802
FXUS63 KARX 130843
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
343 AM CDT TUE AUG 13 2013
.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 343 AM CDT TUE AUG 13 2013
MAIN FORECAST CONCERNS THIS PACKAGE...LATE NIGHT/EARLY MORNING
VALLEY FOG BOTH MORNINGS...DIURNAL -SHRA POTENTIAL WITH YET ANOTHER
PASSING SHORTWAVE TUE AFTERNOON...TEMPERATURES.
06Z FOG PRODUCT IMAGERY SHOWED GENERALLY CLEAR SKIES ACROSS MN/IA/WI
EARLY THIS MORNING. THIS AS CAN HIGH PRESSURE WITH DRIER NORTHERLY
FLOW CONTINUED TO BUILD SOUTH INTO THE UPPER MIDWEST. THE DRIER AIR
AND THE NORTH TO NORTHEAST WINDS LIMITING VALLEY FOG FORMATION SO
FAR THIS MORNING. TEMPS AGAIN ON THE COOL SIDE FOR MID AUG...WITH
40S OVER NORTHEAST MN/WI AND MOSTLY 50S TO LOW 60S ELSEWHERE. EVEN A
38F READING AT LAND-O-LAKES WI EARLY THIS MORNING.
13.00Z MODELS LOOK TO HAVE INITIALIZED WELL...BUT FOR GFS ON THE DRY
SIDE WITH SFC DEW POINTS OVER MUCH OF MN/IA/WI. SOLUTIONS QUITE
SIMILAR FOR TODAY THRU WED AS THE CAN HIGH PRESSURE SETTLES SOUTH
INTO THE UPPER MIDWEST FOR WHAT IS PROMISING TO BE A COUPLE OF DRY
AND SEASONABLY COOL DAYS. DPROG/DT OF 500MB HGTS AT 13.00Z SHOWED
THE MODEL RUNS OF 11.00Z AND 12.00Z VERIFIED QUITE WELL ACROSS NOAM/
EASTERN PAC WITH A RATHER TIGHT CONSISTENCY TREND. BETWEEN MODEL
AND RUN-TO-RUN CONSISTENCY IS GOOD OVER THE WEST 2/3 OF NOAM...WHILE
THERE IS A SLOWING TREND WITH THE EASTERN NOAM TROUGHING. THIS
KEEPS STRONGER NORTHWEST FLOW ALOFT OVER THE REGION THRU THE MIDDLE
OF THE WEEK. CHECK OF OBS VS. MODEL DATA AT 06Z SHOWED ALL TO BE
REASONABLE WITH THE CAN HIGH PRESSURE AND DRIER AIR MOVING SOUTH
INTO THE REGION. PER WV IMAGERY MODELS GENERALLY LOOKED GOOD WITH
THE SHORTWAVE DETAILS OVER NOAM...HOWEVER GFS LOOKING TOO STRONG
WITH PIECES OF ENERGY OVER WY...WHICH COMES INTO PLAY BY THU
NIGHT/FRI. NO ONE MODEL APPEARS BEST AND FAVORED THE RATHER TIGHT
MODEL/ENSEMBLE CONSENSUS. SHORT-TERM FCST CONFIDENCE IS GOOD IN
WHAT IS A RATHER QUIET WEATHER PERIOD.
IN THE SHORT TERM...DRYING NORTHERLY SFC-850MB FLOW OVER THE AREA
LIMITING FOG FORMATION THIS MORNING WITH ONLY KOVS REPORTING 4SM BR
AS OF 07Z. TEMP-DEW POINT SPREAD AT KLSE STILL 6F AT 07Z WITH 88D
VAD WINDS OF 15KTS AT 925MB NEAR THE TOP OF THE INVERSION. WILL
REDUCE VALLEY FOG IN THE GRIDS FOR THIS MORNING TO PATCHY AT MOST
LOCATIONS. WILL LEAVE AREAS OF BR/FG IN THE WI RIVER VALLEY...MORE
PERPENDICULAR TO THE NORTH FLOW. ONCE ANY FOG BURNS OFF...A MOSTLY
SUNNY/DRY DAY EXPECTED ACROSS THE AREA. DEW POINTS FALLING INTO THE
40S ACROSS NORTHERN WI AND THIS AIRMASS TO ADVECT INTO THE FCST
AREA TODAY. MODEL SOUNDINGS SHOWING AN INVERSION BETWEEN 800-750MB
THIS AFTERNOON. WITH MIXED SFC DEW POINTS IN THE 40S THIS
AFTERNOON...EVEN UNDER THE COOLER AIRMASS ALOFT OVER THE NORTHEAST
END OF THE FCST AREA...LITTLE MORE THAN ENOUGH INSTABILITY TO
PRODUCE SOME RATHER HIGH-BASED CUMULUS CLOUDS LATE THIS MORNING/
AFTERNOON. LEFT TODAY DRY. WITH MIXING TO ABOUT 800MB THIS AFTERNOON
AND 850MB DEW POINTS IN THE 8C TO 10C RANGE...A SEASONABLY COOL DAY
IN STORE WITH HIGHS IN THE LOW-MID 70S...EVEN UNDER PLENTIFUL
SUNSHINE.
