AP-WI--LSE-WI SW Area Forecast Discussion, WI
000
FXUS63 KARX 151135
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
635 AM CDT WED JUL 15 2015
.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 342 AM CDT WED JUL 15 2015
MAIN FCST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES LATER TONIGHT...
TEMPERATURES.
06Z DATA ANALYSIS HAD A WEAK BUT BROAD RIDGE OF HIGH PRESSURE ACROSS
THE REGION FROM LK SUPERIOR TO IA AND MO. WEAK SHORTWAVE ENERGY AND
SOME MOISTURE TRANSPORT WERE PRODUCING SOME CLOUDS/SCT SHRA IN
NORTHERN MN. UNDER/EAST OF THE SFC RIDGE AXIS SKIES WERE GENERALLY
CLEAR WITH LIGHT EAST/NORTHEAST FLOW BRINGING DRIER/COOLER AIR TO
MUCH OF WI/SOUTHEAST MN/NORTHEAST IA. EARLY MORNING TEMPS RANGED
FROM THE 40S IN NORTHEAST WI TO THE LOW/MID 70S IN SOUTHWEST IA
WHERE THE IMPACTS OF THE HIGH HAVE YET TO REACH.
15.00Z MODELS INITIALIZED QUITE WELL. MODELS IN GOOD AGREEMENT FOR
SHORTWAVE RIDGING ALOFT TO MOVE QUICKLY EAST ACROSS THE UPPER
MIDWEST TODAY...BEING PUSHED EAST BY SHORTWAVE ENERGY EJECTING OUT
OF THE SOUTHERN ROCKIES INTO THE CENTRAL PLAINS. BY TONIGHT THIS
SHORTWAVE ENERGY IS ALREADY MOVING INTO/ACROSS THE REGION...AHEAD OF
MORE NORTHERN STREAM ENERGY COMING ACROSS THE NORTHERN PLAINS.
OVERALL TREND IS FASTER/STRONGER WITH THESE FEATURES THRU THE FLOW
LATER TODAY/TONIGHT. GIVEN THE REASONABLY GOOD MODEL CONSENSUS...
SHORT TERM FCST CONFIDENCES IS GOOD THIS CYCLE.
IN THE SHORT TERM...THE NORTHERN MN FORCING WEAKENS/STAYS NORTH THIS
MORNING AS THE 850-700MB RIDGE AXIS BUILDS EAST INTO/ACROSS THE
REGION TODAY. THE SFC RIDGE AXIS MOVES FROM WI TO MI THRU THE DAY.
MODELS RATHER CONSISTENT KEEPING THE 925-700MB MOISTURE TRANSPORT
AND MAIN MOISTURE/CAPE AXIS WEST OF I-35 THRU THE DAY. 850MB LOW
LEVEL JET EVEN FURTHER WEST OUT NEAR I-29 AT 00Z THU. THUS EVEN WITH
THE FASTER TREND OF THE MODELS WITH THE SHORTWAVES BY 00Z THU...NOT
SURE WHY MODELS ARE SO QUICK TO SPREAD SHRA/TSRA INTO THE WEST END
OF THE FCST AREA BY 00Z THU. GIVEN THE POSITION OF THE LOWER LEVEL
MOISTURE/FORCING....LEFT TODAY INTO EARLY THIS EVENING DRY. A MORE
COMFORTABLE MOSTLY SUNNY/PARTLY CLOUDY DAY FOR THE AREA WITH MIXED
925MB TEMPS SUPPORTING HIGHS IN THE MID 70S TO LOWER 80S. WITH
APPROACH/PASSAGE OF THE CENTRAL PLAINS SHORTWAVE ENERGY TONIGHT...
LOWER LEVEL THERMO-DYNAMIC FORCING/LIFT QUICKLY TRANSLATE EAST
ACROSS MN/IA INTO WI TONIGHT. LOW LEVEL JET STRENGTHENS...ALONG WITH
ACCOMPANYING MOISTURE TRANSPORT/THETA-E CONVERGENCE...AND IS POINTED
INTO THE FCST AREA BY 12Z THU. THIS WITH INCREASING DIVERGENCE/LIFT
ALOFT. RAISED SHRA/TSRA CHANCES TO 60-90 PERCENT OVER THE WEST/
NORTHWEST HALF OF THE FCST AREA BY LATE TONIGHT DUE TO THE FASTER
SHORTWAVE AND INCREASE OF LOWER LEVEL FORCING. USED A BLEND OF THE
GUIDANCE HIGHS/LOWS FOR TODAY/TONIGHT.
.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 342 AM CDT WED JUL 15 2015
MAIN FCST CONCERNS FOR THU THRU FRI NIGHT...SHRA/TSRA CHANCES AND
HEAVY RAIN THREAT THU INTO THU EVENING...SHRA/TSRA CHANCES AGAIN FRI
NIGHT...TEMPERATURES.
