Weekend Snowfest/Rainfest/Mixed Mess?

[CAPE]

The 3k NAM keeps 850 temps below freezing for the whole event. It also seems to be trying to hone in on where the best fronto forcing/banding may set up- it likes the I-95 vicinity. Rates are really going to be the key as others have mentioned.

[nj2va]

NWS Pitt slowly playing catchup for the mountains.  Forecasted less than 1” yesterday; now showing 2-3” for Canaan/Deep Creek.  They need the snow for the holiday weekend skiers considering the current deluge/flood warnings there.  

[arlwx]

The latest from LWX:

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Surface low pressure will develop over the Tennessee Valley Saturday
morning, driven by a digging upper trough flicking across the Great
Lakes/Ohio Valley. Transient cold air in place will result in a
myriad of precipitation types Saturday afternoon and evening. The
latest guidance has trended a little cooler with a little more
precipitation, with appreciable snow/sleet amounts of 2-4 inches
seeming more likely along the western ridges and the Mason-Dixon
line, tapering to an inch or less south of US 50/E of the Blue
Ridge, and mainly rain for southern Maryland. Snow-to-liquid ratios
are still expected to be below climatology even in areas of all snow
due to most of the column where precipitation is developing being
above -10 C, though upper jet dynamics could compensate for this
somewhat especially over northern Maryland. A light glaze of
freezing rain also appears likely for much of the area except
northern MD (mainly snow) and extreme southern MD (plain rain).
Slightly higher amounts around a tenth of an inch are possible over
the central Shenandoah Valley where shallow cold air would be more
easily trapped. Surface ridge axis/weak wedge orients itself more or
less along I-95 so believe the metros could see a touch of freezing
rain as well (usually along this ridge axis is where lower dew
points/cooler air pools).

Latest guidance is in very good agreement on timing, with little or
no precipitation entering the CWA before noon. Clouds and
precipitation quickly increase from SW to NE between 1 and 4pm, with
the entire area seeing some sort of precipitation by 6 or 7pm.
Conditions clear just as quickly around or shortly after midnight,
perhaps lingering a few extra hours over the western slopes.
 

 

[psuhoffman]

3 hours ago, Ralph Wiggum said:

I posted over in Philly that the spread among guidance at this short of lead time is nothing short of silly quite honestly. Everything from complete misses (quite a few on the ens members) vs big ticket SECS/MECS (quite a few of those as well). Major bust potential on either side with this one.

Doesn't surprise me. I said a while ago these types of setups are super volatile and delicate so the models tend to struggle. 

There is a boundary pressing following a lead wave, and as the next wave begins to amplify it's such a delicate balance. The more ridging or return flow in front of the wave the more it can amp. And the more it amps the more it can push the boundary in front and strengthen the baroclinicity that fuels the storm. It's a feedback loop and any small error in any part of that equation can get exponential and out of control fast.  If the NWP is not strong enough with the cold press in front or the vort is just a bit weaker and the amplification process doesn't start down hill the way they think then suddenly the wave is suppressed. If they under estimate the vort or the boundary in front is slightly less suppressive then suddenly the thing over amps and adjusts north 50 miles. So these things are prone to adjustments on guidance even at the last minute. 

If it's going to go poof though today is the last chance for that imo. Once the wave begins the process of amplification along the boundary it's unlikely to fall apart. At that point a trend more amplified at the last second is more likely. Even at game time that process can cascade and catch models off guard. But if the thing doesn't trend towards a dud today that becomes the far less likely risk. 

[showmethesnow]

GEFS came in snowier (roughly 1/2 inch increase) compared to the 00Z run for from N Va to central MD. Looking at individual members has shown a good improvement on consensus as well for a snowier outcome. Now whether this is a movement by the GEFS for a colder solution is up to debate though. The off runs have tended to be the snowier runs the last couple of days compared to the 12 and 0Z. If we see the 12z come in snowier then I would tend to believe that this may be a real trend fr a colder solution. 

