Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 190310
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1010 PM CDT MON MAY 18 2015

UPDATED AVIATION PORTION FOR 06Z TAF ISSUANCE

.SHORT TERM...TONIGHT AND TUESDAY
ISSUED AT 235 PM CDT MON MAY 18 2015

THE LATEST RAP ANALYSIS AND SATELLITE/RADAR IMAGERY SHOW OCCLUDED
LOW PRESSURE MOVING EAST OVER WESTERN LAKE SUPERIOR.  A VERY CHILLY
AIRMASS FOR THIS TIME OF THE YEAR IS WRAPPING AROUND THE LOW AND
GRADUALLY MOVING EAST OVER THE WESTERN HALF OF WISCONSIN.  THE LOW
STRATUS HAS MOVED VERY LITTLE EASTWARD SO FAR TODAY...BUT SHOULD
GAIN SOME MOMENTUM THROUGH THE AFTERNOON AS THE COLDER AIR AT 850MB
OVER TAKES IT.  PLENTY OF OBS ARE REPORTING LIGHT RAIN/DRIZZLE...AND
EVEN A FEW FLAKES UPSTREAM OVER NORTHWEST WISCONSIN AND NORTHERN
MINNESOTA.  AS THE COLDER AIR AND LIGHT PRECIP SPREAD ACROSS THE
REGION...TEMPS AND PRECIP TRENDS ARE THE MAIN FORECAST CONCERNS.

TONIGHT...OCCLUDED LOW PRESSURE WILL MOVE EAST OVER LAKE SUPERIOR
AND NORTHERN ONTARIO AND WEAKEN AT THE SAME TIME.  AS WINDS SHIFT TO
THE NORTHWEST...COLD ADVECTION WILL CONTINUE ACROSS THE STATE
THROUGH THE NIGHT...DROPPING 850MB TEMPS TO AROUND -8C TO -10C.
DEEPER MOISTURE WILL BE ROTATING ACROSS NORTHERN WISCONSIN AND
COMBINED WITH UPSLOPE FLOW OFF LAKE SUPERIOR AND UNSTABLE
CONDITIONS...SHOULD SEE PERIODS OF LIGHT RAIN/DRIZZLE...MIXED WITH
SNOW AT TIMES.  TEMPERATURES WILL BE FALLING INTO THE 30-32 DEGREE
RANGE OVER NORTHERN WISCONSIN FOR A FEW HOURS LATE TONIGHT.  BUT
AREAS OVER THE UPPER PENINSULA AND NORTHWEST WISCONSIN HAVE NOT
OFFICIALLY STARTED THEIR GROWING SEASONS...SO WILL HIGHLIGHT THE
COLD IN A SPECIAL WEATHER STATEMENT.  ELSEWHERE...LOOK FOR A CLOUDY
AND BLUSTERY NIGHT.

TUESDAY...THERMAL TROUGHING AND FLOW OFF LAKE SUPERIOR ARGUE FOR A
CLOUDY/MOSTLY CLOUDY START TO THE DAY.  BUT SHOULD SEE CLOUDS
GRADUALLY ERODE FROM SOUTHWEST THROUGH NORTHEAST THROUGH THE DAY AS
CYCLONIC FLOW ABATES AND LOW LEVEL TEMPS MODERATE.  LOWERED MAX
TEMPS A DEGREE...AND WENT WITH HIGHS RANGING FROM THE MID 40S NORTH
TO MID 50S SOUTH.

.LONG TERM...TUESDAY NIGHT THROUGH MONDAY
ISSUED AT 235 PM CDT MON MAY 18 2015

FROST/FREEZE HEADLINE POTENTIAL TUESDAY NIGHT AND WEDNESDAY NIGHT...
AND PCPN TRENDS FOR THE MEMORIAL DAY WEEKEND...ARE THE MAIN FCST
CONCERNS.

