Forecast 8/26/09

Synopsis:

An upper level trough is just northwest of the forecast area with a cold front along the same axis.

0Z 200mb:

Discussion:

Very little upper level support for the system entering the forecast area as depicted in the graphic above. The storms to the west of Tulsa are making very slow progress to the east tonight. The main concern is heavy rain tomorrow, not severe weather tonight.

3Z (9PM CDT) Radar Image:

The most likely scenario is a chance of a bit of rain and thunder tonight and then training storms along the cold front tomorrow. Where the front decides to park will determine rainfall amounts. See the current surface map below.

3Z Meso Surface:



Secondary shot of cold air looks to be on track for Sunday after an awesome cool Friday and Saturday. Comments and questions are always welcome. Hope you enjoy the forecast...

Forecast 8/25/09

Synopsis:

The forecast area remains under an upper level trough for the next 36 hours with a cold front to the NW from a low centered over the OK panhandle running to the NE across KS, NE, IA, MN and WI. The cold front was clearly visible on satellite and dovetails nicely with the ridge to the NW.

200mb 12Z:

Surface 12Z: (Note 200mb overlay in light blue)

Discussion:

The strange weather continues for NE OK as what should be the dog days of summer have seemed more like late spring (not that I am complaining about that). Temperatures should be just below seasonal norms through Wed then we will see another cool down and a chance for rain. The ridge we are under should continue to translate east over the next 36 hours with a cool front approaching the region in the overnight hours on Wed. Note the 72 ECMWF 200mb chart below.

ECMWF 72 hour:

The NAM, GFS and ECMWF are all in pretty good agreement that the cold front should be to the south of the forecast area by 7PM on Thursday. Look for a chance of early morning convection Thursday morning with clouds probably lingering in the area for most of the day.

Once we get Thursday's front out of the picture look for another trough and cold front to move into the area during the Sunday timeframe.

120 Hour ECMWF:

Overall we will be below seasonal norms for this time of year and should be able to enjoy temperatures in the mid 80's during the days with temperatures falling into the lower 60's overnight. Not bad for August in OK!

Forecast 8/19/09

Updated 17Z Analysis, new target area is Perry OK.

Synopsis:

An upper level trough sits just to the west and north of the forecast area with a stationary front along the same axis.

12Z 200mb Analysis:

Discussion:

A difficult forecast today with the chances for rain and severe weather through the next 24 hours but great difficulty in nailing down the scenario. The models and the Tulsa WFO blew the call on the crapvection this morning in the Tulsa area. All indicators were that it should have stayed just to the NW, however we have ongoing convection and rain through the late morning hours.

1530Z INX Radar:

The real challenge with this forecast is trying to get a handle on the severe threat later in the day. The RUC and NAM are showing CAPE values in excess of 2000Kjg this afternoon and evening with a CAP that should erode to our NW mid to late afternoon. The models are also showing decent shear to the NW and over the forecast area early evening to overnight. This combination should provide the ingredients for a severe scenario in the late afternoon and the early evening hours. The SPC has a 5% tornado risk just NW of the forecast area and based on the parameters in the latest model runs I agree with this assessment.

At this time the most likely scenario is storms will fire in south central KS in the afternoon and make a run at NE OK in this evening. The best chance for severe weather including tornadoes will be to the NW in the south central KS and north central OK region in the early evening hours. The severe threat should decrease to the south east of this area. My best guess at this time is the storms will stay discreet for a short time in the late afternoon and evening before lining out as an MCS headed for NE OK.

12Z Surface:

If I were chasing today (and the more I think about it, I just might be) I would probably pick somwhere between Wellington KS and Ponca City OK as a target around 20Z. With 0-3km helicity values up to 300, CAPE pushing 3000, LI around 10 and low LCL's, the target area should be prime. Td's in the upper 60's should provide plenty of fuel as long as we get some day time heating, but that is really in question at this point e.g. latest visable sat... http://www.rap.ucar.edu/weather/satellite/displaySat.php?region=ICT&itype=vis&size=small&endDate=20090513&endTime=-1&duration=0

All that said, due to the ongoing convection this morning and cool temperatures the models may be over doing instability and this forecast could bust in NE OK. Conditions will need to be monitored throughout the day as they evolve. Long story short, if the sun breaks through this afternoon we may be in for it tonight...

