ILSNOW

klot aviation Snow is ongoing in a band across Iowa. This band will shift to the east and over the area this evening. Substantial dry air is in place ahead of this band, especially across northern Iowa and northern Illinois. It is plausible that snow/flurries begin as early as 00z, but more likely the accumulating snow will start a few hours later from south to north (1-2z MDW, 3z at ORD). Morning AMDAR soundings show that the dry air is not very strong initially, and should be overcome quickly if no additional dry air moves in, but our latest AMDAR soundings at MDW do show dry air is advecting in. Confidence on snow onset is therefore only medium but current thought is that we may need to push things back a bit if the dry air trends continue. Once snow begins, a prolonged light to moderate snow event will unfold tonight into Saturday over the area TAF sites. Confidence is fairly high in this event beginning over the southern part of the Chicago metro (favoring MDW) before ORD and possibly by several hours. This has the look of 1-2 SM snow for much of this event. Late tonight into Saturday morning, approximately 08Z-15Z, there are some signals for temporary sub 1SM visibility. Ceilings should lower through the MVFR category tonight and temporary IFR is probable Saturday, although when on Saturday morning is still too low of confidence to include at this distance in the TAF. Total accumulation of this dry and powdery snow is forecast at 2 to 3 inches at ORD and MDW by Saturday afternoon. If moderate rates are more frequent, namely at MDW, that could be exceeded.

9z Plumes mean for ORD thru 2-16 is 8.39

both 12z NAM and RGEM bringing decent snows again in the late sun/monday period lets see what the king (GFS) has to say.

12z NAM 2 to 3 inch event tomorrow 12z 3K NAM 2 to 3 with almost a 4 lollipop around cook county

plumes thru monday @ ORD 8.92

GFS is the new King (haha) looking forward 2 another 2 inch refresher

a little late but the 21z Plumes at ORD had jumped up to 7.8 thru monday

KLOT Convergence is maximized on the western shores of southern Lake Michigan. The flow will turn solidly onshore into northeast IL which should allow the dominant band to shift northward. We should also maintain broader lake effect clouds/snow through the afternoon as the convergence will likely become a bit weaker. Rates will be high enough to coat roadways. Flurries should extend well inland across DuPage, Cook, and Lake IL counties. Snow across Iowa is still progged to move through the area this evening. Mid level frontal strengthening (700 mb) combined with modest lapse rates above it in the DGZ should support another period of moderate snow.

12z NAM @ 51 hrs vs GFS same time. How is it possible for them 2 be 100% different? 12z GFS @ 51 hrs

12z RGEM touch wetter general 7-9 area wide includes 2-3 from tonites event

12 z NAM a touch drier and south solid 5-6 inches area wide

KLOT update for tomorrow Our next wave is starting to spread light radar returns across South Dakota at this time, and will be approaching our longitude later Thursday afternoon and (moreso) evening. Latest guidance continues to indicate that snow is a good bet for locales north of I-88, and potentially even towards I-80 as well. The attendant jet streak is fairly robust, and seeing some signs in regional cross sections/BUFKIT soundings that more in the way of convective instability may be present with this system. Latest model consensus continues to support the main corridor of ascent focusing near and north of the state line, but see a potential for a swath of 1-2" of snow north of I-88. Finally, there are some signals pointing towards somewhat more robust LES developing into the northeast Illinois shore tomorrow evening.

0z NAM 0z GFS still significantly different

GFS is a 1-3 with a 4.4 lollipop over cook county GFS para 3-4 with a 5 lollipop over cook county

KLOT (not ricky) Attention will then turn to the Monday/Tuesday timeframe for another round of snow. Ensemble model guidance is in relatively good agreement that a storm system will lift form the Plains to the Great Lakes dropping a swath of snow along the backside. Statistical Cluster Analysis from the Weather Prediction Center (WPC) shows that ~70% of the CMC, GFS, and ECMWF ensemble members drop at least 0.1" of precipitation across northern Illinois and northwest Indiana, with ~50% dropping at least 0.25". The CMC model system is the driest, while the ECMWF is the wettest. With forecast low-level thermal profiles expected to remain cold and squarely in the snowflake growth zone, fluffy snow ratios will again be able to convert even just 0.10" of liquid to several inches of snow. So, we`ll need to keep a keen eye on the Monday/Tuesday timeframe for an impactful snow event somewhere in the Great Lakes.

KLOT (not ricky) First, confidence is increasing that a period of steady snow will occur Saturday as the diffluent right-entrance region of the upper- level jet stream passes overhead. Ensemble QPF from the ECMWF ranges from 0.10" along/south of I-80 to 0.25" along the IL/WI state line. A quick gander at forecast low-level thermodynamic profiles gives credence to very fluffy, perhaps "overperforming" snow ratios with the snowflake growth layer extending well beyond 10,000 feet at times. Plus, a trajectory off Lake Michigan may provide a boost of low-level moisture. Taken altogether, Saturday may end up yet another day to take it slow on the roads due to reduced visibility and accumulations of snow. The current forecast brings 1-2" snow totals from the Kankakee River Valley to I-88, and 2-3" totals from I-88 to the Wisconsin state line. Adjustments upward may be needed in later forecast packages.

18z NAM NEST is interesting it keeps what appears to lake effect going all day in Lake county before the main snows hit

NAM is now officially on on Snow Island there is no model even close to what its showing. Only question is does it just vanish next run or does it take several runs?

12z GFS and the 12Z NAM are slightly different

maybe a touch north with the heavier band.

was 18z EPS close to 12z EPS ?

KLOT update (not Ricky) unimpressed. But the combo of Angrysummons and A-L-E-K will be hard to keep down. Thursday through Tuesday... Continued cold conditions are expected through the remainder of the forecast period, including a reinforcing shot of even colder air for the late weekend into early next week. Multiple periods of snow also remain likely, though different portions of the forecast area are favored with each one, and nothing looks overly significant at least into early next week.

Kuchera ratios on the GEM are between 20-28:1 I think we will do ok

I know that its 84hr NAM but does this look bad?

Skilling said snow ratio was 48:1