JAN 6th-7th Storm Part II

rb924119 wrote:GEFS are just slightly wetter lol



It only makes sense when you take a 1.4-1.8 sigma PWAT and force it to rise and condense:



Now, take that and ram it into a cold air mass.....

colder or warmer?

It's about the same as earlier runs verbatim.

I’m off to bed. Hope to wake up to favorable short term guidance!

rb - can you explain for me what exactly that vorticity map is showing? I'm not well-schooled in that. Thank you!

rbthat gfs would jackpot me or close verbatim. that would be hilarious cuz i had already moved on now ur pulling me back. i still think with a 20-25 mile razor thin line itll be a nowcast unless yoy are far far from the coast. CP def has nada to worry about. ecept the wind and rain storm mid week ugg

Based on a subjective tool that I use to help me figure out rain/snow lines, the red line is what I come up with as the approximate transition zone:



It's interesting, because I didn't hedge this based on the trends that my previous thoughts up to this point have been based on, yet, it would lead to a similar outcome. This makes me think that we may in fact see additional cooling trends as we get closer to the event, but regardless, this will be an interesting test.

rb924119 wrote:Based on a subjective tool that I use to help me figure out rain/snow lines, the red line is what I come up with as the approximate transition zone:



It's interesting, because I didn't hedge this based on the trends that my previous thoughts up to this point have been based on, yet, it would lead to a similar outcome. This makes me think that we may in fact see additional cooling trends as we get closer to the event, but regardless, this will be an interesting test.

Just north of the line. Let’s hope! Will be interesting to see how your thoughts all along play out tomorrow evening.

JT33 wrote:rb - can you explain for me what exactly that vorticity map is showing?  I'm not well-schooled in that.  Thank you!

So let me explain this a bit:

Green line: denotes the 850 hPa warm front
Dark blue line: denotes the 850 hPa cold front
Light blue circle: denotes the central circulation of the 850 hPa low
Thick light blue outline: denotes area of 850 hPa frontogenesis/forcing for ascent/banding

In my original post, I said that you'd want to end up north of the edge of the 850 hPa vorticity (green line), since that is the warm front at this level. Over previous runs, this run shifted significantly further south, which is good. However, this run also showed a much more organized 850 hPa circulation, which is also good, because it helps to tighten up the thermal gradients. This means that even though the center of the circulation may be just as close, because it's more organized, and the thermal gradients are tighter, it means your airmass would be a little colder because the cold advection to the north of the warm front is more efficient. Additionally, the enhanced thermal advection helps to increase vertical motion and enhance precipitation rates, which is why you saw that mega-band over Westchester and western Connecticut.

Hopefully this helps!

UKMET definitely looks better too. So, so far:

Looked notably better:
-NAMs
-GFS
-UKMET
-SREFS

Held serve:
-GEM suite
-ICON

Anxiously awaiting the Euro now lol

rb924119 wrote:

JT33 wrote:rb - can you explain for me what exactly that vorticity map is showing?  I'm not well-schooled in that.  Thank you!

So let me explain this a bit:

Green line: denotes the 850 hPa warm front
Dark blue line: denotes the 850 hPa cold front
Light blue circle: denotes the central circulation of the 850 hPa low
Thick light blue outline: denotes area of 850 hPa frontogenesis/forcing for ascent/banding

In my original post, I said that you'd want to end up north of the edge of the 850 hPa vorticity (green line), since that is the warm front at this level. Over previous runs, this run shifted significantly further south, which is good. However, this run also showed a much more organized 850 hPa circulation, which is also good, because it helps to tighten up the thermal gradients. This means that even though the center of the circulation may be just as close, because it's more organized, and the thermal gradients are tighter, it means your airmass would be a little colder because the cold advection to the north of the warm front is more efficient. Additionally, the enhanced thermal advection helps to increase vertical motion and enhance precipitation rates, which is why you saw that mega-band over Westchester and western Connecticut.

Hopefully this helps!

Thanks, rb!  Definitely helps.  Couple more quick questions:

(1)  How do you read a vorticity map such as the one posted?  (What do the numbers and colors represent?)
(2)  How did you know the green line represents the warm front and blue line represents cold front?

Although the thermals on the UKMET aren't any better. Interesting.

Just wondering if these two images show the same thing in terms of vorticity?  If so, it appears that:
1.  NAM has it shifted a bit to the south (good)
2.  GFS on Tropical Tidbits is different from the GFS on Pivotal Weather (more north on TT)

JT33 wrote:

rb924119 wrote:

JT33 wrote:rb - can you explain for me what exactly that vorticity map is showing?  I'm not well-schooled in that.  Thank you!

So let me explain this a bit:

Green line: denotes the 850 hPa warm front
Dark blue line: denotes the 850 hPa cold front
Light blue circle: denotes the central circulation of the 850 hPa low
Thick light blue outline: denotes area of 850 hPa frontogenesis/forcing for ascent/banding

In my original post, I said that you'd want to end up north of the edge of the 850 hPa vorticity (green line), since that is the warm front at this level. Over previous runs, this run shifted significantly further south, which is good. However, this run also showed a much more organized 850 hPa circulation, which is also good, because it helps to tighten up the thermal gradients. This means that even though the center of the circulation may be just as close, because it's more organized, and the thermal gradients are tighter, it means your airmass would be a little colder because the cold advection to the north of the warm front is more efficient. Additionally, the enhanced thermal advection helps to increase vertical motion and enhance precipitation rates, which is why you saw that mega-band over Westchester and western Connecticut.

