Area Forecast Discussion
Issued by NWS La Crosse, WI

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977
FXUS63 KARX 181732
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1232 PM CDT MON MAY 18 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 347 AM CDT MON MAY 18 2015

MAIN FCST CONCERNS THIS PACKAGE...CLOUD TRENDS AND TEMPERATURES.

DATA ANALYSIS AT 06Z HAD A 997MB LOW OVER NORTH-CENTRAL MN...MOVING
SLOWLY EAST-NORTHEAST AND FILLING AS IT DOES. WV IMAGERY SHOWED THE
MID/UPPER LEVEL LOW OVER NORTH-CENTRAL MN AS WELL...WITH THE DEEPER
MOISTURE/COLDER CLOUDS AND PRECIP WRAPPING AROUND THESE LOWS
GENERALLY CONFINED TO ND AND NORTHERN MN. STRONGER PRESSURE RISES ON
THE SOUTH/WEST SIDES OF THE LOW DRIVING THE COLD FRONT ACROSS IA/WI
EARLY THIS MORNING. WEST WINDS 15-20MPH GUSTING 30MPH WERE COMMON
ACROSS MUCH OF IA/SOUTHERN MN/WESTERN WI...SPREADING A MUCH COLDER
AIRMASS INTO THE REGION BEHIND THE FRONT. TEMPS ALREADY IN THE UPPER
30S IN SOUTHWEST MN EARLY THIS MORNING.

18.00Z MODELS INITIALIZED WELL AND OFFER VERY SIMILAR SOLUTIONS FOR
TODAY/TONIGHT. THIS AS THE MID LEVEL LOW OVER MN FILLS AND MOVES TO
NORTH OF LK SUPERIOR TODAY THEN A TRAILING/SECONDARY SHORTWAVE MOVES
ACROSS THE REGION TONIGHT...WITH FLOW ALOFT BECOMING WEST-NORTHWEST
BY 12Z TUE. TREND FAVORS A TIGHTER COMPROMISE SOLUTION OF THE
PREVIOUS RUNS ON BOTH SPEED/STRENGTH OF THESE FEATURES. SHORT-TERM
FCST CONFIDENCE IS GOOD THIS CYCLE.

IN THE SHORT TERM...SFC-850MB FLOW WILL GRADUALLY BECOME MORE
NORTHWESTERLY ACROSS THE AREA TODAY AS THE LOW LEVEL CIRCULATION
MOVES TO NORTH OF LK SUPERIOR BY LATE IN THE DAY. LOWER LEVEL WRAP-
AROUND MOISTURE/STRATO-CU DECK ALREADY SPREADING INTO THE FCST AREA
ON THE WESTERLY FLOW AROUND THE SOUTH SIDE OF THE SFC-700MB LOW.
MODELS IN GOOD AGREEMENT THAT THE MORE NORTHWESTERLY FLOW OVER THE
AREA WILL SPREAD MORE 925-700MB MOISTURE/CLOUD DECK ACROSS THE
FCST AREA TODAY. THIS AS 925MB TEMPS FALL INTO THE +1C TO +6C
RANGE BY 00Z TUE AND A TIGHT NORTHWEST FLOW PRESSURE GRADIENT
REMAINS OVER THE AREA. MODEL SOUNDINGS SHOWING MIXING TO 875-850MB
THIS AFTERNOON...WITH 25- 30KTS OF WIND IN THE UPPER PORTION OF
THE MIXED LAYER. BKN/OVC STRATO-CU DECK WILL TEMPER THE WINDS/
MIXING A BIT...BUT COMPARED TO THIS PAST WEEKEND A BLUSTERY/COLD
DAY IN STORE FOR THE AREA. WITH THE SFC-700MB LOW MOVING TO NORTH
OF LK SUPERIOR...BULK OF THE WRAP-AROUND/DEFORMATION BAND
CONVERGENCE/LIFT LOOKS TO REMAIN NORTH OF THE FCST AREA TODAY/
TONIGHT. GIVEN CYCLONIC CONVERGENCE AND DEEPER MOISTURE TO ABOUT
700MB...DID ADD A SPRINKLE MENTION TO THE FAR NORTH END OF THE
FCST AREA FOR THIS AFTERNOON/EVENING.

