A new diary was posted at 1130 PM CDT talking about the Friday evening model runs and what they mean for the Saturday tornado outbreak.
843PM CT: Once the 00z (700PM CT) model runs come out, I'll write up another diary on this situation.A major severe weather outbreak is expected across the Central Plains on Saturday afternoon and evening, with an absolutely unprecedented severe weather forecast coming from the Storm Prediction Center. A full two days before the outbreak, the SPC has issued a high risk for severe weather across parts of Oklahoma and Kansas, including the Oklahoma City metro area, as well as Wichita KS.
554PM CT: I changed the title because of some confusion over what the abbreviations meant.
UPDATE 1255PM CT: I've updated to show the latest SPC forecast. The SPC has expanded the high risk/60% zone into parts of Nebraska and Iowa, to include the cities of Omaha, Lincoln, and Norfolk NE. Anyone in the red MDT (moderate) risk zone, and especially in the purple HIGH risk zone, needs to be alert for a major, intense tornado outbreak tomorrow. The environment is capable of supporting EF-4 to EF-5 tornadoes in the moderate risk zone, and especially in the high risk zones. That's why I'm sounding so Chicken Little-y about this. This has the makings to be a very dangerous outbreak, so please alert those you know about the situation and keep a close eye on the weather over the next 48 hours.
PS -- What I mean by "unprecedented" is that the forecast itself is unprecedented, not necessarily the outbreak.
The SPC has, as far as I know, never issued a high risk zone 3 full days in advance of a tornado outbreak, and they've definitely never issued a 60% risk zone for severe weather. Their certainty in this forecast is unprecedented, but in a good way (in that they're getting the word out really early).
They've done this once before on April 6, 2006 for a major tornado outbreak across parts of the southeast. There was also a 60% severe weather risk on that day. The resulting outbreak produced 94 tornado reports, 215 wind damage reports, and 565 hail reports.
PPS -- The tornadoes occurring this evening across Oklahoma are not part of the outbreak mentioned in this diary. The last week or so has been one long severe weather episode across this part of the country, which will come to a head tomorrow with the outbreak mentioned below. The threat will shift east on Sunday.
With extremely strong shear and relatively high amounts of CAPE forecast to be in place on Saturday, any storms that fire from Texas to Iowa are expected to turn quickly severe, with the worst weather occurring over central parts of Oklahoma and Kansas. Helicity -- a measure of spin that can occur inside of a thunderstorm -- is off the charts in this area. As of the model runs at 8PM last night, the helicity in Wichita KS was near 750. A value of 450 is sufficient for violent EF-4 to EF-5 tornadoes to develop.
The SPC is so confident that very dangerous severe weather will occur, that not only have they issued a high risk an unprecedented 2 days in advance, but they've also issued a 60% risk for severe weather, another absolutely unprecedented forecast. Not even during the strongest ongoing severe weather have I seen them issue a 60% risk zone.
I typed this diary at 125AM Central Time, and scheduled it to post at 900AM. I'm likely still sleeping by the time this diary posted, but I wanted to get the word out now that a very dangerous, life-threatening situation is expected to develop on Saturday. If you or anyone you know lives in the area under any threat for severe weather (within the yellow, red, or purple shading), let them know to keep a hawk-like watch on the weather today and tomorrow.
I'll have another diary later this evening on the outbreak, and definitely throughout the day tomorrow.
Here's a link to the Storm Prediction Center.
12:59 PM PT: Just a reminder...keep the ignorant political/religious comments out of here. The people under this threat span all walks of life -- religious, non-religious, Republican, Democrat, white, black, gay, straight. It does nothing but display your ignorance to make dumb comments like the couple I've seen in the thread below. Keep it classy, people.