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Jan 17-18th disco thread--1st big threat of the year

Midlo Snow Maker

By Midlo Snow Maker,
in Mid Atlantic

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wxmeddler

wxmeddler

Posted
Posted

Never saw this before so excuse the newbie question. Is the black the mean and the numbers on the left inches based on all the members?

 

Yes, the mean is the black line and all the other lines are the 21 different members of the ensembles. The scale on the left is in inches of snow.

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AlexD

AlexD

Posted
Posted
I agree. We all know that the models except for the last NAM (18Z, which we all know is the worst) and the Euro (which is not that good inside of 36 hours) are on board with the snow. Why are we throwing in the towel yet? I won't give up until we see another run or two of the NAM that is against the snow, and other models join in. I stick to my guns of 2-4 inches, and I will not flip-flop on the forecast more than Mitt Romney in election season.

So it's one 18z run(usually a ****ty run) of a ****ty model, and the European.....versus......everyone else? Yeah, not good enough reason to give up just yet.....lets see what the gfs says...

thank you for being the voice of reason...... It's soo amusing to see the weenies ready to jump off a bridge, based on one model run....and they're been doing it for years...
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chris87

chris87

Posted
Posted

SREF is supposedly the future of short range model forecasting.. tho im not sure it's there yet. if nothing else it's usually more steady in movement one way or another.

eventually some day we'll be able to run 1000s of simulations each day that better sampling the uncertainty of the system and provide statistically meaningful probabilities....unfortunately probably the more distant future...

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MN Transplant

MN Transplant

Posted
Posted

Never saw this before so excuse the newbie question. Is the black the mean and the numbers on the left inches based on all the members?

 

Yes.  It would indicate that the SREF mean of all of the members is a little over 4" at DCA.  You can play around with it here:  http://www.spc.noaa.gov/exper/sref/fplumes/

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SnowGoose69

SnowGoose69

Posted
Posted

does the 18z NAM carry more weight than the SREF? SREF will likely fold in the next run

 

I've seen cases before where the 15 or 03Z SREFs have trended or are going heavily in one direction and then the 18 or 06Z NAM proceeds to go the opposite way...I'd say 90% of the time when that occurs the ensuing NAM run goes back the other way and caves and not the other way around...the reason being I think the 15Z SREFs may have 12Z RAOB data and the 18Z NAM as we know does not have the degree of data the 12Z runs do.

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WxMan1

WxMan1

Posted
Posted

Folks,

 

A few things I noticed while at work today, some of this you probably already know (knew):

 

1) The 12Z NAM was the most robust with the liquid equiv...0.50 to 0.75 through the DC metro region, though not all of it snow.

2) GFS was slightly drier (closer to 0.5 for DCA), though with the NAM, both NCEP runs were clearly wetter than the non-NCEP suite.

3) EC/UKMet/CMC at 12Z were all drier for the DC metro region, i.e. less than a quarter inch.

3) The 15Z SREF was consistent with the 09Z version, perhaps a smidge wetter for DC, though still more like in a 0.25 to .50 inch, or lighter than the 12Z NAM/GFS.

 

Now, this was most notable:

 

ALL the high-resolution runs at 12Z, which included the NCEP WRFs (ARW and NMM), NAM CONUS-nest, the NSSL WRF, SPC WRF, and the SSEO mean noted a much TIGHTER pcpn gradient on the northern side -- giving DCA more or less the shaft with a tenth of an inch or less of liquid equivalent pcpn -- while much higher QPF remained over central and srn VA.  What was alarming to me was that the NAM's own CONUS nest version (4km) was remarkably different from the parent 12km run with the moisture gradient on the northern side.  That's never a comforting sign.  It's almost as if the higher res runs were trying to resolve the strengthening deformation (frontogenesis) better, and in doing so, yielded a tighter moisture gradient N-S, thereby drying out the DC area.  Take it FWIW...though I'm hearing (though have not yet seen) the 18Z NAM went farther south with the more appreciable QPF.

