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Jan 25th Wintry Mix Obs and Nowcasting

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Just now, NoVaWx said:

Light rain now. Maybe snow when rates get better?

Very precarious set up for us.  1 degree or so could make the difference.  That’s tough for any model to nail down I would imagine.  So we wait and hope.  

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Just now, SnowGolfBro said:

Precip has been light. If we get some rates i think we could change over pretty quick 

Sure, but shouldn’t the light stuff have dried up and cooled the atmosphere some first?  More trying to understand the physics/dynamics

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5 minutes ago, catoctin wx said:

I can hardly remember a day with less diurnal variation than today. So far a low of 30.4 and a high of 35.2. A spread of merely 4.8 degrees.

Sitting nicely at 34.5 / 22.8 while waiting for it to start.


.

Hi neighbor!

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Been busy today. Just saw the WWA in effect for here, Damn, going with 1-3 inches. More bullish than I expected.

Mount Holly AFD-

A complex weather pattern is evolving across the eastern two- thirds of the country. A surface low in the central Plains is ejecting eastward, attendant to a midlevel vort max shearing out in the downstream confluent flow across the Midwest and Northeast. Meanwhile, a strong vort max is digging southeast through the prairies of southern Canada, which will force the eastward acceleration of the southern-stream system. A zonally- oriented baroclinic zone extends to the southern Mid-Atlantic, with precipitation spreading into Virginia and North Carolina this afternoon. As the baroclinic zone lifts northward somewhat this evening, a predecessor perturbation will race through the Mid-Atlantic region. With ambient boundary-layer dry air (sufficiently cool given the overcast spreading northward into the southern/central CWA today), a thump of precipitation will spread into Delmarva this evening. Model soundings suggest a few hours of strong omega in the dendritic growth zone, so if the low levels can saturate, some decent snow rates (up to a half inch per hour) may occur. Combined with wet-bulbing effects, a quick one to two inches of snow may accumulate, as advertised via much of the hi-res guidance. Have issued a winter weather advisory for Delmarva for this threat from 7 pm to 4 am.

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On the dual-pol radar correlation coefficient, there is indication of melting at around 3000 ft (eyeballing the 3.1 degree scan). Something to watch if this disappears as the heavier precip moves in.

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2 minutes ago, kristia said:

Hi neighbor!

Hi!  

Hoping that you all up in Middletown are able to do a bit better today with your elevation.   We wanted to move to Middletown a few years ago but it didn't work out.  Best place to be in Frederick County for events like this :)

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2 minutes ago, catoctin wx said:

Hi!  

Hoping that you all up in Middletown are able to do a bit better today with your elevation.   We wanted to move to Middletown a few years ago but it didn't work out.  Best place to be in Frederick County for events like this :)

Sabillasville is a golden spot as well.

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Just now, Bubbler86 said:

Sabillasville is a gold spot as well. 

It sure is. That whole stretch from Emmittsburg through Sabillasville through Smithsburg (Washington County) is great.

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5 minutes ago, GEOS5ftw said:

On the dual-pol radar correlation coefficient, there is indication of melting at around 3000 ft (eyeballing the 3.1 degree scan). Something to watch if this disappears as the heavier precip moves in.

I've never heard of this technique... Are you using trig and distance from the dish to estimate here? 

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If it's raining in Winchester I assume the mid levels are too warm. I would also assume that since it's rain (not sleet) that they are pretty warm indeed. Can rates really overcome that? 

I really just don't want to get my hopes up for snow if this is just going to be freezing rain. 

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Just now, IUsedToHateCold said:

If it's raining in Winchester I assume the mid levels are too warm. I would also assume that since it's rain (not sleet) that they are pretty warm indeed. Can rates really overcome that? 

I really just don't want to get my hopes up for snow if this is just going to be freezing rain. 

Rates alone can't but if the atmosphere above is dry,  as the snow melts and evaporates the column can cool and help turn the rain to snow.  That's what the models have been advertising. 

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3 minutes ago, SnowDreamer said:

I've never heard of this technique... Are you using trig and distance from the dish to estimate here? 

Pretty much...I don't know of a site that gives good range rings (COD has 50nm) so it could be off. There is a more formal technique called quasi-vertical profiling where you take the average of the higher elevation scans (e.g. 10 degrees) and plot over time - really useful for seeing how the melting layer evolves over time and other things like dendritic growth. It's becoming more popular in research papers but I don't know of a site that does it in real time.

 

eta: the obs of rain/drizzle make sense if the layer is at 3000ft- that's probably too shallow below that to refreeze into sleet pellets.

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Obs competed to modeled already makes the NAM’s wrong as they had precip as snow here by this time. I guess we will see what happens lol

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