Absolute Vorticity

fyrfyter wrote: ↑Wed Dec 21, 2022 3:15 pm

BookNerdCarp wrote: ↑Wed Dec 21, 2022 3:04 pm ILN just extended watch and added Advisory. They are not buying higher totals.

They won’t until tomorrow, if it continues with the higher amounts. Always ultra conservative.

I'm being conservative myself with this storm and not changing what I've already said. If we see some more of those 12Z Euro like runs tonight, then ok but I want to see more personally before going all in.

I love the various opinions from the noaa offices, just like the forums

18Z 3KM NAM pretty much has the same idea but with one difference. A nice 5" band right thru the Metro!

tron777 wrote: ↑Wed Dec 21, 2022 3:18 pm No NAM'ing today. 18Z run is similar to 12Z to be honest. A general 2-4" with isolated higher amounts possible for the region.

It kills those higher runs other models are showing around Indy. Is it trying to transfer the energy off the coast?

I went with 2-4 inches for Grant-Owen-on north to the Ohio River on Facebook and 1-3 south of Grant County. It may not end up that way, but me and the hounds are sticking with it.

fyrfyter wrote: ↑Wed Dec 21, 2022 3:23 pm

tron777 wrote: ↑Wed Dec 21, 2022 3:18 pm No NAM'ing today. 18Z run is similar to 12Z to be honest. A general 2-4" with isolated higher amounts possible for the region.

It kills those higher runs other models are showing around Indy. Is it trying to transfer the energy off the coast?

There's a bit of a surface reflection there, but the model isn't really showing a decent low forming at all. What do you think Aaron? You're a techy guy. These models with such an anomalous pattern, may not be fully capable of handling such a dynamic storm system such as this one. With bitter cold Siberian air, a trough going negative tilt with an upper low diving in along with a system along the East Coast trying to inject moisture into this thing. So many moving parts too! there is a limit to the physics and mathematical computations IMO. That makes it that much harder for us to get right. Thus, my conservatism and not going all in right now.

allowat3 wrote: ↑Wed Dec 21, 2022 3:30 pm I went with 2-4 inches for Grant-Owen-on north to the Ohio River on Facebook and 1-3 south of Grant County. It may not end up that way, but me and the hounds are sticking with it.

That's a very fair call Mark. Very reasonable IMO. It's a good blend between some of those higher end runs and some of the usual runs we've been seeing.

tron777 wrote: ↑Wed Dec 21, 2022 3:33 pm

fyrfyter wrote: ↑Wed Dec 21, 2022 3:23 pm

tron777 wrote: ↑Wed Dec 21, 2022 3:18 pm No NAM'ing today. 18Z run is similar to 12Z to be honest. A general 2-4" with isolated higher amounts possible for the region.

It kills those higher runs other models are showing around Indy. Is it trying to transfer the energy off the coast?

There's a bit of a surface reflection there, but the model isn't really showing a decent low forming at all. What do you think Aaron? You're a techy guy. These models with such an anomalous pattern, may not be fully capable of handling such a dynamic storm system such as this one. With bitter cold Siberian air, a trough going negative tilt with an upper low diving in along with a system along the East Coast trying to inject moisture into this thing. So many moving parts too! there is a limit to the physics and mathematical computations IMO. That makes it that much harder for us to get right. Thus, my conservatism and not going all in right now.

That actually makes a lot of sense- a technological limitation. We know weather models run based on availability of data to input, but also at a predetermined time when the mainframe is available for a set time to run the model. There has to be a time limit for each step, so it’s plausible that it cannot fully calculate the frame and the NAM 18z results are a direct correlation to that.

tron777 wrote: ↑Wed Dec 21, 2022 2:23 pm

rhodesman88 wrote: ↑Wed Dec 21, 2022 2:21 pm

tron777 wrote: ↑Wed Dec 21, 2022 2:13 pm Wow! WAVE 3 is going all in with this one! 4-6" for us? Whoa!

Just saw that! Did he say the 12z Euro is SE???

Yes, and we did on here too.

I see that now! Playing catch up on all the posts!

fyrfyter wrote: ↑Wed Dec 21, 2022 3:40 pm

tron777 wrote: ↑Wed Dec 21, 2022 3:33 pm

fyrfyter wrote: ↑Wed Dec 21, 2022 3:23 pm

tron777 wrote: ↑Wed Dec 21, 2022 3:18 pm No NAM'ing today. 18Z run is similar to 12Z to be honest. A general 2-4" with isolated higher amounts possible for the region.

