677
FXUS63 KARX 020816
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
316 AM CDT FRI JUN 2 2023
DISCUSSION
(TODAY THROUGH THURSDAY)
ISSUED AT 216 AM CDT FRI JUN 2 2023
KEY MESSAGES:
- SCATTERED STORM CHANCES CONTINUE TODAY & SATURDAY INTO SUNDAY
- ANOMALOUSLY WARM TEMPERATURES CONTINUE TODAY & THROUGH THE
WEEKEND
- MORE WIDESPREAD PRECIPITATION POTENTIAL INTO THE NEW WORK WEEK
WITH POTENTIAL PATTERN SHIFT THROUGH LATTER HALF OF THE WEEK
STORM CHANCES TODAY & TONIGHT:
WATER VAPOR SATELLITE THIS MORNING SHOWS AN ESTABLISHED UPPER
LEVEL RIDGE OVER THE GREAT LAKES REGION WITH A WESTWARD EXPANSION
INTO THE UPPER MISSISSIPPI RIVER VALLEY. THIS HAS PUSHED THE
CORRIDOR FOR NORTHWARD MOVING SHORT WAVE TROUGHS OVER THE PLAINS
INTO THE MISSOURI RIVER VALLEY LEAVING THE LOCAL REGION LARGELY
ABSENT FOR FOCUS OF CONVECTION DEVELOPMENT. SOME WEAK WARM AIR
ADVECTION WILL CONTINUE OVER THE AREA ON THE WESTERN FRINGES OF
THE LOW LEVEL RIDGE AXIS TO PRODUCE SOME WEAK ISENTROPIC UP GLIDE
AND HELP AID IN THE DEVELOPMENT OF MORE DIURNAL SHOWERS AND STORMS
DURING THE AFTERNOON AND EARLY EVENING. THIS ACTIVITY COULD POP
UP ALMOST ANYWHERE ACROSS THE AREA, BUT MAY HAVE BIT BETTER CHANCE
FOR HIGHER COVERAGE ACROSS NORTHEAST IOWA AND SOUTHEAST MINNESOTA
INTO NORTH-CENTRAL WISCONSIN COINCIDING WITH AN AXIS OF HIGHER
MLCAPE TO 1000 J/KG ACCORDING TO THE RAP. WITH NO SHEAR OVER THE
AREA, THE ACTIVITY WILL STAY DISORGANIZED AND LIKELY NOT PERSIST
FOR VERY LONG BEFORE THE CORES COLLAPSE. WITH PRECIPTABLE WATER
AMOUNTS OF 1.25 TO 1.75 INCHES, SOME LOCALLY HIGHER RAINFALL
TOTALS COULD OCCUR DUE TO WHAT SHOULD BE SLOW MOVING CELLS. SOME
GUSTY WINDS WILL ALSO BE POSSIBLE AS THE CELLS DISSIPATE FROM THE
COLLAPSING CORES. LOOK FOR THE COVERAGE OF ANY CONVECTION THAT
DOES DEVELOP TO DIMINISH FAIRLY QUICKLY DURING THE EVENING WITH
THE LOSS OF DAYTIME HEATING.
WEEKEND SYNOPTIC SETUP & ANOMALOUSLY WARM SURFACE TEMPERATURES:
ANOMALOUSLY WARM TEMPERATURES ARE EXPECTED TO CONTINUE THROUGH
THE WEEKEND WITH LITTLE CHANGE IN THE SYNOPTIC SETUP. STRONG
MULTI-ENSEMBLE CONFIDENCE (80-100%) SURROUNDS MID/UPPER LEVEL
HIGHER HEIGHTS SITUATED OVER THE NORTHERN PLAINS. THE GEFS
(02.00Z) HAS REBOUNDED ITS CONFIDENCE (70-100%) OVER THE LAST FEW
RUNS FOR THE 80 DEGREE ISOTHERM AFFECTING MUCH OF THE AREA
SATURDAY, SHIFTING SLIGHTLY WEST SUNDAY PRIMARILY AFFECTING WEST
OF THE MISSISSIPPI RIVER. EPS (02.00Z) HAS CONTINUED 100%
CONFIDENCE OVER SEVERAL PREVIOUS RUNS FOR THE 80 DEGREE ISOTHERM
ENVELOPING THE ENTIRETY OF THE UPPER MISSISSIPPI RIVER VALLEY.
