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18z Runs 1/2/14


Allsnow

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Models are horrible at predicting inverted trough features. I'd say most of Long Island, maybe even NYC and coastal NJ are in the game for it.

 

Those TT's and mid-level lapse rates look good for some really nice banding. I just wish that we had

lapse rates that steep for some summer thunderstorm threats that fizzled out.

 

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I know im kind of weenie-ish lol. im only miles from farmingdale in West Islip so I should get into some nice banding. whens the heaviest? post 10 pm?

 

Dude. You've been doing this all day. Stop the IMBY already.

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Two mechanisms are important to the creation of thundersnow and they are elevated instability and strong dynamic lifting. Each of these mechanisms reinforces the other. The CAPE or instability in the troposphere is a function of the tropospheric temperature profile and the initial temperature and dewpoint of a parcel of air. Surface Based CAPE (SB CAPE) can be zero when at the same time lifting from another pressure level produces positive CAPE. The term for convection starting at a pressure level other than the surface is termed ELEVATED_CONVECTION. It helps to have the parcel initially start with a small dewpoint depression since CAPE is more likely to occur than if the dewpoint depression is large. Keep in mind that environmental dewpoint can increase with height or may not fall that much with height. Even if no elevated CAPE is present, CAPE may still be present when lifting occurs at a slant (known as slantwise convection)

Strong dynamic lifting (UVV) can enhance instability by cooling the middle layers of the troposphere. Cooling the middle layers of the troposphere makes elevated convection more possible. The dynamic lifting is also the "trigger" to cause the air to rise and keep rising from a pressure level that eventually results in elevated convection. Very intense dynamic lifting can often build clouds enough so that the clouds have convective characteristics even if no elevated convective CAPE is present.

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Love that the 18Z NAM and GFS both increased precip amounts for most of NJ by 0.1-0.2", bringing the totals up to 0.50-0.75" for most of NJ and to 0.75-0.9" for NE NJ and eastern Monmouth and maybe even eastern Middlesex/Ocean...and that these are similar to the Euro amounts.  If those amounts verify, the low end of most of the NWS forecasts are just about a given now and the high end or even a bit more is becoming likely, i.e., the 4-8" NWS forecasts for most of NJ are much more likely to be 6-10" for most locations with some areas that end up under the unpredictable mesoscale bands getting 12" or so.

 

Taken verbatim, 0.5-0.75" at 15:1 snow/liquid ratios (likely ratios for this storm) translates to 7.5-11.2" of snow and 0.7-0.9" of precip translates to 10.5-13.5". Some areas well to the N and/or NW (NW NJ, Hudson Valley, interior CT, etc.), where it's colder will likely see ratios up to 20:1, such that 0.75" of liquid would translate to 15" of powdery goodness.  Would love to see all of this verify.  Heading out to the local pub soon - it's only a 1/2 mile walk and I love doing that walk in the snow. 

Snow just started in Metuchen around 6:15 pm - woohoo! Radar is filling in nicely - already 1/4" on the ground in the first ~30 minutes or so - let's sit back and watch and enjoy. So glad I'm off again tomorrow, so I can enjoy it. Will be up all night, I'm sure. 

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