Area Forecast Discussion
Issued by NWS La Crosse, WI

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630
FXUS63 KARX 162015
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
315 PM CDT SAT MAY 16 2015

.SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)
ISSUED AT 315 PM CDT SAT MAY 16 2015

MAIN FCST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES MAINLY LATE
TONIGHT THRU SUN EVENING...SEVERE STORM POTENTIAL CENTERED ON SUN
AFTERNOON.

DATA ANALYSIS AT 18Z HAD A 999MB LOW OVER NORTHEAST WY WITH
TROUGHING SOUTH INTO EASTERN CO. BROAD CIRCULATION AROUND THIS LOW
EXTENDED EAST TO WI/IL TO AL...WITH A WARM FRONTAL BOUNDARY NEAR A
KFSD TO WI/IL BORDER LINE. FCST AREA MOSTLY COVERED BY A LOWER
STRATO-CU DECK NORTH OF THE WARM FRONT. FURTHER SOUTH WITH SOME
SUNSHINE LAPS SBCAPE ANALYSIS HAD 1K-2K J/KG AS FAR NORTH AS CENTRAL
IA WITH SPC MESO-ANALYST ANALYSIS SHOWING 1K-2K J/KG OF MUCAPE
ACROSS MUCH OF THE FCST AREA ABOVE THE STRATO-CU. SCT SHRA/TSRA
SPREADING NORTH ACROSS NORTHERN MO/SOUTHERN IA IN AN AREA OF BROAD
ASCENT...THE DEEPER CAPE AND MINIMAL CIN/CAPPING.

16.12Z MODEL RUNS SHOWING A TIGHTENING CONSENSUS AS A MID LEVEL LOW
MOVES TO WEST OF KFSD BY 12Z SUN THEN LIFTS INTO NORTHEAST MN BY 12Z
TUE. TREND FAVORS A COMPROMISE OF THE EARLIER RUNS ON THE STRENGTH/
TRACK OF THIS LOW...ALONG WITH A TIGHTER CONSENSUS ON THE STRENGTH/
TRACK OF THE SFC LOW LATER TONIGHT THRU SUN NIGHT. NAM STILL ON THE
SLOW/SOUTHERN ENVELOPE OF SOLUTIONS...BUT DOES NOT APPEAR AS THE
OUTLIER IS HAS IN SOME PAST RUNS. WITH THE BETTER/TIGHTER CONSENSUS
SHORT-TERM FCST CONFIDENCE IS ON THE GOOD SIDE THIS CYCLE.

IN THE SHORT TERM...MODEL CONSENSUS KEEPS SOME 250-750 J/KG OF MUCAPE
OVER THE AREA TONIGHT...MAINLY OVER THE SOUTHWEST 1/2 TO 2/3 OF THE
FCST AREA. BROAD LOW LEVEL ASCENT/THERMO-DYNAMIC FORCING CONTINUES
TONIGHT...WITH INCREASING MOISTURE TRANSPORT ESPECIALLY AFTER
MIDNIGHT. 0-6KM BULK SHEAR IS IN THE 20KT RANGE MOST OF THE
NIGHT...INCREASING TO AROUND 40KT LATE AS THE 500MB JET BEGINS TO
LIFT UP THE EAST SIDE OF THE MID LEVEL TROUGH LIFTING ACROSS THE
CENTRAL PLAINS. SCT SHRA/TSRA LOOKING TO LIFT ACROSS THE FCST AREA
MUCH OF TONIGHT. SHRA/TSRA CHANCES INCREASE ACROSS THE WEST END OF
THE FCST AREA LATE TONIGHT AS THE MID LEVEL SHORTWAVE ENERGY STARTS
TO APPROACH AND THE LOWER LEVEL MOISTURE TRANSPORT MAXIMIZES. PRECIP
CHANCES IN THE 20-40 PERCENT RANGE MUCH OF TONIGHT...INCREASING TO
40-60 PERCENT ACROSS THE WEST END LATE. TSRA TONIGHT NOT EXPECTED TO
BE SEVERE WITH THE LESSER CAPE AND SHEAR ON THE LOW SIDE.

