTH-CENTRAL AND FAR NORTHEAST WISCONSIN THIS EVENING THROUGH
SUNDAY AFTERNOON. THERE IS A 70-100% CHANCE THAT THE AREA
BETWEEN MERRILL AND IRON MOUNTAIN WILL SEE AT LEAST 0.25" OF ICE
ACCUMULATION.
- THE FREEZING RAIN COULD CREATE SIGNIFICANT DISRUPTIONS IN
TRAVEL, ALONG WITH DAMAGE TO TREES AND POWER OUTAGES. ICE STORM
WARNINGS, WINTER STORM WARNING AND WINTER WEATHER ADVISORIES ARE
IN EFFECT.
- THERE IS A 20-40% CHANCE OF THUNDERSTORMS TONIGHT, HIGHEST
SOUTH. SOME OF THE STRONGER STORMS COULD PRODUCE SMALL HAIL AND
LOCALLY HEAVY RAIN.
- THE STORMS FROM LAST NIGHT AND ADDITIONAL PRECIPITATION THIS
WEEKEND AND NEXT WEEK WILL LEAD TO FAST FLOWS AND RISING RIVERS
AND STREAMS INTO NEXT WEEK. MINOR FLOODING IS EXPECTED FOR SOME
LOCATIONS.
DISCUSSION
ISSUED AT 410 PM CDT SAT MAR 29 2025
HEADLINE CHANGES: UPGRADED SOUTHERN OCONTO, WOOD, PORTAGE AND
WAUPACA COUNTIES INTO THE ICE STORM WARNING AND ADDED BROWN,
WAUSHARA, OUTAGAMIE AND DOOR INTO THE WINTER WEATHER ADVISORY.
HAVE BUMPED UP THE START TIME TO 5PM THIS EVENING AS IMPACTS ON
THE ROADS COULD START LATE THIS AFTERNOON. KEPT THE END TIME OF
7PM SUNDAY, BUT PORTIONS OF THE AREA WILL LIKELY NEED AN EXTENSION
OR TRANSITION TO ANOTHER HEADLINE INTO EARLY MONDAY MORNING.
DISCUSSION: A COMPLEX, MESSY AND COMPLICATED WINTER WEATHER
FORECAST DURING THE NEXT 36 HOURS, WITH A POSSIBLE DESTRUCTIVE ICE
STORM ACROSS PARTS OF CENTRAL AND NORTHEAST WI. WHILE A FEW SPOTS
OVER FAR NORTHEAST WI STRUGGLED TO GET ABOVE FREEZING TODAY, THE
STRONG ALMOST APRIL SUN AND WARMER ROAD TEMPS HAVE KEPT IMPACTS
ON ROADS TO A MINIMUM. THIS WILL CHANGE AS THE SUN SETS AND PRECIP
INCREASES IN COVERAGE AND INTENSITY THIS EVENING. NORTHEAST WINDS
WILL CONTINUE TO FEED THE LOW-LEVELS WITH COLD AIR, WITH A VERY
PRONOUNCED WARM LAYER ALOFT (UP TO ~10C). STRONG BAROCLINIC ZONE
WILL STAY SOUTH OF THE AREA, WITH MOISTURE BEING THROWN UP AND
OVER IT. THIS WILL PROVIDE A CLASSIC SET UP FOR FREEZING RAIN,
ALONG WITH SLEET AT TIMES. IMPACTS VERY DIFFERENT BETWEEN FREEZING
RAIN AND SLEET OF COURSE, SO WILL NEED TO MONITOR TRENDS THROUGH
THE NIGHT. HAVE LOWERED TEMPS JUST SLIGHTLY FOR TONIGHT INTO
SUNDAY, WHICH HAS BROUGHT THE RAIN / FREEZING RAIN LINE A LITTLE
SOUTH, WHICH NECESSITATED THE UPGRADES AND EXPANSION OF THE
HEADLINES. ICE TOTALS OVERALL HAVE REMAINED ABOUT THE SAME, WITH
GROUND ZERO LIKELY SETTING UP FROM MARATHON TO LANGLADE TO
