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February 16th-17th Obs & Nowcasting


nj2va

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Both the NAM and GFS have a "warm layer" of about -5 or -7C from 800-700mb around 6z when we should be getting our best rates.  That's making me a bit cautious on going 15:1.  Not sure where the best omega is falling.  If it's a little higher, that would be good.  The profiles around 0z tonight look ideal for dendrite growth, so we should maximize that lighter precip this evening. 

 

yeah i noticed that -- but i didn't really check the omega profile but as you said I think we really do maximize the lighter period -- and I think those along the MD/PA border stay pretty optimal the entire period (however probably miss out on the better rates around 6z) -- i guess if i was held to a forecast i'd say a QPF-weighted average or 12/13:1 DC and south and 15/16:1 north of DC.

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Overall 15-1 is a fair guess on my part without getting into the #'s too much. I expect higher ratios for some of early and possibly tail end stuff. In the middle could easily be 10-12:1. I highly doubt any period will feature less than 10:1 around here. 

No, it's not going to be less than 10:1. 

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yeah i noticed that -- but i didn't really check the omega profile but as you said I think we really do maximize the lighter period -- and I think those along the MD/PA border stay pretty optimal the entire period (however probably miss out on the better rates around 6z) -- i guess if i was held to a forecast i'd say a QPF-weighted average or 12/13:1 DC and south and 15/16:1 north of DC.

I think that sounds pretty reasonable. 

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Probably up to .3-.5" here in CHO. Really coming down at a nice clip. Fine, powdery snow. Really hoping this means that the dry slot that seemed to be showing up on some of the models isn't going to verify, especially now that the column seems to be nice and damp.

What is the shape of the snowflakes?  Dendrites or other? 

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Looks like the stuff is just south of DC. Seems to be moving in pretty fast. Still 5pm start time for DC, PG, central AA?

Yes, its snowing but of no real consequence. Impact time is probably 4-5 pm, such as Matt stated. But as I say that, a real steady snow is currently ongoing and dusting everything, so who the hell knows.

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what is the general opinion of the ratios on 1/30/10 -- BWI and IAD were both low 20s:1 from the climo data but I get there is some skepticism about the measurements? 

Snow doesn't get into the ASOS buckets very efficiently, especially fluffy snow that's blowing around.  Yes, consensus is the liquid equivalent was underreported. 

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Snow doesn't get into the ASOS buckets very efficiently, especially fluffy snow that's blowing around.  Yes, consensus is the liquid equivalent was underreported. 

 

yeah that makes sense -- i was actually stuck at BWI for that event (connection through CLT was cancelled I think) -- was in DC for an interview on the day before -- too bad we don't have more non-automated measurements of liquid equivalent

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