Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 291732
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1132 AM CST THU JAN 29 2015

.UPDATE...
ISSUED AT 548 AM CST THU JAN 29 2015

THE LIGHT FREEZING DRIZZLE THAT FELL OVERNIGHT SEEMS TO HAVE NOT
HAD MUCH OF AN IMPACT ON AREA ROADWAYS AS MANY COUNTY SHERIFF
DEPARTMENTS HAVE REPORTED THAT THINGS ARE OKAY. THERE HAVE BEEN
SOME SLICK SPOTS THAT HAVE DEVELOPED...BUT SALTING CREWS HAVE
QUICKLY FOUND THESE SPOTS AND TAKEN CARE OF THEM. WITH THE DRIZZLE
ABOUT TO CHANGE OVER TO SOME SNOW SHOWERS/FLURRIES...WILL BE
ALLOWING THE ADVISORY TO EXPIRE HERE AT 6 AM. CAN NOT RULE OUT A
FEW SLICK SPOTS...BUT THE THREAT FOR WIDESPREAD ICING APPEARS
OVER.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 339 AM CST THU JAN 29 2015

MAIN FCST CONCERNS THIS PERIOD...LINGERING WINTRY MIX CHANCES THIS
MORNING...WINDS TODAY...CLOUDS/TEMPERATURES BOTH TODAY/TONIGHT.

DATA ANALYSIS AT 06Z HAD LOW PRESSURE OVER SOUTHEAST IA WITH A
TROUGH NORTHWARD THRU CENTRAL WI TO THE WESTERN U.P OF MI...MAKING
STEADY PROGRESS EAST. LOW CLOUDS/FOG/DZ/FZDZ GENERALLY WEST OF THE
TROUGH AXIS EARLY THIS MORNING...AND SPREADING ACROSS MUCH OF
WESTERN WI...EASTERN MN AND NORTHEAST IA. AIR AND ROAD SFC TEMPS
ACROSS THE FCST AREA GENERALLY A COUPLE DEGREES EITHER SIDE OF
32F...WITH MINIMAL ICING/GLAZING PROBLEMS REPORTED SO FAR. WINDS
INCREASING ACROSS CENTRAL/WESTERN MN/IA AS TIGHT GRADIENT AND
PRESSURE RISE BEHIND THE TROUGH MOVES IN. WIND GUSTS AROUND 30KTS
COMMON WEST OF I-35 EARLY THIS MORNING. VISIBILITIES SLOWING
IMPROVING THESE AREAS WITH THE INCREASE OF THE NORTHWEST WINDS.

29.00Z MODELS INITIALIZED WELL AND SHOW VERY GOOD RUN-TO-RUN
CONSISTENCY WITH THEIR 27.00Z AND 28.00Z RUNS. SOLUTIONS VERY
SIMILAR AS THE MID LEVEL TROUGH AXIS MOVES EAST OF THE AREA TODAY
THEN THE UPPER MIDWEST IS LEFT UNDER NORTHWEST FLOW TONIGHT. TREND
FAVORS A COMPROMISE ON THE SHORTWAVE TO DROP ACROSS LK SUPERIOR AND
MI THIS AFTERNOON/EVENING. BASED ON THIS...SHORT-TERM FCST
CONFIDENCE WOULD BE GOOD. HOWEVER...LOWER LEVEL MOISTURE/CLOUDS
WHICH THE MODELS STRUGGLE WITH REMAIN PROBLEMATIC TO THE FCST.

