00z Runs looking MUCH better for snow in the deep south

[Valkhorn]

The following images show nice vorticity maxing out in sub freezing air at 850mb and at the surface around Central MS:







At 84 hours the vort max has moved towards central AL, and light wintry precip continues in the central gulf states:







24 hour Precip totals show a possibility of .50 inches of water equivalent precip over this area, so my guess is they might start as rain, but towards the end the snow may burst a little.



Surprise events have happened here before, and I wouldn't be surprised if there was accumulating snows in MS or AL all the way to I20 somewhere.

I'm analyzing the other models right now that have initialized for this timeframe. I'll post the findings in this thread.

[Valkhorn]

The ETA is backing off on it for 00z, but then again I doubt it's going to handle this southern branch feature too well at that range.



However that model has the 850mb freezing line hovering around in an odd area so a few degrees either way would make a large difference.

The Navy Nogaps has the cold core deepening into texas as this timeframe, so at least the chance for central texas wintry precip is getting very good.

[Valkhorn]

As an interesting note take a look at the brutal 474dm heights north of New England for Monday



Of course it is the GFS, but the -40C line is there north of Vermont.

If only this polar vortex could phase with that gulf storm we'd have something incredible.

[Stormsfury]

The 00z ETA run, frankly, looks quite odd ... and has drastically jumped off prior runs (12z and 18z runs) and is pronouncely drier with this current system ... possibly a hiccup, but I need to review it a little more in-depth to find out what's the issue here ...

I do know the 00z ETA is keeping the stronger UVV's well south on this run with the current system and that's part of the drastic change ...

SF

[FLguy]

the 850mb temps dont mean sh!t. if the column isnt below freezing, ITS NOT GOING TO SNOW. and with thicknesses of 540 or higher ratios will suck plain and simple, add in marginal boundary layer temps, i doubt anything will stick either. any SN changeover which occurs would take place underneath the H5 low.

well have to see at a later time how favorable things are for snow growth, however its likely that the dendritic layer is fairly high, and most of the best RH and omega will probably be below that layer, so its also unlikely that aspect of the event will compensate for the crappy ratios.

IMO this is nothing to get excited about.

[Valkhorn]

Flguy, I'm on the other side of the freezing line, so for you they mean jack, to me they don't...

I don't see why you're such a downer on this

Plus you don't remember or didn't live through the March 93 snowstorm up here when the mets totally screwed up and instead of us getting a mixed precip event with no accumulation to actually getting 8 inches of snow with 12" drifts the morning after.

They've also bombed here back in 1997 with a surprise snowstorm that dumped 6-8 inches around here, as well. If I can remember the forecast was for a high in the mid 50's, and it verified to a high of 34 with heavy wet snow. And, it stuck with an air temp of 34, and the ground was supposedly too warm for snow to stick before (flurries were forecasted the night before).

Surprise 'bombs' from the gulf happen on occasion, and mets have never nailed those. The 'great' one of '62-'63 that brought us 15 inches of snow wasn't even forecasted either.

Deep south snow events are seldom forecasted accurately down here. I can remember too every winter storm watch/warning that was issued 12 hours before the event occuring never verified, but when one was never issued, surprise surprise.

[FLguy]

Flguy, I'm on the other side of the freezing line, so for you they mean jack, to me they don't...

I don't see why you're such a downer on this

Plus you don't remember or didn't live through the March 93 snowstorm up here when the mets totally screwed up and instead of us getting a mixed precip event with no accumulation to actually getting 8 inches of snow with 12" drifts the morning after.

They've also bombed here back in 1997 with a surprise snowstorm that dumped 6-8 inches around here, as well. If I can remember the forecast was for a high in the mid 50's, and it verified to a high of 34 with heavy wet snow. And, it stuck with an air temp of 34, and the ground was supposedly too warm for snow to stick before (flurries were forecasted the night before).

Surprise 'bombs' from the gulf happen on occasion, and mets have never nailed those. The 'great' one of '62-'63 that brought us 15 inches of snow wasn't even forecasted either.

Deep south snow events are seldom forecasted accurately down here. I can remember too every winter storm watch/warning that was issued 12 hours before the event occuring never verified, but when one was never issued, surprise surprise.

ill try to be as nice about this as possible, it does not matter what side of the 850mb 0C isotherm you are on, there can still be layers at or above freezing aloft. given the marginal boundary layer temps, and high thicknesses (5400 or greater) i cant see this being anything more than just a period of low ratio wet snow. ratios will likely be 5 to 10:1 so unless your region pickes up 1-2" of liquid i dont think you will be seeing those types of accumulations. (heres a simple math lesson on ratios: RATIO*QPF = TOTAL SNOWFALL. or 10*0.5=5").

