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WxUSAF

December 16-17, 2020 Winter Storm Obs/Nowcasting

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Something I'm not understanding... maybe someone smart can explain it to me.  According to SPC Mesoanalysis, the SLP has basically taken a perfect track - the kind of track that had models spitting out ridiculous totals for us even along I95. The models (at least the runs over the past 24h) seemed to have nailed the event for I95 - quick thump, quick changeover, rain rest of the event, 1-3".  What I'm not understanding is that the models came to that conclusion based on an SLP that tracked basically right over Delmarva.  The SLP didn't do that - its at least 25-50 miles east of all guidance but we still ended up with the same result.

Am I missing something?

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Sharpsburg, MD 420' ASL

9:30pm 24 degrees and snowing. It's not pouring but its snowing a good clip. I believe we changed over from sleet about 9pm. I guesstimate we got maybe 1/8 of an inch in sleet accumulation.

Hoping that its starts puking snow again!

 

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Back down to 32 after a high of 32 in N. Arlington.  “Hearing” the rain now so some sleet is in there.

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8 minutes ago, DDweatherman said:

And as @psuhoffman said the NAM was out, it throws us some snow tonight on the 0z.

I wrote that up before any 0z guidance came out...the 12k did jump on board...not to the extent of the euro and rgem/hrdps but a significant move to that camp.  The 3k still wants none of it.  It took a tiny step, it sees it now...but it develops the banding to our northeast in PA.  That is very possible...but so is the euro idea...or anything in between.  The 12k NAM is also warmer...more of if would be mix...but that is a function of it not developing as robust a banding signature to cool the column.  

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17 minutes ago, LP08 said:

I have family in Scranton, they have travel emergency notices going to their phones.  I hope to be getting pics tomorrow morning.

I can believe it, check out google maps traffic, that is a lot of interstate closures in that area.

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5 minutes ago, caviman2201 said:

Something I'm not understanding... maybe someone smart can explain it to me.  According to SPC Mesoanalysis, the SLP has basically taken a perfect track - the kind of track that had models spitting out ridiculous totals for us even along I95. The models (at least the runs over the past 24h) seemed to have nailed the event for I95 - quick thump, quick changeover, rain rest of the event, 1-3".  What I'm not understanding is that the models came to that conclusion based on an SLP that tracked basically right over Delmarva.  The SLP didn't do that - its at least 25-50 miles east of all guidance but we still ended up with the same result.

Am I missing something?

850 low never closed off, allowing warm air to scream north. It’s early winter, barely below freezing, with relatively warm ocean waters compared to deep winter. If we had a closed 850 low south of here, this was an easy 12+ area wide  

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Just now, psuhoffman said:

I wrote that up before any 0z guidance came out...the 12k did jump on board...not to the extent of the euro and rgem/hrdps but a significant move to that camp.  The 3k still wants none of it.  It took a tiny step, it sees it now...but it develops the banding to our northeast in PA.  That is very possible...but so is the euro idea...or anything in between.  The 12k NAM is also warmer...more of if would be mix...but that is a function of it not developing as robust a banding signature to cool the column.  

With the changeover coming W to E just west of us now, I’d favor better thermals occurring. Does the current swath now basically pivot to the NW/SE orientation? Or are we refiring more Precip again. 

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4 minutes ago, caviman2201 said:

Something I'm not understanding... maybe someone smart can explain it to me.  According to SPC Mesoanalysis, the SLP has basically taken a perfect track - the kind of track that had models spitting out ridiculous totals for us even along I95. The models (at least the runs over the past 24h) seemed to have nailed the event for I95 - quick thump, quick changeover, rain rest of the event, 1-3".  What I'm not understanding is that the models came to that conclusion based on an SLP that tracked basically right over Delmarva.  The SLP didn't do that - its at least 25-50 miles east of all guidance but we still ended up with the same result.

Am I missing something?

The exact position of the surface low didn’t end up mattering as much as the upper air features.  The 850 low, which is both broad and late developing, is basically over DC allowing the warm air to flood in.  We always want an 850 track to the south of DC by a fair margin.

