823
FXUS63 KARX 131129
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
629 AM CDT THU MAR 13 2025
KEY MESSAGES
- A POWERFUL SPRING STORM SYSTEM REMAINS ON TRACK TO IMPACT THE
REGION FRIDAY AND LINGER INTO THE WEEKEND. GREATEST LOCAL
IMPACTS WILL BE ON FRIDAY WITH SOUTHERLY WINDS GUSTING AROUND
30-40 MPH DURING THE DAY AND THEN AN INCREASING RISK FOR A
LINE OF SEVERE THUNDERSTORMS DURING THE EVENING HOURS.
DAMAGING WINDS WILL BE THE MAIN THREAT WITH THESE STORMS, BUT
CANNOT RULE OUT AN ISOLATED TORNADO.
- UNSEASONABLY WARM FOR THE NEXT TWO DAYS WITH RECORD HIGHS
LIKELY SHATTERED ON FRIDAY AS TEMPERATURES SURGE WELL INTO THE
70S. WE COOL STEADILY ON SATURDAY WITH HIGHS 30+ DEGREES
COLDER FOR SUNDAY.
- ANOTHER POTENT STORM SYSTEM LOOMS FOR THE MIDDLE OF NEXT WEEK,
WITH HEAVY SNOW BEING THE MAIN CONCERN.
DISCUSSION
ISSUED AT 425 AM CDT THU MAR 13 2025
TODAY: THE CALM BEFORE THE STORM
AN ELONGATED SURFACE HIGH PRESSURE CELL OVER THE GREAT LAKES SHUNTS
EASTWARD AS THE UPSTREAM WEST COAST UPPER TROPOSPHERIC PATTERN
AMPLIFIES WITH THE LANDFALL OF THE DEEP MERIDIONAL TROUGH THAT WILL
SERVE TO BRING AN ACTIVE WEATHER PATTERN TO CLOSE THE WEEK. AT LEAST
FOR TODAY, THE ONLY NOTABLE CHANGES COMPARED TO YESTERDAY WILL BE
WINDIER AND WARMER AS LEE TROUGHING DEEPENS ALONG THE FRONT RANGE.
HIGHS TODAY WILL BEAT YESTERDAY'S TEMPERATURES BY 10+ DEGREES WITH
THE INCREASING WARM AIR ADVECTION. HAVE BUMPED HIGHS A FEW DEGREES
ABOVE THE NBM DETERMINISTIC FORECAST AS TEMPERATURES HAVE
OVERACHIEVED IT BY 2-4 DEGREES EACH OF THE LAST 4 DAYS. IT IS
CONCEIVABLE THAT A FEW LOCATIONS TOUCH 70 DEGREES WITH ABOUT 20% OF
THE NBM MEMBERS HINTING AT THAT POSSIBILITY SOUTH OF I-94.
FRIDAY: RECORD WARMTH - GUSTY WINDS - SEVERE STORM POTENTIAL
FRIDAY'S POWERFUL SPRING STORM SYSTEM WILL BRING A PLETHORA OF
IMPACTS AND HAZARDS FOR THE CENTRAL PART OF THE UNITED STATES. FOR
THE LOCAL AREA, THERE ARE THREE BIG ITEMS WORTH NOTING, RECORD
WARMTH, GUSTY WINDS, AND THE THREAT FOR SEVERE WEATHER IN THE
EVENING. FOR DETAILS ON THE FIRE WEATHER RISK, SEE THE FIRE WEATHER
SECTION OF THE DISCUSSION BELOW.
RECORD WARMTH
THERE IS LITTLE DOUBT THAT WE WILL SEE HIGH TEMPERATURES REACH
RECORD TERRITORY FOR FRIDAY WITH A VERY TIGHT CLUSTERING IN THE
GUIDANCE. THIS ASPECT OF THE FORECAST HAS BEEN WELL-RESOLVED OVER
THE LAST FEW DAYS AND HAVE CONTINUED THE TREND OF NUDGING THE HIGH
TEMPERATURE FORECAST TO THE BETTER-VERIFYING NBM 50TH PERCENTILE
WHICH WOULD SET DAILY RECORDS FOR MOST LOCALES (BUT ONLY BY A FEW
DEGREES, AS HIGHLIGHTED BY THE EFI).
GUSTY WINDS
SSE WINDS INCREASE THROUGH THE DAY WITH FORECAST PROFILES IN
AGREEMENT THAT WE SHOULD GUST TO 30-40 MPH THIS AFTERNOON. WHILE THE
STRONGEST WINDS REMAIN DISPLACED TO THE SOUTH OF THE FORECAST AREA,
THERE IS SOME RISK THAT WE COULD TAP INTO A 40-50 KT 850-MB JET IF
WE MIX DEEPER THAN CURRENTLY FORECAST. THE OVERNIGHT RUNS OF THE
RAP/HRRR HAVE BEEN LEANING ON THIS POSSIBILITY AND WILL NEED TO
ASSESS ANY INCREASES IN WIND SPEED LATER TODAY.
