Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 231801
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1201 PM CST TUE DEC 23 2014

UPDATED AVIATION PORTION FOR 18Z TAF ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND WEDNESDAY
ISSUED AT 306 AM CST TUE DEC 23 2014

COMPLEX WEATHER SYSTEM WILL CONTINUE TO IMPACT THE FORECAST AREA
THE NEXT 36 HOURS.

BROAD...BUT DISORGANIZED AREA OF MIXED PRECIPITATION OVERNIGHT HAS
GENERALLY PUSHED NORTHWARD INTO NORTHERN AND FAR NORTHEAST
WISCONSIN THIS MORNING. MAINLY SCATTERED LIGHT RAIN AND DRIZZLE
WAS REPORTED GENERALLY SOUTH OF A MARINETTE TO WAUSAU LINE WHERE
BOUNDARY LAYER TEMPERATURES HAVE WARMED INTO THE MIDDLE TO UPPER
30S. TO THE NORTH OF THIS LINE...SCATTERED LIGHT SNOW WAS
REPORTED WITH VISIBILITIES GENERALLY IN THE 2 TO 3 MILE RANGE...WITH
GENERALLY A SLUSHY INCH OR TWO OF SNOW REPORTED OVERNIGHT. THE
SNOW HAS CREATED SLIPPERY ROAD CONDITIONS ACROSS MUCH OF CENTRAL
AND NORTHERN WISCONSIN.

CONCERN FOR THIS MORNING WILL BE SOUTHWEST TO NORTHEAST ORIENTATED
BAND OF PRECIPITATION MOVING NORTHWARD OUT OF SOUTHERN WISCONSIN AHEAD
OF PRIMARY SHORTWAVE IMPULSE. PRIMARY RAIN BAND CURRENTLY LOCATED
OVER SOUTHERN WISCONSIN SHOULD BEGIN TO IMPACT THE FOX VALLEY
AROUND 10Z...THEN LIFT NORTHWEST OF THE FOX VALLEY BY 15Z OR 16Z.
APPEARS TO BE FAIRLY DECENT CONSENSUS AMONG THE SHORT-RANGE MODEL
GUIDANCE ON THE TIMING OF THIS PRECIPITATION BAND THIS MORNING. THE
UNCERTAINTY LIES IN THE PRECIPITATION TYPE AS THE PRECIPITATION
BAND LIFTS NORTHWARD INTO THE FOX VALLEY AROUND THE MORNING RUSH
HOUR. GIVEN RATHER ROBUST DYNAMICS/LIFT ASSOCIATED WITH THE
SHORTWAVE IMPULSE EXPECT BAND OF PRECIPITATION TO SOLIDIFY AND
STRENGTHEN SOMEWHAT AS IT PUSHES INTO THE FOX VALLEY. ESTIMATED RAP
ANALYSIS SOUNDINGS SUGGEST THAT THE ELEVATED WARM LAYER HAS
PENETRATED AS FAR NORTH AS STURGEON BAY...TO NEAR MARINETTE AND
PERHAPS WISCONSIN RAPIDS. HOWEVER...FORECAST SOUNDINGS ALSO
SUGGEST THAT ROBUST AND FOCUSED LIFT AHEAD OF THE SHORTWAVE
IMPULSE MAY BRIEFLY COLLAPSE THE ELEVATED WARM LAYER...ALLOWING
FOR A BRIEF PERIOD OF MODERATE SNOW OR SLEET OVER THE FOX VALLEY
AROUND THE MORNING RUSH HOUR. WILL MONITOR THIS CLOSELY OVER THE
NEXT FEW HOURS AS THERE IS POTENTIAL FOR THE SNOWFALL RATES TO BE
HIGH ENOUGH FOR SIGNIFICANTLY REDUCED VISIBILITIES AND A QUICK
SLUSHY COUPLE OF INCHES OF SNOW ACCUMULATION...MAKING FOR SLIPPERY
TRAVEL OVER THE FOX VALLEY THIS MORNING. IF THIS SCENARIO DOES TRANSPIRE
CURRENT PLAN IS TO ADDRESS WITH STRONGLY WORDED SPECIAL WEATHER
STATEMENTS RATHER THAN ISSUING AN ADVISORY...AS PERIOD OF SNOWFALL
IS EXPECTED TO BE RATHER BRIEF.

