Area Forecast Discussion
Issued by NWS La Crosse, WI

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KARX 260439
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1139 PM CDT THU SEP 25 2014

.SHORT TERM...(TONIGHT THROUGH FRIDAY NIGHT)
ISSUED AT 230 PM CDT THU SEP 25 2014

MAIN FORECAST CONCERNS THIS PERIOD...CLOUDS AND TEMPERATURES.

DATA ANALYSIS AT 18Z HAD BROAD HIGH PRESSURE CENTERED OVER NEW
ENGLAND WITH RIDGING WEST TO THE GREAT LAKES AND SOUTHERN PLAINS.
A LEE LOW WAS DEVELOPING OVER MT. WV IMAGERY SHOWED A SHORTWAVE
MOVING SOUTHWEST OVER EASTERN IA...AS STRONG RIDGING WAS BUILDING
ACROSS THE NORTHERN PLAINS/SOUTH-CENTRAL CAN. WV IMAGERY ALSO
SHOWED AN IMPRESSIVE TROUGH OFF THE WEST COAST...WITH RARE TSRA
IN THE BASE OF THE TROUGH OFF THE NORTHERN CA COAST.
MIXING/SUBSIDENCE UNDER THE BUILDING RIDGING WORKING ON THE MID
CLOUD DECKS ACROSS THE REGION... SKIES BECOMING PARTLY TO MOSTLY
SUNNY ACROSS MUCH OF MN/IA/WI EARLY THIS AFTERNOON. TEMPS IN MANY
OF THE SUNNY AREAS RESPONDING INTO THE MID/UPPER 70S.

25.12Z MODELS GENERALLY INITIALIZED QUITE WELL...EXCEPT FOR GFS
ABOUT 5F TOO HIGH ON SFC DEW POINTS ACROSS MUCH OF THE UPPER MS
VALLEY. MODELS STRUGGLING A BIT TO CAPTURE THE DETAIL IN THE
SHORTWAVE ENERGY DROPPING SOUTHWEST ACROSS IA BUT ALL HAVE THE
GENERAL IDEA. MODELS IN GOOD AND IMPROVING AGREEMENT TONIGHT THRU
FRI NIGHT AS STRONG LONGWAVE RIDGING BUILDS OVER THE NORTH-CENTRAL
CONUS. IMPROVING AGREEMENT AS THIS RIDGING DRIVES/PUSHES THE
SHORTWAVE ENERGY SOUTHWEST ACROSS IA AND DEVELOPS A MID LEVEL LOW
WHICH RETROGRADES TO SOUTHWEST IA BY LATE FRI THEN STARTS TO LIFT
NORTH FRI NIGHT. TREND FAVORS A TIGHTER COMPROMISE OF THE EARLIER
RUNS WITH THIS FEATURE. SHORT-TERM FCST CONFIDENCE REMAINS GOOD...
FOR WHAT CONTINUES TO SHAPE UP AS A DRY/QUIET/MILD PERIOD.

IN THE SHORT TERM...WITH THE WEAK DEVELOPING MID LEVEL LOW OVER
IA...AREA REMAINS UNDER CYCLONIC FLOW ALOFT THRU FRI NIGHT. HOWEVER
THIS TRENDS TO BE A NON FACTOR WITH MODEL SOUNDINGS AND X-SECTIONS
SHOWING A DRY AIRMASS ABOVE 700MB AND SFC-850MB HIGH PRESSURE/
RIDGING OVER THE AREA THRU THE PERIOD. MODEL SOUNDINGS SHOW A
CONTINUED DECREASE OF 850-700MB RH/MOISTURE OVER THE AREA TONIGHT.
WITH THE 5K-8K FT CLOUDS ACTUALLY BREAKING/ DISSIPATING TODAY...
CONTINUED THE TREND OF SKIES MOSTLY CLEAR TO PARTLY CLOUDY OVER MUCH
OF THE AREA TONIGHT. LIGHT WINDS/MOSTLY CLEAR SKIES...A RATHER MOIST
BOUNDARY LAYER AND WINDS GENERALLY LESS THAN 10KTS THRU 800MB
TONIGHT WILL RESULT IN PATCHY DENSE FOG IN THE VALLEYS/LOW LAYING
AREAS FOG LATE TONIGHT/EARLY FRI MORNING. THIS WELL TRENDED IN
THE GRIDSET AT THIS TIME. MODEST MOISTURE AROUND 850MB REMAINS
OVER THE AREA FRI/FRI NIGHT. DIURNAL WARMING/MIXING EXPECTED TO
PRODUCE DIURNAL CUMULUS IN THE 17- 00Z PERIOD FRI. MOSTLY CLEAR
SKIES EXPECTED AGAIN FRI NIGHT. SFC WINDS REMAIN LIGHT FRI NIGHT
BUT WINDS ABOVE THE BOUNDARY LAYER MORE IN THE 10-20KT RANGE...NOT
AS FAVORABLE FOR THE LATE NIGHT RADIATIONAL FOG DEVELOPMENT. LEFT
LATE FRI NIGHT/EARLY SAT MORNING FOG MENTION OUT OF GRIDS FOR NOW.
MODEL SOUNDINGS SHOW MIXING TO NEARLY TO 850MB FRI. 925-850MB
TEMPS SUPPORT HIGHS WELL INTO THE 70S FOR MOST LOCATIONS ON FRI.
MODEL/ENSEMBLE CONSENSUS OF LOWS/HIGHS FOR TONIGHT-FRI NIGHT LOOK
GOOD.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 230 PM CDT THU SEP 25 2014

FORECAST CONCERNS FOR SAT THRU SUN NIGHT REMAIN TEMPERATURES AND
CLOUDS.