MODEL RUNS 15.00Z IN GOOD AGREEMENT WITH THE NORTHERN STREAM
SHORTWAVE TO MOVE INTO NORTHERN MN THU THEN PASS QUICKLY EAST OF THE
REGION BY 12Z FRI. IMPROVING SIGNAL FOR SHORTWAVE RIDGING TO MOVE
ACROSS THE UPPER MIDWEST ON FRI...AHEAD OF YET MORE SHORTWAVE ENERGY
DIGGING THRU THE NORTHERN ROCKIES AND AMPLIFYING TROUGHING OVER THE
NORTHWEST CONUS. TREND IS GENERALLY STRONGER WITH SHORTWAVE TROUGHS
AND RIDGES ACROSS THE NORTHERN CONUS IN THE THU THRU FRI NIGHT
PERIOD. FCST CONFIDENCE THIS PERIOD IS GENERALLY GOOD THIS CYCLE.
THU STARTS OUT WITH STRONG LOWER LEVEL THERMO-DYNAMIC FORCING
SPREADING INTO/ACROSS THE FCST AREA. HOWEVER...SURPRISING AMOUNT OF
SPREAD NORTH TO SOUTH ON WHERE MODELS PLACE THE STRONGER OF THE
FORCING/LIFT/CONVERGENCE...AND RESULTING CONVECTIVE COMPLEX/HEAVIEST
RAIN POTENTIAL. NAM FURTHEST NORTH...ECMWF FURTHEST SOUTH...AND HAVE
INCREASED THEIR DIFFERENCES SINCE THE 14.12Z/14.18Z RUNS.
CONFIDENCE IS HIGH IT WILL RAIN ACROSS THE FCST AREA ON THU...BUT
LOWER ON HOW MUCH RAIN MAY FALL WHERE. PW VALUES IN THE 2 INCH
RANGE BY LATE TONIGHT AND FOR THU...WITH WARM CLOUD DEPTHS IN THE
4KM RANGE. POTENTIAL FOR DEEP WARM RAIN PROCESS AND LOCALLY HEAVY
RAINS LATE TONIGHT/THU. WITH THE PASSING SHORTWAVES...ANY
CONVECTION SHOULD BE PROGRESSIVE. FAVORED A COMPROMISE OF MODEL
SOLUTIONS WITH A CONVECTIVE COMPLEX TRACKING ACROSS THE FCST AREA
THU...CENTERED ON ABOUT I-90...WITH RAIN TOTALS OF 1 TO 2 INCHES
APPEARING LIKELY. 1 HOUR FLASH FLOOD GUIDANCE IN THE 2 TO 2.8 INCH
RANGE WITH 3HR FLASH FLOOD GUIDANCE IN THE 2.5 TO 3.5 INCH
RANGE...SO NO FLASH FLOOD WATCH LATE TONIGHT THRU THU FOR NOW.
GIVEN THE TIMING...THE WARM CLOUD DEPTH AND COMPLEX LIKELY TO BE
ELEVATED...MAIN SEVERE THREAT LOOKS TO BE THE HEAVY RAINS WITH
MINIMAL HAIL OR WIND THREATS. CONVECTIVE DEBRIS CLOUDS AND THE
PRECIP TO LIMIT WARMING ON THU...WITH MAIN CAPE POOL AND BULK OF
BOUNDARY LAYER INSTABILITY REMAINING SOUTH OF THE FCST AREA. IF
NAM ENDS UP MORE CORRECT WITH MORE OF A WARM SECTOR INTO THE AREA
THU AFTERNOON...MAY BE MORE THAN A HEAVY RAIN THREAT WITH TSRA THU
AFTERNOON. GIVEN THE NORTH-SOUTH CONVECTION LOCATION DIFFERENCES
ON THU...MARGINAL SEVERE RISK PER SWODY2 OKAY FOR NOW. MID LEVEL
TROUGH AXIS AND SFC LOW PASS THU EVENING...TAKING THE DEEPER
MOISTURE/FORCING/LIFT EAST OF THE FCST AREA. CONTINUED TO TREND
FCST TOWARD DRY AFTER MIDNIGHT THU NIGHT AS THE SYSTEM EXITS AND
WEAK HIGH PRESSURE BUILDS IN. LIGHT WINDS...DECREASING CLOUDS AND
THE RAINS EXPECTED THU SET THE STAGE FOR FOG LATE THU NIGHT INTO
FRI MORNING. ADDED PATCHY FOG MENTION TO ENTIRE AREA FOR LATE THU
NIGHT INTO FRI MORNING. SOME OF THIS MAY END UP LOCALLY DENSE BUT
PLENTY OF TIME TO DETAIL THAT. DRY TREND FOR FRI LOOKS GOOD WITH
SHORTWAVE RIDGING AND WEAK SFC HIGH PRESSURE MOVING EAST ACROSS
THE REGION. PATTERN REMAINS PROGRESSIVE WITH THE NEXT SHORTWAVES
ACROSS THE PLAINS QUICKLY SPREADING A ROUND OF LOWER LEVEL
MOISTURE TRANSPORT/WARM ADVECTION/ISENTROPIC LIFT AND SHRA/TSRA
CHANCES BACK INTO THE AREA FOR FRI NIGHT. TRENDED TOWARD COOLER
OF GUIDANCE HIGHS THU THEN USED A BLEND OF THE GUIDANCE LOWS/HIGHS
FOR THU NIGHT THRU FRI NIGHT.
