Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 151053
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
553 AM CDT MON SEP 15 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 325 AM CDT MON SEP 15 2014

LATEST WATER VAPOR SATELLITE IMAGERY SHOWING VIGOROUS SHORTWAVE
TROUGH OVER THE DAKOTAS. 15.00Z UPPER AIR ANALYSIS INDICATES
STRONG JET CORE AT 300MB ACROSS EASTERN DAKOTAS INTO THE GREAT
LAKES REGION. LATEST MOSAIC RADAR SHOWS LIGHT RAIN EXPANDING
ACROSS SOUTHERN MINNESOTA...EASTERN SOUTH DAKOTA AND CENTRAL
WISCONSIN. THIS IS IN RESPONSE TO LIFT IN THE VICINITY OF THE
RIGHT ENTRANCE OF THE 300MB JET...STRONG PV ADVECTION AND DEEP QG
FORCING PER LATEST 15.00Z NAM/GFS/RAP.

MAIN FORECAST CONCERN TODAY IS MOVING THE PRECIPITATION OUT OF
THE FORECAST AREA TODAY...THEN FOG POSSIBILITIES IN RIVER VALLEYS
AND PATCHY FROST OVER CENTRAL WISCONSIN TONIGHT.

THE LATEST 15.00Z GFS/NAM ARE IN DECENT AGREEMENT IN TRACKING THE
SHORTWAVE TROUGH AND THE ASSOCIATED LIFT/FORCING/MOISTURE EAST OF
THE AREA BETWEEN 18-21Z TODAY. THIS IS IN GOOD AGREEMENT WITH THE
LATEST COMPOSITE REFLECTIVITY FROM THE MESO MODELS OF THE
HRRR/NAMNEST/ARW/NMM IN PUSHING PRECIPITATION EAST OF THE AREA
AROUND 19Z TODAY. HAVE ADJUSTED PRECIPITATION TRENDS AND SKY
CONDITION FOR THIS.

TONIGHT...THE LATEST 15.00Z GFS/NAM/ECMWF PROG SURFACE RIDGE OVER
THE WESTERN DAKOTAS TO BUILD INTO THE FORECAST AREA. LIGHT WINDS AND
CLEAR SKIES WILL ALLOW FOR A GOOD RADIATIONAL COOLING NIGHT. THE
15.00Z GFS/NAM BUFKIT SOUNDINGS SHOW WINDS LESS THAN 10 KNOTS BELOW
1500 FEET AFTER 06Z IN RIVER VALLEYS. THIS WILL ALLOW THE FORMATION
OF PATCHY FOG IN RIVER VALLEYS AND PARTS OF CENTRAL WISCONSIN.
ALSO...WITH LOW TEMPERATURES DROPPING INTO THE MIDDLE 30S ACROSS CENTRAL
WISCONSIN...PATCHY FROST WILL BE POSSIBLE.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 325 AM CDT MON SEP 15 2014

WITH THE SURFACE RIDGE DOMINATING THE FORECAST AREA TUESDAY AND INTO
WEDNESDAY MORNING. AREAS TO PATCHY FOG IS EXPECTED TO FORM
AFTER 06Z WEDNESDAY IN RIVER VALLEYS AND PARTS OF CENTRAL WISCONSIN.

THE LATEST 15.00Z GFS/NAM/ECMWF ARE CONSISTENT IN MOVING A WEAK
FRONT NORTH TO SOUTH ACROSS CENTRAL WISCONSIN WEDNESDAY
AFTERNOON/EVENING. THE MODELS SHOW WEAK 850MB THETA E CONVERGENCE IN
ASSOCIATION WITH THIS FRONT AND THE 15.00Z GFS/NAM GENERATE VERY
LIGHT QPF OVER CENTRAL WISCONSIN BY 00Z THURSDAY. POTENTIAL IS
THERE FOR MAYBE SPRINKLES OR VERY LIGHT RAIN SHOWERS.
HOWEVER...WITH THE BUFKIT SOUNDINGS SHOWING VERY SHALLOW MOISTURE
WILL CONTINUE TO LEAVE FORECAST DRY.

