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PHL Jan 17-19 Snow/Ice/Rain Storm Obs


am19psu

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Yes i am 5 miles NW of Baltimore City and it is snowing a little heavier than light right now.

It is also alot colder then i thought it would be it is 25.7 right now.

That's very interesting. Any mets feel like chiming in?

Even the latest HRRR only has precip as far north as the lower Potomac at 01z:

1ref_t3sfc_f02.png

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7:00pm Monday update:

I really think some forecasters are underplaying this event. It's really a classic set up for an icy mess. Temperatures didn't hardly rise today...a sign of the strong cold air damming in place across the region. Also, dew points remain in the singles and teens early this evening, so the air will cool a bit more when precipitation arrives. Still looks like light snow will develop by mid-evening, and become steady before midnight. An inch or two of snow is possible, but the bigger concern is ice build-up on trees, powerlines, and untreated roads...later tonight into midday Tuesday. A 1/4" of ice (perhaps more in spots) is possible by mid-morning Tuesday, as temps only slowly rise towards 32 degrees. The steady precip will likely end around Noon, and so mos--or all--of the event will occur with below freezing temps. Thus, my concern for a pretty significant event the next 18 hours...one that I think deserves a Winter Storm Warning from the NWS (we are only in a lesser "Advisory", though).

http://snowball.mill...Discussion.html

Interesting be curios how this all plays out tomorrow.

Just read that on the Millersville site. Currently 24 degrees in Lancaster with a dew point of 12. It looks to get real ugly over night.

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That's very interesting. Any mets feel like chiming in?

Even the latest HRRR only has precip as far north as the lower Potomac at 01z:

Typical models and their inability to accurately forecast the onset of warm advection precip... Its not uncommon for it to start earlier than progged.

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Those saying media underplaying, I disagree. Once the mid levels go above freezing we'll see a period of IP, but when it goes over to ZR, I suspect a lot of places won't have as big of an issue with ice accum. Even with surface temps upper 20s to low 30s, the latent heat exchange from heavy rain fall will mean less accum ice then many here are thinking.

Any mets care to comment?

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Typical models and their inability to accurately forecast the onset of warm advection precip... Its not uncommon for it to start earlier than progged.

I've been hearing about that possibility all day, but I didn't think it would start 4 hours early. I was thinking more like 1-2 hours.

Now let's see if it actually holds together...

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Those saying media underplaying, I disagree. Once the mid levels go above freezing we'll see a period of IP, but when it goes over to ZR, I suspect a lot of places won't have as big of an issue with ice accum. Even with surface temps upper 20s to low 30s, the latent heat exchange from heavy rain fall will mean less accum ice then many here are thinking.

Any mets care to comment?

I'm not a met (but I did stay at a Holiday Inn Express last night!) but using my trusty ol' HRRR, I see rather light precip falling around 08z (3am).

Also by this point, 850's and 925's have cleared the PA TPK, so it would be ZR already.

1ref_t3sfc_f09.png

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Just read that on the Millersville site. Currently 24 degrees in Lancaster with a dew point of 12. It looks to get real ugly over night.

Feb, I also think that it could get real nasty tonight into tomorrow around here. Like Horst said earlier, the temps didn't budge at all today...once precip starts we should also drop a few degrees. in events in the past when temps are this low and the majority of precip falls over night, they typically don't rise as fast and we tend to last longer on the frozen side...i'm thinking we see a real messy morning commute tomorrow.

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I've been hearing about that possibility all day, but I didn't think it would start 4 hours early. I was thinking more like 1-2 hours.

Now let's see if it actually holds together...

Eh... I know in a later post you said you were following the Meso's... but the GFS and NAM have both been saying that it would start around TTN between 10PM and midnight.

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you can tell we are dealing with an eroding airmass. Not much virga at all. Actually would of been nice to see some virga.

There usually is not alot of virga with these as you get closer to the coastal areas because the easterly flow ahead of it often gives you enough saturation...virga could kill you to an extent in an event like this since you are strapped for time as far as getting frozen precipitation even though it could indicate as you say you have a fresher cold air mass.

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There usually is not alot of virga with these as you get closer to the coastal areas because the easterly flow ahead of it often gives you enough saturation...virga could kill you to an extent in an event like this since you are strapped for time as far as getting frozen precipitation even though it could indicate as you say you have a fresher cold air mass.

I don't want too much virga as we need to get the snow in before 850s warm. Also, the airmass is plenty cold up here, I'm at 23.4/12 so should be seeing a good bit of evaporational cooling when the snow arrives.

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