Snow! Here It Comes (Sloooooowly)…

It’s going to be a long, drawn out, painfully slow arrival. The primary low is super far south for a big snowstorm.



Indeed, the initial brush from this storm will be unimpressive. Minor coastal flooding, wind gusts over 40 m.p.h. and periods of light snow will be common. The snow likely will struggle to accumulate in the valleys but in the hills an inch or two may add up tonight.

By tomorrow evening, however, this storm is going to get interesting. The large cut-off way south is going to do a fujiwhara dance with a diving (and strengthening) low from the Great Lakes.



With the circulation from the existing low in place with a strong low level jet and TROWAL signature the low that dives south toward us is problematic. Strong quasi-geostrophic forcing will act to “pull” northwest the precipitation shield offshore (this won’t happen physically but it may look like it on radar). Decent snow growth per BUFKIT soundings may promote some big fluffy dendrites overnight.

At this point we’re expecting 2″-4″ of snow tomorrow night but this is the kind of event that can really surprise. Both up and down. While the deterministic forecast we’re showing tonight is the same as last night (3″-6″ total basically statewide) I’ve bumped up the probability forecast quite a bit. Much more confident tonight than last night. I’ve also included low end probabilities of a more substantial snow 8″+ or 12″+ in case tomorrow night’s snow has some banded surprises for us.

chart_3 (1)


2 thoughts on “Snow! Here It Comes (Sloooooowly)…

  1. Ryan,

    Comment links not working tonight so I will pass this along to you directly.

    Is this what weather people call covering your forekeister?


    Thanks for what you do,


  2. Dear Elevated Mixing Level Enthusiasts,

    Here is a wonderful opportunity for you to contemplate the sky hook theory of tornado formation. These guys are wandering around south Dakota, encouraged by the elevated mixing layer and the strong wind shear. Now, if you have any time to devote to my quest for the great tornado-causing skyhook, take a look at the diagram below, the one with the red and green lines sloping off the left. Up/down on that chart represents altitude (atmospheric pressure, actually, but it’s closely correlated with altitude). Temperature (more or less, I will spare you the details) is represented by the left-right axis. Ok, got that?

    Now, focus on the red line. You are going to use the dotted red line as a reference. The atmosphere cools as you go up (what is temperature but the bumping together of molecules and when there are fewer of them to bump, the air is by definition, cooler.) And so the dotted red line drifts to the left. Now look at the bright redline: if drifts to the left as it should, and then at roughly ten thousand feet (700 mb) it moves sharply to the right, before resuming its leftward drift. That air is lots warmer compared to the reference line than it should be. Now look at the green line. It drifts to the right for a while, indicating that the air is becoming moister with increased altitude, and then, at the same altitude where the temp line goes to the right, it goes to the left. The air there is much dryer than the air below it.

    So, above the surface, beginning at around ten thousand feet, lurks a layer of unexpectedly dry, warm air. This is the elevated mixing layer. It’s source is the high deserts of southwest (and also, I suspect, the higher altitudes of the subtropical high off California). It forms a sort of cap on the moist air below it. Air will rise if it is less dense than the air above it. In the surface air, below ten thousand feet, any air that is warmed by the sun will rise as it is heated, and you will get convection. But, according to the standard account, the warm desert air at ten thousand feet will prevent convection above that level until and unless that cap can be broken. Caps get broken by a upper air disturbances, by mountain ranges, by onrushing cold front. Only when the cap is broken, the convection will break through to higher levels of the atmosphere, and severe thunderstorms will form.

    As you all know, I have a passion for elevated mixing layers. I could go with this all day. But you all do not have time for that, and neither, in fact, do it. So, here is the point. As we have observed, that elevated mixing layer is not only warmer than the air below it, but a heluva lot drier. Now dry air is MORE dense that moist air. So, if the elevated layer were not warmer than their below it, it presumably would descend. So, the fact that it is still up there must have to do with the fact that its relative warmth balances its relative dryness, because, according to me, more dense air can never overlie less dense air.

    This, you all will remember, is where meteorologists start throwing things at me. They say, no, no, nick, you dumb former English major. That is a warm dry air mass over running a cool wet air mass and air masses of different characteristics do not mix! The suggestion seems to be that , even if that dry warm air mass were more dense than the air it overlies, some force, some membrane, some skyhook would prevent it’s falling to the surface.

    This is what I need help with.


    By the way, if you want to see the wind shear, look at the

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