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February 19-20th Threat - STORM MODE


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2 minutes ago, mattb65 said:

Who is calling for 3 inches of sleet or 0.25 inches of FZRA???

This one is looking like a standard slop storm - 2-4" for most with some boom potential if rates come in hot and heavy followed by pingers for a while then a little ZR then rain overnight.

Do you think this is going to snow for 3-5 hours then go straight to rain? Is that your call?

 

A sleet period of hours and hours is not all that common around here. Areas near the metros will have rain mix in and take over earlier. It isn't going to bomb sleet for hours, IMO. That is a rare thing around here. This isn't New England. Maybe that stuff happens up there. I don't think calling for some snow, wintry mix for a little while, then mostly rain is a bold call for DCA, especially during the day with a lame airmass...

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Just now, mattb65 said:

Who is calling for 3 inches of sleet or 0.25 inches of FZRA???

This one is looking like a standard slop storm - 2-4" for most with some boom potential if rates come in hot and heavy followed by pingers for a while then a little ZR then rain overnight.

Do you think this is going to snow for 3-5 hours then go straight to rain? Is that your call?

 

I would suppose it depends on what area you are in.  Some areas close to the bay/east of 95 could go from snow to rain.  I don't think the majority of the subforum does.  Some will never go to straight rain like psu. But Phin is right that the surface is not that cold.  Cold for sure for not like it would take a huge jump to go to plain rain with some influence of the city or bay.  its nowcasting all the way so no reason to debate it now. 

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8 minutes ago, jayyy said:

What? As somebody who grew up just NW of NYC in the suburbs just west of the Hudson River, going from snow to rain is extremely common in marginal situations, especially in the later parts of winter. We are expected to hit 60 Thursday, unsure how it’s riridulous that we go to rain with a storm that’s tracking very far to our NW

Dca/bwi are not forecasted to to get above 40 on Thursday by the fv3, gfs, nam 3k, or nam12k. Euro, icon and cmc get us into upper 40’s - low 50’s. 

 

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4 minutes ago, PhineasC said:

A sleet period of hours and hours is not all that common around here. Areas near the metros will have rain mix in and take over earlier. It isn't going to bomb sleet for hours, IMO. That is a rare thing around here. This isn't New England. Maybe that stuff happens up there. I don't think calling for some snow, wintry mix for a little while, then mostly rain is a bold call for DCA, especially during the day with a lame airmass...

Well I think you need to adjust your previous posts - you seemed to indicate a transition Snow straight to Rain is what you expected.

I think most agree with what you said in this post it'll be snow then pingers - duration TBD - NAM/Euro suggest only a few hours before going to ZR/Rn, other models suggest maybe a bit longer. With strong WAA like what is modeled and a retreating HP, I agree that a long duration pinger fest isn't all that likely.

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7 minutes ago, DCTeacherman said:

Wow at the HRPDPS, what a beatdown.  Night and at between the Canadian mesos and the NAMs.  Anyone have 6z Euro?

Is it ever. Even saw some purple on there indicating really heavy snow falling for a short period in Central MD. Very rarely see that show up on models. Sign me up for that.

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2 minutes ago, mattb65 said:

Well I think you need to adjust your previous posts - you seemed to indicate a transition Snow straight to Rain is what you expected.

I think most agree with what you said in this post it'll be snow then pingers - duration TBD - NAM/Euro suggest only a few hours before going to ZR/Rn, other models suggest maybe a bit longer. With strong WAA like what is modeled and a retreating HP, I agree that a long duration pinger fest isn't all that likely.

Yes, the depth of the warm layer increases rather quickly (see the cross-section animation below). The surface is usually the slowest to warm in these types of events with strong HP/ageostrophic low-level flow of cold air.

Guidance from the 06z 3-km NAM shows forcing along the frontal surface decreasing in height with time; the greatest frontogenesis over our area is around 600 mb at ~12z, and the frontogenesis weakens and decreases in height with time (tracing the frontal surface). The dry air present at the low levels ahead of the precipitation makes me question if the more intense (>1-2"/hr) snowfall rates will occur beyond a brief period, especially as the forcing weakens after 12z.

nam3k_xsec.thumb.gif.84857aa631690002d62cc6f4f7e72b6f.gif

By the way, the cross-section feature from Tropical Tidbits is fantastic!

