Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 290433
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1130 PM CDT FRI AUG 28 2015

.SHORT TERM...(TONIGHT THRU SATURDAY NIGHT)
ISSUED AT 300 PM CDT FRI AUG 28 2015

MAIN FCST CONCERNS THIS PERIOD...RAIN/RAIN CHANCES EXITING
TONIGHT...CLOUDS SATURDAY...VALLEY FOG POTENTIAL LATE SAT NIGHT.

DATA ANALYSIS AT 18Z HAD LOW PRESSURE CENTERED OVER WEST-CENTRAL
IA...MOVING SLOWLY BUT STEADILY EAST. WV IMAGERY DEPICTED A RATHER
VIGOROUS MID/UPPER LEVEL CIRCULATION MOVING EAST ACROSS IA. MOISTURE
TRANSPORT AND LOWER LEVEL THERMODYNAMIC FORCING/LIFT AHEAD OF/UNDER
THESE FEATURES AND THE DIVERGENCE ALOFT PRODUCING A BROAD AREA OF
LIGHT TO MDT RAIN OVER MUCH OF WI/SOUTHEAST MN AND NORTHEAST IA. FEW
TSRA ACROSS NORTH-CENTRAL IA IN THE STRONGEST/DEEPEST OF THE LIFT.
TEMPS ON THE COOL SIDE UNDER THE CLOUD/RAIN SHIELD AHEAD OF THE SFC-
MID LEVEL LOW...WITH WARMER TEMPS IN THE REGION TODAY OVER CENTRAL/
NORTHERN MN WITH SOME SUNSHINE.

28.12Z MODELS INITIALIZED WELL FOR THE MOST PART. HOWEVER GFS WAS 3F-
5F TOO LOW WITH SFC DEW POINTS OVER THE WEST 1/2 OF THE REGION AND
THAT MUCH OR MORE TOO HIGH WITH SFC DEW POINTS OVER EASTERN WI/IL.
MODELS IN GOOD AGREEMENT AS THE TROUGH/SHORTWAVE BRINGING RAIN TO
MUCH OF THE AREA TODAY WEAKENS AND MOVES EAST OF AREA TONIGHT. TREND
FAVORS FASTER OF THE EARLIER MODELS WITH THE TROUGH CONTINUING TO
EXITING EAST SAT AND WITH THE RIDGING ALOFT BUILDING IN BEHIND IT
SAT/SAT NIGHT. SHORT-TERM FCST CONFIDENCE IS GOOD THIS CYCLE.

IN THE SHORT TERM...BULK OF THE MID/UPPER LEVEL ENERGY WITH THE MAIN
SHORTWAVE MOVES EAST OF THE AREA BY 06Z. HOWEVER WITH THE SFC-850MB
LOW/TROUGH AXIS MOVING INTO THE WEST SIDE OF THE FCST AREA AROUND
06Z...SOME SFC THRU ABOUT 750MB THERMODYNAMIC FORCING/LIFT AND
MOISTURE TRANSPORT CONTINUE OVER AT LEAST THE SOUTHEAST 2/3 OF THE
FCST AREA TO ABOUT 09Z. THIS AIDED BY A SECONDARY/NORTHERN STREAM
SHORTWAVE NOW SET TO MOVE SOUTH ACROSS THE AREA LATE TONIGHT/EARLY
SAT MORNING. CONTINUED THE DOWNWARD TREND OF RAIN CHANCES ACROSS THE
NORTHWEST 1/2 OF THE FCST AREA THIS EVENING WHILE RAISED EVENING
RAIN CHANCES ACROSS MUCH OF THE SOUTHEAST HALF. LINGERED A BIT MORE
RAIN CHANCE ACROSS THE SOUTHEAST 1/2 OF THE FCST AREA IN THE 06-09Z
PERIOD...THEN DIMINISHED/ENDED THEM WITH PASSAGE OF LOWER LEVEL
TROUGH AXIS 09-15Z. WITH MINIMAL TO NO CAPE...AND THE FORCING/LIFT
SLOWLY WANING...LIMITED ISOLATED TSRA MENTION TO THE EVENING HOURS.
DRY AFTER 15Z SAT AND SAT NIGHT WITH RISING HGTS/HIGH PRESSURE
BUILDING IN BEHIND THE DEPARTING TROUGH. THE 850MB CIRCULATION
REMAINING JUST SOUTHEAST OF THE AREA SAT...AND MODEL SOUNDINGS
SHOWING MOISTURE TRAPPED UNDER AN INVERSION NEAR 900MB. LOWER CLOUDS
IN THE WAKE OF THE SYSTEM MAY BE SLOW TO CLEAR ON SAT...ESPECIALLY
OVER THE SOUTHEAST 1/3 TO 1/2 OF THE FCST AREA. WILL REMAIN
OPTIMISTIC THAT DIURNAL WARMING/MIXING WILL WORK TO ERODE THE CLOUDS
THRU THE AFTERNOON. SFC RIDGE AXIS NEARBY/OVERHEAD...LIGHT THRU THE
LOWER 2KM OF THE COLUMN...CLEAR/MOSTLY CLEAR SKIES AND THE RECENT
RAINS...LATE SAT NIGHT/EARLY SUN MORNING APPEARING VERY FAVORABLE
FOR RADIATIONAL VALLEY FOG FORMATION. FOR NOW ADDED PATCHY TO AREAS
OF FOG IN THE RIVER VALLEYS AND FOG-PRONE LOW LAYING AREAS AFTER 06Z
SAT NIGHT TO 14Z SUN MORNING. PLENTY OF TIME TO DETAIL THIS ONE THE
CURRENT SYSTEM EXITS. USED A BLEND OF THE GUIDANCE LOWS/HIGHS FOR
TONIGHT THRU SAT NIGHT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 300 PM CDT FRI AUG 28 2015

