168
FXUS63 KARX 200958
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
358 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 A 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 /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 1059 PM CST TUE NOV 19 2024
MVFR CEILINGS FROM EARLIER THIS EVENING HAVE MOVED NORTH OF THE TAF
SITES AS DRIER AIR MOVES INTO THE LOW LEVELS. MID-CLOUDS AROUND
10KFT FROM THE CENTRAL PLAINS HAVE BEEN STREAMING INTO THE
REGION AND SHOULD PROVIDE FOR A SCT TO BKN DECK AT THIS HEIGHT
OVERNIGHT BEFORE LOWER CEILINGS RETURN WEDNESDAY MORNING.
THE PRIMARY TAF CONCERN IS SCATTERED TO WIDESPREAD SNOW SHOWERS
EXPECTED WEDNESDAY AND THEIR IMPACTS TO VISIBILITY. STILL
UNCERTAINTY IN EXACT TIMING REGARDING WHEN SNOW SHOWERS IMPACT A TAF
SITE, BUT CONFIDENT THAT VISIBILITIES WILL DETERIORATE IN SNOW
SHOWERS SO HAVE INTRODUCED PROB30 FOR MVFR VISIBILITIES OF 3SM, BUT
VISIBILITIES WILL RAPIDLY BE REDUCED TO 1/2SM OR LESS IN THE MORE
ROBUST SNOW SHOWERS. GUSTY WEST TO NORTHWEST WINDS WILL
ACCOMPANY THE SNOW SHOWERS THROUGHOUT THE DAY WEDNESDAY. STILL
EXPECT SNOW ACCUMULATIONS TO BE LIGHT AND CONFINED TO GRASSY
AND COLD ELEVATED SURFACES, BUT PAVEMENT WILL BECOME WET.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...ZAPOTOCNY
AVIATION...FALKINHAM
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