DRYING DEW POINTS TODAY THROW POTENTIAL FOR VALLEY FOG LATER TONIGHT
INTO QUESTION. LIGHTER WINDS IN THE SFC TO ABOUT 900MB LAYER TONIGHT
FAVORABLE FOR STRONG DECOUPLING/INVERSION DEVELOPMENT. QUESTION
WILL BE HOW MUCH CAN DEW POINTS RECOVER IN THE VALLEYS NEAR AND
SHORTLY AFTER SUNSET. SOUNDINGS SHOWING A DRY COLUMN ABOVE 800MB
TONIGHT FOR WHAT WOULD BE STRONG RADIATIONAL COOLING BUT INDICATIONS
FOR SOME MOISTURE 850-800MB TO SPREAD ACROSS THE AREA TONIGHT...
ASSOCIATED WITH YET ANOTHER WEAK SHORTWAVE ROTATING SOUTH ACROSS WI.
WITH THE STRONG RADIATIONAL COOLING AND POTENTIAL FOR LOWS IN THE 40S
ACROSS MUCH OF THE AREA...WILL LEAVE VALLEY FOG MENTION IN GRIDS FOR
LATE TONIGHT/EARLY WED MORNING AS IS FOR NOW.
ANOTHER MOSTLY SUNNY DAY WED ONCE ANY FOG BURNS OFF. 850MB TEMPS IN
THE 10C-12C RANGE BY 00Z THU FOR WHAT SHOULD BE ABOUT A CATEGORY
WARMER DAY THAN TODAY. USED A BLEND OF THE NUMERICAL GUIDANCE
HIGHS/LOWS FOR TODAY THRU WED.
.LONG TERM...(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 343 AM CDT TUE AUG 13 2013
MAIN FORECAST CONCERNS FOR THE WED NIGHT THRU THU NIGHT PERIOD ARE
VALLEY FOG POTENTIAL AGAIN THU MORNING AND SHRA/TSRA CHANCES THU
NIGHT.
MODELS REMAIN IN RATHER GOOD AGREEMENT FOR THIS PERIOD...AT LEAST
WITH THE LARGER SCALE FEATURES OF THE FLOW. SOME DIFFERENCES WITH
SHORTWAVE ENERGY TO COMING OUT OF MT/WY WED NIGHT AND MOVING INTO
WESTERN IA/MO BY FRI MORNING. TREND SEEMS TO BE STRONGER/SLOWER/
MORE DIGGING WITH THIS SHORTWAVE ENERGY BY 12Z FRI. FCST CONFIDENCE
GOOD WED NIGHT/THU THEN AVERAGE THU NIGHT.
DRY/QUIET/SEASONABLY COOL WEATHER CONTINUES WED NIGHT/THU WITH THE
CAN HIGH FIRMLY ENTRENCHED OVER THE REGION. SFC RIDGE AXIS IS STILL
OVER THE AREA AT 12Z THU...WITH ANOTHER NIGHT OF STRONG RADIATIONAL
COOLING UNDER A DRY MID/UPPER LEVEL COLUMN AND LIGHT/CALM SFC WINDS.
WINDS ON TOP THE BOUNDARY LAYER WED NIGHT DO LOOK TO INCREASE TO 10-
15KTS AS THE CORE OF THE SFC-925MB HIGH MOVES SOUTH OF THE AREA.
WITH SOME DEW POINT RECOVERY WED NIGHT...WILL LEAVE PATCHY TO AREAS
OF VALLEY FOG IN GRIDS CENTERED ON 12Z THU AS IS. 850MB TEMPS WARM
INTO THE 11C TO 14C RANGE BY 00Z FRI...WITH HIGHS THU TO AGAIN BE A
CATEGORY OR SO WARMER THAN THOSE OF THE PREVIOUS DAY.
WITH THE SFC-850MB HIGH SOUTH OF THE AREA BY LATER THU/THU NIGHT...
