185
FXUS63 KARX 201133
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
533 AM CST WED NOV 20 2024
KEY MESSAGES
- SCATTERED SNOW SHOWERS TODAY AND THIS EVENING WITH BREEZY
WINDS. EXPECT POTENTIAL TRAVEL IMPACTS WITH BRIEF REDUCTIONS
IN VISIBILITY. SNOW ACCUMULATIONS MOSTLY FROM A TRACE/0.1" TO
1.5".
- GUSTY NORTHWEST WINDS 30 TO 40 MPH+ THURSDAY ALONG WITH A
RAIN/MIX ESPECIALLY EAST OF THE MISSISSIPPI RIVER.
DISCUSSION
ISSUED AT 330 AM CST WED NOV 20 2024
OVERVIEW:
AN INTENSE 989MB AREA OF LOW PRESSURE WAS LOCATED OVER SOUTHWEST
MINNESOTA AT 08Z WITH A STRONG PRESSURE GRADIENT ACROSS THE DAKOTAS
INTO MN. THE LATEST WSR-88D RADAR SHOWED LIGHT RAIN DEVELOPING
IN A BAND JUST EAST OF THE FORECAST AREA TOWARD MSN/MKC INTO
ILLINOIS AND A BROAD AREA OF SNOW ACROSS THE DAKOTAS INTO
MINNESOTA. THE LEADING EDGE OF THE PRECIPITATION WAS A MIX OF
RAIN AND SNOW. EVEN SOME LIGHTNING WAS NOTED NEAR FSD/SOUTHWEST
MN PER THE GLM DATA. LOCALLY, SURFACE TEMPERATURES WERE IN THE
30S AND 40S WITH SOUTHWEST TO WEST WINDS AT 5 TO 15 MPH.
WATER VAPOR SATELLITE IMAGERY, AND HEIGHTS, SHOWED THE CENTER OF THE
CLOSED LOW OVER NORTHERN MINNESOTA WITH TROUGHING EXTENDING
SOUTHWARD TOWARD IOWA. A RIDGE WAS LOCATED FROM MONTANA THROUGH UTAH
TOWARD ARIZONA WITH ANOTHER AREA OF CLOSED LOW PRESSURE OFF THE WEST
COAST.
SCATTERED SNOW SHOWERS TODAY AND THIS EVENING WITH BREEZY
WESTERLY WINDS. EXPECT POTENTIAL TRAVEL IMPACTS WITH BRIEF
REDUCTIONS IN VISIBILITY. SNOW ACCUMULATIONS MOSTLY FROM A TRACE
A 0.1" TO 1.5".:
THE SHOWERS TO THE SOUTHEAST WERE FORMING ALONG AN AREA OF
FRONTOGENESIS AND THE LEADING EDGE OF THE COLDER AIR. THROUGH
TODAY, THE MID-TROPOSPHERIC CLOSED LOW IS FORECAST TO ELONGATE
AND DROP SOUTHEAST ACROSS WISCONSIN TOWARD THE OHIO RIVER
VALLEY. REINFORCING COLD AIR ACCOMPANIED BY DEEPENING MOISTURE
WILL CONTINUE THROUGH THE DAY. THIS COMBINATION IS ALREADY
PRODUCING A LARGE AREA OF SNOW TO OUR WEST, ESPECIALLY WHERE
850MB TEMPERATURES ARE -9 DEG C OR COLDER. INITIAL AMOUNTS WERE
A TRACE, BUT FARTHER TO THE NORTHWEST IN THE DEEP AIR WITHIN THE
DENDRITIC GROWTH ZONE, 3HR PRECIPITATION AMOUNTS WERE FROM A
TRACE TO 0.07.
STEEP LAPSE RATES AND SATURATION THROUGH THE DENDRITIC GROWTH ZONE
ARE STILL FORECAST WITH CONVECTIVE TEMPERATURES BEING MET.
INSTABILITY IS SLIGHTLY LOWER 40 TO 80 J/KG, THE MOST RECENT RUNS OF
THE NAM/RAP HAVE A SNOW SQUALL PARAMETER LOWER THAN YESTERDAY, MORE
IN THE 1 TO 2 RANGE AND THE SLIGHT STRONGER SIGNAL ON THE RAP IS
GOING TO OUR SOUTHWEST OVER PARTS OF IOWA THIS MORNING, HOWEVER
STILL INCREASE IT IN THE 1 TO 4 RANGE FOR PARTS OF IOWA AND
SOUTHERN WI 18-00Z. THE SNOW SHOWERS WILL BE VARIABLE, BUT LIGHT
SNOW ACCUMULATIONS STILL LOOK REASONABLE FOR GRASSY AREAS AND
HIGHER ELEVATIONS FROM TRACE/0.1" TO 1.5". 20.00Z HREF HAS 30
TO 70% CHANCE OF MEASURABLE SNOW (0.1" OR MORE) OF SNOW AND 0 TO
10% PROBABILITY OF 1" OR MORE. PROBABILITIES FOR VISIBILITY
LESS THAN 1 MI. ARE 10 TO 60%, INCREASING TONIGHT WITH THE
DEEPENING OF THE COLD AIR/DEPTH OF MOISTURE. THE AXIS OF
STRONGER WINDS WITH GUSTS 25 TO 35KTS IS FROM MINNESOTA INTO
IOWA AND WIND ADVISORIES HAVE BEEN POSTED THERE.