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3 minutes ago, jewell2188 said:

I think most can agree 2-4 inches is a good call area wide. Kinda reminds me of the mid November snow we had....I think totals ranged from 1-3 with some 4 inch amounts before it change to sleet and rain eventually. 

depends on your location -- 95 and east stayed below 4", then it went 4-6+" up to the PA line. 

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6 minutes ago, jewell2188 said:

I think most can agree 2-4 inches is a good call area wide. Kinda reminds me of the mid November snow we had....I think totals ranged from 1-3 with some 4 inch amounts before it change to sleet and rain eventually. 

I agree with you yet LWX says 4-6 for me so I’ll hug that.  

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16 minutes ago, mappy said:

depends on your location -- 95 and east stayed below 4", then it went 4-6+" up to the PA line. 

I had 7” here. There were some 8” totals along the PA line just to my west.  I missed the storm though stuck in Baltimore trying to get home in god awful traffic and road conditions. 30 was a mess!

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Euro doesn’t have one consolidated band. It sends waves. An unitial band comes across VA to DC. Then another across MD and into PA. There is “some” minimum between the two that you can see there but the two thumps overlap enough that no one gets screwed too bad. As a result there is no 8-10” area but a very big area of 4-6”. Not a bad idea. 

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2 minutes ago, psuhoffman said:

11C2EADC-6876-4AFF-8218-37B071987CDB.thumb.png.6c232c5144fdc409d16279d566fdbe08.png

Checking temps, we (DC) are at 0C at 700 by 15z so its really only a few hours of snow before we flip to sleet (I think I read yesterday we want -2c 700 temps for snow).  NE MD holds on until 18z at 700.

 

EDIT: We don't lose the surface until 21z in and near the city.

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Just now, LP08 said:

Checking temps, we (DC) are at 0C at 700 by 15z so its really only a few hours of snow before we flip to sleet (I think I read yesterday we want -2c 700 temps for snow).  NE MD holds on until 18z at 700.

As others have stated, and i have noticed with these setups, the warm push above the surface comes faster than modeled and the cold at the surface moves out slower than modeled, so I believe it. 

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2 minutes ago, DCTeacherman said:

As others have stated, and i have noticed with these setups, the warm push above the surface comes faster than modeled and the cold at the surface moves out slower than modeled, so I believe it. 

All of the snow in DC and northern VA comes with that initial wave between 5am and 11am.   On the euro at least. 

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Just now, psuhoffman said:

All of the snow in DC and northern VA comes with that initial wave between 5am and 11am.   On the euro at least. 

It's nice to see the euro on board with it finally with what other guidance had been showing (To a degree).  I agree with DC, we will go to sleet faster than any model shows so we will need to maximize what window we have.

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Saw mention of the freezing rain accumulation with temps near freezing .......... no, it won't accumulate on roads, or even hard surfaces many times, but as we saw out here last week out here, it can accumulate easily on trees and power lines.  We had temps right around the 30-32 degree mark (KOKV reported 32 the whole time) and ice was able to accumulate to 1/3 - 1/2" on trees and power lines.  Many trees down and thousands without power for over 24 hours.  So hopefully when we transition it's to sleet then to rain.

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4 minutes ago, WinterWxLuvr said:

Saw mention of the freezing rain accumulation with temps near freezing .......... no, it won't accumulate on roads, or even hard surfaces many times, but as we saw out here last week out here, it can accumulate easily on trees and power lines.  We had temps right around the 30-32 degree mark (KOKV reported 32 the whole time) and ice was able to accumulate to 1/3 - 1/2" on trees and power lines.  Many trees down and thousands without power for over 24 hours.  So hopefully when we transition it's to sleet then to rain.

Just drove out that way this weekend.  Headed west to Petersburg WV from Winchester.  The tree damage was pretty serious in the elevated valleys....There were areas where almost every tree was topped off.  I'm sure it looked like a war zone out there...

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2 minutes ago, Hyphnx said:

Rain switch over seems to be happening around 4pm. Ice looks to be a threat more so than before. I think the models are picking up on the CAD

in RIC?  so you are frozen until that point?  interesting I wouldn't have thought that.  location dependent there too for sure. 

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