FOR SUNDAY THRU MONDAY NIGHT...

MAIN FCST CONCERNS THIS PERIOD...LATE NIGHT/EARLY MORNING VALLEY
FOG... TEMPERATURES.

28/12Z MODELS IN GOOD AGREEMENT ON RISING HGTS/RIDGING ALOFT TO
CONTINUE BUILDING INTO THE UPPER MIDWEST SUN/SUN NIGHT. TREND AT 12Z
MON IS TOWARD THE LESS ROBUST OF THE EARLIER MODELS WITH THE
RIDGING/HGTS OVER THE REGION. GOOD CONSENSUS FOR THE MID LEVEL RIDGE
AXIS TO QUICKLY PUSH EAST OF THE REGION FOR MON/MON NIGHT. THIS
RESULTS IN MORE BROAD SOUTHWEST FLOW ALOFT AS SOME OF THE ENERGY
EJECTS OUT OF THE NORTHWEST CONUS TROUGHING AND ACROSS THE NORTHERN
PLAINS...WITH SOME LOWERING OF HGTS OVER THE REGION BY 12Z TUE.
GIVEN THE REASONABLE MODEL CONSENSUS...FCST CONFIDENCE IN THE SUN
THRU MON NIGHT PERIOD GENERALLY REMAINS GOOD THIS CYCLE.

SUN THRU MON NIGHT CONTINUES TO SHAPE UP AS A DRY/QUIET/WARMING
PERIOD UNDER THE RIDGING ALOFT BUILDING ACROSS THE REGION. SOUTHWEST
LOWER LEVEL FLOW BETWEEN LEE TROUGHING IN THE WESTERN/NORTHERN
PLAINS AND HIGH PRESSURE OVER THE EASTERN CONUS RETURNS WARMER AND
MOIST AIR NORTHEAST ACROSS THE UPPER MIDWEST SUN THRU MON NIGHT.
925MB TEMPS IN THE 20C-24C RANGE BY 00Z MON AND 23C TO 27C RANGE BY
00Z TUE. HIGHS LOOKING TO BE NEAR NORMAL SUN THEN ABOVE NORMAL MON.
MODELS DO TRY TO BRING A WEAKENING TROUGH/FRONT INTO MN MON...BUT
BULK OF MOISTURE TRANSPORT AND FORCING AHEAD OF/ALONG THIS FRONT
REMAINS WELL WEST/NORTH OF THE FCST AREA. OTHERWISE...BROAD RIDGING
NORTHWEST OF THE HIGH CENTERED OVER THE APPALACHIANS HOLDS OVER THE
AREA FOR SUN THRU MON NIGHT. WITH LIGHT WINDS THRU A GREATER DEPTH
OF THE COLUMN...MOSTLY CLEAR/CLEAR SKIES AND THE MOIST LOWER LEVEL/
BOUNDARY LAYER AIRMASS...WILL HAVE TO WATCH FOR VALLEY/LOW LAYING
AREA FOG DEVELOPMENT AGAIN LATE SUN NIGHT/MON MORNING. DID NOT AT
THIS TO THE FCST GRIDS AT THIS POINT. APPEARS STRONGER WINDS JUST
ABOVE THE NOCTURNAL INVERSION WOULD LIMIT RADIATIONAL FOG POTENTIAL
LATER MON NIGHT/EARLY TUE MORNING. TRENDED TOWARD WARMER OF GUIDANCE
HIGHS SUN/MON AND USED THE MODEL CONSENSUS LOWS FOR SUN/MON NIGHTS.

FOR TUESDAY THRU FRIDAY...DAYS 4 TO 7...

MAIN FCST CONCERNS THIS PERIOD...WARM TEMPERATURES...POTENTIAL SMALL
SHRA/TSRA CHANCES MOST OF THE PERIOD.