ENVIRONMENT OVER THE FCST AREA CHANGES QUICKLY SUNDAY WITH THE SFC
THRU MID LEVEL LOW LIFTING INTO EASTERN SD. 0-6KM SHEAR INCREASES
INTO THE 50+KT RANGE BY 18Z AS THE 500MB JET ROTATES UP THE EAST
SIDE OF THE TROUGH. ONE BAND OF SHRA/TSRA EXPECTED TO BE ONGOING/
LIFTING NORTHEAST ACROSS THE FCST AREA SUN MORNING. WITH CLOUDY
SKIES/ONGOING CONVECTION...CAPE OF ANY KIND NOT EXPECTED TO INCREASE
MUCH THRU SUN MORNING. ANY TSRA SUN MORNING EXPECTED TO BE NON-
SEVERE. ONCE THIS BAND OF CONVECTION WOULD CLEAR THE FCST AREA...
SB/MU CAPE PROGGED TO INCREASE RAPIDLY INTO THE 1.5K TO 3K J/KG
RANGE. THIS AHEAD OF A PRE-FRONTAL SFC-925MB TROUGH ASSOCIATED
WITH A STRONGER LOBE OF VORTICITY LIFTING AROUND THE EAST SIDE OF
THE MID LEVEL LOW/TROUGH. THE LIFT/DIVERGENCE ALOFT LOOK TO
MAXIMIZE DURING THE AFTERNOON...ALONG WITH ENHANCED SFC-1KM
HELICITY NEAR THE SFC TROUGH. SFC-700MB CAPE PROGGED TO BE IN THE
200-300 J/KG RANGE...FOR RAPID ASCENT OF LOWER LEVEL PARCELS.
ENVIRONMENT LOOKING VERY FAVORABLE FOR ROTATING SUPER-CELL TSRA
SUN AFTERNOON. GIVEN ALL THIS...WOULD EXPECTED A LINE OF TSRA TO
DEVELOP NEAR/WEST OF I-35 BY MID AFTERNOON SUN...LIFTING QUICKLY
NORTH/NORTHEAST ACROSS THE FCST AREA LATER SUN AFTERNOON/EARLY SUN
EVENING...BECOMING STRONG TO SEVERE AS THEY DO.

HOWEVER...2 CONTINGENCIES EXITS. 1/...THE SB/BOUNDARY LAYER CAPE
INCREASE LATE SUN MORNING/EARLY SUN AFTERNOON DEPENDS ON SOME
SUNSHINE FOR DIURNAL WARMING/MIXING BEHIND ANY MORNING SHRA/TSRA.
BASED ON MODEL 925-850MB RH PROGS AND SOUNDINGS...THIS IS NOT A
GIVEN. 2/...THE AREA IS UNDER THE RIGHT FRONT EXIT REGION OF THE 500-
300MB JET MAX UNTIL LATER IN THE AFTERNOON. THIS MAY SUPPRESS/LIMIT
CONVECTION UNTIL IT PASSES LATER IN THE AFTERNOON...BUT ONCE IT DOES
ANY TSRA WOULD BE UNDER VERY FAVORABLE MID/UPPER LEVEL LIFT/
DIVERGENCE. STORM PREDICTION CENTER RAISED THE SEVERE RISK FOR
SUNDAY TO ENHANCED FOR MUCH OF THE FCST AREA AND THIS QUITE
REASONABLE AT THIS POINT. SEE SWODY2 FOR MORE DETAILS. DEEPER
MOISTURE/LIFT/CAPE ARE SWEPT OUT OF THE FCST AREA AS THE TRAILING
COLD FRONT PUSHES THRU AND EAST OF THE FCST AREA BY LATER SUN
NIGHT. FCST TRENDS DRY ACROSS MOST OF THE FCST AREA BY 12Z MON AS
LOWER LEVEL DRYING/COLD AIR SPREAD IN. USED A BLEND OF THE GUIDANCE
LOWS/HIGHS FOR TONIGHT THRU SUN NIGHT.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 315 PM CDT SAT MAY 16 2015

MAIN FCST CONCERNS FOR MON THRU TUE NIGHT...COLDER TEMPERATURES AND
FROST POTENTIAL BOTH MON/TUE NIGHTS.

