Absolute Vorticity

tron777 wrote: ↑Mon Jan 23, 2023 4:20 pm

Trevor wrote: ↑Mon Jan 23, 2023 3:59 pm @Les, yay for me being added to the WSW

I’m counting down the days to spring as you damn well know. Wanna trade places until then??

You're the one who chose to move! I knew this was going to happen. You get more snow in the winter but the trade off is better storm chances for severe wx as well. You get the best of both worlds.

I am quite the tornado/severe weather magnet that’s for sure! I’ve lived through three tornadoes; one direct hit (1999), one that was essentially feet away from my house (derecho spinners 2020), and one that touched down a couple miles off campus but the funnel went right over us after it lifted (2010). Lebanon better be ready this Spring

@Les, I’ll hit you up side-bar in a bit to discuss the upcoming storm a bit more.

18Z RGEM doing the odd low track again like the 12Z run. This time, it is E of Memphis to Bowling Green, KY to around Frankfort or Ft. Knox. Then it shoots east over to the KY / OH / WV border then north over Eastern Ohio.

Trevor wrote: ↑Mon Jan 23, 2023 4:26 pm
@Les, I’ll hit you up side-bar in a bit to discuss the upcoming storm a bit more.

Sure! I am working until 5 so if I don't answer you right away that is why.

tron777 wrote: ↑Mon Jan 23, 2023 4:28 pm

Trevor wrote: ↑Mon Jan 23, 2023 4:26 pm
@Les, I’ll hit you up side-bar in a bit to discuss the upcoming storm a bit more.

Sure! I am working until 5 so if I don't answer you right away that is why.

No worries man. Call whenever you’re finished up.

Grab a beer and read the AFD from the boys - Excellent read! They are mentioning (finally lol) many of the things on here that we have been discussing.

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Some breaks in the clouds are moving slowly from central into
eastern Indiana late this afternoon and a few peaks of sun are
possible before sunset especially west of I-75. Shortwave
ridging builds into the Ohio Valley this evening which may aid
in the skies temporarily breaking up a bit more, but as flow
backs to southwesterly ahead of a weak shortwave moving through
Wisconsin and Michigan, low level warm advection will probably
begin adding some moisture and allow for lower levels to remain
quite saturated. There has been some hints in the HRRR/NAM for a
some speckled QPF to show up from time to time, and this is a
manifestation of the low level warm advection omega acting on
the ~1km deep nearly saturated layer. This is a marginal signal
for freezing drizzle, and while it has not been included in the
forecast due to diminished confidence, we`ll need to watch
trends especially along and north of I-70 in the period after
midnight where the omega/moisture overlap is maximized.
Otherwise, any breaks in the clouds over yesterday`s snow packs
could drop temps quickly into the mid 20s, or perhaps even
colder if a longer period of clearing is realized. Right now
this is not anticipated, as it is expected the lower clouds will
hang in and redevelop as the night wears on.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY/...

Quiet weather during the day Tuesday as strong shortwave trough
digs through the base of the longer wave trough to the west and
begins to rapidly eject out into the Ohio Valley by Wednesday
morning. Surface low to slowly deepen as the wave moves through
the Ohio Valley.

Primary concern is the development of an WNW-ESE oriented band
of heavy precipitation on Tuesday night after midnight moving
quickly northeast across the forecast area through Wednesday
morning. This is on the nose of strong low level jet, with
accompanied very strong frontogenetical response and lateral
banding. Forecast soundings suggest that despite tremendous low
level warm advection, that this will be offset by the degree of
vertical motion. Dynamic cooling of arriving warm nose seems to
suggest a 3-5 hour period of heavy snow is likely to cross much
of the forecast area centered on the morning commute. This is
concerning for travel/impacts. This signal right now seems most
centered on southwest Ohio/southeast Indiana, but there is a
trend to involving more of Kentucky with successive receipt of
ensemble and deterministic runs. Have expanded the Winter Storm
Watch collaboratively southward with this forecast cycle, but
starting to feel strongly with late arriving ensemble
information this afternoon that more expansion - and
significantly so - is perhaps needed. While there is some
concern with warm nose walking right up to the 0C line in
forecast soundings that overall warm advection becomes so strong
that sleet/mix may dominate in northern Kentucky which would
greatly limit totals, but regardless, this would still make for
a treacherous morning commute so further shifts will need to
consider an expansion of the watch south into more of the Ohio
River area if ensemble trends hold. This is much less about
criteria - and much more about heavy />1" hour/ rates of
snow/sleet arriving right before and during the morning commute
for a large portion of the forecast area.