MARINETTE COUNTY WHERE PROBABILITIES OF 0.50" ARE OVER 70%. ICE
TOTALS DECREASE AS YOU HEAD NORTH/SOUTH AWAY FROM THIS AREA. MORE
SLEET AND EVENTUALLY SNOW WILL MIX IN OVER THE FAR NORTH, KEEPING
LOWER ICE TOTALS THERE. THERE WILL BE A SHARP CUT-OFF IN ICE
TOTALS SOMEWHERE IN OR JUST WEST OF THE FOX VALLEY AS SURFACE
TEMPS WILL BE TEETERING WITH THE FREEZING MARK. THE BEST AREA OF
MOISTURE/FORCING ARRIVES LATER TONIGHT, WITH A ROUND OF MODERATE
TO HEAVY RAIN INTO EARLY MONDAY MORNING. THE HEAVIER NATURE OF THE
PRECIP MAY ACTUALLY HINDER THE BETTER ICE ACCRETION AS MUCH OF IT
WILL RUN OFF RATHER THAN FREEZE. BUT IN THE END, THIS WOULD ONLY
KEEP ICE TOTALS FROM GETTING OVER THE INCH MARK AND NOT REALLY
AFFECT THE ICING IMPACTS. THE COMBINATION OF ICE, SNOW AND GUSTY
NORTHEAST WINDS WILL CREATE DANGEROUS TRAVEL CONDITIONS FOR ALL
BUT FAR EAST CENTRAL WI, ALONG WITH TREE DAMAGE AND POWER OUTAGES.
SOME LOCATIONS COULD SEE A REPRIEVE FROM THE ICING ON SUNDAY AS
TEMPS TRY TO CREEP UP A DEGREE OR TWO, ALONG WITH LULLS IN THE
PRECIP, ESPECIALLY ON THE SOUTHERN EDGE OF THE HEADLINES, WHERE
TEMPS WILL BE A LITTLE WARMER.
ELEVATED INSTABILITY WILL BUILD FROM THE SOUTH TONIGHT, ALONG
WITH SOME STEEP 700/500MB LAPSE RATES, BRINGING THE CHANCE FOR A
FEW STORMS, MAINLY TO CENTRAL AND EAST CENTRAL WI. THE CONVECTION
COULD PLAY A ROLE IN CHANGING P-TYPES AT TIMES AND PRODUCE SOME
HEAVIER DOWNPOURS AND SMALL HAIL. AS NORTHEAST WINDS SHIFT TO THE
NORTH AND NORTHWEST AS THE SYSTEM DEPARTS LATE SUNDAY INTO MONDAY
MORNING, LOOK FOR THE FREEZING RAIN/MIX TO TRANSITION TO SNOW.
MODELS HAD A SLIGHT UPTICK ON THE SNOW ON THE BACKSIDE OF THE
SYSTEM, BUT STILL LOOKING LIKE AN INCH OR TWO. WE MAY NEED
ADDITIONAL WINTER HEADLINES AFTER 7PM SUNDAY TO DEAL WITH THE
WINTRY MIX TO SNOW TRANSITION. WHILE MOST OF THE FALLING PRECIP
WILL BE OVER BY MONDAY MORNING, SOME IMPACTS WILL LIKELY BE
ONGOING WHICH COULD IMPACT THE MONDAY MORNING COMMUTE.
ANOTHER STRONG LOW PRESSURE SYSTEM WILL TRACK INTO THE GREAT
LAKES TUESDAY AFTERNOON/EVENING INTO WEDNESDAY. DETAILS STILL TO
BE WORKED OUT WITH TRACK/INTENSITY, BUT IT IS LIKELY TO BRING
ANOTHER WINTRY MESS TO THE REGION, ALONG WITH WINDY CONDITIONS AND
POSSIBLY SOME STORMS. THERE LOOKS TO BE ANOTHER WARM LAYER ALOFT,
SO FREEZING RAIN WILL ONCE AGAIN BE AN ISSUE; HOWEVER, THE
FREEZING RAIN THREAT LOOKS TO BE A SHORTER PERIOD WITH THE PRECIP
CHANGING TO RAIN AS THE WARM FRONT LIFTS NORTHWARD.