MID LEVEL LOW AND TROUGH AXIS MOVE EAST OF THE FCST AREA TONIGHT
WITH PASSAGE OF THE SECONDARY SHORTWAVE. LOWER MOISTURE STARTS TO
DECREASE FROM WEST TO EAST LATER TONIGHT WHILE GRADIENT GRADUALLY
RELAXES. WINDS STILL LOOK TO REMAIN 10-20 MPH TONIGHT FOR BOUNDARY
LAYER MIXING. THIS PLUS THE CLOUD BLANKET MUCH OF THE NIGHT TO KEEP
LOWS ABOVE FREEZING...EVEN AS 925MB TEMPS END UP IN THE 0C TO -4C
RANGE BY 12Z TUE. USED A BLEND OF THE GUIDANCE HIGHS FOR TODAY THEN
FAVORED WARMER OF GUIDANCE LOWS TONIGHT.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 347 AM CDT MON MAY 18 2015

MAIN FCST CONCERNS FOR TUE THRU WED NIGHT...FROST CHANCES TUE
NIGHT...-SHRA CHANCES ACROSS THE SOUTH END OF THE FCST AREA WED...
TEMPERATURES THRU THE PERIOD.

MODEL RUNS OF 18.00Z TRENDING TOWARD A TIGHTER CONSENSUS AS A SERIES
OF NORTHWEST FLOW SHORTWAVES DROP TOWARD/ACROSS LK SUPERIOR TUE/TUE
NIGHT. MODELS WITH IMPROVING AGREEMENT AS THE LAST OF THESE WAVES
INTERACTS WITH ENERGY COMING ACROSS NEB/SD WED. TREND FAVORS MORE
PHASING OF THESE PIECES OF ENERGY OVER THE SOUTH HALF OF THE REGION
WED. GOOD AGREEMENT AS THE PHASED TROUGH AXIS WOULD THEN DROP SOUTH
OF THE FCST AREA WED NIGHT. WITH THE IMPROVED MODEL CONSENSUS FCST
CONFIDENCE IN THE TUE THRU WED NIGHT PERIOD IS GOOD THIS CYCLE.

SFC-850MB LOW/TROUGH CONTINUES MOVING EAST TUE WITH ANTI-CYCLONIC
LOWER LEVEL FLOW AND HIGH PRESSURE RIDGING BUILDING INTO THE REGION.
SKIES EXPECTED TO BECOME PARTLY CLOUDY/MOSTLY SUNNY BY TUE AFTERNOON
WITH LIGHTER WINDS AS THE GRADIENT CONTINUES TO RELAX AND THE SFC
RIDGE AXIS APPROACHES. 925-850MB TEMPS START TO RECOVER TUE...BUT
MODEL SOUNDINGS MIXED TO 850MB STILL ONLY LOOKING TO SUPPORT HIGHS
IN THE LOW-MID 50S. SFC RIDGE AXIS DRIFTS OVERHEAD TUE NIGHT. WITH
LIGHT WINDS/MOSTLY CLEAR SKIES AND THE COOL/DRY AIRMASS...PATCHY TO
AREAS OF FROST CONTINUE TO LOOK POSSIBLE IN AREAS ALONG/NORTHEAST OF
I-94 LATE TUE NIGHT/EARLY WED MORNING. LATER SHIFTS WILL HAVE TO
MONITOR THIS FOR POTENTIAL FROST ADVISORY THESE AREAS. ELSEWHERE THE
SHORTWAVE TROUGH MOVING ACROSS THE CENTRAL PLAINS SPREADS INCREASING
MID/HIGH LEVEL MOISTURE/CLOUDS ACROSS THE SOUTHWEST 1/2 TO 2/3 OF
THE FCST AREA AFTER MIDNIGHT...LIMITING LATE-NIGHT RADIATIONAL
COOLING AND LOWS. AT LEAST PARTIAL PHASING OF THE NORTHWEST FLOW
SHORTWAVE AND PLAINS SHORTWAVE ON WED SPREADS MORE 850-700MB
MOISTURE...700-500MB QG CONVERGENCE AND 500-300MB PV ADVECTION
ACROSS THE SOUTH PORTIONS OF THE FCST ON WED. RAISED -SHRA CHANCES
ACROSS THE SOUTHWEST 1/3 OF THE FCST AREA MAINLY WED AFTERNOON WITH
APPROACH/PASSAGE OF THE SHORTWAVE ENERGY. COOLER OF THE HIGHS ON WED
LOOKING TO BE ACROSS THE SOUTH PORTIONS OF THE FCST AREA WITH THE
THICKER CLOUDS AND POTENTIAL -SHRA IN THE AFTERNOON. 850-500MB
TROUGH AXIS PASS LATE WED AFTERNOON/EARLY WED EVENING WITH
DRYING/SUBSIDENCE NORTHWEST FLOW BEHIND IT QUICKLY PUSHING THE
MOISTURE/CLOUDS SOUTH OF THE FCST AREA FOR WED NIGHT. ANOTHER COOL
NIGHT WITH LIGHTER WINDS AND CLEAR/MOSTLY CLEAR SKIES. MY NEED TO
WATCH FOR DECOUPLING WINDS AND PATCHY FROST IN THE NORMALLY COLDER
LOW LAYING AREAS AGAIN WED NIGHT. USED A BLEND OF THE GUIDANCE
HIGHS/LOWS FOR TUE THRU WED NIGHT.

