Absolute Vorticity

Yea Goodluck measuring the difference of a 3 or 4 inch snowfall in those conditions. Not sure how exactly cvg and the other airports of noaa are going to measure

Bgoney wrote: ↑Wed Dec 21, 2022 8:31 am Yea Goodluck measuring the difference of a 3 or 4 inch snowfall in those conditions. Not sure how exactly cvg and the other airports of noaa are going to measure

No doubt! The drifting, esp in open areas is going to be very "interesting" that is for sure.

Bgoney wrote: ↑Wed Dec 21, 2022 8:31 am Yea Goodluck measuring the difference of a 3 or 4 inch snowfall in those conditions. Not sure how exactly cvg and the other airports of noaa are going to measure

Snow collects in a large metal box at the airport, to try to keep wind affect on accumulation to a minimum. The white snowboard at the bottom is measured every 6 hours and wiped clean after each measurement. At the end it’s all added together for the total.

By the way... Happy Winter Solstice to everyone! At 4:47pm EST is when it is officially winter! Mother Nature will be playing the part soon.

tron777 wrote: ↑Wed Dec 21, 2022 8:29 am Time for some nowcasting... SPC mesopage shows our storm, which is currently a 1010 MB low in Central Idaho. Pressure falls suggest that this thing will be dropping down the Rockies and into the OK / TX Panhandle area later. The further south this thing goes before lifting NE, the better off we'll be. I'd like to see it dig deeper into Texas, so that's one of things I will be watching today.

Good Morning Les and great couple of posts by you as usual. No doubt the further south this thing digs the better chance for a little more preicp to flow into the system as well. When and where does this storm finally blow up is key to where some of the bigger totals of snow form. Nowcasting is probably more important than the models though we will still look at them as they may give a few hints of where the low closes off. I believe the amounts of snow is sort of downplaying this storm and I believe that is the time folks get surprised. Ice is never good and I have seen where a 15 minute snow shower in late afternoon has shut down the city for several hours because it turned to ice as temps dropped and we lost daylight.

tpweather wrote: ↑Wed Dec 21, 2022 8:46 am

tron777 wrote: ↑Wed Dec 21, 2022 8:29 am Time for some nowcasting... SPC mesopage shows our storm, which is currently a 1010 MB low in Central Idaho. Pressure falls suggest that this thing will be dropping down the Rockies and into the OK / TX Panhandle area later. The further south this thing goes before lifting NE, the better off we'll be. I'd like to see it dig deeper into Texas, so that's one of things I will be watching today.

Good Morning Les and great couple of posts by you as usual. No doubt the further south this thing digs the better chance for a little more preicp to flow into the system as well. When and where does this storm finally blow up is key to where some of the bigger totals of snow form. Nowcasting is probably more important than the models though we will still look at them as they may give a few hints of where the low closes off. I believe the amounts of snow is sort of downplaying this storm and I believe that is the time folks get surprised. Ice is never good and I have seen where a 15 minute snow shower in late afternoon has shut down the city for several hours because it turned to ice as temps dropped and we lost daylight.

Good morning Tim! Our NW counties have a shot at getting something in that 4-6" range is things break right. I think for CVG Land, Dayton, and Columbus if things break right 2-4" range is solid. 2" or less our East / SE Counties. Something like that is probably the high end ceiling we will have with this system in my mind if you're exclusively talking about max snow potential. Could those numbers go higher? Yes... if this system truly does track very close to us and not NW of us. That's the only way that can happen. Otherwise, the well advertised call of that 1-4" range from NW to SE across the area is still very solid at this time.

Overnight thinking from the boys and their reasoning to wait on issuing winter weather headlines for us...


.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
The high exits to the east tonight. This will cause winds to
veer to the southeast at the surface. Meanwhile, a digging mid-
level trough to the west will initiate increasing WAA at and
above 850mb, producing weak isentropic lift during the pre-dawn
hours Thursday. With warm air aloft, the very light
precipitation will likely stay as rain.