WITH IT BEING THE POTENTIAL FOR THE FIRST ACCUMULATING SNOW IF
TRAVELING, CHECK THE LATEST FORECAST AND ROAD CONDITIONS BEFORE
HEADING OUT. TYPICALLY THE FIRST 1" OF SNOW AT ROCHESTER IS NOV. 21
AND FOR LA CROSSE, IT IS NOV. 27TH!
GUSTY NORTHWEST WINDS 30 TO 40 MPH+ THURSDAY ALONG WITH A
RAIN/MIX ESPECIALLY EAST OF THE MISSISSIPPI RIVER:
THE LARGE CLOSED LOW OVER MUCH OF THE GREAT LAKES AREA IS FORECAST
TO HAVE 850MB WINDS OF 50 TO 65+KTS ROTATING AROUND IT. THERE IS
NOT GREAT AGREEMENT ON HOW STRONG THE WINDS WILL BE. NEARLY ALL THE
ECE MODELS HAVE GUSTS OF 40 MPH+ AT KLSE, WHILE THE GEFS MODELS
ONLY 10% HAVE GUSTS 40 MPH+. THE FORECAST SOUNDINGS DO NOT SHOW
GREAT COLD AIR ADVECTION OR UNIDIRECTIONAL WINDS ALOFT, HOWEVER
TO HAVE A VERY STRONG ISALLOBARIC COMPONENT TO THE WIND. USING
ALL AVAILABLE GUIDANCE, THE PROBABILITIES FOR 40+ MPH WIND GUSTS
FOR THURSDAY RANGE FROM 30 TO 70%. IN ADDITION, A RAIN SNOW MIX
WILL BE POSSIBLE, WITH LIGHT AMOUNTS AND LITTLE TO NOW SNOW
ACCUMULATIONS AT THIS TIME.
RIDGING BUILDS IN FOR FRIDAY AND SATURDAY. LIGHT PRECIPITATION
COULD TRY TO DEVELOP NORTH OF A WARM FRONT SUNDAY AND ALSO WITH THE
COLD FRONTAL PASSAGE LATER IN THE DAY INTO SUNDAY NIGHT WITH A
WINTRY MIX
HIGHS TODAY THROUGH THE WEEKEND AND EARLY NEXT WEEK SHOULD MOSTLY
BE IN THE 30S AND 40S.
AVIATION /12Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 533 AM CST WED NOV 20 2024
SNOW SHOWERS AND MVFR CEILINGS WILL BE THE PREDOMINANT DRIVERS OF
THE FORECAST OVER THE NEXT 24 HOURS AS LOW-LEVEL SATURATION
INCREASES INTO THE DENDRITIC GROWTH ZONE WITH ALONG WITH LIFT
ASSOCIATED WITH A LOW PRESSURE SYSTEM TO OUR NORTHWEST. AS WE
CONTINUE THROUGH THE MORNING AND INTO THE AFTERNOON, SNOW
SHOWERS WILL MOVE IN FROM THE WEST AND INCREASE IN COVERAGE INTO
THE AFTERNOON HOURS. ADDITIONALLY, EXPECTING CEILINGS TO DROP
TO MVFR AS THIS OCCURS. FURTHERMORE, WOULD NOT RULE OUT
OCCASIONAL VSBY DROPS TO IFR AT EITHER KLSE OR KRST TODAY,
HOWEVER CONFIDENCE (~10% CHANCE) REMAINS LOW ON HOW THIS WOULD
MANIFEST. REGARDLESS, SNOW SHOWERS WILL LIKELY BRING SOME MVFR
VSBY REDUCTIONS AND ACCUMULATIONS ON MAINLY GRASSY SURFACES
THROUGHOUT THE DAY. SNOW SHOWERS WILL DIMINISH INTO THE EVENING
WITH MVFR CIGS HOLDING STEADY THROUGH THE OVERNIGHT. AS A
SURFACE PRESSURE GRADIENT TIGHTENS ASSOCIATED WITH THE
AFOREMENTIONED LOW, WINDS WILL INCREASE INTO FRIDAY MORNING FROM
THE NORTHWEST TO 15-20 KTS WITH GUSTS APPROACHING 30 KTS BY 12Z
ON FRIDAY.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...ZAPOTOCNY
AVIATION...NAYLOR
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