WEAK SOUTHWEST FLOW AROUND THIS HIGH INTO MN/IA/WI SPREAD SOME 850MB
MOISTURE TRANSPORT/INCREASE TOWARD/INTO THE AREA THU NIGHT. PW
VALUES INCREASING TO AN INCH OR MORE BY 12Z FRI...WITH SOME LOWER
LEVEL THERMODYNAMIC FORCING AND FALLING HGTS/WEAK DIVERGENCE ALOFT
AHEAD OF A MID LEVEL TROUGH AXIS DROPPING ACROSS THE REGION.
HONORED THE WEAK BUT SOMEWHAT CONSISTENT SIGNAL WITH A SMALL SHRA/
TSRA CHANCE OVER THE WEST END OF THE FCST AREA THU NIGHT. FAVORING
THE MODEL/ENSEMBLE CONSENSUS...USED A BLEND OF THE NUMERICAL GUIDANCE
FOR LOWS/HIGHS WED NIGHT THRU THU NIGHT.
FOR FRIDAY THOUGH MONDAY...
MEDIUM RANGE MODEL RUNS OF 13.00Z IN DECENT AGREEMENT FRI THRU MON
WITH WHAT LOOKS TO BE A SHIFT IN THE 500MB FLOW PATTERN ACROSS NOAM.
STRONG TROUGHING MOVING INTO THE GULF OF AK FRI/SAT GIVES THE WEST
COAST BLOCK A SHOVE WITH THE RIDGING OVER THE ROCKIES MOVING INTO/
ACROSS THE NORTHERN PLAINS. EASTERN CAN TROUGH/VORTEX LIFTS OUT
WITH SOME WEAKER SOUTHERN STREAM TROUGHING REMAINING OVER THE
SOUTHEAST CONUS. END RESULT IS NEARLY ZONAL FLOW ACROSS SOUTHERN
CAN BY SUN/MON...PUTTING AN END TO THE NORTHWEST FLOW ALOFT THAT HAS
BEEN OVER THE REGION FOR THE PAST FEW WEEKS. DECENT MODEL CONSENSUS
FOR A SHORTWAVE IN THIS ZONAL FLOW TO MOVE INTO THE REGION MONDAY.
DAY 4-7 FCST CONFIDENCE AVERAGE TO ABOVE AVERAGE THIS CYCLE.
MID LEVEL TROUGH AXIS AND SOME WEAK LOW LEVEL THERMODYNAMIC
FORCING/MOISTURE TRANSPORT SPREAD ACROSS THE AREA FRI. CONTINUED THE
SMALL CONSENSUS SHRA/TSRA CHANCE FOR MUCH OF THE AREA FRI. RIDGING
ALOFT NOSING INTO THE REGION LATER FRI THEN BUILDING ACROSS THE
REGION SAT/SUN SPREADS INCREASING SOUTHWEST LOWER LEVEL FLOW/WARM
ADVECTION EASTWARD ACROSS THE REGION THRU SUNDAY. 925MB TEMPS OVER
THE AREA IN THE 20C TO 22C RANGE BY 00Z MON...WITH HIGH TEMPS SAT
NEAR NORMAL...THEN ABOVE NORMAL SUNDAY. WITH APPROACH OF THE SFC-
MID LEVEL TROUGH MON...WHICH LOOKS TO REMAIN WEST OF THE FCST AREA...
LEFT MON DRY PER THE MODEL/ENSEMBLE CONSENSUS. HOWEVER MAY YET
NEED A SHRA/TSRA CHANCE MON IF FORCING/LIFT TRENDS STRONGER OR
TROUGH TRENDS FASTER. MODEL/ENSEMBLE CONSENSUS HIGHS/LOWS FOR FRI
THRU SAT LOOK WELL TRENDED AT THIS TIME WITH NO CHANGES MADE.
&&
.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1145 PM CDT MON AUG 12 2013
VFR CONDITIONS EXPECTED. SOME RIVER VALLEY FOG MAY BE AROUND
TUESDAY MORNING BUT IT WILL BE ISOLATED AND SHOULD NOT AFFECT THE
AIRFIELD AT KLSE.
IFR RIVER VALLEY ON WEDNESDAY MORNING LOOKS MORE LIKELY AT KLSE.
THIS COULD BE AN LIFR EVENT WITH MULTIPLE HOURS OF LESS THAN
1/4SM. STAY TUNED FOR UPDATES WITH FUTURE TAFS.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&
$$
SHORT TERM...RRS
LONG TERM...RRS
AVIATION...BAUMGARDT