Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 222310
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
610 PM CDT WED OCT 22 2014

.SHORT TERM...(TONIGHT THROUGH THURSDAY NIGHT)
ISSUED AT 250 PM CDT WED OCT 22 2014

MAIN FORECAST CONCERNS THIS PERIOD...SHRA CHANCES TONIGHT/THU...
TEMPERATURES.

18Z DATA ANALYSIS HAD HIGH PRESSURE OVER MI WITH RIDGING TO AR. LOW
PRESSURE WAS LOCATED OVER SOUTHERN MAN WITH A TROUGH/FRONT SOUTH TO
THE KS/CO BORDER. THE HIGH WAS HOLDING CLEAR SKIES ACROSS MUCH OF
WI/IL/EASTERN IA WHILE CLOUDS WERE INCREASING ACROSS MN/WESTERN IA
AHEAD OF A RATHER STRONG TROUGH/SHORTWAVE ENERGY SEEN IN WV IMAGERY
MOVING EAST ACROSS THE DAKOTAS/NEB. SHRA/TSRA EARLY THIS AFTERNOON
GENERALLY ALONG/BEHIND THE SFC-850MB TROUGH/FRONT IN THE EASTERN
DAKOTAS TO CENTRAL NEB.

22.12Z MODELS INITIALIZED WELL...EXCEPT GFS WITH ITS 3-5F HIGH BIAS
ON SFC DEW POINTS ACROSS THE UPPER MIDWEST/NORTHERN PLAINS. SOLUTIONS
TRENDING TOWARD A TIGHTER CONSENSUS AS THE PLAINS TROUGH AXIS MOVES
INTO WESTERN IA/MN 12Z THU...INTO EASTERN WI BY 00Z FRI THEN INTO MI
AND OH VALLEY BY 12Z FRI. LATEST TIGHTER CONSENSUS FAVORS FASTER OF
THE EARLIER RUNS WITH THE APPROACH/PASSAGE OF THE TROUGH TONIGHT
THRU THU NIGHT. SHORT-TERM FCST CONFIDENCE IS GOOD THIS CYCLE.

FOR THE SHORT TERM...BULK OF THE 500-300MB PV ADVECTION WITH THE
APPROACHING SHORTWAVE ENERGY/TROUGH MOVES ACROSS THE WEST HALF OF
THE FCST AREA LATER TONIGHT AND ACROSS THE EAST HALF THU MORNING.
THIS WITH MDT LOWER LEVEL THERMO-DYNAMIC FORCING/ISENTROPIC LIFT
WITH/AHEAD OF THE SFC-700MB TROUGH...PW VALUES OF 1 TO 1.25
INCHES AND 85-100 PERCENT SATURATION IN THE 850-500MB LAYER.
PRESENT TIMING HAS THE STRONGEST/DEEPEST LIFT/MOISTURE MOVING
ACROSS KRST AROUND 09Z... KLSE AROUND 12Z AND KVOK AROUND 15Z.
USED THIS TO TIME 85-95 PERCENT SHRA CHANCES EAST ACROSS THE FCST
AREA...MAINLY BETWEEN 06Z AND 18Z. NAM/GFS SHOWING WEAK MUCAPE OF
UP TO 150 J/KG WHEN LIFTING 850MB PARCELS THIS EVENING INTO THE
OVERNIGHT HOURS. ADDED AN ISOLATED -TSRA MENTION BETWEEN ROUGHLY
07Z-15Z WHEN THE STRONGEST/DEEPEST OF THE LIFT PASSES. MOST
PRECIP AMOUNTS TONIGHT/EARLY THU CONTINUE TO TREND ON THE LIGHT
SIDE WITH WEAKENING 925-700MB MOISTURE TRANSPORT/THETA-E
CONVERGENCE AS THE TROUGH PASSES.

WITH THE TREND TOWARD FASTER...SUBSIDENCE/DRYING AT AND ABOVE 925MB
BEHIND THE SFC-500MB TROUGH SPREADS INTO THE FCST AREA THU
AFTERNOON. LOCATIONS ALONG/WEST OF THE MS RIVER ONCE AGAIN HAVE A
CHANCE OF SEEING THE PARTIAL SOLAR ECLIPSE LATE THU AFTERNOON. WITH
ANOTHER WEAK SFC-500MB TROUGH/SHORTWAVE INTO MN/IA BY 12Z FRI...ANY
COOLING BEHIND THE THU MORNING TROUGH IS WEAK/SHORT LIVED. 925MB
TEMPS IN THE +12C TO +15C RANGE AT 12Z FRI...UNDER SOUTHWEST FLOW/
WARM ADVECTION ALOFT. USED A BLEND OF THE GUIDANCE LOWS/HIGHS FOR
TONIGHT/THU THEN TRENDED TOWARD WARMER OF GUIDANCE LOWS FOR THU
NIGHT.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 250 PM CDT WED OCT 22 2014

FORECAST CONCERNS FOR FRI THRU SAT NIGHT...TEMPERATURES THRU THE
PERIOD.