It kills those higher runs other models are showing around Indy. Is it trying to transfer the energy off the coast?

There's a bit of a surface reflection there, but the model isn't really showing a decent low forming at all. What do you think Aaron? You're a techy guy. These models with such an anomalous pattern, may not be fully capable of handling such a dynamic storm system such as this one. With bitter cold Siberian air, a trough going negative tilt with an upper low diving in along with a system along the East Coast trying to inject moisture into this thing. So many moving parts too! there is a limit to the physics and mathematical computations IMO. That makes it that much harder for us to get right. Thus, my conservatism and not going all in right now.

That actually makes a lot of sense- a technological limitation. We know weather models run based on availability of data to input, but also at a predetermined time when the mainframe is available for a set time to run the model. There has to be a time limit for each step, so it’s plausible that it cannot fully calculate the frame and the NAM 18z results are a direct correlation to that.

Thanks for the feedback. I'm glad that you agree with what I posted. I'm decent with tech but well behind your knowledge.

Feeling big bust potential one way or the other with this system.

mainevilleweather wrote: ↑Wed Dec 21, 2022 3:42 pm Feeling big bust potential one way or the other with this system.

That's exactly the vibe that I am getting so I'm not changing a thing right now.

rhodesman88 wrote: ↑Wed Dec 21, 2022 3:41 pm

tron777 wrote: ↑Wed Dec 21, 2022 2:23 pm

rhodesman88 wrote: ↑Wed Dec 21, 2022 2:21 pm

tron777 wrote: ↑Wed Dec 21, 2022 2:13 pm Wow! WAVE 3 is going all in with this one! 4-6" for us? Whoa!

Just saw that! Did he say the 12z Euro is SE???

Yes, and we did on here too.

I see that now! Playing catch up on all the posts!

All good Byron! You always know when there is a storm coming with the amount of posts flying around in here. I love it! Hope you and the family are doing well and Merry Christmas!

We still have the 18Z RGEM and 18Z GFS to take a look it over the next hour and change. In the meantime, the US National Radar Loop showing the various pieces of the storm. Wait until we look at that tomorrow.

18z HRRR still coming in with .20-30" qpf of snow in about a 4 hour period, so factor in all the variables we have going on at that time and what do yyou come up with?

Nice water vapor loop here guys.


https://www.eldoradoweather.com/current ... t-loop.php


Check out the trough... dig baby dig! Keep on digging! You can also see the STJ coming in from the SW as well as the very cold air in Canada.

Bgoney wrote: ↑Wed Dec 21, 2022 3:56 pm 18z HRRR still coming in with .20-30" qpf of snow in about a 4 hour period, so factor in all the variables we have going on at that time and what do yyou come up with?

18Z RGEM looks good for the call... 5" or so in our far NW to around 1.5" in far SE.

A long read from the boys:

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Thursday:

The well-advertised low that will bring snow and an arctic blast to
the area will continue undergoing the initial stages of cyclogenesis
on Thursday. During the morning hours, an upper level PV anomaly
dives into the northern Plains approaching a strong arctic cold
front stretching from the upper Great Lakes southwest toward the
southern Plains. A surface wave along the arctic boundary starts to
become more discernible late morning as mutual amplification of the
surface and upper level PV anomalies begins.

The deepening surface low and amplifying upper level PV anomaly
support a surge of relatively high theta e air east of the surface
boundary into the Ohio Valley through the day. Clouds increase and
the chance for light rain develops into the evening. Forecast highs
moderate into the 40s with southerly flow in place.

Thursday night:

Remarkable mutual amplification of the strong surface and upper
level PV anomalies continues overnight and leads to explosive
cyclogenesis over the region. Remarkably, the surface low may deepen
20 hPa in 12 hours overnight. This type of pressure drop is usually
only seen in the strongest east coast bomb cyclones.

While the low rapidly deepens, winds increase across the region due
to a strengthening pressure gradient. Additionally, the arctic cold
front associated with the low accelerates southeastward into the
Ohio Valley by late Thursday evening. This front will cause a rapid
drop in temperatures from west to east overnight (40s to the single
digits in a matter of hours) and transition rain to snow very
quickly. Any snow that falls in the dropping temperatures will
likely stick relatively easily and could become wind blown. The good
news is moisture may rapidly pull east with the front and lead to an
end to snowfall by daybreak. However, wind chills approach -25 to -
30f by sunrise.

