Weekly Forecast from Greg at Fox 25

** Scattered Flash Flooding Expected Across Northern OK Sunday night **
** Severe Weather with Damaging Winds Sunday in Northern OK Sunday Evening **
** Widespread storms on Monday **

Models hinted at this change yesterday. A cold front will sink southward into the northern TX panhandle, Northwest OK, and south-central KS on Sunday. Storms are expected to develop along the front. Initial thinking is development will start around 4 p.m. Right now it appears the front will extend from roughly Alva to Arnett by 7 pm. 0Z NAM has quite a bit of precipitation across southwest and Central OK which appears to be bogus and is not verifying from the new 4 km WRF. 4 km WRF has ruled the roost as far as model convection lately.

SPC has the main threat as large hail. While this may be true up in Kansas and Nebraska, our main threat will be from damaging winds. This is because the freezing level is 16,000 feet up, much too high for large hail formation without seeing an incredibly tall storm. Hail will melt with the freezing level that high. Therefore, I think outflow gust fronts/bow echos are the main threat. Some storms may have quarter size hail at the worst case scenario. Tornado formation does not appear likely either. Helicity is poor up until nighttime, and by then, the storms will have already formed into a squall line which favors straight line winds rather than tornadoes.

I was concerned about severe flash flooding initially and still can't rule it out. None of the regular models have performed well lately, and I think this is the case again tonight. There may be some training of storms across northwest Oklahoma during the evening and early overnight, but I do not expect the 6 to 7 inches of rain from Woodward to Alva that the 0Z NAM dumps out, or the huge 5" the GFS dumps out over Wichita. 4 km WRF (superior model) creates a substantial gust front (possible severe damaging wind event) along the leading edge of the storms which drives them southeast into OKC by midnight. This results in 4" totals from roughly Gage to Alva with possible locally higher amounts to 6" but in very small areas. WRF 4 km also has some scattered 3-4" amounts along and south of I-40 from Cordell to Poteau for Monday. If 4 km WRF is correct, rain could end across northwest OK by 2 a.m. Monday but linger across the southern 2/3rds of the state as we go into 7 am Monday (end of the model run).

There is a significant upper level trough passing on Monday as well. It should be in the eastern TX panhandle by 1 pm, which would support continued rainfall across the state. The front may bring some relief from the windy conditions and some relief from the heat. Where it rains all day, it may not get out of the 70s. I'm going 83 right now for OKC with a 60% pop only because I had 20% yesterday. From the looks of things, we may need to go close to 100% for Monday.Unseasonably hot weather sets back in for Tuesday with plenty of sun. GFS indicates temperatures may climb back into the mid 90s and ECMWF supports this solution. I used mostly the IPS meteostar spot hourly temps vs. MOS for the extended forecast, and the NWS forecast (#99) appears completely naive to what will likely happen. He/she went almost straight GFS MOS with the new run. 12z GFS had some major problems. First off, it drives the front for Monday well past the Red River. We have seen this before with it doing that and then the front hangs up near I-40. Why would this one be any different? Same thing with next Thursday night. Actually, the DGEX and NAM seem to have a better handle on the upcoming situation. I have used DGEX wind fields and model precip over GFS for the extended as a result. DGEX drives a front into the state on Sunday morning that the GFS hints at too. Tuesday through Thursday looks windy to breezy. On Wednesday, GFS hints at a short wave moving through northwest OK. A significant vort max (upper storm) passes through Thursday evening. I have upped pops to 50% given good agreement between GFS and DGEX and previous GFS runs. There may be redevelopment on Friday if the upper wave gets far enough east by afternoon to get us out of the NVA (downward moving air) area. DGEX hints at some redevelopment mainly east of OKC. I have left 20% pops in. GFS shows an upper storm passing around 7 pm in western Kansas on Saturday night. DGEX shows a front moving southeast into OK, reaching OKC around 4 a.m. Sunday. New 0z GFS has the front arriving Saturday afternoon. I am throwing 30% on this for now which is a continuation of the previous forecast. I'm keeping 30% Sunday as well from the looks of things from the GFS.

As we head into the week of the 17th-18th, there is little model consistency. 12z yesterday indicated a ridge building over, sending highs in western OK over 100. New 0z run has a low in the TX panhandle and an MCS crossing through (albeit positioning looks too far north) on the 17th and delays the ridge building. It does look like west Texas will get really hot.

OKC 76/92 73/83 63/90 72/94 75/92 65/90 70/92 65/84 69/90 71/93 73/95 75/96Pops 20% Sunday, 60% Monday, 50% Thursday, 20% Friday, 30% Saturday-Sunday.Light winds: Monday, Friday, Sunday.Forecast graphics at www.okcfox.com