22.12Z MODELS CONVERGING ON A TIGHTER CONSENSUS FRI/FRI NIGHT...AS
ONE WEAK SHORTWAVE SLIDES ACROSS THE UPPER MIDWEST FRI AND A SECOND
STRONGER WAVE DROPS TOWARD/ACROSS LK SUPERIOR FRI NIGHT. TREND IS
STRONGER WITH THE FRI NIGHT WAVE. GOOD CONSENSUS FOR THIS WAVE TO
CONTINUE QUICKLY EAST SAT AND FOR RIDGING/RISING HGTS TO BUILD
ACROSS THE NORTHERN PLAINS INTO THE REGION SAT NIGHT. WITH THE GOOD
MODEL CONSENSUS THRU SAT NIGHT...FCST CONFIDENCE IN THIS PERIOD IS
GOOD THIS CYCLE.

WEAK SHORTWAVE MOVING ACROSS THE REGION FRI HAS A MODEST SFC-700MB
TROUGH WITH IT. AHEAD OF THIS ROUGH IS A ROUND OF LOWER LEVEL WARM
ADVECTION AND MOISTURE INCREASE. FORCING/LIFT ALOFT IS WEAK AND THE
SYSTEM IS MOVING RATHER QUICKLY ACROSS THE AREA. THE MOISTURE
INCREASE IS PROGGED MAINLY IN THE 925-850MB LAYER. WILL LEAVE ANY
MENTION OF -SHRA OUT OF THE GRIDS ON FRI BUT DID INCREASE THE CLOUD
COVER MUCH OF FRI INTO FRI EVENING AS THE MOISTURE AXIS PASSES.
925MB TEMPS IN THE +13C TO +17C RANGE FRI AFTERNOON. FULLY REALIZED
THESE 925MB TEMPS WOULD ALLOW FOR HIGHS IN THE UPPER 60S TO MID 70S
ON FRI. GIVEN THE LOWER STRATO-CU CLOUD POTENTIAL...TRENDED HIGHS
MORE IN THE LOW-MID 60S FOR NOW. WAVE DROPPING ACROSS LK SUPERIOR
FRI NIGHT SENDS A ROUND OF SUBSIDENCE/ DRYING AND STRONGER LOW LEVEL
COLD ADVECTION ACROSS MN/IA/WI FRI NIGHT/SAT. WARMEST 925MB AIRMASS
MOVES ACROSS THE AREA FRI EVENING AHEAD OF THE COLD FRONT. EVEN WITH
THE FRONTAL PASSAGE...LOWS FRI NIGHT TO BE ON THE MILD SIDE WITH
SOME WINDS FOR BOUNDARY LAYER MIXING AHEAD OF/BEHIND THE FRONT. SAT/
SAT NIGHT CONTINUE DRY/QUIET AS CAN HIGH PRESSURE BUILDS IN. 925MB
TEMPS STILL IN THE +8C TO +12C RANGE SAT AFTERNOON...FOR ABOVE
NORMAL HIGHS. SFC RIDGE AXIS IS OVER THE AREA SAT NIGHT...WITH CLEAR
SKIES/LIGHT WINDS FOR STRONG RADIATIONAL COOLING. MODEL/ENSEMBLE
CONSENSUS OF THE HIGHS/LOWS FOR FRI THRU SAT NIGHT LOOK GOOD...
THOUGH DID RAISE FRI NIGHT LOWS DEGREE OR 2 ABOVE THESE VALUES.

FOR SUNDAY THROUGH WEDNESDAY.../DAYS 4 TO 7/...

FORECAST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES LATE SUN INTO
TUE... TEMPERATURES THRU THE PERIOD.

22.00Z AND 22.12Z MEDIUM RANGE MODELS IN GOOD AGREEMENT SUNDAY FOR
RIDGING ALOFT TO MOVE ACROSS THE REGION...AHEAD OF STRONGER/LONGWAVE
TROUGHING MOVING INTO THE ROCKIES. IMPROVING CONSENSUS AS THE
ROCKIES TROUGH/ENERGY MOVES INTO THE CENTRAL/SOUTHERN PLAINS MON.
TREND SUN/MON LEANS TOWARD THE SLOWER THE EARLIER RUNS WITH THE
ROCKIES/PLAINS TROUGH. MODELS HAVE THE PATTERN REMAINING PROGRESSIVE
TUE...BUT PLENTY OF DETAIL DIFFERENCES AS THE TROUGH MOVES INTO THE
MID/UPPER MS VALLEY. STILL A BETTER/SLOW CONSENSUS THAN THE PREVIOUS
RUNS ON TUE. CONSIDERABLE MODEL DIFFERENCES WITH THE FLOW ACROSS
NOAM BY WED...WITH RUN-TO-RUN CONSISTENCY ON THE LOW SIDE BY DAY 7.
FCST CONFIDENCE ABOVE AVERAGE SUN/MON THEN BELOW AVERAGE BY WED.

