March 20-21 Potential - STORM MODE THREAD

[RDM]

17 minutes ago, Bob Chill said:

Check out these temps...snowing at 0z and continuing overnight with sub freezing surface. Can anyone tell I'm STOKED?

What about the warm nose aloft ivo 850 we saw on the soundings a couple of hours ago?  Did that get pushed south or was that for daytime Tues local? Am hoping the whole column stays below 0C to support sn start to end.  If not throughout, at least overnight Mon into Tues am.  If the rates on Tues during daylight can sustain at least sn- w/o it turning to drizzle until the second wave arrives, all the better.  Even sn- would help offset the daytime loses Tues.

[cae]

We're just getting into range of the RGEM ensemble, but here are some maps through 72 hours.  The first is from 24-72 hours, and the probability maps (the next two) are only from 48-72 hours.  I can only generate those for 24-hour blocks of time.

There is very likely more to come.  The GEPS says we're only about 1/2 done after 72 hours.  FWIW, the 12z GEPS backed off a little compared the 00z imby, but not much. 

 

[wkd]

17 minutes ago, clskinsfan said:

Yes. It is rare to see the Euro that juiced up. It is actually in line with the NAM as far as total QPF goes. 

Maybe we can bring back the old EE rule.

[BristowWx]

1 minute ago, RDM said:

What about the warm nose aloft ivo 850 we saw on the soundings a couple of hours ago?  Did that get pushed south or was that for daytime Tues local? Am hoping the whole column stays below 0C to support sn start to end.  If not throughout, at least overnight Mon into Tues am.  If the rates on Tues during daylight can sustain at least sn- w/o it turning to drizzle until the second wave arrives, all the better.  Even sn- would help offset the daytime loses Tues.

I assume DC loses the 850s at some point or do they hold on the Euro?  Trying to figure how much is lost to rain and how close to DC that 850 warm nose is?  

[Climate175]

Accuweather has me getting a coating to an inch through Monday night to Wed, and The Weather Channel has me getting 1-3 inches during that period as well lol.

[clskinsfan]

2 minutes ago, BristowWx said:

I assume DC loses the 850s at some point or do they hold on the Euro?  Trying to figure how much is lost to rain and how close to DC that 850 warm nose is?  

Just push the forward arrow. 

https://weather.us/model-charts/euro/2018031812/virginia/temperature-850hpa/20180319-1800z.html

[gymengineer]

13 minutes ago, RDM said:

What about the warm nose aloft ivo 850 we saw on the soundings a couple of hours ago?  Did that get pushed south or was that for daytime Tues local? Am hoping the whole column stays below 0C to support sn start to end.  If not throughout, at least overnight Mon into Tues am.  If the rates on Tues during daylight can sustain at least sn- w/o it turning to drizzle until the second wave arrives, all the better.  Even sn- would help offset the daytime loses Tues.

For DC and immediate suburbs, we start as rain and don't change to snow until around sunrise at best. So, I wouldn't be worrying about trying to hold onto snow during the daytime hours of Tuesday. I think it's best to assume snow is not accumulating during the day in that period. Again, the focus for the lower elevations now is from late afternoon Tuesday into Wednesday. 

[nj2va]

1 minute ago, BristowWx said:

I assume DC loses the 850s at some point or do they hold on the Euro?  Trying to figure how much is lost to rain and how close to DC that 850 warm nose is?  

DC 850s don’t drop below 0 until Wed 00z.  Basically anyone N/W of a line from western Loudoun to Baltimore city and on NE from there is below 0 at 850 the whole time.  Closer in burbs between DC and western Loudoun are 0 to +1 but drop to -1 by Wed 00z.  

[blue sky]

14 minutes ago, BaltimoreWxGuy said:

At least we have DTs first guess map on our side!