FOR THURSDAY THRU SUNDAY...DAYS 4 TO 7...

MAIN FCST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES SAT THRU SUN...
TEMPERATURES.

MEDIUM RANGE MODEL RUNS OF 18.00Z SHOWING GOOD BETWEEN MODEL AND RUN-
TO-RUN CONSISTENCY FOR NORTHWEST FLOW ALOFT ACROSS THE UPPER MIDWEST
THU/FRI. CONSISTENCY REMAINS GOOD FOR HGTS TO RISE/SHORTWAVE RIDING
TO BUILD ACROSS THE REGION FRI NIGHT INTO SAT NIGHT...WITH HGTS TO
START FALLING LATE SAT NIGHT/SUN AS STRONGER TROUGHING MOVES INTO
THE PLAINS. TREND IS TOWARD MORE SHORTWAVE RIDGING OVER THE REGION
SAT AND SLOWING OF THE TROUGHING CROSSING THE PLAINS SUN. FCST
CONFIDENCE IS GOOD THU/FRI THEN AVERAGE SAT/SUN...GIVEN THE NUANCES
OF PLAINS TROUGHING AND RESULTING SHRA/TSRA CHANCES ACROSS THE
REGION.

DRY WEATHER CONTINUES ACROSS THE UPPER MIDWEST THU/FRI AS CAN
HIGH PRESSURE MOVES ACROSS THE REGION UNDER THE NORTHWEST FLOW
ALOFT. WITH WHAT SHOULD BE PLENTY OF SUNSHINE THU/FRI...LOWER
LEVEL TEMPS TO SLOWLY MODERATE/WARM. HIGHS BY FRI LOOKING TO BE
CLOSE TO NORMAL. SOUTHERLY FLOW/MOISTURE STARTS TO RETURN
SAT...BUT MORE SHORTWAVE RIDGING HOLDING OVER THE REGION AND THE
SLOWING OF THE TROUGHING MOVING INTO THE PLAINS KEEPS THE MAIN
MOISTURE RETURN AXIS AND SHRA/TSRA CHANCES WEST OF THE FCST AREA
ON SAT. SMALL CONSENSUS SHRA/TSRA CHANCES ACROSS THE WEST HALF OF
THE FCST AREA ON SAT OKAY FOR NOW BUT WITH FURTHER SLOWING SAT
WOULD END UP A DRY DAY ACROSS THE FCST AREA. MOISTURE TRANSPORT/
INCREASE INTO THE REGION CONTINUE SAT NIGHT/SUN AS SFC-700MB
LOW/TROUGHING WOULD MOVE EAST ACROSS THE PLAINS. PLENTY OF MESO-
SCALE DETAIL DIFFERENCES BY SAT NIGHT/SUN BUT INCREASING PRECIP
CHANCES SAT NIGHT/SUN APPEAR REASONABLE FOR NOW. STRONGER SIGNAL
FOR SUN/MON OF THE HOLIDAY WEEKEND TO BE UNSETTLED BUT TIME WILL
TELL ON THE DETAILS. MODEL/ENSEMBLE CONSENSUS HIGHS/LOWS FOR THU
THRU SUN LOOK WELL TRENDED AT THIS TIME.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1232 PM CDT MON MAY 18 2015

MVFR STRATOCUMULUS WILL PERSIST AT THE TAF SITES THROUGH TONIGHT
WITH CLOUD BASES OF 2K-3KFT. ALSO...WINDY CONDITIONS WILL
CONTINUE WITH WEST WINDS OF 18 TO 22 KTS WITH GUSTS APPROACHING 30
KTS AT TIMES. THE WINDS WILL DIMINISH SLIGHTLY TONIGHT. CLOUDS
SHOULD START TO SCATTERED OUT BY MID MORNING ON TUESDAY WITH A
RETURN TO VFR CONDITIONS.

&&

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

$$

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



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