Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 151944
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
244 PM CDT WED OCT 15 2014

.SHORT TERM...(TONIGHT AND THURSDAY)
ISSUED AT 244 PM CDT WED OCT 15 2014

TALE OF TWO SIDES OF THE RIVER TONIGHT AS STACKED UPPER LOW
CONTINUES TO IMPACT GREAT LAKES AND OHIO VALLEY REGIONS WITH STRATUS
AND LIGHT RAIN. MEANWHILE SHORT TERM RIDGE HAS KEPT SKIES CLEAR OVER
MOST OF MINNESOTA AND IOWA WITH JUST SOME CIRRUS SPILLING INTO THE
UPPER MIDWEST. WESTERN EDGE OF CLOUDS AND HOW QUICKLY THAT MAY CLEAR
TONIGHT IS MAIN CHALLENGE...WHICH WILL HAVE IMMEDIATE IMPACT ON FOG
POTENTIAL AND OVERNIGHT LOWS.

AS IMPULSES AROUND UPPER LOW CONTINUE TO CREATE WOBBLE OR CLOUD EDGE
OSCILATIONS...QUESTION IS WILL EDGE PUSH EAST SINCE MODELS CONTINUE
TO SUGGEST LOW WILL MOVE EAST AS WELL TONIGHT BASED ON UPSTREAM
KICKER. RELATIVE HUMIDITY FIELDS...THAT SEEM TO BE TRACKING EDGE
WELL...ARE MORE BULLISH THOUGH...PERSISTING THROUGH MUCH OF THE
NIGHT IN WISCONSIN. WILL ACCOUNT FOR SOME CLEARING BUT SLOW THE
PROGRESS. THREAT FOR PRECIPITATION SEEMS MINIMAL BUT STRATUS COULD
STILL BE LINGERING IN MORNING...ESPECIALLY ACROSS CENTRAL WISCONSIN.

GIVEN THREAT FOR MORE CLOUDS ON WISCONSIN SIDE...HAVE LOWERED FOG
RISK A BIT TO PATCHY. 15.06Z SREF VISIBILITY PROBABILITIES SUGGEST
BEST RISK FOR FOG COULD BE CENTERED ALONG MISSISSIPPI RIVER VALLEY
REGION ON EDGE OF CLEARING. IF CLOUDS CLEAR QUICKER...FOG WOULD BE
MORE WIDESPREAD PER EARLIER FORECASTS.

SHORT WAVE TROUGH EJECTING OUT OF PACIFIC NORTHWEST...WHICH IS THE
UPSTREAM KICKER PREVIOUSLY MENTIONED...WILL MOVE INTO THE NORTHERN
STATES THURSDAY AND COULD CONTINUE TO SPREAD SOME MAINLY HIGH CLOUDS
IN FROM THE WEST. OTHERWISE SHOULD BE MUCH IMPROVED WITH HIGHS AT OR
SLIGHTLY HIGHER THAN SEASONAL NORMALS.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 244 PM CDT WED OCT 15 2014

SMALL RAIN THREATS WITH PASSING SHORT WAVE TROUGHS IN NORTHWEST FLOW
ARE EXTENT OF FORECAST CHALLENGES.

FIRST IMPULSE...MENTIONED IN SHORT TERM DICUSSION...COULD BRING A
THREAT FOR PASSING SHOWERS ON FRIDAY AND FRIDAY NIGHT...MAINLY ALONG
AND NORTHEAST OF INTERSTATE 94. BEST FORCING IS LIMITED NORTH AND
LIFT MAY NOT BE ENOUGH TO SATURATE AIRMASS FURTHER SOUTH. SOME
DIFFERENCES IN MEDIUM RANGE GUIDANCE WITH HOW FAR SOUTHWEST THREAT
COULD REACH BUT TOOK A CONSERVATIVE BLEND.

AS AMPLIFICATION IN UPPER FLOW BUILDS OUT WEST...ANOTHER SHORT WAVE
TROUGH DROPS INTO NORTHWEST FLOW ON SUNDAY BUT THIS SYSTEM APPEARS
MUCH WEAKER AND AGAIN WILL ONLY PRODUCE SMALL THREAT AS IT PASSES.

AFTER THAT 15.12Z GUIDANCE STILL HINTING AT UPPER RIDGE ESTABLISHING
OVER THE NATIONS MID SECTION. SHOULD MAKE FOR A QUIET SPELL EARLY
NEXT WEEK UNTIL RIDGE PASSAGE LEADS TO SOUTHWEST FLOW DEVELOPMENT
TOWARDS THE LATTER HALF.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1147 AM CDT WED OCT 15 2014

CLOUD COVER AND POTENTIAL FOR FOG DEVELOPMENT CONTINUE TO BE A
CHALLENGE. CURRENTLY...VISIBLE SATELLITE/SURFACE OBSERVATIONS
SHOWING AN EXPANSIVE FIELD OF STRATOCUMULUS ACROSS THE SOUTHEAST 1/2
OF WI AND ACROSS A SMALL PORTION OF SOUTHEAST MN AND EASTERN IA.
CEILINGS RANGED FROM IFR ACROSS EASTERN WI...TO VFR ALONG THE
MISSISSIPPI RIVER. THESE CLOUDS WERE ASSOCIATED WITH BROAD
CYCLONIC FLOW AROUND LOW PRESSURE EXTENDING FROM THE GREAT LAKES
INTO THE OHIO RIVER VALLEY REGION. THIS LOW IS EXPECTED TO CONTINUE
PUSHING EAST TONIGHT AS A RIDGE OF HIGH PRESSURE BUILDS INTO THE
AREA FROM THE PLAINS. THIS RIDGE LOOKS TO BE DIRECTLY OVER THE
MISSISSIPPI RIVER VALLEY REGION IN THE 06-12Z TIME FRAME...THEN EAST
OF THE MISSISSIPPI RIVER BY 12-15Z. THINKING THIS STRATOCUMULUS STAY
SCATTERED TO BROKEN MAINLY EAST OF THE MISSISSIPPI. THIS PRODUCES
SOME UNCERTAINTY ON FOG DEVELOPMENT. HOWEVER...GIVEN VERY MOIST
CONDITIONS FROM RECENT RAINFALL...WOULD TAKE MUCH TO PRODUCE IFR
FOG/STRATUS IF CLOUDS DO INDEED SCATTER OUT. FOR NOW...WENT WITH A
TEMPO 1SM BR BKN003 AT KLSE IN THE 11-13Z TIME FRAME. AT
KRST...PROBLEM WILL ALSO BE INCREASING SOUTH WINDS AFTER MIDNIGHT
WHICH COULD HOLD BACK GOOD FOG DEVELOPMENT. IN ADDITION...LOOKS LIKE
SOME DRYING TAKING PLACE TODAY WITH FULL SUNSHINE AND BREEZY
NORTHWEST WINDS. FOR THE 18Z KRST TAF...WENT WITH A 4SM BR SCT020
CONDITION IN THE 08-15Z TIME FRAME. THIS FORECAST WILL HAVE TO
MONITORED CLOSELY.

&&

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

$$

SHORT TERM...SHEA
LONG TERM...SHEA
AVIATION...DAS



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