The passage of a weak shortwave and surface trough after midnight into the very early morning hours on Thursday is expected to bring winds around from the W to NNW over Lake Erie.  This should allow a brief burst of snow to push off the lake with EL heights of around 7k feet and steep lapse rates, good moisture, and some lift in the DGZ.  A brief period of subsidence behind this wave, rapidly shifting winds, and a brief period of dry air/low inversion heights suggest any lake effect late tonight behind the first shortwave will be minimal.  Think amounts will generally be 2” or less across the primary Snowbelt in NE OH/NW PA tonight and less than 1” in the Cleveland metro, with little farther south and west.

Another little wave/vort max will pass mid-morning through the early afternoon on Thursday, bringing improved moisture and higher inversion heights along with some modest large scale lift.  This, combined with a Lake Huron connection getting set up, should allow for a decent increase in snow Thursday morning and into the early afternoon.  850mb winds and RH from the GFS, NAM, and Euro all get the enhanced moisture from as far west as Cleveland east to near the OH/PA boarder in Ashtabula/western Erie County during this timeframe.  This suggests that much of the primary Snowbelt in NE OH and some surrounding areas like eastern Cuyahoga County and perhaps northern Summit/Portage and likely Trumbull Counties will get in on this lake effect snow Thursday morning and early afternoon.  EL heights rise to 7-8k feet with good moisture/lapse rates/lift in the DGZ, which is a moderate amount of instability and a suggestion of efficient snow.  There is some directional shear below the inversion so any bands may be disorganized/transient, but upslope enhanced snow will likely occur for a few hours mid-morning into the afternoon.  Rates of half an inch to an inch per hour will be broadly possible in the higher terrain, which may result in a 2-4” type accumulation in the favored areas through early afternoon in the higher terrain of the primary NE OH Snowbelt.  Thinking 1-3” in NW PA Thursday morning/early afternoon in the higher terrain.

Tough forecast in the secondary Snowbelt as the models show a wedge of dry air between upstream connections nosing into west and south of Cleveland.  The models are initializing with a frozen lake upstream of the secondary Snowbelt.  GOES16 imagery from this morning showed the gusty S-SW winds over the last day or so have pushed out and broken up a lot of that thin/newly formed ice, creating a lot of open water.  Although the lack of an upstream connection will hurt, favorable snow growth and likely a lot more moisture flux than the models show could result in an inch or two of snow in the higher terrain of the secondary Snowbelt as well.

Winds will slowly back a little bit (gain a more westerly component) Thursday afternoon, pushing the Huron fetch east of the east side of Cleveland and into more of NW PA.  May see another inch or locally two of snow in the higher terrain of the primary Snowbelt in NE OH/NW PA Thursday afternoon between the morning burst and later burst.  Another vort max will approach Thursday late afternoon and pass during the evening, resulting in another general increase in snow.  By evening 850mb temps will drop to -23 to -24C, pushing the DGZ below the cloud layer and limiting snow growth.  This will limit ratios and the efficiency of any snow accumulation.  The NAM and GFS both have super-saturation with respect to ice at the top of the DGZ Thursday night, suggesting some snow growth, but the NAM especially tends to over-do surface dew points in lake effect situations, and any error means little good snow growth.  Suspect ratios may hang up around 12-15:1 under any more coherent bands that could help push the DGZ a little higher through latent heat release, but that will still be down from earlier in the day (likely well over 20:1) and may not be realized in areas of lighter snow.  The Huron connection into Ashtabula County and NW PA will likely see the heaviest snow, though with snow growth beginning to suffer rates will likely struggle to exceed half an inch to inch per hour.  The rest of the higher terrain in the NE OH Snowbelt should also see an uptick, but again with an increasingly inefficient snow the rates will not be great.  Have similar questions about the lack of snow in the secondary Snowbelt given some open water upstream of that higher terrain, and think the higher terrain in southern Cuyahoga/northern Medina and surrounding areas sees another little uptick late Thursday afternoon into the evening.  With EL heights of near 8k feet at CLE and over 10k feet at ERI with instability becoming extreme and well-aligned winds, do think there could be some decent bursts of snow at times during the late afternoon and evening Thursday.  Given lowering ratios, suspect the evening uptick will result in 2-3” new by midnight in the higher terrain of NW PA where the Huron band effects, 1-2” in the higher terrain of the primary NE OH Snowbelt west of the Lake Huron enhancement, and perhaps up to 1” in the higher terrain of the secondary Snowbelt though likely less for most.

