February 19-20th Threat - STORM MODE

[BaltimoreWxGuy]

2 minutes ago, Fozz said:

How good are the WRF models (ARW and NMM)?

The 0z runs all show a good hit for MD.

Maybe someone can correct if I’m wrong but I think they’re usually too amped and wet. 

[MillvilleWx]

Maybe someone can correct if I’m wrong but I think they’re usually too amped and wet. 

ARW has a known wet bias and NMM actually can run dry. They are used in ensemble packages and are better utilized for convective purposes.


.

[high risk]

34 minutes ago, psuhoffman said:

It's really hard to use the GFS in these situations because its lack of resolution really forces you to assume a lot about the details.  But the GFS blasts our area with some heavy precip between 11am and 3pm.  At 18z the column is still cold enough for snow across northern MD...barely.  By 0z its toast.  But how long it can hold on with mixing of the warm layer with those heavy rates would determine our fate.  If we can hold on an extra hour or two during that band (not a crazy idea given the typical mixing and dynamic cooling in such bands) the GFS implies a really good thump up here.  

 

          we CAN see the in-between hours for the GFS on the mag.ncep.noaa.gov site which has the full hourly output.    You'll see that the changeover is well before 00z, but as has been noted, the GFS is well-known for being way too fast in breaking down inversions and warming the low levels

[Snowchaser]

Weather channel is bullish 

[SnowGoose69]

Looks like UKMET didn’t come in today or is delayed.  At least on the meteocentre site 

[yoda]

12z HRDPS is crushing DC metro at 12z WED with 8mm/hr

[MN Transplant]

3 minutes ago, yoda said:

12z HRDPS is crushing DC metro at 12z WED with 8mm/hr

3”/hr.  Totally checks out.

[BaltimoreWxGuy]

LWX updated their snow maps. Doesn’t look to be much of a change. If I get 5” I’ll be very happy 

[SnowGolfBro]

10 minutes ago, yoda said:

12z HRDPS is crushing DC metro at 12z WED with 8mm/hr

4mm/hr would be a crushing. 8mm/hr would be epic 

[notvirga!]

Just now, BaltimoreWxGuy said:

LWX updated their snow maps. Doesn’t look to be much of a change. If I get 5” I’ll be very happy 

They went from 4-6 to 6-8 in my area and moved the heavier snow north 

[yoda]

12z HRDPS 0.35 to 0.40 QPF all snow for DCA through 14z WED

[Scraff]

11 minutes ago, yoda said:

12z HRDPS is crushing DC metro at 12z WED with 8mm/hr

Well it’s definitely been consistent with the beat downs on the last few runs. Hope it’s right!

[yoda]

12z HRPDS brings a "squall line" I guess through 18z to 21z... I95 corridor and to the N and W are still below freezing at 22z

[SomeguyfromTakomaPark]

8 minutes ago, yoda said:

12z HRPDS brings a "squall line" I guess through 18z to 21z... I95 corridor and to the N and W are still below freezing at 22z

It’s still a beatdown in DC metro.  6+ for the whole area.  I hope this time tomorrow we’re singing “oh Canada”. 

[winterymix]

1 hour ago, psuhoffman said:

It's really hard to use the GFS in these situations because its lack of resolution really forces you to assume a lot about the details.  But the GFS blasts our area with some heavy precip between 11am and 3pm.  At 18z the column is still cold enough for snow across northern MD...barely.  By 0z its toast.  But how long it can hold on with mixing of the warm layer with those heavy rates would determine our fate.  If we can hold on an extra hour or two during that band (not a crazy idea given the typical mixing and dynamic cooling in such bands) the GFS implies a really good thump up here.  

@HighStakes

It totally depends on the banding.  Think of the similar events to this...Feb 2007 (NOT the VD storm the second one), December 2013, Feb 2015 had some similarities too... the area's that get under the heavy bands will hold the column longer.  The VV's and heavy precip will help to mix out the mid level warm layer from WAA for a time.  If we get under that banding we will get thumped.  If we don't...the mid level warmth will race north and its congrats PA.  We know the drill.  I have no idea where that banding will set up.  No one does.  We can all make educated guesses.   But the idea of a duel max is gaining some traction imo today.  Even the guidance that hits our area pretty good "sees" the banding associated with the jet streak up over PA its just not killing the STJ WAA moisture plume into our area as much and is hitting that band up there less.  Figuring out those kind of details are above my pay grade though.  

So my goalposts from 2 days ago are still in the same place LOL...

