Area Forecast Discussion
Issued by NWS La Crosse, WI

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KARX 020438
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1138 PM CDT MON SEP 1 2014

.SHORT TERM...(TONIGHT THROUGH TUESDAY NIGHT)
ISSUED AT 305 PM CDT MON SEP 1 2014

MAIN FORECAST CONCERNS THIS PERIOD...POTENTIAL SMALL -SHRA CHANCES
LATE TONIGHT AND TUE...TEMPERATURES.

DATA ANALYSIS AT 18Z HAD LOW PRESSURE OVER NORTH-CENTRAL. TRAILING
COLD FRONT EXTENDED ACROSS THE REGION NEAR A KRHI-KLSE-KDSM LINE...
MAKING STEADY PROGRESS SOUTHEAST AT 25-30KTS. THE TRAILING MN/IA
SHORTWAVE AND THE FRONT PRODUCING A BKN LINE OF SHRA/ISOLATED TSRA
ACROSS WI INTO NORTHEAST IA EARLY THIS AFTERNOON. HEAVIER OF THESE
PRODUCING A QUICK 1/4 TO 1/2 INCH OF RAIN AS THEY PASS. BEHIND THE
FRONT/SHORTWAVE/LINE OF SHRA VIS IMAGERY SHOWING GENERALLY SCT CU/
STRATO-CU ACROSS MUCH OF MN/NORTHWEST IA/WI WITH DEW POINTS FALLING
INTO THE MID 50S TO LOWER 60S.

01.12Z MODEL INITIALIZATIONS NOT AS TIGHT AS THE PAST COUPLE DAYS
BUT NO GLARING ERRORS NOTED. INITIALIZATIONS SHOWED EARLY MODELS
WERE ALL ON THE WEAK SIDE WITH THE SECONDARY SHORTWAVE OVER SOUTHERN
MN/NORTHERN IA THIS MORNING. THIS WITH LITTLE IMPACT BEYOND THIS
AFTERNOON THOUGH. MODELS OFFER A TIGHT CONSENSUS AS A SHORTWAVE OVER
WY TRACKS EAST TONIGHT...PASSING MAINLY SOUTH OF THE FCST AREA LATE
TONIGHT/TUE MORNING. TIGHT CONSENSUS FOR TUE AFTERNOON/NIGHT AS
HGTS RISE BEHIND THIS FEATURE AND AHEAD OF THE NEXT TOUGH INTO THE
PAC NORTHWEST. TREND FAVORS FASTER OF THE EARLIER RUNS WITH THE
ENERGY INTO NORTHERN ID/WESTERN MT BY 12Z WED. WITH THE TIGHT
MODEL CONSENSUS AND A QUIETER WEATHER PERIOD...SHORT-TERM FCST
CONFIDENCE IS GOOD THIS CYCLE.

TRAILING SOUTHERN MN/NORTHERN IA SHORTWAVE WILL PASS EAST OF THE
AREA THIS AFTERNOON...TAKING THE SCT -SHRA ALONG/AHEAD OF IT WITH
IT. DISTANCE SPEED TOOL HAS THIS AREA OF -SHRA EAST/SOUTH OF THE
FCST AREA AROUND 23Z. MODEL SOUNDINGS SHOW SOME PERSISTENT 250-500
J/KG OF CAPE OVER THE AREA THIS EVENING/OVERNIGHT...ESPECIALLY WHEN
LIFTING 800-700MB PARCELS. THIS AHEAD OF THE WY SHORTWAVE DUE IN
AROUND 12Z...AND THE 300-500MB PV ADVECTION/DIVERGENCE ALOFT AHEAD
OF IT. THIS WAVE PRODUCING SCT -SHRA OVER NORTHEAST WY/WESTERN SD
THIS AFTERNOON AND SEVERAL OF THE HI-RES/WRF MODELS INDICATING IT
WILL PRODUCE A FEW -SHRA AS IT PASSES ACROSS MN/IA/WI LATE TONIGHT/
EARLY TUE MORNING. THUS HAVE ADDED ISOLATED -SHRA TO ROUGHLY THE
SOUTHWEST 2/3 OF THE FCST AREA IN THE 06Z-15Z TIME-FRAME. INCREASING
MID CLOUDS LATER TONIGHT SHOULD KEEP ANY LATE NIGHT/EARLY MORNING
RADIATIONAL FOG TO A MINIMUM. 500-1000 J/KG OF CAPE INDICATED ACROSS
THE NORTHEAST 1/2 OF THE FCST AREA TUE...WITH LITTLE IF ANY CAPPING
BY TUE AFTERNOON. THIS WITH SOME WEAK PV ADVECTION AHEAD OF A WEAK
SHORTWAVE TRACKING ACROSS CENTRAL MN/ NORTHERN WI AND WEAK 850MB
MOISTURE TRANSPORT AND 700-500MB FN CONVERGENCE. CONTINUED A 20
PERCENT -SHRA/TSRA CHANCE ACROSS MAINLY THE NORTHEAST 1/3 OF THE
FCST AREA MUCH OF TUE GIVEN THE CONSISTENCY OF THIS SIGNAL. RISING
HGTS/WANING CAPE LATE TUE AFTERNOON/NIGHT... FOR WHAT SHOULD FINALLY
BE A DRY PERIOD WITH A WEAK RIDGE OF HIGH PRESSURE OVER WI/MN.
MODEL/ENSEMBLE CONSENSUS OF LOWS/HIGHS FOR TONIGHT-TUE NIGHT LOOKS
TO HAVE TEMPERATURES WELL TRENDED.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 305 PM CDT MON SEP 1 2014

