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Indystorm

Feb. 23 Storm Svr aspects

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    Okay, I'll bite.  Both PAH and IND keep talking about possibility of svr on Sat.  12z GFS for Wed. shows 60 degree temps from central IL and IN southward, low 60 dews up the Wabash Valley 114 knot 500 mb jet,  relatively low surface CAPE of 438 down by EVV with 400-500 0-3 km helicity and supercell composite of 3.  Could be low CAPE, high kinematic event if trends increase.    Discuss.

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This morning's SPC Day 4-8 discussion suggested severe probabilities may need to be expanded northward into the southern Great Lakes.  Would be impressive to get a severe threat this far north in February.

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Been awhile since the central CONUS saw a storm like that if it verifies...too bad I'll likely be too far south for the big time snows and too far north for severe...a not uncommon spot for S. WI/N. IL/E. IA in late winter/early spring.

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NAM is trending weaker and further south over the last few runs, affecting the anticipated moisture return in the lower Ohio Valley and moving the warm front location closer to the Ohio River.  It's not much further south, but a weaker storm would lower the potential for severe further north whereas a stronger storm further to the N or NW would allow for more moisture return.  Beyond the range of the NAM, it seems that many of the models are suggesting a "Freshwater Fury" storm with pressure dropping to near or below 980 mbar over Ontario.  The GFS and GFS-FV3, plus the ECMWF, are displaying a system below 975 mbar.  If this storm were to bomb before reaching the Lakes the severe potential would likely be even higher.

I would expect the strongest storms to be in the eastern part of my sub (AR and LA) and also W TN and W MS by the looks of things, though.

EDIT: SPC is now saying that E AR, the western 2/3 of TN, N MS, and the western half of KY (up to a point SW of Louisville) will be in a Day 3 Enhanced risk at the 30% hatched level; this also includes small slivers of SE MO, S IL, and S IN along the Mississippi and Ohio rivers.

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NAM is a lot farther south and somewhat weaker with the low (at least initially) which would temper the severe potential some but brings a lot more snow into MBY. Suddenly 34 and rain isn't looking like the guaranteed outcome with this system.

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If anything similar to some of the top 15 CIPS analogs verify Saturday, Central IL could also be in for a very long evening.  Some big severe days in and near the current ILX CWA among these analogs: 

http://www.eas.slu.edu/CIPS/ANALOG/DFHR.php?reg=MV&fhr=F060&rundt=2019022112&map=tbl

 

--#2 analog is 2/20/2014: http://www.eas.slu.edu/CIPS/ANALOG/Event.php?reg=MV&fhr=F060&rundt=2019022112&dt=2014022018

--#4 analog is 3/13/2006 0300 (9PM Mar. 12, 2006--just one hour after the first round of tornadoes hit the south and east sides of Springfield): http://www.eas.slu.edu/CIPS/ANALOG/Event.php?reg=MV&fhr=F060&rundt=2019022112&dt=2006031312

--#10 analog is 1/7/1989 1800--the same day as the F4 Allendale, IL tornado: http://www.eas.slu.edu/CIPS/ANALOG/Event.php?reg=MV&fhr=F060&rundt=2019022112&dt=1989010718

 

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Winds 80+ knots at 850 mb Saturday Night could easily translate to damaging winds 60-70 MPH Saturday Night with the thunderstorm activity. 

0z 3km NAM 850 Winds Valid 04z Sunday.JPG

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5 hours ago, Indystorm said:

Yes, SPC is relying heavily upon the NAM with WAA not proceeding as far north as originally thought.  My Sat. temp max dropped locally from 60 to 55.  Good luck Memphis.

Have a hard time figuring out why they are following the NAM so closely when it has been struggling with this system (playing catchup).  Also, this looks to me like a case where the NAM is again mishandling temps in the warm sector.  There is no snowcover to worry about so I see little reason to think that temps won't overperform what the NAM is suggesting.  This should help some sfc based instability to get farther north... to what extent is the question of course.   

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20 minutes ago, Hoosier said:

Have a hard time figuring out why they are following the NAM so closely when it has been struggling with this system (playing catchup).  Also, this looks to me like a case where the NAM is again mishandling temps in the warm sector.  There is no snowcover to worry about so I see little reason to think that temps won't overperform what the NAM is suggesting.  This should help some sfc based instability to get farther north... to what extent is the question of course.   

Because Darrow and the NAM are in an intimate relationship. It’s always been that way.

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Luckily SPC adjusted back north again, though still not far enough north.

They honestly have been lost ever since the SPC-WRF was discontinued, which they clearly heavily relied on.


.

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Further north across the Ohio Valley, scattered thunderstorms are
   forecast to move northeastward into western Kentucky and southern
   Indiana during the afternoon. Forecast soundings at 21Z for Paducah
   show MLCAPE near 800 J/kg with 0-6 km shear of 65 kt. This combined
   with strong low-level shear will be sufficient for severe storms
   capable of producing tornadoes and wind damage. Most of the severe
   convection should remain south of the Ohio River. Due to the weaker
   instability in the Ohio Valley, severe coverage is expected to be
   less.      From SPC day One with moderate risk in TN and northern MS.

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SPC has extended the marginal risk northwest across much of southern and central IL and sw IN with a slight risk along the Ohio River in se IL and sw IN primarily for hail.  998 mb surface low now in TX panhandle and expected to cross over IA as it moves ne and rapidly deepens.  We'll see what happens with later updates and nowcasts.  Could be a significant day for the mid south with tornadoes.  I'll want to watch where those elevated storms currently in Arkansas and Missouri are headed wrt our sub forum area.

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If any of you have been following the TN valley subforum on svr wx it seems that the NWS has been having multiple problems with software during this severe episode....Polygons are absent or stuck for warnings.....items are not updating.....sheesh!   Not a good situation for a moderate risk day at the start of the svr wx season.

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