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Friday, May 31, 2019

ARX AREA FORECAST DISCUSSION 530 AM CDT FRI MAY 21 2019

 
362 
FXUS63 KARX 311030 
AFDARX 
 
AREA FORECAST DISCUSSION 
NATIONAL WEATHER SERVICE LA CROSSE WI 
530 AM CDT FRI MAY 31 2019 
 
SHORT TERM 
(TODAY AND TONIGHT) 
ISSUED AT 341 AM CDT FRI MAY 31 2019 
 
A SLOW-MOVING UPPER LOW CONTINUES TO CREEP EASTWARD ACROSS CENTRAL 
ILLINOIS EARLY THIS MORNING AND WILL SOON DEPART INTO THE OHIO 
VALLEY AS A FLATTENING UPSTREAM RIDGE BUILDS INTO THE MID- 
MISSISSIPPI VALLEY. WARM AIR ADVECTION ALOFT IS ONGOING OUT AHEAD OF 
THIS RIDGING WITH H8 TEMPS OVER LA CROSSE CLIMBING FROM AROUND 13C 
THURSDAY EVENING TO 16C BY DAYBREAK. AT THE SURFACE, LOW PRESSURE 
SITS OVER NORTH-CENTRAL MINNESOTA WITH A WEAK BOUNDARY EXTENDING 
SOUTHEASTWARD THROUGH CENTRAL WISCONSIN.   
 
GOING TO BE A TOASTY END TO MAY ACROSS THE AREA TODAY. DESPITE THE 
UPPER RIDGING BEING DAMPENED AS IT BUILDS OVERHEAD, 850MB TEMPS WILL 
CLIMB FURTHER TO AROUND 18C THIS AFTERNOON WITH 925MB TEMPS FLIRTING 
WITH 25C (2-3 STANDARD DEVIATIONS ABOVE THE MEAN). DEEP 
UNIDIRECTIONAL WESTERLY FLOW PICKS UP THIS AFTERNOON (SOME GUSTS OF 
25-30 MPH POSSIBLE) AS THE LOW OVER NORTHERN MN ADVANCES INTO 
NORTHERN WI. THIS WILL PROVIDE DEEP BOUNDARY LAYER MIXING TO EASILY 
TAP INTO THAT SIGNIFICANT WARMTH, WITH FORECAST SOUNDINGS SUGGESTING 
MIXING ALL THE WAY UP TO ALMOST 600 MB. LIKELY VERY LITTLE CLOUD 
COVER THROUGH AT LEAST MID AFTERNOON, BUT DO ANTICIPATE SOME 
LINGERING SMOKE ALOFT AS PER LATEST HRRR AND RAP VERTICALLY 
INTEGRATED SMOKE PRODUCTS...PROBABLY NOT AS THICK AS IT WAS ON 
THURSDAY. ALL THIS POINTS TO A FAVORABLE SETUP FOR EFFICIENT DAYTIME 
HEATING, BUT RAW GUIDANCE IS JUST NOT CAPTURING THE MAGNITUDE VERY 
WELL. HAVE THEREFORE LEANED TOWARDS BIAS-CORRECTED GUIDANCE WHICH 
HAS MANY LOCALES FLIRTING WITH 90 DEGREES THIS AFTERNOON. 
 
SHOWERS AND STORMS WILL DEVELOP LATER THIS AFTERNOON IN THIS 
UNSTABLE AIRMASS, WITH THE POTENTIAL STILL THERE FOR SOME STRONG TO 
SEVERE STORMS IN OUR NORTHERN ZONES. MOISTURE WILL BE ADEQUATE WITH 
THE REGION BLANKETED BY PWATS NEAR 1.2 INCHES AND SURFACE DEWPOINTS 
HOVERING AROUND 60 DEGREES, THOUGH FORECAST SOUNDINGS SHOW A RATHER 
DRY INVERTED-V PROFILE IN THE LOW LEVELS. RAP PAINTS AROUND 1000- 
2500 J/KG OF MLCAPE ACROSS THE FORECAST AREA THIS AFTERNOON. IN 
TERMS OF FORCING, A CORRIDOR OF FRONTOGENESIS WILL SAG SOUTHWARD 
WITH TIME INTO TAYLOR AND CLARK COUNTIES, PROVIDING THE MAIN IMPETUS 
FOR STORM DEVELOPMENT THIS AFTERNOON. BEST 0-6KM SHEAR OF 30-40 
KNOTS WILL GENERALLY BE CONFINED TO THE IMMEDIATE VICINITY OF THE 
FRONT AS IT DROPS SOUTH, SO OUR FAR NORTH WILL SEE THE GREATEST 
CHANCE FOR ANY STRONG TO SEVERE STORMS. IN TERMS OF TIMING, CAPPING 
LOOKS TO ERODE IN THE 2-4PM WINDOW, BUT STORM DEVELOPMENT LOOKS TO 
BE DELAYED A LITTLE LONGER UNTIL THE FRONT DROPS IN FROM THE NORTH. 
CAMS SHOW A BROKEN LINE OF STORMS DEVELOPING ALONG THE FRONT AS IT 
ENTERS TAYLOR AND CLARK COUNTIES ROUGHLY BETWEEN 5-7PM, WITH STORM 
INTENSITY DIMINISHING TOWARDS SUNSET AS THE LINE PROGRESSES 
SOUTHEAST. LATEST HREF DOES SHOW SOME WEAK UPDRAFT HELICITY IN THE 
75-150 M2/S2 RANGE ACROSS THE CHIMNEY COUNTIES, SO THAT WILL BE THE 
AREA TO WATCH FOR MORE ORGANIZED STORMS AND SEVERE POTENTIAL. GIVEN 
THE INVERTED-V SOUNDING PROFILE, GUSTY WINDS WOULD BE THE MAIN 
THREAT. LOWER THREAT FOR LARGE HAIL, AS LOW LEVELS LOOK TOO DRY AND 
TOO WARM. ONE OTHER AREA TO NOTE LATE THIS AFTERNOON INTO EARLY 
EVENING WILL BE FAR SOUTHWEST WI INTO NORTHEAST IA WHERE A RICHER 
POOL OF INSTABILITY WILL DEVELOP, PERHAPS SUPPORTING SOME PULSE 
POP-UP STORMS DOWN THAT WAY. BUT THOSE ARE NOT LIKELY TO POSE A 
SEVERE THREAT GIVEN THE LACK OF SHEAR. 
 