9BA64448-8EF3-417B-B2CA-A6F88FD516C5.gif.d6d7e51c5e6cac7c48c4ff5d794db7f2.gif

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1 minute ago, DDweatherman said:

With the changeover coming W to E just west of us now, I’d favor better thermals occurring. Does the current swath now basically pivot to the NW/SE orientation? Or are we refiring more Precip again. 

Check that, now back to snow mixed in down in Westminster even before the good returns move back in. 

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2 minutes ago, jayyy said:

850 low never closed off, allowing warm air to scream north. It’s early winter, barely below freezing, with relatively warm ocean waters compared to deep winter. If we had a closed 850 low south of here, this was an easy 12+ area wide  

Is that why we didn’t see the usual pivot and spin on radar typical for winter storms? Or is that more of a different kind of storm?

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People are skidding all up and down Blunt Road near me and it's so unfortunate. That road is a car trap any time we have frozen precip.

Also: Am I the only one that is fine with sleet fests? Like, seeing sleet just filled my heart with joy after the last 3-4 hours of rain. Getting a lot of sleet seems to add some good staying power. One of my most memorable storms was... was it 2017? With the absolute epic sleet bomb 3.5" of sleet in Gaithersburg.

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2 minutes ago, MN Transplant said:

The exact position of the surface low didn’t end up mattering as much as the upper air features.  The 850 low, which is both broad and late developing, is basically over DC allowing the warm air to flood in.  We always want an 850 track to the south of DC by a fair margin.

9BA64448-8EF3-417B-B2CA-A6F88FD516C5.gif.d6d7e51c5e6cac7c48c4ff5d794db7f2.gif

By the way, look at the ridiculous lack of northerly wind barbs in this image.  Southerly 850s in Erie!

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4 minutes ago, jayyy said:

850 low never closed off, allowing warm air to scream north. It’s early winter, barely below freezing, with relatively warm ocean waters compared to deep winter. If we had a closed 850 low south of here, this was an easy 12+ area wide  

Exactly...ERS caught this early on and no one wanted to hear it but he was 100% right.  December coastal with super warm SST and no closed mid level circulation is a big problem...nothing to cut off the easterly fetch to the north of the low.  This could have worked in 2 ways...true arctic airmass, phased system.  In the end we got the perfect track...the blocking did its dirty work...but other parts didn't come together.  December is a HARD month to get a BIG snow here.  We are almost better off with progressive wave type systems that cant scorch the mid levels with screaming easterlies.  December is a good month to waste a good pattern unfortunately.  But give me this look again...anytime between xmas and March 10...and I will take my chances.  

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Just now, psuhoffman said:

Exactly...ERS caught this early on and no one wanted to hear it but he was 100% right.  December coastal with super warm SST and no closed mid level circulation is a big problem...nothing to cut off the easterly fetch to the north of the low.  This could have worked in 2 ways...true arctic airmass, phased system.  In the end we got the perfect track...the blocking did its dirty work...but other parts didn't come together.  December is a HARD month to get a BIG snow here.  We are almost better off with progressive wave type systems that cant scorch the mid levels with screaming easterlies.  December is a good month to waste a good pattern unfortunately.  But give me this look again...anytime between xmas and March 10...and I will take my chances.  

Don’t look now but there is a slight pivot to a more N/S Orientation on our radar, and snow is picking up here with occasional pingers mixed in. 

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4 minutes ago, ErinInTheSky said:

People are skidding all up and down Blunt Road near me and it's so unfortunate. That road is a car trap any time we have frozen precip.

Also: Am I the only one that is fine with sleet fests? Like, seeing sleet just filled my heart with joy after the last 3-4 hours of rain. Getting a lot of sleet seems to add some good staying power. One of my most memorable storms was... was it 2017? With the absolute epic sleet bomb 3.5" of sleet in Gaithersburg.

Nope I like it if it’s between choosing sleet or zrain because zrain practically never lives up to the hype. Also, one of my favorite all time storms was Valentine’s Day 2007 when we got 7 inches of sleet and froze solid the next day day and didn’t melt for weeks. 

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