Hopefully this helps!

Thanks, rb!  Definitely helps.  Couple more quick questions:

(1)  How do you read a vorticity map such as the one posted?  (What do the numbers and colors represent?)
(2)  How did you know the green line represents the warm front and blue line represents cold front?

1. So, the color scale is just a measure of the strength of the vorticity - the darker the colors, the stronger the vorticity. The wind barbs are obviously a measure of the wind direction/speed at whatever level you're looking at, and the black lines are the height lines (outline the streamflow based on the winds at that level). The height lines, though, are the location of that pressure surface in the vertical. So, think of the height lines like a 3-D version of a topographical map; troughs at a particular pressure surface (in this case, 850 hPa) would show up as a valley, while the ridges would show up as mountains. But the surface that you are looking at is all the 850 hPa pressure surface. Hopefully that makes sense lol

2. Experience haha no, but seriously, low-level vorticity, such as at the 850 hPa level, is usually associated with a frontal structure, especially when it's as intense as modeled. Now, since there isn't too much vertical distance between the surface and the 850 hPa level, let's test this in real time. First image will be the 850 hPa image that I annotated, and the second will be the same annotations over a surface map of temperatures (colored contours) and winds (barbs):





Notice how the cold front and the warm front (dark blue line and green line, respectively) both align with the wind shifts (change in the direction of the wind flow) AND the the changes in the thermal profiles (blue line aligns with the maximum tongue of warm air, with progressively lower temperatures behind it, green line aligns with progressively cooler air ahead of it/warmer air behind it). In essence, we just defined what vorticity actually is; it's a measure of cyclonic spin, and in this case, it's being created by wind shear (the change of direction and/or speed of wind in the horizontal plane of a particular pressure surface).

JT33 wrote:Just wondering if these two images show the same thing in terms of vorticity?  If so, it appears that:
1.  NAM has it shifted a bit to the south (good)
2.  GFS on Tropical Tidbits is different from the GFS on Pivotal Weather (more north on TT)

They don't DIRECTLY show vorticity at the 850 hPa level, HOWEVER, you can actually approximate it based on the wind field

Man, I can't believe that I'll be the only one posting about the Euro, especially on a Friday night! aha Oh well, you're with me in spirit guys (and gals)! I'll try to put da team on my back and will it to a good solution haha

I can't lie, this looks pretty good to me so far on satellite:



It's getting that classic "S" shape to it with the baroclinic leaf, and then look at the inflow already off the Atlantic. Pretty cool.

Euro initializing.....

What time on EURO. 1 ?

oldtimer wrote:What time on EURO. 1 ?

Still initializing. First frames should be coming out momentarily, but we'll probably have to wait until about 1:15am or so before we start getting enough graphics to see the whole picture (or at least most of it) lol

Thank you u do great work Only if I could interperate one quarter lol

Uh oh...don't shoot the messenger, but........

The Euro looks pretty freakin' good to me. Waiting on more maps to confirm.

rb924119 wrote:Based on a subjective tool that I use to help me figure out rain/snow lines, the red line is what I come up with as the approximate transition zone:



It's interesting, because I didn't hedge this based on the trends that my previous thoughts up to this point have been based on, yet, it would lead to a similar outcome. This makes me think that we may in fact see additional cooling trends as we get closer to the event, but regardless, this will be an interesting test.

As always I dont read weather like you guys but I remember ttends ovee years of time and based ob that what yoh drew is exactly what I was thinking.

rb924119 wrote:Uh oh...don't shoot the messenger, but........

The Euro looks pretty freakin' good to me. Waiting on more maps to confirm.

Man, that was an odd run. It was pretty stingy on precip, which is weird given its high PWAT anomalies. I'm going to take it as a win, though, because the lower levels were definitely better and colder. The jet structure looked a little better, and the other two levels, H7 and H5, looked relatively unchanged.

oldtimer wrote:Thank you  u do great work  Only if I could interperate one quarter lol

Thanks! You'll get there! haha

2004blackwrx wrote:

rb924119 wrote:Based on a subjective tool that I use to help me figure out rain/snow lines, the red line is what I come up with as the approximate transition zone:



It's interesting, because I didn't hedge this based on the trends that my previous thoughts up to this point have been based on, yet, it would lead to a similar outcome. This makes me think that we may in fact see additional cooling trends as we get closer to the event, but regardless, this will be an interesting test.

As always I dont read weather like you guys but I remember ttends ovee years of time and based ob that what yoh drew is exactly what I was thinking.

We'll see what happens haha I like testing these things, because if they work, it's another tool to add to my toolbox. Just like with the ratios that I've been discussing with Dunnz, heehaw, and Frank. That's also another test of a different algorithm that I like to use. You don't learn if you don't ever try, you know?

Here's a comparison of the snow maps from tonight's 00z (left) and the earlier 12z run (right):



Not as impressive as I was expecting given the things I mentioned above, but you can see that there is a colder signature there.

Good night, all!