MODEL RUNS OF 16.12Z OFFER A TIGHTENING CONSENSUS AS A SECONDARY
SHORTWAVE AND THE MID LEVEL TROUGH AXIS ROTATE ACROSS THE UPPER
MIDWEST MON/MON NIGHT. TREND FAVORS SLOWER/STRONGER OF EARLIER
MODELS WITH THE SECONDARY SHORTWAVE TO PASS MON NIGHT. IMPROVING
CONSENSUS FOR A STRONGER NORTHWEST FLOW SHORTWAVE TO DROP INTO
NORTHERN MN TUE THEN SOUTHEAST ACROSS THE WESTERN GREAT LAKES WED
NIGHT. GIVEN THIS SHAPING UP TO BE A DRY/QUIETER PERIOD AND THE
IMPROVING MODEL CONSENSUS...FCST CONFIDENCE IN THE MON THRU TUE
NIGHT PERIOD IS GENERALLY GOOD THIS CYCLE.

STRONG LOW LEVEL COLD ADVECTION...DEEPER LAYERED SUBSIDENCE SPREAD
ACROSS THE AREA MON/MON NIGHT IN THE WAKE OF THE STRONG/FILLING LOW
AS IT MOVES EAST ACROSS LK SUPERIOR. SOME DEFORMATION BAND MOISTURE
IN THE 925 TO ABOUT 800MB LAYER TO ROTATE ACROSS THE FCST AREA
LATER MON/MON NIGHT...HOWEVER ANY LIFT IN THIS LAYER PROGGED TO
PASS MAINLY ACROSS NORTHERN WI. WILL LIMIT ANY -SHRA CHANCES THESE
PERIODS TO FAR NORTH END OF THE FCST AREA. 925MB TEMPS PROGGED TO
FALL INTO THE 0C TO -3C RANGE BY 12Z TUE. WOULD USUALLY BE CONCERNED
ABOUT FROST WITH THESE TEMPS...HOWEVER WITH THE 925-800MB MOISTURE/
CLOUD DECK MOVING ACROSS THE FCST AREA AND SFC GRADIENT WINDS IN
THE 10-15 MPH RANGE...MON NIGHT NOT SHAPING UP TO BE A STRONG
RADIATIONAL COOLING NIGHT AND DID NOT MENTION FROST LATE MON NIGHT/
EARLY TUE MORNING. NEXT SHORTWAVE PASSES BUT THIS OVER THE TOP OF
SFC-850MB RIDGING AND A DRYING LOW LEVEL AIRMASS. BY WED MORNING
THE SFC HIGH PRESSURE RIDGE AXIS IS PROGGED TO BE OVER THE FCST
AREA...WITH LIGHT WINDS AND CLEAR/MOSTLY CLEAR SKIES AND THE DRY
LOW LEVEL AIRMASS. TUE NIGHT APPEARING MORE FAVORABLE FOR STRONGER
RADIATIONAL COOLING AND FROST POTENTIAL. ADDED PATCHY FROST MENTION
TO THE NORMALLY COLDER LOCATIONS ALONG/NORTHEAST OF I-94 FOR LATER
TUE NIGHT INTO EARLY WED MORNING. USED A BLEND OF THE GUIDANCE
HIGHS/LOWS FOR MON THRU TUE THEN FAVORED COOLER OF GUIDANCE LOWS
FOR TUE NIGHT.

FOR WEDNESDAY THROUGH SATURDAY...DAYS 4 TO 7...

MAIN FCST CONCERNS THIS PERIOD...COOLER TEMPERATURES...POTENTIAL
-SHRA CHANCES WED AND AGAIN SAT.

