Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 240324
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1024 PM CDT WED APR 23 2014

UPDATED AVIATION PORTION FOR 06Z TAF ISSUANCE

.UPDATE...
ISSUED AT 907 PM CDT WED APR 23 2014

00Z GRB SOUNDING HAS MOISTENED ABV 600 MB...BUT WAS STILL VERY DRY
BELOW. WATCHING PCPN OUT IN MN...A FEW SITES OVER NRN MN HAVE HAD
PCPN GO OVER TO SNOW WHEN THE INTENSITY INCREASED. THINK THIS IS
PROBABLY AN PRECURSOR OF WHAT WL HAPPEN OVER FAR NRN WI TOMORROW.

NEW NAM IS PERHAPS A BIT WARMER IN THE BOUNDARY LAYER...AND
MAYBE INITIALLY AT 850 MB. BUT IT CONTS TO SHOW TEMPS DROPPING WHEN
THE HEAVIER PCPN ARRIVES. BUT THAT MAY NOT BE UNTIL LATER
TOMORROW...AS DRY AIR CONTS TO SLOW THE NEWD ADVANCE OF THE PCPN.

WOULD REALLY HAVE LIKED TO SEEN A LITTLE COLDER TEMPS ON THE RAP
AND NAM TO GIVE ME MORE CONFIDENCE IN PCPN GOING TO PREDOMINANTLY
SNOW OVER THE FAR N. INSTEAD...WE SEEM TO BE IN A SITN WHERE PCPN
WL FLIP BACK AND FORTH...WITH LIGHTER PCPN FALLINGS MORE AS RAIN
AND THE HEAVIER PCPN FALLING AS SNOW. WL ADJUST THE GRIDS TO HAVE
MORE FZN PCPN ACRS THE FAR N TOMORROW. WL ALSO ADD SOME
ACCUMULATION...THOUGH THAT WL PROBABLY BE A SLUSHY ACCUMULATION
MAINLY ON THE GRASS. HOPE THIS ALL WORKS OUT OKAY...BUT CONFIDENCE
ISN/T HIGH.

UPDATED GRIDS AND FCST PRODUCTS WL BE OUT ASAP. WL ALSO ISSUE AN
SPS FOR THE FAR N.

UPDATE ISSUED AT 556 PM CDT WED APR 23 2014

FCST FOR LATE TNGT AND THU ACRS THE N VERY TRICKY. 12Z GRB RAOB
SAMPLED VERY DRY AIR ALOFT. WE/LL SEE THE 00Z RAOB SOON AND AM
CURIOUS TO SEE HOW MUCH DRY AIR REMAINS. THE PROBLEM IS THE DRY
AIR IS LIKELY TO PLAY HAVOC WITH PRECIP TYPE ONCE PCPN ARRIVES FM
THE W LATER THIS EVENING/OVERNIGHT. SFC TEMPS WARMED INTO THE
LOWER 50S ACRS THE N TDA...BUT DWPTS WERE ONLY IN THE TEENS. SO
THERE SHOULD BE A SIG DROP OFF IN TEMPS THIS EVENING...AND
ADDITIONAL COOLING COULD OCCUR VERY QUICKLY AT LOW-LEVELS ONCE
PCPN STARTS. 850 MB TEMPS WERE ONLY A DEG OR TWO ABV ZERO...AND
THAT AIR WL BE ABLE TO EVAPORATIVELY COOL AS WELL. MODEL FCST
SOUNDINGS BY LATE TNGT AND CONTG WELL INTO THE DAY THU SUGGEST
TEMPERATURE PROFILES THAT ARE DEEP-ISOTHERMAL NR ZERO...WITH NO
PRONOUNCED WARM LAYER ALOFT. SO PCPN TYPE WL PROBABLY COME DOWN TO
THE BOUNDARY LAYER TEMPS...AND IT/S TOUGH SEEING THOSE HOLDING UP
ENOUGH TO KEEP PCPN ALL OR EVEN PREDOMINANTLY LIQUID...ESP
CONSIDERING THE CONTD INFLUX OF DRY /POTENTIALLY COOL/ AIR FM THE
E. AS PREVIOUS FCSTR MENTIONED...CONFIDENCE IN HOW THIS WL EVOLVE
IS LOW...BUT AM REAL NERVOUS WITH FCST AS HEAVILY WEIGHTED TOWARD
LIQUID AS WHAT WE HAVE GOING. IT MAY BE VERY DIFFICULT TO GET MUCH
SNOW TO ACCUMULATION ON ROADS DURING THE DAY THIS LATE IN THE
SEASON...EVEN IN NRN WI. BUT WE COULD STILL HAVE PCPN FALLING AS
MAINLY SNOW WELL INTO THE AFTN ACRS THE FAR N.