AVIATION
FOR 06Z TAF ISSUANCE
ISSUED AT 1032 PM CDT SAT MAR 29 2025
POOR AND DANGEROUS FLYING CONDITIONS WILL PREVAIL THROUGH THE TAF
PERIOD AS A SIGNIFICANT ICE STORM SETS UP OVER MUCH OF THE
FORECAST AREA AND CEILINGS/VSBYS SETTLE INTO THE IFR/LIFR
CATEGORIES. EXPECTING ICE ACCUMULATIONS OF A QUARTER TO THREE-
QUARTERS OF AN INCH OVER MUCH OF THE FORECAST AREA, WITH MORE OF A
FREEZING RAIN/SLEET/SNOW MIX NORTH OF A LINE FROM RHI-IMT, AND
MAINLY RAIN IN THE FAR SE PART OF THE AREA (INCLUDING MTW). COLDER
AIR WILL WORK ITS WAY SOUTHEAST LATE SUNDAY AFTERNOON AND EVENING,
CAUSING THE MIXED PRECIPITATION AND RAIN TO EVENTUALLY CHANGE TO
SNOW.
THERE WILL BE A SLIGHT CHANCE OF THUNDERSTORMS AS ELEVATED
INSTABILITY ARRIVES IN CENTRAL WI OVERNIGHT AND REMAINS ACROSS
MAINLY THE SOUTHERN PART OF THE FORECAST AREA THROUGH MOST OF
SUNDAY. WILL PROBABLY HOLD OFF ON MENTIONING IN THE TAFS, AS
CONFIDENCE IS STILL ON THE LOW SIDE.
WINDS WILL REMAIN NORTHEAST TO NORTH THROUGH SUNDAY EVENING,
GUSTING TO 20 TO 25 KTS, BUT HIGHER NEAR THE BAY AND LAKE. THERE
ALSO MAY BE SOME POCKETS OF LLWS ACROSS MAINLY NORTHERN WI ON
SUNDAY EVENING.
HYDROLOGY
ISSUED AT 410 PM CDT SAT MAR 29 2025
THE LOCALLY HEAVY RAIN LED TO A PRETTY GOOD RIVER RISE ON PARTS
OF THE WISCONSIN RIVER, ALONG WITH REPORTS OF WATER OVER ROADS AND
A WASH OUT IN NORTHERN MARATHON AND SOUTHERN LINCOLN COUNTIES. THE
BANDS OF HEAVIER RAIN EXPANDED INTO MENOMINEE/OCONTO/MARINETTE/DOOR
COUNTIES. THE ADDITIONAL RAIN OVER THE NEXT 36 HOURS, ALONG WITH
THE SYSTEM MID NEXT WEEK, WILL LEAD TO ADDITIONAL RIVER RISES, AND
MINOR FLOODING OF MAINLY LOW- LAND AND LOW- LYING AREAS. THREAT
FOR WIDESPREAD FLOODING LOOKS LOW, SO DON'T THINK THERE IS A NEED
FOR A FLOOD WATCH AT THIS TIME, BUT AREAS THAT WERE HARDER HIT
LAST NIGHT WILL NEED TO BE MONITORED FOR MORE FLOODING.
GRB WATCHES/WARNINGS/ADVISORIES
WINTER STORM WARNING UNTIL 7 PM CDT SUNDAY FOR WIZ005.
ICE STORM WARNING UNTIL 7 PM CDT SUNDAY FOR WIZ010>013-018>022-
030-031-035>037-073-074.
WINTER WEATHER ADVISORY UNTIL 7 PM CDT SUNDAY FOR WIZ038-039-045.
UPDATE.........KIECKBUSCH
DISCUSSION.....BERSCH
AVIATION.......KIECKBUSCH
HYDROLOGY......BERSCH
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