Indystorm Posted January 20, 2018 Share Posted January 20, 2018 Based on 18z 3k NAM and latest SPC outlook mentioning possible upgrade to slight risk as far north as MO if buoyancy improves have decided to open a thread for any possible svr aspects of this system for MO and IL. Feel free to discuss as the situation may warrant via models or nowcast observations as the episode unfolds. Convection expected to develop Sunday evening and move northeastward. Link to comment Share on other sites More sharing options...
Hoosier Posted January 20, 2018 Share Posted January 20, 2018 I could see some threat evolve, especially in Missouri, but overall lack of better moisture/instability is a real negative. Otherwise we'd probably be talking about a pretty legit squall line in a bigger chunk of the region with this setup. Link to comment Share on other sites More sharing options...
Indystorm Posted January 20, 2018 Author Share Posted January 20, 2018 Yes, the recent scouring of the Gulf doesn't help much in this regard, but I was surprised to see SPC even think about a possible upgrade to slight. Link to comment Share on other sites More sharing options...
cyclone77 Posted January 20, 2018 Share Posted January 20, 2018 DVN mentioning the T word for Monday over parts of IL where some small surface-based cape should develop beneath the dry slot. As far as convection goes, there is a chance for elevated convection associated with the terminus of the H85 LLJ. This is why isolated thunder has been kept in the forecast. What does appear possible now is clear slot convection Monday morning across the eastern CWA. At this time, upper level divergence and a jet streak will lead to chances for rain. During this period, all of the guidance suggests that 0-3km CAPE will be around 100 - 125 J/kg. Looking at the low level wind field, strong 0-1km shear also exists. The sfc winds are backed and the 0-1km shear vector is out of the SW. This appears to be a good set-up for HSLC tornadoes. If the CAMs develop cells on the clear slot, or even a broken line, there will be a threat for HSLC tornadoes, especially as the 0-3km shear increases from 12z to 18z on Monday. This will need to be monitored by later shifts. Link to comment Share on other sites More sharing options...
Hoosier Posted January 20, 2018 Share Posted January 20, 2018 12 minutes ago, cyclone77 said: DVN mentioning the T word for Monday over parts of IL where some small surface-based cape should develop beneath the dry slot. As far as convection goes, there is a chance for elevated convection associated with the terminus of the H85 LLJ. This is why isolated thunder has been kept in the forecast. What does appear possible now is clear slot convection Monday morning across the eastern CWA. At this time, upper level divergence and a jet streak will lead to chances for rain. During this period, all of the guidance suggests that 0-3km CAPE will be around 100 - 125 J/kg. Looking at the low level wind field, strong 0-1km shear also exists. The sfc winds are backed and the 0-1km shear vector is out of the SW. This appears to be a good set-up for HSLC tornadoes. If the CAMs develop cells on the clear slot, or even a broken line, there will be a threat for HSLC tornadoes, especially as the 0-3km shear increases from 12z to 18z on Monday. This will need to be monitored by later shifts. Very conditional setup but sometimes those can be sneaky. SPC doesn't even have general thunder area there on Monday. Link to comment Share on other sites More sharing options...
cyclone77 Posted January 20, 2018 Share Posted January 20, 2018 50 minutes ago, Hoosier said: Very conditional setup but sometimes those can be sneaky. SPC doesn't even have general thunder area there on Monday. 3km may be overdoing it but it has looked pretty interesting the past few runs. Sharp dry line kicking east across downstate IL with 300-400J/kg surface cape out ahead of it. Strong vort moving in. Also shows that general area getting in on some snows about 9hrs later. Link to comment Share on other sites More sharing options...
cyclone77 Posted January 21, 2018 Share Posted January 21, 2018 00z NAMs upped instability a little more to between 400-700J/kg surface cape from Galesburg to Saint Louis around noon. Nice arc of convection showing up fairly consistently on the CAMS the past few runs. Some pretty respectable 0-1km shear on a few of the soundings I looked at, particularly after 18z when surface flow backs a little bit. Link to comment Share on other sites More sharing options...
