December Med/Long Range Discussion Part 2

[psuhoffman]

25 minutes ago, eurojosh said:

Further sig run to run differences on gfs - really holding the lp back this run, with the center over NV vs WY in the 18z at 84 hrs

That is a double edged sword though, holding back the energy could lead to weaker waves and a south solution, but IF, as this run does both waves still manage to cut west holding back the energy simply weakens the frontrunner and thus eliminates our "thump" on the front end.  If its going to cut we would be better of with a stronger faster ejection of energy.  Still a lot of time for this to be resolved. 

[Amped]

13 minutes ago, WxUSAF said:

Looks weird, but GFS has a bullseye of precip over us in the 3 hour period between 12-15z on Saturday and it falls as snow.  Don't really buy it as it seems the whole system is dry up until that point and then it snatches victory from the jaws of defeat.  

 5" in 3 hrs before the changeover is typical SNE thump. Hard to get down here.

[WxUSAF]

Nice little event next Tuesday/Wednesday, but iffy lower-level temps between 950-850mb.  Maybe a couple inches for spots N of DC.  

[Bob Chill]

If we fail Saturday at least the gfs give us another chance to fail shortly after. 

[yoda]

GGEM is fine with me

[ErinInTheSky]

I'm new around here - how do these front end thumps usually work? Get some snow and then it transitions to freezing rain/rain, I'm guessing that quickly washes the snow away?

[psuhoffman]

17 minutes ago, WxUSAF said:

Looks weird, but GFS has a bullseye of precip over us in the 3 hour period between 12-15z on Saturday and it falls as snow.  Don't really buy it as it seems the whole system is dry up until that point and then it snatches victory from the jaws of defeat.  

I am not saying its right, but the GFS has done that a few runs in a row because of where it has the deeper cold air.  If you look at the thermal profile the southerly flow ahead of the system doesn't really hit much resistance from deep enough cold until it hits our area.  Then of course suddenly there is lift produced by the WAA over the cold and it creates the heavy burst.  I can see why its happening, but depending on the model to accurately predict exactly where that zone is going to be 5 days out is kinda foolish.  The euro has it to, to some extent, but had it being more to our northeast in eastern PA the last couple runs.  Problem is it will be a relatively narrow area that gets it.  As is typical in these types of things.  Think feb 2015.  Yea we loved it but it wasnt much south and north of here.  Same with Feb last year, south of DC it was great, I barely got an inch up here.  Where the WAA hits the cold resistance there is a burst of snow then once the cold caves the warm rushes north and there isnt really that same effect north of where it initially sets up.  A relatively small area gets a thump and everywhere else its not that significant an event.  Luckily there is some history to that thump being in our general area, historically we actually do OK in this kind of setup.  Ok relative to the overall crappy nature of this setup, we really shouldnt expect anything form a low cutting into Michigan, yet we sometimes score a surprise.  I remember a cutter in dec 2003 dropping a quick 5" on northern VA from such a WAA thump surprise. 

[Bob Chill]

1 minute ago, supernovasky said:

I'm new around here - how do these front end thumps usually work? Get some snow and then it transitions to freezing rain/rain, I'm guessing that quickly washes the snow away?

Depends. This particular event would go that way. But another normal way is when we have a real cad setup where temps remain near freezing after precip shuts off and the below freezing after frontal passage so everything turns to concrete. 

[Bob Chill]

18z para was another nice hit and more believable with snowfall. Really ramps up the WWA precip in advance and comes in solid before ice takes over 

[yoda]

18z para GFS looks decent... 4-6" it would appear... 00z GGEM is around 3"

[psuhoffman]

7 minutes ago, supernovasky said:

I'm new around here - how do these front end thumps usually work? Get some snow and then it transitions to freezing rain/rain, I'm guessing that quickly washes the snow away?

depends on the setup... in a situation like this where the low is cutting well northwest usually its a bit of snow and ice to rain and it washes away.  Sometimes we can get a surprise but honestly we hope more then it actually happens if the low actually cuts up into the lakes.  What is more often a "win" around here is if the cold resists enough to force the system to be weaker and have enough surface low reflection to reform south along the trough axis to prevent a strong low cutting up to our west.  Similar to Feb 2015.  We can do well in that setup.  The best setup is if a low cuts a little to our west, say into KY or southern OH, but with a nice arctic high over new england, then the storm is forced to transfer to the coast.  Models will often forecast snow to rain but in the end we get a 4-8" thump then dryslot and end as drizzle.  Of course our real "wins" come from lows up the coast to our east, but we can do well in a west track if there is a high to our north and the storm doesn't cut too far west.  This is very tenuous, high is kinda moving out too fast and there is a bit too much ridging up the coast allowing the low to cut a bit much.  Root for something like the UK shows with a weaker wave staying at our latitude or below it.  We dont need a strong low in this situation the precip will come from WAA over the arctic air, not dynamics, so a strong storm is unnecessary.  The PDII blizzard for instance, was a WAA overrunning system and it was a weak strung out mess of a surface storm but we got 20" from it. 

[yoda]

1 minute ago, Bob Chill said:

18z para was another nice hit and more believable with snowfall. Really ramps up the WWA precip in advance and comes in solid before ice takes over 

Looked just short of warning criteria snow-wise

[psuhoffman]

15 minutes ago, Bob Chill said:

If we fail Saturday at least the gfs give us another chance to fail shortly after. 

