Yep, I am surprised at the lack of convection and shear...but no reason to get bogged down in the details yet...it is the NAM
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Do I need to turn the April Fool's filter back on? Never A Miss (NAM)
ARCC
Member
GFS is either gonna score big or go down with the ship. Based on history probably the latter.
Well it still has Canada on its side.
Well it still has Canada on its side.
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Equus
Member
Enhanced risk on brand new D3. Seems to favor a faster solution, the highest categorical risk being over SE and E AL and most of GA into SC.
ARCC
Member
Now the GFS is slower than even the NAM with a 997mb slp sitting over southern MO at 18z 4/5. Normally that is a extremely dangerous position, yet the models want to keep directional shear low as winds are very unidirectional.
Yep, it's ignoring the isallobaric response from the surface pressure falls and the mid-level height falls. I'd kinda buy that some if there was a LLJ disruption with it shifting away, from the predawn/morning convection. But this run does not have that. It has a 40-45 kt LLJ up through AL at 18Z, with a solid tongue of 75+ temps up to the OH Valley. There are no leftover cold pools or weird surface wind signatures associated with effective boundaries. So, that means it isn't because of convective contamination... it's because the GFS isn't responding to the pressure falls. It's something both the NAM and GFS are notorious for doing until almost the last minute... and is the reason the NAM only had 0-3 km SRH of 250-300 over AL 36 hrs before 4/27....
ARCC
Member
I remember you and I talking about the very same thing then.
http://www.spc.noaa.gov/exper/sref/gifs/latest/SREF_wind_vector_10m_f063.gif
The SREF mean has a 10m wind of about 180-185 degrees on the synoptic scale. We've had more than one F5 day in this state with a 180-190 deg surface wind under a 40 kt 850mb jet. You account for the fact that, on the storm scale in response to a mesocyclone, the winds nearby would be 165-170 degrees.... a due south or half a hair veered of due south wind would be plenty enough to raise red flags. If we've had tornadoes that intense without a southeast surface wind and 60 kt 850mb jet... I know, with similar thermodynamics and favorable forcing geometry for a non-linear storm mode... we could easily be talking about strong+ tornadoes of a lesser magnitude than top of the scale... with a similar wind profile to what the SREF suggests, and what the GFS would have if it had any bit of an isallobaric response in the low-level wind fields.
The SREF mean has a 10m wind of about 180-185 degrees on the synoptic scale. We've had more than one F5 day in this state with a 180-190 deg surface wind under a 40 kt 850mb jet. You account for the fact that, on the storm scale in response to a mesocyclone, the winds nearby would be 165-170 degrees.... a due south or half a hair veered of due south wind would be plenty enough to raise red flags. If we've had tornadoes that intense without a southeast surface wind and 60 kt 850mb jet... I know, with similar thermodynamics and favorable forcing geometry for a non-linear storm mode... we could easily be talking about strong+ tornadoes of a lesser magnitude than top of the scale... with a similar wind profile to what the SREF suggests, and what the GFS would have if it had any bit of an isallobaric response in the low-level wind fields.
Meanwhile...
...only ONE GFS ensemble member on the 06Z run has a non-threatening solution, and look how far west the warm sector extends on quite a freaking lot of those.
...only ONE GFS ensemble member on the 06Z run has a non-threatening solution, and look how far west the warm sector extends on quite a freaking lot of those.
Good point Fred, the NAM epecially has issues with low level shear in this kind of environment. Based on what I see this morning, the SPC needs to expand the probabilities a westward. There are several ingredients here that could make it a dangerous day.
Kory
Member
They barely have places with >1500 J/KG CAPE in the thunder category. Why am I not shocked anymore?
ARCC
Member
Yeah Fred that SREF mean is very nasty. Everyone gets caught up that you need southeast surface wind for a outbreak when I think it was you that pointed out years ago that most of the red letter days in AL come with a south to slightly SSW wind.
Speaking of insanity I'm pretty sure I saw a dew point of 73 around Montgomery on the 6z GFS.
Speaking of insanity I'm pretty sure I saw a dew point of 73 around Montgomery on the 6z GFS.
darkskys25
Member
How much futher west in your opinion. Not that they its gospel or anything but the high res nam does not show any storm initiation until about Tuscaloosa Co. Assuming storms build from there that falls in line with current risk area nicely. You guys thinking this initiates in MS putting more of AL in play? Or are you saying a slight shift to the west? Cape looks pretty good to me.
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I could see storm initiation around central Mississippi with the front around 10am...I am thinking much of Alabama will be in play.
Based on performance so far, this new 3 km NAM is what you'd want to look at to see what won't happen. I wouldn't be ready to just lock onto a big western expansion yet for sure... but there is a LOT of data that suggests the warm sector may extend as far west as I-55 in central MS, or even a little further west than that, at 18Z Wednesday.
12Z nam showing cold front just west of TCL st 21z. Cape is over 3000. SRH is very meager but I am sure the NAM is underplaying.
warneagle
Member
I was wondering about the SRH on the last two runs of the NAM. Seemed too low.
Kory
Member
The trend to close off the trough is meaning a slight slowdown in solution for Wednesday. One fly in the ointment might be a southern stream perturbation that fires off convection early and doesn't allow a focus for the afternoon....
Either way, thermos are still a powder keg.
Either way, thermos are still a powder keg.
Psalm 148:8
Member
So what are the latest models showing for this system? I know you folks love the thrill, but I got to make a driving plan for Wednesday....my personal hope is fir a bust! Just like our pathetic little winter systems this year.
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GTWXAlum
Member
The threat is certainly still there on the 12z suite that I can see so far