[showmethesnow]

32 minutes ago, psuhoffman said:

Doesn't surprise me. I said a while ago these types of setups are super volatile and delicate so the models tend to struggle. 

There is a boundary pressing following a lead wave, and as the next wave begins to amplify it's such a delicate balance. The more ridging or return flow in front of the wave the more it can amp. And the more it amps the more it can push the boundary in front and strengthen the baroclinicity that fuels the storm. It's a feedback loop and any small error in any part of that equation can get exponential and out of control fast.  If the NWP is not strong enough with the cold press in front or the vort is just a bit weaker and the amplification process doesn't start down hill the way they think then suddenly the wave is suppressed. If they under estimate the vort or the boundary in front is slightly less suppressive then suddenly the thing over amps and adjusts north 50 miles. So these things are prone to adjustments on guidance even at the last minute. 

If it's going to go poof though today is the last chance for that imo. Once the wave begins the process of amplification along the boundary it's unlikely to fall apart. At that point a trend more amplified at the last second is more likely. Even at game time that process can cascade and catch models off guard. But if the thing doesn't trend towards a dud today that becomes the far less likely risk. 

Go poof? As in a weak farther south solution? Or poof as in snow/no snow solution? 

If you are talking weak and south I tend to agree that the noon runs will probably shut the door on that idea one way or the other. Though at this point I feel pretty confident on the solution the EPS has been spitting out for awhile.

Now if you are talking snow/no snow I might disagree somewhat. Now if we see an improvement on the models (in particular the Euro) once again on temps from 850 on down (with the focus on the 925) then I tend to agree with you. At that point my confidence level will increase quite a bit that we are very close to the final solution. But if we see a status quo or even a degradation with the temps I think this will basically come down to now casting where we are looking up into the sky every hour to see what is falling. The temps are just so marginal from 850 down to the surface where just one of several factors could tip the scale one way or the other. ***Really wish I could get soundings for the Euro***

[wawarriors4]

Going skiing up at Liberty tomorrow, thinking of staying the night somewhere up in N MD/S PA (between Gettysburg and Frederick). What do yall think the best location would be for a decent little snowstorm? Gotta get out of Stafford for this one and see some actual snow.....

[mappy]

4 minutes ago, losetoa6 said:

Per Euro:

Has tonight getting into the   20s and low 20s far n+w burbs.  Tomorrow only reaching mid 30s . Most models had low 40s for Saturday a couple days  ago for many areas - probably due to earlier overcast and overall colder trends. Also it  shows dews from 10 - 15 or so  before precip onset . This should set the stage hopefully . Throw in decent precip rates and game on .

I think we are in good spots for this one. You, Highstakes and PSU better than me, of course, but overall we should come out at least 3-4" i think. 

[showmethesnow]

4 minutes ago, losetoa6 said:

Per Euro:

Has tonight getting into the   20s and low 20s far n+w burbs.  Tomorrow only reaching mid 30s . Most models had low 40s for Saturday a couple days  ago for many areas - probably due to earlier overcast and overall colder trends. Also it  shows dews from 10 - 15 or so  before precip onset . This should set the stage hopefully . Throw in decent precip rates and game on .

I am thinking you as well as the other northern tier people will do very well. If it wasn't for the fact I think Valley Forge will do better I would be kind of irked that I was taking a trip when this could possibly be my biggest event of the winter.

[Chris78]

3 minutes ago, wawarriors4 said:

Going skiing up at Liberty tomorrow, thinking of staying the night somewhere up in N MD/S PA (between Gettysburg and Frederick). What do yall think the best location would be for a decent little snowstorm? Gotta get out of Stafford for this one and see some actual snow.....

There' s a hotel right off of route 15 in Emmitsburg  Md. About 15 minutes from liberty. Should be a good location. 

Sorry for the banter.

[psuhoffman]

18 minutes ago, showmethesnow said:

Go poof? As in a weak farther south solution? Or poof as in snow/no snow solution? 