THEREFORE, SIMILAR TO PREVIOUS FORECASTS IN COLLABORATION WITH
NEIGHBORS, HAVE SLIGHTLY BUMPED MAXIMUM DAYTIME TEMPERATURES AWAY
FROM DETERMINISTIC NATIONAL BLEND GUIDANCE USING 50TH PERCENTILE
NATIONAL BLEND PROBABILISTIC GUIDANCE. SPREAD BETWEEN THE TWO HAS
GREATLY DECREASED WITH THE MOST DETERMINISTIC MEMBERS ALIGNING
TOWARDS THE 50TH PERCENTILE IN THE VIOLIN PLOT, PROVIDING
INCREASED CONFIDENCE.
SATURDAY STORM SETUP & FORECAST DIFFERENCES:
ALSO SIMILAR TO PREVIOUS FORECASTS, THE EXACT LOCATION OF THE
AFOREMENTIONED HIGHER GEOPOTENTIAL HEIGHTS WILL DETERMINE
PRECIPITATION CHANCES THIS WEEKEND INTO EARLY NEXT WEEK. UNLIKE
PREVIOUS FORECASTS, SHORT TERM HIGH RESOLUTION MODELS HAVE BEGUN
TO PICK UP THE SATURDAY AFTERNOON-EVENING FORECAST HOUR, WHICH
HAS PREVIOUSLY BEEN CRUCIAL FOR RESOLVING CONVECTION THIS PAST
WEEK WITHIN THIS PATTERN; ESPECIALLY WHEN COMPARED TO THE OVERLY-
SATURATED AND DISAGREEING LONG TERM GLOBAL MODELS. UNFORTUNATELY,
DISAGREEMENT BETWEEN SHORT TERM MODELS ALSO ABOUNDS, RESULTING IN
BINARY HREF CONFIDENCE (I.E., YES/NO) AND LIMITING ITS OVERALL
USEFULNESS. THEREFORE, THIS FORECASTER HAS RESORTED TO A LENGTHY
DISCUSSION OF THE HIGH RESOLUTION DIFFERENCES AND IMPACTS:
SYNOPTICALLY, DISAGREEMENT STEMS FROM THE AFOREMENTIONED
PERTURBATION SLIDING ALONG THE EASTERN PERIPHERY OF THE UPPER
LEVEL HIGHER HEIGHTS AND THE RESULTANT USHERING IN OF A LOW LEVEL
DRY PUNCH; VARYING IN MAGNITUDE FROM 43 TO 60 DEGREE FORECASTED
SURFACE DEWPOINT TEMPERATURES. THE RAP/HRRR (02.03/06Z) HAS THE
DRIEST SOLUTION WITH 43 DEGREE MINIMA DEWPOINTS ADVECTING WEST
ACROSS THE FORECAST AREA SATURDAY AFTERNOON. THIS LIMITS MLCAPE
TO AREAS WEST OF MISSISSIPPI RIVER WHILE POTENTIALLY PROVIDING
FORCING. IT APPEARS THESE MODELS AND THERE PBL SCHEMES ARE TOO
MIXED AND SHOULD THEREFORE BE TAKEN WITH A GRAIN OF NACL. ON THE
OTHER END OF THE SPECTRUM, THE NSSLWRFARW/FV3 (02.00Z) DO NOT
ADVECT DRY AIR THIS FAR WEST AND KEEP DEWPOINTS IN THE UPPER 50S
TO LOW 60S. THIS RESULTS IN A SOLUTION SIMILAR TO TODAY AND
THURSDAY WITH A LACK OF FORCING OUTSIDE OF DIURNAL-INFLUENCED
INSTABILITY, AN OVERALL MORE WIDESPREAD MLCAPE POOL, AND SCATTERED
STORMS THAT INCREASE IN COVERAGE OUTSIDE OF THE LOCAL AREA.
BETWEEN THESE SOLUTIONS LIES THE ARW (02.00Z) WITH MID TO LOW 50
DEGREE DEWPOINTS AND AN AXIS OF GREATER THAN 1000 J/KG MLCAPE AND
ACCOMPANYING STORMS ADVECTING THROUGH THE FORECAST AREA SATURDAY
AFTERNOON-EVENING.
