Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 231033
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
530 AM CDT WED JUL 23 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 257 AM CDT WED JUL 23 2014

QUIET REGIME FOR SHORT TERM IN NORTHWEST UPPER FLOW AND SURFACE
RIDGE BUILDING INTO WESTERN GREAT LAKES. DRIER AIR CONTINUES TO
FUNNEL IN BUT AS WINDS LIGHTEN UP TOWARDS SUNRISE...COULD STILL SEE
SOME SHORT LIVED FOG FORM IN PARTS OF CENTRAL AND NORTH CENTRAL
WISCONSIN. OTHERWISE JUST SOME DEBRIS CIRRUS AND GENERALLY QUIET
CONDITIONS.

WITH RIDGE AXIS AND SURFACE HIGH SETTLING IN LATER TODAY AND
TONIGHT...EXPECT SOME DIURNAL CUMULUS TODAY AND MOSTLY CLEAR SKIES
TONIGHT WITH LIGHT/CALM WINDS. THIS COULD LEAD TO VALLEY FOG IN
FAVORED AREAS...ALONG WITH COOL READINGS IN FAVORED LOW/BOG
LOCATIONS IN WISCONSIN.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 257 AM CDT WED JUL 23 2014

FOCUS IN LATER PERIODS CENTERS ON RAIN THREATS AS UPPER LOW MOVES UP
INTO SOUTHERN CANADA AND THEN DROPS INTO GREAT LAKES THROUGH NEXT 5
TO 6 DAYS. MOST POTENT WEATHER COULD BE EARLY ON IN THIS PROCESS
WITH POSSIBLE MCS THURSDAY NIGHT.

ON THURSDAY...AS SHORT WAVE RIDES ACROSS NORTHERN PLAINS...LOW LEVEL
WARM AIR ADVECTION AND MOISTURE TRANSPORT WILL INITIALLY FOCUS WEST
OF AREA...BUT SHIFT INTO OUR REGION THURSDAY NIGHT AS FORCING
FOCUSES MORE ON SOUTHERN MINNESOTA...NORTHERN IOWA AND INTO WESTERN
WISCONSIN. THIS WILL LIKELY DRIVE ELEVATED CONVECTION WITH MOST
LIKELY TRACK ACROSS MAINLY NORTHEAST IOWA HEADING INTO EARLY FRIDAY
MORNING. SOME QUESTION ON TIMING BUT FAIRLY GOOD GUIDANCE
CONSISTENCY WITH THIS SOLUTION...ESPECIALLY WITH 23/00Z NAM/ECMWF.
SOME 0-3KM SHEAR TO WORK WITH BUT STORMS SHOULD BE ELEVATED IN
NATURE AND FAIRLY PROGRESSIVE WITH HEAVY RAIN AND WIND THREATS. SEE
TEXT HIGHLIGHTED IN SPC DAY 3 OUTLOOK HAS GOOD DISCUSSION ON SET UP.
HAVE RAISED RAIN THREATS AND QPF VALUES FOR THURSDAY NIGHT/FRIDAY
MORNING TO ACCOUNT FOR HIGHER CONFIDENCE IN THIS SCENARIO.

THINGS GET A BIT MORE DIFFUSED FOR FRIDAY AND BEYOND. LOW LEVEL
FORCING DIMINISHES QUITE A BIT AFTER FRIDAY MORNING SO CONFIDENCE
DROPS AS MEDIUM RANGE GUIDANCE GETS MUCH MORE DIVERSE. WHILE THERE
COULD BE SOME MINOR SHORT WAVE TROUGHS THAT EJECT AHEAD OF MAIN
UPPER LOW AND TRIGGER A BIT MORE CONVECTION LATER FRIDAY INTO FRIDAY
NIGHT...UNSURE HOW EXPANSIVE THAT WOULD BE. AT SOME POINT EXPECT TO
BE IN BETWEEN THE BETTER LOW LEVEL FORCING TO THE EAST AND UPPER LOW
APPROACHING FROM THE NORTHWEST. THIS COULD HAPPEN ON SATURDAY AS
WARM SECTOR LIKE DRYING TAKES PLACE WITH WEST WINDS AND SEASONAL
TEMPERATURES.

LATTER HALF OF WEEKEND INTO EARLY NEXT WEEK WILL BE FOCUSED BY
PASSAGE OF UPPER LOW WITH PERIODIC SHOWERS EXPECTED. HAVE LOWERED
THUNDERSTORM CHANCES WITH COOLER AIR AND LIMITED CAPE. EXPECT MAINLY
SHOWERS WHICH COULD HOLD DOWN HIGH TEMPERATURES LOWER THAN
PREDICTED. LOW COULD BE FAR ENOUGH EAST BY MONDAY TO KEEP RAIN
THREAT EAST AND ALLOWING SOME MODERATION IN TEMPERATURES.
&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 530 AM CDT WED JUL 23 2014

EXPECT VFR CONDITIONS INTO TONIGHT...AS THE REGION COMES UNDER THE
INFLUENCE OF HIGH PRESSURE. THAT SAID...A WEAK RIPPLE IN THE UPPER
LEVEL FLOW COULD SPARK SCT-BKN 4-6KFT LATE THIS MORNING-AFTERNOON.

AVIATION CONCERNS TURN TO THE POTENTIAL FOR VALLEY FOG AT KLSE FOR
EARLY THU MORNING. SFC WINDS WILL DECOUPLE QUICKLY...STAYING LIGHT
THROUGH THE NIGHT. DIRECTION COULD BE VARIABLE...BUT MORE FROM THE
SOUTHEAST...A FAVORABLE DIRECTION. THE DEPTH OF THE LIGHT WIND LAYER
EXTENDS UPWARDS OF 5 KFT...WITH WEAK SUBSIDENCE THROUGH THE COLUMN.
BOTH CONDUCIVE FOR DENSE FOG FORMATION. THE MAIN QUESTION WILL BE
HOW MUCH MIXING-DRYING OUT OF THE DEWPOINTS WILL OCCUR THIS
AFTERNOON...AND IF THE T/TD SPREAD CAN BE OVERCOME TONIGHT.
CLIMATOLOGICALLY ITS NOT A FAVORED TIME OF THE YEAR EITHER...WITH
LESS HOURS OF DARK FOR RADIATIONAL COOLING. ALL SAID...MOST
VARIABLES SAY YES TO DENSE FOG AND WILL ADD IN BCFG FOR NOW. LATER
FORECASTS SHOULD BE ABLE TO DETERMINE IF T/TD SPREAD WILL BE CLOSE
ENOUGH FOR FG TO BE LIKELY. IF IT DEVELOPS...PROBABLY WOULDN/T LAST
PAST 13-14Z.

&&

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

$$

SHORT TERM...SHEA
LONG TERM....SHEA
AVIATION.....RIECK


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