FORECAST CONCERNS FOR WED THROUGH THU NIGHT...SHRA/TSRA CHANCES WITH
THE NEXT APPROACHING/PASSING LOW/COLD FRONT...TEMPERATURES.

01.12Z MODEL CONSENSUS FAVORS FASTER OF THE EARLIER RUNS WITH THE
ID/MT SHORTWAVE EAST TO NORTHERN ND/SOUTHERN MAN BY 12Z THU. THE
FASTER TREND CONTINUES THU/THU NIGHT AS THE MAIN SHORTWAVE LIFTS TO
NORTH OF LK SUPERIOR BY 12Z FRI. TREND ALSO FAVORS A STRONGER
SECONDARY SHORTWAVE TO DROP INTO MT/WY BY 12Z FRI. WITH THE TIGHT
AND IMPROVING MODEL CONSENSUS...FCST CONFIDENCE IN THE WED THRU
THU NIGHT PERIOD IS AVERAGE TO GOOD THIS CYCLE.

THE MID LEVEL TROUGHING INTO MT ON WED DEEPENS THE LEE LOW INTO
EASTER WY/WESTERN SD. SOUTHERLY LOW LEVEL FLOW STRENGTHENS IN THE
PLAINS WITH 850-700MB MOISTURE TRANSPORT/INCREASE QUICKLY SPREADING
NORTHEAST ACROSS THE REGION ON WED. PW VALUES BACK IN THE 1.5 TO
1.75 INCH RANGE BY 00Z THU. CAPE INCREASES AS WELL. SFC-850MB WARM
FRONT AHEAD OF THE LOW LOOKS TO LIFT ACROSS THE AREA WED...TO
CENTRAL MN TO NEAR KGRB BY 00Z THU. STRONGER OF THE LOWER LEVEL
CONVERGENCE LIFT ALONG/NORTH OF THIS FRONT ON WED. LIMITED SMALL
SHRA/TSRA CHANCES WED TO THE NORTH END OF THE FCST AREA CLOSER TO
THE WARM FRONTAL ZONE AS APPEARS AIRMASS SOUTH OF THE WARM FRONT IS
LIKELY TO BECOME CAPPED. LOWER LEVEL THERMODYNAMIC FORCING OVER THE
AREA INCREASES WED NIGHT AHEAD OF THE SFC-850MB LOW/TROUGH/FRONT.
MAIN CAPE POOL AND LOWER LEVEL CONVERGENCE/LIFT APPEARS FOCUSED OVER
CENTRAL MN WED EVENING...WHERE A CONVECTIVE COMPLEX LOOKS TO FORM.
CORFIDI VECTORS WOULD THEN TAKE THIS COMPLEX EAST-SOUTHEAST ACROSS
NORTHERN INTO EASTERN WI. CARRIED HIGHEST SHRA/TSRA CHANCES LATER
WED NIGHT OVER THE NORTHEAST 1/3 OF THE FCST AREA.  850-700MB
WARMING CONTINUES THU...WITH CAPPING STRENGTHENING OVER THE FCST
AREA. LIMITED SHRA/TSRA CHANCES THU TO MAINLY THE NORTHEAST SIDE OF
THE FCST AREA AND IN THE MORNING. THIS EVEN AS THE LOW LIFTS TO
NORTH OF LK SUPERIOR FRI AND THE TRAILING COLD FRONT IS DRAGGED INTO
THE AREA. MODEL SOUNDINGS SHOWING CAP EROSION THU NIGHT AS THE 850-
500MB TROUGH AXIS/COOLING MOVE INTO THE AREA. SFC FRONT TO PUSH
ACROSS THE AREA THU NIGHT...WITH A SCT-BKN BAND OF SHRA/TSRA ALONG/
BEHIND IT. CONSENSUS RAIN CHANCES AROUND 50 PERCENT THU NIGHT
REASONABLE. USED A BLEND OF THE GUIDANCE HIGHS/LOWS FOR WED AND
WED/THU NIGHTS. WITH THE CAPPING AND 925MB TEMPS AGAIN IN THE +22 TO
+26C RANGE THU...FAVORED WARMER OF GUIDANCE HIGHS IN THE MID/UPPER
80S FOR THU.

