Chicago snowstorm still in the works..or not?

[PurdueWx80]

gives Chicagoland a 5-8" snowstorm (assuming a 10:1 ratio) out of this baby comin' out of the SW. The depth, track and amount of "phasing" are much more in question this time around than during the last storm, so I don't quite believe this scenario just yet (although the Eta outperformed the track and strength of the surface low for the last storm, and the pattern is similar, so I give it some credence). The last 2 runs of the Eta have had a more powerful upper low coming out of the SW, with indications of a 150+ kt jet streak on the SE side of the negatively tilted shortwave trough (and hence, a stronger surface low than any other model). The ULL should be better sampled by observing stations this evening, so the models should hone in on this storm with more consistency and accuracy within the next day or so. The strength and placement of the mid/upper low will dictate just where the heaviest snow can fall. It will obviously also be a matter of where the surface air is cold enough to support freezing precip. Another hint I'm using as to how much of the trough will come out of the SW is the upper low just west of Hawaii. If it stays over or very near Hawaii the trough will see more of a split, but if it comes just east of the Islands, a more powerful trough/low/vort will come out of this, only leaving a stream of vorticity in its wake.

EDIT: Removed old model runs...

[Wnghs2007]

Thats really cool Purdue. Whens the next severe chance down south?

[PurdueWx80]

Looks to me like Tuesday will be a big severe weather day in the South once again. The upper-level support is there (no matter how it works out in the end), but it will come down to the behavior of the warm front, resulting surface temps and dewpoints in the afternoon, and the track of the surface low.

Discussion from SPC:

...GULF COAST STATES...
DISCREPANCIES DEVELOPING AMONG MODELS AND LATEST MODEL RUNS ARE
CONTRIBUTING TO SUBSTANTIAL UNCERTAINTY WITH REGARD TO EXTENT OF
CONVECTIVE POTENTIAL ACROSS THE GULF COAST STATES TUESDAY INTO EARLY
WEDNESDAY. LATEST MODEL RUNS APPEAR TO BE TRENDING TOWARD DEEPER
POLAR LOW IN NORTHERN BRANCH OF THE WESTERLIES ACROSS SOUTHEASTERN
CANADA BY EARLY TUESDAY...WHILE ALSO TRENDING TOWARD WEAKER SOUTHERN
BRANCH SYSTEM APPROACHING THE PACIFIC NORTHWEST COAST. THESE TRENDS
NOW APPEAR LIKELY TO SUPPORT NORTHEASTWARD ACCELERATION OF SOUTHERN
BRANCH CLOSED LOW/TROUGH OUT OF THE FOUR CORNERS STATES LATE MONDAY.
BY EARLY TUESDAY...SUBSTANTIAL WEAKENING OF UPPER SYSTEM APPEARS
LIKELY AS IT ACCELERATES INTO CONFLUENT REGIME BETWEEN POLAR LOW AND
SUBTROPICAL RIDGE...WHICH WILL EXTEND ACROSS THE GULF OF MEXICO AND
THE SOUTH ATLANTIC COAST STATES INTO THE WESTERN ATLANTIC.

GIVEN PRESENCE OF SIGNIFICANT SURFACE RIDGE ALONG THE ATLANTIC COAST
STATES EARLY IN THE PERIOD...AND SURFACE COLD FRONT SURGING INTO THE
LOWER MISSISSIPPI VALLEY AND WESTERN GULF COASTAL AREAS...BREADTH OF
EVOLVING WARM SECTOR APPEARS LIKELY TO BE LIMITED. THIS...IN
CONJUNCTION WITH MORE LIKELY WEAKER SURFACE LOW DEVELOPMENT ON
NORTHERN END OF INVERTED TROUGH ACROSS THE TENNESSEE VALLEY...WILL
MINIMIZE RISK OF MORE SUBSTANTIAL CONVECTIVE OUTBREAK AND SEVERE
WEATHER THREAT DURING THIS FORECAST PERIOD.

