09/18/05: NOW: CENTRAL PLAINS

[nickgrillo]

Strong to extreme instability is spread across the warm sector in eastern NE/KS... With the cap slowly eroding due to insolation, with temperatures in the 85-90F range across the region. I'd expect SFC-based convection to develop within the next few hours... Given the degree of deeplayer/vertical shear and instability - isolated supercells will be likely...

 

[afischer]

Not too shabby an environment shaping up across northeast NE for September... certainly better than I anticipated. Neligh profiler indicates that hodographs, though modestly sized, have respectable low-level curvature. Storm motions may only be 15kts or so, not adding much to local SRH magnitudes... but with the strong vertical veering, deep shear should support supercells.

Ongoing severe-warned cells west of O'Neill are still immediately to the cool side of the inverted trough... tornado threat will of course be better if they can move and/or redevelop eastward a tad to where boundary layer instability exists.

Looking forward to seeing pix from Mike H. :lol:

 

[afischer]

NWS LBF issued a tornado warning for the no-man's land of Rock county NE at 4:56PM local time based on dopplar radar. This is the western of two storms... is probably very near the boundary which may act as a source of vorticity though surface parcels are probably only 75/62 or so. A weak echo region is present based on base/composite reflectivity.

 

[nickgrillo]

Thinking that the storms in northern Nebraska could be somewhat elevated - which would negate any real tornado possibilities. However, the strong mesos would certainly help enhance the already very large hail threat. The storm in Rock county could be surface-based, since the very high reflectivities (65-75dbz) are a sign that it's drawing in the strongly unstable surface airmass.

 

[Andrew Khan]

I'm thinking their is going to be some pretty large hail in the south central area of boyd/holt. I'm not sure, but VIL is appearing to be pretty High. I can not see any extremely strong rotation. I'm not sure why you think these storms are high based? There is now a rotation indicated of 3.5 nm. Tornado warning has just been withdrawn.

 

[Dustin Wilcox]

Still here in Arlington waiting for maybe something further south to get going, Columbus area would be good!! I left my laptop and scanner at school so if I head out it will be with just eyes, and I dont want to venture far with just them.

 

[afischer]

Western cell has become disorganized as noted above. Eastern cell still SVR-warned, and its updraft is about to pass south of O'Neill. These two storms' inflow is NEly to ENEly, which I suppose does not help matters any w.r.t. tornado potential since it is constantly being rain-cooled.

Cells forming farther "out" in the warm sector may fare better with slightly more veered (ESEly) surface flow, assuming sufficient SRH. In fact, a new updraft is trying to form now near Bartlett.

 

[Andrew Khan]

Well, it looks like I was right. There was hail in the hold area, it was 0.88 Inches, reported by a trained spotter. There is also a tornado warning in the Holt County area...there are also two meso rotations indicated, and the two cells in the Antelope and Holt counties have began to merge.

 

[nickgrillo]

HP / small-scale bow continues to push eastward through Antelope county... With VILs in the 65-75 region on KOAX radar. Strong instability and deeplayer shear will continue to be available in northeastern NE and into IA through tonight. My thoughts are the convection in northeast Nebraska will continue to grow as it pushes eastward... Bringing the potential for large hail and damaging winds into IA by the next few hours - with the thread extending into the early morning hours, given the strong mid-upper level winds (>40kts at 500MB and >80kts at 250MB) and moderate instability.

 

[Dustin Wilcox]

Convection now fireing in N Washington and S Burt Counties in E Nebraska

 

[Andrew Khan]

The southern cell in South Dakota is expressing
Very strong rotation. The cell in NE is still giving off a LOT
of hail, and soon to come, damaging winds.

 

[afischer]

Doesn't look like it made the SPC storm reports... but at least one tornado was reported today by LEOs. This was over extreme southeast Holt co. with the new storm that developed to the southeast of the first pair of storms... and occurred about when the storm changed its course from NNE to E.

 

[Andrew Khan]

The storm in southern South Dakota, is expressing tornadic characteristics, with, a mild hook forming southern bound. There is also twin TVS's,
near Lake and McCook Counties. Rotation is very strong, just takea look at
the velocities of this thing, and you'll see.