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February 17-18 Threat Discussion


The Iceman

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2 minutes ago, Ralph Wiggum said:

I want to hold judgment until 1:30pm-ish after the 12z has completed (save for the eps). I will try and post thoughts but tied up with appointments most of the morning. Hopefully those rates u mentioned hold steady. Nervous about a shift since the energy will just be nearing the West coast at 12z runs. 

 

 

Agreed...12z may see changes as we get better sampling...but I will also be leery of any big shifts as the models may also be overcorrecting themselves with the better data. I think 00z tonight will be the important runs for this event as they will have better sampling and be adjusted from that sampling. This has been one of those winters where we have gotten lucky many times even though we never got a big storm. lets hope that luck continues. The eagles won the super bowl, anything is possible now :lol:

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IMO with the rates shown on the NAM, I don't think anywhere west of the delaware would turn over with that track and those rates. It's only just barely over to rain and I just think we'lls ee enough dynamic cooling to offset that. I think it's a great run, ignore the clown maps. This would be close to a WSW event for SE PA and looks very similar to the Euro.

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I think we will be ok thermally. Front isn't arctic but it is still a fresh airmass of cold air. The 50-50 is in a great spot and we have a -AO albeit transient. Accumulating snow now seems like a certainty for just about everyone. The question now is will we see a WWA or WSW and the thermals will play a big part. The qpf is there though to support WSW totals if we get the thermals. With such a razors edge for the temps I really wouldn't trust thermals until about 48 hours out. The models are no where near perfect with temps this far out and a 2 degree shift either way is massive in this set up. I'm hoping we see 6" so that no matter what plays out in march we can say we had at least one significant storm but expectations right now should be set at around 2". Less than that and I feel you have a legitimate gripe but there is the possibility for much more. These late season events thermally are very hard to nail down. For every storm that is unexpectedly cooler and sticks more than projected there is another that fails to accumulate. It's hard to be confident towards either direction especially after last march's event. We have much better climo in this situation though.  Be happy with any accumulating snow that you receive in this pattern and be overjoyed if we get a WSW level event is the best way to go into this storm. High bust potential on both sides...true roll of the dice here with such a progressive pattern. 

 

Another thing to add is I think there will be a sharp gradient between the wet snow and accumulating snow. Area's 5 miles apart could see 3 or 4" difference with the thermals. 

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I think we should be rooting for this storm to come in a bit faster than progged. The quicker we get precip into the area the longer we will be staying as snow. The RGEM at the end of it's range hints at being more progressive with the southern wave than the NAM and GFS. This would definitely impact thermals as well. Get precip in faster while temps are lower and they will struggle to rise with the heavy precip. Once again, the timing here is really on our side for once. A day time snow would almost certainly have been white rain outside of elevation areas.

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Euro continues to look nice but we don't have much wiggle room in inland New jersey and extreme SE PA. I think the heavy rates will keep temps down especially since we ll have good wet bulbs at the onset of precip to knock temps down. this is one tough forecast here. mt holly hasnt updated but this is what they had this morning. seems like they are thinking we will be cool enough to be all snow but there is uncertainty in if it will accumulate or not. They seem optimistic that we will definitely see heavy rates for a good likely 6 hours overnight.

 

Quote

For Saturday and Sunday...The guidance is in good agreement with a
stronger short wave sliding east along the southern side of a broad
upper-level trough centered near Hudson Bay Canada. This feature may
sharpen the trough some as it quickly shifts eastward, however there
are still several questions regarding the details. Looks like a
precipitation event will occur, however some guidance is a little
farther south although some associated ensembles suggest a farther
north track. In addition, boundary layer temperatures will be key
regarding the extent of snow accumulations as the surface will be
warmer leading into this. However, the snow will be falling at night
which will help cool the ground and if the intensity of the
precipitation is heavier this will also improve the accumulation
efficiency. The forecast soundings are rather dry prior to the
arrival of the precipitation which would lead to more evaporational
cooling. High pressure will be moving into the Canadian Maritimes
which would allow some warming, however the initially very dry air
may help with wet bulbing and keep the airmass cooler. Overall,
temperatures look to be close to freezing where snow occurs and the
snow to liquid ratios will be low allowing the snow to be wetter.

