Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 202336
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
530 PM CST THU NOV 20 2014

.SHORT TERM...(TONIGHT THROUGH FRIDAY NIGHT)
ISSUED AT 251 PM CST THU NOV 20 2014

MAIN FCST CONCERNS THIS PERIOD...DZ/FZDZ CHANCES FRI NIGHT...
COLD TEMPERATURES TONIGHT...WARMING TEMPS FRI/FRI NIGHT.

DATA ANALYSIS AT 18Z HAD A RIDGE OF HIGH PRESSURE FROM SOUTHERN MAN
TO THE MID MS VALLEY. CLEAR SKIES NEAR/EAST OF THE RIDGE AXIS OVER
MUCH OF THE UPPER MIDWEST TODAY. CLOUDS GENERALLY LIMITED TO THE
NORTHEAST 1/3 OF WI IN THE FLOW DOWNSTREAM OF LK SUPERIOR. EVEN WITH
ALL THE SUNSHINE...COLD LOW LEVEL AIRMASS AND THE SNOW COVER WAS NOT
ALLOWING TEMPS TO WARM MUCH. NOON READINGS ONLY IN THE TEENS TO MID
20S OVER MUCH OF MN/IA/WI.

20.12Z MODELS INITIALIZED WELL. SOLUTIONS VERY SIMILAR FOR TONIGHT/
FRI AS THE EASTERN CONUS TROUGH LIFTS INTO THE CAN MARITIMES AND
WEAK/TEMPORARY SHORTWAVE RIDGING BUILDS OVER THE UPPER MIDWEST.
TIGHTENING CONSENSUS ON THE SHORTWAVE TROUGH/ENERGY TO COME ACROSS
THE NORTHERN PLAINS FRI NIGHT...FAVORING A COMPROMISE OF THE EARLIER
RUNS. SHORT-TERM FCST CONFIDENCE IS GOOD THIS CYCLE.

FOR THE SHORT TERM...QUIET/COLD WEATHER CONTINUES TONIGHT AS THE SFC
RIDGE AXIS DRIFTS ACROSS MN/IA/WI. 925-850MB WARM ADVECTION STARTS
TO SPREAD IN LATER TONIGHT BUT BY THEN BOUNDARY LAYER SHOULD BE
DECOUPLED UNDER CLEAR/MOSTLY CLEAR SKIES. EVEN WITH THE LOW LEVEL
WARM ADVECTION...925MB TEMPS STILL IN THE -8C TO -12C RANGE AT 12Z
FRI. FRI MORNING LOOKING TO BE THE COLDEST MORNING OF THE RECENT
WELL BELOW NORMAL STRING...WITH LIGHT WINDS...CLEAR SKIES AND THE
SNOW COVER ALLOWING TEMPS TO DIP TO NEAR AND BELOW ZERO. HIGH
QUICKLY SLIPS OFF FRI WITH SOUTH GRADIENT WINDS AND LOW LEVEL WARM
ADVECTION INCREASING ACROSS THE AREA. 925MB TEMPS CLIMB INTO THE -2C
TO -6C RANGE BY 00Z SAT...THEN CONTINUE WARMING INTO THE -1C RANGE
/TAYLOR CO./ TO +2C TO +4C OVER THE SOUTH END OF THE FCST
AREA. MODEL SOUNDINGS/X-SECTIONS INDICATE THERE SHOULD BE A
REASONABLE AMOUNT OF SUNSHINE THRU MIDDAY FRI WITH AN INCREASE OF
MID/HIGH LEVEL MOISTURE/CLOUDS THRU THE AFTERNOON. SOUTH WINDS OF 10-
15MPH FOR THE AFTERNOON FOR MIXING. HIGHS FRI MAKE A RUN AT 30F IN
THE RIVER VALLEYS AND LOCATIONS WITH STRONGER LOW LEVEL MIXING.

