Tuesday/Wednesday Storm = Love

Another couple of model runs, and even more confidence that the storm that occurs Tuesday/Wednesday is going to be "the one" for the winter of 2009-10, at least so far. If you want to know what in the atmosphere is causing this storm to occur, scroll down to the last few posts...today I'm going to focus on what the different models are showing. Then, I'll use the current model guidance to make a preliminary snowfall map and state my thoughts on the chances of a snow day.

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Forecast Model Images:

NAM

This image of the NAM shows a very heavy band of snow affecting anyone from M-59 north in SE Michigan from 1 a.m. - 7 a.m. Wednesday Morning:

This image of the NAM shows that band affecting us in simulated radar form, just another look at the band of snow:

Finally, this image of the NAM shows storm total snowfall. It paints the highest accumulations (likely 10-15") over the M-59 and I-69 corridors:

GFS

This image of the GFS shows moderate-to-heavy snow affecting everyone in NW Ohio and SE Michigan. Note the tighly packed black lines. This represents a strong pressure gradient and the likely result would be near blizzard or even low end blizzard conditions from 1 a.m. - 7 a.m. Wednesday Morning:

This image of the GFS shows storm total snowfall. It paints the highest accumulations (likely 10-15") over the I-94 corridor down to NW Ohio:

GGEM

This image of the GGEM shows a band of heavy snow impact NW Ohio. Moderate snow is still falling in SE Michigan:

This image of the GGEM shows storm total snowfall. It paints the highest accumulations (likely 11-17") over NW Ohio:

ECMWF

No pictures with the ECMWF due to its horrible resolution, but it is similar to the GFS in its precipitation output.

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Forecast Model Preference:

The forecast models are tightly clustered with regards to track, generally tracking a low up Western Ohio passing just east of or over Detroit, before the energy transfers to a secondary low on the east coast. Due to the high confidence in the track, I will take the "middle of the road" models when it comes to precipitation. This means disregarding the further north NAM and further south GGEM as outliers when it comes to precipitation, and relying on the ECMWF and GFS.

Therefore, for my snow map, I will assume that the highest precipitation totals will be from the I-94 corridor south, with precipitation amounts gradually tapering off as you head to the north.
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Snow Map:

With my snow map, I will assume a general 15:1 snow-to-water ratio, just to be on the safe side. Ratios could definitely be higher, but ratios have fallen short of what has been expected too often for me to feel comfortable using anything higher than 15:1.

For Detroit south, I will assume they will get anywhere from 0.75 - 1.0" of water equivalent. With a 15:1 ratio, this is equivalent to anywhere from 11.25-15" of snow. Due to the possibility that higher precipitation amounts could shift, I will give them a low end accumulation of 8". I also see any accumulations of over 14" being highly localized. They could happen, but to keep it safe 60 hours out, I will forecast 8-14" with a "Locally Higher" label from I-94 south.

Between Saginaw and Detroit, I will assume we will get anywhere from 0.5-0.7" of water equivalent. With a 15:1 ratio, this is equivalent to anywhere from 7.5-10.5" of snow. Once again, due to the possibility that higher precipitation amounts could shift, I will give us a low end accumulation of 6". Considering it's still 60 hours out, I will round down the 10.5" to a high end of 10" of accumulation. Therefore, my forecast for this area will be 6-10" of snow.

North of Saginaw, I will assume they will get anywhere from 0.3-0.5" of water equivalent. With a 15:1 ratio, this is equivalent to anywhere from 4.5-7.5" of snow. North of Saginaw, any shift to the north or south could have a fairly significant effect on accumulations. Therefore I'll round the low end down and the high end up for a forecast of 4-8" of snow.

This is reflected in the following snow map:


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Snow Day Chances:

The timeframe of this storm has moved back even a little further. Snow is now expected to start Tuesday Afternoon, continuing through Wednesday Afternoon, with the heaviest snow falling early Wednesday Morning. Obviously, this is pretty much perfect timing for a snow day, and if precipitation ends late enough on Wednesday, we could get two...but for now I will only talk about the snow day chances on Wednesday.

Considering it's early February, and we haven't had a snow day yet, I think anywhere from 5"+ could get us a snow day. Obviously, the low end of my snowfall forecast is for 6" of snow, so the amount of snow should also suffice.

Finally, one more thing in our favor is that at the height of the storm, near blizzard conditions are likely. I could easily see winds gusting up to 30-35 mph with a tight air pressure gradient over our region. This will result in whiteout conditions, and extensive blowing and drifting of snow. I would expect some drifts to be over 2'.

Obviously, the road commission is not going to be able to keep up with this mess. The only reason I won't move the snow day grade to an "A" is that we're still over 2 days out, but if everything looks the same at this time tomorrow, I will move it to an "A". For now though, I'll keep it at a "B" (good chance of a snow day, but not a lock yet). This is pretty much as confident as I'll ever be for a storm that's still 2 days away. I'd expect the National Weather Service to have Winter Storm Watches up either this afternoon or tomorrow morning. Should be a fun next few days tracking this one...