There looks to be some sort of mixed precipitation zone that
meanders some, however this may end up being a rain/snow mix. We did
not carry any ice accumulations at this time given the uncertainty.
Our first take on snow amounts will post early this morning and we
went more conservative given the uncertainty with the thermal fields
and even surface temperatures. This translates into a swath of 1-3/2-
4 inches with less farther south across Delmarva and eastward toward
the New Jersey Shore. Some guidance, which shows higher QPF, looks
to be hinting at a ribbon of enhanced ascent northwest of the
surface low as the thermal gradient aloft may tighten for a time
allowing for stronger frontogenetic forcing. If this were to occur,
an embedded area of heavier rates would result. As of now this is of
lower confidence, but cannot be ruled out. In addition, our region
is forecast to be within the right entrance region of a potent 250
mb jet Saturday night which would enhance the large scale ascent
across the Mid-Atlantic.

The flow aloft is progressive therefore this system should be quick
moving. As a result, precipitation should end by daybreak Sunday and
therefore continued with a dry day Sunday. High pressure looks to
quickly start building in Sunday afternoon and night, however the
airmass is not forecast to be all that cold following the storm.

 

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1 hour ago, The Iceman said:

I think we should be rooting for this storm to come in a bit faster than progged. The quicker we get precip into the area the longer we will be staying as snow. The RGEM at the end of it's range hints at being more progressive with the southern wave than the NAM and GFS. This would definitely impact thermals as well. Get precip in faster while temps are lower and they will struggle to rise with the heavy precip. Once again, the timing here is really on our side for once. A day time snow would almost certainly have been white rain outside of elevation areas.

Without it this is a non storm/white rain event. That 1/30 storm made me nuts. Snowing at good clips all day and nothing to show for it...ugghh. All and all I think we'll have something to look at Sat night. If anything the trees/shrubs should get plastered w/the white stuff which is cool to look at...

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Since we are getting close to 60 hours until the event I'm putting out a first call.

Shore points Central to S Jersey - 1-2" to a mix/white rain/or plain rain

inland S and Central jersey up to Philly and lower bucks - 2-6" amounts higher end as you go further inland and north...possible change to rain or mix towards the end of the storm

Central bucks up to lehigh valley and points south west - 4-8" - all snow, no precip issues...isolated spots of 10"

North of Allentown into the poconos - 3-6" - zero issues with temps but precip amounts will be less. 

 Overall I think this is  winter storm watch worthy from 95 points N and west at this point in the game. I think they are usually hoisted 36 hours out from an event so that would be with tomorrow mornings package. Will be interesting to see mt hollys thoughts. The AM disco could be a great one.

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Call it blind faith but I just think we see thermals improve as we get closer. the 3k NAM at 60 is much cooler than the globals. Obviously it doesn't show the full storm evolution yet but it is encouraging the meso models look cooler off the bat. Combined with zero sun factor and a fresh dry air mass  to lower wet bulbs, I think most of the area will be fine with all snow. Now I may be wrong which is why I have the wide range in my first call but I think there are several encouraging signs pointing towards thermals being cooler than what is being shown on the globals currently.

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Since we are getting close to 60 hours until the event I'm putting out a first call.
Shore points Central to S Jersey - 1-2" to a mix/white rain/or plain rain
inland S and Central jersey up to Philly and lower bucks - 2-6" amounts higher end as you go further inland and north...possible change to rain or mix towards the end of the storm
Central bucks up to lehigh valley and points south west - 4-8" - all snow, no precip issues...isolated spots of 10"
North of Allentown into the poconos - 3-6" - zero issues with temps but precip amounts will be less. 
 Overall I think this is  winter storm watch worthy from 95 points N and west at this point in the game. I think they are usually hoisted 36 hours out from an event so that would be with tomorrow mornings package. Will be interesting to see mt hollys thoughts. The AM disco could be a great one.
I dont usually model hug but I'll give you a hug. Have my area 4-6"+.....we take!
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I dunno....I didn't love the 12z run tbh. Wasn't horrible but mid levels get roasty all the way back thru Central Bucks and there is no denying this. This was the trend I wanted to see end. WAA can be a storm killer daytime or night time, but this time of year with the antecedent airmass being borderline at best and rotting as it pulls away, Im not nearly as bullish as Ice. I also didn't care much for the slightly lower precip totals. We need every bit of heavier precip we can manufacture to cool the column. I dont have specific totals but sticking with my original thoughts on a sloppy slushy 1-3"/2-4" (so 1-4" for now) in extreme SE PA. LV should do a little better. Im not bailing, believe me. I've never really been on board for a warning type storm here. Still time to change that but I still have that same uneasy feeling.