I am an old poster...love to hear all opinions.  So hang in there. Stormtracker may seem tough...But he wants the snow! This incarnation of wright brothers( weather forum) is has it always has been....Don't piss on an upcoming storm.  lol

I am in Montco county Pa.   I like the trends.

[McQuackleton]

 

 

[BristowWx]

2 minutes ago, gymengineer said:

For DC and immediate suburbs, we start as rain and don't change to snow around sunrise at best. So, I wouldn't be worrying about trying to hold onto snow during the daytime hours of Tuesday. I think it's best to assume snow is not accumulating during the day in that period. Again, the focus for the lower elevations now is from late afternoon Tuesday into Wednesday. 

Thank you.  

[BristowWx]

2 minutes ago, nj2va said:

DC 850s don’t drop below 0 until Wed 00z.  Basically anyone N/W of a line from western Loudoun to Baltimore city and on NE from there is below 0 at 850 the whole time.  Closer in burbs between DC and western Loudoun are 0 to +1 but drop to -1 by Wed 00z.  

And thank you sir.  Will hope for the best.  

[H2O]

1 minute ago, nj2va said:

DC 850s don’t drop below 0 until Wed 00z.  Basically anyone N/W of a line from western Loudoun to Baltimore city and on NE from there is below 0 at 850 the whole time.  Closer in burbs between DC and western Loudoun are 0 to +1 but drop to -1 by Wed 00z.  

Sadly this is the concern I've had all along when people keep asking for a N trend.  Dec 5th 2009 seems like an analog right now as places S&E of DC just couldn't crack good temps and it ended up mostly as white rain.  This will be another elevation dependent storm.  17 years at my current location and I know what a storm like this will ultimately end up doing unless CCBs and deform bands set up overhead.

 

That doesn't happen very often.  

 

 

[EastCoast NPZ]

24 minutes ago, AcePuppy said:

https://www.washingtonpost.com/news/capital-weather-gang/wp/2018/03/18/two-waves-of-wintry-weather-possible-in-d-c-area-this-week-with-some-snow-accumulation-possible/

Wow, talk about a wet blanket.  But probably very prudent to heed such caution.

[Bob Chill]

28 minutes ago, csnavywx said:

Has the same thermal issues as the NAM with wave 1 (no surprise there with that LLJ/WCB w/o a closed low aloft). A lot of that QPF, especially around DC, is rain, sleet or even freezing rain/and freezing drizzle. However wave 2 structurally looks better.

Absolutely. That's one of the reasons I don't like posting snow maps and stick to QPF panels. The 1.4" or whatever in my yard is absolutely not all snow. Rain to start and then non-accum for a while while the surface cools. Impossible to know exactly how it will go down. Way too many variables. Going off the euro run I would rain then mix but should get into decent rates Tuesday during that day that will overcome wet/warmth. Then as we lose the sun and (hopefully) drop below freezing the landscape will change fairly quickly. I would say that 4" would probably be a good number in the north side of the beltway burbs when it's all said and done if it goes down exactly like the euro showed. Yes, I'm excited with the chance at getting 4" of snow. That sounds pretty good. 

Wave 2 is very much a wildcard. Very close to CCB/deform through the region and the trend has been moving that way. If it all broke right then I could see 6"+ even in the cities. At least another 24 hours before figuring out those details. 

The sweet spot is the obvious spots. I already told PSU that I could easily get more precip and he could easily get more snow. The euro did exactly that. I'm fine with those details. I'm very aware of our micro-climos through the region. All in all the euro was a very good run and was close to an excellent one and epic is within the range of possibilities. 

Half the fun for me is watching snow fall. Even if it doesn't stick well, heavy rates are a blast. I'm looking forward to this one. An epic fail is becoming less and less likely for all of us until you get pretty far south and east. 

[snowmagnet]

14 minutes ago, AcePuppy said:

 

 

They are being very conservative, along with the NWS.  I prefer the discussions in here better.  

