Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 191743
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1243 PM CDT TUE MAY 19 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 339 AM CDT TUE MAY 19 2015

MAIN FCST CONCERNS THIS PERIOD...CLOUD TRENDS TODAY...LOWS AND
POTENTIAL FROST TONIGHT.

06Z DATA ANALYSIS HAD LOW PRESSURE OVER QUEBEC WITH TROUGHING TO THE
SOUTHWEST INTO WI. A BROAD CANADIAN HIGH WAS CENTERED OVER ND WITH
RIDGING SOUTH INTO KS/MO. WV IMAGERY SHOWED A COUPLE OF SHORTWAVES
ROTATING ACROSS THE REGION. THIS WITH THE LOWER LEVEL TROUGH/
CYCLONIC FLOW HELPING TO MAINTAIN A BROAD STRATO-CU DECK ACROSS MUCH
OF MN/IA/WI...THOUGH WITH PASSAGE OF THE WAVES CLOUDS HAVE STARTED
TO BREAK/DECREASE ACROSS CENTRAL MN SINCE 05Z. NORTHWEST WINDS OF 10-
20 MPH CONTINUED ACROSS MUCH OF THE REGION. THE WINDS AND THE CLOUDS
HELPING KEEP EARLY MORNING TEMPS ACROSS MOST OF THE UPPER MIDWEST
RATHER UNIFORM IN THE MID 30S TO MID 40S.

NO PROBLEMS NOTED WITH 19.00Z MODEL INITIALIZATIONS. RATHER GOOD
BETWEEN MODEL AND RUN-TO-RUN CONSISTENCY FOR TODAY/TONIGHT AS ONE
NORTHWEST FLOW SHORTWAVE DROPS INTO NORTHERN MN TODAY...THEN A
SECOND NORTHWEST FLOW WAVE AT LEAST PARTLY PHASES WITH SHORTWAVE
ENERGY COMING ACROSS NEB/SD TONIGHT. SOME SHORTWAVE DETAIL
DIFFERENCES BY 12Z WED BUT THIS NOT UNEXPECTED. SHORT-TERM FCST
CONFIDENCE REMAINS GOOD THIS CYCLE.

FOR THE SHORT TERM...BROAD STRATUS SHIELD OVER WI AND MUCH OF MN/IA
IS SLOWLY ADVECTING SOUTHEAST THIS MORNING WITH ALL MODELS
LOOKING TO HAVE A GOOD HANDLE ON THE 925-850MB RH DEPICTING IT.
THE SHORTWAVES WILL MOVE WELL EAST OF THE REGION BY 12Z AND THE
SFC-850MB TROUGH SOUTHEAST OF THE AREA BY 18Z. MODELS REMAIN
OPTIMISTIC THAT THE MORE NEUTRAL TO ANTI-CYCLONIC LOW LEVEL FLOW
BEHIND THESE FEATURES AND DEEPER LAYERED SUBSIDENCE WILL CLEAR OUT
THE CLOUDS TODAY. WITH CLOUDS ALREADY BREAKING/CLEARING ACROSS
CENTRAL MN...WILL SIDE WITH THE MODEL CONSENSUS AND MAINTAIN THE
OPTIMISM THAT THE CLOUDS WILL CLEAR OUT OF MOST OF THE AREA BY MID
DAY. MODEL SOUNDING SHOW MIXING TO NEAR 850MB THIS
AFTERNOON...WITH THE 850MB TEMPS SUPPORTING HIGHS IN THE LOW-MID
50S. GRADIENT RELAXES AS WELL TODAY...WITH WINDS MORE IN THE
10-15MPH RANGE. AS THE LOW CLOUDS EXIT/DISSIPATE TODAY... MOISTURE
ABOVE 700MB AHEAD OF THE SHORTWAVE ENERGY COMING ACROSS THE PLAINS
QUICKLY SPREADS EAST INTO THE REGION LATE TODAY/TONIGHT. BULK OF
THIS...AND DEEPER MOISTURE IN THE 850-700MB LAYER PROGGED TO
SPREAD ACROSS THE SOUTHWEST 2/3 OF THE FCST AREA TONIGHT. MAIN
FORCING/LIFT AND UPWARD MOTION...EVEN AT THE 500MB LEVEL...REMAINS
ACROSS THE SOUTHWEST 2/3 OF THE FCST AREA AS WELL...SOUTH OF THE
NORTHERN/SOUTHERN STREAM AXIS OF CONFLUENCE. CLEAR/MOSTLY CLEAR
SKIES EXPECTED MUCH OF THE NIGHT OVER THE NORTHEAST 1/3 OF THE
FCST AREA. WITH THE SFC RIDGE AXIS NEARBY/OVERHEAD TONIGHT...A
STRONGER RADIATIONAL COOLING NIGHT STILL EXPECTED ACROSS THE
NORTHEAST SIDE OF THE FCST AREA...WITH LOWS DIPPING INTO THE LOW-
MID 30S AND PATCHY TO AREAS OF FROST DEVELOPING. WILL ISSUE A
FROST ADVISORY FOR THE COUNTIES ALONG/NORTHEAST OF I-94 FOR 06Z-
13Z WED. ELSEWHERE THE CLOUDS LOOK TO KEEP LOWS IN THE UPPER 30S-
LOW 40S.