MEDIUM RANGE MODEL RUNS OF 28.00Z/28.12Z IN PRETTY GOOD AGREEMENT
FOR RIDGING ALOFT OVER EASTERN NOAM AND TROUGHING OVER WESTERN NOAM
TUE/WED...WITH THE RIDGE AXIS WELL EAST OF THE UPPER MIDWEST. TREND
IS FOR A LITTLE FLATTER RIDGING OVER THE REGION TUE/WED...WITH
SHORTWAVE ENERGY COMING OUT OF THE WESTERN CONUS TROUGH RIPPLING
TROUGH THRU THE FLOW. REASONABLE AGREEMENT FOR THE FLOW TO AMPLIFY
AND THE RIDGE AXIS TO RETROGRADE TO BE OVER THE WESTERN GREAT LAKES
THU/FRI. FCST CONFIDENCE IN THE DAY 4-7 PERIOD REMAINS GOOD FOR
ABOVE NORMAL TEMPERATURES BUT IS BELOW NORMAL WITH THE SMALL SHRA/
TSRA CHANCES.

WITH SFC HIGH PRESSURE OVER THE OH VALLEY AND LEE TROUGHING IN THE
CENTRAL/NORTHERN PLAINS MOST OF THE PERIOD...THE AREA REMAIN UNDER
DEEP LAYERED SOUTHWEST FLOW. AIRMASS OVER THE REGION IN THIS FLOW
PROGGED TO BE RATHER MOIST /PW VALUES 1-2 STD DEVIATIONS ABOVE
NORMAL/...WITH 500-2K J/KG MUCAPE OVER MUCH OF THE UPPER MIDWEST
DURING THE AFTERNOONS. THIS WITH A FEW WEAKER AND DIFFICULT TO TIME
SHORTWAVES TO RIPPLE THRU THE SOUTHWEST FLOW ALOFT AND ACROSS
IA/MN/WI THRU THE PERIOD. DEPENDING ON HOW MUCH CIN THERE MAY BE
ANY ONE AFTERNOON...CANNOT RULE OUT THE WEAK SHORTWAVES BRINGING
AT LEAST SMALL CHANCES OF SHRA/TSRA TO THE AREA ON ANY OF THE DAYS.
ALSO POTENTIAL FOR ONE OF THE WAVES TO INITIATE A CONVECTIVE
COMPLEX WELL NORTHWEST OF THE FCST AREA ONE OR MORE EVENINGS...
WITH CORFIDI VECTORS INDICATING POTENTIAL FOR ANY COMPLEXES TURN
AND TRACK SOUTHEAST ACROSS THE REGION AS THEY MATURE OVERNIGHT.
NOT MUCH FOR CONFIDENCE IN THE DETAILS NEXT WEEK BUT NUMEROUS
SMALL SHRA/TSRA CHANCES PER THE MODEL CONSENSUS OKAY FOR NOW. MORE
CONSISTENT SIGNAL FOR 925MB TEMPS THIS PERIOD TO BE IN THE 24C TO
28C RANGE...SUPPORTING HIGHS IN THE MID 80S TO AROUND 90...SOME
10F-15F ABOVE NORMAL. AGAIN RAISED HIGHS FRO TUE-FRI A BIT OVER
THE CONSENSUS BLEND...MAINLY IN THE RIVER VALLEYS. CONSENSUS BLEND
OF THE GUIDANCE LOWS CONTINUES TO LOOK WELL TRENDED.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1130 PM CDT FRI AUG 28 2015

RAIN HAS MOVED EAST...AND FORECAST FOCUS TURNS TO LOWER CIGS/VSBY.
SUB 1KFT CLOUD LAYER HAS DEVELOPED NORTH/WEST OF A SFC LOW OVER
SOUTHERN IA...AND MESO MODELS ARE ADAMANT THAT THIS ADVANCES
NORTHWARD ACROSS THE TAF SITES BY OR SHORTLY AFTER 06Z. LATEST
FOG/STRATUS SATELLITE IMAGERY DOES SHOW A SLOW PUSH NORTH. IN
ADDITION...SOME FOG WITH THE LOW STRATUS...WITH CURRENT TRENDS
SUGGESTING MVFR. HOWEVER...SOME OF THE MODELS SUGGEST THERE COULD BE
SUB 1SM FOG. NOT SOLD ON THIS...AND WILL CONTINUE THE MVFR BR FOR
NOW. THE LOWER CIGS WILL HOLD THROUGH SAT MORNING...WITH SOME
INCREASING HEIGHTS/BREAKING UP INDICATED VIA BUFKIT SOUNDINGS LATER
IN THE AFTERNOON.

WITH CLEAR SKIES EXPECTED SAT NIGHT...LIGHT DEEP WIND FIELD...AND A
RECENTLY SATURATED GROUND...AREAS OF FOG...ESPECIALLY IN THE RIVER
VALLEYS...ARE LIKELY FOR SUNDAY MORNING. PRETTY GOOD SETUP FOR 1/4SM
AT KLSE AND PROBABLY AT LEAST 2-3SM FOR KRST. SOMETHING TO WATCH.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION.....RIECK


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