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February 8 Storm Obs/Discussion


NoVaWx

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I can't decide if it's an interesting coincidence or sad irony that I'm actually taking that map seriously.

Everyone wants it and more as we would all cheer if the NAM was right with precip. But many of us know the reality of what will likely occur. Some will see a nice bit of snow tomorrow for sure.

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One of the more promising events I've forecast this winter...

Plenty of cold air aloft, but surface temperatures look to hurt the initial snowfall accumulations before either the rates get high enough of the surface temperature cools to the freezing mark. Higher elevations stand a better chance of snow (both for surface temperatures and for snow ratios).

Pretty good call imo with one exception. The 1-2" line misses my backyard by a 1/16th of an inch. Could you move it about an 1/8" further s&e in Moco so I can get in on the fun please?

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What's up with the NCEP site? Dumb question, huh?

Anyway, can't get the sref mean, but the members I can see, look to be a touch wetter. Don't really know if this is a valid observation as it was done very quickly.

NCEP was having problems running the 12z GFS Ens. earlier... not sure if it's related or not.

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Study this map. Topograhic influence is pretty strong in md during many winter events. You can clearly see the fall line run along the pg, moco, hoco, and aa county lines. Then you get an extra kick in elevation from damascus, mt airy, westminster, and the parrs ridge area.

Generally speaking, anwhere w of the fallline > than areas east with most common setups.

Edit: I want to add some of the reasons behind this too. Many already know this stuff but for those who don't, generally speaking you lose 3 degrees in temp for every 1k feet in elevation gain (called lapse rate). Mt. Airy and Westminster are around 800' in elevation and areas along parrs ridge are up to 1k. I'm at 400' in elevation in Rockville. It doesn't seem like much difference but the elevation change can make a huge difference sometimes. Just think how many times there are marginal surface temps around here? A little elevation change can make a world of difference. While I'm sitting @ 34 here watching flakes melt on contact, my friends in Mt Airy are sitting @ 32 and watching it stick to the roads.

Another thing elevation does is add some lift to the atmosphere (called orographic influence). We generally only think of Garrett Co and lake effect areas for this but the piedmont and parrs can add just enough orographic influence to squeeze out some extra moisture.

Frederick kinda gets shortchanged because of this. You would think that they would do well becuase they are further n&w of dc but Frederick sits in the shadow of the catoctins and parrs depending on whice direction the ll flow is from. It's really cool when you break down the little microclimates around here. Such subtle things can have a pretty decent impact on how things shake out.

Well said. I'm pretty excited that I'll have my Davis equipment up for a whole calendar year to see if there really is a precip hole in Frederick County, MD. Another and larger microclimate is the I-81 corridor south of Winchester. A few pockets seem to be borderline desert! I'm just joking with that term but their annual precip is on average much lower than areas to the west and east.

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18z NAM not as wet as 12z, but still more QPF than the other models. Over 0.2" for the airports.

edit - good deal warmer than 12z, unfortunately

It looks like it almost has .25 for most but it is warmer...dca is 36 or so during the best part of the storm. However, the warm layer is really shallow. I don't think it changes anything from the earlier forecast.

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