NAM THE MOST ROBUST WITH SHORTWAVE ENERGY CROSSING THE PLAINS AND
APPROACHING THE AREA LATE TONIGHT. THIS QUICKLY SPREADS A STRONGER
SHOT OF FORCING/LIFT INTO THE WEST END OF THE FCST AREA ALONG WITH
MORE MOISTURE IN THE 850-700MB LAYER. HOWEVER WILL LEAVE LATE
TONIGHT DRY ACROSS THE SOUTHWEST END OF THE FCST AREA AS NEIGHBORS
TO THE SOUTH LEFT OUR COMMON BORDER AREAS DRY. USED A BLEND OF THE
GUIDANCE HIGHS/LOWS FOR TODAY/TONIGHT.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 339 AM CDT TUE MAY 19 2015

MAIN FCST CONCERNS FOR WED THRU THU NIGHT...-SHRA CHANCES SOUTH ON
WED...TEMPERATURES.

19.00Z MODELS IN GOOD AGREEMENT FOR THE SHORTWAVES TO CONTINUE
PHASING OVER THE REGION WED...WITH THE LEADING WAVE/TROUGH AXIS
QUICKLY PASSING BY 00Z THU. SECONDARY SHORTWAVE/TROUGH AXIS TO DROP
THRU THE AREA WED NIGHT WITH ALL MODELS SPREADING DEEPER NORTHWEST
FLOW ALOFT OVER THE UPPER MIDWEST FOR LATER WED NIGHT THRU THU
NIGHT. CONFIDENCE IN THE WED THRU THU NIGHT PORTION OF THE FCST IS
GOOD THIS CYCLE.

BULK OF THE 850-500MB MOISTURE AND LIFT IN THIS LAYER SPREAD ACROSS
THE FCST AREA WED MORNING AND EARLY WED AFTERNOON WITH THE FIRST
/PLAINS SHORTWAVE/ TO PASS. -SHRA CHANCES ACROSS THE FAR SOUTHWEST
END OF THE FCST AREA ARE A BATTLE OF MOST OF THE MOISTURE/LIFT BEING
ABOVE 700MB AND THE DRIER SFC-700MB AIRMASS. CONTINUED SOME SMALL
-SHRA CHANCES MAINLY ACROSS NORTHEAST IA WED...MAINLY DURING THE
LATE MORNING/EARLY AFTERNOON HOURS WITH THE STRONGEST PV ADVECTION
ALOFT WITH THE LEAD SHORTWAVE. PASSAGE OF THE SECOND SHORTWAVE WED
NIGHT AND MID/UPPER LEVEL FLOW BECOMING NORTHWEST CLEARS OUT THE
MOISTURE WITH SUBSIDENCE AND A DRY AIR THRU A RATHER DEEP PORTION OF
THE COLUMN OVER MOST OF THE UPPER MIDWEST FOR LATER WED NIGHT THRU
THU NIGHT. A COOL DAY YET WED UNDER MOSTLY CLOUDY TO CLOUDY SKIES
AND 850MB TEMPS ONLY IN THE +2C TO +4C RANGE. CONSISTENT SIGNAL
AMONG THE MODELS FOR 925-850MB WARM ADVECTION TO SPREAD ACROSS THE
REGION WED NIGHT/THU. TEMPS TO BE COOL AGAIN WED NIGHT WITH LIGHT
WINDS/CLEARING SKIES FAVORING STRONGER RADIATIONAL COOLING. WITH THE
WARMING...850MB TEMPS IN THE +5C TO +7C RANGE BY THU AFTERNOON...
SUPPORTING HIGHS CLOSE TO NORMAL IN THE UPPER 60S TO LOWER 70S.
ANOTHER SFC RIDGE AXIS IS OVER THE UPPER MIDWEST THU NIGHT...
FAVORING STRONGER RADIATIONAL COOLING AND A LARGER THAN NORMAL
DIURNAL TEMP DROP. FAVORED A BLEND OF THE GUIDANCE HIGHS/LOWS FOR
WED THRU THU NIGHT.

FOR FRIDAY THROUGH MONDAY...DAYS 4 TO 7...

