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