PRECIPITATION BAND SHOULD THEN LIFT INTO THE CURRENT ADVISORY
AREA OVER CENTRAL AND NORTHERN WISCONSIN AFTER ABOUT 15Z WHERE
MAINLY SNOW AND PERHAPS SOME SLEET WILL BE THE PRIMARY
PRECIPITATION TYPE. STILL ANTICIPATE ANOTHER 2 TO 4 INCHES OF WET
SNOW ACCUMULATIONS IN THE ADVISORY AREA THIS MORNING AND INTO THE
AFTERNOON CAUSING CONTINUED SLIPPERY ROADS AND HAZARDOUS TRAVEL
THERE. ACROSS THE FOX VALLEY...MIXED RAIN AND SNOW SHOULD
TRANSITION TO MAINLY DRIZZLE FOR THE REMAINDER OF THE DAY AS
STRONGEST LIFT SHIFTS NORTH AND MID-LEVEL DRYING OCCURS AFTER
ABOUT 16Z.

WITH STRONGEST LIFT AND DEEPEST MOISTURE SHIFTING NORTH INTO UPPER
MICHIGAN...APPEARS WILL BE A LULL IN SIGNIFICANT PRECIPITATION
OVERNIGHT OVER MOST OF THE FORECAST AREA. HOWEVER...STILL
ANTICIPATE SOME LIGHT SNOW ALONG AND WEST OF THE 700 MB
DEFORMATION ZONE AXIS THAT WILL BE ORIENTATED SOUTHWEST TO
NORTHEAST FROM ABOUT MARINETTE TO WISCONSIN RAPIDS AROUND 06Z
WEDNESDAY. PATCHY DRIZZLE/FREEZING DRIZZLE AND FOG IS POSSIBLE
ELSEWHERE.

FOR CHRISTMAS EVE DAY...STILL MUCH UNCERTAINTY AS TO HOW
CYCLOGENESIS WILL EVOLVE OVER THE UPPER MIDWEST AND GREAT LAKES
REGION AS PRIMARY UPPER-LOW FINALLY LIFTS NORTHEAST DURING THE
DAY. 06Z NAM TAKES DEEPENING SURFACE LOW ACROSS NORTHWEST
INDIANA WHILE THE 00Z GFS...REGIONAL CANADIAN AND WRF ARW TRACK
THE SURFACE LOW ACROSS LOWER MICHIGAN...WITH DEFORMATION COMMA
HEAD PENETRATING INTO EASTERN WISCONSIN AND FAR SOUTHEAST PORTION
OF THE FOX VALLEY. GUT AT THIS POINT IS TO LEAN TOWARD A MORE
WESTERN CYCLONE TRACK FOR CHRISTMAS EVE DAY AND WILL ADJUST POPS
UPWARD FROM THE FOX VALLEY EASTWARD. PRECIPITATION TYPE WILL ALSO
BE AN ISSUE...ESPECIALLY ALONG THE LAKESHORE. LATER SHIFTS WILL
NEED TO CONTINUE TO MONITOR THIS EVOLUTION FOR CHRISTMAS EVE DAY
CLOSELY AS THERE IS CERTAINLY POTENTIAL FOR ACCUMULATING
SNOWS OVER EASTERN WISCONSIN...IN ADDITION TO MORE WIND.