We lose some of the large scale lift the rest of Thursday night after late evening, but lake effect parameters don’t drop off much with extreme instability, OK but not great EL heights, decent moisture to 4-5k feet, and well-aligned winds.  Winds do back a little bit more overnight Thursday night shifting the upstream enhancement more firmly into NW PA, but some upslope enhancement should allow mainly light snow to continue overnight in the higher terrain in NE OH and at least some light snow showers in the higher terrain south of CLE as well.  Forecast soundings for CLE show considerably drier/colder low-levels than ERI, but given my belief there will be considerably more moisture flux east of the islands (and even some west) than modelled due to poor ice-cover initialization (and the fact that there is some moisture flux through ice, especially relatively new ice) I do not buy this.  The air upstream of CLE is not anymore cold/dry than the air upstream of ERI, and given my belief the models are under-doing moisture flux upstream of CLE the soundings there may end up looking a bit more like ERI than the forecasts for CLE do.  The models appear to have a faux convergence band into the eastern suburbs and Geauga County overnight due to a sharp temperature differential between ice/no ice north of Cleveland over the lake that I don’t think will be there.  There may be some shoreline convergence that enhances snow a little bit into the secondary Snowbelt and perhaps Cuyahoga/northern Summit/southern Geauga  given a flow around 290 to 300 degrees late Thursday night into Friday morning.  Given poor snow growth though and a relatively short fetch/no upstream connections in this area, don’t think any of this snow in NE OH will result in more than an additional inch to locally 2” in the higher terrain between midnight-7am Friday.  Better shot at around 2” or so in that timeframe in the higher terrain in NW PA where the moisture from Lake Huron allows for some better snow.

The day Friday will probably be pretty dull.  Expect general modest lake effect to continue with extreme instability and ok EL heights (pretty good at ERI) along with well-aligned winds, but with a dry airmass, short fetch, and poor snow growth only expecting 1 to locally 3” in the higher terrain in the NE OH primary Snowbelt, less than 1” in the secondary Snowbelt, and 2-3” in the higher terrain of NW PA where moisture from Lake Huron helps the cause some…maybe a local 4” in NW PA, but most likely less.

One last pretty decent shortwave passes Friday night, bringing some large scale lift, increasing moisture depth some, and raising inversion heights a bit.  Winds will also veer to a more NNW direction for a few hours behind it late Friday night.  Expect a general increase in snow in the primary and secondary NE OH Snowbelts and also in NW PA downwind of Lake Huron for a good few hours Friday evening into the early overnight hours.  Snow growth will still be poor, though if a stronger band develops it and ratios may locally improve.  Extreme instability, EL heights rising to over 10k feet at CLE and ERI, and moisture depth increasing to 5-6k feet along with some lift from the shortwave should allow moderate snow to occur in the higher terrain, perhaps locally heavy downwind of Lake Huron.  Some shoreline convergence may also direct a bit of a band into the secondary Snowbelt, on top of the Lake Huron enhancement into NW PA and general orographic lift snow elsewhere.   The Huron band may briefly swing into Ashtabula County early Saturday morning, before everything shifts NE and inversion heights really lower on Saturday, finally winding down the snow during the afternoon.  With poor snow growth not expecting more than 2-3” in the higher terrain of NE OH/NW PA Friday night into early Saturday from the uptick from the shortwave, expect for perhaps locally 4” or so if a good Huron enhanced band can develop over Ashtabula County or into NW PA.

Adding up the period to period snowfall amounts does yield amounts potentially exceeding a foot in the heart of the NE Ohio Snowbelt and inland NW PA, with local amounts of up to 15 or 16” not impossible in NW PA.  Amounts will be considerably less near the lakeshore.  Given decent enhancement expected into eastern Cuyahoga County Thursday morning and enough terrain for orographic lift there through the rest of the event, think amounts of over half a foot will occur into eastern Cuyahoga.  Similar story in some of the northern extremities of counties south of the Snowbelt.  Will put 1-3” in for the secondary Snowbelt, though it’ll be apparent early on if there will be enough moisture flux for higher amounts there.  If so, could see how it eventually adds up to around half a foot through Friday night in parts of northern Medina County.