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

MAIN CONCERNS THIS PERIOD...COOLER TEMPERATURES FRI THRU SUN...
SHRA/TSRA CHANCE MONDAY.

MEDIUM RANGE MODEL RUNS OF 01.00Z AND 01.12Z CONTINUE THE TREND OF A
STRONGER MID LEVEL TROUGH TO PASS ACROSS SOUTHERN CAN/NORTHERN GREAT
LAKES FRI. DECENT MODEL CONSENSUS LINGERS SOME BROAD TROUGHING/
NORTHWEST FLOW OVER THE UPPER MIDWEST SAT...PROGRESSING THIS EAST
WITH NEARLY ZONAL FLOW ACROSS THE NORTHERN CONUS FOR SUNDAY. THE
NEARLY ZONAL FLOW APPEARS SHORT-LIVED ONCE AGAIN WITH MODELS SHOWING
MORE ENERGY/TROUGHING TO DIG INTO THE WESTERN CONUS MON AND FALLING
HGTS OVER THE NORTH-CENTRAL CONUS. WITH REASONABLE AGREEMENT AMONG
THE LATEST MODEL RUNS...FCST CONFIDENCE IN THE DAY 4 TO 7 PERIOD IS
AVERAGE THIS CYCLE.

TREND IS A BIT FASTER WITH THE TROUGH MOVING NORTHEAST OF LK
SUPERIOR FRI...WHICH DRIVES THE SFC COLD FRONT WELL SOUTH OF THE
AREA MORE QUICKLY ON FRI. DRIER/COOLER CAN HIGH PRESSURE BUILDS IN
MORE QUICKLY BEHIND IT ON FRI WITH FRI NOW TRENDING MAINLY DRY.
THIS DRIER/COOLER HIGH THEN SLATED TO DOMINATE THE UPPER MIDWEST/S
WEATHER THRU THE WEEKEND. 925MB TEMPS FALL TO THE +12C TO +16C
RANGE FRI...REMAIN THERE SAT THEN MODERATE A BIT TO +14C TO +17C
SUN. FRI- SAT-SUN LOOKING TO BE 3 COOLER...MORE FALL-ISH DAYS
WITH HIGHS IN THE UPPER 60S-MID 70S AND LOWS IN THE UPPER 40S-MID
50S. LEE TROUGHING DEVELOPS IN THE PLAINS MONDAY IN RESPONSE TO
THE WESTERN CONUS TROUGHING AND A LEAD PIECE OF ENERGY EJECTING
INTO THE NORTHERN PLAINS. THE CAN HIGH MOVES EAST MON WITH
SOUTHERLY FLOW... WARM ADVECTION...MOISTURE TRANSPORT RETURNING
NORTHWARD THRU THE PLAINS AHEAD OF THE LOW/LEE TROUGH. GFS MORE
PROGRESSIVE WITH THE LOW/MOISTURE RETURN AND WOULD SPREAD SHRA/
TSRA CHANCES INTO THE FCST AREA LATE SUN NIGHT/MON. SMALL SHRA/
TSRA CHANCE MON PER THE MODEL/ENSEMBLE CONSENSUS OKAY FOR NOW.
MODEL/ENSEMBLE HIGHS/LOWS APPEAR TO HAVE FRI-MON HIGHS/LOWS WELL
TRENDED.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1138 PM CDT MON SEP 1 2014

SMALL CONVECTIVE CLUSTER ACROSS NORTHEAST NEBRASKA AS OF 02.0430Z
WILL MOVE SLOWLY ACROSS IA OVERNIGHT...BUT LATEST HIGH RESOLUTION
MODEL GUIDANCE SUGGESTS IT WILL DIVE SOUTH INTO HIGHER INSTABILITY
BEFORE WEAKENING AROUND 02.15Z ACROSS EAST-CENTRAL IOWA. STILL A
SLIGHT CHANCE FOR SHOWERS AND PERHAPS A RUMBLE OF THUNDER OVERNIGHT
INTO TUESDAY AS UPPER LEVEL DISTURBANCE ACROSS NEBRASKA MOVES
ACROSS THE UPPER MISSISSIPPI RIVER VALLEY. STILL NOT ENOUGH
CONFIDENCE TO MENTION IN 02.06Z TAF ISSUANCE. MID-HIGH CLOUDS
AHEAD OF THIS WAVE COMBINED WITH 10 TO 20 KTS NEAR THE TOP OF THE
NOCTURNAL INVERSION SHOULD LIMIT FOG DEVELOPMENT. LIGHT SURFACE
WINDS THROUGH THE PERIOD WILL PERSIST FROM THE WEST-SOUTHWEST.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...ROGERS


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.