Clear as Mud!

Good eve (or morning),

What is making this forecast a bear is the amount of warm air being pulled into the storm aloft (~5,000 ft up)  as it comes up the coast.  This is vastly different from model to model.  The NAM keeps the warm layer aloft to our east, and pounds us with snow.  Meanwhile, the European model from this morning has temps well above freezing ~ 5,000 ft up by 10 am on Thrs, and is a sucky sleet and rain fest.  Even the GFS and Canadian Models from this morning pulled this stunt at some point on Thrs, where snow changed to sleet and rain due to warm air aloft.  Man… if we stay all snow, this could end up 10 to 20″… but if it doesn’t (which was how it appeared this afternoon), then 4 to 8″, maybe 10″ before changing over.  Suspect we’ll be sorting this out into Thrs morning, cos we really don’t know for sure until the bloody thing starts to come up the coast.  Clear as mud, eh?!

A few other things.

This is looking like a three-part storm:

The first part of the storm for Weds night is really straight forward.  The initial slug of moisture coming up the coast will encounter some really cold air entrenched over the region, and there will be a period of moderate to heavy snow Weds night.  Due to the cold air, this snow will also stack up quickly, with a high snow-to-liquid ratio.  This “part” of the storm is good for 4 to 8″ of snow, perhaps even 10″.

Part two is the coastal low passing to our east, or perhaps inland Thrs morning.  This is where we could either see snow pile up or change to sleet, freezing rain, and rain.  We’ll be tracking the weather features about 5,000 ft up (850 mb) to sort this out. This is the make-or-break part of the storm… and will occur during the morning and early afternoon Thrs.

Part three is the “parent” upper-air low, the feature that helped generate the surface coastal low.  This will come thru Thrs afternoon and evening, and will likely be responsible for a bonus round of light to moderate snow or sleet. We often see this with big storms… the upper-air energy (aka “vort”) that spawned the whole bloody mess comes barreling thru after you think it’s all over, and drops another 2 to 4″of snow.

On to what is rolling in at this hour.  The Short-Range Ensemble models (SREFs) offer zero clarity… with everything to 1-2 feet of snow to snow and a whole lot of rain.  More notable is the latest NAM (00z), which is still all about a heavy snow event… keeping the warm layer aloft to our east.  So far, that’s all we have.

Well, will update u tomorrow.


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