SEVERE WEATHER RISK
AN ARCING LINE OF CONVECTION DEVELOPS OVER CENTRAL IOWA AT PEAK
HEATING ALONG THE PACIFIC FRONT AND PLOWS NNE AT SPEEDS OF 30 TO 40
MPH, ARRIVING IN NORTHEAST IOWA AROUND THE 5 TO 6 PM TIMEFRAME,
CROSSING THE MISSISSIPPI RIVER AROUND 10PM, AND REACHING CENTRAL
WISCONSIN AFTER MIDNIGHT. THE BIGGEST CHANGE IN THE OVERNIGHT
GUIDANCE HAS BEEN THE MUCH DEEPER MIXING DEPICTED BY THE HRRR/RAP IN
THE WARM SECTOR 2 TO 4 HOURS AHEAD OF THE QLCS. THIS RESULTS IN LCLS
JUMPING TO 1500-2000 M AND VERY PROMINENT INVERTED-V SOUNDINGS UP TO
700 MB.
WHILE THIS SCENARIO WOULD AMPLIFY THE DOWNBURST THREAT, IT ALSO
ERODES THE SBCAPE TO THE POINT THAT THE STRENGTH OF THE UPDRAFTS
(AND ASSOCIATED DOWNDRAFTS AND DAMAGING WINDS) COULD BE CALLED INTO
QUESTION. HOWEVER, THE STRONG SYNOPTIC DYNAMICS AND 50-70 KT 850-MB
JET THAT COULD BE TAPPED TO ENHANCE SURFACE WIND GUSTS MAY STILL BE
SUFFICIENT TO OVERCOME THIS LOSS OF INSTABILITY. THE LOSS OF SBCAPE
WOULD ONLY FURTHER DECREASE THE WIND AND TORNADO THREAT.
IF WE DO NOT MIX OUT AND TORNADOES ARE STILL IN THE CARDS, THE SSE
TO NNW ORIENTATION OF THE LINE COMPARED TO THE S-N ORIENTATION OF
THE 0-3-KM SHEAR VECTOR MEANS THAT ANY BOWING LINE SEGMENT WOULD
NEED TO UNDERGO SUBSTANTIAL REORIENTATION TO REALIZE A QLCS TORNADO
POTENTIAL. THE DEEPER SHEAR ORIENTATION LOOKS TO BE SOMEWHAT MORE
FAVORABLE COMPARED TO YESTERDAY FOR UPDRAFT MAINTENANCE.
SATURDAY - SUNDAY: STEADILY COOLING, RAW, SCATTERED RAIN/SNOW SHOWERS
THE TRUE SURFACE COLD FRONT PLOWS EASTWARD THROUGH THE FORECAST AREA
SATURDAY MORNING AS THE OCCLUDING SURFACE LOW PIVOTS AND EJECTS TO
THE NORTHEAST OVERNIGHT INTO SATURDAY MORNING. EXPECT HIGHS ON
SATURDAY TO BE REACHED IN THE EARLY MORNING HOURS WITH FALLING
TEMPERATURES THROUGH THE DAY. ALSO LOOK FOR PERIODS OF SHOWERS
WRAPPING AROUND THE OCCLUDED CYCLONE AND THROUGH THE FORECAST AREA
ON SATURDAY, GRADUALLY BECOMING MORE SCATTERED INTO THE EVENING.
EVEN THOUGH THE LOW IS PULLING AWAY BY SATURDAY AFTERNOON, A
LINGERING 500-MB VORT LOBE/WAVE SHOULD KEEP THE RISK FOR SHOWERS
THROUGH THE NIGHT INTO SUNDAY MORNING, WITH ENOUGH COLDER AIR
FILTERING DOWN TO CHANGE THE PRECIPITATION TYPE TO SNOW. AMOUNTS
LOOK TO BE VERY LIGHT, IF ANYTHING. WINDS ON SATURDAY WILL GUST TO
25 TO 35 MPH, WHICH WHEN COMBINED WITH THE FALLING TEMPERATURES AND
RAIN, WILL MAKE FOR A RATHER RAW DAY.
MONDAY - TUESDAY: REBOUNDING TEMPERATURES
THE SUNDAY COOL DOWN WILL BE SHORT-LIVED AS THE UPPER LEVEL TROUGH
MIGRATES EASTWARD AND WARMER AIR SURGES NORTHWARD WITH AN ADVANCING
WARM FRONT. HOW FAR NORTH THIS WARM FRONT ADVANCES IS THE BIG
QUESTION WITH A 10-15 DEGREE SPREAD IN THE INTERQUARTILE RANGE OF
THE NBM MEMBERS (UPPER 40S TO MID 60S). THE NORTHERN EXTENT OF THIS
BAROCLINIC ZONE WILL ALSO HELP DRIVE THE TRACK OF OUR MIDWEEK SNOW
STORM...
MIDWEEK: HEAVY SNOW?