 

Very, very high-bust potential forecast either way, because obviously not all the QPF farther south (into cen VA) would be all snow.  Still, that part of the world (EZF-RIC) would stand the best chance on getting in on the deformation axis steadier snows after 21Z or so, to a point where 35-36F can quickly cool to 32-33F.  Looks to me like the event late last year in which the RIC area got 4-6" or so, while little if any fell in the DC area.

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dtk

dtk

Posted
Posted

I've seen cases before where the 15 or 03Z SREFs have trended or are going heavily in one direction and then the 18 or 06Z NAM proceeds to go the opposite way...I'd say 90% of the time when that occurs the ensuing NAM run goes back the other way and caves and not the other way around...the reason being I think the 15Z SREFs may have 12Z RAOB data and the 18Z NAM as we know does not have the degree of data the 12Z runs do.

Except it has more data as well as more recent data, most notably all of the obs we receive from aircraft (there are lots of flights during the day, so we have plenty of data).  The real problem with interpreting trends in the NAM and SREF is the use of partial cycling.

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Scarlet Pimpernel

Scarlet Pimpernel

Posted
Posted

Had to throw that stupid a$$ political comment in there, didn't you?

 

No more so than having one contained in one's avatar picture! :whistle:   Actually, I thought it was pretty funny...would have been equally funny if someone said "...model changes quicker than Bill Clinton can swap interns" or something like that.

 

Now, back to the weather...

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usedtobe

usedtobe

Posted
Posted

Folks,

 

A few things I noticed while at work today, some of this you probably already know (knew):

 

1) The 12Z NAM was the most robust with the liquid equiv...0.50 to 0.75 through the DC metro region, though not all of it snow.

2) GFS was slightly drier (closer to 0.5 for DCA), though with the NAM, both NCEP runs were clearly wetter than the non-NCEP suite.

3) EC/UKMet/CMC at 12Z were all drier for the DC metro region, i.e. less than a quarter inch.

3) The 15Z SREF was consistent with the 09Z version, perhaps a smidge wetter for DC, though still more like in a 0.25 to .50 inch, or lighter than the 12Z NAM/GFS.

 

Now, this was most notable:

 

ALL the high-resolution runs at 12Z, which included the NCEP WRFs (ARW and NMM), NAM CONUS-nest, the NSSL WRF, SPC WRF, and the SSEO mean noted a much TIGHTER pcpn gradient on the northern side -- giving DCA more or less the shaft with a tenth of an inch or less of liquid equivalent pcpn -- while much higher QPF remained over central and srn VA.  What was alarming to me was that the NAM's own CONUS nest version (4km) was remarkably different from the parent 12km run with the moisture gradient on the northern side.  That's never a comforting sign.  It's almost as if the higher res runs were trying to resolve the strengthening deformation (frontogenesis) better, and in doing so, yielded a tighter moisture gradient N-S, thereby drying out the DC area.  Take it FWIW...though I'm hearing (though have not yet seen) the 18Z NAM went farther south with the more appreciable QPF.

 

Very, very high-bust potential forecast either way, because obviously not all the QPF farther south (into cen VA) would be all snow.  Still, that part of the world (EZF-RIC) would stand the best chance on getting in on the deformation axis steadier snows after 21Z or so, to a point where 35-36F can quickly cool to 32-33F.  Looks to me like the event late last year in which the RIC area got 4-6" or so, while little if any fell in the DC area.

 

Good post.  I pretty much agree.  I'm not sure I trust the SREF with a system having such a tight gradient. 

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wxmeddler

wxmeddler

Posted
Posted

...

ALL the high-resolution runs at 12Z, which included the NCEP WRFs (ARW and NMM), NAM CONUS-nest, the NSSL WRF, SPC WRF, and the SSEO mean noted a much TIGHTER pcpn gradient on the northern side -- giving DCA more or less the shaft with a tenth of an inch or less of liquid equivalent pcpn -- while much higher QPF remained over central and srn VA.  What was alarming to me was that the NAM's own CONUS nest version (4km) was remarkably different from the parent 12km run with the moisture gradient on the northern side.  That's never a comforting sign.  It's almost as if the higher res runs were trying to resolve the strengthening deformation (frontogenesis) better, and in doing so, yielded a tighter moisture gradient N-S, thereby drying out the DC area.  Take it FWIW...though I'm hearing (though have not yet seen) the 18Z NAM went farther south with the more appreciable QPF.

