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2/20 -2/22 Storm Threat Discussion


Zelocita Weather

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OT, but is the 57F in CP right now correct? Newark's in the low 50s.

The latest update from Central Park was 55/42 with fair skies...talk about a torch.

It's 45/39 here in Southern Westchester with a few passing clouds floating by, although doubtless snow-covered areas in the woods are much colder.

Will be quite a dramatic change when we are tracking imminent snowstorms and wearing heavy jackets next week as temperatures struggle to hit freezing.

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Heat island is really showing up tonight. Several Weather Underground stations in Manhattan are also in the mid 50s. Even in most of Brooklyn/Queens it's in the mid to upper 40s. It's odd - LGA is usually warmer than NYC, but tonight they're running about 8F cooler. Most likely the ocean influence due to S winds earlier in the night helped to cool LGA off.

OT, but is the 57F in CP right now correct? Newark's in the low 50s.

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Evaporational cooling will help out with the 1st wave and perhaps keep the initial burst of precip. as snow. The air mass ahead of it is very dry aloft. Notice how the NAM shows temporary cold advection at 850 mb as the shield of precip. arrives by 12z Mon - that's due to evaporational cooling.

post-88-0-78719800-1298015693.jpg

Here's the NAM RH profile for LGA - it has 15-30% RH in the 800-950 mb layer just ahead of the precip. arrival on Sun night:

post-88-0-93524200-1298015479.png

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Sunday night will be interesting, we will go from 25,000 ft Cirrus OVC at 6 PM with 15 mile visibility to 1/2 vis SN 800 ft stratus OVC right around midnight. Will probably wake up with 3-4 inches of snow Monday morning on Long Island with WAA burst of 5 hour moderate 1/2 mile snowfall. Monday probably turns into a 33 degree drizzle once the WAA ends. Hoping Tuesday trends into a 3-7 inch snow deal with north trending and possibly enough moisture to be injected into the cold air supply. My forecast would be for 2-4 inches of snow Sunday night into Monday followed by cold drizzle as temps go from 25 to 33. For Monday night into Tuesday looks like snow moves in at moderate intensity with temps 20-22 and ratios 15 to 1 for powder snowfall with sufficient cold air to get powder opposed to wet. Mets please comment. For the end of week temps should struggle to 38-40 with Canada getting massive cold supply throughout and a feeble attempt at a cutter that will likely become a Miller B off Cape Cod or Nantucket next Friday. 1050 mb high over North Central Canada will overwhelm all of Canada and northern US in 6-7 days. NYC might just miss next Friday event, but New England could get a 4-8 inch event. This is how I see it. Please grade me on this after we go through the event. It will be fun to see how I do with the tricky pattern. Thanks.

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Sunday night will be interesting, we will go from 25,000 ft Cirrus OVC at 6 PM with 15 mile visibility to 1/2 vis SN 800 ft stratus OVC right around midnight. Will probably wake up with 3-4 inches of snow Monday morning on Long Island with WAA burst of 5 hour moderate 1/2 mile snowfall. Monday probably turns into a 33 degree drizzle once the WAA ends. Hoping Tuesday trends into a 3-7 inch snow deal with north trending and possibly enough moisture to be injected into the cold air supply. My forecast would be for 2-4 inches of snow Sunday night into Monday followed by cold drizzle as temps go from 25 to 33. For Monday night into Tuesday looks like snow moves in at moderate intensity with temps 20-22 and ratios 15 to 1 for powder snowfall with sufficient cold air to get powder opposed to wet. Mets please comment. For the end of week temps should struggle to 38-40 with Canada getting massive cold supply throughout and a feeble attempt at a cutter that will likely become a Miller B off Cape Cod or Nantucket next Friday. 1050 mb high over North Central Canada will overwhelm all of Canada and northern US in 6-7 days. NYC might just miss next Friday event, but New England could get a 4-8 inch event. This is how I see it. Please grade me on this after we go through the event. It will be fun to see how I do with the tricky pattern. Thanks.

Comparing the 6Z GFS to the 0Z - this is definetly a thread the needle event for NYC Metro. THe 6Z once again came in colder then the OZ in NYC Metro - the first storm takes a more southerly track and starts as snow and ends as snow - BUT this forces the second storm on the 6Z totally south of NYC a complete miss. 50 to 100 miles makes the difference with both systems...........impossible to predict at 3 - 4 days out with any model used as guidance...

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Still lots of uncertainty with the 2nd storm. I'd expect the 1st event (Monday) to overperform in some areas, given the very sharp temperature contrasts and strong frontogenesis. Model QPF seems low given the setup, especially the Euro. The 0z and 6z GFS make more sense. The enhanced snows will probably be in a narrow band and only forecast well by mesoscale models. Could even see near warning criteria snows in some spots.

However, as usual with SW flow events where the 850 mb low passes near or north of NYC, the most likely areas to get significant snow are areas well north of NYC, like from Orange County NY eastward toward interior southern CT.

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Still lots of uncertainty with the 2nd storm. I'd expect the 1st event (Monday) to overperform in some areas, given the very sharp temperature contrasts and strong frontogenesis. Model QPF seems low given the setup, especially the Euro. The 0z and 6z GFS make more sense. The enhanced snows will probably be in a narrow band and only forecast well by mesoscale models. Could even see near warning criteria snows in some spots.

However, as usual with SW flow events where the 850 mb low passes near or north of NYC, the most likely areas to get significant snow are areas well north of NYC, like from Orange County NY eastward toward interior southern CT.

FWIW the 6Z GFS Means for the 2nd storm are north of the OP - 12 hour Mean Here -

http://raleighwx.americanwx.com/models/gfsensemble/06zgfsensemblep12096.gif

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Still lots of uncertainty with the 2nd storm. I'd expect the 1st event (Monday) to overperform in some areas, given the very sharp temperature contrasts and strong frontogenesis. Model QPF seems low given the setup, especially the Euro. The 0z and 6z GFS make more sense. The enhanced snows will probably be in a narrow band and only forecast well by mesoscale models. Could even see near warning criteria snows in some spots.

However, as usual with SW flow events where the 850 mb low passes near or north of NYC, the most likely areas to get significant snow are areas well north of NYC, like from Orange County NY eastward toward interior southern CT.

More interested in the second wave, since the first one doesnt look to be a big deal-- hopefully they both trend north.

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