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Dec 27-29th LES/Snow Event


Chicago Storm

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MKX AFD

WEAK LOW PRESSURE MOVES FROM THE CENTRAL PLAINS TO MISSOURI

TONIGHT...THEN EAST TO CENTRAL ILLINOIS ON FRIDAY. SHORTWAVE TROUGH

ALSO SHIFTS EASTWARD TO EASTERN IOWA/MINNESOTA BY 00Z SATURDAY AS

WELL. MODEST AT BEST UPWARD VERTICAL MOTION IS SEEN MOVING INTO THE

AREA FROM WEST TO EAST BETWEEN 06Z AND 15Z FRIDAY. LOW TO MID LEVEL

FRONTOGENESIS RESPONSE FIELDS ARE WEAK TO MODEST...THOUGH Q VECTOR

CONVERGENCE IS STRONGER IN THE 700MB TO 300MB LAYER. INVERTED

SURFACE TROUGH SHOULD HELP WITH UPWARD VERTICAL MOTION FRIDAY

AFTERNOON. AREA FORECAST SOUNDINGS SHOW MODEST AT BEST UPWARD

VERTICAL MOTION IN A LARGE DENDRITE GROWTH ZONE.

THUS...CONTINUED TREND OF TIMING IN HIGH END POPS FROM WEST TO EAST

BETWEEN 06Z AND 15Z FRIDAY. LIGHT SNOW WILL THEN PREVAIL THROUGH THE

DAY. AXIS OF HIGHEST QPF/SNOW WILL BE FROM NEAR THE DELLS TO

MILWAUKEE. A GENERAL 1 1/2 TO 3 INCHES ARE EXPECTED BY 00Z SATURDAY

ACROSS THE AREA.

A WINTER WEATHER ADVISORY WAS CONSIDERED FOR FRIDAY INTO FRIDAY

NIGHT...BUT LONG DURATION OF LIGHT SNOW...ALMOST 24 HOUR

DURATION...SUGGESTS THAT 3 TO 5 INCH CRITERIA WITHIN 12 HOURS WILL

NOT BE MET. WILL SEND AN UPDATED SPECIAL WEATHER STATEMENT TO

HIGHLIGHT THE SNOW FOR FRIDAY AND FRIDAY NIGHT. LATER SHIFTS WILL

HAVE TO MONITOR TRENDS AND CONSIDER AN ADVISORY...AS SNOW WILL

AFFECT THE FRIDAY MORNING COMMUTE IN MADISON...AND THE FRIDAY

EVENING COMMUTE IN MADISON AND MILWAUKEE.

.SHORT TERM...FRIDAY NIGHT THROUGH SUNDAY.

FRIDAY NIGHT...FORECAST CONFIDENCE MEDIUM.

FORCING WITH MAIN/INITIAL 500 MB TROUGH AXIS...AS WELL AS 850MB

AND 700MB LOW CENTERS...MOVE EAST OF FORECAST AREA BETWEEN 06Z AND

12Z SATURDAY...HOWEVER TRAILING VORT MAXES KEEP REGION UNDER BROAD

UPPER TROUGH. MODELS ALL KEEP SNOW GOING ACROSS THE NORTHEAST HALF

OF THE CWA INTO THE OVERNIGHT HOURS...WITH CONVERGENCE ON APEX OF

INVERTED SURFACE TROUGH REMAINING NEARLY STATIONARY THROUGH 06Z

SATURDAY...THEN SLOWLY DROPPING SOUTH THROUGH THE CWA. THIS HAS

THE POTENTIAL TO ADD ANOTHER 0.5 INCH TO 1.8 INCHES OF SNOW OVER

THE FORECAST AREA...WITH THE HIGHER ADDITIONAL AMOUNTS IN THE

NORTHEAST HALF. WILL END UP WITH SNOW TOTALS OF 3 TO 5 INCHES

ACROSS SOUTHERN WISCONSIN...HIGHER NEAR THE LAKE BUT OVER A

30-HOUR PERIOD.

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DTX thoughts on this potential.

