Tallis Rockwell Posted February 18, 2019 Share Posted February 18, 2019 ZCZC SPCSWOD48 ALL ACUS48 KWNS 180956 SPC AC 180956 Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0356 AM CST Mon Feb 18 2019 Valid 211200Z - 261200Z ...DISCUSSION... Models continue to indicate that blocking will remain prominent within the mid-latitude westerlies across the northeastern Pacific through this period. Downstream, it appears that flow may transition to a broadly confluent regime across the Pacific coast, Rockies, and Plains, and a less amplified regime in general across the southern tier of the U.S., by late next weekend into early next week. As this takes place, one more vigorous short wave impulse is forecast accelerate east-northeastward out of the Southwest. There appears increasing consensus, within and among the various model output, that this feature will provide support for strong surface cyclogenesis to the lee of the southern Rockies by this weekend. Guidance generally indicates that the cyclone center will rapidly migrate from the Texas/Oklahoma Panhandle region into the Great Lakes on Saturday. This probably will include intensifying lower/mid tropospheric flow (to 50-70 kt in the 850-500 mb layer) across an evolving warm sector boundary layer that will become at least weakly unstable, across lower portions of the southern Plains through the mid to lower Mississippi Valley region. This environment may become conducive to the evolution of an organized mesoscale convective system, and perhaps discrete supercell development ahead of it, accompanied by the risk for damaging wind gusts and tornadoes. It remains unclear whether destabilization eastward and southeastward, toward the Mid Atlantic and Southeast, on Sunday will remain sufficient to support an appreciable continuing severe weather threat. ..Kerr.. 02/18/2019 Link to comment Share on other sites More sharing options...
bdgwx Posted February 20, 2019 Share Posted February 20, 2019 12Z Euro looks potent for Arkansas. We'll have to watch southern MO for signs of elevated CAPE closer to the warm front where wind shear could be even more favorable for tornadic cells. Link to comment Share on other sites More sharing options...
cheese007 Posted February 21, 2019 Share Posted February 21, 2019 Day 3 enhanced risk issued. Kinda surprising for late February Link to comment Share on other sites More sharing options...
bdgwx Posted February 21, 2019 Share Posted February 21, 2019 There are some heavy hitters in the CIPS analog list for this event including multiple moderate and high risk days. Link to comment Share on other sites More sharing options...
Tallis Rockwell Posted February 23, 2019 Author Share Posted February 23, 2019 It is official .THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF NORTHERN MISSISSIPPI...SOUTHWEST TENNESSEE AND FAR NORTHWEST ALABAMA... ...SUMMARY... Scattered severe thunderstorms are expected to develop today from the Arklatex region and lower to mid Mississippi Valley eastward into the Tennessee and Ohio Valleys. Tornadoes, wind damage and isolated large hail will be possible across much of the area. ...Significant tornado and wind damage event expected across parts of the lower to mid Mississippi and Tennessee Valleys today... ...Arklatex/Lower to Mid Mississippi Valley/Tennessee and Ohio Valleys... A well organized negatively-tilted upper-level trough will move across the southern Plains today as a 90 to 100 kt mid-level jet moves through the base of the trough. At the surface, a low will gradually deepen and move northeastward across the central Plains into the lower Missouri Valley. A surface trough is forecast to extend southward into the lower Mississippi Valley with a moist airmass located across the region. Surface dewpoints in the upper 60s and lower 70s F will overspread northern Louisiana, southeast Arkansas and most of Mississippi by midday. At the start of the period, a cluster of thunderstorms should be ongoing from northern Mississippi into western and middle Tennessee. The stronger storms embedded in the cluster may have an isolated severe threat. This activity is forecast to move northeastward away the moderate risk area allowing for the moist sector to warm up late this morning. In response, a corridor of moderate instability is expected to be in place by midday from northeast Louisiana into far southeast Arkansas and western Tennessee. As large-scale ascent increases ahead of the southern Plains upper-level trough, thunderstorms are forecast to develop during the morning along the surface trough in the Arklatex with this convection moving northeastward into southeastern Arkansas by midday. More isolated thunderstorms will be possible across the moist sector from northern Louisiana into north-central Mississippi. During the early to mid afternoon, convective coverage should increase with scattered thunderstorms moving east-northeastward across the Enhanced and Moderate Risk areas. RAP forecast soundings across the Moderate Risk area from north-central Mississippi into southwest Tennessee at 21Z show moderate instability and impressive kinematic profiles. MLCAPE is forecast to be from 1000 to 1200 J/kg with 0-6 km shear in the 50 to 55 kt range. This will support supercell formation with cells that remain discrete. In addition, hodographs are long and looped with 0-3 km storm relative helicity values in the 350 to 450 m2/s2 range. This low-level shear environment will be favorable for tornadoes. A potential for long-track significant tornadoes will exist across the Moderate Risk area from late this morning through much of the afternoon. Wind damage and isolated large hail will also be possible with supercells. A squall-line is also expected to develop and move across the Enhanced and Moderate risk areas during the late afternoon and early evening. Wind damage, isolated large hail and a few tornadoes will also be possible with the stronger thunderstorms embedded in the line. This squall-line with wind damage potential should move across middle Tennessee and north-central Alabama during the evening. 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. ..Broyles/Bentley.. 02/23/2019 Link to comment Share on other sites More sharing options...
