Absolute Vorticity

For Tues night and Wed of next week... most models want to track the low right over us. We will start as snow, go over to rain, then receive back end snow showers. At this early stage of the game, timing wise, snow should move in after midnight Tues night, change to rain on Wed from South to North, then back to snow shower activity for Wed night. Snow showers will continue on Thurs as well. This is a strong system and a longer duration event. There is still a chance that the track can shift around. Another 50 miles south, more snow for everyone. 50 miles NW more rain for everyone. Currently, I cannot ignore the data, so this system will probably track over us unless that changes. The way it can change? Get a later phase going. That's what we would need to have happen. Could it? Low chance IMO but the chance certainly isn't dead.

Good Morning Les and not many changes overnight for the system on Sunday. You made the best point and that is how heavy is the precip and we need that for several hours to put down some accumulation. Will wait for the mid-day runs but still believe some folks get that 1-2 inches of slush while folks to the southeast will get a touch of snow early then quickly to rain and end as snow.

Concerning the mid-week system and this one is interesting as there is some decent cold air around and though not perfect at this point a Snow-Rain-Snow outcome is possible. How long though is it raining during the storm for different areas. The track of this system is big and we can say that about plenty of storms. No forecast yet and though models are somewhat close on the track the thermals of the storm are tricky even with the more westerly track. Will talk about this more later and see what the models are showing and not even sure if the piece of energy has entered the west coast.

The storm should end as snow and no doubt could see a little accumulation from that and then a decent shot of cold for late week and next weekend.

Good morning Tim! Maybe you should create thread for next week's system? It does deserve one IMO. Now looking beyond that system, more snow is possible on Friday from a totally separate system dropping in on NW Flow. We have quite an active week ahead of us. Looking even further, late Jan and early Feb, the GFS wants to keep the fun and games going with cold and snow chances while the Euro continues the warmer look with better chances for rain. An interesting model pattern showing up and the potential for either an overrunning situation is there or another big ticket southern stream system. At least we've got a lot to talk about!

Les I will wait because it seems like bad luck when we pin to early lol. Has the pattern changed enough for winter weather and the answer is yes. The cold air that resided on this side of the globe for much of December has been gone for about 2-3 weeks is returning. Can we tap that cold is the main question and at the moment it looks busy as several troughs look to form over the central and hopefully eastern USA. Longer term and we see the gfs and euro going in different directions so that is another area we will need to visit after we get through next week. Will the PV be disrupted and if so how does that look for winter weather here later in February.

Fair enough Tim! I can't blame you. There are several things to watch for next week's system:

1) Energy should start to get sampled by Sunday afternoon / evenings models.
2) Watch for trends at 500 MB to see how much the energy digs over the SW US. The more it digs, the harder time it will have coming more north and west.
3) Degree of phasing and wave interaction will determine how fast or slow the low pressure system deepens. As always, the faster it deepens the more NW it will cut. A weaker system will track more SE.
4) Trough orientation. A negatively titled trough will allow the low to deepen rapidly where a positively tilted trough would allow for a much weaker system.
5) Watch for more energy dropping into the trough via NW flow. There are several pieces of energy with this system. You've a piece of energy dropping in to create widespread snow shower activity on the backside Wed night and Thurs. Then a separate feature for Friday. A messy set up like that depending on how the wave spacing is, can also impact how this system evolves and develops.

Great Post Les. Plenty of action on the table. A great point about whether we get a negatively tilted trough. Sure it would provide for a bigger system and stronger system but where this happens is key. I tend to use the Mississippi River as a dividing point and no its not perfect but at least it gives a point on the map I can easily see. I guess the excitement shows with this storm because the only true winter system we had was the one before Christmas.

Would love to see this trend continue today. Below are the SLP Clusters from the various ensembles. GEFS, GEPS (Canadian), and EPS. Note how the SLP clusters are a bit south from previous runs.

0Z GEFS vs 6Z GEFS


18Z EPS from last evening vs 0Z EPS. 6Z not out yet on freebie sites.


12Z GEPS from yesterday vs 0Z GEPS. It is only run twice a day.

tpweather wrote: ↑Sat Jan 21, 2023 8:31 am Great Post Les. Plenty of action on the table. A great point about whether we get a negatively tilted trough. Sure it would provide for a bigger system and stronger system but where this happens is key. I tend to use the Mississippi River as a dividing point and no its not perfect but at least it gives a point on the map I can easily see. I guess the excitement shows with this storm because the only true winter system we had was the one before Christmas.

Definitely Tim! This system is not as strong so no blizzard like conditions are expected. We'll have some wind sure but nothing on the order of that. Also no true arctic air either so we are relying on a true thread the needle situation where the trough stays more positive to neutrally titled to get the right track needed for us. I like your MS River thought as to when things begin to deepen and get more cranked up. That sounds about right to me.

Great Maps Les. The GOM really has not been touched much this year even with all the systems that came into the west coast. Of course once we head into later January through the remainder of winter the GOM is more open for business normally. A shift in this system by just 75 miles can make a huge difference with the outcome. Concerning arctic air and you are correct its just seasonal cold though by the end of the week some decent cold is getting involved. I believe that is why this system is showing a decent shot of snow on the back end of the system and probably a little more than we normally would end up with.

tpweather wrote: ↑Sat Jan 21, 2023 8:42 am Great Maps Les. The GOM really has not been touched much this year even with all the systems that came into the west coast. Of course once we head into later January through the remainder of winter the GOM is more open for business normally. A shift in this system by just 75 miles can make a huge difference with the outcome. Concerning arctic air and you are correct its just seasonal cold though by the end of the week some decent cold is getting involved. I believe that is why this system is showing a decent shot of snow on the back end of the system and probably a little more than we normally would end up with.