The deepening trough will provide a second increase in WAA
Thursday, particularly during the afternoon through early
evening hours ahead of a strong surface cold front. Most of the
latest guidance, to include the 06Z HRRR, speeds the front up a
bit. This means the frontal band of showers approaches east
central Indiana, western Ohio and northern Kentucky toward the
end of the short term period. Temperatures ahead of the front
will reach around 40 to the mid 40s, so rain is the expected
precipitation type.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
A potent upper level low will rotate east across the Great Lakes and
Ohio Valley Thursday night. Surface cyclogenesis will be underway
near central Indiana Thursday evening, deepening as it rotates
northeast to a position near Lake Huron by Friday morning. As this
takes place, an Arctic cold front will blast east through our
region. Rain with the front will very quickly change to snow as very
cold air pours in. Right now it looks like most areas will see 1 to
2 inches of snow with perhaps slightly higher amounts in our far
west. With the rapid drop in temperatures from above freezing to
below freezing expected, along with increasing wind, the potential
for a flash freeze event exists during this period. So, at some
point a winter headline will need to cover this. Temperatures
are expected to fall into the single digits to a few degrees
below zero by Friday morning. At some point, wind chill
headlines will be needed as well as wind chills dip well below
zero, which are at dangerously low levels.

00Z models have now trended more progressive with the parent 700 mb
low with aforementioned storm system (GFS the outlier) for Friday.
Thus, pcpn Thursday night may end up tapering off much faster on
Friday, and now there is less confidence in the prospect of
additional snow accumulations across our north from wrap around
pcpn. The main key to the current Winter Storm Watch in effect for
parts of east central Indiana and west central Ohio was with the
previous forecast prospects of additional powdery snow of 1 to
2 inches that is forecast to fall Thursday night (some of this
which may become crusted over with a quick freeze). With this
looking less likely, there may not be sufficient loose snow,
despite very strong winds, to produce critical definite blowing
snow conditions and significantly reduced visibilities. So, it
has been decided at this juncture to leave the watch as is, and
wait to see if indeed the trend remains that we do not get
additional snowfall on Friday, and then we can decide what to do
with this headline (upgrade or issue as an advisory). As a
result, there is no plan at this juncture to expand the watch to
other areas to the east and north given the current trends. As
stated, it will be windy on Friday with wind gusts ranging from
near 40 mph south to near 55 mph north. Wind Advisory headlines
will also be needed at some point as well. Highs will barely
budge from morning lows given cold Arctic area in place.

For the period Friday night into Saturday, overall system will
gradually pivot north and east. It will continue to be windy
with the highest gusts continuing into Friday night. Clouds will
linger. It will be very cold with wind chill values dangerously
low. After lows in the single digits to a few degrees below
zero, highs on Saturday will range from near 5 north to 15
south.

High pressure is expected to build east into the Ohio Valley
Christmas Day into Christmas night (Sunday). Winds will diminish,
but some lingering cold wind chills are expected Christmas morning.
Clouds will diminish Christmas Day followed by some increasing
clouds Christmas night. After lows in the single digits and a few
degrees below zero Christmas morning, highs on Christmas Day will
range from near 10 north to near 20 south.

ILN brings up some good points esp about the uncertainty in the back end snows for Friday. That is going to be key to hitting those higher totals. If your location misses out 1-2" will work. 3-4" is possible should the back end snows occur at your location. That's pretty much in my mind, is what we're dealing with here. Timing, as everyone knows is critical. If the models are wrong and this thing blows up quicker, the snowfall forecast will suffer as a result. The longer it takes to get going, the more snow we should receive. It's going to be an interesting storm to watch unfold once it arrives here.

Interesting when talking about ratios and Kuchera.

12Z NAM vs 6Z is a tick SE and a tad stronger. 0.18" now for rain which isn't good for the flash freeze prospects. We really need under a tenth of an inch for lesser impacts, but that may not be the case. Thankfully, the rain portion of this system isn't heavy or the flash freeze would be much, much worse. The unfortunate part, is the speed of this system is much faster vs 6Z also. Snow shuts off faster as a result. Just something else to keep in mind when forecasting snow amounts. I just don't see how 6" is going to be achievable in our CWA due to the track and speed of the storm. 4" in some isolated locations in our NW, ok I can buy that. I'm seeing nothing really to cause me to bump it up. Just not seeing it. I think the call we have on here is very good.

snowbo wrote: ↑Wed Dec 21, 2022 9:19 am Interesting when talking about ratios and Kuchera.