 

Eta: looking at bl and surface temps....ratios for my area points s and e 8:1 - 10:1 maybe 12:1 at best at the very onset

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^^^completely rational forecast. I admit I am going against 12z guidance at the moment, but I really just have a gut feeling this produces better than we think. I could see your call verifying easily...this is a very delicate situation. a degree either way is likely going to be the difference between a paste job and white rain.

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^^^completely rational forecast. I admit I am going against 12z guidance at the moment, but I really just have a gut feeling this produces better than we think. I could see your call verifying easily...this is a very delicate situation. a degree either way is likely going to be the difference between a paste job and white rain.

This is your storm my man.....your thread and you are really feeling this and havent waivered. I am probably pulling for your calls to verify more than anyone else in this subforum. Your contributions here have been well-received this year and a breath of fresh air to actually have another solid poster to discuss in detail.

 

With that said, the 12k NAM says the Iceman Storm cometh! A mere 6-8" widespread event verbatim SE PA. Bring it home Iceman!

 

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I take this with a large grain of ice-melt, but I believe we've been officially nam'd!
 
Nammed-2-15-18.thumb.jpg.dd5bffba2318f9aa976985e19dff8324.jpg
Yes we have.....the pivotal wx clown map which i blieve factors in sleet etc has widespread 1-3" snow for everyone in se pa....the rest is all taint as mid levels roast even under a weaker lp. Very few totals higher than that anywhere in se pa. Awaiting 3k twin.
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9 minutes ago, hurricane1091 said:

I wouldn't hold your breath for 5-8 inches on Philly or SE NJ. I'm expecting some temp issues just based off how this tends to play out.

Sent from my Pixel XL using Tapatalk
 

Hence the large grain of salt. Getting nam'd a day or 2 out is an old tradition that hasn't happened for a while, so it's a fun thing - kind of like an encouragement. How's the leg/foot?

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3k is what I was talking about earlier... Meso models are much cooler in the mid levels. Even the 12k nam is very close and with the heavy rates I believe the column will cool just enough. The 12k nam was significantly cooler than 12z even if it wasn't cool enough yet. That's what we wanted to see.
GFS is wonky....farther S and E with lp and not quite as amped yet warmer and c-2" all around. Maybe lighter precip rates to blame? You cant make this stuff up. The GFS has either been totally clueless all week irt this system or it might score the coup of the winter.
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18z ICON followed the GFS....weaker lp, flatter, farther s and e, lighter precip. Cut totals quite a bit from 12z. We've seen this song and dance where the NAM goes nuts with qpf and the others all cut back quite a bit. The NAM unfortunately usually ends up wrong and slowly corrects itself by 12z tomorrow latest.

 

 

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20 minutes ago, Ralph Wiggum said:

18z ICON followed the GFS....weaker lp, flatter, farther s and e, lighter precip. Cut totals quite a bit from 18z. We've seen this song and dance where the NAM goes nuts with qpf and the others all cut back quite a bit. The NAM unfortunately usually ends up wrong and slowly corrects itself by 12z tomorrow latest.

 

20 minutes ago, Ralph Wiggum said:

18z ICON followed the GFS....weaker lp, flatter, farther s and e, lighter precip. Cut totals quite a bit from 18z. We've seen this song and dance where the NAM goes nuts with qpf and the others all cut back quite a bit. The NAM unfortunately usually ends up wrong and slowly corrects itself by 12z tomorrow latest.

I think after 12z tomorrow it's time to put a lot more weight on the meso models. Also, after the last few years I don't badmouth the nam like mny others do. 

Iceman, I second Ralph's high grades for your contribution in this subfotum. Where have you been?

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Remember, a stronger, more amped low could actually help keep the midlevels colder by keeping the winds more out of the north/northeast and keep things ageostrophically cooler. Someone asked me how much I think we will get Saturday and I said 2-4" with potentially higher. Think that's a good call?

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