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Saint Patrick's Day Snow Event


stormtracker

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Euro member output is solid. 23 members show 6"+. Only 3 show no snow. 11 show 12"+.

Just about 6" on the means for kgai. DC not out yet. Pretty unanimous for a snow event of some sort.

ETA: Considering it's prob not going to be 10:1 snow and there will be surface problems during the first part those #'s are obviously inflated. Decent support for a 3-6" event with some upside.

 

That would be similar in amount to the event on March 3 (though not as cold and "dry" of a snow)...which would be more impressive occurring on March 17th.

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models don't really "split the difference" -- take for example the full envelope of uncertainty which you can express as a probability density function based on the initial condition -- a particular model solution is a discrete point on that pdf -- a *single* model has no knowledge whatsoever of the shape of the actual pdf (which we can assume in this case ranges from a good deal of energy being left int he SW on one end of the distribution to a consolidated system on the other end, as you correctly pointed out). 

 

So this idea that models can "split the difference" which in your case would be taking an average of the bimodal pdf you describe isn't correct -- frankly if you take your explanation from a physical standpoint today's solution of a "weaker" system would have been the least likely scenario to show up, when in fact, most guidance have something in between what you described were the two "most likely" scenarios.

 

And just from a fundamental standpoint, its false to just assume that the current model solutions are any less correct  than the two "likely" scenarios you described. 

To build on that - since some weather solutions are self-reinforcing (heavy snow brings more cold air brings more accumulation -  whereas moderate snow lets marginal temps linger meaning less accumulation) it's realyl hard to "split the difference" and end up with a useful solution. Here's an oversimplifaction of how "splitting the difference" can give you a solution that is actually very unlikely.

 

2cxddn9.png

 

I feel like DC-proper is often in this predicament, and we may be again on Monday. 

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18Z NAM looks pretty juiced up toward the end of its run, 850-mb temps look good, and surface goes below freezing around 03Z Sunday night it appears. Ducking for cover for analyzing the later periods of the 18Z NAM, but someone had to do it!! :bag:

It is quite cold with HP strong to the north. If we were able to expand it out it might have a sharp gradient to the precip with the HP trying to suppress the heavy stuff south. Plenty cold though on this 18z run.

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odd......NCEP maps put us around -3C at 850 while soundings place us around 0C

to illustrate, below is the sounding off the READY site for BWI at 84 hrs and the bottom link is the NCEP 850 map at 84 hrs.

1014.    51.   -1.5   -2.7    47.4     8.1 1000.   166.   -2.9   -3.7    49.4    11.6  975.   366.   -4.6   -5.0    52.6    15.3  950.   570.   -6.2   -6.9    55.6    17.7  925.   778.   -7.6   -8.6    56.3    18.5  900.   991.   -7.6   -8.8    49.1    16.6  875.  1211.   -3.9   -4.6    47.1    10.8  850.  1443.    0.3    0.0    95.9     2.4  825.  1682.   -0.7   -1.0   174.6     3.9  800.  1927.   -0.9   -1.0   194.9     7.3  775.  2181.   -1.5   -1.6   197.7    10.3  750.  2442.   -3.3   -3.6   199.2     8.8  725.  2709.   -5.3   -5.8   211.4     7.5  700.  2983.   -6.4   -7.0   215.5    11.8  650.  3562.   -7.7   -8.3   192.4    24.1  600.  4181.  -10.9  -11.8   208.1    24.2  550.  4845.  -14.6  -16.0   232.6    22.5  500.  5561.  -18.7  -20.6   239.2    23.1

http://mag.ncep.noaa.gov/Image.php?fhr=084ℑ=data%2Fnam%2F18%2Fnam_namer_084_850_temp_ht.gif&model=nam&area=namer&param=850_temp_ht&group=Model+Guidance&preselected_formatted_cycle_date=20140313+18+UTC&imageSize=L&ps=model

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to illustrate, below is the sounding off the READY site for BWI at 84 hrs and the bottom link is the NCEP 850 map at 84 hrs.

1014.    51.   -1.5   -2.7    47.4     8.1 1000.   166.   -2.9   -3.7    49.4    11.6  975.   366.   -4.6   -5.0    52.6    15.3  950.   570.   -6.2   -6.9    55.6    17.7  925.   778.   -7.6   -8.6    56.3    18.5  900.   991.   -7.6   -8.8    49.1    16.6  875.  1211.   -3.9   -4.6    47.1    10.8  850.  1443.    0.3    0.0    95.9     2.4  825.  1682.   -0.7   -1.0   174.6     3.9  800.  1927.   -0.9   -1.0   194.9     7.3  775.  2181.   -1.5   -1.6   197.7    10.3  750.  2442.   -3.3   -3.6   199.2     8.8  725.  2709.   -5.3   -5.8   211.4     7.5  700.  2983.   -6.4   -7.0   215.5    11.8  650.  3562.   -7.7   -8.3   192.4    24.1  600.  4181.  -10.9  -11.8   208.1    24.2  550.  4845.  -14.6  -16.0   232.6    22.5  500.  5561.  -18.7  -20.6   239.2    23.1

http://mag.ncep.noaa.gov/Image.php?fhr=084ℑ=data%2Fnam%2F18%2Fnam_namer_084_850_temp_ht.gif&model=nam&area=namer&param=850_temp_ht&group=Model+Guidance&preselected_formatted_cycle_date=20140313+18+UTC&imageSize=L&ps=model

 

I think the NCEP site uses a little more smoothing.  On IWM you can see that east of the Potomac it warms some.

 

post-1746-0-73873600-1394748584_thumb.gi

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ok...see ya next winter :( I'm going to enjoy it.

I'm going more on soundings and climatology, not those silly snow maps.

I'm with you. 3-5" is perfectly acceptable, worth the track, and would be thrilled if it verifies. It's a fluke setup with perfect timing. Expecting a fluke monster is a but much.

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