HOWEVER...STRONG UNIDIRECTIONAL...SOUTHWESTERLY FLOW FIELD IS
PROGGED TO DEVELOP ACROSS THE LOWER MISSISSIPPI VALLEY AND CENTRAL
GULF COAST STATES TUESDAY...AS A 100 KT 500 MB JET STREAK DEVELOPS
FROM THE VICINITY OF ARKANSAS INTO TENNESSEE. WITH AT LEAST A
NARROW CORRIDOR OF WEAK SURFACE-BASED INSTABILITY EXPECTED TO
DEVELOP WITH MOISTURE RETURN AHEAD OF COLD FRONT...SOME POTENTIAL
EXISTS FOR DEEP CONVECTIVE DEVELOPMENT AND SUBSEQUENT EVOLUTION OF
SQUALL LINE. THIS APPEARS MOST PROBABLE ACROSS FROM SOUTHEAST
LOUISIANA THROUGH SOUTHERN MISSISSIPPI INTO WESTERN ALABAMA TUESDAY
AFTERNOON. CONVECTION MAY BE VIGOROUS ENOUGH TO AID DOWNWARD
TRANSFER OF HIGHER MOMENTUM TO THE SURFACE...ENHANCING RISK OF
DAMAGING WIND GUSTS.

[PurdueWx80]

Bump - The 12z Eta is now going bonkers with this storm in Chicago. While thicknesses appear to become cold enough to support snow after some rain has fallen, the dynamics and strength of this storm as well as the fact that much of the precipitation will fall Tuesday night lead me to believe most of the QPF will be snow in Chicagoland. There is somewhat better agreement this morning now that the upper low's progression and evolution is being better sampled, but there is still a rather large degree of uncertainty in the track and depth of the surface low (specifically between the GFS and Eta). The 12Z UKMET and NOGAPS agree moreso with the GFS' further east track. Another major difference is with the strength (and placement) of the deformation zone on the back side of the upper low. The Eta's is stronger (thus suggesting the possibility of a 6-10" storm in Chicago and parts of IN/MI) and thus further west, while the GFS suggests a weaker def-zone will be across central IN to eastern MI. This is all basically still a matter of how they are handling the ejection of the upper low over the 4 corners. The kicker (powerful storm plowing into the Pac NW and BC, Canada) is rounding the bend and will be sampled by tonight's balloon launch, thus increasing the probability of better agreement and a resulting better simulation of the atmosphere downstream. Of note is the fact that the 4 corners region is relatively sparsely sampled by upper soundings, thus the strength of the low has been noted to be underdone by models.

Quote from Northern IN morning AFD:

MAIN FEATURE OF INTEREST WILL COME AT THE BEGINNING OF THE LONG TERM
ON TUE/TUE NGT. A LOOK AT MODEL INITIALIZATION FIELDS THIS MORNING
SHOWS THAT BOTH THE ETA/GFS ARE NOT CAPTURING THE STRENGTH OF THE
SOUTHWEST US CUTOFF LOW. AT H5 BOTH MODELS ARE TOO HIGH WITH HEIGHTS
NEAR THE CENTER OF THE CUTOFF LOW. NOT SURPRISING CONSIDERING THE
FACT THAT IT IS CENTERED OVER AN UPPER AIR DATA HOLE NEAR THE
UTAH/ARIZONA BORDER. BOTH THE ETA AND GFS ARE NOW STRONGER AND
FURTHER NW WITH MID LEVEL AND SURFACE FEATURES COMPARED TO PREVIOUS
RUNS. WOULD EXPECT THE TREND OF A STRONGER SOLUTION TO CONTINUE AS
THE MODELS BEGIN TO CAPTURE THE TRUE STRENGTH OF THE SOUTHWEST US
CUTOFF. AS IT STANDS NOW THE MID LEVEL LOW EJECTS INTO THE SOUTHERN
PLAINS BY TUESDAY MORNING AND THEN SHEARS NORTHEAST RAPIDLY CROSSING
THE CWA LATE TUES NIGHT. WOULD NOT BE SURPRISED TO SEE FUTURE MODEL
RUNS HOLD ON TO A CLOSED LOW FOR MUCH LONGER AS IT EJECTS NORTHEAST
ACROSS THE COUNTRY...WHICH WOULD TEND TO LEAD TOWARDS A LITTLE
SLOWER SOLUTION.

