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The feb 4-5 storm (Obs/Discussions)


Ji

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I think so...this stuff looks to head through DC as well...maybe the 0z NAM will be right...goodness you would think it could get a 12 hour forecast right.....

the 0z nam spit out an underwhelming 0.02" qpf after 6z at DCA. so if it's right, we'll get some flurries/sprinkles inside the beltway...

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I just use 36-37 as general idea of going to snow as I don't think this setup supported a prolonged rain event if one could maintain that temp or lower based on my experience....If one looks at old metars which I do all the time we see that over and over in rain to snow events....obviously the 925-950mb layer is the one that actually matters, but 36-37 or lower usually suggests that that layer is there or getting there soon

Yes...as long as there is no inversion (which you have stated many times) then its usually a pretty good temp to base a mix/changeover on. 36 seems to be a favorite number here when we are changing over in a a situation with no warm layers aloft.

Realistically you want that 0C height getting below 950mb as the flakes have a hard time surviving more than 400 meters of above freezing air....but seeing 925-950mb on the models knowing mod/heavy precip will be around ensures that the 0C will continue to lower without aid of warm air advection which this type of event clearly lacked. So that's why its typically good to look for those wetbulb zero heights on the soundings when steady precip is around...it can kind of give a threshold for changeovers. Models generally don't lower those wetbulb heights fast enough in those setups. N and central MD saw this play out with more snow in the afternoon than models gave originally.

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Weatherbug's are not always accurate...33 seems low to me based on surrounding obs, but maybe you were close....point is you were going to go to snow (you were already mixing) assuming we actually had more precip....I don't ever recall an event in mid winter where the column from 875-900 mb and up was below freezing and it was a prolonged synoptic rain event with temps in the mid 30s....and this event was no different.....nobody was going to get hour after hour of rain and 34 with this setup...I'm not saying anyone advanced that idea, but when it looked like more of a prolonged event into the overnight hours, anyone suggesting an all rain event with temps in the low to mid 30s would have busted

It was my ob. There are plenty of events that have all rain when the first 100 mb are above freezing, anyone with a basic knowledge of atmospheric thermodynamics and cloud physics would agree. Snow doesn't usually fall though that deep of a warm layer especially in this case, with light to moderate rates in a saturated column.

Yes it would had eventually changed over due to CAA, but the precip was over before the column was cool enough to support it.

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Yep...I was just thinking this batch right now looks to run through dc....everything is light overnight for sure

i wasn't saying nam is necessarily right... just that if it is, we're talking next to nothing. we want the nam to be wrong if this is going to overperform... the localized nature of these bands will be make this stuff overnight hard to model right....

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It was my ob. There are plenty of events that have all rain when the first 100 mb are above freezing, anyone with a basic knowledge of atmospheric thermodynamics and cloud physics would agree. Snow doesn't usually fall though that deep of a warm layer especially in this case, with light to moderate rates in a saturated column.

Yes it would had eventually changed over due to CAA, but the precip was over before the column was cool enough to support it.

cool...show me an example of a prolonged synoptic rain event in mid winter with surface temps in the mid 30s here that fits that criteria....I am certainly willing to be proven wrong....

and congrats on having the same temp as HGR when they were getting moderate snow and I was 5-10 miles to your south at 37-39....

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cool...show me an example of a prolonged synoptic rain event in mid winter with surface temps in the mid 30s here that fits that criteria....I am certainly willing to be proven wrong....

and congrats on having the same temp as HGR when they were getting moderate snow and I was 5-10 miles to your south at 37-39....

Sure thing I'll dedicate the thread to you!

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35/35 for me and you...I suspect Silver Spring might be in the upper teens by now

I'm sorry you didn't get snow tonight and your "silver bullet" changeover temperature was a sham for DC. Sounds like thermodynamics > local knowledge > model soundings!

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