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Potential Major East Coast Storm on Saturday Part 2


IsentropicLift

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I mean I don't know if I'm misreading the upper air charts...but the NAM progs seem to have the 850 Low pass south of Long Island off the central NJ coast, no?

On the soundings for JFK on the 0z NAM:

 

Date: 9 hour Eta valid 9Z SAT 24 JAN 15

Station: 40.65,-73.78

Latitude: 40.65

Longitude: -73.78

-------------------------------------------------------------------------------

LEV PRES HGHT TEMP DEWP RH DD WETB DIR SPD THETA THE-V THE-W THE-E W

mb m C C % C C deg knt K K K K g/kg

-------------------------------------------------------------------------------

SFC 1008 7 0.2 -0.0 98 0.2 0.1 45 5 272.8 273.4 272.9 283.0 3.78

1 1000 67 -0.1 58 8 273.0

2 950 477 -0.8 -1.3 97 0.4 -1.0 100 6 276.3 277.0 274.8 286.4 3.67

3 900 910 -0.2 -0.5 98 0.3 -0.3 171 11 281.3 282.0 278.0 292.7 4.10

4 850 1368 -0.3 -0.6 98 0.3 -0.5 250 11 285.8 286.5 280.4 298.0 4.29

5 800 1852 -1.2 -1.4 98 0.3 -1.3 192 27 289.9 290.7 282.3 302.4 4.31

6 750 2366 -2.6 -2.8 98 0.3 -2.7 190 40 293.8 294.5 283.8 306.0 4.14

 

Winds from 950mb and above are coming from a southerly component, so there's WAA from that level and above. 

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Its an open 850 low now vs a closed and stronger one on the models yesterday...here is the 12Z NAM...one of the Mets in the SNE forum joked this was almost transitioning to a southwest flow event

 

 

 

Could you offer me a fast lecture on that stuff 'cause I'm not an authority on how that discrepancy tends to influence both temperature & precip in this area...and I would like to better comprehend it. 

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Could you offer me a fast lecture on that stuff 'cause I'm not an authority on how that discrepancy tends to influence both temperature & precip in this area...and I would like to better comprehend it. 

 

Weak 850 low better in a marginal event if you're going to be near or just west of it, a stronger 850 low will more likely flood you with warm air if you're near or just west of it since it'll have stronger flow around its east side wrapping the warm air back around to the west somewhat. 

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The only bad thing I see so far is that the obs in SE PA and SWRN NJ don't seem to have VIS correlating well with the radar echoes, its possible that there is a layer somewhere not saturated right away or that their thermals in the mid layers down there are not as good, we'll see what happens as it gets up here.

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SREF plumes, now along with the RAP/HRRR as well as the NAM show 5-7" of snowfall in and around NYC as well as on LI. I've seen the HRRR overdo it many times though only to scale back the amounts in the runs that follow. We will see if that happens this time, or if they stick to these amounts

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Nick Gregory just said a lot of the new data tonight is indicating there will be more sleet with this system. Hard to believe NYC will get 6 inches with the amount of mixing that's expected. 2 to 4 seems more reasonable which is what Nick's map shows.

Think this is a decent call but theres just a few uncertanties I'm still mixed about.

How much precip falls in this front end thump? Surface looks to stay fine until low pushes near us and the 850-900 area warms. When does this happen? 8 am? If so, when do we hit our dry slot?

Having these heavy echos crawl up towards us, do we areas change from SN+ to Sleet with such heavy areas of precip? If so, do they ever change back to just snow? Etc.

Really a tough one to nail down. There is no clear cut consensus from anything that we can infer at the moment. Upton/Mt Holly going cautiously on the lower side of things, most mets are too, despite some of the models coming out within the last few hours.

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Shocking cutoff on the 0z Nam...6 to 8 inches N. Jersey...NYC & L.I....only an inch or two from Sandy Hook, NJ south...shades of the winter of 1993-94. 

post-747-0-85362600-1422069550_thumb.gif

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NAM is quite borderline for NYC in terms of seeing mostly snow or a mix. At 9z, all layers at JFK are just below freezing, but a warm layer at 750-800 mb looks to move in soon after, meaning at least sleet. At Islip, the 850mb temp is literally 0.0 at 9z (every other layer below freezing). It'll be very interesting to see how the R/S line advances overnight. Maybe it can be held off if precip is heavy enough. Central Park looks slightly colder than these but the 750mb warm layer breaks through after 9z. The front part of the storm looks to be done by or just after 12z.

 

Yea the warm nose between 850-700 hPa is showing up on the HRRR as well by 1600 UTC.

 

http://www.atmos.albany.edu/student/ppapin/lb13_img/hrrr/hrrr_ncep_snd_jfk.php

eDUB7i9.png

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Its 36 in the metro area ( I realize cooling will take us down to near freezing but like being in upper 20s to give us some extra time on front end), not a good strting point and would support NAM's warm start. Im hoping for a healthy CCB/back end scenario. Not buying the RAP scenario. the good news is the 850 freezing is around AC and if it moves slowly enough we should be good till sun rise. Ill take 2-4 front end and 2-3 back end and smile all the way to the bank.

That will wet bulb to low 30s no problem

Sent from my iPhone using Tapatalk

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Weak 850 low better in a marginal event if you're going to be near or just west of it, a stronger 850 low will more likely flood you with warm air if you're near or just west of it since it'll have stronger flow around its east side wrapping the warm air back around to the west somewhat. 

 

 

Thanks.  One more question...the CMC-HRDPS is the GEM-LAM, correct?   The GEM-LAM is the best snowfall predictor of all time in my experience.

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looks like the gfs is coming in west & wet. little warm from prior runs.

 

The GFS in a last minute mesoscale situation...I would only use it if I were running low on Scots. 

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