Chicago Storm Posted January 21, 2018 Share Posted January 21, 2018 Looks like the first shot at a t'storm around here this year, tomorrow evening-Monday. Link to comment Share on other sites More sharing options...
Indystorm Posted January 21, 2018 Author Share Posted January 21, 2018 This could get a bit interesting for central and southern IL on Monday afternoon if there is enough insolation in the dry slot and lapse rates steepen. Link to comment Share on other sites More sharing options...
cyclone77 Posted January 21, 2018 Share Posted January 21, 2018 New day 2 has added a marginal risk for portions of central IL. It will need to be extended north to I-80 or I-88 in later outlooks if model trends continue. Link to comment Share on other sites More sharing options...
Hoosier Posted January 21, 2018 Share Posted January 21, 2018 Can probably throw the NAM thermal profiles in the garbage for tomorrow. Good mid level lapse rates too and while I'm a bit skeptical of a severe threat this far north/east, can't entirely rule it out. Link to comment Share on other sites More sharing options...
Chicago Storm Posted January 21, 2018 Share Posted January 21, 2018 2 hours ago, Hoosier said: Can probably throw the NAM thermal profiles in the garbage for tomorrow. Good mid level lapse rates too and while I'm a bit skeptical of a severe threat this far north/east, can't entirely rule it out. Yep, have been discussing this elsewhere. The NAM (and some other guidance) has been over estimating lingering effects of snow cover, which is unrealistically keeping 2M temps lower. Link to comment Share on other sites More sharing options...
RCNYILWX Posted January 21, 2018 Share Posted January 21, 2018 Here's the 12z Euro's take on instability tomorrow afternoon. Looks pretty reasonable and supports extending the marginal risk farther north as cyclone mentioned. Sent from my SM-G935V using Tapatalk Link to comment Share on other sites More sharing options...
cyclone77 Posted January 21, 2018 Share Posted January 21, 2018 Great disco from DVN this afternoon. Can't believe it's Jan 21st and looking at a legit chance for tors near/in the area tomorrow lol. This kind of came out of nowhere, but the Euro has been sort of pointing at a low-topped convection threat going back to late last week for north IL. The main threat for severe weather will be associated with the clear slot. Consistent signal in the CAMs suggests thunderstorm development tomorrow afternoon. This would coincide with the triple point across the central CWA. Low levels winds are backed in the lowest 1km of the atmosphere. This coupled with 0-3km CAPE forecast to be near 200 J/kg in the 18z NAM (320-360 J/kg in the 12Z NAM) will lead to a HSLC tornado threat from these storms. The 0-3km CAPE drops off as the system pulls north later in the afternoon. This may be premature as the models still think there is snow there. Updraft helicity in the NAMnest suggests that virtually every updraft could rotate. The question of rotation to the ground will be tied to where the 0-3km CAPE is. SPC has introduced a marginal risk for our far southeast tomorrow. This event will need to be watched for potential increased messaging as an off-season fast moving event could lead to greater impacts. If the convection and the 0-3km CAPE do not overlap near the triple point, then the threat for tornadoes would be very low. That said, this event looks like an almost textbook example for cold-core low tornadoes. This needs to be monitored, especially if thermal trends do not hold as currently forecast. Link to comment Share on other sites More sharing options...
Hoosier Posted January 21, 2018 Share Posted January 21, 2018 Normally I would be inclined to post NAM forecast soundings, but given the likely issue with being underdone with surface temps, here is the GFS for a location near the IL/IN border around Kankakee. Not much to look at here but maybe just enough to get something. Link to comment Share on other sites More sharing options...
Hoosier Posted January 22, 2018 Share Posted January 22, 2018 RAP and HRRR have low 50s dewpoints in northern IL, which is a bit more than the GFS and of course the NAM. Link to comment Share on other sites More sharing options...
Indystorm Posted January 22, 2018 Author Share Posted January 22, 2018 Dewpoint is 53 at St. Louis and 50 here in Indpls at 10 p.m. EST this Sunday evening. Moisture will be advecting northward. Link to comment Share on other sites More sharing options...