The impacts of the rapidly strengthening cyclone in the vicinity of
the Ohio Valley are expected to be significant:

1) Dangerously cold wind chills approaching -30f are expected late
overnight behind the arctic cold front due to a combination of
temperatures near 0 and wind gusts around 35 mph. A Wind Chill Watch
has been issued to account for dangerously cold wind chills that
could lead to frostbite on exposed skin in as little as 30 minutes.
Please use extreme caution if traveling and have an emergency kit
ready. Also, have a backup plan to stay warm while at home/work in
case of a power loss caused by strong winds.

2) Dangerous travel conditions are increasingly likely due to
accumulating snow resulting in slippery conditions and reduced
visibilities. Visibilities may be further reduced by blowing snow.
Winter Storm Watches and Warnings account for the areas likely to
experience the most difficult travel. A Winter Weather Advisory has
been issued for other areas that will still feel travel impacts, but
may be less severe than the watch/warning areas. Please note,
despite the snowfall forecasts calling for less snow than normally
required for Winter Storm Watch/Warning issuance, impacts may be
significant due to a combination of snow, arctic temperatures, and
strong winds.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Most 12Z guidance suggests that dry air will have pushed into the
area by the start of the period. Some light snow showers may be
lingering in northeast counties, although the GFS continues to
advertise that it may be a bit more robust than that. However,
travel impacts from snow that occurs Thursday night will likely
linger into Friday.

Big issue will be wind and extreme cold. Air temperatures Friday
morning will be in the single digits either side of zero, with a
trend towards even colder temperatures. Any diurnal rebound will be
extremely limited with highs in the single digits above zero. Winds
will be gusting 40 to 55 mph during the day and into the evening
before slowly starting to decrease. This will result in wind chill
in the -20 to -30 range. We have decided to handle the wind chill
separate from the travel/infrastructure impacts from the snow
Thursday night since the hazards from the wind chill will last much
longer. So a separate wind chill watch has been issued into Friday
night. Wind chill, more into the advisory range, will continue
beyond the watch period through Saturday and into Saturday night.

Bgoney wrote: ↑Wed Dec 21, 2022 3:56 pm 18z HRRR still coming in with .20-30" qpf of snow in about a 4 hour period, so factor in all the variables we have going on at that time and what do yyou come up with?

Bgoney and we talked about that earlier and what are the snow ratios going to be at any given time and how do you really come up with a correct ratio. Many times with systems cold air comes in slowly and you start at 30 degrees and maybe 8 hours later you are at 22 so the ratio went form 8-1 to maybe 12-1 over that period. This is shorter duration and we may go from 45 to 15 in two hours time. So do you go 8-1 for 30 minutes and then 12-1 for next 30 minutes and continue to go higher over the next 3 hours. I love numbers but this one is a moving target.

I have a sneaking suspicion that a certain hammer time guy is going to make an appearance very soon. All the recent trends are leading for his Christmas appearance

Pete1 wrote: ↑Wed Dec 21, 2022 4:18 pm I have a sneaking suspicion that a certain hammer time guy is going to make an appearance very soon. All the recent trends are leading for his Christmas appearance

I usually only post him when we've got a real shot at 6". For most of us, I just don't see that happening. However... this is more of an impact driven storm with the flash freezing, wind driven snow, rapidly falling temps, wind chills, and the biggest travel period of the year! I'll think about it.

The good thing imo is always go with your forecast and once you have done that you can adjust as we get closer. I agree that this has always been about the flash freeze,winds and then the snow was probably in 3rd place. Do we get 1 inch or 5 inches and how much a difference will that make in driving conditions. I am not even sure what road crews do when you have a flash freeze because if you clear the snow you may have just a layer of ice. I know with my driveway and sidewalk it will have snow on it for traction.My driveway goes straight down hill and I am in the middle house on the street and it goes uphill in both directions once I back out of my driveway.

As I've posted before, my driveway is also downhill and I live at the bottom of a hill in a cul-de-sac. So glad I work from home and don't have to get out in this mess! Got plenty of food and beverages to get thru this storm and Christmas!

Another MD for snow squalls in the Western US.

https://www.spc.noaa.gov/products/md/md2056.html