FOR THE SHORT TERM...SFC TROUGH AXIS QUICKLY MOVES TO LK MI/EASTERN
IL BY 12Z THIS MORNING. A TIGHT PRESSURE GRADIENT BETWEEN IT AND A
1036-1040MB HIGH BUILDING INTO THE CENTRAL/NORTHERN PLAINS SPREADS
ACROSS MN/IA/WI TODAY. BROAD AREA OF LOW CLOUDS...MAINLY IFR...AND
1-5SM VSBYS IN FOG BEHIND THE TROUGH AXIS TO SPREAD ACROSS THE
FCST AREA THIS MORNING. MODEL SOUNDINGS/X-SECTIONS INDICATE
LINGERING LIFT IN THE LOWER SATURATED SFC-850MB LAYER THRU TODAY...
EVEN AS STRONGER GRADIENT NORTHWEST FLOW AND LOW LEVEL COLD
ADVECTION SPREADS ACROSS THE AREA. DIMINISHING MAINLY -FZDZ
CHANCES THRU THE MORNING REASONABLE AT THIS POINT. BY AFTERNOON...
TOP OF THE MIXED LAYER/MOISTURE IS AROUND -10C. WITH WEAK
LINGERING LIFT IN THIS LOWER LAYER MAY YET NEED A FLURRY MENTION
FOR THE AFTERNOON HOURS. LEFT THIS OUT OF THE GRIDS FOR NOW. WITH
THE WEAK LIFT AND CYCLONIC FLOW...LEFT SKIES MOSTLY CLOUDY TO
CLOUDY THRU THE DAY. WITH THE COLD ADVECTION/BRISK NORTHWEST
WINDS...HIGHS WILL BE THIS MORNING THEN STEADY/SLOWLY FALLING
TEMPS THRU THE DAY.

STEEP LAPSE RATES IN THE MIXED LAYER TO AROUND 900MB TODAY...WITH
WINDS AT THE TOP OF THE MIXED LAYER IN THE 35-40KT RANGE. STRONGEST
OF THE POST-TROUGH PRESSURE RISES ARE THIS MORNING...WEAKENING THRU
THE AFTERNOON. WIND GUSTS IN THE STRONGEST PRESSURE RISE AREAS EARLY
THIS MORNING IN THE 35-40KT RANGE...WITH THIS PRESSURE RISE AREA
PASSING SOUTHWEST OF THE FCST AREA. WITH CLOUDY SKIES THIS MORNING
AND WEAK LOW LEVEL LIFT VS. A STRONG DOWNWARD FLUX OF MOMENTUM
SIGNAL WILL HOLD OFF ON A WIND ADVISORY FOR THE WEST 1/3 OF THE FCST
AREA FOR NOW. WILL STILL BE WINDY THERE THRU THE MORNING/EARLY
AFTERNOON...20-30 MPH G40 MPH. WINDS ELSEWHERE TODAY 15-25MPH G30-35
MPH. SFC RIDGE AXIS BUILDS IN TONIGHT WITH WINDS QUICKLY DIMINISHING
THIS EVENING AS THE GRADIENT RELAXES. SFC RIDGE AXIS IS OVER THE
AREA AT 12Z FRI...WITH 925MB TEMPS IN THE -10C TO -16C RANGE. WOULD
THINK SKIES WOULD CLEAR TONIGHT IN STRONG ANTICYCLONIC FLOW IN THE
925-850MB RIDGE AXIS AND STRONGER SUBSIDENCE ALOFT. HOWEVER MODELS
STUBBORNLY HANG ONTO MOISTURE IN THE 925MB LAYER STUCK UNDER THE
INVERSION NEAR 900MB. MOISTURE PROGGED TO BECOME QUITE SHALLOW AND
WITH THE STRONGER LOW LEVEL RIDGE AXIS/ANTICYCLONIC FLOW WILL REMAIN
OPTIMISTIC FOR LOW CLOUDS TO DECREASE/CLEAR TONIGHT. USED A BLEND OF
THE GUIDANCE HIGHS/LOWS FOR TODAY/TONIGHT.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 339 AM CST THU JAN 29 2015

FCST CONCERNS FOR FRI THRU SAT NIGHT...CLOUDS/TEMPERATURES THRU THE
PERIOD...SNOW CHANCES SAT NIGHT.

MODEL RUNS OF 29.00Z IN GOOD AGREEMENT FOR FRI THRU SAT WITH MINOR
DIFFERENCES IN THE DETAILS THESE PERIODS LOOKING TO HAVE MINIMAL
IMPACT ON THE SENSIBLE WEATHER. BY SAT NIGHT...MODELS DIFFER ON THE
STRENGTH OF A NORTHERN STREAM SHORTWAVE TO DROP INTO THE NORTHERN
AND CENTRAL PLAINS. NAM/CAN-GEM STRONGER/SLOWER...ECMWF/GFS FASTER/
FLATTER/MORE SHEARED AND INDICATE LITTLE OR NO PHASING WITH ANY
ENERGY FROM THE CA BAJA LOW. GIVEN A LARGE SPREAD SEEN IN BOTH THE
SREF AND GFS ENSEMBLES BY SAT NIGHT...NO ONE DETERMINISTIC MODEL
FAVORITE THIS CYCLE AND PREFERRED THE MODEL/ENSEMBLE CONSENSUS FOR
NOW. FCST CONFIDENCE GENERALLY GOOD FRI THRU SAT THEN BELOW AVERAGE
SAT NIGHT.