Chicago Storm Posted January 22, 2018 Share Posted January 22, 2018 Decent shot at isolated strong/severe storms across IL/E. IN tomorrow... Low CAPE, modest shear, modest DP's for this time of year, temps into the low 60's, nice dry slot ahead of the incoming UL/SFC lows. Looks like we'll have a broken arc of storms develop midday/early afternoon from around the MLI-PIA-SPI-STL areas, rapidly pushing NE. Probably isolated tor and small hail threat. Will be interesting to see how it pans out. Link to comment Share on other sites More sharing options...
JPOracle Posted January 22, 2018 Share Posted January 22, 2018 Lots of low topped convection shows up in overnight period across Upper Ohio Valley and Applachians during the overnight period, i wouldn't be shocked to see tornadoes and microbursts from this activity during the night Link to comment Share on other sites More sharing options...
cyclone77 Posted January 22, 2018 Share Posted January 22, 2018 SPC made the adjustment north with the marginal risk up to just south of the I-88 corridor, and also includes a 2% nader risk. Link to comment Share on other sites More sharing options...
ConvectiveIA Posted January 22, 2018 Share Posted January 22, 2018 That's a pretty cool line of storms heading east currently through Indiana. It's not quite summer-red, but It really has that convective look to it. Link to comment Share on other sites More sharing options...
CheeselandSkies Posted January 22, 2018 Share Posted January 22, 2018 I don't think I've ever seen an SPC outlook use the word "parsimonious" before. Sent from my SM-G955U using Tapatalk Link to comment Share on other sites More sharing options...
snowlover2 Posted January 22, 2018 Share Posted January 22, 2018 Marginal area in IL dropped. Quote ...IL/IN to KY/TN late this afternoon/evening... Isolated low-topped thunderstorms will be possible later this afternoon/evening along the cold front (within the midlevel dry slot to the southeast of the surface cyclone) from northeastern IL across IN. However, destabilization will be marginal at best, and the threat for severe storms will be limited by the modest buoyancy and relatively weak low-level shear where destabilization is more probable. Deep-layer vertical shear will be stronger with southeastward extent into parts of the OH Valley/KY/TN. Any destabilization in the wake of the morning pre-frontal rain/convection should be limited given the low sun angle and modest upstream moisture/lapse rates, which will likewise limit any potential for strong-severe storms late this afternoon into this evening along the cold front. Link to comment Share on other sites More sharing options...
cyclone77 Posted January 22, 2018 Share Posted January 22, 2018 6 minutes ago, snowlover2 said: Marginal area in IL dropped. The CAMS have really backed off on the convection so I'm not too surprised. Still wouldn't totally write it off however. Link to comment Share on other sites More sharing options...
Hoosier Posted January 22, 2018 Share Posted January 22, 2018 29 minutes ago, cyclone77 said: The CAMS have really backed off on the convection so I'm not too surprised. Still wouldn't totally write it off however. Overall the setup hasn't changed too much and a nice clear slot is evident on satellite in western IL, so I'm with you about not totally writing off some (isolated) severe. Link to comment Share on other sites More sharing options...
Indystorm Posted January 22, 2018 Author Share Posted January 22, 2018 Just some heavy rain and wind gusts to 35 mph here this morning as the line came through. Nice dissipating shelf cloud however before the rain hit. Will have to see what this afternoon or evening may bring even though marginal was dropped. Link to comment Share on other sites More sharing options...
cyclone77 Posted January 22, 2018 Share Posted January 22, 2018 First look at towering cumulus for the year. Line of TCU right overhead now. Looks like it's on the verge of taking off. Link to comment Share on other sites More sharing options...
Chicago Storm Posted January 22, 2018 Share Posted January 22, 2018 SPC looking foolish, per usual.. Link to comment Share on other sites More sharing options...
snowlover2 Posted January 22, 2018 Share Posted January 22, 2018 Couple of t-storm warnings just west of Springfield IL now. Link to comment Share on other sites More sharing options...
cyclone77 Posted January 22, 2018 Share Posted January 22, 2018 ^Yeah already a 1" hail report. Link to comment Share on other sites More sharing options...
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