Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 281145
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
545 AM CST WED JAN 28 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 332 AM CST WED JAN 28 2015

MAIN CONCERNS THIS PERIOD...DZ/FZDZ CHANCES TONIGHT...CLOUDS AND
TEMPERATURES BOTH TODAY AND TONIGHT.

06Z DATA ANALYSIS HAD HIGH PRESSURE OVER THE OH VALLEY AND DEEPENING
LOW PRESSURE OVER THE CENTRAL/NORTHERN PLAINS. SFC OBS AND FOG-
PRODUCT IMAGERY SHOW AN IFR/MVFR STRATUS DECK ACROSS MUCH OF WI/MN
AND EASTERN IA. LATEST AVAILABLE PILOT REPORTS INDICATED THIS CLOUD
DECK ABOUT 1000 FT THICK. THIS MOISTURE/CLOUDS TRAPPED UNDER A
STRONG AND STRENGTHENING INVERSION NEAR 900MB. THE CLOUD BLANKET AND
INCREASING SOUTHEAST GRADIENT WINDS HOLDING TEMPS STEADY IN THE
MID/UPPER 20S ACROSS MUCH OF THE REGION EARLY THIS MORNING.

INITIALIZATIONS OF 28.00Z MODELS GENERALLY LOOK QUITE GOOD.
SHORTWAVE RIDGING QUICKLY MOVES ACROSS THE UPPER MIDWEST TODAY AND
NORTHERN/SOUTHERN STREAM ENERGY CARVES OUT TROUGHING IN THE CENTRAL/
NORTHERN PLAINS. THE 2 PIECES OF ENERGY NEARLY PHASE TONIGHT AS THEY
AND DEEPENING MID LEVEL TROUGHING MOVES ACROSS THE MID/UPPER MS
VALLEY. THE TIGHTER CONSENSUS FOR TODAY/TONIGHT FAVORS A COMPROMISE
OF THE EARLIER 26.00Z/27.00Z RUNS. SHORT TERM FCST CONFIDENCE
REMAINS GOOD BUT THE FCST HINGES ON LOWER LEVEL MOISTURE WHICH THE
MODELS TYPICALLY STRUGGLE WITH.

IN THE SHORT TERM...THE STRATUS DECK WILL ONCE AGAIN BE PROBLEMATIC
TODAY FOR HIGH TEMPS. SOUTHEAST TO SOUTHWEST SFC-850MB GRADIENT FLOW
INCREASE ACROSS THE AREA TODAY AS THE PLAINS LOW MOVE TO NEAR
KFSD/KOMA THIS AFTERNOON. INVERSION OVER THE AREA REMAINS STRONG
UNDER THE INCREASING 925-850MB WARM ADVECTION. BY THIS AFTERNOON...
DEEPER/STRONGER LIFT ARRIVES...WITH AN INCREASE OF LOWER LEVEL
MOISTURE. ALL THIS POINTS TO THE LOWER STRATUS HANGING TOUGH OVER
THE AREA TODAY WITH LITTLE IF ANY SUNSHINE. CIRRUS SHIELD AHEAD OF
THE MID/UPPER LEVEL TROUGH MOVES OVER THE REGION FOR THE AFTERNOON
AS WELL. SOUTH-SOUTHEAST WINDS OVER AND LOW LEVEL WARM ADVECTION
OVER THE AREA TODAY...SO EXPECT TEMPS TO WARM A LITTLE...BUT ONLY TO
THE MID/UPPER 30S ACROSS MOST OF THE FCST AREA.

SFC THRU MID LEVEL TROUGH AXIS MOVES ACROSS THE AREA TONIGHT...WITH
MOISTURE/SATURATION IN ROUGHLY THE SFC-800MB PORTION OF THE COLUMN.
LOWER LEVEL LIFT/CONVERGENCE WITH THE SFC-850MB TROUGH AXIS...WITH
DEEP LAYERED LIFT/DIVERGENCE ALOFT AHEAD OF THE SHORTWAVES AND MID
LEVEL TROUGH AXIS. MODEL SOUNDINGS CONTINUE TO SHOW COLDEST TEMPS IN
THE LOWER SATURATED PORTION OF THE COLUMN AROUND -5C...INDICATING NO
ICE IN THE CLOUD DEPTH. PRECIP CHANCES TONIGHT REMAIN MAINLY -DZ/
-FZDZ. CONFINED THE HIGHEST CHANCES BETWEEN 03Z-09Z WHEN THE SFC-
850MB TROUGH AXIS AND ITS CONVERGENCE SLIDES ACROSS THE FCST AREA.
MORE CONSISTENT SIGNAL AMONG THE MODELS FOR LIGHT PRECIP PRODUCTION
REMAINS OVER THE NORTHEAST HALF OF THE FCST AREA...WITH HIGHER
PRECIP CHANCES THERE TONIGHT. GREATER THREAT OF MINOR ICING IS OVER
THE NORTHEAST HALF OF THE FCST AREA WERE TEMPS TODAY/TONIGHT WILL BE
MORE IN THE LOWER 30S AND ROAD TEMPS WILL REMAIN CLOSER TO OR BELOW
FREEZING. MAY YET NEED A FREEZING RAIN/DRIZZLE ADVISORY FOR THE
NORTHEAST 1/3 TO 1/2 OF THE FCST AREA. WILL LET DAY CREW HAVE
ANOTHER CYCLE OF MODELS TO LOOK AT AND SEE WHAT SFC TEMPS DO TODAY
TO MAKE THE CALL ON THAT. WITH THICKER LOW CLOUDS TONIGHT...THE
DZ/FZDZ CHANCES AND SOME PATCHY FOG...NEARLY STEADY TEMPS EXPECTED
DURING THE EVENING... THEN FALLING LATE AFTER THE TROUGH AXIS
PASSES/LOW LEVEL COLD ADVECTION/INCREASING NORTHWEST WINDS SPREAD
ACROSS THE AREA. BY THIS TIME BULK OF THE DEEP LAYERED LIFT HAS
SHIFTED EAST OF THE AREA WITH THE TROUGH AXIS AND DZ/FZDZ CHANCES
WILL BE DECREASING. TRENDED TOWARD COOLER OF GUIDANCE HIGHS TODAY
AND WARMER OF GUIDANCE LOWS TONIGHT.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 332 AM CST WED JAN 28 2015

