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wdrag

Wintry mix potential weekend of Jan 18-19, 2020

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2 minutes ago, Tatamy said:

I am seeing visibility’s of less than 1/4 mile on traffic cameras just west of Allentown right now.

Reading at 10 AM is reporting Heavy Snow

READING        HVY SNOW  21  18  88 S7        30.50R VSB 1/4 WCI  12    

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Wind changed from NNW to ESE here in Suffolk county
Temps inching up steadily from 19 degrees at 5 AM to 24 degrees now

Sent from my SM-N975U using Tapatalk

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1 hour ago, Allsnow said:

Final call 

KNYC 2

KEWR 3

KLGA 1.5

KJFK .9

KBDR 4 

 

I like the call.

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For what it's worth....  I've added the thermal profile for LGA from there 12z NAM. Some forecasters get concerned about Ice Pellets (IP) once the temp aloft nudges zero. In this case at about 22z, there is a modeled hint of IP  before upward motion and wet bulbing may cool the sounding enough to permit snow til about 0030z. The sfc temp may not be cold enough to support much if any additional accumulation after 00z. 

Also RGEM from the 12z run is slightly warmer aloft and seems like less qpf in NJ.

Hope am wrong about the warming aloft trends.

 

I've added the Sparta NJ hourly type for any forum members in nw NJ.  Hope it's right about only 1 hr IP.

 

Walt 1530z/18

 

 

 

 

Screen Shot 2020-01-18 at 10.23.18 AM.png

Screen Shot 2020-01-18 at 10.19.16 AM.png

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4 minutes ago, purduewx80 said:

The models unanimously weaken that fronto forcing between 700-500mb where the DGZ is, so if this is correct, +SN may not make it into the area this afternoon.

floop-rap-2020011814.500hvv.conus.gif.c40ecf72f1f1d6b33a86293a1885218c.gif

 

Yeah, looking likely that will weaken by the time it gets here.  We'll get some light to moderate stuff early, then main precip shield in that late afternoon/evening window.   

 

SE wind is helping to moisten the column a bit already though, it won't totally fizzle even if best fronto forcing is the west. 

 

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11 minutes ago, purduewx80 said:

The models unanimously weaken that fronto forcing between 700-500mb where the DGZ is, so if this is correct, +SN may not make it into the area this afternoon.

floop-rap-2020011814.500hvv.conus.gif.c40ecf72f1f1d6b33a86293a1885218c.gif

Hopefully the same the dry air helps us stay snow as the main slug comes in later this afternoon 

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1 minute ago, NittanyWx said:

Yeah, looking likely that will weaken by the time it gets here.  We'll get some light to moderate stuff early, then main precip shield in that late afternoon/evening window.   

SE wind is helping to moisten the column a bit already though, it won't totally fizzle even if best fronto forcing is the west. 

Agreed - I like the ~6-8PM window for potential +SN in northern Queens/LI, Manhattan, CT and points north.

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1 minute ago, purduewx80 said:

Agreed - I like the ~6-8PM window for potential +SN in northern Queens/LI, Manhattan, CT and points north.

Isn't there a mix/rain risk at that time though?

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3 minutes ago, ILoveWinter said:

Isn't there a mix/rain risk at that time though?

Walt's post above addresses this. Parts of the 5 boroughs may see some mixing prior to going back to mdt/hvy snow, but I think this (mix/rain) is most likely in SI, BK, southern Queens/LI due to the rapidly increasing LLJ off the relatively milder ocean. For now most of the soundings support this scenario. 

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NAM and HRRR actually give Long Island more snow than northern Jersey now. Doesn't make much sense since LI was supposed to get less due to warming. Models have suddenly cut way back for my area, showing closer to 1 inch. Bad trends here at the last minute for this area. I know people say it doesn't matter because it's nowcasting time, but models are supposed to be more accurate the closer they get to an event. So they should be more accurate now than they were last night, but it's hard to believe LI could get more than northern NJ in this kind of setup.

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1 minute ago, winterwx21 said:

NAM and HRRR actually give Long Island more snow than northern Jersey now. Doesn't make much sense since LI was supposed to get less due to warming. Models have suddenly cut way back for my area, showing closer to 1 inch. Bad trends here at the last minute. I know people say it doesn't matter because it's nowcasting time, but models are supposed to be more accurate the closer they get to an event. So they should be more accurate now than they were last night, but it's hard to believe LI could get more than northern NJ in this kind of setup.

Short-term model guidance is part and parcel of "nowcasting" IMO. Otherwise it's just called looking at radar loops. 

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2 minutes ago, winterwx21 said:

NAM and HRRR actually give Long Island more snow than northern Jersey now. Doesn't make much sense since LI was supposed to get less due to warming. Models have suddenly cut way back for my area, showing closer to 1 inch. Bad trends here at the last minute for this area. I know people say it doesn't matter because it's nowcasting time, but models are supposed to be more accurate the closer they get to an event. So they should be more accurate now than they were last night, but it's hard to believe LI could get more than northern NJ in this kind of setup.

Nam looked good for nnj. 3k nam was a sleet fest. Gfs still has 2-3 as we flip to mod snow between 6-8pm 

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6 minutes ago, Allsnow said:

Nam looked good for nnj. 3k nam was a sleet fest. Gfs still has 2-3 as we flip to mod snow between 6-8pm 

12z NAM is giving nnj only about 2 inches now while it gives parts of Long Island 3 inches. But yeah, GFS does look much better for our area. NAM, RGEM and HRRR give us only 1 to 2 inches here now though. A cutback from what they were showing last night and I find it odd that some models are now giving LI more snow than our area. Hopefully GFS is correct for us.

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The radar looks to me like it's filling in down in western Maryland and that looks like what's moving towards us. Hopefully any lull isn't too long.

 

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As this burst of snow progresses to the east it looks like the snow has shut off in the Harrisburg PA area where earlier it was snowing hard.  This aligns with model progs calling for a break in the precip for a time during the day in many areas.

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39 minutes ago, wdrag said:

For what it's worth....  I've added the thermal profile for LGA from there 12z NAM. Some forecasters get concerned about Ice Pellets (IP) once the temp aloft nudges zero. In this case at about 22z, there is a modeled hint of IP  before upward motion and wet bulbing may cool the sounding enough to permit snow til about 0030z. The sfc temp may not be cold enough to support much if any additional accumulation after 00z. 

Also RGEM from the 12z run is slightly warmer aloft and seems like less qpf in NJ.

Hope am wrong about the warming aloft trends.

 

I've added the Sparta NJ hourly type for any forum members in nw NJ.  Hope it's right about only 1 hr IP.

 

Walt 1530z/18

 

 

 

 

 

 

Walt - I know you know a ton more about meteorology than I do, but I have a ton of knowledge about heat transfer/physical chemistry (PhD in chem eng'g) and I'd quibble with one point in your post.  Once there is a layer of frozen precip on the ground (and there will be) the 2M surface temp becomes largely irrelevant to whether falling snow will accumulate at the surface, since the "actual surface" is snow, which, by definition, has a maximum temp of 32F and can't ever get warmer than that (will melt at 32F).  If you're talking about bare paved surfaces (plowed or treated), then the actual surface will quickly warm to the 2M surface temp and further snow accumulations on the paved surfaces could be more difficult, unless, of course the falling snow rate exceeds the melting rate at the surface and with moderate snow or heavier, that will occur, as melting rates after dark at 33-34F should be <1/4" per hour.  

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