25.12Z MODELS OFFER AN IMPROVING CONSENSUS FOR THE WEAK MID LEVEL
LOW TO LIFT NORTH INTO SOUTHWEST MN SAT...THEN OPEN UP AND DRIFT
EAST SAT NIGHT THRU SUN NIGHT...MOVING EAST OF THE REGION BY SUN
NIGHT. THIS A MORE PROGRESSIVE CONSENSUS THAN THE EARLIER RUNS.
GIVEN THE TIGHTER CONSENSUS...FCST CONFIDENCE IN THE SAT THRU SUN
NIGHT PERIOD IS GOOD FOR WHAT ALSO SHAPES UP TO BE A DRY/QUIET/
MILD LATE SEPT PERIOD.

WEAK MID LEVEL LOW LIFTING NORTH SAT THEN OPENING UP AND MOVING EAST
SAT NIGHT THRU SUN NIGHT GENERALLY REMAINS A NON-FACTOR WITH MODEL
SOUNDING AND X-SECTION SHOWING THE 700-400MB PORTION OF THE COLUMN
TO BE QUITE DRY. MODEST MOISTURE REMAINS IN THE SFC-700MB LAYER...
FOR WHAT SHOULD RESULT IN SOME SCT DIURNAL CUMULUS BOTH DAYS. MODEL
SOUNDINGS SHOW MIXING TO 900-875MB BOTH DAYS...WITH 925MB TEMPS IN
THE 18C TO 20C RANGE BOTH DAYS. QUESTION REMAINS THE POTENTIAL FOR
ISOLATED SHRA ACROSS THE WEST END OF THE FCST AREA SAT AFTERNOON.
THIS AS THE WEAK MID LEVEL LOW/SHORTWAVE ENERGY LIFTS NORTH INTO
SOUTHERN MN AND MODELS PROG 250-500 J/KG SB/MU CAPE OVER MUCH OF IA/
SOUTHERN MN SAT AFTERNOON. THIS INSTABILITY TIED TO MODELS
GENERATING SFC DEW POINTS IN THE LOW-MID 60S SAT AFTERNOON. THESE
LOOK TOO HIGH. AS OF SEPT 21...60-100 PERCENT OF THE SOYBEAN CROP
FROM MO TO MN AND NEB TO INDIANA WAS REPORTED LEAVE TURNING COLOR OR
DROPPING. 19 TO 75 PERCENT OF THE CORN CROP ACROSS THIS SAME AREA
WAS REPORTED MATURE. BOTTOM LINE IS EVAPO-TRANSPIRATION TO LOAD THE
BOUNDARY LAYER WITH MOISTURE IS SHUTTING DOWN OR NOW MINIMAL ACROSS A
SIGNIFICANT PORTION OF THE LANDSCAPE NORTH OF THE MO/OH RIVERS. DEW
POINTS MORE IN THE 55F TO 60F RANGE SAT RESULT IN LITTLE IF ANY
CAPE. LEFT BOTH SAT AFTERNOON...AND SUN AFTERNOON WITH THE WEAK MID
LEVEL TROUGH OVER THE AREA...DRY. 925MB TEMPS MENTIONED ABOVE...WITH
SOME SUNSHINE...SUPPORT SAT/SUN HIGHS MOSTLY IN THE 75-80 DEGREE
RANGE. BLEND OF THE GUIDANCE FOR HIGHS/LOWS SAT THRU SUN NIGHT HAS
THEM WELL TRENDED.

FOR MONDAY THROUGH THURSDAY.../DAYS 4 TO 7/...

MAIN DAY 4-7 FORECAST CONCERNS...SHRA/TSRA CHANCES TUE NIGHT TO THU.