MAIN FCST CONCERNS FOR THU THRU FRI NIGHT...LINGERING DZ/FZDZ
CHANCES THU MORNING...CLOUD/TEMPERATURE TRENDS THRU THE PERIOD.

28.00Z MODELS IN GOOD AGREEMENT FOR A SECOND NORTHERN STREAM
SHORTWAVE TO DROP QUICKLY ACROSS THE WESTERN GREAT LAKES THU
AFTERNOON/EVENING. GOOD BETWEEN MODEL AND RUN-TO-RUN CONSISTENCY FOR
HGTS TO THEN RISE FRI/FRI NIGHT...AHEAD OF THE NEXT NORTHERN/
SOUTHERN STREAM ENERGY HEADED TOWARD THE CENTRAL CONUS. FCST
CONFIDENCE IN THE THU THRU FRI NIGHT PERIOD IS GOOD THIS CYCLE.

THIS PERIOD SHAPING UP TO BE A COOLER/DRY/QUIET PERIOD BEFORE THE
NEXT STRONGER SYSTEM TAKES AIM AT THE UPPER MIDWEST FOR THE WEEKEND.
LOW LEVEL COLD ADVECTION AND DEEPER LAYERED SUBSIDENCE CONTINUE TO
SPREAD ACROSS THE AREA THU MORNING. MAINLY LIMITED ANY LINGERING DZ/
FZDZ CHANCES TO THE 12-15Z PERIOD OVER THE EAST HALF OF THE FCST
AREA. SHORTWAVE DROPPING ACROSS THE WESTERN GREAT LAKES THU
AFTERNOON/EVENING MAINLY PROVIDES THE AREA WITH A REINFORCING SHOT
OF LOW LEVEL COLD ADVECTION. APPEARS HIGHS THU WILL BE IN THE
MORNING WITH STEADY/SLOWING FALLING TEMPS THRU THE DAY UNDER THE
STRONGER COLD ADVECTION. STRONGER SUBSIDENCE/COLD ADVECTION AND CAN
HIGH PRESSURE BUILDING IN SHOULD CLEAR OUT THE LOWER CLOUDS THU
AFTERNOON/NIGHT. SFC RIDGE AXIS DRIFTS ACROSS THE AREA LATE THU
NIGHT/FRI MORNING...UNDER WHAT SHOULD BE MOSTLY CLEAR SKIES. THU
NIGHT LOWS LOOKING TO BE CLOSER TO NORMAL THAN THEY/VE BEEN DURING
THE PAST 2 WEEKS. LOW LEVEL WARM ADVECTION RETURNS FRI AS THE SFC-
850MB RIDGE AXIS MOVES SOUTH OF THE AREA. STRONGER OF THIS SPREADS
ACROSS THE AREA FRI NIGHT...WITH LOWS LOOKING TO BE FRI EVENING THEN
SLOWLY RISING TEMPS AFTER MIDNIGHT AS CLOUDS START TO INCREASE AND
SOUTHWEST GRADIENT WINDS FOR BOUNDARY LAYER MIXING INCREASE A BIT.
USED THE MODEL/ENSEMBLE BLEND OF GUIDANCE HIGHS/LOWS FOR THU THRU
FRI NIGHT.

FOR SATURDAY THRU TUESDAY.../DAYS 4 TO 7/...

MAIN FCST CONCERNS THIS PERIOD...SNOW CHANCES LATE SAT/SAT
NIGHT/SUN...COLD TEMPERATURES MOM-TUE.