nwohweather Posted February 23, 2019 Share Posted February 23, 2019 Is this going to be the main thread for today? That warm sector looks absolutely vicious for this afternoon Link to comment Share on other sites More sharing options...
DanLarsen34 Posted February 23, 2019 Share Posted February 23, 2019 1 hour ago, nwohweather said: Is this going to be the main thread for today? That warm sector looks absolutely vicious for this afternoon That’s part of why I’m surprised this thread hasn’t taken off yet. This could be a big event! Link to comment Share on other sites More sharing options...
Sydney Claridge Posted February 23, 2019 Share Posted February 23, 2019 And I'm shocked hardly that people in the TN Valley or SE subforums are not really talking about this event either. Right now the warm front appears to be in northern LA and central MS (based on the northernmost edge of the surface CAPE) but we all know that is going to move north into TN over the next several hours. I guess I'm just getting a bit concerned about contamination of the warm sector here given the current location of storms in the Arklatex (but those aren't even in an area with surface CAPE at the moment) and the current precipitation over northern MS and TN. I'm not worried about contamination in MS, but more so in TN. Link to comment Share on other sites More sharing options...
Torchageddon Posted February 23, 2019 Share Posted February 23, 2019 1 hour ago, DanLarsen34 said: That’s part of why I’m surprised this thread hasn’t taken off yet. This could be a big event! My impression is this is underhyped so maybe things are really going to get out of hand later on. Link to comment Share on other sites More sharing options...
andyhb Posted February 23, 2019 Share Posted February 23, 2019 MLCAPE is already >1500 J/kg over a sizable chunk of the risk area at 17z so that element is basically checked off going forward. Going to come down to storm mode and whether the storm relative wind profiles are favorable enough for longer lived/strong mesocyclones (read: if the surface winds can remain at least southerly). Link to comment Share on other sites More sharing options...
DanLarsen34 Posted February 23, 2019 Share Posted February 23, 2019 In keeping with the “under the radar” theme of today: Just issued watch is 90-70 for MS, AR, and LA. A little surprised the initial watch across the moderate risk area in MS isn’t PDS. SPC said last year that the significant tornado percentage in the watch has to be 80% or higher to warrant the PDS language. Won’t derail the thread with the language discussion, but I think it’s worth debating at some point whether that language should be reserved for set-ups where several significant tornadoes are likely, which is what SPC says it’s for, or if we should use for it set-ups where, even if there aren’t “several,” there could still be 1-2 violent long-track tornadoes. Link to comment Share on other sites More sharing options...
cheese007 Posted February 23, 2019 Share Posted February 23, 2019 Wonder where the first tor warning is gonna pop up? Link to comment Share on other sites More sharing options...
Upper Level LOL Posted February 23, 2019 Share Posted February 23, 2019 Now Link to comment Share on other sites More sharing options...
Chinook Posted February 23, 2019 Share Posted February 23, 2019 1 minute ago, Upper Level LOL said: Now I saw this post on the board about 3 seconds before the warning polygon showed up on my GRLevel3 radar screen. I am always amazed by these things. A few days ago, the NAM most-unstable CAPE was barely 500 J/kg. Now we have the SPC Mesoanalysis saying that there is 2500 J/kg of surface based CAPE and a STP value of 3-4 in northern Mississippi. I really don't know how the models miss the instability forecast. Nevertheless, the SPC posted an enhanced risk on this yesterday, moderate risk today. So that all seems to make sense given the parameters measured today. Link to comment Share on other sites More sharing options...
Tallis Rockwell Posted February 24, 2019 Author Share Posted February 24, 2019 Please don't let this day be represent of the year. Link to comment Share on other sites More sharing options...
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