It's a shame this event will begin as soon as tomorrow afternoon...the NWSFOs in Chicago, N. IN, Lincoln, IL, Grand Rapids, MI and Detroit, MI will have a tough time deciding whether or not to issue Winter Storm Watches this afternoon, although I think it would be a good idea.

[PurdueWx80]

Update...neither Northern IN or Detroit have gone with a watch...they think a later switchover will reduce amounts to sub-warning criteria. Sounds to me like they don't trust the Eta (in fact Detroit trusts the GFS "because of it's performance during the Thanksgiving week storm"). I'm not sure what they're talking about, but the Eta stomped all over the GFS last week from my recollection. The 18Z Eta isn't much different.

I'm gonna have to agree with the Eta once again in this situation. I'd look for a general 4-6" snowstorm that'll include central IL, Chicago, Grand Rapids, Detroit, South Bend and perhaps Ft. Wayne. I think parts of MI may see up to a foot where the lake will contribute to instability and moisture. Thundersnow is once again not out of the realm of possibility, especially with the rapidly deepening storm depicted in the Eta. There is some hint of frontogenetic forcing at 850 and 700 mb, but a TROWAL feature is also seen near the deformation zone, which is why I think a few places may see 6-10" or up to a foot where heavy bands persist. If the GFS (weaker surface and upper lows) comes to fruition, reduce everything by half and move it further east/south.

[Guest]

Update...neither Northern IN or Detroit have gone with a watch...they think a later switchover will reduce amounts to sub-warning criteria. Sounds to me like they don't trust the Eta (in fact Detroit trusts the GFS "because of it's performance during the Thanksgiving week storm"). I'm not sure what they're talking about, but the Eta stomped all over the GFS last week from my recollection. The 18Z Eta isn't much different.

I'm gonna have to agree with the Eta once again in this situation. I'd look for a general 4-6" snowstorm that'll include central IL, Chicago, Grand Rapids, Detroit, South Bend and perhaps Ft. Wayne. I think parts of MI may see up to a foot where the lake will contribute to instability and moisture. Thundersnow is once again not out of the realm of possibility, especially with the rapidly deepening storm depicted in the Eta. There is some hint of frontogenetic forcing at 850 and 700 mb, but a TROWAL feature is also seen near the deformation zone, which is why I think a few places may see 6-10" or up to a foot where heavy bands persist. If the GFS (weaker surface and upper lows) comes to fruition, reduce everything by half and move it further east/south.

Agreed 100% ! Not sure myself of why N.Indy and Detroit would say that. And like last week (With N.IN anyways) i suspect at the last moment they will change thier minds and issue some watches and or warnings.

[PurdueWx80]

No watches by any NWSFO....makes some sense since there is such poor agreement this close in. I wish they would at least have some guts in this situation since there is at least the possibility of a MAJOR storm that would begin in 24 hours.

Quote from Chicago afternoon discussion basically agrees with me:

WITH GFS WUD APPEAR THAT MAIN SNOW BAND WILL BE FROM LASALLE AND
LIVINGSTON ON NE THRU CHI AND VALPARAISO WITH 2 TO 4 INCHES POSSIBLE
BUT MAYBE MORE LIKE 1 TO 3 DEPENDING ON RAIN/SNOW TIME RATIO. IF ETA
WERE IN CHARGE OF THIS SYSTEM...SNOWFALL WUD PROBABLY DOUBLE. THUS
WITH DISUNITY IN MODELS...WILL HOLD OFF ON ANY HEADLINES FOR TUESDAY
NIGHT BUT WUD ADVERTISE TO ALL TO KEEP MONITORING EACH LATEST
DEVELOPMENT

[Anonymous]

Well look at it this way:

You'll find out how much snow will fall soon enough.

-Jeb

[PurdueWx80]

LOL...true Jeb...it's just fun to try to predict this stuff and it gets really annoying when the guidance differs this much. Ya just have to go with your gut based on the education and experience you've had with these systems.