MEDIUM RANGE MODEL RUNS OF 16.00Z/16.12Z IN RATHER GOOD AGREEMENT
FOR CONFLUENT NORTHWEST FLOW ALOFT OVER THE REGION ON WED. GOOD
SIGNAL FOR SHORTWAVE TROUGHING/ENERGY TO BE CROSSING NEB/SD ON
WED...WITH THIS ENERGY GETTING CAUGHT UP IN THE CONFLUENT FLOW AND
THE BULK OF THE FORCING/LIFT TO BE SHUNTED SOUTH OF THE FCST AREA
LATER WED/WED NIGHT. MODELS MAINTAIN DECENT CONSENSUS FOR THE UPPER
MIDWEST TO BE UNDER STRONGER/DEEPER NORTHWEST FLOW THU/FRI. SOME
CONSENSUS FOR HGTS TO RISE/SHORTWAVE RIDGING TO QUICKLY BUILD ACROSS
THE REGION SAT...WITH SOUTHWEST FLOW ALOFT WEST OF THE MS RIVER SAT
NIGHT. DAY 4-7 FCST CONFIDENCE IS AVERAGE THIS CYCLE GIVE THE
IMPROVED BETWEEN MODEL AND RUN-TO-RUN CONSISTENCY.

SHORTWAVE ENERGY COMING ACROSS THE PLAIN WED WOULD BRUSH THE
SOUTHWEST SIDE OF THE FCST AREA WITH SOME INCREASE OF MOISTURE/LIFT
AS IT PASSES LATER WED/WED NIGHT. HOWEVER...THE CONFLUENT MID LEVEL
FLOW LOOKS TO KEEP THIS FROM SPREADING TOO FAR NORTH/EAST INTO THE
FCST AREA. SMALL -SHRA CHANCE ACROSS THE SOUTHWEST END OF THE FCST
AREA THESE PERIODS REASONABLE FOR NOW. INCREASED NORTHWEST FLOW
THU/FRI SENDS ANOTHER CAN HIGH AND DRIER AIRMASS SOUTHEAST ACROSS
THE FCST AREA FOR LATE IN THE WEEK. INCREASING SOUTHERLY FLOW/LOW
LEVEL WARM ADVECTION UNDER THE RISING HGTS/SHORTWAVE RIDGING SPREADS
INCREASING MOISTURE AND SOME ISENTROPIC LIFT ACROSS AT LEAST THE
WEST HALF OF THE FCST AREA ON SAT. SMALL -SHRA CHANCE SAT MAINLY
WEST OF THE MS RIVER LOOKS OKAY AT THIS TIME. NAEFS INDICATES 850MB
TEMPS SOME 1 TO 2 STD DEVIATIONS BELOW NORMAL WED/THU...SLOWLY
MODERATING TOWARD NORMAL BY SAT. HIGHS WED/THU CONTINUE TO TREND
BELOW NORMAL... WARMING BACK TO NEAR NORMAL BY SAT. MODEL/ENSEMBLE
CONSENSUS OF HIGHS/LOWS FOR WED THRU SAT APPEAR WELL TRENDED AT THIS
TIME.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1251 PM CDT SAT MAY 16 2015

IFR/MVFR CONDITIONS EXPECTED THROUGH LATE AFTERNOON AS A WARM FRONT
LIFTS NORTHWARD ACROSS THE TAF SITES. CONDITIONS SHOULD IMPROVE TO
VFR IN THE WAKE OF THE FRONT THIS EVENING. ANOTHER SURGE OF MOISTURE
PUSHES INTO THE REGION TONIGHT AHEAD OF A STRONG LOW PRESSURE
SYSTEM. LOOK FOR IFR/MVFR CONDITIONS TO RETURN ALONG WITH THE CHANCE
FOR SHOWERS AND THUNDERSTORMS ...ESPECIALLY  AT KRST. THUNDERSTORM
CHANCES INCREASE TOMORROW AFTERNOON WITH THE POTENTIAL TO SEE SEVERE
STORMS CAPABLE OF STRONG GUSTY WINDS...HAIL...AND POSSIBLY AN
ISOLATED TORNADO OR TWO.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION.....WETENKAMP



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