 

[RDM]

13 minutes ago, H2O said:

Sadly this is the concern I've had all along when people keep asking for a N trend.  Dec 5th 2009 seems like an analog right now as places S&E of DC just couldn't crack good temps and it ended up mostly as white rain.  This will be another elevation dependent storm.  17 years at my current location and I know what a storm like this will ultimately end up doing unless CCBs and deform bands set up overhead.

 

That doesn't happen very often.  

 

 

Echo your thoughts.  Lived here since 85 and the mention of a warm nose earlier this am on the sounding running through DC caught my eye.  Whenever we see/hear about an intrusion at mid-levels, it's often not a good thing.   More often than not that nose ends up being worse than anticipated unless a deform band cools the column and pushes it out.  Not being DD here, just realistic. 

As sharp as the cutoff may be to the north, mixing may cut down on ratios down here IVO of 66 and south.  Hopefully we can get a deform to setup in a favorable location.  I'm just far enough NW to be largely outside the UHI effects of Tyson's and inside the beltway.  What we get typically mirrors IAD.  Just rather not be in a position of having to thread the needle for once.  Not expecting anything like Nrn MOCO and the Mason Dixion.  Just rather have white rain than drizzle any day.

[SomeguyfromTakomaPark]

1 minute ago, snowmagnet said:

They are being very conservative, along with the NWS.  I prefer the discussions in here better.  

 

I don’t think this is overly conservative for wave 1...gonna be a lot of rain/mix/white rain Monday night and Tuesday inside the beltway. 

[Amped]

DT is excited. 

 

[nj2va]

10 minutes ago, H2O said:

Sadly this is the concern I've had all along when people keep asking for a N trend.  Dec 5th 2009 seems like an analog right now as places S&E of DC just couldn't crack good temps and it ended up mostly as white rain.  This will be another elevation dependent storm.  17 years at my current location and I know what a storm like this will ultimately end up doing unless CCBs and deform bands set up overhead.

 

That doesn't happen very often.  

 

 

Yeah as things stand now, if anyone DC/south thinks they’re going to accumulate during the day on Tuesday, then you’re probably setting yourself up for failure.  

This could be a storm where I have 2” on my grass/mulch/grill cover while NW Arlington (300’ elevation) has 4-5” after all is said and done.  The key for us will be to get rates especially in the evening Tuesday through the overnight - would love CCB to center over the 95 corridor.  Tracking is half the fun for me so at least this is making the delayed spring somewhat enjoyable from a tracking perspective.  

[Bob Chill]

6 minutes ago, RDM said:

Echo your thoughts.  Lived here since 85 and the mention of a warm nose earlier this am on the sounding running through DC caught my eye.  Whenever we see/hear about an intrusion at mid-levels, it's often not a good thing.   More often than not that nose ends up being worse than anticipated unless a deform band cools the column and pushes it out.  Not being DD here, just realistic. 

As sharp as the cutoff may be to the north, mixing may cut down on ratios down here VIO of 66 and south.  Hopefully we can get a deform to setup in a favorable location.  I'm just far enough NW to be largely outside the UHI effects of Tyson's and inside the beltway.  What we get typically mirrors IAD.  Just rather not be in a position of having to thread the needle for once.  Not expecting anything like Nrn MOCO and the Mason Dixion.  Just rather have white rain than drizzle any day.

Keep in mind that not all warm noses are created equal. The losing ones are in a progressive pattern with a retreating high. This one actually has a 1030 just north of lake superior pressing down during onset so there is resistance instead of mid level flow overwhelming. The warm nose (and surface) is no doubt an issue but in this case it starts off as a problem and then loses to the force of HP to the north. Once things flip to snow it should stay that way no problem. More often than not a warm nose ruins an ongoing event. The only reason we're starting off bad is because it's late march. If this was 4 weeks ago it would be 100% snow without a question. 