So not only do we have some uncertainty about the
magnitude of the warm advection and how this impacts
rates/amounts in this warm advection band, but there is
uncertainty on the path of the low moving through the forecast
area. A track up the west side of the forecast area would mean a
faster transition to rain and warming boundary layer from south
to north on Wednesday, while a track across southern Ohio would
slow this warming and delay improvement especially along/west of
I-71. A very complex storm and forecast adjustments to snow
totals and watch / warning alignments should be expected.

With the main deformation/comma head snows remaining /mostly/
west of the forecast area (west central Ohio and southeast
Indiana will get in on some of this), the primary concern with
this system for our forecast area is centered on this band of
heavy precipitation Tuesday night into Wednesday morning,
especially as it relates to impacts surrounding the morning
commute.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Depending on the speed of the low pressure center, some rain may
linger into the beginning of Wednesday night before colder air
rushes in and provides a full changeover to snow. Moisture will
continue to wrap around the low pressure center, and with subtle
forcing aloft, kept a chance of snow in the forecast through the
remainder of the night. Accumulations at this stage will likely be
limited to a few tenths of an inch to up to a half an inch at the
most. With the tight surface pressure gradient, windy conditions
persist through the overnight.

Snowfall expected to linger through Thursday as models show a
shortwave trough traversing the upper Midwest region. Thermal
soundings also show saturation in the DGZ with just a little bit of
instability, which could produce some pockets of snow showers on
Thursday. Another few tenths of an inch certainly possible on
Thursday given this signa

18Z GFS has a Paducah to IND to Sandusky, OH track. Pretty much like the 12Z, maybe a hair stronger with the SLP. Heck of a front end thump with like 0.80" of QPF at CVG from midnight to 7am! Wow! Then we all get light rain and dry slotted.

I can’t bring myself to post the 10:1, so we’ll roll with Kuchera… 18z GFS

tron777 wrote: ↑Mon Jan 23, 2023 4:59 pm 18Z GFS has a Paducah to IND to Sandusky, OH track. Pretty much like the 12Z, maybe a hair stronger with the SLP. Heck of a front end thump with like 0.80" of QPF at CVG from midnight to 7am! Wow! Then we all get light rain and dry slotted.

Wow 0.80 that is rather impressive. How much are they showing as snow Les. I know the ratios are going to be lower so maybe even 8-1 but if that is all snow we are over 6 inches. I agree there is a big surge of moisture heading north and my main problem with the forecast is how long does that heavier precip hang around.

fyrfyter wrote: ↑Mon Jan 23, 2023 5:07 pm I can’t bring myself to post the 10:1, so we’ll roll with Kuchera… 18z GFS

5CF889E6-7D14-4C17-A83E-818BACA06187.jpeg

There is a map showing a couple of miles makes a huge difference between several inches and nothing.

fyrfyter wrote: ↑Mon Jan 23, 2023 5:07 pm I can’t bring myself to post the 10:1, so we’ll roll with Kuchera… 18z GFS

5CF889E6-7D14-4C17-A83E-818BACA06187.jpeg

NAM coming in with a quick thump of snow to sleet/freezing rain. For the record, the NAM performed badly on the last system. Something to watch.

Will be back on later this evening. One other item is the winds could pick up with this system so this can cause some added problems.

18z GFS looks nice, but if the low gets that's strong ,995mb, warmer thermals would more likely rush in quicker and shorten the 5-6hour window of snow

Trevor wrote: ↑Mon Jan 23, 2023 4:06 pm I haven’t really read and caught up on previous posts on here today due to work and catching up on doing my own forecasting for this to friends and fam, so apologies if anything I say has already been said. I’ll just go on ahead and post the message I sent out in my group chat.

“ Before getting into the upcoming winter storm, let’s talk about the elephant in the room and that elephant happens to be yesterday’s snow and a truly terrible forecast performance by myself, The National Weather Service, and TV meteorologists alike. I had a forecast for 1-3” of slushy snow with minimal travel impacts for reasons I thought were sound and solid at the time. That 1-3” quickly turned into 4-6” with high-level travel impacts for the first part of the day. Failing grade lol! The system came in colder and more moisture-laden than expected. There are other more technical reasons but I’ll save you all from that considering this is already going to be a long post lol. I specially mentioned to a friend Saturday evening that two higher-resolution models were coming in with 3-5” right along 71 but I discounted that data as outliers and said “no way.” Well we saw what happened there .

Moving forward, we have another round of wintry weather in store for tomorrow night and Wednesday. I’ll break it down with bullet points per my classic style back in the day doing updates on my website and social media:

-a period of heavy, wet snow (cement-style, like we saw with the last one) is expected between 3-9am Wednesday morning

-the snow will accumulate rapidly (1” per hour at times)

-temperatures will be marginal (30-32), but we will have maximum accumulation ability given that this will happen before sunrise

-expect 2-5” of accumulation; I would say most in the 275 loop will hit the 3 or 4” mark

-morning commute on Wednesday is going to be a total mess

-temperatures will then rise above freezing by mid morning and any remaining precipitation will change to rain showers or drizzle and roads should improve rather quickly

Having said all of that, I expect all schools across the area to delay on Wednesday, with most probably going with a close due to timing — even though roads should be great by midday.”

