February 17-18 Threat Discussion

[penndotguy]

Very strange WSW for 4-6 I thought our criteria was 6+ 

[Ralph Wiggum]

" * WHERE...Most of southeastern Pennsylvania and northern New
Jersey."
I'm pretty shocked at the amounts...
http://tinyurl.com/ycdf593u

 

Wow. Now that's a surprise. I still question whether it ever gets to warning status here tho in extreme SE PA?

[Hurricane Agnes]

58 minutes ago, penndotguy said:

Very strange WSW for 4-6 I thought our criteria was 6+ 

I think in this instance "WSW" = Winter Storm Watch which could become a Winter Weather Advisory or Winter Storm Warning depending on criteria.

[penndotguy]

8 minutes ago, Hurricane Agnes said:

I think in this instance "WSW" = Winter Storm Watch which could become a Winter Weather Advisory or Winter Storm Warning depending on criteria.

Yeah after I posted that I realized that’s probably the case. Thanks

[Hurricane Agnes]

1 minute ago, penndotguy said:

Yeah after I posted that I realized that’s probably the case. Thanks

I think you guys are on the higher side of what is progged in any case!  At least an advisory.

[wkd]

I still think the nam may have a better idea on the outcome due to its better handling of mesoscale processes. I  believe of the globals the euro also is better at this. We shall see. In any case I don't expect to see much accumulation Sunday morning but I'll probably stay up Saturday night staring at my snow light.

[Ralph Wiggum]

ICON slashed totals again like Kmart prices on a blue light special or a Walmart rollback. More in line now with the GEM. I am starting to think my original call for 1-4" Eastern PA lesser amts extreme SE higher part of range N and W of Central Bucks I've stuck with may be too aggressive? Will await 12z before considering adjusting.

 

 

 

 

 

 

[The Iceman]

Mt Holly must be reading my posts and ive got them bought in anyway EE rule still in effect... 3k nam trended colder yet again. Euro held steady for about the 6th run in a row. Trust the EE rule...

[The Iceman]

Watch the meso models at 12z. Very good chance they have a better read on temps this far out. 

[Ralph Wiggum]

I still think the nam may have a better idea on the outcome due to its better handling of mesoscale processes. I  believe of the globals the euro also is better at this. We shall see. In any case I don't expect to see much accumulation Sunday morning but I'll probably stay up Saturday night staring at my snow light.

NAM may be handling the colder temps better, that part I wont disagree with as it has a tendency to sniff out thermal features fairly well. As for qpf? NAM was likely overdone 18z then 0z before starting to correct itself at 6z more inline with majority of other guidance that sees this as a lighter precip maker. Even the Euro, as consistent as it has been, has been stubbornly and slowly backing down on overall amounts since about 12z Wednesday.

[Ralph Wiggum]

Watch the meso models at 12z. Very good chance they have a better read on temps this far out. 

Im really not sure temps are the issue tho. The problem now is twofold: 1) much lighter qpf totals showing up on guidance as a whole and 2) progressive speed of this system.....continues to move out quicker every time a new model suite rolls in. 12z needs to buck the trend if we want a miracle warning event to verify, otherwise the writing is probably already on the wall.

[Birds~69]

22 hours ago, Birds~69 said:

God help us if people can't understand percentages but I'm sure many will be confused.

It's more of a look of "what may happen" in advance which I don't mind. (Kinda like DT's 1st call) Then nail it down w/numbers later. The other networks didn't give anything last night ...didn't see them this morning so they may have updated.

My "off the top of my head prediction"....sloppy 2".

Damnit, I'm sticking to this! Trees/grass everything plastered white....back roads slushy/wet...main roads wet.

Think you may have to go Lehigh Valley N for better action...

[wkd]

7 minutes ago, Ralph Wiggum said:

13 minutes ago, The Iceman said:

Watch the meso models at 12z. Very good chance they have a better read on temps this far out. 

Im really not sure temps are the issue tho. The problem now is twofold: 1) much lighter qpf totals showing up on guidance as a whole and 2) progressive speed of this system.....continues to move out quicker every time a new model suite rolls in. 12z needs to buck the trend if we want a miracle warning event to verify, otherwise the writing is probably already on the wall.

Surface temps will make a difference regarding snow accumulation though. A slower moving system may give more qpf but if more of it is sleet or it melts on contact what good is it?

[Hurricane Agnes]

1 minute ago, wkd said:

Surface temps will make a difference regarding snow accumulation though. A slower moving system may give more qpf but if more of it is sleet or it melts on contact what good is it?

Actually a layer of sleet starts chilling the ground and any further precip can accumulate on top of that - notably on the colder surfaces. If the dynamics is strong enough to cool the column then you can get a period of snow at that point that could lay on top of any sleet. But as the upper air temps rise (warm nose), it will do the changeover and all of it will eventually melt anyway.

