CASA Forecast Discussion

…THUNDERSTORMS MOVING INTO TESTBED SHORTLY…

…DISCUSSION…
Thunderstorms are just about to enter the testbed. The RFD from the storms have pushed out in front of the trailing supercell and new thunderstorm development is occurring along the surging outflow. This new convection is forming in a region of enhanced vorticity and thus will pose a threat for tornado development. At present a TORNADO WARNING exists for northwest Caddo county (just outside the testbed). On its current track, this storm will move into the northwest portion of the testbed in the next 30-60 minutes.

In addition to possible weak tornadoes, very large hail is expected with these storms.

Further south, the outflow from the storms will move into western Cyril and eventually Lawton in the next 1-2 hours. This boundary should be evident on these radars.

…DEVELOPING ROTATION WEST OF THE TESTBED…

…DISCUSSION…
Presently three supercells exist west of the testbed moving east around 20-25 miles per hour. Over the past 20 minutes or so the low-level rotation signatures have dramatically increased based on KFDR. These storms are within 40 km of the northwest portion of the testbed. Area VADs indicate that hodographs are conducive for the development of low-level rotation in sustained storms. Storm motion is generally toward the east, thus, Cyril and Chickasha radars are the most likely to be impacted over the course of the next several hours.

…SEVERE WEATHER POSSIBLE LATE TONIGHT…

…DISCUSSION…
Repeat of previous days’ forecasts with strong storm system well to our west and rich, moist atmosphere in place. Thunderstorms should develop in the Texas panhandle north into southern Kansas during the overnight hours and then slowly grow upscale into an MCS. This MCS will initially move slowly eastward during the evening hours, but as the cold pools congeal and strengthen, the MCS should pick up speed and surge southeast into central Oklahoma.

As in previous days, best tornado threat will remain in Kansas and very large hail / damaging winds will be the primary severe threat. The northern portions of the testbed is in the most likely location to experience severe weather. The severe threat will persist through much of the evening.

…SEVERE WEATHER POSSIBLE ACROSS ENTIRE TESTED…

…HIGHEST THREAT ACROSS NORTHWESTERN AND THEN NORTHERN PORTIONS…

…DISCUSSION…
Thunderstorms developed along the retreating dryline across portions of the Texas panhandle as forecast. The environment across western Oklahoma is conducive for these thunderstorms to persist well into the overnight. These thunderstorms will continue to push eastward along the I-40 corridor possible affecting the northern portion of the testbed. Additional development to the south cannot be ruled out.

The MCS will put down an outflow boundary that will affect the forecast tomorrow. More on this tomorrow.

…SEVERE WEATHER IS ONCE AGAIN POSSIBLE (BUT NOT IMMINENT) ACROSS THE TESTBED…

…DISCUSSION…
Two nights of MCSs have left a very complex forecast in place. At present the deeper moisture has been shunted eastward into eastern Oklahoma. However, 60F dewpoints still remain across all of the eastern 2/3 of Oklahoma. Additionally, last night’s southern MCS has left a MCV across portions of central Oklahoma and at 14Z, this MCV was centered near Oklahoma City.

Thunderstorm development will be possible throughout most of the day as a myriad of boundaries exist in Oklahoma. Daytime heating combined with boundary interactions should allow for the development of thunderstorms. Better wind fields exist further north into Kansas with better instability further south in Texas. Thus, while thunderstorms are possible, the higher tornado threat (albeit still small) will be across northern Oklahoma with very large hail the primary threat across southern Oklahoma.

Today is very similar to the past 3 days with best chance of severe weather to the west and north of the testbed. However, with the presence of an MCV in the area, severe weather cannot be ruled out - but is not a guarantee. Watch for updates this afternoon as evolution of today’s severe weather event unfolds.

…SEVERE WEATHER POSSIBLE LATE AFTERNOON INTO OVERNIGHT HOURS…

…DISCUSSION…
Large tornado outbreak over central and western Kansas occurred late afternoon into the overnight hours yesterday. This outbreak of supercells congealed into a very large MCS across northern Oklahoma and southern Kansas and then pushed east into Missouri. This large MCS has complicated the forecast today quite considerably.

Outflow boundary from overnight convection is currently located across northern Oklahoma and stretched east-southeastward into Arkansas. North of the boundary winds are east and the atmosphere is a little more stable than south of this boundary. Across western Oklahoma a wind shift line is providing the western boundary to the more unstable airmass. Thunderstorm initiation is possible anywhere along the western boundary - particularly at the intersection with the outflow boundary - later this afternoon as daytime heating allows for extreme instability to develop.

Combining model guidance with a little bit of persistence would indicate that thunderstorms presently developing in central Kansas will continue through most of the day and that south and east of these thunderstorms is where the greatest severe threat will be. However, while this region has greater instability, shear is considerably less than further north. Visible satellite trends lead me to believe that the stronger instability will overcome the weaker shear and that thunderstorms should develop down the wind shift later this afternoon potentially impacting the testbed by late evening. While tornadoes cannot be ruled out due to the extreme instability, very large hail and damaging straightline winds will be the primary threat. After sunset, as the low-levels cool a bit and the low-level jet develops, a slight increase in the tornado threat can be expected with any discrete storms.

…ACTION STATEMENT…
All persons should be alert for the possibility of severe thunderstorms in and near the testbed this afternoon. This activity could persist well into the overnight hours as the wind shift should not push very far east.

…SEVERE WEATHER THREAT IS ONCE AGAIN POSSIBLE TODAY, BUT THREAT LEVEL IS LOW…

…DISCUSSION…
Severe thunderstorms are once again possible in portions of western Oklahoma today as a repeat of yesterday appears likely today. Another large tornado outbreak (potentially larger today) should take place across the western half of Kansas. Further south, the same concerns from yesterday hold true today. Namely, the strength of the CAP and the weaker mid-level winds. However, models are persistent in developing convection southward along the dryline late in the evening and thus, thunderstorms in western Oklahoma cannot be ruled out. Depending on the eastward component of movement, the western and northwestern portions of the testbed may catch a glancing blow from any convection the develops.