FOR SATURDAY THRU TUESDAY...DAYS 4 TO 7...
MEDIUM RANGE MODELS OF 15.00Z IN DECENT AGREEMENT ON SAT FOR
TROUGHING OVER THE NORTHWEST 1/3 OF THE CONUS AND RIDGING CENTERED
OVER THE LOWER MS VALLEY...LEAVING THE UPPER MIDWEST UNDER WEST TO
SOUTHWEST FLOW ALOFT AND WEAK WAVES RIPPING THRU THIS FLOW.
REASONABLE AGREEMENT FOR A PORTION OF THE NORTHWEST CONUS TROUGH
ENERGY TO COME EAST ACROSS THE NORTHERN PLAINS SUN...MOVING ACROSS
THE UPPER MIDWEST SUN NIGHT. TREND OF THIS MODEL SET FAVORS RISING
HGTS OR SHORTWAVE RIDGING OVER THE REGION MON WITH FALLING HGTS BY
TUE. HOWEVER...BETWEEN MODEL AND RUN-TO-RUN CONSISTENCY BY MON/TUE
IS LESS THAN DESIRABLE. FCST CONFIDENCE AVERAGE SAT/SUN THEN BELOW
AVERAGE MON/TUE.
WEST/SOUTHWEST FLOW ALOFT SAT...WITH POTENTIAL FOR SHORTWAVES TO BE
RIPPLING THRU THIS FLOW AND A WARM...MOIST AIRMASS OVER THE
REGION...CONSENSUS 20-40 PERCENT SHRA/TSRA CHANCES FOR SAT
REASONABLE. MID LEVEL TROUGH MOVING ACROSS THE NORTHERN PLAINS SAT
NIGHT THEN INTO THE REGION SUN SPREADS AN INCREASING LOWER LEVEL
MOISTURE AND ANOTHER ROUND OF STRONGER LOWER LEVEL THERMO-DYNAMIC
FORCING ACROSS THE AREA SAT NIGHT/SUN. SHRA/TSRA CHANCES LOOKING TO
CONTINUE THRU THE WEEKEND. CONTINUED SIGNAL FOR A RATHER WARM LOW
LEVEL AIRMASS OVER THE REGION SAT...SUPPORTING HIGHS IN THE MID 80S
TO AROUND 90. AIRMASS COOLS A BIT FOR SUN...BUT SUNDAY HIGHS ALSO
LIKELY TO BE TEMPERED BY MORE CLOUDS. MODEL CONSENSUS OF DRIER FOR
MON/TUE REASONABLE FOR NOW AS HIGH PRESSURE WOULD BUILD INTO/ACROSS
THE UPPER MIDWEST IN THE WAKE OF THE SFC THRU MID LEVEL TROUGH THAT
WOULD PASS SUN NIGHT. GIVEN AVERAGE CONFIDENCE AT BEST IN THE DAY 4-
7 PERIOD...STAYED WITH THE MODEL/ENSEMBLE CONSENSUS OF HIGHS/LOWS
THRU THE PERIOD.
&&
.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 635 AM CDT WED JUL 15 2015
THE MAIN CONCERN FOR THIS SET OF FORECASTS IS HOW FAST THE RAIN
MAY MOVE IN TONIGHT. A SHORT WAVE TROUGH OVER KANSAS AND NEBRASKA
THIS MORNING WILL MOVE NORTHEAST TOWARD THE AREA REACHING CENTRAL
MINNESOTA AND IOWA BY LATE TONIGHT. GOOD FORCING WITH THIS WAVE
WILL PRODUCE A WIDESPREAD AREA OF SHOWERS AND STORMS THAT MAY
AFFECT BOTH TAF SITES LATE TONIGHT. DIFFERENCES AMONG THE MESO
MODELS ON THE TIMING WITH THE 15.06Z NAM AND 15.00Z HI-RES NMM
MOVING THE LEADING EDGE OF THE CONVECTION INTO WESTERN WISCONSIN
BY 16.12Z. THE 15.00Z HI-RES ARW IS A SOUTHERN SOLUTION KEEPING
ALL THE CONVECTION SOUTH OF BOTH TAF SITES WHILE THE 15.06Z CR-NAM
NEST LOOKS TO BE A MORE MIDDLE OF THE GROUND SOLUTION AND HAVE
USED IT FOR TIMING. THUS WILL INTRODUCE A VCTS AT KRST STARTING AT
16.08Z AND AT KLSE AT 16.10Z. THE FORECAST SOUNDINGS FROM THE NAM
SUGGEST CONDITIONS SHOULD REMAIN VFR UNTIL IT HAS BEEN RAINING
FOR A FEW HOURS WITH MVFR AND EVEN IFR CONDITIONS POSSIBLE AFTER
16.12Z.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&
$$
SHORT TERM...RRS
LONG TERM....RRS
AVIATION...04
Delivered by Weather Underground Inc. Wed Jul 15 2015 7:35AM EDT