CANADIAN HIGH PRESSURE WILL BE RIDGED OVER THE WSTRN GREAT LAKES
ON TUESDAY NIGHT...AND WILL BRING LIGHT WINDS TO THE FORECAST AREA.
EXPECT SKIES TO BE MOSTLY CLEAR OVER NORTHERN WI...LEADING TO
WIDESPREAD SUB-FREEZING TEMPERATURES. AVERAGE MIXING RATIOS OF
2.5 TO 3 G/KG SUPPORT THE POTENTIAL FOR MIN TEMPS AS COLD AS
20 TO 25 AT THE CLIMATOLOGICALLY FAVORED COLD SPOTS. HIGH CLOUDS
ARE EXPECTED TO INCREASE OVER C/EC WI...ON THE ANTICYCLONIC SHEAR
SIDE...AND WITHIN THE RRQ...OF A STRONG UPPER JET STREAK. WHILE
THIS LIKELY WILL NOT PREVENT FROST DEVELOPMENT IN OUR SOUTHERN
COUNTIES...IT SHOULD AT LEAST KEEP MOST PLACES ABOVE FREEZING.
WILL NOT ISSUE ANY HEADLINES WITH THIS FORECAST PACKAGE...BUT
FROST/FREEZE HEADLINES APPEAR IMMINENT.

THE POTENTIAL FOR FROST WILL CONTINUE INTO WEDNESDAY NIGHT...
BUT SHOULD SHIFT TO MAINLY NORTHERN WI...WHERE MIN TEMPS ARE
EXPECTED TO DROP INTO THE LOWER TO MIDDLE 30S.

A WEAK BACK DOOR COLD FRONT IS EXPECTED TO DROP SOUTH THROUGH
THE REGION SOMETIME DURING THE WEDS NGT TO THU NGT PERIOD. THE
GFS IS FOCUSING ON WEDS NGT/THU...WHILE THE ECMWF IS SLOWER
AND BRINGS THE FRONT THROUGH THU AND EARLY THU NGT. A VERY
DRY AIR MASS SHOULD PRECLUDE ANY PCPN DEVELOPMENT.

CANADIAN HIGH PRESSURE WILL RETURN TO THE WSTRN GREAT LAKES
FRIDAY...AND SHOULD HOLD ANY PCPN AT BAY THROUGH AT LEAST
SATURDAY.

A COLD FRONT/INVERTED SFC TROF AND UPPER TROF WILL IMPACT THE
REGION FOR THE LATTER HALF OF THE MEMORIAL DAY WEEKEND...BUT
TIMING DIFFERENCES ARE SIGNIFICANT BETWEEN THE MODELS. THE GFS
HAS PCPN OVER THE REGION FROM SAT NGT THROUGH MONDAY...WITH THE
HEAVIEST QPF FCST ON SUNDAY. THE ECMWF IS SLOWER...AND FOCUSES
MOST OF THE PCPN DURING THE SUNDAY NIGHT AND MONDAY PERIODS.
DUE TO THE TIMING DIFFERENCES...HAVE BACKED OFF ON LIKELY POPS
FOR ANY SPECIFIC PERIOD...BUT OVERALL TRENDS SUPPORT AT LEAST
A PERIOD OR TWO OF MODERATE RAINFALL.

SLIGHTLY BLO NORMAL TEMPERATURES ARE EXPECTED AT THE BEGINNING
AND END OF THE EXTENDED PERIOD...WITH NEAR NORMAL READINGS FOR
THE REST OF THE DAYS.
&&

.AVIATION...FOR 06Z TAF ISSUANCE
ISSUED AT 1009 PM CDT MON MAY 18 2015

CLOUDS AND COLD AIR WILL CONTINUE TO POUR INTO THE
AREA OVERNIGHT ON NORTHWEST WINDS. MAINLY MVFR CIGS ACROSS THE
AREA OVERNIGHT WITH POCKETS OF IFR CIGS AND MVFR VSBYS DUE TO
SHOWERS OVER NORTHERN WISCONSIN. GUSTY WINDS WILL CONTINUE TO
SUBSIDE OVERNIGHT. COOL DRY HIGH PRESSURE SETTLING INTO THE GREAT
LAKES REGION WILL PRODUCE VFR CIGS LATER TUESDAY.
&&

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

$$

SHORT TERM.....MPC
LONG TERM......KIECKBUSCH
AVIATION.......TDH





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