[Valkhorn]

The 00z ETA run, frankly, looks quite odd

It does. It's much drier to the south and much colder to the north.

My guess is it could be taking into account something it didn't see earlier. If there's one consistency with models, it's that they don't see what's really going to happen until it gets immediate. It's approaching the 72 hour mark for the 'snow' event in the deep south and Texas, so that's going to get very interesting. The 72 hour mark for the polar vortex north of Montreal is coming up in a day or so so that could get interesting as well. The vortex doesn't have to be on top of NYC for the city to flirt with record lows.

[FLguy]

and you can look at partial thicknesses, (1000-850mb and 850-500mb), have those IMPLY snow, but after taking a look at soundings, lets say (for example) you see an above FRZ layer at 825mb.

then the question becomes the depth of the warm layer below it, which will determine IP from ZRA.

SOUNDINGS ARE THE MOST EFFECTIVE WAY TO DIAGNOSE PRECIPITATION TYPE. BOTTOM LINE --- END OF STORY.

[Valkhorn]

Well low ratio snow is all we will ever get in the deep south. Do you honestly think other than the flurries of Feb '96 we got any ratios greater than 10:1? This is the deep south, not Siberia. We hardly ever get below 17 on average each year. We're not going to be getting any arctic ratios anytime soon here. March of '93 was low ratio down here, December of '97 was as well. However the QPF's were just enough to give significant snowfalls.

You forget down near the gulf our precipitable water values are usually a lot higher on average than places to our north, as well. Last year we got 74" of rain alone, and so far this month we're already 3 inches ahead of schedule.

My gut still says the mets won't handle this properly, they never do with a thing like this.

In addition, it wouldn't take but an extra burst of precip to tag another inch or two onto the totals.

In addition the 'soundings' don't have a resolution high enough to say 100% one way or the other what will happen. Two degrees either way is all it might take with this, and that is less than one isobar on the map, heights or C lines.

[FLguy]

The 00z ETA run, frankly, looks quite odd

It does. It's much drier to the south and much colder to the north.

My guess is it could be taking into account something it didn't see earlier. If there's one consistency with models, it's that they don't see what's really going to happen until it gets immediate. It's approaching the 72 hour mark for the 'snow' event in the deep south and Texas, so that's going to get very interesting. The 72 hour mark for the polar vortex north of Montreal is coming up in a day or so so that could get interesting as well. The vortex doesn't have to be on top of NYC for the city to flirt with record lows.

no but a fresh snow pack, and optimal conditions for radiational cooling would be a BIG, BIG help. clear skies, light winds, etc...

oh and those dashed lines on the 6-hr precip figures are NOT height lines they are thicknesses.

[Valkhorn]

I stand corrected, thicknesses, but it's still pretty darned cold either way you slice it, or whatever name you call it.

[FLguy]

Well low ratio snow is all we will ever get in the deep south. Do you honestly think other than the flurries of Feb '96 we got any ratios greater than 10:1? This is the deep south, not Siberia. We hardly ever get below 17 on average each year. We're not going to be getting any arctic ratios anytime soon here. March of '93 was low ratio down here, December of '97 was as well. However the QPF's were just enough to give significant snowfalls.

You forget down near the gulf our precipitable water values are usually a lot higher on average than places to our north, as well. Last year we got 74" of rain alone, and so far this month we're already 3 inches ahead of schedule.

My gut still says the mets won't handle this properly, they never do with a thing like this.

In addition, it wouldn't take but an extra burst of precip to tag another inch or two onto the totals.

In addition the 'soundings' don't have a resolution high enough to say 100% one way or the other what will happen. Two degrees either way is all it might take with this, and that is less than one isobar on the map, heights or C lines.

it does not matter, and if the best omega and RH arent within the -12 to -15C portion of the column, flurries is all you are going to have. you fail to remember that if those two features arew below that critical layer, your not going to see big snowflakes. those three things which MUST coincide with one another in order for ratios to max out in an environement where temps are marginal.

also the march 1993 suprestorm was characterized by strong UVM throughout a deep layer of the atmosphere. thus the reason why you saw those kind of snowfall rates and that type of snowfall growth.

now one has to consider CI or CSI. elevated CAPE in the sounding, dry adiabatic lapse rate, and steep theta-e drops w/ height would help bholster the situation, and strongly argues for convective instability, and better precip efficiency.

[Valkhorn]

Here's something interesting of our late southern branch systems that have been plowing through here. Of course you live in Daytona Beach so you're not in the path of all this, but I'll give you a synopsis.

