Hoosier

This is kind of a funny look. Sort of a triple band off the lake.

Solid afd Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 149 PM CST Sun Nov 10 2019 .SHORT TERM... 149 PM CST Through Monday night... Primary near term concern is the accumulating snowfall expected tonight into Monday. Water vapor imagery early this afternoon shows upper trough over western Canada digging southeast into the northern tier of states. Guidance is in excellent agreement in showing an amplification of this trough as it digs southeast into the northern Plains Monday and Great Lakes Monday night into Tuesday. This trough will dislodge a lobe of record breaking early season Arctic air and drive into the Midwest and our area Monday night into Tuesday. As this trough digs southeastward, tightening geopotential height gradient ahead of the trough will result in a strengthening jet streak downwind of the trough with guidance developing a 140-150kt 250mb jet from the Cornbelt east-northeast into southeast Canada. This will place northern IL and adjacent areas in the favorable right entrance region of the jet, where thermally direct ageostrophic circulation will result in strengthening low-mid level frontogenetical circulation tonight into Monday. The result will be an expansion and some intensification of the swath of precipitation currently over South Dakota into southwest Minnesota. Precipitation should spread into northern IL this evening with thermal profiles initially supporting some rain before a quick change over to snow most areas. The exception will likely be immediately downwind of Lake Michigan where marine influences will hold temps up a bit and delay the change over to snow until after midnight most likely. Forecast vertical cross sections across the tightening thermal gradient show 2 to 3 different f-gen circulations with this band tonight into Monday morning. Generally speaking, omega is not forecast to be overly strong during the event and overall not seeing any strong indications of instability (slant-wise or upright) that would point toward any convective enhancement to the snowfall. None the less, all indications are that there will be an extended period of light to moderate snow, likely resulting in widespread 2-6" accumulations, heaviest along/north of I-88/290 corridors and near the lake in northwest Indiana. Hi-res models continue to suggest there will be a lake enhancement to the snowfall into northeast IL late tonight into early Monday morning, and into northwest IN Monday morning into the afternoon. Initially, the depth of the cold air tonight isn`t terribly great resulting in marginal lake induced equilibrium levels which would certainly support some lake enhancement but suggests the lake enhanced snow won`t get too out of hand. Depth and magnitude of the cold air will be on the increase Monday, resulting in stronger lake induced instability and deeper convection/more vigorous lake enhanced snow. As the lake effect parameters improve the band is expected to become increasing progressive and shifting east into and across northwest Indiana. There are a lot of moving parts that introduce potential errors in our forecast snowfall over the immediate Chicago area and far northwest Indiana. Above freezing temps should result in a portion of the initial QPF advertised in the models not contributing to snow accumulations and either falling as rain or melting snow. Conversely, lake effect is notorious for being fickle and difficult to forecast. Similar set-ups ave been known to over- perform with heavier snowfall rates and totals and this is certainly possible, especially Monday as the instability increases. For now, just mentioned the potential for isolated higher totals (>6") near the lake, but it is possible that areas near the lake could end reaching warning criteria. At this juncture, given the uncertainties, felt an advisory was the reasonable route to go and not get too hung up on the threat for some isolated totals reaching warning criteria (>=6" in 12 hours). Northerly winds of 15 to 25 mph with some gusts to 30 mph are expected Monday which could result in some minor blowing and drifting problems in open areas, but winds are expected to be pretty marginal for blowing/drifting. The exception will likely be near the lake, particularly in northwest Indiana where gusts of 35 to 40 mph are likely Monday and should result in a more substantial blowing and drifting problem. - Izzi

Pretty bad when a 1012 mb low triggers lakeshore flooding. Pressure gradient is decent though with that incoming high. Lakeshore Hazard Message National Weather Service Chicago IL 928 AM CST Sun Nov 10 2019 ILZ006-014-102300- /O.CON.KLOT.LS.Y.0017.191111T0300Z-191112T1800Z/ Lake IL-Cook- 928 AM CST Sun Nov 10 2019 ...LAKESHORE FLOOD ADVISORY REMAINS IN EFFECT FROM 9 PM THIS EVENING TO NOON CST TUESDAY... * LAKE SHORE FLOODING...Northeast winds will increase to 30 mph tonight with waves building to 8 feet. Winds will increase to 35 mph Monday as winds shift more northerly with waves building to 10 feet. Winds will shift to the northwest Monday night. * TIMING...Late this evening through late Tuesday morning. * IMPACTS...Flooding and beach erosion are possible in flood prone and low lying areas along the Lake Michigan shoreline in northeast Illinois. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Lakeshore Flood Advisory indicates that onshore winds will generate flooding of low areas along the lakeshore. && $$ INZ001-002-102300- /O.CON.KLOT.LS.A.0001.191111T1200Z-191112T2200Z/ Lake IN-Porter- 928 AM CST Sun Nov 10 2019 ...LAKESHORE FLOOD WATCH REMAINS IN EFFECT FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON... * LAKE SHORE FLOODING...North winds will increase to 35 mph on Monday and then shift to the northwest Monday night. Waves are expected to build to 12 feet. * TIMING...Monday morning through Tuesday afternoon. * IMPACTS...Flooding and beach erosion are possible along the Lake Michigan shoreline in northwest Indiana. Freezing spray will also be possible Monday night. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Lakeshore Flood Watch means that conditions favorable for lakeshore flooding are expected to develop. Residents on or near the shore should take action to protect property...and listen for later statements or warnings. && $$ Kluber

The overall read I am getting from the models is that if a stall/slower movement of the band happens, it is more likely to be north of the city in Lake/northern Cook. However it is possible that it is fairly progressive even through that area. It does look progressive through a good chunk of Cook, Lake IN and possibly even Porter.