[Birds~69]

30 minutes ago, Ralph Wiggum said:

36 minutes ago, The Iceman said:

Watch the meso models at 12z. Very good chance they have a better read on temps this far out. 

Im really not sure temps are the issue tho. The problem now is twofold: 1) much lighter qpf totals showing up on guidance as a whole and 2) progressive speed of this system.....continues to move out quicker every time a new model suite rolls in. 12z needs to buck the trend if we want a miracle warning event to verify, otherwise the writing is probably already on the wall.

It's outta here by 3-4am rather than the 7am earlier thinking...it's moving right along.

[The Iceman]

My map would pretty much mirror mt hollys. very well done imo..think we'll definitely see 6" in places N and W.

 

[The Iceman]

Shout out to MGorse if you still lurk these boards. A++++ long range disco this morning. Great stuff.

 

Quote

For Saturday and Sunday...The guidance continues to show a quick
moving but potent system developing just off the Mid-Atlantic coast
later Saturday then quickly tracking northeastward away from our
area early Sunday. While the guidance is in good agreement that
precipitation will occur, there continues to be more uncertainty
with the precipitation amounts northwestward and also the
precipitation type especially near and east of I-95. We start with
clouds increasing during the day Saturday and if these thicken
rather quickly, surface heating will be slowed. The airmass in place
is forecast to be chilly but also rather dry in the lower levels
especially.

The guidance differs some with the large scale ascent to the
northwest of the surface low. This will be key in determining not
only the precipitation amounts but the rates. Some guidance suggest
that a ribbon of enhanced lift occurs associated with a rapid
increase in frontogenetic forcing between about 850 mb and 700 mb.
This may become enhanced for a time Saturday night as our region is
within the right entrance region of a potent 250 mb jet. This will
be a quick hitting storm, however there is the potential for a swath
of snowfall rates of near 1 inch per hour. As of now, we are
thinking this is near and just north and west of I-95. However
despite the surface high well east-northeast of our area, some hints
of cold air damming lingering and this could be enhanced some due to
wet bulbing effects. Therefore, a thumping of snow may very well
occur for parts of our region namely near and west of I-95. Farther
to the northwest across our area, there looks to be less QPF but
snow to liquid ratios should be the highest in the vicinity of the
Poconos. Farther south and east across Delmarva and central to
especially southern New Jersey, enough warming should result in a
zone of some mixing (mainly rain/snow but some sleet is possible
briefly) with any snow going over to rain closer to the coast. In
between these zones, a wetter snow if enough accumulates at a fast
rate could result in some power outages. We continue to not include
any ice amounts as freezing rain may be limited and this is much
less certain given marginal surface temperatures where it could
occur.

Given the above, the quick hitting nature of this event and our
latest forecast snow amounts, we opted to go with a Winter Storm
Watch for Saturday night for all of eastern Pennsylvania (except
Delaware and Philadelphia counties) and northern New Jersey. It is
here where we have the highest snow amounts which could approach
warning criteria for some areas but this is uncertain, as is the
western fringe due to potentially less QPF. Since there is the
potential for some higher totals and enhanced rates and to also help
with our messaging efforts, we felt a watch was a good way to go at
this point. To the east of the watch area, a tier of advisories will
be possible. Our precipitation types were derived from a blend of
several models with some adjustments then made.

The system quickly moves away early Sunday and all the precipitation
should be done by 5 AM. As the flow turns northwest and increases
some with drier air arriving, clouds are expected to clear out for
much of the area. The flow is progressive however and therefore
Sunday afternoon will be on the milder side with plenty of snow
melting occurring.

 

[The Iceman]

What that disco says is there will likely be banding as this comes through enhancing precip rates. Definitely gives some credence to the NAM and Euro solutions. Really a great write up above. Never go against the EE rule...

[ChescoWx]

Wxsim not terribly enthused with 6z model forecasts at this time....

Saturday: Partly cloudy in the morning, becoming mostly cloudy to cloudy in the
 afternoon. Patchy light fog in the morning. A chance of rain in the afternoon.
 High 44. Wind east around 2 mph in the morning, becoming south-southeast in the
 afternoon. Chance of precipitation 30 percent. Precipitation mostly less than a
 tenth of an inch.
 
 Saturday night: Dense overcast in the evening, becoming mostly cloudy to cloudy
 after midnight. Patchy light fog in the evening, then light to moderate fog
 after midnight. A mix of rain and snow likely in the evening, then a chance of
 snow after midnight. Low 30. Wind south-southeast around 2 mph in the evening,
 becoming west after midnight. Chance of precipitation 70 percent. Precipitation
 (liquid equivalent) mostly between a quarter and half an inch. Snow accumulation
 about half an inch.