If you are talking weak and south I tend to agree that the noon runs will probably shut the door on that idea one way or the other. Though at this point I feel pretty confident on the solution the EPS has been spitting out for awhile.

Now if you are talking snow/no snow I might disagree somewhat. Now if we see an improvement on the models (in particular the Euro) once again on temps from 850 on down (with the focus on the 925) then I tend to agree with you. At that point my confidence level will increase quite a bit that we are very close to the final solution. But if we see a status quo or even a degradation with the temps I think this will basically come down to now casting where we are looking up into the sky every hour to see what is falling. The temps are just so marginal from 850 down to the surface where just one of several factors could tip the scale one way or the other. ***Really wish I could get soundings for the Euro***

Yea I meant the storm go poof in general as in weak suppressed not specifically our snow chances which could get hurt if it over amplifies also. 

[The Iceman]

mt hollys write up this morning was fantastic...may not be region specific but details discussed have implications for you guys further south...good implications

 

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.

 

[HighStakes]

22 minutes ago, mappy said:

I think we are in good spots for this one. You, Highstakes and PSU better than me, of course, but overall we should come out at least 3-4" i think. 

I agree. I felt all along this has 3-4  written all over it. 

[showmethesnow]

Quick glance but it looks as if the NAM is coming in a little warmer and wetter. 

[showmethesnow]

Snowfall map (10 to 1)shows improvement though. DC is getting in on the initial slug of moisture again and they do well. I will let you figure out what is snow or not on your own.

[LP08]

2 minutes ago, showmethesnow said:

Snowfall map (10 to 1)shows improvement though. DC is getting in on the initial slug of moisture again and they do well. I will let you figure out what is snow or not on your own.

It's the only hope we have down here in the "lowlands" as Bob has been harping on for a couple days.  Hot and heavy or its white rain and sprinkles.

[showmethesnow]

1 minute ago, LP08 said:

It's the only hope we have down here in the "lowlands" as Bob has been harping on for a couple days.  Hot and heavy or its white rain and sprinkles.

Not only does that initial slug add to the overall snow totals it also sets the stage for what comes after. Without those good rates initially to cool the column the temps will go hell for the rest of the event.

 

[WestminsterSnowCapitalMA]

looks like borderline warning event for the region this run verbatim on the NAM. Lets see how LWX reacts 

[Bob Chill]

5 minutes ago, LP08 said:

It's the only hope we have down here in the "lowlands" as Bob has been harping on for a couple days.  Hot and heavy or its white rain and sprinkles.

Maybe I'm too optimistic but I always like snow to possible mix events versus the other way around. We have a pretty tight spread now and the euro has done really well with qpf at short leads more often than not this year. Especially with snow events. It came in dry with the recent light events and pretty much nailed it. I'm feeling really good after the 0z euro. Cooled thing in the mids and surface and had fairly widespread .5 qpf. If that holds at 12z then it's pretty locked in.

The tl;dr version is I'm looking forward to my 2-3" and loseoa6/mappy/Psu may get their wsw criteria met. 

[LP08]

5 minutes ago, Bob Chill said:

Maybe I'm too optimistic but I always like snow to possible mix events versus the other way around. We have a pretty tight spread now and the euro has done really well with qpf at short leads more often than not this year. Especially with snow events. It came in dry with the recent light events and pretty much nailed it. I'm feeling really good after the 0z euro. Cooled thing in the mids and surface and had fairly widespread .5 qpf. If that holds at 12z then it's pretty locked in.

The tl;dr version is I'm looking forward to my 2-3" and loseoa6/mappy/Psu may get their wsw criteria met. 

I hope they get a WSW, would probably be a better slug for us.  It's really clear in the soundings using the 3k and see just how close it is above the surface.  Heavy precip-isothermal and white missles, lighter and warm layers show up.  Should be fun the watch it unfold!