MEDIUM RANGE MODELS OF 25.00Z/25.12Z IN REASONABLY GOOD AGREEMENT
MON/TUE AS THE GREAT BASIN MID LEVEL LOW SLOWLY OPENS UP AND LIFTS
INTO THE NORTHERN PLAINS BY 00Z WED. GFS THE ODD MODEL OUT DROPPING
A NORTHERN STREAM SHORTWAVE SOUTHEAST ACROSS THE GREAT LAKES MON
NIGHT/TUE...BUT IT DOES STRUGGLE WITH RUN-TO-RUN CONSISTENCY ON THIS
FEATURE. DETERMINISTIC GFS RUN THE STRONGEST AMONG IT OWN ENSEMBLE.
HOWEVER ECMWF/CAN-GEM HAVE TRENDED TOWARD A STRONGER FEATURE BUT
OPEN WAVE TO DROP ACROSS THE GREAT LAKES LATER MON/MON NIGHT.
REASONABLE AGREEMENT TUE NIGHT/WED AS THE TROUGH/ENERGY IN THE
NORTHERN PLAINS LIFTS INTO WESTERN ONT AND MORE ENERGY/TROUGHING
DIGS INTO THE ROCKIES. THE TREND OF THE 25.12Z RUNS IS WEAKER/FASTER
THU AS THE TROUGH/ENERGY EJECTS INTO THE PLAINS TOWARD THE REGION
THU...AS YET MORE ENERGY DIGGING INTO THE NORTHERN ROCKIES THU.
GIVEN THE SHIFTS AND LESSER RUN-TO-RUN CONSISTENCY AMONG THE 25.00Z
AND 25.12Z RUNS...FCST CONFIDENCE FOR MON THRU THU IS AVERAGE.

DETERMINISTIC GFS RUNS DRIVE A STRONG BACKDOOR COLD FRONT SOUTH
ACROSS THE REGION LATE MON/MON NIGHT...OTHERWISE MILD HIGH
PRESSURE GENERALLY REMAINS OVER THE REGION INTO TUE. WITH
ECMWF/GEM TRENDING TOWARD A BIT OF A FRONT TO PUSH IN MON
NIGHT...DID CARRY SOME SMALL -SHRA CHANCES ACROSS THE NORTH/EAST
ENDS OF THE FCST AREA MON/MON NIGHT...AND SOME COOLER HIGHS TUE.
HIGHS BOTH MON/TUE STILL LOOKING TO BE MOSTLY IN THE 70S. ROUND
OF LOWER LEVEL THERMODYNAMIC FORCING/LIFT WITH THE SHORTWAVE
TROUGH LIFTING FROM THE NORTHERN PLAINS TOWARD WESTERN ONT MOVES
INTO/ACROSS THE AREA TUE NIGHT/WED. THIS WITH SOME 850-700MB
MOISTURE TRANSPORT...PW VALUES INCREASING TOWARD 1.5 INCHES AND
SOME WEAK TO MDT MUCAPE SPREADING ACROSS THE AREA TUE NIGHT/WED.
ADDED ISOLATED TSRA MENTION TUE NIGHT AND CARRIED A CHANCE OF TSRA
ACROSS THE ENTIRE AREA WED. FEED OF MOISTURE RICH AIR CONTINUES
INTO THE AREA WED NIGHT THU...AHEAD OF THE NEXT LOW/MID LEVEL
TROUGH LIFTING NORTHEAST THRU THE PLAINS. GFS/ECMWF NOW AT ODDS
WITH STRENGTH OF THE LOWER LEVEL FEATURES/FORCING TO LIFT ACROSS
THE AREA WED NIGHT/THU. PER THE MORE CONSISTENT ECMWF...WEAK TO
MDT MUCAPE INDICATED IN THE AIRMASS AHEAD OF THE LOW/TROUGH.
CONTINUED A TSRA MENTION WITH THE RAIN CHANCES WED NIGHT/THU.
TEMPS TRENDING COOLER WED/THU...MAINLY DUE TO MORE CLOUD COVER BUT
GFS/ECMWF ALSO NOW AT ODDS WITH LOW LEVEL WARM VS. COLD ADVECTION
ACROSS THE REGION WED NIGHT/THU. FOR NOW...STAYED WITH THE MODEL/
ENSEMBLE CONSENSUS HIGHS/LOWS FOR MON-THU UNTIL MODELS SETTLE DOWN
AND A BETTER CONSENSUS IS REACHED.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1139 PM CDT THU SEP 25 2014

WITH SKIES CLEARING OUT...THE POTENTIAL FOR VALLEY FOG HAS GONE UP
AT LSE. WINDS HAD GONE CALM BUT THEN CAME BACK UP OUT OF THE
SOUTHEAST AT 7KTS AT 4Z. WITH THE CLOUD COVER HOLDING BACK
RADIATIONAL COOLING...EXPECT THAT THE FOG WILL TAKE A LITTLE
LONGER TO FORM SO HAVE TARGETED THE 10-14 TIMEFRAME FOR THIS
POTENTIAL FOG. INCLUDED SOME FOG AT RST AS WELL THOUGH CONFIDENCE
IS NOT AS HIGH THAT IT WILL FORM THERE COMPARED TO LSE WHERE SKIES
HAVE ALREADY CLEARED. CONDITIONS WILL IMPROVE AROUND 15Z FRIDAY
MORNING WITH WINDS STAYING UNDER 10KTS AND CIGS ABOVE 5KFT INTO
FRIDAY EVENING.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...HALBACH


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.