Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 212144
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
344 PM CST FRI NOV 21 2014

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 345 PM CST FRI NOV 21 2014

SPENT MOST OF THE FORECAST TIME TRYING TO GET THE CORRECT IMPACT
MESSAGING OUT FOR THIS PERIOD WITH ICING POTENTIAL MOVING IN AND
CONCERNS A BIT HIGHER IN WI WITH MANY TRAVELING FOR DEER HUNTING
WEEKEND.

WATER VAPOR CLEARLY SHOWING SHORTWAVE TROUGH ENERGY FOR TONIGHT
OVER NEB-KS...WITH SUNDAYS STRONG WAVES IN THE DESERT SOUTHWEST
AND NRN STREAM COMING INTO THE PACIFIC NORTHWEST. VISIBLE IMAGERY
SHOWING TONIGHTS WALL-OF-MOISTURE COMING AT THE FORECAST AREA WITH
THE LEADING EDGE NOW IN SOUTHERN IA. THERE ARE TWO MOIST SURGES
AND WARM FRONTS...ONE ON THE LEADING CLOUD LINE FROM KOMA-KSTL
AND THE MORE POTENT AREA NEAR AND SOUTH OF WICHITA KS. MANY 12Z
SOUNDINGS SHOWING THE AIR MASS FORECAST BY THE MODEL GUIDANCE TO
ADVECT IN OVERNIGHT...KTOP /INITIAL MOIST SURGE/...KSGF AND KLIT
/DEEPER MOIST SURGE/. SO...CONFIDENCE OF THE CHARACTER OF THIS AIR
MASS IS HIGH BASED ON SIMPLY ADVECTING NORTHWARD WHAT WE SEE IN
THE OBSERVATIONS /50-60F DEWPOINTS WOW/.

STRUGGLES WITH CONFIDENCE LIE IN THE NORTHWEST EXTENT OF THE
PRECIPITATION. SURFACE-BASED MOIST LAYER IS DEEPEST ACROSS SWRN
WI/EASTERN NE IA AT ABOUT 1.5 KMS...WITH A SHALLOWING NW OF KLSE
TO ABOUT .75 KMS AT KRST/KEAU. IN FACT...ACROSS THE SOUTH THERE IS
SOME SMALL SIGNAL FOR CONVECTIVE ELEMENTS THAT WOULD CAUSE A DEEP
CLOUD PROCESS AND RADAR THIS AFTERNOON IN ERN KS DOES CONFIRM SOME
CONVECTIVE BUMPS. SHOULD IT BE SHALLOW CLOUD OR DEEP CLOUD...THE
RESULT IS RA/FZRA/DZ/FZDZ DEPENDING ON SURFACE TEMPERATURE.
THUS...HAVE INCREASED PRECIPITATION AMOUNTS AND ICING IN SWRN WI
AND NERN IA BASED ON BETTER PARAMETER SPACE FOR THE WARM CLOUD
RAINFALL PROCESS /0.10 INCHES/...AND LIFTED ADVISORY NORTHWARD
MIDDAY TO ACCOUNT FOR I-90 IN WI/FAR EASTERN MN WHERE WE FEEL A
COMPROMISE OF JUST ENOUGH DEPTH TO SURFACE-BASED CLOUD AND JUST
ENOUGH LIFT EXIST FOR SOME VERY LIGHT ICING. WITH ABOVE NORMAL
TRAVEL OCCURRING TONIGHT IN WI...FELT THIS WAS THE PRUDENT CHOICE
EVEN THROUGH CONFIDENCE DIMINISHES FOR OUTCOMES FURTHER NORTHWEST
TONIGHT. CONFIDENCE IS LOWER ON THE LIFT WITHIN THE CLOUD LAYER
FURTHER NORTH AS ONLY WEAK WARM ADVECTION AFFECTS THE LOW-LAYER
CLOUD. KS/NEB SHORTWAVE TROUGH ENERGY SEEMS TO WORK ON THE
UPSTAIRS CLOUD...ABOVE SAY 600 MB. LATE EVENING THROUGH ABOUT 3-5
AM SHOULD BE THE MAIN GLAZE PERIOD.

TEMPERATURES ARE WARMING OVERNIGHT AS WARM FRONTS APPROACH...BUT
WITH PROLONGED SUB-FREEZING TEMPERATURES OVER THE PAST 9
DAYS...HAVE KEPT FZRA EVEN WITH AMBIENT AIR TEMPERATURES ABOVE
32F. ROAD TEMPERATURES TODAY WITH SUNSHINE HAVE REACHED THE
30S...AND THESE MAY HOLD OR RISE OVERNIGHT. BUT LESSER TRAVELED
ROADS AND UNTREATED SURFACES WILL CAUSE PROBLEMS TOO OVERNIGHT.
SATURDAY MORNING SHOULD SEE QUICKLY IMPROVING CONDITIONS AFTER A
LIGHT GLAZING OVERNIGHT AS TEMPERATURES QUICKLY WARM.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 345 PM CST FRI NOV 21 2014

NEXT MOIST SURGE MOVES IN WITH A STRONG WARM FRONT SATURDAY
EVENING AND OVERNIGHT. MODEL SIGNALS OF WARM FRONTAL
LIFT...850MB MOISTURE TRANSPORT CONVERGENCE...AND MOISTURE
ADVECTION SEEM TO SCREAM RAIN CHANCES SHOULD BE HIGHER THAN MODEL
SOLUTIONS IN PRECIPITATION FIELDS. THUS...HAVE INCREASED SATURDAY
EVENING RAIN CHANCES WITH WARM FRONT MOVING IN AND ONSET
PRECIPITATION TIME IS EARLIER THAN PREVIOUS FORECASTS. STILL
LOOKING AT ALL RAIN AND SATURDAY NIGHT SHOULD HAVE A NICE WARMING
INTO THE 40S. HAVE ALSO INCREASED FOG COVERAGE SATURDAY NIGHT...IT
COULD GET PRETTY THICK...AND A DENSE FOG ADVISORY MAY BE NEEDED.

