Area Forecast Discussion / Severe Weather Outlook

** Wind Damage, Large Hail Potential High Thursday Night across northern through east-central OK **
** Tornados, Large Hail Possible in South Central and Central OK on Friday **

New models from 0Z are in good agreement for today's weather. Very high humidity will be across the state as dew points surge into the 70s southeast of I-44 by afternoon.
Forecasts:
Altus - 92, S 10-15 wind
Ardmore - 87
Clinton - 88
Enid - 87
Guymon - 87, NE 10-15 wind
OKC - 86, SE 8-15 wind
Sallisaw - 86
Woodward - 89, SW to NE wind, 7-12
Afternoon heat index will be around 91 with 50% relative humidity. With not much wind, it's going to be like Florida.

By afternoon, a cold front will extend from from near Manhattan, KS to near Woodward, OK to north of Plainview, TX. A low will be near Plainview with a trailing weak dry line draping south to near Midland, TX. Although instability is present, there is no upper level support to speak of. Early AM water vapor shows a shortwave crossing through the Pacific Northwest US through Utah. This system is to remain to our north with the tail sheering out as it comes across late tomorrow. By afternoon, CAPE values in excess of 2,500 j/kg will exist just east of the cold front through most of OK except the far northwest. CAPE as high as 4,000 may be present near Duncan, with an area of helicity from 250-350. However there is no surface boundary in that location to cause convection, despite a weak cap. CAPE of over 1,500 with high helicity will exist over central Missouri where WRF initiates severe storms by late afternoon.

A very narrow window of opportunity may exist from 6-9 pm for a storm to develop along or northeast of the triple point from north of Plainview, TX to south of Gage, OK when cap strength may weaken enough along the front for a storm to develop. Movement would likely be east-southeast. 4 KM WRF, WRF-NMM and GFS hold cap and do not generate convection. Vertical Velocity fields are most favorable in this region yet are marginal.

Of greater concern is what will happen after dark. WRF-NMM and GFS are in excellent agreement on a severe complex developing after 1 a.m. in northwest OK and south-central KS which will likely evolve into a large severe MCS and roar across north-central into east-central OK, possibly affecting OKC. Large damaging hail appears likely and I cannot rule out tornado genesis especially during the first part of this event after 1 a.m. I would not be surprised to see a severe high wind event bow echo develop along the line at some point as well, as it moves east-southeast.

1 to 3 km sheer goes balistic from north-central to central OK in a large area. This is due to a strong low level jet developing after dark from near Midland to Childress and will eventually shift east to a Lubbock - OKC line during the night while increasing to near 60 mph. There is extremely good stacking of the vertical velocity fields just north of OKC by 7 a.m. The southward extent and development of the complex of storms will be limited by a strong capping inversion developing south of a line from Arnett to OKC to Durant. WRF suggests the complex may stay a bit further north than that. This system will eventually push into Arkansas.
A second opportunity for significant severe weather will exist late Friday afternoon and evening, especially across central OK. I suspect a significant tornadic storm could develop between Lawton and Chickasha, and move east with some deviant motion left or right. SPC already has a moderate risk out and this might be warranted for a small area.

By that time, the WRF-NMM shows the cold front extending from north of St. Louis, MO to Bartlesville, OK to northwest OKC to Altus to Plainview, TX and back northwest south of Dalhart, then up to the Rocky mountains in a sagging U. A dry line extends from a triple point near or northeast of Wichita Falls, TX. Afternoon and evening CAPE values of 3,500 j/kg should exist from the triple point northeast into OKC. After dark, a 60 mph southwesterly low level jet develops from near Abilene to near Purcell. This causes sheer to go balistic again across south-central, central and much of western OK, with the highest 1-3 km sheer values from Wichita Falls to Chickasha. However, capping inversion becomes very strong south of a line from Altus to Lawton to Chickasha to Durant to Mena, AR. Cap only weakens briefly ahead of the dry line before becoming quite strong so I think the dry line will remain quiet across north Texas. With the cap limiting southward development, and sheer so high in a confined area of southwest, south central and central OK, I believe we can limit the extremely severe weather to this area. Of note, there may be some early afternoon convection in northeast OK before the big stuff develops back down in southwest/south-central OK.

The cold front then presses through allowing for lower humidity and cooler afternoons. Northwest OK will get to enjoy this on Friday.Friday first guess forecast:
Altus - 97 *depending on front/dry line location, southwest wind switching to northeast.
Ardmore - 89
Clinton - 84
Enid - 78
Guymon - 77, NNE 10-15
OKC - 85, S 12-18
Sallisaw - 77Woodward - 79, NE 8-12

Can't rule out some overrunning general storms on Mother's Day, mainly southern 1/2 of the state. Another round of severe weather possible, perhaps next Thursday.
Greg