18z GEFS was really hot and heavy on next week as a window of opportunity.  They couldn't agree on exactly which wave would do it but in general they threw waves up the coast along the boundary all week most clipping us with at least one of them. Problem is no single one seemed high probability and it seems over the years when we have lots of low prob windows, the ensembles will give a false good signal by having one or two members hitting on each opportunities, but in reality each is likely to fail on its own. 

[yoda]

[Thanatos_I_Am]

Don't forget ground will be frozen leading up to the event. Any snow that falls will stick instantly! Hoping for a nice wintry scene.

[psuhoffman]

I know a few have discussed the disconnect between the temperatures and the H5 means on the long range ensembles and I think I discovered the disconnect.  Looking at the last few op runs of the GFS I suspect the means are giving a false impression of what the period may actually be like.  The first issue is that north America will be flooded with cold air when this +epo +nao period starts.  That means for a while the cold may well be able to push and encroach further into the area of h5 ridging then you would normally expect.  Also, the op runs seem to imply storms will be cutting across into the area of general ridging in the east during this period.  If you look at the links below, you can see that overall the heights are high along the east coast if you take an average of the entire period, but twice storms are able to cut into the ridging and end up in a place that puts us in the game.  however, due to timing differences at this range, any ensemble mean is simply going to show ridging in our area and not indicate the storm that cuts through for a day since the ridging is in place 70% of the time during the 10 day period.  It is a much more fluid and volatile pattern then the means suggest.  Now the longer we stay in such a pattern the worse it will get.  The cold will relax and once it does it could get ugly.  But the pattern may not be stable and lock in for long so if we can hold off the torch for a week we may not have to suffer long before things reshuffle.  Just wearing my rose glasses tonight. 

 

[psuhoffman]

GEFS evolving towards something less awful in the long range actually.  heights building in NAO domain.  Ridging becoming a weaker signal in the east.  Much less hostile then it was 24 hours ago heading towards New Years.  Not a great look as is, but something that is workable and a really easy transition to a good pattern from there.  Roll it forward and its moving towards blocking with a trough in the east. 

[Heisy]

Im actually starting to get more interested in this follow up wave that is just starting to show up on the data. The Day 5 low heads into the Lakes (the one we're focused on right now)....The cold front clears, but the models across the board starting to show energy being left behind in the Southwest that heads east. Tonight's GFS actually had 3-6" type snows in N VA/ SE PA from this wave. The EURO has it as well. 

[showmethesnow]

00Z Euro is further separating the WAA  mixed bag thump from the subsequent cold front associated precip with a 1/2 day + lull. Snowfall map shows roughly 1/2" to 1 inch snowfall area wide. Afterwards the Euro remains unsettled with bringing several pulses up from the gulf possibly bringing further opportunities through the remaining 10 day period.  Though at this point it only shows a minimal increase on snowfall.

00Z EPS is more bullish on the Saturday event and has ticked up on the snowfall means. Roughly an 1/2"  increase area wide to where we see 2" bordering DC and up to 3" in Northeast MD. For the remainder of the 10 day period we see roughly an inch added to the totals area wide.

 

[midatlanticweather]

6z was very unimpressive with everything. 

[Wxdavis5784]

2 minutes ago, midatlanticweather said:

6z was very unimpressive with everything. 

I agree.... 

[AmericanWxFreak]

34 minutes ago, midatlanticweather said:

6z was very unimpressive with everything. 

Not what I wanted to wake up to :/

[mappy]

meh, GFS isn't the worst. I still get some snow 

[Wxdavis5784]

2 minutes ago, mappy said:

meh, GFS isn't the worst. I still get some snow 

Mappy,

For now. 6z was a trend in the wrong direction, im certainly interested in the 12z runs to see if they wobble back.

[mappy]

Just now, wdavis5784 said:

Mappy,

For now. 6z was a trend in the wrong direction, im certainly interested in the 12z runs to see if they wobble back.

I'm aware. I did look at the model. However -- I still get snow. Which was my point. 

[dallen7908]

Euro has 850 temperatures at DCA above freezing with a surface temperature of 31 by 12 UT Saturday with only 0.06" of precip by that time.  

it also shows shorts for Sunday morning (upper 60s) with temperatures plummeting later in the morning into the afternoon. 

 

UMCP has final exams on Saturday. 

[Wxdavis5784]

Just now, mappy said:

I'm aware. I did look at the model. However -- I still get snow. Which was my point. 

I got your point. And my point was to say if the trend continues, you wont.

[mappy]

Just now, wdavis5784 said:

I got your point. And my point was to say if the trend continues, you wont.

Again. Meh. The models have been fluctuating every 6 hours, and again, with this pattern, even 3+ days out it will be hard to nail anything down. I'm not concerned, which is why I can brush this run off without being "worried about a trend". 

[Wxdavis5784]

1 minute ago, mappy said:

Again. Meh. The models have been fluctuating every 6 hours, and again, with this pattern, even 3+ days out it will be hard to nail anything down. I'm not concerned, which is why I can brush this run off without being "worried about a trend". 

Fair enough.

[pasnownut]

1 minute ago, wdavis5784 said:

I got your point. And my point was to say if the trend continues, you wont.

One run is not a trend.  Its a bad run.  The only trends right now are the volatility meter being off the charts.

Several solutions left until we know in this butt ugly pattern.  Still better than last year....so far.  That may change, but I'm not closing any blinds yet.

Nut