So you are living in the Midwest now? For a while I wasn't sure if you were just vacationing. Welcome.

Increasingly optimistic about 4-5" here. Could be a bit of a sluggish start with temps above freezing and not so great precip rates but that lake band should pound and make up for lost time even if fairly transient. Speaking of which, still have some differences on timing that lake enhanced band through the LOT cwa.

Shaping up to be a nice advisory type snow for a decent chunk of real estate... and the more borderline areas that haven't really had snow yet will probably get one. Still have about 50% or so leaf coverage on my block. I am figuring on the first 2-3" being of the denser/wetter variety before it gets fluffier toward the end. Lost less leaves than I would've thought on Halloween but I suspect the trees may be a little more willing to part with them this time.

Here's a 3 km NAM forecast sounding from the lake enhanced band. A ton of omega. Not the greatest colocation of that lift within the DGZ but a good amount does get into that DGZ and I suspect it will be ripping fatties at 1-2" per hour in that band at maturity.

Map?

Fwiw, the HRRR and RAP are toward the eastern side of the lake with the enhanced band even at 6z Monday. Maybe we can get a model blend of the western and eastern solutions and park it over my head for like 6 hours.

Gotta appreciate the rarity of getting multiple snows this early in Chicago. There have only been 3 years when multiple 1"+ snows occurred by 11/15. If we restrict it to 4"+ snows, it has only happened once. 10/29-30/1906: 2.2" ; 11/11-12/1906: 2.1" 11/3/1951: 4.4" ; 11/6-7/1951: 9.3" 11/9/2018: 1.0" ; 11/15/2018: 1.1" 10/30-31/2019: 4.6" ; TBD

Deutschland's model came in hot.

Midweek looking good for a 1-2" refresher.

Most of the non-Euro models are quicker to break down the onshore flow/convergence in northeast IL and shift it more into Indiana. One exception is the HRDPS (hi-res RGEM) which handles it a lot like the Euro.

I think about 3" is a reasonable starting point around here. At least that is about where I would put the floor. That is factoring in only a very small contribution to totals from the lake band due to concerns about residence time and boundary layer temps, except perhaps as CAA increases and the band is exiting and winds flip a little more offshore. If the band lingers longer than expected and temps aren't an issue, then totals around 5-6" would become more likely.

NAM is really a low outlier as far as qpf. I'd say the GFS sort of splits the difference between the NAM and the foreign models. On another note, starting to get in range of the extended HRRR and RAP runs that go out 36 and 39 hours, respectively, and will be interesting to see how they handle the lake enhanced band.

That is the one I mentioned, but couldn't remember if it was 1996 or 1997. Somebody did a case study on it that I read many years ago... I thought maybe it was LOT that wrote it but I can't find it now. Anyway, that event looks like it had 850 mb temps around -6C to -8C which cooled to -9C or -10C.

Thanks for the thoughts as always. Looking quickly at Chicago snow records in the first half of November, there's not a whole lot of significant snow events to try to use to compare 850 temps, and even fewer since the better upper air data started back in the late 1940s into the 1950s. Might be worth taking a look at what kind of setup was in place in the mid November 1996 or 1997 event that dumped on Lake county IL, though I think a mesolow may have been responsible for that.

Should clarify that I meant getting higher totals near the lake in northeast IL is not easy to do this early. This setup is better than many at this time of year, but I have a hard time believing that the shore will outsnow places farther inland like ORD/MDW. Who knows though with how this winter has started lol

It is not easy to get lake enhanced snow into Chicago in early to mid November. Here's why. Progged low level flow is basically full fetch down the lake over all that mid 40s to nearly 50 degree water. A lot of November setups will fail because the airmass just isn't cold enough. One example is 11/24/2004, which had a distinct snow minimum surrounding the lake. Another case which Alek will remember is 11/21/2015, which kept it raining in downtown Chicago for the majority of the time (while hammering inland toward ORD) until finally switching over toward the end. In the 2004 case, 850 mb temps were around -5C. In 2015, they were more in the -6C to -8C range. This time they are progged to fall to -10C while the low level flow is still directed into the IL shore. Typically by the time 850 mb temps are that cold at this time of year, the flow has already shifted to favor IN or MI.

NAM is a mess.

So the big question for the area around Chicago proper and into my area is what are temps going to be like for the bulk of the snow? Is it 32-33 or more like 34-35, because that makes a difference. In any case, going to be looking at locally lower ratios near the shore. Water temps near the shore are low-mid 40s while still in the upper 40s farther out in the lake.

The thread that Thundersnow was too lazy to make.