 

Completely agreed, and it's what I was trying to get at earlier. It's that the global models are going to make the gradient more diffuse than it will actually be. These convergence zone cut-off are notorious for having grass to 4" within 10 miles and the GFS and other global models and to some extent the Op. NCEP 12km NAM can't handle that kind of gradient. This is what also concerns me also about the SREF, which has a 16km horizontal grid resolution.

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dtk

dtk

Posted
Posted

If you go to the PSU Ewall and click the DGEX links and then go up top to where it says 00/06/12/18 UTC and click there it takes you to a page where you can view the regional breakdowns for the NAM/GFS/ARW and the "NMM" which is the old ETA.

Gotcha, it's just a labeling thing.  The NMM (non-hydrostatic mesoscale model) is not actually the old eta, though it evolved from it in some regards (and may share some commonality).

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WxMan1

WxMan1

Posted
Posted

Good post.  I pretty much agree.  I'm not sure I trust the SREF with a system having such a tight gradient. 

 

Wes,

 

Agreed.  The SREF mean is obviously going to spread out the 0.10", 0.25", and 0.50" a bit more.  Moreover, with the "new" SREF, we're swapping out all those old ETA and RSM members with WRF members, which could tell a pretty interesting story once the 21Z SREF comes in (after what we've seen with the 18Z NAM).

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Scarlet Pimpernel

Scarlet Pimpernel

Posted
Posted

Folks,

 

A few things I noticed while at work today, some of this you probably already know (knew):

 

1) The 12Z NAM was the most robust with the liquid equiv...0.50 to 0.75 through the DC metro region, though not all of it snow.

2) GFS was slightly drier (closer to 0.5 for DCA), though with the NAM, both NCEP runs were clearly wetter than the non-NCEP suite.

3) EC/UKMet/CMC at 12Z were all drier for the DC metro region, i.e. less than a quarter inch.

3) The 15Z SREF was consistent with the 09Z version, perhaps a smidge wetter for DC, though still more like in a 0.25 to .50 inch, or lighter than the 12Z NAM/GFS.

 

Now, this was most notable:

 

ALL the high-resolution runs at 12Z, which included the NCEP WRFs (ARW and NMM), NAM CONUS-nest, the NSSL WRF, SPC WRF, and the SSEO mean noted a much TIGHTER pcpn gradient on the northern side -- giving DCA more or less the shaft with a tenth of an inch or less of liquid equivalent pcpn -- while much higher QPF remained over central and srn VA.  What was alarming to me was that the NAM's own CONUS nest version (4km) was remarkably different from the parent 12km run with the moisture gradient on the northern side.  That's never a comforting sign.  It's almost as if the higher res runs were trying to resolve the strengthening deformation (frontogenesis) better, and in doing so, yielded a tighter moisture gradient N-S, thereby drying out the DC area.  Take it FWIW...though I'm hearing (though have not yet seen) the 18Z NAM went farther south with the more appreciable QPF.

 

Very, very high-bust potential forecast either way, because obviously not all the QPF farther south (into cen VA) would be all snow.  Still, that part of the world (EZF-RIC) would stand the best chance on getting in on the deformation axis steadier snows after 21Z or so, to a point where 35-36F can quickly cool to 32-33F.  Looks to me like the event late last year in which the RIC area got 4-6" or so, while little if any fell in the DC area.

 

This is a pretty good analysis.  Makes me wonder all the more whether LWX perhaps jumped the gun a bit in extending the watch farther northeast into the metro DC area.  Clearly southwest of here has a much better chance.  But could they have waited until the late evening forecast on whether or not to push it up this way?  On the other hand, I can see the concern over the timing and getting some kind of notice out that would get peoples' attention.  I guess there were already arguments on this earlier this afternoon when the watch came out.

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