WHILE SEVEN DAYS OUT, THE SIGNAL FOR A HEAVY SNOW OVER THE NORTH-
CENTRAL CONUS BETWEEN LATE TUESDAY AND EARLY THURSDAY IS SOLIDLY
PEGGED IN THE LONGER RANGE ENSEMBLES. THERE ARE STILL APPRECIABLE
DIFFERENCES IN THE LONGWAVE PATTERN WITHIN THE ENSEMBLE CLUSTER
SPACES, WITH ABOUT A 50/50 SPLIT IN A MORE PROGRESSIVE AND SHALLOW
WAVE THAT TAKES THE SURFACE LOW FURTHER NORTH AND ONLY GRAZES THE
FORECAST AREA WITH SNOW WHEREAS THE OTHER HALF DEEPEN THE WAVE AND
BRING UP A STRONG CYCLONE THAT LAYS OUT A DEFORMATION ZONE THROUGH
THE REGION.
THE ENSEMBLE MEMBERS THAT DO DEVELOP THIS DEFORMATION ZONE ARE
GENERATING RESPECTABLE SNOW AMOUNTS WITH 50% OF THE TOTAL EPS
MEMBERS (WITH A 10:1 SLR) BRINGING 6 INCHES OF SNOW AND 30% OF THE
MEMBERS DROPPING 12-18 INCHES OF SNOW. THE OPERATIONAL EC SURFACE
FIELDS ALSO RAISE THE CONCERN THAT STRONG WINDS COULD ACCOMPANY THIS
SNOW, BUT SUCH DETAILS ARE HARD TO PIN DOWN THIS FAR OUT. THE GEFS
IS LESS RAMBUNCTIOUS WITH SNOW AMOUNTS HERE GIVEN THAT MORE OF ITS
MEMBERS FAVOR THE SHALLOWER WAVE THAT BRINGS THE HEAVY SNOW FURTHER
NORTH INTO NORTHERN MINNESOTA, BUT THE FEW MEMBERS THAT DO HAVE THIS
MORE AMPLIFIED PATTERN ARE ALSO SPITTING OUT SIMILAR SNOW AMOUNTS.
SPRING IS CERTAINLY HERE!
AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 630 AM CDT THU MAR 13 2025
VFR CONDITIONS PREVAIL THROUGH THE TAF PERIOD. SOME HIGH LEVEL
CLOUDS (20KFT TO 25KFT) DURING THE DAY. A MORE DEFINED CEILING
OF THESE HIGH LEVEL CLOUDS OCCURS FOR EARLY FRIDAY MORNING.
SOUTHEAST WINDS INCREASE SLIGHTLY TODAY, MAINLY IN SOUTHEAST
MINNESOTA WHERE GUSTS OF 20 TO 25 MPH WILL BE POSSIBLE.
FIRE WEATHER
ISSUED AT 425 AM CDT THU MAR 13 2025
NEAR CRITICAL FIRE CONDITIONS FOR NORTHEAST IOWA FRIDAY
AFTERNOON...
WHILE THE RISK FOR STRONG SSE WINDS GUSTING TO 30 TO 40+ MPH IS
WELL RESOLVED IN THE FORECAST FOR FRIDAY AFTERNOON, THE DEGREE
TO WHICH WE MIX IN THE AFTERNOON AHEAD OF THE APPROACHING STORMS
(AND ITS EFFECT ON HUMIDITY VALUES) IS THE BIGGEST WILD CARD IN
THE FORECAST. THE OVERNIGHT RUNS OF THE RAP AND HRRR HAVE BEEN
VERY AGGRESSIVE IN MIXING THE BOUNDARY LAYER TO UPWARDS OF 5 TO
10 KFT, DROPPING DEWPOINTS INTO THE MID-40S. COMBINED WITH
RECORD WARM TEMPERATURES IN THE MID TO EVEN UPPER 70S, HUMIDITY
VALUES COULD CRASH TO AROUND 30% OR EVEN LOWER IN THE AFTERNOON.
THIS IS A LOW CONFIDENCE FORECAST RIGHT NOW AND WILL NEED TO BE
REASSESSED AS WE GO THROUGH THE DAY.
IN IOWA, THE GFDI IS ALREADY GETTING INTO EXTREME LEVELS FOR
THE AFTERNOON ON FRIDAY WITH THE HIGHER DEWPOINTS CURRENTLY
SUPPLIED BY THE NBM. FIRE WEATHER HEADLINES MAY BE NEEDED IF THE
DEWPOINTS FALL ANY FURTHER THAN FORECAST.
CLIMATE
ISSUED AT 425 AM CDT THU MAR 13 2025
POSSIBLE RECORD WARMTH (RECORD / FORECAST):
MAXIMUM MINIMUM
THURSDAY (03/13)
ROCHESTER, MN 68 (2024) / 64 N/A
LA CROSSE, WI 71 (2015) / 69 N/A
FRIDAY (03/14)
ROCHESTER, MN 74 (2012) / 72 49 (2012) / 50
LA CROSSE, WI 75 (2012) / 77 49 (1990) / 47
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...SKOW
AVIATION...CECAVA
FIRE WEATHER...SKOW
CLIMATE...SKOW
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