Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 230518
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1118 PM CST THU JAN 22 2015

.SHORT TERM...(TONIGHT THROUGH FRIDAY)
ISSUED AT 225 PM CST THU JAN 22 2015

BLANKET OF LOW CLOUDS HANGING ACROSS THE REGION SHOWING SOME
EASTWARD MOVEMENT...PER LATEST SATELLITE IMAGERY. RH FIELDS SUGGEST
THESE WILL FINALLY CLEAR NORTH-EAST OF THE FORECAST AREA OVERNIGHT.
SOME SIGNIFICANCE TO THE CLEARING OF THE LOW CLOUDS AS THEY WOULD
HAVE A BEARING ON PCPN TYPE WITH A TROUGH ON FRIDAY.

AS FOR THIS TROUGH...AN UPPER LEVEL SHORTWAVE IS SLATED TO MOVE FROM
WESTERN CANADA TO ACROSS THE GREAT LAKES ON FRIDAY. THE BULK OF THE
UPPER LEVEL FORCING WILL STAY NORTH OF THE FORECAST AREA...BUT IT
WILL DRAG A SFC TROUGH ACROSS THE REGION. SOME WEAK THERMODYNAMICS
AND FRONTOGENETIC LIFT ALONG IT...ENOUGH TO PRODUCE LIGHT PCPN
DEPENDING ON THE SATURATION. IF THE AFOREMENTIONED LOW CLOUDS WOULD
HANG AROUND...SOME OF THAT PCPN TYPE COULD INITIALLY BE IN THE FORM
OF DRIZZLE/FREEZING DRIZZLE. BUFKIT SOUNDINGS YESTERDAY POINTED TO
THIS. HOWEVER...THE LAST COUPLE MODEL RUNS HAVE SATURATION IN A TOP-
DOWN FASHION...MAKING SNOW/RAIN MORE LIKELY.

LOW LEVEL WARMING GOING TO BE A FACTOR IN PCPN TYPE TOO. SOUTHWEST-
NORTHEAST RUNNING X-SECTIONS SHOWS A NEAR SFC WARM LAYER PRESSING
NORTHEAST ACROSS THE FORECAST AREA FRI AFTERNOON. IT COULD BE ENOUGH
FOR PARTIAL MELTING AND A SHORT PERIOD OF SLEET. DOESN/T LOOK LIKE
IT WOULD LAST LONG AS ANY PCPN WOULD QUICKLY COOL THAT WARM/DRY
LAYER.

OVERALL...RAIN OR SNOW LOOKS MOST LIKELY...WITH THE HIGHER PCPN
CHANCES ALONG/NORTHEAST OF THE I-94 CORRIDOR. QPF LOOKS MINOR...AND
THUS SO DOES ACCUMULATIONS OF WHATEVER FALLS.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 225 PM CST THU JAN 22 2015

THE GFS AND ECMWF REMAIN IN GOOD AGREEMENT WITH BUILDING AN UPPER
LEVEL TROUGH OVER THE WEST COAST...GRADUALLY PUSHING EAST TOWARD THE
PLAIN STATES BY MID WEEK. THE RIDGE AXIS NEVER QUITE MAKES IT TO THE
UPPER MISSISSIPPI RIVER VALLEY...SHIFTING BACK TO THE WEST AS AN
EAST COAST TROUGH REASSERTS ITSELF. AROUND +2 TEMP/HEIGHT ANOMALIES
UNDER THE RIDGE...AND ALTHOUGH WEST OF THE FORECAST AREA...THIS
SCENARIO SHOULD KEEP TEMPS AT OR ABOVE THE SEASONABLE NORMALS.

WITH THE REGION STAYING UNDER NORTHWEST FLOW...EXPECT VARIOUS UPPER
LEVEL PERTURBATIONS TO PASS THROUGH/NEAR THE AREA. DIFFICULT TO ADD
ANY REFINEMENT TO TIMING/LOCATION OF THESE POTENTIAL LIGHT SNOW
MAKERS...AND WILL STICK WITH CONSENSUS SOLUTION FOR NOW. OUTSIDE OF
THE SAT NIGHT/SUN SYSTEM...DON/T EXPECT MUCH IN THE WAY OF
ACCUMULATIONS AT THIS TIME.

SPEAKING OF SAT NIGHT/SUN...MODELS ARE IN GOOD AGREEMENT THAT THERE
IS GOING TO BE PRECIPITATION...WITH SNOW THE MAIN PRECIPITATION TYPE.
WHAT IS NOT CLEAR IS THE TRACK OF THE SNOW MAKER...AND THUS WHERE
THE HIGHER AMOUNTS ARE MOST LIKELY. THE GFS/NAM/GEM CURRENTLY FAVOR
A TRACK THAT WOULD BRING THE UPPER LEVEL SHORTWAVE/SFC LOW FROM
NORTHERN MN INTO SOUTHERN WI OVERNIGHT SAT-SUN MORNING. THE HIGHER
ACCUMULATIONS WOULD LIKELY FALL ACROSS NORTHERN/EASTERN WI. THE
ECMWF ON THE OTHER HAND IS FARTHER WEST AND FASTER...WITH ITS
PCPN BAND LAYING OUT WEST OF THE MISSISSIPPI RIVER. AMOUNTS IN
EITHER SCENARIO STILL SUGGEST 1 TO 4 INCHES...AND THE POTENTIAL
FOR AN ADVISORY WHEREVER THE MAIN SNOW BAND SETS UP.
HOWEVER...GIVEN THE MODEL DIFFERENCES...CONFIDENCE IS LOW IN
DETAILING WHERE THE HIGHER THREAT WILL LIE. WILL KEEP THE HIGH
CHANCES/LOW END LIKELY POPS FOR NOW.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1118 PM CST THU JAN 22 2015

BREEZY SOUTH TO SOUTHWEST WINDS ARE HELPING TO PUSH THE
PERSISTENT IFR/MVFR STRATUS DECK OFF TO THE EAST. RST SHOULD CLEAR
WITHIN THE NEXT 1-2 HRS WITH LSE IN 3-4 HRS. VFR CONDITIONS SHOULD
THEN PREVAIL UNTIL LATE AFTERNOON WHEN A COLD FRONT ARRIVES. ANY
PRECIPITATION ASSOCIATED WITH THIS FRONT SHOULD STAY TO THE NORTH.
HOWEVER...PLAN ON ANOTHER LOW STRATUS DECK TO MOVE IN BEHIND THE
FRONT. CEILINGS SHOULD START OFF MVFR...THEN FALL TO IFR AT RST
DURING THE EVENING...AIDED BY COOLING TEMPERATURES. THIS STRATUS
DECK WILL LIKELY REMAIN IN PLACE THROUGH SATURDAY.

REGARDING THE WINDS...A TIGHT PRESSURE GRADIENT IN PLACE WILL KEEP
A 10-20 KT BREEZE GOING UNTIL THE COLD FRONT ARRIVES. GUSTS OF
20-30 KT ARE ALSO POSSIBLE EARLY THIS MORNING AT RST WITH A
STRONGER WIND CORE COMING THROUGH ALOFT. EXPECT THE WINDS TO SWING
AROUND TO THE WEST AND EVENTUALLY NORTHWEST WITH THE PASSAGE OF
THE COLD FRONT. SPEEDS SHOULD DIMINISH SLIGHTLY LATE IN THE
EVENING WITH LOSS OF DAYTIME HEATING.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION...AJ



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