[CAPE]

16 minutes ago, showmethesnow said:

Not only does that initial slug add to the overall snow totals it also sets the stage for what comes after. Without those good rates initially to cool the column the temps will go hell for the rest of the event.

 

Last couple runs of the 12k and 3k NAMs suggest maybe I should snow chase back towards my yard lol. Heavier precip gets in fast and stays in, and mid levels remain just cold enough. For places along and east of I-95, good rates could overcome the marginal column and result in a super wet paste bomb. If the low passes any further north or strengthens closer to the coast, those areas are definitely going to turn to rain though.

[KingJWx]

Looks like north and west burbs stay all snow on 3km NAM, rain/snow line close to DC throughout

[Bob Chill]

3k nam looks excellent all things considered. 2-3 runs in a row showing hot and heavy onset and a good pasting. I'll lock that run in no problem.  

[MD Snow]

12k and 3k backed off a bit on total precip for the event. Just something to think about for future runs. 

[MN Transplant]

3 minutes ago, Bob Chill said:

3k nam looks excellent all things considered. 2-3 runs in a row showing hot and heavy onset and a good pasting. I'll lock that run in no problem.  

The 3km NAM really shows it to be a very quick storm.  Basically 5 hours in DC.  Hard to get a lot of accumulation in that timeframe, but if the qpf is even ballpark it'll be pretty heavy stuff.

[SnowGolfBro]

I forget the exact date, but this storm reminds me of the Commutageddon setup.  A marginal setup with borderline temps.  The precip came in hot and heavy and gave most of the area a 4-6 inch paste bomb.  The frontal passage today will be important.  If the cold air is potent then we could all be in for a decent event.

[Bob Chill]

2 minutes ago, MN Transplant said:

The 3km NAM really shows it to be a very quick storm.  Basically 5 hours in DC.  Hard to get a lot of accumulation in that timeframe, but if the qpf is even ballpark it'll be pretty heavy stuff.

It is quick. I'm only interested in the heavy precip. Light stuff isn't going to do much for my yard other than look good coming down. I can envision all my accumulations happening in a 4 hour window regardless of how long the overall duration is. Sure looks like guidance is converging on a nice slug. Gfs will probably finally cave at 12z tomorrow.  Lol. 

[MN Transplant]

5 minutes ago, SnowGolfBro said:

I forget the exact date, but this storm reminds me of the Commutageddon setup.  A marginal setup with borderline temps.  The precip came in hot and heavy and gave most of the area a 4-6 inch paste bomb.  The frontal passage today will be important.  If the cold air is potent then we could all be in for a decent event.

Commutageddon (Jan 2011), which I missed and am still salty about, had an incredible upper-air signature.  Great 700 VVs and hence the thundersnow.  This doesn't really have that.  Someone mentioned 3/25/13 before, and that type of paste job is our best scenario.

[high risk]

1 minute ago, MN Transplant said:

Commutageddon (Jan 2011), which I missed and am still salty about, had an incredible upper-air signature.  Great 700 VVs and hence the thundersnow.  This doesn't really have that.  Someone mentioned 3/25/13 before, and that type of paste job is our best scenario.

    Yep, other than marginal temps, there really is no comparison.     That was a rain turning to snow event with an incredibly dynamic setup.

    I really like the Ferrier accumulation NAM3 map.    Shows it struggling to accumulate along Rt 50 with a stripe of heavier amounts across northern and north-central MD.

 

[RodneyS]

3 minutes ago, high risk said:

    Yep, other than marginal temps, there really is no comparison.     That was a rain turning to snow event with an incredibly dynamic setup.

    I really like the Ferrier accumulation NAM3 map.    Shows it struggling to accumulate along Rt 50 with a stripe of heavier amounts across northern and north-central MD.

 

Commutageddon was Wednesday afternoon and evening, January 26, 2011, and featured 1.52 inches of precipitation at DCA and 1.31 inches at IAD.  Nothing like that is being forecast for Saturday's storm in the DC area.