HIGH PRESSURE HOLDS OVER MUCH OF THE REGION SUN...SLIDING EAST OF
THE REGION SUN NIGHT. INCREASING WARM ADVECTION AND 850-700MB
MOISTURE TRANSPORT SPREADING ACROSS WESTERN/CENTRAL MN/IA SUN
AFTERNOON THEN INCREASE ACROSS MN/IA/WI SUN NIGHT. INITIALLY A
RATHER DEEP DRY AIRMASS OVER THE AREA SUN...WITH MAINLY INCREASING
MID CLOUDS. PW VALUES INCREASE TO AN INCH OR MORE SUN NIGHT. THIS
WITH SOME MUCAPE OF 200 TO 500 J/KG IN THE INFLOW AIRMASS SUN
NIGHT...THEN MUCAPE OF 200 TO 500+ J/KG OVER THE AREA MON/MON NIGHT.
MOISTURE/LIFT CONTINUE TO SPREAD ACROSS THE AREA MON INTO TUE...BUT
DIFFERENCE WITH TIMING/TRACK OF LOWER LEVEL FEATURES AND STRONGER
FORCING BY MON...THEN WITH TIMING OF THE MID LEVEL TROUGH AXIS
PASSAGE TUE. DID ADD AN ISOLATED TSRA MENTION FOR SUN NIGHT THRU MON
NIGHT GIVEN THE CAPE AND WHAT SHOULD BE AT LEAST BROAD FORCING FOR
ASCENT OVER THE REGION. LINGERING -SHRA CHANCE TUE WITH THE MID
LEVEL TROUGH STILL IN THE REGION. TUE NIGHT/WED SHOULD BE A DRY/
COOLER PERIOD IN THE WAKE OF THE PASSING TROUGH AND RISING HGTS OVER
THE UPPER MIDWEST...HOWEVER MODELS AT ODDS WITH THE TIMING OF ONE
TROUGH EXITING AND THE NEXT ONE APPROACHING. WILL LEAVE THE MODEL/
ENSEMBLE CONSENSUS AS IS FOR TUE/WED.

SUN/MON CONTINUE TO TREND TOWARD A SEASONABLY MILD PERIOD WITH 925MB
TEMPS IN THE +7C TO +11C RANGE AT 00Z MON AND +8C TO +15C RANGE AT
18Z MON...1 TO 1.5 STANDARD DEVIATIONS ABOVE NORMAL. CLOUDS/SHRA
LIKELY TO IMPACT HIGHS MON BUT BOTH SUN/MON SHOULD SEE HIGHS IN THE
UPPER 50S TO MID 60S. LOW LEVEL COLD ADVECTION SPREADS ACROSS FOR
MON NIGHT/TUE... BUT TEMPS FOR TUE/WED LOOK TO ONLY TREND BACK
TOWARD LATE OCT NORMALS. MODEL/ENSEMBLE CONSENSUS OF HIGHS/LOWS FOR
SUN THRU WED HAS THIS WELL TRENDED FOR NOW.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 610 PM CDT WED OCT 22 2014

COLD FRONT ACROSS THE DAKOTAS AND NEBRASKA WAS MOVING EAST LATE
THIS AFTERNOON WITH A LINE OF SHOWERS AHEAD OF IT ACROSS WESTERN
MINNESOTA INTO EASTERN NEBRASKA. MOST CEILINGS WITH THE RAIN ARE
EITHER VFR OR MVFR. LOOKING AT THE 22.18Z NAM AND 22.12Z HI-RES
ARW...THERE IS GOOD AGREEMENT ON BRINGING THE SHOWERS INTO THE
AREA LATE TONIGHT AND WITH THEM REACHING KRST AROUND 09Z AND KLSE
NEAR 11Z. THE NAM CONTINUES TO BE VERY PESSIMISTIC WITH THE
CEILINGS WHEN THE SHOWERS COME IN AND WANTS TO TAKE BOTH SITES
DOWN TO IFR. CONFIDENCE IN THIS IS NOT HIGH GIVEN THE LACK OF IFR
CONDITIONS CURRENTLY...BUT WILL CONTINUE TO SHOW THIS HAPPENING AT
KRST WITH MVFR CEILINGS AT KLSE. THESE SHOWERS SHOULD MOVE PAST
BOTH SITES BY 18Z WITH A RETURN TO VFR CONDITIONS FOR THE
AFTERNOON.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...04



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