LOWER LEVEL MOISTURE...SFC TO AROUND 850MB...INCREASES FRI NIGHT
WITH THE CONTINUED 925-850MB WARMING. 850MB TEMPS IN THE +2C TO +5C
RANGE BY 12Z SAT. CLOUD TOP TEMPERATURES PROGGED TO BE 0C AT THE
COLDEST...TOO WARM FOR ICE IN THE CLOUDS. LOWER LEVEL THERMO-
DYNAMIC FORCING PRODUCES SOME LIFT IN THE 925-700MB LAYER FRI
NIGHT...FOR A CONTINUED DZ/FZDZ MENTION IN THE FCST GRIDS.
INCREASING BOUNDARY LAYER MOISTURE OVER THE COLD/SNOW COVERED
GROUND...ADDED A PATCHY FOG MENTION ALONG/WEST OF THE MS RIVER
LATER FRI NIGHT. TRENDED TOWARD COLDER OF GUIDANCE LOWS TONIGHT
THEN USED A BLEND OF THE HIGHS/LOWS FOR FRI/FRI NIGHT. LOWS FRI
NIGHT TO BE EARLY IN THE EVENING...THEN STEADY/SLOWLY RISE
OVERNIGHT.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 251 PM CST THU NOV 20 2014

MAIN CONCERNS FOR SAT THRU SUN NIGHT...PRECIP TYPES/CHANCES AND
TEMPERATURES THRU THE PERIOD.

SAT THRU SUN NIGHT CONTINUES TO TREND TOWARD A MESSY LATE NOV
WEEKEND...WEATHER-WISE. 20.12Z OFFER A TIGHTENING CONSENSUS AS
ENERGY ON THE PAC NW COAST AT 12Z SAT DIGS INTO THE NORTHERN
PLAINS BY 12Z SUN...THEN DIGS INTO THE MID/UPPER MS VALLEY BY 12Z
MON. TREND FAVORS SLOWER OF THE EARLIER MODELS WITH THIS FEATURE
BY 12Z MON. TREND EJECTS THE SOUTHERN STREAM ENERGY SOUTHWEST OF
TX AT 12Z SAT ON A MORE EASTERLY TRACK...THRU THE OH VALLEY
EASTERN GREAT LAKES THRU THE PERIOD. THIS WITH LESS APPARENT
PHASING WITH THE SLIGHTLY SLOWER NORTHERN STREAM SHORTWAVE TROUGH.
GIVEN THE TIGHTENING CONSENSUS...FCST CONFIDENCE IN THE SAT THRU
SUN NIGHT PERIOD IS AVERAGE TO GOOD THIS CYCLE.