28.00Z MEDIUM RANGE MODELS SHOW IMPROVING AGREEMENT SAT/SUN FOR
NORTHERN/SOUTHERN STREAM ENERGY TO AT LEAST PARTIALLY PHASES OVER
THE CENTRAL CONUS. TREND IS A BIT STRONGER/MORE PHASED WITH THE
STREAMS/SHORTWAVES OVER THE CENTRAL CONUS BY SUNDAY. GOOD BETWEEN
MODEL AND RUN-TO-RUN CONSISTENCY FOR THE TROUGH AXIS TO THEN MOVE
ACROSS THE MID/UPPER MS VALLEY SUN NIGHT...LEAVING THE DOOR OPEN FOR
NORTHWEST FLOW AND A STRONGER SHOT OF CANADIAN/ARCTIC AIR TO DROP
INTO THE UPPER MIDWEST FOR EARLY NEXT WEEK. GIVEN SOME LOWER LEVEL
DETAIL DIFFERENCES...FCST CONFIDENCE FOR SAT THRU TUE REMAINS
AVERAGE THIS CYCLE.

PHASING SHORTWAVES/DEEPENING TROUGH OVER THE PLAINS SAT/SUN SENDS
INCREASING MOISTURE NORTHWARD TOWARD THE UPPER MIDWEST FOR THE
WEEKEND. PW VALUES OF AROUND 1/2 INCH INDICATED IN THE INFLOW
AIRMASS AHEAD OF THE DEVELOPING TROUGH/SFC LOW. THIS MOISTURE BEING
PUSHED INTO A COLUMN WITH SFC-600MB TEMPS FAVORING A DEEP DENDRITIC
GROWTH ZONE AND FAVORABLE LIFT/DIVERGENCE IN THE MID/UPPER LEVELS
AHEAD OF THE PLAINS TROUGH. MODEL SOUNDINGS/X-SECTIONS SHOWING
COLUMN SATURATED FROM THE SFC TO 300MB OVER MUCH OF THE FCST AREA
FOR BY LATER SAT NIGHT AND FOR SUN. DETAIL DIFFERENCES INCLUDE HOW
MUCH AND QUICKLY PHASING ACTUALLY OCCURS AND HOW FAR NORTHWARD THE
GREATER THE 925-700MB MOISTURE AND THERMODYNAMIC FORCING ENDS UP
OCCURRING. POTENTIAL ALSO EXISTS FOR A LONGER DURATION PERIOD OF
SNOW FOR PARTS OR ALL OF THE FCST AREA FROM SAT NIGHT INTO SUN
NIGHT. SNOW CHANCES IN THE 30-50 PERCENT RANGE FOR SAT NIGHT/SUNDAY
LOOK GOOD FOR NOW...UNTIL THE DETAILS GET SORTED OUT. OVER WHAT
WOULD BE FRESH SNOW COVER FOR MUCH/ALL OF THE AREA...NORTHWEST
FLOW BEHIND THE TROUGH SENDS ANOTHER CAN/ARCTIC HIGH INTO THE
UPPER MIDWEST FOR SUN NIGHT INTO TUE. 925MB TEMPS PROGGED IN THE
-15C TO -20C RANGE MON INTO MON NIGHT. TEMPS TO START NEXT WEEK
CONTINUE TO TREND BELOW TO MUCH BELOW NORMAL. MODEL/ENSEMBLE
CONSENSUS OF HIGHS/LOWS FOR SAT THRU TUE LOOKS GOOD AT THIS TIME.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 545 AM CST WED JAN 28 2015

IFR TO MVFR CONDITIONS ARE EXPECTED TO PERSIST ACROSS THE REGION
THROUGH TOMORROW MORNING AS A LOW PRESSURE SYSTEM MOVES IN FROM
THE WEST. CONDITIONS ARE IFR TO LIFR AT RST AND ALMOST IFR AT LSE
AT THE MOMENT WITH SOME IMPROVEMENT EXPECTED LATER THIS MORNING.
THERE IS A CHANCE THAT THESE CLOUDS WILL CLEAR OUT LATER TODAY AS
THE SOUTHERN EDGE IS ERODING NORTHWARD ACROSS SOUTHEAST IOWA. PURE
EXTRAPOLATION OF THIS EROSION WOULD BRING THE BACK EDGE OF THE LOW
CLOUDS INTO RST/LSE AROUND 21Z. DRIZZLE AND FREEZING DRIZZLE IS
LIKELY TONIGHT AT BOTH SITES WITH THE ICING POTENTIAL DEPENDENT ON
WHAT TEMPERATURES DO THIS AFTERNOON LEADING UP TO TONIGHT. THE
MAIN TIME FRAME FOR THE MORE WIDESPREAD DRIZZLE IS BETWEEN 9PM AND
3AM. EXPECT THAT CONDITIONS WILL DROP AS THIS DRIZZLE BEGINS WITH
IFR LIKELY. WINDS WILL SHIFT AROUND FROM THE SOUTHEAST TO THE
NORTHWEST AS THE LOW PASSES THROUGH WITH A COLD FRONT.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...HALBACH



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