That said, the more I look at this, the more I agree with the Eta. A 130-160 kt jet at 300 mb will be oriented so that the left front quad is over the surface low tomorrow night. There is plenty of surface convergence already along an old cold front (which is now an inverted trough axis), warm air advection is underway and strong vorticity advection will begin as the low is ejected. I honestly don't see why this storm won't bomb out like the Eta shows (1012 mb tomorrow afternoon to ~988 mb 24 hours later). I guess I'll shut up unless something changes drastically but there are probably going to be some PO'd people tomorrow evening when much more snow falls than they were led to believe.

By the way, Kansas City, Kirskville and the Quad Cities will probably see a dusting to several inches out of this as well...I've just been concentrating on the main event as the low develops tomorrow evening.

[Guest]

BTW have picked up a dusting so far with the little batch of moisture moving thu sw MI. Still snowing to.

[Anonymous]

LOL...true Jeb...it's just fun to try to predict this stuff and it gets really annoying when the guidance differs this much. Ya just have to go with your gut based on the education and experience you've had with these systems.

That said, the more I look at this, the more I agree with the Eta. A 130-160 kt jet at 300 mb will be oriented so that the left front quad is over the surface low tomorrow night. There is plenty of surface convergence already along an old cold front (which is now an inverted trough axis), warm air advection is underway and strong vorticity advection will begin as the low is ejected. I honestly don't see why this storm won't bomb out like the Eta shows (1012 mb tomorrow afternoon to ~988 mb 24 hours later). I guess I'll shut up unless something changes drastically but there are probably going to be some PO'd people tomorrow evening when much more snow falls than they were led to believe.

I encourage all of you to go on evaluating the weather and the models because I AM learning and one day it will be ME, JEB, doing the evaluating. Then everyone can judge my storm eval.

That's my dream.

-Jeb

[Anonymous]

BTW have picked up a dusting so far with the little batch of moisture moving thu sw MI. Still snowing to.

You LUCKY Dog!!! Always getting snow!!!

Enjoy it King, this is only the beginning, you're gonna get so much snow this winter that you will be tired of digging snow!

-Jeb

[Guest]

Well GRR isnt biting yet. Them like the models are doing the EXACT same thing that happend a week ago. Gonna wait till the last possible moment.

[PurdueWx80]

So no one bit...yet. I suppose that was the thing to do, but if the Eta doesn't budge this evening, and the 18 or 00Z GFS move toward it, a watch must be issued overnight. Another thing I just noticed is that this system is about to get a big influx of tropical moisture from the East Pacific (check out the area from 10-20N and 120-130W roughly). That should get chucked in front of the upper low in time for it to contribute to moisture that will be converted to precip.

http://www.ssd.noaa.gov/PS/TROP/DATA/RT ... -loop.html

The Gulf is also wide open with dewpoints in the mid-70's on the TX coast and widespread 60's in the rest of the area:

[Anonymous]

Here's another DP chart:

http://vortex.plymouth.edu/cgi-bin/gen_ ... d=&zoom=.6


And another:



You can readily see a "nose" of higher dewpoints in the GOM just waiting to be pulled up ahead of the developing storm.

[Guest]

What i find ironic about all this with GRR and the others is the unwillingness to let go of the rain and just go with mainly snow. TODAY should have given them a clue on that as none of the models are even them went with what i have gotten anyways. which btw is at a 1/2 inch on the ground and its still comming down.

My thinking is the precip will possibly start out briefly as some rain perhaps but once it gets going there will be a quick change to snow as the heavier precip will help to pull down some colder air such as todays event did. Another thing working against the rain is that everything will be comming in at night.

Good catch on the Pacific plume comming in. I suspect by Morning GRR and surrounding offices will upgrade to a winterstorm watch for all areas in GRR and as well all of N.IN/S.MI and the NW OH counties from the N.IN office.

[Wnghs2007]

Looks to me like Tuesday will be a big severe weather day in the South once again. The upper-level support is there (no matter how it works out in the end), but it will come down to the behavior of the warm front, resulting surface temps and dewpoints in the afternoon, and the track of the surface low.

