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OBS-NOWCAST: Back-Back snow accumulation risk (late March 16). This thread focused on March 19, 2021


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548A/17: Advisory situation may be coming to a portion of the forum-not a lock, for the Friday morning commute, despite probable less than official criteria amounts NYC/LI due to sharply falling temps to between 25-30F with sleet to snow in the 5A-8A time frame and gusty n-ne wind of 30-40 MPH. Snow ends sometime late morning-midday with temps recovering above freezing in the afternoon. Wind gusts for a few minutes between midnight and 8A could reach 50 MPH in parts of the area. Added wind event to the thread.  Snowfall for NYC-LI T- at most 2", while a bit heavier seems likely I84 corridor extreme nw NJ of 1/2 to possibly 3". Think the best chance for 2+" in our subforum is CT. If the precip ends more abruptly, then we escape the advisory and amounts will be under 1" with the lesser snowfall of the 00z/17 cycle ICON, UKMET, 12K NAM considered.  

Note: as the transition to snow occurs, the first hour or two may be melting on most surfaces and certainly pack down to snow ratios less than 10 to 1, possibly closer to 7 to 1 or something like that.

Some of the modeling has complications not only Friday, but also next Monday.  For Friday, there could be two bands of halfway decent accumulative snow,  one across I84 and the other just south of I78 across central or s NJ? TBD. 

Then, next Monday:  the 00z/17 EPS and GEPS want to form a deep cyclonic circulation off the mid or south Atlantic coast this weekend and drift it north or northeast early next week, spreading rain back into the area.  Depending on latitude of formation, will determine how much warming aloft occurs.  ENS have 850 temps in the +3/+4C range next Monday, too warm for snow, provided all the excessive height rises and warming aloft that is modeled in the northeast occurs. If that shifts north, then there is a real long shot (very low chance) we might be looking at some marginal thermal profiles for a bit of wet snow in CT.  At this time, I wouldn't be promising mostly clear skies and dry weather for Sunday afternoon-Tuesday morning. 

Added the 0841z/17 NWS ensemble prob for >1" of snow Friday.  You can see the concern for going too heavy. 

---

 

Strong cold high pressure approaching Quebec Friday-Saturday will combine with an eastward moving and opening closed low in the Ohio Valley, to permit a period of wet snow here on Friday. Duration and intensity are uncertain along with resultant amounts (T-2"?) and will be related to the proximity of the positive tilt 500MB trough. For now, this could be considered a back-back system, modeled way back as early as the 00z/7th modeling cycle, that could provide as much snow to the parts of the forum, as whatever occurs late 16-17. 

The fresh influx of colder BL air from the north may even allow measurable snow into NYC?

Most of the modeling favors a few hours of snow Friday morning with marginal accretion temps. Still, for an event at the tail end of winter for NYC, it could provide a little fun? This especially if the GEPS-NAEFS solutions of keeping the low close enough to continue significant qpf going into early Saturday.  Then we would be talking about some potentially plowable snow to near NYC, but this is an outlier possibility for now and best at this time (D5) to favor conservative ,minor impact, at worst. 

Finally, if this storm system does hang around nearby to our south all weekend (low chance), it might make a northward drift into the CT/LI part of the forum Monday the 22nd, but by that time, the snow temp profiles have warmed to rain (probably exhausted the snow profile cold air supply). 

Screen Shot 2021-03-17 at 5.36.39 AM.png

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I believe this event is all about the timing and interaction and positioning of the strong HP moving southeast from central Canada mid to late week VS. the slow moving LP moving west to east passing south of Chicago Thursday and through PA early Friday  - this has significant snowfall potential somewhere in the region IMO looking at the current guidance

sn10_024h.us_ne.png

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15 hours ago, NEG NAO said:

I believe this event is all about the timing and interaction and positioning of the strong HP moving southeast from central Canada mid to late week VS. the slow moving LP moving west to east passing south of Chicago Thursday and through PA early Friday  - this has significant snowfall potential somewhere in the region IMO looking at the current guidance

sn10_024h.us_ne.png

is that 10 inches near ACY?

 

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13 minutes ago, jm1220 said:

To me it looks like a mainly I-90 event with maybe some snow at the end down to NYC. Northern posters might get a few inches. I’m not too interested unless we get significant changes. 

yeah new NAM is mostly heavy rain-with temps in the 50's Thursday, nothing would really stick on the back end anyway, maybe some white rain, whoopdeedoo

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namconus_ref_frzn_neus_43.png

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21 minutes ago, Brian5671 said:

yeah new NAM is mostly heavy rain-with temps in the 50's Thursday, nothing would really stick on the back end anyway, maybe some white rain, whoopdeedoo

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namconus_ref_frzn_neus_43.png

This is backside white rain at best before it ends Friday morning, less than an inch, even for Rockland, Westchester, Bergen, Passaic.  Mainly an all rain event 

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44 minutes ago, jm1220 said:

To me it looks like a mainly I-90 event with maybe some snow at the end down to NYC. Northern posters might get a few inches. I’m not too interested unless we get significant changes. 

1-3 looks good for us in northern sections of this forum. NE may see some heavy snows right at the worst possible time. The commute could be nightmarish

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The old GFS is the only model I can see bringing anything decent to near NYC/LI. Para GFS is largely a washout south of I-84 like the NAM and Euro. We could use the rain so that's a win I guess. There probably will be a changeover to snow/slush as it ends but it would be brief near the coast. I-90 corridor is heavily favored here. 

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23 minutes ago, jm1220 said:

The old GFS is the only model I can see bringing anything decent to near NYC/LI. Para GFS is largely a washout south of I-84 like the NAM and Euro. We could use the rain so that's a win I guess. There probably will be a changeover to snow/slush as it ends but it would be brief near the coast. I-90 corridor is heavily favored here. 

The airmass in front of the storm is warm-it will be near 50.  Heaviest precip falls while it's still warm, by the time the cold air drills in, most of the heavy precip is done.   Like you said, white rain or a car topper north....

gfs_T2m_neus_9.png

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Typically these rain to snow / cold crash situations typically shut off before it gets overly interesting. These 6 hour grabs aren't particular helpful in illustrating that. Exact timing and track location are key here, tricky forecast yet but certainly N/W favored here if anyone is to be favored.  

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45 minutes ago, MJO812 said:

Taken from mid Atlantic thread

This is a stretched low pressure. It is possible some areas will see accumulating snow even down here.

F2135CB0-046F-47BF-B9B5-681C367E7F89.thumb.png.b98e31f0e9d910caae451f96f1025d89.png

This is beginning to remind me of this event - which was impossible to predict accumulations region wide - Walt must remember this storm....I got lucky in Northern Ocean County - 8 inches - BUT lost power for several hours the heavy wet snow was weighing down tree limbs and then fallen power lines......

Snow storm, April 9-10, 1996 - Storm Summary (raymondcmartinjr.com)

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11 minutes ago, NEG NAO said:

This is beginning to remind me of this event - which was impossible to predict accumulations region wide - Walt must remember this storm....I got lucky in Northern Ocean County - 8 inches - BUT lost power for several hours the heavy wet snow was weighing down tree limbs and then fallen power lines......

Snow storm, April 9-10, 1996 - Storm Summary (raymondcmartinjr.com)

I was only 7 years old. Must have been a nice storm.

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57 minutes ago, MJO812 said:

I was only 7 years old. Must have been a nice storm.

That storm produced nada in my area. Didn't know it hit Ocean county at all; but a ride north from here into union co and I saw snow OTG. April7 2003 did produce here, and famously April 82; and April 1 2018. But, I am confident and would bet the farm we are done for this year. 

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