MAIN FCST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES LATER SAT THRU
MONDAY...TEMPERATURES.

19.00Z MEDIUM RANGE MODELS QUITE GOOD AGREEMENT FOR RISING HGTS/
RIDGING ALOFT OT BUILD INTO THE REGION FRI/FRI NIGHT...AS THE NEXT
STRONGER TROUGH/ENERGY DIGS INTO THE CENTRAL/SOUTHERN ROCKIES. EVEN
GOOD AGREEMENT FOR THE RIDGING TO FLATTEN A BIT ON SAT AS A WEAK
SHORTWAVE TOPS IT. BY SUN/MON MODELS ARE TRENDING TOWARD MORE
SHORTWAVE RIDGING OVER THE REGION AS THE PATTERN SLOWS AND THE
ROCKIES TROUGHING/ENERGY IS SLOWER TO EJECT EASTWARD INTO THE
PLAINS. LATEST CONSENSUS DOES PUSH THE MID LEVEL RIDGE AXIS EAST
OF THE REGION LATE SUN/SUN NIGHT AS PIECES OF ENERGY START TO
EJECT OUT OF THE WESTERN CONUS TROUGH. RATHER STRONG SOUTHWEST TO
SOUTH FLOW ALOFT PROGGED OVER THE UPPER MIDWEST BY MONDAY. FCST
CONFIDENCE IS GOOD FRI/SAT THEN GIVEN THE SLOWING TREND IS AVERAGE
FOR SUN/MON.

HIGH PRESSURE TO HOLD OVER THE REGION FRI WITH 850MB TEMPS AND WHAT
SHOULD BE PLENTY OF SUNSHINE SUPPORTING HIGHS NEAR AND ABOVE NORMAL.
THE HIGH REMAINS NEARBY SAT BUT THE WEAK WAVE TOPPING THE MID LEVEL
RIDGING AND LEE TROUGHING DEVELOPING AHEAD OF THE ROCKIES TROUGHING
SPREAD INCREASING MOISTURE QUICKLY NORTH/EAST INTO THE REGION ON
SAT. GIVEN THE GENERAL BETWEEN MODEL AND RUN-TO-RUN AGREEMENT FOR
SAT...THE SMALL CONSENSUS SHRA/TSRA CHANCE ACROSS THE WEST HALF
OF THE FCST AREA LOOKS OKAY FOR NOW. LEE TROUGHING/LOW PRESSURE
REMAINS OVER THE CENTRAL/NORTHERN PLAINS FOR SAT NIGHT INTO MON.
DEEP SOUTH TO SOUTHWEST FLOW EAST OF THIS LOW AND THE ROCKIES
TROUGH CONTINUES THE FLOW OF GULF MOISTURE NORTHWARD WITH PW
VALUES OVER MUCH OF THE UPPER MIDWEST IN THE 1.5 INCH RANGE BY SUN
NIGHT/MON. THOUGH THE EXACT DETAILS REMAIN UNCLEAR...THE INCREASE
OF MOISTURE/INSTABILITY INTO THE REGION AHEAD OF FALLING
HGTS/TROUGHING MOVING ACROSS THE PLAINS...SPELLS AND UNSETTLED
PERIOD FOR THE SUN/MON PORTION OF THE HOLIDAY WEEKEND.
MODEL/ENSEMBLE CONSENSUS OF THE HIGHS/LOWS FOR FRI THRU MON LOOK
WELL TRENDED AT THIS TIME.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1243 PM CDT TUE MAY 19 2015

LOW CLOUDINESS 2-3KFT LINGERING ACROSS THE REGION IN THE COLD POOL
BEHIND THE DEPARTING WEEKEND SYSTEM. SUBSIDENCE NOTED IN VISIBLESATELLITE
IMAGERY BEHIND SYSTEM AND WITH PASSING GRAVITY WAVE. STRATO-CU
VERY FLAT LOOKING AT WEB CAMS ACROSS THE REGION. REMAINING LOW
CLOUD WILL LIFT SLOWLY TO VFR AND THIN FURTHER THROUGH THE
AFTERNOON. ATTENTION THEN TURNS TO APPROACHING SYSTEM FROM THE
SOUTHWEST. HIGH CLOUD AHEAD OF IT ALREADY DRIFTING IN. EXPECT THIS
TO THICKEN THROUGH THE NIGHT...AND SOME MID LEVEL SHOULD BUILD IN
AS WELL. WINDS WILL BECOME LIGHT BY SUNSET AFTER SOME BRIEF
GUSTINESS THIS AFTERNOON.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...FROST ADVISORY FROM 1 AM TO 8 AM CDT WEDNESDAY FOR WIZ017-029-
     034-042>044.

MN...NONE.
IA...NONE.
&&

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...MW



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