FOCUS THEN SHIFTS TO THURSDAY NIGHT INTO SATURDAY...AS THE 15.00Z
GFS/ECMWF/GEM INDICATE UPPER LEVEL RIDGE BREAKING DOWN AND DEVELOP
WEST TO EAST ZONAL FLOW ALOFT ACROSS THE NORTHERN TIER STATES. THE
BIGGEST DIFFERENCE BETWEEN THE MODELS WILL BE TIMING AND PLACEMENT
OF THE SHORTWAVE TROUGHS/SURFACE FEATURES ACROSS THE UPPER MIDWEST
AND GREAT LAKES REGION FRIDAY INTO FRIDAY NIGHT. THE LATEST 15.00Z
GFS/ECMWF/GEM ARE IN GOOD AGREEMENT IN INCREASING MOISTURE INTO THE
FORECAST AREA WITH DECENT MOISTURE TRANSPORT AT 925-850MB THAT
WILL PRODUCE HIGHER PRECIPITABLE WATER VALUES. THE LATEST 15.00Z
GFS ALSO SHOWS ENOUGH SHEAR AND SURFACE/ELEVATED INSTABILITY OVER
PORTION OF THE FORECAST AREA FRIDAY INTO FRIDAY NIGHT THAT COULD
LEAD A FEW OF THE THUNDERSTORMS TO POSSIBLY BE SEVERE. CONFIDENCE
IN THE EXACT PLACEMENT AND TIMING OF ANY OF THE THUNDERSTORMS AT
THIS TIME REMAINS LOW.

THE GREAT LAKES REGION REMAINS UNDER THE INFLUENCE OF THE UPPER
LEVEL TROUGH AND CYCLONIC FLOW SATURDAY INTO SUNDAY...PER THE 15.00Z
GFS/ECMWF. WILL CONTINUE TO LINGER SMALL PRECIPITATION CHANCES
ACROSS THE FORECAST AREA.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 552 AM CDT MON SEP 15 2014

WEATHER SYSTEM WITH EXCELLENT LIFT IS CURRENTLY MOVING ACROSS THE
TAF SITES. MOISTURE FOR RAIN IS NOT ABUNDANT AND OBSERVATIONS ARE
MAINLY VFR UNDER RADAR ECHO WHICH STRETCHES WEST TO KFSD-KMPX. AS
SHRA CONTINUE AT TAF SITES...SLOW CLOUD BASE LOWERING IS EXPECTED.
IT IS DIFFICULT TO SAY HOW LOW THE CIGS/VSBYS WILL GET IN THE
SHRA...BUT IT SEEMS THE PROBABILITIES PER CURRENT OBSERVATIONS IN
SRN MN AND RADAR ECHOES WOULD SAY VFR WILL PREVAIL FOR THIS
SYSTEM. CANNOT RULE OUT SOME JUST-MVFR CONDITIONS...BUT HAVE
DECIDED TO ONLY TEMPO THESE AT THE AIRFIELDS. IN EITHER CASE...IT
SHOULD BE LOW IMPACT TO AVIATION.

HAVE INCLUDED SOME FOG MENTION AT KLSE TUESDAY MORNING. CONFIDENCE
IS LOW ON THIS FOG BUT WITH RAIN TODAY...COOLER TEMPERATURES...AND
CLEARING...THE STAGE IS SET FOR FOG DEVELOPMENT. LIGHT WIND FLOW
IS SHALLOW ABOVE THE RIVER VALLEYS...AND WOULD LIKE TO SEE LIGHTER
WINDS IN A DEEPER LAYER TO REDUCE VSBYS MORE AT KLSE. BUT, KLSE
DOES HAVE A FEW ITEMS THAT WILL PROMOTE AIRFIELD FOG.

&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...BAUMGARDT



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