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Feb. 23-25th Winter Storm Part 2


Chicago Storm

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Funny tho, IWX mentions thinking heavier snow may creep N into its adv. counties and leaving the evening shift to monitor the northward momentum of the snow. Sometimes frustrating to see the different interpretations from different WFO's and even what models to hug or blend.

Maybe more impressive mid level dyamics = potential for further north defo band? I don't know, but based on the pressure change map SpartyOn posted, the RUC might be right.

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DTX>>>>>>

WINTER STORM WARNINGS AND ADVISORIES HAVE BEEN ISSUED FOR PORTIONS

OF SOUTHEAST MICHIGAN FROM LATE TONIGHT INTO FRIDAY MORNING.

A SWATH OF HEAVY SNOW IS EXPECTED LATE TONIGHT INTO FRIDAY MORNING

ON THE NORTH SIDE OF AN INTENSIFYING LOW PRESSURE SYSTEM TRACKING

FROM OKLAHOMA THROUGH THE OHIO VALLEY. REGIONAL 12Z SOUNDINGS SHOWED

A VERY DRY AIRMASS ABOVE 850MB ASSOCIATED WITH A RIDGE OF HIGH

PRESSURE BUT THE ATMOSPHERE IS EXPECTED TO MOISTEN RAPIDLY ACROSS

THE SOUTHERN TWO THIRDS OF THE FORECAST AREA AFTER MIDNIGHT. DRIER

AIR HOLDING ON ACROSS NORTHERN LOWER MICHIGAN AND LAKE HURON WILL

CONTINUE TO FUNNEL INTO THE AREA AS NORTHEAST WINDS INCREASE

OVERNIGHT...LIMITING THE NORTHERN EXTENT OF THE SWATH OF SNOW.

SPECIFIC HUMIDITIES CLIMB TO ABOUT 2 G/KG THROUGH 700MB AS FAR NORTH

AS THE M-59 CORRIDOR FOR ROUGHLY A 6-8 HOUR WINDOW OVERNIGHT.

SYSTEM RELATIVE ISENTROPIC ASCENT DOES INCREASE ABOVE 700MB(ROUGHLY

SOUTH OF A LINE FROM MACOMB TO ADRIAN) THIS EVENING AND WILL HELP IN

MOISTENING THE LOW LEVELS. DEFORMATION ABOVE 600MB WILL THEN BE THE

PRIMARY SOURCE OF LIFT ON THE NORTH SIDE OF THE OPEN MID-LEVEL WAVE

SLIDING ACROSS INDIANA AND NORTHERN OHIO. THE ENTRANCE REGION OF A

160 KNOT UPPER LEVEL JET WILL ALSO HELP TO STRENGTHEN THE FRONTAL

CIRCULATION IN THE 700-500MB LAYER. CONFIDENCE IS HIGH IN WIDESPREAD

SNOWFALL ALONG AND SOUTH OF THE M-59 CORRIDOR BUT SOME LIMITING

FACTORS ARE IN PLACE. CONVECTION CONTINUES TO LIGHT UP IN THE

WARM SECTOR FROM EASTERN TEXAS TO MISSOURI AND IT IS UNCLEAR IF THIS

WILL HAVE A NEGATIVE EFFECT ON MOISTURE TRANSPORT. THE TRACK OF THE

LOW COULD ALSO END UP BEING JUST A TOUCH FURTHER SOUTH AS THE LOW

LEVEL JET VEERS. THE STRONGEST LIFT ASSOCIATED WITH THIS STORM WILL

BE LIMITED TO A 4-6 HOUR WINDOW BETWEEN 3AM AND 8AM WITH LIGHTER

SNOW LINGERING FOR A FEW HOURS INTO FRIDAY MORNING. MODELS ARE

ADVERTISING BETWEEN .3-.4 INCH QPF ACROSS MOST OF THE AREA WITH A

10:1 OR 12:1 SNOW RATIO. WHILE MOST OF THE MODELS SHOW THE QPF

DECREASING TOWARDS THE M-59 CORRIDOR...THE 12Z NAM IS HIGHLIGHTING

JUST AS MUCH QPF IN THAT AREA AS DEFORMATION AXIS SETS UP AND PIVOTS

SLIGHTLY FURTHER NORTH. CERTAINLY THINK THE NAM MAY BE ON TO

SOMETHING WITH A SHARP DECREASE IN ACCUMULATIONS JUST NORTH OF THAT

LINE. WITH SOME RESERVATIONS ABOUT IF THE NAM PLACES THIS BAND IN

THE RIGHT LOCATION AND A SHIFT BACK TO THE SOUTH ON THE 18Z

NAM...WILL KEEP THE HIGHEST SNOWFALL ACROSS THE SOUTH AND TAPER

SNOWFALL AMOUNTS DOWN RAPIDLY NORTH OF THE M-59 CORRIDOR. MOST OF

THE METRO DETROIT AREA DOWN TO THE OHIO BORDER IS FORECAST TO HAVE 3

TO 5 INCHES OF SNOW WHICH IS RIGHT ON THE VERGE OF WARNING/ADVISORY

CRITERIA. GIVEN THAT HIGH PRECIP RATES ARE EXPECTED DURING THE

MORNING COMMUTE HAVE DECIDED TO GO WITH A LOW END WARNING FOR

LENAWEE/MONROE/WAYNE COUNTIES...AND AN ADVISORY FOR WASHTENAW/THE

M-59 CORRIDOR/ST CLAIR(MAINLY FOR SOUTHERN PORTIONS OF THE COUNTY)

FOR ROUGHLY 2-4 INCHES OF SNOW. OVERALL ACCUMULATIONS HAVE BEEN

TWEAKED DOWN JUST A TOUCH AND THE HEADLINES WILL NOT START UNTIL 2

AM. NORTHEASTERLY WINDS WILL INCREASE INTO THE 15-20 MPH RANGE LATE

TONIGHT WITH GUSTS TO 30 MPH POSSIBLE...CONTRIBUTING TO LOWER

VISIBILITIES AND POOR CONDITIONS.

