Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 192320
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
620 PM CDT FRI SEP 19 2014

.SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)
ISSUED AT 222 PM CDT FRI SEP 19 2014

CONCERN FOCUSED ON CONVECTION/SEVERE POTENTIAL TONIGHT.

WATER VAPOR/RAP 500MB ANALYSIS SHOWING A FAIRLY VIGOROUS MID-LEVEL
TROUGH MOVING EAST ACROSS THE DAKOTAS. AT THE SURFACE...LOW PRESSURE
WAS LOCATED OVER SOUTHERN MANITOBA CANADA WITH A TRAILING TROUGH
THROUGH THE EASTERN DAKOTAS INTO CENTRAL NEB. RADAR MOSAIC SHOWING
SCATTERED SHOWERS/ISOLATED THUNDER ACROSS PORTIONS OF ND INTO
NORTHERN MN IN RESPONSE TO CORRIDOR OF 850MB MOISTURE TRANSPORT/310K
ISENTROPIC LIFT AHEAD OF THE APPROACHING TROUGH. OTHERWISE...BREEZY
SOUTH WINDS IN PLACE ACROSS THE FORECAST AREA THIS AFTERNOON WITH
MOSTLY SUNNY SKIES. TEMPERATURES WERE IN THE UPPER 60S TO THE MIDDLE
70S.

FOR TONIGHT...LOOK FOR THAT MID-LEVEL/SURFACE TROUGH TO ROTATE
SOUTHEAST ACROSS THE AREA TONIGHT. MODELS OFFERING UP VARIOUS
SOLUTIONS ON CONVECTIVE SCHEMES BASED ON FAIRLY STRONG CAP IN PLACE.
THINKING WITH INCREASING 850MB MOISTURE TRANSPORT/EVENTUAL
STEEPENING OF MID-LEVEL LAPSE RATES AND LIFT WITH THE TROUGH
PASSAGE...THIS WILL BE ENOUGH FORCING TO SEE AT LEAST A SCATTERED
BAND OF THUNDERSTORMS. THINKING THIS CONVECTION WILL INITIALLY START
OUT ELEVATED IN NATURE ABOVE THE CAP...BUT THEN CAP WEAKENS LATE
THIS EVENING INTO THE OVERNIGHT HOURS ALLOWING FOR AN UPTICK IN
THUNDERSTORM COVERAGE. STILL THINKING THERE IS A MARGINAL SEVERE
THREAT. MODEL CONSENSUS SHOWING 0-3KM MUCAPE VALUES OF 1000-200J/KG
ALONG WITH EFFECTIVE BULK SHEAR AROUND 30KT. THIS COULD PRODUCE A
FEW VIGOROUS/ROTATING UPDRAFTS CAPABLE OF LARGER HAIL PRODUCTION
AND DAMAGING WIND POTENTIAL.

LINGERING SHOWERS/THUNDERSTORMS WILL BE POSSIBLE ACROSS SOUTHERN WI
INTO NORTHEAST IA ON SATURDAY AS THE TROUGH CONTINUES TO ROTATE
SOUTHEAST OUT OF THE AREA. FOR LATER SATURDAY AFTERNOON INTO
SATURDAY EVENING...MODELS SHOWING A FAIRLY COMPACT/VIGOROUS PV-
ANOMALY ROTATING SOUTHEAST OUT OF THE NORTHERN PLAINS IN OUR AREA.
THE BULK OF THE FORCING WITH THIS FEATURE SEEMS TO BE FOCUSED ALONG
AND NORTHEAST OF I-94. AS SUCH...WENT WITH THE LIKELIHOOD OF
SHOWERS/ISOLATED THUNDER NORTHEAST OF I-94 AND TAPERED TO LOWER-END
CHANCES ACROSS NORTHEAST IA/FAR SOUTHWEST WI. WITH THE WARMER START
TO SATURDAY...LOOK FOR HIGHS TO PERK UP INTO THE 70S TO A FEW LOWER
80S ALONG AND SOUTH OF I-90. LOOK FOR THE SHOWERS AND ISOLATED
STORMS TO TAPER OFF/MOVE EAST OF THE AREA BY MIDNIGHT SATURDAY
NIGHT WITH OVERNIGHT LOWS DIPPING INTO THE 50S.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 222 PM CDT FRI SEP 19 2014

COOLER CYCLONIC FLOW ALOFT ON SUNDAY WILL PRODUCE COOLER
TEMPERATURES IN THE 60S ALONG WITH BREEZY NORTHWEST WINDS. ALSO
LOOKS LIKE THERE WILL ALSO BE ENOUGH INSTABILITY NORTHEAST OF I-94
TO PRODUCE A FEW SHOWERS.