SUNDAY BRING THE COMBINATION OF MOISTURE FROM THE SOUTHERN STREAM
AND THE SHORTWAVE TROUGH ENERGY FORCING...AND A WELL-AGREED UPON
RAINY DAY STILL FROM NERN IA INTO NERN WI. THE QUESTION STILL
REMAINS ON WHERE THE WESTERN EDGE OF THIS PRECIPITATION WILL SET
UP. NOT A GREAT DEAL OF CHANGE SUNDAY AND SUNDAY NIGHT FROM
PREVIOUS FORECAST. RAINFALL AMOUNTS OF 0.50 TO 1.00 INCHES SEEMS
ABOUT RIGHT FOR SWRN-CTRL WI. WE DO NOT BELIEVE THIS WILL CAUSE
RIVER ISSUES AT THIS TIME BUT WILL CONTINUE TO MONITOR IT. ICE IS
NOT THICK ENOUGH...NOR WILL RIVERS RISE ENOUGH TO CAUSE ICE JAM
ISSUES.

AT THIS TIME...IT APPEARS THE MODEL CONSENSUS AGREES THAT ONLY
MINOR PRECIPITATION WOULD GO INTO SNOW SUNDAY NIGHT AS COLDER AIR
MOVES IN. HAVE INCREASED THE CENTRAL WI SNOWFALL AMOUNTS TO 1
INCH. HOWEVER...THERE IS STILL SPREAD ON THIS PERIOD ON WESTERN
PRECIPITATION EDGE AND THE WRAP AROUND DEFORMATION VERSUS DRY
PUNCH COMING INTO THE SYSTEM. SO...THIS PERIOD WILL BE REFINED IN
FUTURE FORECASTS.

ANOTHER COLD PERIOD BEGINS MONDAY AND CURRENT THANKSGIVING HIGHS
ARE IN THE TEENS AS A COLD AIR MASS SETTLES IN AFTER A WEAK SYSTEM
WEDNESDAY. THIS AIR MASS IN THE NAEFS IS ABOUT 2 STANDARD
DEVIATIONS BELOW NORMAL FOR THURSDAY...BUT THE DETERMINISTIC RUNS
/ECMWF 22.12Z/ SUGGEST VALUES CLOSER TO 3 DEVIATIONS...UNUSUAL/RARE
COLD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1131 AM CST FRI NOV 21 2014

INCREASING SOUTHERLY WINDS THIS MORNING...IN THE 10-20 KT RANGE
AND STRONGEST AT RST...HAS HELPED BRING MORE MOISTURE INTO THE TAF
SITES. THE BREEZY WINDS WILL CONTINUE THROUGH SATURDAY...BRINGING
IN A STRATUS DECK THATS RACING NORTHEASTWARD OUT OF THE CENTRAL
PLAINS. THOSE WINDS ARE PROGGED STRONG ENOUGH TO EVEN WARRANT A
LOW LEVEL WIND SHEAR MENTION AT LSE FOR MUCH OF TONIGHT. ANTICIPATING
THE STRATUS DECK TO MOVE INTO THE TAF SITES IN THE 02-03Z TIME
WINDOW AS AN MVFR CEILING...LOWERING TO IFR AT RST BY 05Z. SOME
FREEZING DRIZZLE IS POSSIBLE AROUND 06Z AT LSE AT THE ONSET...
CHANGING OVER TO DRIZZLE A FEW HOURS LATER AS AIR TEMPERATURES
WARM. BOTH SITES SHOULD SEE FURTHER LOWERING OF CEILINGS AS WE
APPROACH 12Z SATURDAY IN RESPONSE TO CONTINUED MOISTURE BEING
PUSHED INTO THE COLDER AIR HERE. VISIBILITIES COULD EVEN START TO
BE IMPACTED...ESPECIALLY AT THE HIGHER TERRAIN OF RST WHERE MVFR
MENTION IS ADDED.

LOOKING AHEAD...CONDITIONS REMAIN FAVORABLE FOR A DENSE FOG EVENT
SATURDAY NIGHT INTO SUNDAY MORNING...ESPECIALLY AT RST.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...FREEZING RAIN ADVISORY FROM 9 PM THIS EVENING TO 8 AM CST
     SATURDAY FOR WIZ054-055-061.

     FREEZING RAIN ADVISORY FROM 11 PM THIS EVENING TO 8 AM CST
     SATURDAY FOR WIZ041>044-053.

MN...FREEZING RAIN ADVISORY FROM 11 PM THIS EVENING TO 8 AM CST
     SATURDAY FOR MNZ096.

IA...FREEZING RAIN ADVISORY FROM 9 PM THIS EVENING TO 8 AM CST
     SATURDAY FOR IAZ008>011-018-019-029-030.

&&

$$

SHORT TERM...BAUMGARDT
LONG TERM...BAUMGARDT
AVIATION...AJ


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