[The Iceman]

FWIW the 3K nam nailed the super bowl sunday event. was perfect with temps and precip. holding my breathe for 12z that it continues to hold serve and other mesos begin to also show the banding like the NAM and Euro to an extent.

[Ralph Wiggum]

12k NAM slid the axis of heaviest precp/banding South into Southern NJ and cut back the NW fringes. Awaiting 3k.

[The Iceman]

16 minutes ago, Ralph Wiggum said:

12k NAM slid the axis of heaviest precp/banding South into Southern NJ and cut back the NW fringes. Awaiting 3k.

3k is similar...but important to note both models bring that band of heavy precip up to extreme SE PA. Lower bucks/montco/and philly also do really well on both models but north of their precip was cut. SNJ is slowly going from looking like a lot of taint to possibly being in the best spot of everyone. Both models show a quick but hard hitting 4-6" from bucks county S and E. Temps again were cooler than 6z and 00z. The negative thing is this was much worse for N and W areas. 95 S and E special on this run. Like Mt Holly said, the axis of heaviest snow is going to be where that narrow band of forcing at 850 and 700 mb sets up. Before it was favoring N and W of 95 but this run clearly shifted to 95 and just east for that. Wherever that band sets up is going to be our winner...south of that, the subsistence will likely hinder rates and either changeover precip or make it light enough so it has trouble sticking and north of that zone will struggle to pick up enough precip for it to be anything major as rates won't be as heavy. This to me has shifted from a widespread possible wsw event to a localized winter storm warning event with advisories for everyone else. based on the strong banding the higher res models are picking up, i don't think temps will be an issue for whoever sets up under that banding and that is who will over perform in this one. Very interested to see the NMM and ARW hires nests. They have done very well in borderline situations this year as well and I also like them for picking up the possible banding.  Our threat for 4 inches or more is not dead yet though chances have decreased overall. 

[Ralph Wiggum]

3k NAM cut qpf substantially. Hardly a 2-4" event now and that is in extreme SE PA. Precip expanse reduced on the NW fringes and like the 12k it slid the heaviest axis from upper bucks to along or just east of the Delaware River.

[WoodyMPW]

Hello Lucy.

[hazwoper]

as expected NAM is dropping its totals.  expect Mt Holly to do the same.  1-2" with a stray 3" here and there

[Newman]

I guess my call for 2-4" will work out fine. I would say most will verify with 2 or 3 inches, maybe 4 tops. These storms always tend to cut back on QPF even when temperatures trend better. I'm just glad it'll be gone in a day or two. 

[The Iceman]

Rgem cooler and similar banding structure to the NAM. The trends on the mesos have been great if you live in extreme SE PA and inland towards the delaware river in South and Central Jersey. That 4-6" band has definitely trended south today. Unfortunate for N and W of 95 though as precip totals were definitely cut big time. 

[RedSky]

RGEM puts a 4-4.5" band through Bucks Chester and Montco. Looks like I'm hugging that it's the lone model hanging with the ECM, which assuredly will cut it's qpf at 12z 

 

 

 

 

 

 

 

[The Iceman]

The rgem actually shows perfectly that when the heavier echoes come in, they rapidly cool the column and produce heavy snow. While the lighter echoes will be light rain or light white rain. Like I've mentioned already this is coming down to where ever that death band sets up for who will see the most snow. Any one outside of it though will likely only see 1-3". My second call right now is as follows. Leaning heavily on the NAM, RGEM, and Euro.

 Lehigh Valley south to central bucks - 1-3" with isolated lolli's of 4 in area's that see heavier echoes

Lower bucks south and east to the western half of South and Central jersey 3-6" with isolated higher amounts in area's that get the heaviest banding. snowfall rates of 1" and hour will be common at the height of the storm in this area.

Eastern half of South and Central Jersey - c-2" precip issues along the shore and being in the area of substinence from the death band cuts down on heavier rates leading to likely a wet slush accumulation on grass. However, with current trends, this area may be close to getting into the heavier echoes and changing to snow.

[Ralph Wiggum]

Rgem cooler and similar banding structure to the NAM. The trends on the mesos have been great if you live in extreme SE PA and inland towards the delaware river in South and Central Jersey. That 4-6" band has definitely trended south today. Unfortunate for N and W of 95 though as precip totals were definitely cut big time. 

The trends on the mesos are great for places like DC. Looks like 4-8" band setting up down that's way as guidance continues to hone in on where the banding sets up S of our region and into Southern NJ. The Mid Atl deserves this one as we continue to nickel and dime our way to avg seasonal snowfall in SE PA. We take.