WL AWAIT 00Z RAOB DATA AND PROBABLY THE START OF SOME OF THE
EVENING GUIDANCE PRODUCTS BEFORE I START MAKING CHGS...BUT SUSPECT
I/LL EVENTUALLY NEED TO PUSH THE FCST MORE TOWARD SNOW OR AT LEAST
MORE OF A RAIN/SNOW MIX.
&&

.SHORT TERM...TONIGHT AND THURSDAY
ISSUED AT 332 PM CDT WED APR 23 2014

CONFIDENCE LEVEL IN THE FORECAST BEYOND ABOUT 06Z TONIGHT IS
RATHER LOW. THE 12Z GRB SOUNDING WAS DRY BELOW 250MB AND MPX WAS
DRY BELOW 750MB...SO THE APPROACHING AREA OF SHOWERS WAS HAVING A
TOUGH TIME MAKING MUCH EASTWARD PROGRESS. HAVE THE SHOWERS MOVING
INTO CENTRAL WISCONSIN 00Z-06Z INTO ALL BUT THE FAR NORTHEAST PART
OF THE STATE 06Z-12Z. PRECIPITATION TYPE IN THE NORTHERN PART OF
THE FORECAST AREA IS QUESTIONABLE WITH SURFACE TEMPERATURES
FORECAST TO REMAIN ABOVE FREEZING DURING THE NIGHT. WPC GUIDANCE
WAS SHOWING AN AREA OF AT LEAST 2 INCHES OF ACCUMULATION ALONG THE
UPPER MICHIGAN BORDER BUT HAVE GONE WITH RAIN AND SNOW WORDING IN
THE NORTH WITH UP TO AN INCH OF NEW SNOW THERE THROUGH THURSDAY
MORNING. MOS 3-HOURLY TEMPERATURES WELL ABOVE FREEZING SHOULD KEEP
PRECIPITATION MOSTLY IN LIQUID FORM. OTHERWISE...HAVE A SLIGHT
CHANCE FOR THUNDER GOING ON THURSDAY...THOUGH COULD NOT FIND ANY
CAPE OR STEEP MID LEVEL LAPSE RATES AND SPC DAY 2 DOES NOT INCLUDE
ANY OF WISCONSIN. CANNOT REALLY RULE OUT THUNDER WITH 40 TO 50
KNOT 850MB JET AND ADJACENT GRIDS HAVE IT MENTIONED TO THE
WEST...SOUTH AND EAST.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY
ISSUED AT 332 PM CDT WED APR 23 2014

FLOW TO BECOME STRONGLY AMPLIFIED THIS WEEKEND AS A STRONG UPPER
TROF DIGS TOWARD THE CENTRAL ROCKIES AND UPPER RIDGING OCCURS
DOWNSTREAM OVER CENTRAL NORTH AMERICA. THIS UPPER TROF IS EXPECTED TO
CLOSE OFF INTO AN UPPER LOW OVER THE CENTRAL PLAINS AND SLOWLY DRIFT
EAST TOWARD THE MID-MS VALLEY EARLY NEXT WEEK. ISSUES CONTINUE
BETWEEN MODEL RUNS WITH HOW FAR NORTH LOW WILL TRACK. AT THIS TIME
SOME CONSENSUS SEEN IN A FURTHER SOUTH TRACK THROUGH FIRST HALF OF
THE WEEK...WITH DRY SURFACE HIGH TO THE NORTH KEEPING CONDITIONS
DRY AT LEAST THROUGH WEEKEND. HAVE TRENDED TOWARDS GFS ENSEMBLE
MEAN FOR LATER PERIODS. THOUGH CONFIDENCE LOW AS MODEL SPREAD
QUITE SIGNIFICANT OVER WI BY WED.

IN THE NEAR TERM...THE NEGATIVELY-TILTED TROF TO CONTINUE TO LIFT
NORTHEAST THROUGH STATE AT BEGINNING OF THIS PERIOD...WITH COLD
FRONT MOVING THROUGH STATE THURSDAY NIGHT. GOOD UPPER DYNAMICS
WITH COUPLED JET FEATURE TO LEAD TO SIG PCPN INTO THE EVENING
HOURS. MODEL SOUNDINGS SUGGEST RAIN THROUGH MIDNIGHT...THEN A
SWITCH TO SOME SNOW NORTH HALF AFTER MIDNIGHT. BY TIME TEMP
PROFILES FAVORABLE FOR SNOW...MUCH OF MOISTURE NORTH OF CWA...ONLY
CARRYING AND INCH OR TWO ATTM.

THE UPPER TROF/LOW IS FCST TO SLOWLY DRIFT ACROSS THE NORTHERN
GREAT LAKES ON FRI KEEPING CYCLONIC FLOW ACROSS WI. MODELS SHOWING
SIG COLD AIR ALOFT AND INSTABILITY FOR MUCH OF FRI FOR THOUGHTS OF
SCATTERED SHOWERS FOR MUCH OF THE DAY.

TEMPERATURES FOR THIS PERIOD TO CONTINUE THEIR BELOW NORMAL TREND.
&&

.AVIATION...FOR 06Z TAF ISSUANCE
ISSUED AT 1020 PM CDT WED APR 23 2014

NEED TO SLOW THE EWD ADVANCE OF THE PCPN AGAIN AS VERY DRY AIR
CONTS TO FEED IN FM THE E. THAT AS ALSO MAINTAINING CIGS IN VFR
CATEGORY EVEN WHERE PCPN WAS OCCURRING. WL ADJUST 06Z TAFS
ACCORDINGLY. WL MAINTAIN LLWS TNGT INTO TOMORROW.
&&

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

$$

UPDATE.........SKOWRONSKI
SHORT TERM.....MG
LONG TERM......TE
AVIATION.......SKOWRONSKI






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