.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY
ISSUED AT 306 AM CST TUE DEC 23 2014

ALTHOUGH JUST ABOUT A DAY AND A HALF AWAY...MANY QUESTIONS REMAIN
ON HOW FAR WEST PRECIPITATION WILL WORK INTO EASTERN WISCONSIN
WEDNESDAY NIGHT AS A SECONDARY LOW PRESSURE SYSTEM MOVES ACROSS
THE WESTERN GREAT LAKES. THE COMBINATION OF THE 850MB THERMAL
GRADIENT...DEEPENING 500MB TROUGH AND COUPLED JET STREAK AT 300MB
LEAD ME TO BELIEVE PRECIPITATION WILL MOVE ACROSS FAR EASTERN
WISCONSIN WEDNESDAY EVENING AS I WAS LEANING ON A MORE WESTWARD
TRACK THAN THE 00Z ECMWF. PROBABLY WILL BE A SHARP CUT OFF TO THE
PRECIPITATION FROM PAST EXPERIENCE. FIRST ESTIMATE IS ABOUT A HALF
INCH OF SNOW ALONG THE LAKESHORE. ONE CONCERN IS THAT BOUNDARY LAYER
TEMPERATURES MAY INHIBIT ACCUMULATIONS DURING THE EARLY EVENING HOURS
IF PRECIPITATION IS LIGHT.

NEXT SYSTEM WILL BRING A CHANCE OF LIGHT SNOW TO THE NORTH
THURSDAY NIGHT...AND A CHANCE OF LIGHT RAIN OR LIGHT SNOW ACROSS
THE ENTIRE REGION FRIDAY. TEMPERATURES SHOULD REMAIN ABOVE NORMAL
THROUGH FRIDAY...THEN TEMPERATURES SHOULD RETURN CLOSE TO NORMAL
FOR THE WEEKEND INTO EARLY NEXT WEEK.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1201 PM CST TUE DEC 23 2014

AVIATION TRAVEL WL CONT TO BE IMPACTED BY A PAIR OF SYSTEMS
AFFECTING THE GREAT LAKES OVER THE NEXT 24 HOURS. THE FIRST SYSTEM
ALREADY IN WI AND WAS PRODUCING MAINLY IFR CIGS/VSBYS IN EITHER
SNOW...A RAIN/SNOW MIX OR DRIZZLE. CIGS/VSBYS COULD RISE INTO THE
MVFR RANGE LATER THIS AFTERNOON/EVENING OVER ERN WI AS A DRY SLOT
ROTATES NEWD OVER LAKE MI. THIS SYSTEM TO SLOWLY MOVE NE AND
WEAKEN TNGT...HOWEVER PLENTY OF LOW-LEVEL MOISTURE LEFT BEHIND TO
KEEP IFR CONDITIONS INTACT. THE NEXT SYSTEM IS FCST TO LIFT NE
TOWARD THE ERN GREAT LAKES ON WED AND COULD CLIP FAR ERN WI WITH
LIGHT SNOW. IFR CONDITIONS ARE FCST TO CONT THRU MOST OF WED WITH
PERHAPS A BRIEF CLIMB TO MVFR IN THE AFTERNOON.
&&

.HYDROLOGY...
ISSUED AT 306 AM CST TUE DEC 23 2014

MILD CONDITIONS ARE EXPECTED OVER EAST CENTRAL WISCONSIN THROUGH
WEDNESDAY ALONG WITH THE POTENTIAL FOR STORM TOTALS OF 0.25 TO
0.50 INCHES OF RAIN TUESDAY...WITH THE HIGHEST AMOUNTS OVER THE
SOUTHEAST THIRD OF THE FORECAST AREA. WHILE THE RAIN WILL PRODUCE
SOME RUNOFF...PRIMARY ISSUE IS THE AFFECTS ON ICE CONDITIONS ON
AREA RIVERS AND LAKES.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR WIZ005-
010>012-018-019-030-035.
&&

$$

SHORT TERM.....ESB
LONG TERM......ECKBERG
AVIATION.......KALLAS
HYDROLOGY......ESB/ECKBERG






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