ACTIVITY WILL WEAKEN AND BECOME LESS ORGANIZED AS IT PROGRESSES 
SOUTHWARD OVERNIGHT. LOWS TONIGHT WILL RANGE FROM LOW 50S NORTH 
BEHIND THE FRONT TO LOW 60S IN THE FAR SOUTH. 
 
LONG TERM 
(SATURDAY THROUGH THURSDAY) 
ISSUED AT 341 AM CDT FRI MAY 31 2019 
 
THE SURFACE LOW AND COLD FRONT WILL HAVE PROGRESSED SOUTH OF I-90 BY 
SATURDAY MORNING. AN INCOMING SHORTWAVE WILL PROVIDE SOME ADDITIONAL 
SUPPORT FOR MORE SHOWERS AND STORMS THROUGH THE MORNING, WITH THE 
BEST FORCING THEN MOVING OFF TO OUR EAST IN THE AFTERNOON AS HIGH 
PRESSURE ENCROACHES FROM THE WEST. DO NOT ANTICIPATE ANY SEVERE 
STORMS ON SATURDAY WITH VERY LITTLE SHEAR IN PLACE. A COMPARATIVELY 
MUCH COOLER DAY IN STORE WITH HIGHS NEAR 70 NORTH TO MID 70S SOUTH. 
 
LOOKS LIKE A STRETCH OF RATHER QUIET, DRY WEATHER WITH SEASONABLE 
(IF NOT SLIGHTLY COOL) TEMPERATURES AS THE SURFACE HIGH SLOWLY 
BUILDS OVERHEAD THROUGH THE REMAINDER OF THE WEEKEND INTO EARLY NEXT 
WEEK. NEXT BEST SHOT FOR RAIN WILL COME HEADING INTO TUESDAY AS 
STRONGER MOISTURE TRANSPORT DEVELOPS OVER THE PLAINS AND EDGES INTO 
THE MISSISSIPPI VALLEY. PLENTY OF MODEL TIMING VARIANCE BEING THIS 
FAR OUT, BUT IT LOOKS LIKE TUESDAY AFTERNOON AND EVENING WOULD BE 
THE MOST FAVORED TIMEFRAME FOR ACTIVITY ACROSS OUR AREA. 
 
SURFACE HIGH PRESSURE IS PROGGED TO SETTLE IN BEHIND THAT SYSTEM FOR 
WEDNESDAY AND THURSDAY WITH A RETURN TO QUIETER WEATHER. 
TEMPERATURES REMAIN SEASONABLE THROUGH THE MIDDLE OF NEXT WEEK WITH 
HIGHS IN THE MID TO UPPER 70S. 
 
 
 
AVIATION 
(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING) 
ISSUED AT 530 AM CDT FRI MAY 31 2019 
 
PATCHY MORNING FOG IN SOME RIVER VALLEYS WILL GIVE WAY VFR 
CONDITIONS THROUGH THE DAY WITH WEST TO SOUTHWEST WINDS GUSTING UP 
TO AROUND 20 KTS DURING THE AFTERNOON WITH DEEPER MIXING. WINDS 
WILL SUBSIDE THIS EVENING. SOME HIGH CIRRUS AND SMOKE IN THE 
UPPER ATMOSPHERE FROM CANADIAN WILDFIRES ARE EXPECTED AT TIMES. A 
COLD FRONT WILL APPROACH FROM THE NORTH OVERNIGHT TONIGHT. 
ALTHOUGH A SHOWER/STORM COULD NOT BE RULED OUT THIS EVENING, 
HIGHER CHANCES LOOK TO REMAIN NORTH AND WEST OF KLSE/KRST INTO 
TONIGHT. DID INCLUDE VCSH LATE TONIGHT AT KRST AND LEFT KLSE DRY, 
BUT SOME ADJUSTMENTS ARE POSSIBLE AS CONVECTIVE TRENDS BECOME MORE 
CLEAR TODAY. 
 
 
 
ARX WATCHES/WARNINGS/ADVISORIES 
 
WI...NONE. 
MN...NONE. 
IA...NONE.