Notice even the guidance that thumps us still has some enhancement up in central PA associated with the jet streak?  Its just the NAM is going nuts with that and killing the WAA/STJ moisture feed south of it.  The other guidance has more of a duel max idea hinted at between those two areas.  That is a much better result for us.  

Good and detailed analysis.   Personally, I'm taking the prerogative of using the model that gives me the most snow in my backyard.  For now, with my limited analysis, that shall be the GFS.  The dominant precipitation type gives mby snow from hour 24 to hour 33.  The QPF is about 0.7... with heavy wet snow and ratio of 8:1 (YAG) I'm hoping for 5" to 6".

[Interstate]

31 minutes ago, yoda said:

12z HRDPS is crushing DC metro at 12z WED with 8mm/hr

What is the verification score on the HRDPS?

[snowdude]

Interesting observation from Mount Holly. Maybe models underdoing the initial banding lifting north, especially eastern edge? Or maybe it means nothing.

 

...930 AM Update: No changes made yet to the forecast for this
period, as we are waiting to see more of the 12Z guidance.
However, it is interesting to note that the current
precipitation shield extends further east (across the Carolinas)
than what the models had depicted. I am not sure this will
result in any significant changes for our area as models already
had the precip extending across our region by late tomorrow. We
will have a complete update on this system with the 4 PM update.

[yoda]

1 minute ago, snowdude said:

Interesting observation from Mount Holly. Maybe models underdoing the initial banding lifting north, especially eastern edge? Or maybe it means nothing.

 

...930 AM Update: No changes made yet to the forecast for this
period, as we are waiting to see more of the 12Z guidance.
However, it is interesting to note that the current
precipitation shield extends further east (across the Carolinas)
than what the models had depicted. I am not sure this will
result in any significant changes for our area as models already
had the precip extending across our region by late tomorrow. We
will have a complete update on this system with the 4 PM update.

Would this mean an earlier start or heavier precip at the start due to increased banding?  If it meant something?

[WEATHER53]

4 minutes ago, snowdude said:

Interesting observation from Mount Holly. Maybe models underdoing the initial banding lifting north, especially eastern edge? Or maybe it means nothing.

 

...930 AM Update: No changes made yet to the forecast for this
period, as we are waiting to see more of the 12Z guidance.
However, it is interesting to note that the current
precipitation shield extends further east (across the Carolinas)
than what the models had depicted. I am not sure this will
result in any significant changes for our area as models already
had the precip extending across our region by late tomorrow. We
will have a complete update on this system with the 4 PM update.

Yes there is a decided eastern move but looks like lifting north is starting. 1040 still west of us and that’s a good sign for cold not substantially being east of us come crunch time and then see what effect it has on changeover 

[Snowchaser]

Updated Maps!

[snowdude]

3 minutes ago, yoda said:

Would this mean an earlier start or heavier precip at the start due to increased banding?  If it meant something?

I believe they’re hinting at an earlier start. But I can also see a more organized system meaning more precip. But again we’ll see. 

[Eskimo Joe]

As of 1pm, the cirrus function on GOES-16 shows a thicker cloud deck streaming into the area from the west...our EOC wx station shows the solar energy dropping off from 300 watts at 11am to just 40 now.  That should really cut down on temperatures across the area for the rest of the day.

[LP08]

12z Euro looks like it will be a better thump than 0Z through 24.

[ers-wxman1]

35/12 at IAD and 39/8 at DCA...midday readings. CAD setting up. That’s some dry air and clouds starting to stream in. 

[Deck Pic]

Euro is meh for me. 

[feloniousq]

We have this discussion a fair amount, but the expected/low/high graphics packages just make no sense.  Leesburg's "expected" is 6-8 but the "high end" (10%) is 7?

[Kleimax]

Just now, feloniousq said:

We have this discussion a fair amount, but the expected/low/high graphics packages just make no sense.  Leesburg's "expected" is 6-8 but the "high end" (10%) is 7?

Right! Was just about to say that. Makes 0 sense 

[jaydreb]

1 minute ago, feloniousq said:

We have this discussion a fair amount, but the expected/low/high graphics packages just make no sense.  Leesburg's "expected" is 6-8 but the "high end" (10%) is 7?

Expected is 6-8.  Only a 10% chance of more than 7.  So I guess they are keying in on 6-7”?

[LP08]

Better than 0z, slightly drier than 6z.  Still a general 2-4 before flip.

[SomeguyfromTakomaPark]

Just now, LP08 said:

Better than 0z, slightly drier than 6z.  Still a general 2-4 before flip.

I think the goal posts are set.  Tossing the Canadian crew we have a general 2-4 for DC and immediate burbs.