I agree... with a couple of additional pieces of energy dropping into the trough, it'll keep the snow shower machine going Wed night, Thurs and even on Friday as well despite what happens on Tues night and Wed with the main system passing thru. Going to be a busy week or two! If we can get a snowpack down or nearby (which should happen) then we may have better chances for wintry vs wet late Jan and into early Feb too. Overall, I'm pretty pleased with what I'm seeing. It is by no means a shut the blinds period at all.

The good thing is we are getting into the Nam output for the next system and this run has the low digging well south from 24 hours ago. Yesterday the low was in northwest Oklahoma compared to the most recent run and the low is in Northern Mexico. Is this a good sign and probably yes but lets see if that trend continues from overnight

Great post Tim! I'm in complete agreement. 540 line is ticking further and further south with each run. Noticed that on the last several GFS runs too. At 72 hours on the NAM, the upper low is just west of El Paso and the surface low is well down into Mexico. This is certainly peaking my interest.

Will be fun to see the afternoon models.

12Z RGEM at 84 hours has the surface low down in S LA and some snow over the Ozarks in NW AR. If we can see just a bit further of a SE tick from that spot, this is going to get rather interesting for next week.

GFS is on the clock. I believe too much NFL on my mind this weekend.

The slight SE tick continues on the 12Z GFS. Still not going to be enough to keep us all snow so the call of snow to rain then back to snow is still valid. I checked DAY and it is mainly frozen precip (sleet and snow) so this could be a good system for ILN's northern counties. Paging Eric... Then everyone gets the back end snow shower machine Wed night into Thurs.

The next shortwave / front dropping in really holds my interest. We've got cold air to work with and the air coming in behind it is arctic in nature. Could squeeze out a fluffy inch or two to be completely honest. Then, the model has a clipper diving down by next Sunday that phases with a southern stream system. Could be the next big ticket item of interest. Wow... it is sure busy around here! Love it!

tpweather wrote: ↑Sat Jan 21, 2023 10:38 am GFS is on the clock. I believe too much NFL on my mind this weekend.

That's awesome Tim! Your sense of humor is great! I'll need to make a beer run today at some point.

Plenty going on and trying to break it down. First still waiting for the Euro but the Gfs and Cmc continues to move the system further east.. Two reasons right off the bat and first being the storm takes a little longer in gaining strength which keeps it further south for a longer time. Second the models had a rather strong high pressure in southeast Canada and the models could not get the storm to track towards the high so it went north at first before the high moved away. The current models show this high further northeast and not as strong so the storm can head that way sooner so you don't quite get the northern bump.

tpweather wrote: ↑Sat Jan 21, 2023 11:28 am Plenty going on and trying to break it down. First still waiting for the Euro but the Gfs and Cmc continues to move the system further east.. Two reasons right off the bat and first being the storm takes a little longer in gaining strength which keeps it further south for a longer time. Second the models had a rather strong high pressure in southeast Canada and the models could not get the storm to track towards the high so it went north at first before the high moved away. The current models show this high further northeast and not as strong so the storm can head that way sooner so you don't quite get the northern bump.

Great post Tim and to add... I also like seeing it dig more and more into the SW and Mexico before the trough begins to eject. Very important...

tron777 wrote: ↑Sat Jan 21, 2023 11:28 am

tpweather wrote: ↑Sat Jan 21, 2023 10:38 am GFS is on the clock. I believe too much NFL on my mind this weekend.

That's awesome Tim! Your sense of humor is great! I'll need to make a beer run today at some point.

Les I did my beer run on Thursday so I am good to go unless the Bengals game gets to intense then I forget how much beer I have drank because my nerves get out of hand lol. When Hubbard returned that great defensive play into a touchdown that is probably the loudest I have screamed in years.

tpweather wrote: ↑Sat Jan 21, 2023 11:32 am

tron777 wrote: ↑Sat Jan 21, 2023 11:28 am

tpweather wrote: ↑Sat Jan 21, 2023 10:38 am GFS is on the clock. I believe too much NFL on my mind this weekend.

That's awesome Tim! Your sense of humor is great! I'll need to make a beer run today at some point.

Les I did my beer run on Thursday so I am good to go unless the Bengals game gets to intense then I forget how much beer I have drank because my nerves get out of hand lol. When Hubbard returned that great defensive play into a touchdown that is probably the loudest I have screamed in years.

No doubt! Could be the highlight of that man's career! Always good when a hometown boy does good.

12Z Canadian is oh so close! Pull that low SE by 50-75 miles and we'd get nailed! Still... snow to rain then back to snow is exactly what the model shows.

I forgot to look at the UKMET for the system on Wed. the 0Z run had that SE track that we needed and it's a big hit for us! Wow! This model is 2nd in verification scores. Euro 1st. CMC 3rd and the awful GFS is dead last. Waiting on the 12Z UKIE to come out as it's on the clock now.

While we are waiting on the British model, the 12Z GEFS is in and it's similar to the 6Z that I posted earlier. Here's the SLP Clusters Map for the newest run.

Great post Les and like you mentioned just a 50-75 mile further south track and we are in business. Of course 50-75 miles further north and west we are ending up with more rain than snow.

Another nice run from the UKIE. It's a little weaker and even more SE then the 0Z run but the best snows are right up the OH River. 2nd nice run in a row from the UKIE. Interesting...