[csnavywx]

6 minutes ago, WxWatcher007 said:

Just want to echo what Bob said earlier. I don't post much winter wx analysis (summer/tropical is more my thing) but you and some of the others here are just great. It's nice to just sit back and learn things. 

What specifically do you think is the most important thing folks in the cities should be looking for on the guidance in the next 24 hours? Is it a quicker closing off of the low aloft or some other feature?

Well, thermals are the number one concern with the first wave. Saturation aloft becomes an issue later but where and how strong that warm nose aloft is vs. where the strongest lift is will determine who gets snow vs. a lot of sleet/rain/freezing rain (and freezing drizzle). The first wave will also have access to a warm conveyor belt that is entraining unstable Gulf air into it, so convection is also a possibility (or an issue, depending on where it sets up).

For the second wave, thermals are drastically better, so the top concerns are speed, tilt and spacing with the first wave (you generally want less spacing). For snow, you'd want more negative tilt and a bit better consolidation of the vorticity field aloft. Getting that to close off at 500/700 faster wouldn't hurt either as you'll need some help pulling in moisture.

[87storms]

looks like sometime mid afternoon tuesday is when temps really start to crash in our favor.   the only thing i noticed when running the loops on the euro is that front end heavier stuff falls when temps are borderline.  however, once temps crash, it looks like we stay light/steady for the entire night thru the morning.  that's the main difference i see between the last 2-3 runs of the euro.  the last run was much drier post-temp crash.  we're clearly more impacted by the upper level energy now, so the next step would be to get another shift or two west of that coastal.  based off of all those panels i'd say 2-4"+ for dc and more further north/northeast would be a safe bet (rough estimate).

[RDM]

8 minutes ago, Bob Chill said:

Keep in mind that not all warm noses are created equal. The losing ones are in a progressive pattern with a retreating high. This one actually has a 1030 just north of lake superior pressing down during onset so there is resistance instead of mid level flow overwhelming. The warm nose (and surface) is no doubt an issue but in this case it starts off as a problem and then loses to the force of HP to the north. Once things flip to snow it should stay that way no problem. More often than not a warm nose ruins an ongoing event. The only reason we're starting off bad is because it's late march. If this was 4 weeks ago it would be 100% snow without a question. 

Thanks Bob/csnavy - appreciate the insight and explanations.  Something to remember for the future.

7 minutes ago, csnavywx said:

Well, thermals are the number one concern with the first wave. Saturation aloft becomes an issue later but where and how strong that warm nose aloft is vs. where the strongest lift is will determine who gets snow vs. a lot of sleet/rain/freezing rain (and freezing drizzle). The first wave will also have access to a warm conveyor belt that is entraining unstable Gulf air into it, so convection is also a possibility (or an issue, depending on where it sets up).

For the second wave, thermals are drastically better, so the top concerns are speed, tilt and spacing with the first wave (you generally want less spacing). For snow, you'd want more negative tilt and a bit better consolidation of the vorticity field aloft. Getting that to close off at 500/700 faster wouldn't hurt either as you'll need some help pulling in moisture.

 

[snowmagnet]

12 minutes ago, Amped said:

DT is excited. 

 

I'm not sure he is excited... his first guess is very different than what the new models are showing.  His first guess map was based on southern VA getting hit hard again with the second wave and Northern VA and MD with the first.  

[tstate21]

Sterling isn't buying into the snowier Euro solution - leaning towards the GFS. 

Through the period of Monday night through Tuesday night, a low
pressure system will reach the Appalachian Front and transfer
its energy to the East Coast to form the coastal low that is
expected to intensify as it moves to the northeast. Still, there
are variations in the timing of the formation of this coastal
low, the track of this low, and the precipitation type.