Good stuff, Trev, don't beat yourself up over Sunday. It's not like you were alone in missing it, seems it was pretty widespread forecast fail, so obviously that one had a few tricks up its sleeve. Do you see the statement about roads improving quickly carrying as far north as the Dayton area, or will that warmth not make it that far?

All of Tri-State added to Winter Storm Watch. 2-4" across the area.

House of Cards wrote: ↑Mon Jan 23, 2023 6:28 pm

Trevor wrote: ↑Mon Jan 23, 2023 4:06 pm I haven’t really read and caught up on previous posts on here today due to work and catching up on doing my own forecasting for this to friends and fam, so apologies if anything I say has already been said. I’ll just go on ahead and post the message I sent out in my group chat.

“ Before getting into the upcoming winter storm, let’s talk about the elephant in the room and that elephant happens to be yesterday’s snow and a truly terrible forecast performance by myself, The National Weather Service, and TV meteorologists alike. I had a forecast for 1-3” of slushy snow with minimal travel impacts for reasons I thought were sound and solid at the time. That 1-3” quickly turned into 4-6” with high-level travel impacts for the first part of the day. Failing grade lol! The system came in colder and more moisture-laden than expected. There are other more technical reasons but I’ll save you all from that considering this is already going to be a long post lol. I specially mentioned to a friend Saturday evening that two higher-resolution models were coming in with 3-5” right along 71 but I discounted that data as outliers and said “no way.” Well we saw what happened there .

Moving forward, we have another round of wintry weather in store for tomorrow night and Wednesday. I’ll break it down with bullet points per my classic style back in the day doing updates on my website and social media:

-a period of heavy, wet snow (cement-style, like we saw with the last one) is expected between 3-9am Wednesday morning

-the snow will accumulate rapidly (1” per hour at times)

-temperatures will be marginal (30-32), but we will have maximum accumulation ability given that this will happen before sunrise

-expect 2-5” of accumulation; I would say most in the 275 loop will hit the 3 or 4” mark

-morning commute on Wednesday is going to be a total mess

-temperatures will then rise above freezing by mid morning and any remaining precipitation will change to rain showers or drizzle and roads should improve rather quickly

Having said all of that, I expect all schools across the area to delay on Wednesday, with most probably going with a close due to timing — even though roads should be great by midday.”

Good stuff, Trev, don't beat yourself up over Sunday. It's not like you were alone in missing it, seems it was pretty widespread forecast fail, so obviously that one had a few tricks up its sleeve. Do you see the statement about roads improving quickly carrying as far north as the Dayton area, or will that warmth not make it that far?

Thanks man! Yeah Sunday was a “paper bag on head” type day for sure for forecasters

You folks up north with stay cooler longer, so conditions will take a bit longer to improve. But to be honest, temps will be marginal with this system everywhere in our area. Once the sun comes up and the heavier rates subside, it should be quite a quick transition from snowy/slushy roads to wet pavement. Way different than pre-Xmas; no brutal cold air. Salt and plowing should yield clean lots, roads, etc. It’s just going to be a huge pain when it’s coming down!

Several inches of snow is always a pain to remove, especially if it’s the cement type. But temps will be marginal and salt and other road treating chemicals will work very well. Nightmare morning commute expected Wed AM, then clear roads by midday. I guarantee that

Good evening all! Sorry for the delay with me coming back to post. Had a long talk with a great guy, Trev Then I had to get something to eat. But I'm back! I am kind of shocked at the Winter Storm Watch for the Metro. I really wasn't expecting that.

One thing that we need to watch is this... will it be all snow due to heavier precip rates or do we see a lot of sleet which could cut into the snow totals. Trev and I were talking about Sunday which was either rain or snow. There was no transition precip type. We could see that occur with this system so something to keep in mind when you look at QPF totals and the model snow maps. Just wanted to put that out there. Yeah the 18Z GFS has 0.80" of frozen precip for CVG, but I'll betcha that won't be all snow. So we need to be cautious when making our final calls for this storm.

18Z Euro is pretty much a carbon copy of 12Z 0.35" QPF for CVG that falls as frozen before the changeover. Low tracks just a hair SE of Cincy. The thermals to me look awfully sleety so you had better get very heavy precip rates and very strong frontogenic forcing (like we had on Sunday) for this to fall as all snow. Otherwise you may get some sleet in there. Unfortunately, this may boil down to a nowcast. It is so tough this far out 24-36 hours out, for models to get this right.

tron777 wrote: ↑Mon Jan 23, 2023 7:55 pm Good evening all! Sorry for the delay with me coming back to post. Had a long talk with a great guy, Trev Then I had to get something to eat. But I'm back! I am kind of shocked at the Winter Storm Watch for the Metro. I really wasn't expecting that.