DZ/FZDZ SIGNAL REMAINS ACROSS THE AREA SAT INTO SAT EVENING.
HOWEVER...DRYING INDICATED AT 850MB...MAKING THE DEPTH OF LOW LEVEL
MOISTURE IN THE COLUMN MARGINAL FOR DRIZZLE. SFC-850MB WARM
ADVECTION CONTINUES FOR SOME LIFT IN THE LAYER...BUT TEMPS CONTINUE
TO CLIMB AS WELL WITH SFC TEMPS RISING INTO THE MID 30S-LOW 40S.
GIVEN THE SHALLOWER MOISTURE AND WEAKENING OF THE FORCING/LIFT...
TRENDED THE DZ MENTION DOWN/OUT FOR MUCH OF THE FCST AREA SAT.
BIGGER PROBLEM MAY BE FOG AS THE WARMING/LOW LEVEL MOISTURE SPREADS
NORTHWARD OVER THE COLD/SNOW COVERED LANDSCAPE. POTENTIAL FOR SOME
FOG TO PERSIST ACROSS THE AREA MUCH OF THE LATE FRI NIGHT INTO SUN
PERIOD. SAT NIGHT PERIOD WITH SOME LIGHTER WINDS AND SHALLOWER MIXED
LAYER ALREADY HAS A FOG MENTION ACROSS MUCH OF THE FCST AREA. DEEPER
MOISTURE AND LIFT AHEAD OF THE APPROACHING NORTHERN STREAM
SHORTWAVE/TROUGH SPREADS INTO/ACROSS THE FCST AREA LATER SAT NIGHT
INTO SUN NIGHT. WITH THE FURTHER EAST/SOUTH TRACK OF THE EJECTING
SOUTHERN STREAM WAVE...APPEARS THE DEEPER OF THE MOISTURE WITH IT
SPREADS ACROSS MAINLY THE SOUTHEAST 2/3 OF THE FCST AREA. FURTHER
MODEL SHIFTS MAY YET TAKE THIS MOISTURE MORE EAST/SOUTH OF THE FCST
AREA. COLUMN/BOUNDARY LAYER WARM ENOUGH FOR MAINLY RAIN LATER SAT
NIGHT/SUN. RAIN CHANCES IN THE 60-80 PERCENT RANGE OVER THE
SOUTHEAST 2/3 OF THE FCST AREA SUN GOOD FOR NOW. AS THE SOUTHERN
STREAM PORTION LIFTS INTO THE EASTERN GREAT LAKES SUN NIGHT...THE
LOWER LEVEL FLOW TURNS WEST/NORTHWEST ADVECTING COLDER AIR WEST TO
EAST ACROSS THE FCST AREA SUN NIGHT. COLUMN QUICKLY COOLS ENOUGH TO
CHANGE PRECIP SUN NIGHT TO SNOW. QUESTION IS...BY THE TIME THE
COLDER AIR ARRIVES...HOW MUCH OF THE DEEPER MOISTURE/MORE SATURATED
COLUMN REMAINS OVER THE FCST AREA. BULK OF ANY PRECIP SUN NIGHT
LOOKS TO BE DURING THE EVENING WHEN THE SFC-850MB LAYER IS STILL
ABOVE 0C. BY THE TIME THE COLDER AIR ARRIVES LATER SUN NIGHT...
PRECIP MAY BE ON ITS WAY OUT OF THE FCST AREA...WITH ANY SNOW
ACCUMULATIONS QUITE MINOR. 50-70 PERCENT PRECIP CHANCES SUN NIGHT
OKAY FOR NOW BUT IF PRESENT TRENDS CONTINUE THESE MAY END UP TOO
HIGH OVER THE WEST HALF OF THE FCST AREA. USED A BLEND OF THE
GUIDANCE HIGHS LOWS FOR SAT THRU SUN NIGHT. IF LOW CLOUDS/FOG END
UP MORE PERSISTENT/WIDESPREAD THIS PERIOD...HIGHS MAY BE A
CATEGORY TOO WARM AND LOWS A CATEGORY TOO COOL.

FOR MONDAY THROUGH THURSDAY...DAYS 4 TO 7...

MAIN CONCERNS THIS PERIOD...SNOW CHANCES MUCH OF THE PERIOD...RETURN
OF MUCH BELOW NORMAL TEMPERATURES.

MEDIUM RANGE MODEL RUNS OF 20.00Z AND 20.12Z IN GOOD AND IMPROVING
AGREEMENT MON ON LONGWAVE TROUGHING OVER MUCH OF THE CONUS WITH A
MID LEVEL LOW OVER THE UPPER MIDWEST. DECENT AGREEMENT FOR THIS
FEATURE TO SLOWLY FILL/MOVE EAST MON NIGHT THRU TUE NIGHT. TREND MON
FAVORS A COMPROMISE OF THE EARLIER RUNS THEN SLOWER OF EARLIER RUNS
TUE. REASONABLE CONSENSUS FOR EASTERN NOAM LONGWAVE TROUGHING FOR
WED...BUT DIFFERENCES BY WED WITH THE SPEED/STRENGTH OF SHORTWAVES
IN THE NORTHWEST FLOW OVER CENTRAL NOAM. BY THU ECMWF/GFS AT ODDS
WITH WESTERN VS. EASTERN CONUS TROUGHING...WITH EACH MAINTAINING
SOME CONSISTENCY WITH ITS PREVIOUS RUNS. DAY 4-7 CONFIDENCE AVERAGE
TO GOOD MON/TUE THEN NEAR/BELOW AVERAGE WED/THU.