The NAM, GFS and European model do not agree on a lot of these
mentioned factors prior to 18z Tuesday. The NAM during the past
couple model runs has been flipping back and forth with
significant amounts of snow to a small amount of a mix of rain
and snow after some rain. The GFS has been consistent with snow
amounts across the region with an average of 2 to 4 inches of
snow after a period of rain. The latest European model should be
used with a little caution, considering it is showing most areas
receiving several inches of snow Tuesday into Tuesday night. A
couple of days ago, it was revealing the same scenario, but the
last model run or two, it backed off on the amounts. Lately, and
possibly to this minute, our forecast has been a blend of the
GFS and European model with a lean toward the GFS model.

Where the three models tend to agree is around the 18z time of
Tuesday. All three models have the newly-formed coastal low on
Tuesday about 50 miles to the east of Norfolk, Virginia with a
trailing trough of low pressure to the southwest then northwest
into southwest Virginia. At least with this position, we have a
potential of seeing several inches of snow, especially north and
west of the I-95 corridor.

As the coastal low passes by to our east then northeast later
Tuesday morning and Tuesday afternoon, colder air will get
drawn in from the north. The colder air will move into place
shortly ahead of the next shortwave that will be on the heels of
the first coastal low. A lull in the precipitation is most
likely later Tuesday in between the two lows.

Precipitation will fill in as the second coastal low develops
Tuesday night. Guidance still diverges on how strong the low
will be and consequently how much precipitation fills in. It
does appears that the best chance for precipitation will be
across the west and south...closer to the track of the low.
Thermal profiles will be colder due to northerly winds and this
will cause the p-type to be snow for most areas. Accumulating
snow is possible.

[poolz1]

EPS looking sweet...Lots of very nice hits and jump up in the mean from 00z

[showmethesnow]

Looking over the 500's (trough/energy) on the Euro run leading into our possible coastal and I think I will reserve my judgment on how I feel about it. Saw some positives, saw some negatives at least I think I did. The setup is so convoluted it is very difficult to play through my mind the impact of any changes we do see.

But I did want to point out one thing. We are seeing the confluence breaking down quicker to our NE compared to the 00z. At this point it is a little too late to benefit our region as the low begins responding meaningful to this break down of the blocking to our NE. But if we can see that breakdown occur 8-12 hours sooner it could have a very meaningful impact as it would allow an adjustment of the track more northerly (vs. NEasterly) closer into the coast through our region. Needless to say this would also mean less separation between the surface low and the upper level support allowing for a quicker capture of the low hopefully in a more favorable location for the DC/Balt region.

[BornAgain13]

4 minutes ago, poolz1 said:

EPS looking sweet...Lots of very nice hits and jump up in the mean from 00z

Hey guys, from the Southeast forum here! Looks like yall have a legitimate shot at this one... how does the EPS Mean look for southern VA?

[csnavywx]

5 minutes ago, Bob Chill said:

Keep in mind that not all warm noses are created equal. The losing ones are in a progressive pattern with a retreating high. This one actually has a 1030 just north of lake superior pressing down during onset so there is resistance instead of mid level flow overwhelming. The warm nose (and surface) is no doubt an issue but in this case it start off as a problem and then loses to the force of HP to the north. Once things flip to snow it should stay that way no problem. More often than not a warm nose ruins an ongoing event. The only reason we're starting off bad is because it's late march. If this was 4 weeks ago it would be 100% snow without a question. 

The rather stout 925mb CAA that arrives ahead and during the start of the event is kind of why I'm leaning towards sleet and/or ice. Typically speaking, modeling has more trouble with shallow cold layers and underestimating the strength of elevated warm layers during strong advection. In this case, adjusting the strength of the frontal slope/inversion upwards probably isn't a bad call. That'll result in more sleet and ice and less rain and snow. The fact that both the EC and 3km NAM are strongly suggesting a non-diurnal surface temperature trend during the day Tuesday is also strong hint, especially in late March.

It's a darn good thing that tomorrow is going to get into the 50s. 2-inch soil temps are running 38-40F, so with tomorrow's temps, we may just get enough space to prevent a major issue.