Discussion from SPC:

...GULF COAST STATES...
DISCREPANCIES DEVELOPING AMONG MODELS AND LATEST MODEL RUNS ARE
CONTRIBUTING TO SUBSTANTIAL UNCERTAINTY WITH REGARD TO EXTENT OF
CONVECTIVE POTENTIAL ACROSS THE GULF COAST STATES TUESDAY INTO EARLY
WEDNESDAY. LATEST MODEL RUNS APPEAR TO BE TRENDING TOWARD DEEPER
POLAR LOW IN NORTHERN BRANCH OF THE WESTERLIES ACROSS SOUTHEASTERN
CANADA BY EARLY TUESDAY...WHILE ALSO TRENDING TOWARD WEAKER SOUTHERN
BRANCH SYSTEM APPROACHING THE PACIFIC NORTHWEST COAST. THESE TRENDS
NOW APPEAR LIKELY TO SUPPORT NORTHEASTWARD ACCELERATION OF SOUTHERN
BRANCH CLOSED LOW/TROUGH OUT OF THE FOUR CORNERS STATES LATE MONDAY.
BY EARLY TUESDAY...SUBSTANTIAL WEAKENING OF UPPER SYSTEM APPEARS
LIKELY AS IT ACCELERATES INTO CONFLUENT REGIME BETWEEN POLAR LOW AND
SUBTROPICAL RIDGE...WHICH WILL EXTEND ACROSS THE GULF OF MEXICO AND
THE SOUTH ATLANTIC COAST STATES INTO THE WESTERN ATLANTIC.

GIVEN PRESENCE OF SIGNIFICANT SURFACE RIDGE ALONG THE ATLANTIC COAST
STATES EARLY IN THE PERIOD...AND SURFACE COLD FRONT SURGING INTO THE
LOWER MISSISSIPPI VALLEY AND WESTERN GULF COASTAL AREAS...BREADTH OF
EVOLVING WARM SECTOR APPEARS LIKELY TO BE LIMITED. THIS...IN
CONJUNCTION WITH MORE LIKELY WEAKER SURFACE LOW DEVELOPMENT ON
NORTHERN END OF INVERTED TROUGH ACROSS THE TENNESSEE VALLEY...WILL
MINIMIZE RISK OF MORE SUBSTANTIAL CONVECTIVE OUTBREAK AND SEVERE
WEATHER THREAT DURING THIS FORECAST PERIOD.

HOWEVER...STRONG UNIDIRECTIONAL...SOUTHWESTERLY FLOW FIELD IS
PROGGED TO DEVELOP ACROSS THE LOWER MISSISSIPPI VALLEY AND CENTRAL
GULF COAST STATES TUESDAY...AS A 100 KT 500 MB JET STREAK DEVELOPS
FROM THE VICINITY OF ARKANSAS INTO TENNESSEE. WITH AT LEAST A
NARROW CORRIDOR OF WEAK SURFACE-BASED INSTABILITY EXPECTED TO
DEVELOP WITH MOISTURE RETURN AHEAD OF COLD FRONT...SOME POTENTIAL
EXISTS FOR DEEP CONVECTIVE DEVELOPMENT AND SUBSEQUENT EVOLUTION OF
SQUALL LINE. THIS APPEARS MOST PROBABLE ACROSS FROM SOUTHEAST
LOUISIANA THROUGH SOUTHERN MISSISSIPPI INTO WESTERN ALABAMA TUESDAY
AFTERNOON. CONVECTION MAY BE VIGOROUS ENOUGH TO AID DOWNWARD
TRANSFER OF HIGHER MOMENTUM TO THE SURFACE...ENHANCING RISK OF
DAMAGING WIND GUSTS.

Thanks for the update

[Wnghs2007]

Here's another DP chart:

http://vortex.plymouth.edu/cgi-bin/gen_ ... d=&zoom=.6


And another:



You can readily see a "nose" of higher dewpoints in the GOM just waiting to be pulled up ahead of the developing storm.

Looks like Moisture is starting to draw up into the Louisiana and E Texas area. It is being pulled up like you said

[PurdueWx80]

All I have to say this morning is !!!

More later, but I'll go ahead and make a guess that "surprise" winter storm warnings will come up this afternoon in parts of MI (and advisories or perhaps warnings in IN and IL as well). The Eta hasn't budged (nor has the GFS until this morning's run)...more to come...

