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Feb 18/19 Disco/Obs


nj2va
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10 minutes ago, MN Transplant said:

They will be launching the balloon from Dulles in a few minutes.  We’ll get the results in 45-60 min.  The SPC mesoanalysis page has a model-derived estimate of the upper air structure right now.  850s are a problem (more than 700 or 925).  I’m guessing there is even a worse layer in there above 850.

80 degrees! Heh.

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50 minutes ago, osfan24 said:

No, but the much-ridiculed NAM once again lead the way on this. What a winter it has had. You can take the GFS, HRRR, and Euro and throw them in the trash can.

I'm sitting at 25 with a mix of sleet and freezing rain. Seems to go to all sleet in heavier bands. This is probably the most frustrating winter I can remember. At least some previous winters, you just closed the blinds and took the loss and took your lumps because you were coming off a run of really good winters. The amount of time I've spent tracking essentially nothing this winter makes me understand why Bob Chill stepped away.

This was so much more bearable just hugging the NAM from the start. There’s still a good storm to be salvaged here, just relies on getting enough sleet to look like snow 

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1 minute ago, frd said:

Imagine your rates , darker blues, banding, etc., and location is helping too , here is it meh. Many corporations  in northern Delaware closed due to the winter storm warning. I doubt we see 4 to 6 inches of snowfall here. But,  I will wait before declaring complete failure for 3 out of the 4 storms this season Oh, I shouldn't even use the word storms, implies something major, not.  

 

Static map

 

This event is a good example of why these "precip-type" radar maps are often flawed. The indicated precip type is not based purely on radar data; they add supplemental model data to determine the likeliest precip type at the location of each radar observation. The dual-polarization observations, however, show the sleet/snow line from southern Carroll County northeastward into PA, where reflectivity (ZH) and differential reflectivity (ZDR) values are enhanced due to bright banding, and correlation coefficient is reduced due to a mix of melting particles with different shapes. SImilarly, the rain/freezing rain transition is where the correlation coefficient increases south of Anne Arundel County, with both ZDR and ZH values decreasing here as raindrops dominate the backscatter.

One other thing to note is the higher correlation coefficient and lower ZH and ZDR closer to the radar site in northern VA. The lack of a melting signature here is because the radar beam is closer to the ground at these locations and thus propagates beneath the melting layer; once the radar beam is higher off the ground at locations farther from the radar site, the polarimetric melting layer signature is visible. When the beam gets high enough, it samples above the melting layer and the signature disappears, as correlation coefficient becomes close to 1 and ZH and ZDR values decrease.

20210218_1140_klwx.thumb.png.49bf2ed1834ce644f6ca47267aed3416.png

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11 minutes ago, mappy said:

Been texting Ava since I woke up, a "forecasting nightmare" as she put it. 

 

10 minutes ago, SomeguyfromTakomaPark said:

So the NAM from a few days ago as our far NW outliner wins again.  Sheesh.  

The NAM won this 24 hours ago. I called it yesterday morning. When the NAM says no. It's no.

Light slop

27

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39 minutes ago, Rhoady said:

11z: 26F/25, light mix, 80/20 PL/ZR, 1.2"

 

The meso analysis that dec pic posted is relevant at least afa precip changing back from 90% ZR to 80-90% PL an hr or so later imby 

12z: 28F/25, light mix, 60/40 PL/ZR-, 1.3". 

The accumulated precip is the worst to drive or walk on rn. Mini-glaciers forming. 

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1 minute ago, dailylurker said:

 

The NAM won this 24 hours ago. I called it yesterday morning. When the NAM says no. It's no.

Light slop

27

Yup, I learned my lesson this season. If there's confusion as to where the sleet line is going to be, always rely on the NAM. Even yesterday while models were giving everyone 5" of snow, the NAM was insistent on saying it would be all sleet.

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1 minute ago, MN Transplant said:

7am CoCoRaHS report was .06” precip, T snow.

DCA 0.09” so far.

IAD at 6 miles vis.  It is hard to look out the window and tell that anything is falling.

Woof.  that's a pretty dry start

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