Last week before the 4-7 inches of rain we got here locally (with some confirmed tornado touchdowns) there wasn't (a) significant severe weather mentioned 12 hours before the event (b) any tornadic weather mentioned 6 hours before the event (c) any QPF totals greater than 3 inches predicted by the NWS about 36-48 hours before the event.

With this current soaker we're getting, (a) within 24 hours of the event the two inch rain totals we're creeping up on were not even hinted at (b) the main corridor of rain 24 hours beforehand was 150 miles to the south of where it is now and (c) the energy derived in this system wasn't even known or on the models in its full form until about 36 hours before said event.

The GFS is going to waffle around, but the trend is there. It usually always underdoes southern branch features (its one of its weaknesses) this far out, so I would definately expect it to be a little wetter, and with an upper level disturbance a little stronger and a little wetter the evaporative cooling will be much more significant.

[FLguy]

i will say though ---- thicknesses of 4680 underneath the PV are down right EVIL.

[Valkhorn]

Sorry if I'm sounding a little angry, that's not my intention. But, lately it is becoming aggrivating how these weak southern branch systems get more and more wretched before they occur, and the local mets here just shrug their shoulders and turn the other way.

These southern branch systems have had one thing in common in this pattern and I don't see it waffling any time soon. That is that they always are ending up much wetter than originally forecast.

[FLguy]

Here's something interesting of our late southern branch systems that have been plowing through here. Of course you live in Daytona Beach so you're not in the path of all this, but I'll give you a synopsis.

Last week before the 4-7 inches of rain we got here locally (with some confirmed tornado touchdowns) there wasn't (a) significant severe weather mentioned 12 hours before the event (b) any tornadic weather mentioned 6 hours before the event (c) any QPF totals greater than 3 inches predicted by the NWS about 36-48 hours before the event.

With this current soaker we're getting, (a) within 24 hours of the event the two inch rain totals we're creeping up on were not even hinted at (b) the main corridor of rain 24 hours beforehand was 150 miles to the south of where it is now and (c) the energy derived in this system wasn't even known or on the models in its full form until about 36 hours before said event.

The GFS is going to waffle around, but the trend is there. It usually always underdoes southern branch features (its one of its weaknesses) this far out, so I would definately expect it to be a little wetter, and with an upper level disturbance a little stronger and a little wetter the evaporative cooling will be much more significant.

first of all ---- when dealing with evap cooling, some of the QPF goes into saturating the column SO THAT YOU CAN GET PRECIP. the more time it takes to eat through the dry layer, the less QPF will accumulate at the surface.

and since obviously im not the forecaster at any one of your local NWS officies, i cant comment on that.

[FLguy]

Sorry if I'm sounding a little angry, that's not my intention. But, lately it is becoming aggrivating how these weak southern branch systems get more and more wretched before they occur, and the local mets here just shrug their shoulders and turn the other way.

These southern branch systems have had one thing in common in this pattern and I don't see it waffling any time soon. That is that they always are ending up much wetter than originally forecast.

well i dont shrug my shoulders at any event. be it a tropical system, winter storm or tornado outbreak, wildfire, noctilucent clouds, whatever. i look at everything.

[Valkhorn]

Well I remember three weeks ago the snows in NC were grossly underestimated. There was a lot of evaporative cooling, but the moisture content was enough that it knocked the temp all the way down to a dewpoint of 17 degrees in Greensboro around the 25th from a high the previous day of 60. That's very interesting, and that's a lot of moisture to do that. There was some CADing going on as well, but I remember the radar returns out of Chattanooga before the event, and the line between virga and heavy rain was pretty sharp the night before.

[Stormsfury]

Sorry if I'm sounding a little angry, that's not my intention. But, lately it is becoming aggrivating how these weak southern branch systems get more and more wretched before they occur, and the local mets here just shrug their shoulders and turn the other way.

These southern branch systems have had one thing in common in this pattern and I don't see it waffling any time soon. That is that they always are ending up much wetter than originally forecast.

Now I can attest to the validity of that ... and yes, the southern stream systems that do get an efficient tap of GOM moisture are quite moisture laden ... and IF they have the subtropical feed, even more so ... The moisture tonight, has had to go through a bit of evapo cooling tonight, and

The 00z ETA seems too dry.
The 00z GFS seems to be ok with QPF's.

So far, I haven't really seen too much in the way of strong convective precip as of yet. Sometimes, especially the GFS sometimes can mishandle QPF's becuase of convective feedback, which right now, I'm not seeing on the outputs this go around ... and the temperatures have responded by falling down to 44º here tonight (and finally more sustaining light rain) ...

Actually, I stand corrected, I'm seeing a couple of strong bands of convective precip on the national radar loop setting up across South Central Louisiana and another band right around Southern MS/AL ...

SF