[therock1811]

Issued from Grand Rapids (this does include King BTW):

ALLEGAN-BARRY-CALHOUN-CLINTON-EATON-GRATIOT-INGHAM-IONIA-JACKSON-
KALAMAZOO-KENT-MONTCALM-OTTAWA-VAN BUREN-
INCLUDING THE CITIES OF...ALMA...BATTLE CREEK...CHARLOTTE...GRAND
HAVEN...GRAND RAPIDS...GREENVILLE...HASTINGS...HOLLAND...IONIA...
JACKSON...KALAMAZOO...LANSING...SOUTH HAVEN...ST JOHNS
1117 AM EST TUE NOV 30 2004

...SNOW ADVISORY IN EFFECT FROM 6 PM EST TUESDAY UNTIL 6 AM EST
WEDNESDAY...

THE NATIONAL WEATHER SERVICE IN GRAND RAPIDS HAS ISSUED A SNOW
ADVISORY.

A MIXTURE OF RAIN AND SNOW WILL DEVELOP LATER THIS AFTERNOON AND
EARLY THIS EVENING. THE PRECIPITATION WILL CHANGE TO ALL SNOW BY
MIDNIGHT AND COULD BE HEAVY AT TIMES OVERNIGHT. 3 TO 6 INCHES OF NEW
SNOW IS EXPECTED BY DAYBREAK WEDNESDAY.

TRAVEL CONDITIONS WILL DETERIORATE QUICKLY TONIGHT AS THE WET SNOW
DEVELOPS AND BEGINS TO ACCUMULATE. ANYONE WITH TRAVEL PLANS SHOULD
BE PREPARED FOR POOR VISIBILITIES AND SLIPPERY ROADS.

Likewise from Detroit:

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1122 AM EST TUE NOV 30 2004

...SNOW ADVISORY IN EFFECT FOR LATE TONIGHT...

.DEVELOPING LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY REGION WILL
INTENSIFY AND MOVE TOWARD THE SOUTHERN GREAT LAKES THIS AFTERNOON AND
EVENING. AS THE LOW APPROACHES... WIDESPREAD PRECIPITATION WILL MOVE
OVER SOUTHEAST LOWER MICHIGAN. MUCH OF THIS PRECIPITATION WILL START
AS RAIN OR A MIX OF RAIN AND SNOW. TOWARD MIDNIGHT... PRECIPITATION
WILL CHANGE TO MOSTLY SNOW AND QUICKLY ACCUMULATE... WITH AMOUNTS
APPROACHING 6 INCHES NORTH OF A LINE FROM HOWELL TO PORT HURON.

MIZ048-049-053>055-060>062-068-302200-
/X.NEW.KDTX.SN.Y.0005.041201T0400Z-041201T1100Z/
BAY MI-GENESEE MI-HURON MI-LAPEER MI-LIVINGSTON MI-SAGINAW MI-
SANILAC MI-SHIAWASSEE MI-TUSCOLA MI-
INCLUDING THE CITIES OF...BAD AXE...BAY CITY...CARO...FLINT...
HOWELL...LAPEER...OWOSSO...SAGINAW AND SANDUSKY
1122 AM EST TUE NOV 30 2004

...SNOW ADVISORY IN EFFECT FROM 11 PM THIS EVENING TO 6 AM EST
WEDNESDAY...

THE NATIONAL WEATHER SERVICE IN DETROIT/PONTIAC MI HAS ISSUED A SNOW
ADVISORY.

WIDESPREAD SNOW DEVELOPING TOWARD MIDNIGHT WILL BRING SNOWFALL
ACCUMULATIONS OF 3 TO 6 INCHES BY MORNING ACROSS THE REGION.

A SNOW ADVISORY IS ISSUED WHEN SNOW IS EXPECTED TO DEVELOP, BUT
ONLY ENOUGH TO CAUSE INCONVENIENCES SUCH AS TRAVEL DELAYS. NO
SEVERE WINTER WEATHER IS EXPECTED AT THIS TIME.

$$