heavy_wx

Getting some melting snow here in the heavier bursts of precip.

Wet snowflakes just starting to mix in here.

Snow mixing with sleet now in North Bethesda.

Aggregates starting to get bigger here as the temperatures warm aloft and the band of heavier snow approaches.

Flurries here in North Bethesda.

Some flurries now in North Bethesda.

39.14N,  76.85W

Moderate-sized aggregates falling now.

Light snow with small flakes here.

1 hour ago, CAPE said:

Wed looks glorious. Under full late Feb sun too. Condolences to those protecting their snowpack.

If the clouds do hold off ahead of the cold front, it could be one of those days where the models underestimate surface solar radiation (and thus surface temperatures) owing to the lack of foliage this time of year.

Moderate snow with wet aggregates here.

Pretty much all sleet here in North Laurel.

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.  

 

 

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.

I measured 2.5" here with light snow currently. The amount of sleet mixing in last night definitely contributed to the south-north snowfall gradient in Howard County.

Mostly sleet here in southern Howard County with a coating of frozen precip on the ground.

Light snow here.

I got about 0.5" here in North Laurel.

Light rain with some wet aggregates mixed in here.

2 minutes ago, WxUSAF said:

Measured 0.5” at 830. Measured 0.5” at 940. 

The coating of snow that was on the pavement here has melted.

Snow sizes have become much smaller here just east of the highest reflectivity (~40 dBZ) over Montgomery County.

Moderate snow with some very large aggregates falling right now.

All snow now with large, wet aggregates.

Mix of rain and wet snow here.

26 minutes ago, WxUSAF said:

This is definitely true. Look at temps, snow growth, etc. 

But despite all our talk, we rarely get snow ratios outside a 8-12:1 range. With the look of the soundings we’ve seen on the NAM and even GFS, I don’t see this storm being different. So unless a storm probably has substantial sleet (not the case Sunday) then the 10:1 snow maps are probably decent. 

If surface temperatures were a couple degrees below freezing, I would feel more confident that ratios would be > 10:1. But while the antecedent air mass is fairly cold, there isn't a much of a surface high or mid-level confluence to our northeast promoting a low-level flow of cold air. Surface melting during the precipitation will definitely reduce ratios.

1 hour ago, WxMan1 said:

11Z Sunday over the District per the 06Z 3km NAM. Nice lift in the DGZ. If it comes to fruition, we would see MUCH better dendrites than we saw last Sunday. Thus much better (faster) accumulation efficiency. Like 4+ inches within 12 hours instead of having to wait 24-36 hours (lol).

Yes, this is a much better sounding compared to what we saw last Sunday, where cloud tops were only around -10C. There's also some convective instabilitiy at cloud top near -20C that would be favorable for ice crystal generating cells; when these ice crystals fall into the saturated dendritic growth layer below, they grow rapidly and stick together, forming fluffy aggregates. If these profiles simulated by the 3-km NAM were to verify, I think the snow-liquid-ratio would be > 10:1 with fairly intense precipitation rates. FWIW, the profiles on the 06z-GFS have similar features around this time.