12Z 500mb:

12Z 700mb:

12Z 850mb:

Forecast 8/18/09

Synopsis:

An upper level trough lies just to the NW of the forecast area and should translate east over the next couple of days. A stationary front lies just to the N of the forecast area and has been the focus of ongoing convection.

12Z 200mb analysis


Discussion:

15Z Meso Surface

The overnight convection is ongoing to the W and N of the Tulsa area and has shown a weakening trend over the last few hours. An area of high pressure over NE OK is holding the convection off to the west and keeping the stationary front just to the N of the forecast area. Overcast skies due to debris from the convection to our west will hold temperatures down today and keep the chances of severe whether pretty much in check. There will be the possibility of hit or miss rain during the afternoon, but the best chances should stay to the north and west of Tulsa.

The best chance for rain appears to be in the Wednesday night time frame as the atmosphere should recover some instability during the day tomorrow. Shear should also increase during the late afternoon and evening hours Wednesday. At this time I am expecting an MCS to form to our NW during the late afternoon hours on Wed and enter the Tulsa area late in the evening. While there is the potential for some severe storms, rain should be the main mode for this complex.

Things should clear out after Wednesday and temperatures this weekend look to be at or below seasonal norms. While there is not a great agreement among the models at this time, it looks like temperatures may ramp up early next week with generally dry conditions prevailing.

12Z Regional Surface:
12Z 850mb
12Z 700mb
12Z 500mb

Nowcast 8/17/09

Here is the radar for Tom out in New Prue.

Forecast 8/17/09

Synopsis:

NW Flow remains just N of the forecast area with an upper level low centered over NW North Dakota. A stationary front runs from a surface low over the OK/TX panhandles to the NE into the upper mid west.

Surface 12Z

Discussion:

Overnight convection has been able to sustain through the morning hours just to the south of the stationary front. North central OK saw rain fall amounts in excess of 6" overnight with some damaging winds in the Enid area. The stationary front is progged to move slowly south over the afternoon and evening hours. However, the best area of shear will remain to the NW of the forecast area. An out flow boundary from the overnight convection lies over Osage county to the NW of Tulsa and has been making slow progress to the SE of the last few hours. Depending on where the boundary ends up, it should serve as the focus for additional convection this afternoon in the forecast area.

The shear environment should improve near the Tulsa area during the late afternoon hours after 21Z. If the out flow boundary makes it far enough south there is a good chance for scattered severe storms during the late afternoon and evening hours. The unknown at this point is whether the day time heating potential will be realized due to the high clouds from the morning convection. If the clouds manage to clear out in the next couple of hours the chance for storms will increase.

I know there are a lot of "ifs" in the above, but that is just how it goes with late summer thunderstorm forecasting...

700mb 12Z

850mb 12Z
200mb 12Z

Forecast 8/8/09

Target Area:

Lake Wilson, MN

Timing:

20Z

Storm Mode:

All modes of convection are possible with super cell / multi cell favored late afternoon to early evening.

Synopsis:

An upper level ridge is centered over the target area per the 12Z soundings. Winds at 200mb are WSW at ~80kts. There is a surface low centered on KSFD as of 18Z with a warm front extending to the ENE on a line from KSFD to, Redwood falls MN, Glenwood City WI, then to the ESE. There is a trough of low pressure extending from the surface low to the N and extending from the surface low to the SSW according to a 17Z hand analysis.

12Z 200mb

Discussion:

Convection is ongoing to the W of the target area as of 18Z with one cell already warned to the W of KSFD. The RUC shows very little movement in the surface low over the next 12 hours. The low should continue to slide ENE along the nearly stationary warm front over the target area. The latest RUC runs show a trend to keep surface winds backed through 22Z in SW MN. With CAPE values in excess of 3000Jkg and 0-3km helicity values over 100 the atmosphere is certainly primed for potentially serious convection through the late afternoon and evening hours.

The activity should continue into the evening moving through an environment with sustained shear and an excellent inflow of 70+Td's from the SE. Deep moisture is available with 850mbTd's approaching 70 over southern MN according to the 12Z RUC run. 700mb temps are progged to be in the 12 degree range at 20Z, however given the convection to the west, the trough of low pressure and the warm front, there should be plenty of forcing available to break the cap with CinH values falling to -50 by 21Z.

The only down side I see to this setup is the probability that it will line out into an MCS/MVC later in the evening. However, if cells can remain discrete during the late afternoon and early evening hours this is very chaseable.

18Z Surface (Don't have a scanner at the house for my hand surface analysis so here is one from DA)