COLD...CANADIAN HIGH PRESSURE MOVES ACROSS THE REGION FRI. LOW LEVEL
WARM ADVECTION RETURNS FOR FRI AFTERNOON/NIGHT AS THE SFC-850MB
RIDGE AXIS MOVES SOUTH OF THE AREA. 925MB TEMPS BACK IN THE 0C TO -
8C RANGE BY 12Z SAT. A WEAK SHORTWAVE MOVES INTO NORTHERN MN FRI
AFTERNOON THEN SLIDES SOUTHEAST ACROSS NORTHERN WI FRI NIGHT. THIS
WAVE LOOKS TO DO LITTLE MORE THAN INCREASE MID/HIGH CLOUDS OVER THE
NORTHEAST 1/3 TO 1/2 OF THE FCST AREA FRI AFTERNOON/NIGHT. IT DOES
STRENGTHEN THE LOWER LEVEL SOUTHWEST FLOW/WARM ADVECTION FOR FRI
NIGHT. FRI NIGHT LOWS STILL TRENDING TO BE IN THE EVENING WITH
STEADY/SLOWLY RISING TEMPS AFTER MIDNIGHT. SFC TROUGH WITH THIS WAVE
TO PUSH ACROSS THE AREA WITH LITTLE MORE THAN A WIND SHIFT. THIS
WIND SHIFT TO USHER THE CAN/ARCTIC HIGH INTO THE UPPER MIDWEST LATER
SAT/SAT NIGHT. PLENTY OF TIMING DETAIL DIFFERENCES WITH ARRIVAL OF
THE COLDER AIR...AS LAST 28.21Z AND 29.03Z SREF HAVE SHOWN A 30F
TEMP SPREAD AT KLSE AT 01.00Z. FOR NOW SIDED WITH THE MODEL/ENSEMBLE
CONSENSUS FOR HIGHS/LOWS FRI THRU SAT. STRONGER...MORE DIGGING
SHORTWAVE OF THE NAM/CAN-GEM SPREADS MORE 850-500MB WARM ADVECTION/
ISENTROPIC LIFT/MOISTURE...AND SNOW CHANCES...NORTHWARD OVER THE LOW
LEVEL COLD DOME INTO THE FCST AREA SAT NIGHT. FLATTER GFS/ECMWF
SOLUTIONS KEEP THE THERMODYNAMIC FORCING/LIFT MORE ACROSS THE MID MS
VALLEY. WITH THE BIG ENSEMBLE SPREAD AND LOWER CONFIDENCE BY SAT
NIGHT...STAYED WITH THE MODEL/ENSEMBLE CONSENSUS OF 20-40 PERCENT
SNOW CHANCES /HIGHEST SOUTH/ THIS PERIOD. STAYED NEAR THE MODEL/
ENSEMBLE CONSENSUS OF HIGHS/LOWS FOR FRI THRU SAT NIGHT AS WELL.

FOR SUNDAY THRU WEDNESDAY...DAYS 4 TO 7...

MAIN FCST CONCERNS THIS PERIOD...SNOW CHANCES SUNDAY AND AGAIN MON
NIGHT/TUESDAY...COLDER TEMPERATURES THRU THE PERIOD.

MEDIUM RANGE MODEL RUNS OF 29.00Z OFFER GENERAL AGREEMENT FOR SOME
FORM OF MID LEVEL TROUGH TO BE APPROACHING/MOVING ACROSS THE
MID/UPPER MS VALLEY SUN/SUN NIGHT. BETTER CONSENSUS FOR COLDER
NORTHWEST FLOW OVER THE REGION MON WITH HGTS TO THEN RISE AHEAD OF A
STRONGER NORTHERN STREAM WAVE TO DROP INTO/ACROSS THE NORTHERN
PLAINS/UPPER MIDWEST MON NIGHT/TUE. REASONABLE AGREEMENT FOR COLD
CYCLONIC FLOW/TROUGHING OVER THE REGION FOR THE MIDDLE OF NEXT WEEK.
FCST CONFIDENCE REMAINS BELOW AVERAGE DUE TO THE DIFFERENCES COMING
OUT OF SAT NIGHT. CONFIDENCE FOR SUN NIGHT THRU WED IS AVERAGE FOR A
DAY 5 THRU 7 PERIOD.