Great post Bo showing that illustration. I brought up this point also the other day. Another limiting factor so we don't go all crazy with amounts.

The one item that continues to pop up here and there is a low pressure forming of the North Carolina coast. This is not a transfer of energy but a separate system. Matter of fact some of that moisture is trying to work west over the apps mountains. Always hard to get that moisture to far west and especially when you have a strong cold front heading east. I am just not sure how this will help or hurt the system but something to watch over the next 12 hours.

Radar this morning shows all of the players on the field. WAA snows over MN and snow over ND (that's the arctic front). Rain over the Carolinas with that separate low Tim talked about. I believe I may have misposted myself calling it a transfer the other day. That was wrong. Tim is correct. It is a completely separate system along the East Coast. We'll need to watch how those features interact, if any today and esp tomorrow.

Wow... per the SPC mesopage, we've got a 100 - 120 knot jet streak coming in to the Pacific NW to give this thing a kick over the Rockies. Models are all showing that increasing to 140+ knots today. A lot of energy at play here.

12Z RGEM ranges from 2" or less SE of I-71. 3" NW of I-71 and pockets of isolated 4-5" totals in our Northern and NW counties.

Great Point about the energy coming eastward. This was part of my equation as I kept seeing this energy with the jet increasing as it came eastward. How far does that jet deep will also impact snow totals. Even if it continues as shown I believe when the low closes off snow just increase around the low and you see cold air coming in from the southwest quickly. If the low gets wrapped up around Indy we still get the lower end of 2 inches imo. If this one wraps up say around Chicago then we will get much less and only the amount the front itself can produce. Really is an interesting storm as not one we see often and makes it somewhat harder to figure out and my guess there will be surprise snow totals both high and low from the plains into the Ohio Valley and Great Lakes.

6z Euro has the low tracking over us. Doesn’t seem like there is much snow shower activity on Friday, everything happens overnight.
It still gives us 4” of snow.

That's been the trend... to end the snow quicker and less in the way of wrap around on Friday. We really need the low SE of us for that to happen. Just don't see that happening with this one unfortunately.

Quite the pressure gradient already developing as expected... 1048 MB pressures pushing into Montana with the 1008 MB Low now over S Wyoming.

tron777 wrote: ↑Wed Dec 21, 2022 10:24 am That's been the trend... to end the snow quicker and less in the way of wrap around on Friday. We really need the low SE of us for that to happen. Just don't see that happening with this one unfortunately.

That has been the trend and you can see from the plains into the Ohio Valley plenty of totals in that 2-5 inch range where the other day the models were giving places in Iowa,Illinois and Missouri a much higher snowfall. We are looking for that 4-6 hour period after the front comes through and if you get into a band of heavier snow for 1 or 2 hours your totals will be closer to 5 inches and if you don't get one of those heavier pockets then 2 inches seem correct.

Too bad most of this seems to be happening as we are sleeping. Would like to see the snow being whipped around by the wind.

Also worried about those winds and the trees next to my house. Hopefully without leaves it wont be an issue.

mainevilleweather wrote: ↑Wed Dec 21, 2022 10:35 am Too bad most of this seems to be happening as we are sleeping. Would like to see the snow being whipped around by the wind.

Also worried about those winds and the trees next to my house. Hopefully without leaves it wont be an issue.

Yeah... you're going to have to stay up late to see the best part of the storm... snowfall wise. No doubt about that.

tpweather wrote: ↑Wed Dec 21, 2022 10:29 am

tron777 wrote: ↑Wed Dec 21, 2022 10:24 am That's been the trend... to end the snow quicker and less in the way of wrap around on Friday. We really need the low SE of us for that to happen. Just don't see that happening with this one unfortunately.

That has been the trend and you can see from the plains into the Ohio Valley plenty of totals in that 2-5 inch range where the other day the models were giving places in Iowa,Illinois and Missouri a much higher snowfall. We are looking for that 4-6 hour period after the front comes through and if you get into a band of heavier snow for 1 or 2 hours your totals will be closer to 5 inches and if you don't get one of those heavier pockets then 2 inches seem correct.

That pretty much sums it up Tim!

Wow... check out the temp drop in Montana...

I’ll take the 12z Gfs!