Taylor Wright
EF2
It's time to start a discussion on this Friday's event which has looked pretty impressive on the GFS for awhile and is within 60 hrs which is probably the trustworthy range of NAM. That being said, the NAM has been pretty poor handling a lot of these recent days so I take its output with a major grain of salt in this forecast.
You have a very broad mid-level trough ejecting from the west, with two main impulses appearing likely. One in the Dakotas, primarily North Dakota, and one over the southern Rockies into eastern CO. The gulf has essentially been wide open with moisture trajectories into the plains since the landfall of Alberto, and mid to upper 60s dews will make it as far north as North Dakota near a strengthening low associated with the mid-level speed max. Dewpoints into the 70s should make it well into Kansas, and it appears into southwest Nebraska. Mixing will obviously be in question with most of the northern plains surface temps in mid to upper 80s. Because of this I compared GFS, Euro, NAM and NAM 3km dews in the image below to get an idea of realistic moisture and dryline orientation.
![0z Dews.jpg 0z Dews.jpg](https://stormtrack.org/data/attachments/33/33823-467477682061509998d102769bc0b441.jpg)
It's evident NAMs and Euro are in pretty impressive agreement with 70 dews making it into southwest Nebraska, in addition to the placement of the dryline itself being farther west than originally depicted by the GFS. This should allow for 1200-1500 meter LCLs which while not ideal, can certainly get it done and should lower quite a bit near sunset. If the moisture wraps around that low into Colorado, you could be looking at high 60s dews in northeast Colorado much closer to the ejecting 500s.
0-1 km SRH is definitely more impressive on GFS than NAM, however this was an issue the NAM depicted on all three days Sun-Tues and a main reason I didn't chase, and I was burned on every one of them. The morning of, it was clear the NAM was out to lunch and boundaries would enhance those SRH values significantly, leading to 3 days of tornado producers. While it doesn't look like a boundary will be in play Friday, the NAM shows significant SRH at 03z with the surface inversion still weak in central Nebraska which leads me to believe the NAM is just a bit late with the strengthening of the low level jet and storms could be surface based well after sunset.
One primary issue I see is the 500 mb jet is displaced 100 miles south of where convection is likely near the surface trough in west Nebraska on the NAM. It ejects over western KS where 700 mb temps are much more toasty (15-17 C), and as such doesn't appear convection is likely in KS. This means for Nebraska target you're looking at closer to 30 kt 500s and less synoptic support. The GFS solution of more broad 500 mb flow would favor better mid-level venting.
Right now, the primary targets appear to be the triple point in North Dakota or Canada and the secondary low/dryline intersection in southwest Nebraska. The northern target will likely be MCS or HP supercells initially with weaker storm relative winds and strong forcing, not to mention light years of driving, but the low level jet near that low is much stronger and as such expect very impressive SRH values and tornadoes regardless. As it stands, I will be targeting somewhere near North Platte, NE and likely make an adjustment from there in the morning, with the main show maybe being late from 7-9 pm if storms can remain discrete. Unfortunately roads are pretty poor north of I-80 so hoping that we can get initiation farther southwest.
You have a very broad mid-level trough ejecting from the west, with two main impulses appearing likely. One in the Dakotas, primarily North Dakota, and one over the southern Rockies into eastern CO. The gulf has essentially been wide open with moisture trajectories into the plains since the landfall of Alberto, and mid to upper 60s dews will make it as far north as North Dakota near a strengthening low associated with the mid-level speed max. Dewpoints into the 70s should make it well into Kansas, and it appears into southwest Nebraska. Mixing will obviously be in question with most of the northern plains surface temps in mid to upper 80s. Because of this I compared GFS, Euro, NAM and NAM 3km dews in the image below to get an idea of realistic moisture and dryline orientation.
![0z Dews.jpg 0z Dews.jpg](https://stormtrack.org/data/attachments/33/33823-467477682061509998d102769bc0b441.jpg)
It's evident NAMs and Euro are in pretty impressive agreement with 70 dews making it into southwest Nebraska, in addition to the placement of the dryline itself being farther west than originally depicted by the GFS. This should allow for 1200-1500 meter LCLs which while not ideal, can certainly get it done and should lower quite a bit near sunset. If the moisture wraps around that low into Colorado, you could be looking at high 60s dews in northeast Colorado much closer to the ejecting 500s.
0-1 km SRH is definitely more impressive on GFS than NAM, however this was an issue the NAM depicted on all three days Sun-Tues and a main reason I didn't chase, and I was burned on every one of them. The morning of, it was clear the NAM was out to lunch and boundaries would enhance those SRH values significantly, leading to 3 days of tornado producers. While it doesn't look like a boundary will be in play Friday, the NAM shows significant SRH at 03z with the surface inversion still weak in central Nebraska which leads me to believe the NAM is just a bit late with the strengthening of the low level jet and storms could be surface based well after sunset.
One primary issue I see is the 500 mb jet is displaced 100 miles south of where convection is likely near the surface trough in west Nebraska on the NAM. It ejects over western KS where 700 mb temps are much more toasty (15-17 C), and as such doesn't appear convection is likely in KS. This means for Nebraska target you're looking at closer to 30 kt 500s and less synoptic support. The GFS solution of more broad 500 mb flow would favor better mid-level venting.
Right now, the primary targets appear to be the triple point in North Dakota or Canada and the secondary low/dryline intersection in southwest Nebraska. The northern target will likely be MCS or HP supercells initially with weaker storm relative winds and strong forcing, not to mention light years of driving, but the low level jet near that low is much stronger and as such expect very impressive SRH values and tornadoes regardless. As it stands, I will be targeting somewhere near North Platte, NE and likely make an adjustment from there in the morning, with the main show maybe being late from 7-9 pm if storms can remain discrete. Unfortunately roads are pretty poor north of I-80 so hoping that we can get initiation farther southwest.
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