One thing that we need to watch is this... will it be all snow due to heavier precip rates or do we see a lot of sleet which could cut into the snow totals. Trev and I were talking about Sunday which was either rain or snow. There was no transition precip type. We could see that occur with this system so something to keep in mind when you look at QPF totals and the model snow maps. Just wanted to put that out there. Yeah the 18Z GFS has 0.80" of frozen precip for CVG, but I'll betcha that won't be all snow. So we need to be cautious when making our final calls for this storm.

Hey Les and that is why I asked that question. Generally the area that ends up with sleet is a more narrow area and sometimes hard to pin down this early. Just happy we are busy compared to the first half of the month. Next week looks just as busy and trends are for colder air to move in but you still have some warmth especially in Florida. Will talk about that in the other thread but love what I am seeing and how the pattern has changed.

tron777 wrote: ↑Mon Jan 23, 2023 7:55 pm Good evening all! Sorry for the delay with me coming back to post. Had a long talk with a great guy, Trev Then I had to get something to eat. But I'm back! I am kind of shocked at the Winter Storm Watch for the Metro. I really wasn't expecting that.

One thing that we need to watch is this... will it be all snow due to heavier precip rates or do we see a lot of sleet which could cut into the snow totals. Trev and I were talking about Sunday which was either rain or snow. There was no transition precip type. We could see that occur with this system so something to keep in mind when you look at QPF totals and the model snow maps. Just wanted to put that out there. Yeah the 18Z GFS has 0.80" of frozen precip for CVG, but I'll betcha that won't be all snow. So we need to be cautious when making our final calls for this storm.

I've been figuring that into the equation all along . We'll lose some qpf in the beginning to a mix/ rain and towards the end of the snow period as well especially near the river.

The two pieces of energy stand out very well with the southern system in southeast New Mexico and the northern piece in eastern Montana. How these two start to dance will make things interesting. A few days back some of the overseas models not grasping on the piece up north and had this low go up the apps. That has changed and the gfs has been the leader of this storm if it goes off as shown on most models this evening.

Like to mention the winds on Wednesday as they could be quite strong. Places that get hit with heavy snow along with strong winds can knock down power lines and tree limbs as well. The good thing about this storm is frz/rain will not be a problem as that would cause more problems. Behind the main system we have more energy moving through that could give us some snow showers Thursday and Friday. Again these are much harder to predict exactly where they will hit but the air will be colder and few stronger snow showers especially later in the day Thursday could cause some slick spots and minor accumulations.

Great discussions going on here Tim and Bgoney. This is a much more complex storm as you both know then what we had on Sunday. High bust potential due to precip type, low track, and warm air advection. Sure glad we don't get paid to do this. It makes busting easier to take.

tron777 wrote: ↑Mon Jan 23, 2023 8:30 pm Great discussions going on here Tim and Bgoney. This is a much more complex storm as you both know then what we had on Sunday. High bust potential due to precip type, low track, and warm air advection. Sure glad we don't get paid to do this. It makes busting easier to take.

I agree Les and this is a much larger storm and of course stronger with tons of moisture from the GOM. Though the system will get stronger as it heads this way it will be moving at a decent clip. I will probably wait until mid-day on Tuesday and even though the models have come to some agreement on the track we have other factors that can bust a forecast. Timing on when you get the heavier burst of precip is important as well and sometimes does not match up exactly like a model may show. Of course having a now cast after midnight is not easy but I seem to be up quite ofter during the night so what the heck.

Here's the new 21Z SREF Plume for CVG. I have posted the precip type map from the run just to illustrate the challenges in forecasting snowfall. This ties in perfectly to Bgoney's post.


What the image shows, for those who may not know is that we start as rain briefly, then change to snow then back to rain then back to snow Wed night and Thurs. So unless you get big time dynamic cooling and very high 700 MB frontogenic forcing like on Sunday, It is going to be tough to see winter storm warning criteria snow at CVG if you believe this model. We've got to keep a close eye on the dynamics of this system. High bust potential here both negatively and positively.

If you want to check a station closer to your own hood, go here. I clicked on p-type POP for the above image.


https://www.spc.noaa.gov/exper/sref/srefplumes/

Great Post Les and snow cover already on the ground. We talked about this a little over the weekend and how it can affect other systems. Snow cover if deep enough and fairly recent can change the baroclinic zone and change the path of the low somewhat. The problem is some of the snow will melt on Tuesday and may be a mute point but yes snow cover can no doubt change the path of systems. Maybe some models picked up on this when you had the sort of weird solutions that went north to a certain extent and then a straight shot to the east.