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NYC CWA January 26-27 OBS and Discussion Thread


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Discussion

We had a minor 1-3 inch snowfall event last night lasting into midday today. This was underforecast. The culpret was a short wave trof aloft that combined with warm air advection to spark the light snow. Props to the RGEM in that it at least showed some snow, mainly N/W of the area, but it too wasn't far enough south with the precip axis.

The temps today recovered to near normal across the area, but with thicker cloud cover persisting, areas well inland managed to stay below the forecasted highs.

Currently, the latest water vapor imagery clearly shows our developing winter storm. The trof aloft is located over the ARKLATEX region over the deep south. Plenty of moisture is streaming up from the gulf of mexico ahead of the system. There is a lot of strong convection ongoing over the central/eastern gulf at this time and this is playing havoc with some of the guidance with respect to the handling of the surface low that heads our way. More on that in a bit. The surface low is located near the FL panhandle late this afternoon with a coastal front extending up to just east of the delmarva region. The low will look to follow this baroclinic zone on its track up the coast.

Low clouds are socked in from PA on westward with some clearing over S NJ and the delmarva region before the beginnings of the moisture aloft starts to encroach from the SW associated with the winter storm. There is a small window for some brief clearing this evening and the guidance actually have us going mainly clear for a while. This was toyed with in the forecast, but based on the latest trends, I decided to keep the prev forecast with partly cloudy then increasing clouds. The flow aloft is from the SW so those clouds coming up the coast should have no problems getting into the region tonight. I removed the slight chance of snow from the prev forecast for tonight as the system is still on the slow side.

For the handling of the winter storm, I used an equal blend of the 00/12z Euro/GGEM/UKMET/15z SREF. The NAM/GFS models both appear to be having difficulty with the convection ongoing over the gulf now and with that, the models both creep the sfc Lo too far east as early as tomorrow 7am compared to the guidance I chose to follow. Yesterday's GFS was similar to the preferred combo today so not many changes were needed to the forecast.

By early tomorrow AM, the sfc Lo should be near the coast of SC with the coastal front/baroclinic zone still holding firm off the coast. The upper level low at 500 millibars is still strong/closed off near Atlanta. The 2 features will come up the coast during the afternoon hours. I feel there is a decent (50%) chance of precip developing before noon, especially over S NJ, but it will take a bit longer to reach the city and points N. Thus, I feel the highest pops should be after the noon hour, and especially as we get twds 3-5 pm. The eve rush looks messy from central NJ on N and E. For S NJ, the precip looks to stay rain there the longest before a change over to snow by evening. With there not being a really cold air mass in place ahead of the storm, temps will be marginal for snow and 850 mb temps are just the same. I feel that maybe an inch or less of snow is all we see for the city by evening since we start as a mix of rain/snow before going to all snow late. The rain/snow should be brief at best and there may even be some sleet mixed in before the transition to all snow. Needless to say, travel may become difficult as we work twds 6-7 pm across most of the area.

The 700 mb low by early eve is closed off with deformation banding starting to get going in earnest between 8pm-1am. Strong frontogenically forced snow bands look to set up outside of the city, mainly over the lower hudson valley, CT, and NW NJ. That axis of heavy snow pulls east overnight and it does hit the city and the rest of the area as the comma head develops. Very strong omega (lift) develops in the snow growth region aloft which will mean heavy snowfall for the area. Can't rule out some thundersnow with this since the dynamics are so strong. The deform band associated with the closed upper low will push from SW to NE thru the night. Snow will start to lessen over my western zones twds dawn but will still be going strong over the city and points N and E.

For now, I am starting the snow totals with a general 6-12 inches for the entire area, with about 6-10 in the city itself, and likely 8-12 over the interior due to it snowing there longer and there being less of a mixing issue early on. We will have a snowfall map out this evening so please check that for details.

As the sfc Low bombs out off the coast, winds will become an issue. There will be a 50 knot low level jet to work with during the height of the storm. As the storm passes, we will likely see gusts to over 40 mph along the coastal plain creating near blizzard conditions at times with the heavy snow.I went with likely pops for early snow for the city on east before 6am on Thursday. This means the Thurs AM rush will likely be very difficult so plan accordingly. The storm rapidly moves away from the area after that so expect clearing skies by mid to late morning. -RC

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Lee Goldberg on channel 7 is calling for 3-6" for NYC metro, most of central and northern New Jersey and Long Island with 6-9" for most of Connecticut. I think he is way too low with those amounts considering the latest 12z and 18z model runs. Moreover, he is predicting a rainstorm next week with temperatures near 50* F.

he said 6 in nyc is a good bet...Manhattan within the 6-9 band and so is the bronx

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Guest Patrick

Thanks for laying it all out like that in plain text... literally and figuratively (there is only so much map-reading one can do on a droid!)

Fantastic discussion*, it's impressive how you so plainly lay out the timing and impacts. I am not sure why you aren't working for the NWS. They do a fantastic job on a shoestring budget, but it would be nice to see slightly more depth in the 'general public' products regarding this event....especially true because of the timing during an evening rush hour. I get that most people really only care about when & how much....and even at that, they always seem to become deaf to the bottom of the scale. But just a *little* more detail, in the format you shared, could go a long way toward making tomorrow safer.

ok, brown-nosing over.

*especially cool that we seem to agree that the CCB sets up most impressively right between our neighborhoods again

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he said 6 in nyc is a good bet...Manhattan within the 6-9 band and so is the bronx

He said 6-9 for NYC and 3-6 for Long Island but based on the latest model runs, he said he will probably have to extend the 6-9 south and east-- basically, he's seeing what we're seeing on the models.

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He said 6-9 for NYC and 3-6 for Long Island but based on the latest model runs, he said he will probably have to extend the 6-9 south and east-- basically, he's seeing what we're seeing on the models.

exactly, which leads me to believe people sometimes don't listen and just see numbers on a tv screen and run with it lol

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just a heads up...at this time frame the RGEM was very accurate for our last event. Suggested around 0.4 QPF for the region, NYC recorded 0.41. This time its 1.2in so we'll see if its got the right idea

RGEM is an excellent short term model.

People overlook it too much.

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will most likely look like the 2 other classic CCB's from this winter. I mean how many more times can this type of situation occur in the next 6-10 wks?

6-10 more times. :P lol NYC might just receive more than 10" in one week alone, from today, thursday, and saturday.

This CCB might more pronounced though, especially wherever the intense banding sets up, but overall similar to the past.

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