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snip from LOT

THE DRY AIR WILL BE THE WILD CARD. 18Z DATA JUST COMING IN IS REALLY EMPHASIZING THE IMPACT OF THE DRY AIR ACROSS THE CENTRAL PART OF THE AREA OR JUST NORTH OF THE BEST WARM ADVECTION AND SOUTH OF FORCING MORE DIRECTLY TIED WITH THE UPPER LEVEL TROUGH. DO NOT WANT TO UNDERPLAY THE MITIGATING EFFECTS OF THE DRY AIR BUT DO HAVE CONCERNS THAT THE LATEST GUIDANCE IS OVERDOING THE IMPACT. PAST EVENTS THIS SEASON HAVE SHOWN THAT THE NAM IN PARTICULAR HOLDS OFF PRECIP TOO LONG IN THESE SITUATIONS. COMBINE THAT WITH THE IMPRESSIVE FORCING AND PRECIP MAY QUICKLY BREAK OUT. SO WILL NEED TO WATCH FOR NEAR TERM ADJUSTMENTS IN TIMING AND RESULTANT AMOUNTS BUT RIGHT NOW HAVE ENOUGH CONFIDENCE TO MAKE LITTLE CHANGE TO THE FORECAST AND CONTINUE WITH HEADLINES AS IS.

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Looking at the text output at the 12z HWRF, it doesn't match the clown maps. Has heavy snow down in Muncie and even Dayton.

I'd trust that. I only use the maps for a generalized bigger picture. I'm really liking that corridor I just mentioned...they are starting off with cooler surface temps and have a lot of qpf so the big question is what happens aloft.

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How likely is that? Is the NAM accurate this far in?

I wouldn't completely rule it out. I wouldn't go as high as what the NAM is showing for Indy, but the potential is there for amounts much higher than forecast. Other models and current trends support a slightly colder solution. This is a true nowcast event for central Indiana.

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Huge bust potential in the IND metro area. I'd watch the area from the north side of the city over toward Muncie and Winchester. That area could get clocked if it's mostly snow.

I agree completely, I am at 34 here, and all day we were forecast to be 40 or higher, and when I read the AFD and watch/adv statements I was shocked. Things are colder and qpf is high, huge bust potential.

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I live in northern Del county, so I use the Indy zones, but also the IWX zones for Blackford/Jay, and IWX has just updated their zones, and for Blackford/Jay, 8-9" total......

Yeah that's interesting...those amounts look to be a bit higher than the previous forecast. Usually offices won't update that soon after the afternoon package especially when the event hasn't started yet.

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Looking to me like the northern edge of this system in Iowa may bust. There is a heavy band from southeast Nebraska into southern Iowa, but it is not making any progress northward. Omaha was supposed to get 2-4 inches, but the northern half of the city apparently hasn't received a flake and the snow is pulling away. Des Moines has 2-5 for their metro and it appears they are only getting brushed by the band with nothing being reported north of Des Moines.

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MESOSCALE DISCUSSION 0128

NWS STORM PREDICTION CENTER NORMAN OK

0520 PM CST THU FEB 24 2011

AREAS AFFECTED...SERN IA...NERN MO...PORTIONS OF NRN/CNTRL IL/IN

CONCERNING...HEAVY SNOW

VALID 242320Z - 250515Z

SNOWFALL WILL SPREAD E-NEWD ACROSS SERN IA...NERN MO...AND PORTIONS

OF NRN/CNTRL IL/IN THIS EVENING. RATES WILL INCREASE TO 1 INCH PER

HOUR...WITH LOCALLY HIGHER AMOUNTS POSSIBLE.

STRONG ASCENT IN ASSOCIATION WITH THE INTENSE EXTRATROPICAL CYCLONE

APPROACHING THE MISSISSIPPI VALLEY REGION WILL ALLOW PRECIPITATION

TO EXPAND E-NEWD ACROSS THE DISCUSSION AREA. WHILE THERMAL PROFILES

WILL INITIALLY BE SUPPORTIVE OF RAIN ACROSS PORTIONS OF IL/IN...

RUC/NAM FORECAST SOUNDINGS INDICATE SUFFICIENT LOWER TROPOSPHERIC

COOLING THROUGH THE EVENING FOR THE PRECIPITATION TO CHANGE TO SNOW.

THIS WILL BE IN RESPONSE TO COLD AIR ADVECTION WEST OF THE CYCLONE

AND WILL BE AUGMENTED BY ADIABATIC COOLING ASSOCIATED WITH INTENSE

FORCING.

SNOWFALL RATES ARE EXPECTED TO REACH 1 INCH PER HOUR THROUGH THE

EVENING...AS LOW/MID-LEVEL FRONTOGENESIS QUICKLY STRENGTHENS INVOF

THE BAROCLINIC ZONE DRAPED ACROSS THE OHIO VALLEY REGION. ACROSS SRN

PORTIONS OF THE DISCUSSION AREA...SNOWFALL RATES TO 2 INCHES PER

HOUR WILL BE POSSIBLE. IN THIS REGION...THE JUXTAPOSITION OF AN AXIS

OF DEEPER MOISTURE PER RECENT TPW IMAGERY WITH INCREASING SLANTWISE

INSTABILITY WILL LIKELY SUPPORT PRECIPITATION BANDING AND LOCALLY

HIGHER RATES...ESPECIALLY IF AN ISOLATED THUNDERSTORM WERE TO OCCUR.

..COHEN.. 02/24/2011

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