COLD SFC THRU MID LEVEL LOW/TROUGH ROTATES OVER THE AREA MON INTO
TUE WITH A DEFORMATION BAND OF MOISTURE/LIFT/PRECIP TO PIVOT SLOWLY
EAST/SOUTHEAST ACROSS THE REGION. COLUMN BACK TO BEING COLD ENOUGH
FOR SNOW AS THE PRECIP TYPE FOR NEXT WEEK. DEEPEST/STRONGEST OF THE
DEFORMATION BAND MOISTURE/LIFT IS CLOSER TO/NORTH OF THE 850-500MB
LOW TROUGH OVER LK SUPERIOR...WITH HIGHEST -SN CHANCES ACROSS THE
NORTH/EAST PORTIONS OF THE FCST AREA MON/MON NIGHT. NEXT SHORTWAVE
TROUGH THRU THE FLOW...MUCH STRONGER IN THE ECMWF...SPREADS A ROUND
OF INCREASING LOWER LEVEL MOISTURE/THERMO-DYNAMIC FORCING...AND -SN
CHANCE INTO THE FCST AREA WED. WITH MUCH BELOW NORMAL TEMPS IN THE
LOWER PORTION OF THE COLUMN...WILL NOT TAKE MUCH MOISTURE/LIFT TO
SATURATE SOME PORTION OF IT AND PRODUCE A SMALL -SN CHANCE. ECMWF
LINGERS THIS TROUGH OVER THE AREA THU WHILE GFS IS MORE PROGRESSIVE
WITH RIDGING ALOFT...AND LOWER LEVEL WARM ADVECTION RETURNING FOR
THANKSGIVING DAY. AS MUCH AS A 10C SPREAD IN 850MB TEMPS OVER THE
AREA AT 28.00Z. GIVEN THE LESSER CONFIDENCE IN THE DETAILS BY
WED/THU...SMALL MODEL/ENSEMBLE CONSENSUS -SN CHANCES IN THE 20-30
PERCENT RANGE REASONABLE FOR NOW. ENSEMBLE/MODEL CONSENSUS OF THE
HIGHS/LOWS FOR MON-THU LOOKS TO HAVE THOSE WELL TRENDED TOO..THOUGH
IF GFS IS MORE CORRECT...THANKSGIVING DAY HIGHS WOULD BE TOO COOL.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 530 PM CST THU NOV 20 2014

HIGH PRESSURE WILL INFLUENCE THE REGION TONIGHT...KEEPING SKIES
CLEAR AND FAVORING LIGHT WINDS.

THE HIGH WILL SLIP QUICKLY SOUTHEAST ON FRIDAY...WITH A TIGHTENING
PRESSURE GRADIENT AHEAD OF AN APPROACHING SHORTWAVE TROUGH. WINDS
WILL BECOME SOUTHERLY AND INCREASE EARLY FRIDAY MORNING.

HIGH/MID LEVEL CLOUDS WILL MOVE IN FROM WEST TO EAST ON
FRIDAY...THICKENING AND LOWERING FRIDAY NIGHT. BUFKIT SOUNDINGS ARE
FAVORING A LOW SATURATION FRIDAY NIGHT - ESPECIALLY OVERNIGHT INTO
SATURDAY. THIS STRATUS DECK WOULD INTERACT WITH LOW LEVEL WARM AIR
ADVECTION AND ADDITIONAL LIFT...WHICH COULD RESULT IN AREAS OF
DRIZZLE. WITH TEMPS AND ROADS SFCS BELOW ZERO...FREEZING DRIZZLE
WOULD BE THE PCPN TYPE. LIGHT ICING WILL BE POSSIBLE ON EXPOSED SFCS
IF THE FREEZING DRIZZLE DEVELOPS AS ANTICIPATED. TEMPS QUICKLY WARM
SAT MORNING...AND THEN SHOULD STAY WARM ENOUGH THROUGH THE WEEKEND
FOR ANY ADDITIONAL PCPN TO FALL AS RAIN.

IN ADDITION TO THE LOW CLOUDS AND POTENTIAL FOR DRIZZLE...THE
INCREASE IN THE LOW SATURATION AND MILDER AIR COULD TRANSLATE INTO
AREAS OF FOG. ALREADY ANTICIPATING IFR/MVFR CIGS AND VSBYS FROM THE
CLOUDS/PCPN...BUT THE FOG COULD FURTHER HINDER VISIBILITIES.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION.....RIECK



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