NAM/CAN-GEM FORCING/LIFT SIGNAL/SNOW CHANCES FROM SAT NIGHT WOULD
CONTINUE TO TRANSLATE ACROSS THE FCST AREA SUN AHEAD OF THE MID
LEVEL TROUGH AXIS. THIS WHILE GFS/ECMWF WOULD PRODUCE LITTLE MORE
THAN FLURRIES. AGAIN STAYED WITH THE MODEL/ENSEMBLE CONSENSUS FOR
SUNDAY. BETTER CONSENSUS FOR COLDER/DRIER HIGH PRESSURE TO MOVE
ACROSS THE UPPER MIDWEST MON. LOW LEVEL THERMODYNAMIC FORCING WOULD
INCREASE ACROSS THE AREA LATER MON/MON NIGHT AND INTO TUE AS THE SFC-
700MB LOW/TROUGH WITH THE NEXT NORTHWEST FLOW SHORTWAVE MOVES TOWARD
AND ACROSS MN/IA/WI. GFS/ECMWF/CAN-GEM ALL LOOK TO PRODUCE SOME -SN
WITH THIS ROUND OF LIFT...QUESTIONS ARE WHERE AND HOW MUCH WHICH AT
THE DAY 5 TO 6 TIMEFRAME IS NOT UNEXPECTED. SMALL CONSENSUS -SN
CHANCES MON NIGHT/TUE REASONABLE FOR NOW. ANOTHER SURGE OF CAN/
ARCTIC AIR/HIGH PRESSURE THEN POISED TO DROP SOUTH INTO THE REGION
FOR TUE NIGHT/WED. WITH AVERAGE CONFIDENCE AT BEST...AT THIS TIME
SIDED WITH THE MODEL/ENSEMBLE CONSENSUS HIGHS/LOWS FOR SUN-WED.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1132 AM CST THU JAN 29 2015

MAIN AVIATION CONCERNS THROUGH TAF PERIOD ARE MVFR CONDITIONS AND
STRONG NORTHWEST WINDS THIS AFTERNOON INTO TONIGHT. LATEST SURFACE
ANALYSIS SHOWS TIGHT PRESSURE GRADIENT ACROSS THE UPPER MIDWEST WITH
LATEST METARS INDICATING SUSTAINED WIND SPEEDS AROUND 20 KNOTS AND
GUSTS UP TO 30 KNOTS. THE PRESSURE GRADIENT REMAINS TIGHT ACROSS
MUCH OF THE REGION THROUGH THIS EVENING...AS A WEAK COLD FRONT
PUSHES INTO SOUTHERN IOWA THIS AFTERNOON. THIS WILL ALLOW WINDS TO
REMAIN AT 15 TO 20 KNOTS SUSTAINED AND GUST UP TO AROUND 25 KNOTS
THROUGH 05-07Z FRIDAY. HIGH PRESSURE BUILDS INTO WESTERN WISCONSIN
AND EASTERN IOWA AFTER 06Z FRIDAY AND DIMINISHES THE WINDS TO 5 TO
10 KNOTS BY 12Z FRIDAY AT BOTH RST AND LSE TAF SITES. LATEST METARS
ACROSS THE AREA ARE REPORTING MVFR CONDITIONS. MVFR CONDITIONS WILL
CONTINUE AT BOTH TAF SITES THROUGH TONIGHT. THEN CONDITIONS WILL
IMPROVE TO VFR FRIDAY MORNING WITH HIGH PRESSURE BUILDING IN AND
STRATUS DECK BECOMES SCATTERED AT TAF SITES.

&&

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

$$

UPDATE...HALBACH
SHORT TERM...RRS
LONG TERM....RRS
AVIATION...DTJ


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