SNOW WILL BE BACK IN THE WEATHER PICTURE AS EARLY AS FRIDAY

AFTERNOON BUT IS EXPECTED TO BE JUST AN INCH OR TWO OF ACCUMULATION

ADDED TO YESTERDAY`S STORM. THE RESPONSIBLE SYSTEM IS MOVING SLOWLY

THROUGH THE CENTRAL PLAINS TODAY WITH A WELL ORGANIZED LEAD WAVE IN

THE UPPER LEVELS. THE LATEST MODEL SOLUTIONS SHOW THIS FEATURE

SHEARING WEST AND NORTH OF LOWER MICHIGAN TONIGHT TRAILED BY A NEW

ROUND OF MODEST HEIGHT FALLS FROM THE CENTRAL ROCKIES INTO THE

CENTRAL PLAINS. IT IS THE LARGER SCALE WAVE THAT WILL AFFECT OUR

AREA FRIDAY AFTERNOON THROUGH FRIDAY NIGHT WITH A GOOD COMBINATION

OF DCVA AND ISENTROPIC LIFT. SYSTEM RELATIVE ISENTROPIC LIFT IS

INDICATED IN MODEL DATA TO START OUT BY EARLY AFTERNOON IN THE 700

TO 500 MB LAYER WHERE STABILITY IS QUITE LOW ACCORDING TO CROSS

SECTIONS OF THETA, THETA-E, AND THETA-T. THIS WILL LIKELY RESULT

IN A DEEP LAYER OF MODERATE VERTICAL MOTION COMPARED TO WHAT WE

MIGHT EXPECT BY JUST VISUAL INSPECTION OF THE SURFACE TO 500 MB

WAVE IN THE MODEL DATA. THEN, LATER IN THE DAY INTO FRIDAY NIGHT,

ISENTROPIC LIFT MIGRATING INTO THE 850 TO 700 MB LAYER WILL

COMBINE WITH INCREASED SHORT WAVE FORCING TO MAINTAIN THE PATTERN

OF SNOW. PRESSURE ADVECTION ON THE 285K SURFACE CONSISTS OF SOME

SHARP GRADIENTS AROUND 750 MB IN BOTH THE NAM AND GFS SOLUTIONS

THAT HINT AT A LINGERING COMPONENT OF LOW STABILITY THAT WILL BE

GOOD FOR A FEW BURSTS OF HEAVIER SNOW SHOWERS BEFORE FORCING WANES

TOWARD MIDNIGHT. USING CARE TO ALLOW GULF COAST CYCLOGENESIS TO

INTERCEPT SOME LOW LEVEL MOISTURE IN THE SOUTHERN WAVE, PLAN TO

MAINTAIN OUR GOING 1 TO 2 INCH FORECAST WHICH ALREADY LEANS TOWARD

THE HIGHER END OF MODEL POP AND QPF OFFERINGS. THE BROAD LARGER

SCALE UPPER TROUGH AND ASSOCIATED COLD POOL, COMBINED WITH LAKE

EFFECT IN NORTHWEST LOW LEVEL FLOW, WILL THEN KEEP A CHANCE OF

SNOW SHOWERS IN THE FORECAST THROUGH SATURDAY. ALL OF THESE

TOGETHER COULD ADD UP TO ANOTHER INCH AROUND THE AREA BY SATURDAY

NIGHT.

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Hellz yeah!

...ACCUMULATING SNOW IN SOUTHERN WISCONSIN BEGINS LATE TONIGHT...

LIGHT SNOW ASSOCIATED WITH A SLOW-MOVING WEATHER SYSTEM WILL

SPREAD INTO SOUTH CENTRAL WISCONSIN LATE TONIGHT AND EARLY FRIDAY

MORNING...AND INTO SOUTHEAST WISCONSIN BY MID-MORNING FRIDAY.

SNOW WILL CONTINUE TO FALL THROUGH THE DAY AND DIMINISH LATE FRIDAY

NIGHT. THE SNOW WILL GENERALLY REMAIN LIGHT...WITH BRIEF PERIODS

OF MODERATE SNOW.

SNOWFALL ACCUMULATIONS WILL BE IN THE 3 TO 4 INCH RANGE...WITH

THE HIGHER AMOUNTS FROM WISCONSIN DELLS TO MADISON TO MILWAUKEE.

SNOW WILL BE FALLING IN MADISON DURING THE MORNING COMMUTE...AND

WILL BE ONGOING DURING THE AFTERNOON COMMUTE IN BOTH MADISON AND

MILWAUKEE. IN ADDITION...LOCALIZED LAKE ENHANCED SNOWFALL WILL BE

POSSIBLE IN MILWAUKEE AND PORT WASHINGTON AREAS.

Radar loop reminds me alot of a disorganized tropical storm, circulation center roaming around in the Dakotas with the precip activity all sheared off to the east. Classic positive vorticity advection by the thermal wind leading to upward motion and precip. http://tempest.aos.w...wcompflash.html

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Lol, that band is just crawling along! I don't think any of the models suggested a 12 hour stay over Cook County!

Makes me wonder where the receiving end will be tomorrow as the mesolow looks to stay in place over the lake.

It's a nice band but it should steadily shift location throughout the event due to the changing wind direction. I'd be surprised if the lakefront sees crazy snow totals, I'm expecting more like 1-4 inches over a broad area.

Lots of virga and not much precipitation right now as far as the real snow event goes, it's early but that's probably a sign that totals will be less than anticipated. Dewpoints are forecast to stay much lower than the temp throughout the event.

Regardless, I'm excited for some accumulating snow, whether it be half an inch or 6.

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It's a nice band but it should steadily shift location throughout the event due to the changing wind direction. I'd be surprised if the lakefront sees crazy snow totals, I'm expecting more like 1-4 inches over a broad area.

Lots of virga and not much precipitation right now as far as the real snow event goes, it's early but that's probably a sign that totals will be less than anticipated. Dewpoints are forecast to stay much lower than the temp throughout the event.

Regardless, I'm excited for some accumulating snow, whether it be half an inch or 6.

Would the lake effect help seed the clouds around here tonight? Limit the amount of virga to fall?

Looks like that band is staying in Cook County for awhile!

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