HIGH PRESSURE BUILDS OVER THE UPPER MISSISSIPPI RIVER VALLEY REGION
SUNDAY NIGHT. CLEAR SKIES AND LIGHT/CALM WINDS WILL SET UP IDEAL
RADIATIONAL COOLING FOR AREAS OF FOG...ESPECIALLY FAVORED RIVER
VALLEY LOCATIONS AND THE SANDY/BOG COUNTRY OF CENTRAL WI. PLAN ON
LOWS IN THE LOWER 40S OVER CENTRAL WI...AND IN THE MIDDLE/UPPER 40S
ELSEWHERE ACROSS THE FORECAST AREA.

AFTER A COOL/POTENTIALLY FOGGY START...HIGH PRESSURE LOOKS TO
PROVIDE A DRY/QUIET/MOSTLY SUNNY MONDAY WITH HIGHS MIDDLE 60S TO
NEAR 70.

FOR TUESDAY THROUGH FRIDAY...A RIDGE OF HIGH PRESSURE TRIES TO
ESTABLISH ITSELF OVER THE CENTRAL CONUS. HOWEVER...MODELS SHOWING A
TROUGH EJECTING OUT OF THE INTERMOUNTAIN WEST INTO THE UPPER
MISSISSIPPI RIVER VALLEY BY WEDNESDAY INTO THURSDAY. BELIEVE THIS
MAY BE A BIT OVER DONE...BUT WILL GO WITH MODEL CONSENSUS AT THIS
POINT AND INCLUDE SMALL-END SHOWER/THUNDER CHANCES IN THE TUESDAY
NIGHT THROUGH THURSDAY PERIOD. AS THE TROUGH MOVES OFF TO THE
EAST...THE RIDGE RE-ESTABLISHES ITSELF ON FRIDAY FOR DRIER/WARMER
CONDITIONS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 620 PM CDT FRI SEP 19 2014

STILL SOME UNCERTAINTY ON WHERE AND IF CONVECTION WILL DEVELOP
ACROSS THE AREA THIS EVENING. THE MAJORITY OF THE MESO SCALE
MODELS ARE NOW FOCUSING ON NORTHWEST IOWA AS THE INITIATION POINT
AHEAD OF THE INCOMING SHORT WAVE TROUGH FROM THE DAKOTAS...UNDER
THE RIGHT ENTRANCE REGION OF THE UPPER LEVEL JET AND ALONG THE
NORTHERN EDGE OF THE MID LEVEL CAP. THE DIFFERENCES IN THE MODELS
ARE WITH HOW MUCH CONVECTION THEN FILLS IN TO THE NORTHEAST ALONG
THE FRONT. THE 19.20Z HRRR WANTS TO SHOW SOME SCATTERED ACTIVITY
POSSIBLY IMPACTING BOTH TAF SITES WHILE THE 19.12Z HI-RES ARW
WOULD SUGGEST THE ACTIVITY WOULD NOT FILL IN ALONG THE FRONT UNTIL
IT WAS PAST THE TAF SITES. THE 19.18Z NAM IS SIMILAR TO THE HI-RES
ARW WHILE THE 19.18Z CR-NAMNEST IS CLOSER TO THE HRRR. SO FOR
NOW...UNTIL IT BECOMES CLEARER WHAT IS GOING TO TRANSPIRE...WILL
STAY WITH THE PREVIOUS TRENDS OF SHOWING A VCTS AT BOTH SITES THIS
EVENING INTO THE EARLY OVERNIGHT HOURS. AFTER THAT...EXPECT VFR
CONDITIONS THROUGH SATURDAY WITH THE WINDS COMING AROUND TO THE
NORTHWEST WITH THE PASSAGE OF THE COLD FRONT.

&&

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

$$

SHORT TERM...DAS
LONG TERM...DAS
AVIATION...04



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