SATURDAY STORMS POTENTIAL IMPACTS:
IN SUMMARY, WHILE SHORT TERM MODELS HAVE BEGUN TO PICK UP SATURDAY'S
PRECIPITATION POTENTIAL, DISAGREEMENTS ABOUND. LONGER RANGE
GLOBAL MODELS CONTINUE THE TRENDS THEY HAVE HAD ALL WEEK, WITH
THE GEFS/GFS (02.00Z) BEING THE WETTER SOLUTION, FARTHER WEST WITH
THE HIGHER HEIGHTS THAN THE DRY-SOLUTION EPS (02.00Z). AGREEMENT
DOES REACH SEVERITY WITH LITTLE TO NO SHEAR AT NEARLY ALL LEVELS
IN ALL HIGH RESOLUTION CAMS. GIVEN THE PREVIOUS LENGTHY DESCRIPTION
OF DIFFERENCES IN MOISTURE OF INCOMING AIR MASS, HAVE REDUCED
SURFACE DEWPOINT TEMPERATURES FOR SATURDAY USING THE ARW (02.00Z).
WHILE THE DEPTH AND MAGNITUDE OF THE PBL DRY AIR IS IN
DISAGREEMENT BETWEEN HIGH RESOLUTION MODEL SOUNDINGS, THEY DO
AGREE ON DIFFERING MAGNITUDES OF A LOW LEVEL INVERTED V.
THEREFORE, STRONG WINDS POSSIBLE WITH STORMS AS CORES COLLAPSE.
NEW WEEK PRECIPITATION CHANCES & POTENTIAL PATTERN CHANGE:
THE UPPER LEVEL PATTERN EXPECTED TO REMAIN IN PLACE FOR THE START
OF THE NEW WORK WEEK WITH LACKLUSTER CONFIDENCE (40-70%) FOR
GREATER THAN A TENTH OF RAINFALL (GEFS/EPS 02.00Z). MOST
WIDESPREAD PROBABILISTIC PRECIPITATION PROBABILITIES SWING
THROUGH THE UPPER MISSISSIPPI RIVER VALLEY MONDAY INTO TUESDAY
FROM ANOTHER QUASI-ZONAL WOBBLE ALONG THE EASTERN PERIPHERY OF
INCREASED UPPER LEVEL HEIGHTS. HAVE CONTINUED WITH NATIONAL BLEND
POPS WHICH PROVIDES "CHANCE" FOR STORMS. THROUGH MIDWEEK, HIGH
CONFIDENCE (80-100%) FOR THE UPPER LEVEL HIGH NOW OVER THE CENTRAL-
NORTHERN PLAINS REDUCING STRENGTH. THIS IS EVIDENT IN PROBABILITIES
FOR 582 DAM ISOHEIGHTS AT 500 MB ADVECTING SOUTH JOINING THE MEAN
FLOW OVER THE SOUTHERN UNITED STATES. CONFIDENCE IN PLACEMENT OF
THE 576 DAM ISOHEIGHT AT 500 MB WAVERS BETWEEN AND WITHIN RUNS OF
LONG TERM GLOBAL MODELS. GENERAL CONSENSUS FOR THE UPSTREAM RIDGE
TO SLOWLY RETROGRADE THROUGH THE WEEK, PLACING THE LOCAL AREA ON
THE EASTERN PERIPHERY WITHIN NORTHWEST FLOW. THEREFORE, COULD BE
A CHANGE IN THE OVERALL PATTERN AND PRECIPITATION CHANCES.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1030 PM CDT THU JUN 1 2023
VFR CONDITIONS EXPECTED TO CONTINUE THROUGH THIS TAF PERIOD.
ANTICIPATE ANOTHER AFTERNOON OF SCATTERED POP UP SHOWERS AND
STORMS AFTER 19Z FRIDAY. WEAK FORCING AND LIMITED MOISTURE LEADS
TO LOWER CONFIDENCE IN WHETHER THESE MAY SPECIFICALLY IMPACT
THE TERMINALS, SO HAVE TRIED TO CONFINE VCTS TO THE FAVORED
AFTERNOON - EARLY EVENING HOURS. LOCALIZED HEAVY RAIN, BRIEF
VISIBILITY REDUCTIONS, AND SOME GUSTY WINDS WOULD BE POSSIBLE.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...04/JAR
AVIATION...KURZ
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