Equus
Member
Seems like this is about the time before the event when models tend to downtrend for a bit, but would be nice if that continued as we get closer to the event this time.
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Clancy
Member
Uncertainty is certainly normal during this period, though hopefully the downward trend continues.
tennessee storm chaser
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Yeah normal thing around this timeframe ...
Gail
Member
Jackson NWS afternoon discussion...
“
Wednesday and Wednesday night: Our next surface cyclone will take
shape over the Southern Plains states in association with a
potent shortwave/upper low, lifting into the mid-Mississippi
Valley through the day. An attendant cold front will then advance
into our region Wednesday afternoon into Wednesday night.
Unfortunately, the timing of this system looks to fall in a prime
window for destabilization in the warm sector with moderate to
strong instability forecast. Given guidance indicating a time
window during the day ahead of the development, I actually tweaked
forecast highs up a degree or two across central and eastern
portions of the area. Deep layer shear will remain strong while
stronger upper forcing overspreads the region, making convective
development likely ahead of the front, heading through the day
into the afternoon. Storms may still be ongoing into the early
evening before the front clears some portions of the area. The
current setup continues to suggest all modes of severe weather are
in play, and we will continue to advertise an enhanced risk for
severe storms areawide. Additional future adjustments to add more
detail will still be required as the event gets closer. For
instance, forecast mid level lapse rates, model LHP, and forecast
soundings suggest we may need to highlight the potential for hail
larger than the current golfball size. Some of our better proxy
parameters for strong tornadoes suggest those could be a
possibility. We will continue to assess the latest guidance
information and make further tweaks as confidence increases in
this type of detail over the coming days. We would continue to
urge people across our region to review their personal severe
weather safety plans and be prepared to take action during the
severe weather threats this coming week.”
“
Wednesday and Wednesday night: Our next surface cyclone will take
shape over the Southern Plains states in association with a
potent shortwave/upper low, lifting into the mid-Mississippi
Valley through the day. An attendant cold front will then advance
into our region Wednesday afternoon into Wednesday night.
Unfortunately, the timing of this system looks to fall in a prime
window for destabilization in the warm sector with moderate to
strong instability forecast. Given guidance indicating a time
window during the day ahead of the development, I actually tweaked
forecast highs up a degree or two across central and eastern
portions of the area. Deep layer shear will remain strong while
stronger upper forcing overspreads the region, making convective
development likely ahead of the front, heading through the day
into the afternoon. Storms may still be ongoing into the early
evening before the front clears some portions of the area. The
current setup continues to suggest all modes of severe weather are
in play, and we will continue to advertise an enhanced risk for
severe storms areawide. Additional future adjustments to add more
detail will still be required as the event gets closer. For
instance, forecast mid level lapse rates, model LHP, and forecast
soundings suggest we may need to highlight the potential for hail
larger than the current golfball size. Some of our better proxy
parameters for strong tornadoes suggest those could be a
possibility. We will continue to assess the latest guidance
information and make further tweaks as confidence increases in
this type of detail over the coming days. We would continue to
urge people across our region to review their personal severe
weather safety plans and be prepared to take action during the
severe weather threats this coming week.”
MikeP
Member
Wonder if tomorrow's system is affecting resolution for Wednesday a bit.....
The 00z NAM has gone toward the other models with the warm front not making it into middle TN because of a delayed low-level jet. This run doesn't have the stronger low-level jet ramp up until sunset and after. 2000+ CAPE still extends up to the warm front, and looking at soundings, high effective inflow layer SRH extends a little bit north of the warm front. This is one of those cases where the tornado threat wouldn't magically go to zero immediately north of the warm front. If you get a supercell established in the warm sector and it crosses the warm front, this could easily be a case where you can have a strong or violent tornado going farther into the cool side of the boundary than you would usually expect. However, unless this trends back, the threat is decreasing a good deal for Tennessee except maybe Highway 64 and south in southern/middle areas... and the warm front may never fully make it past western HSV metro to Guntersville area. We're at the point where models can often underdo the low-level winds though; so, this can trend back the other way. I don't think the caliber of the overall threat has decreased. We may be delaying the start of the higher-end tornado threat (we're talking straight-up violent potential, not just strong potential) until near and after sunset though.
GFS ramping back up significantly. 55kts at 850 in the late evening. NAM ramps up overnight for a nocturnal tornado event across Central AL.
Evan
Member
You're just full of good news tonight.
UKMET also comes in with full support of a strong low-level jet (55-almost 60 kts at 850mb, 45-50 kts at 925mb) overnight. One thing to remember is that the UKMET is also notoriously slow with systems.
Bamamuscle
Member
Will areas N of the TN river in AL get in on this?
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Yes. The NAM is the southernmost solution with the warm frontal placement, and it gets the Shoals, at least the west side of the greater HSV metro, and far southern middle TN from Pulaski westward into the threat. GFS, para GFS, and UKMET are north into southern middle TN with the warm front. Given that, even on the NAM, the steady rain in the afternoon is up in northern middle TN instead of on the warm front and southerly winds are intensifying with time, I think the NAM is incorrect about the warm frontal positioning... after seeing the other data come in tonight.
Likely not. I expect the warm front to make it into west-middle and southern middle TN to far northeast AL or northwest GA based on what I see now.
You need to be on guard. There is still a severe weather risk. However, I think the highest threat is to your south.
Euro is coming in stronger with the system, and stronger and more widespread with the late afternoon to overnight low-level jet surge. It also has mid 60 dewpoints up to Highway 412 in middle TN by early/mid-afternoon and in the face of widespread convective contamination that is highly likely to be significantly overdone. The height falls on the leading edge of the upper trough were coming onshore to be sampled in the 00z obs tonight, and all the models went stronger. I think we're starting to see the true face of this thing, and I expect this trend to not back off.
Scott81
Member
Is it possible somebody could see a high risk day?
With this trend, and it happening now that the trough is starting to get sampled in upper air observations, it's becoming less and less unlikely.
6z NAM/6z 3k NAM continues the upward trend that started in all the models during the evening. We're now talking about a large 50 kt 850mb jet over Mississippi into west Tennessee by midday and early afternoon. After a brief "lull" in the 850mb jet in the 21z-00z timeframe (still 40-50 kts with sickle-shaped hodographs), it ramps up to 55-65 kts over AL/TN after sunset, with widespread 0-1 km SRH of 400-500. And given the steady trends with the 850mb jet, I'm becoming more and more skeptical of this afternoon "lull" in the intensity. This run was also farther north with the morning warm frontal action and has the warm sector once again going deep up into west/middle and southern/middle Tennessee. It's becoming apparent that the trend in the data is now that we have gotten some of the wave sampled in the upper air network. The potential for this to be a major severe weather event from east Arkansas and northeast Louisiana, across Mississippi, across Alabama, and into areas of western and southern-middle Tennessee is increasing. The potential for multiple long-tracked supercells capable of strong or possibly a few violent tornadoes is increasing.
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CheeselandSkies
Member
SPC in with the Day 3 Enhanced covering most of AL and MS, SW TN, the eastern half of AR, NE LA and far SE MO. That is a big chunk of real estate in a 30% zone at Day 3, with most of that encompassed by a hatched (10%+ probability of significant severe) area.
