11/24/10 (OK/MO) Severe Weather Post-Analysis

A lot of chasers ventured out today, anxious for a late season tornado catch! A powerful upper level system, combined with a unseasonably warm air mass was expected to set the stage for supercell thunderstorms with the potential for tornadoes across Oklahoma, Arkansas and Missouri. At the end of the day,only one tornado has been reported, although a few supercells were spotted. Let's dig a little further and see what happened today.

General Synoptic Setup
The large scale synoptic pattern featured a strong positive tilt trough centered across the western US. This set the stage for strong southwesterly flow in the mid and upper levels. At the surface, low pressure was deepening across far western Kansas and Colorado. A stationary boundary was located across Texas early in the period, and was lifted northward as a warm front through the day in response to the aforementioned deepening low pressure. To the south of this boundary, temperatures rose into the mid 70's by afternoon. Thunderstorms were expected to develop along and especially ahead of the encroaching cold front, amidst increasing large scale forcing and a moderately unstable environment, owing to a unseasonably moist airmass in place, with dew points rising into the mid 60's by afternoon.

By Early Afternoon...
By 18z, special soundings from NWS Springfield, MO and the NWS Norman, OK gave a slightly better insight into the atmosphere. The Norman, OK sounding showed an unstable environment, where only some mid level clouds had persisted through early afternoon. The Springfield, MO sounding however, shows a very stable environment. It appears as though the warm front has just passed through Springfiield from this sounding, but the true warm air had yet to reach the area. Both soundings exhibit impressive deep layer shear values, with 88kts on the Springfield sounding!! Although the Springfield sounding showed a lack of appreciable instability, continued clearing along and south the warm front would continue to aid in destabilization, especially in the mid levels in the afternoon hours. At 19z low and mid level clouds were still persisting across all of eastern Oklahoma, with the main breaks in the clouds now occurring across extreme northeast Oklahoma, and along I-44 through central Missouri. In addition, higher clouds were still evident across central Oklahoma.

The 18z run of the HRRR ( High Resolution Rapid Refresh) pegged a few thunderstorms to develop around 22z along the I44 corridor in far northeast Oklahoma into southwest and central Missouri. With recent satellite trends, showing maximized destabilization potential over that area, this made sense. By 22z severe thunderstorms were already ongoing across far southeast Kansas into central Missouri. In the presence of strong low level shear, these storms briefly exhibited increased low level rotation, but no tornadoes were reported. A quick look through mesoanalysis data, and radar information as the event unfolded, shows that although storms were semi organized they were likely not surface based. A stable low level atmosphere kept the storms from tapping into the available moisture at the surface. 0-3km CAPE values however were indicative of sufficient instability to support strong thunderstorms updrafts. In the presence of the strong shear, any storm that was able to realize this mid level instability and sustain itself for a period of time, was able to take on supercell characteristics, as seen across southwestern Missouri. One storm in particular near Brighton, MO was able to produce a brief EF-1 tornado that caused some minor farm damage. This storm exhibited very strong low level rotation, and appeared to become surface based for a short time, noted by the wind reports from the storm.

What Went Wrong...
In general, rather meager low level lapse rates, and a lack of surface instability, in the presence of excessive shear, likely prevented a larger scale and more significant event. Morning clouds, and slightly over-forecast moisture values offered less instability than was expected. Those storms that were able to sustain themselves were able to transfer strong mid level winds to the surface, and a few storms in Missouri exhibited strong low level rotation, in the presence of impressive low level shear, and one produced a tornado. Ultimately though, today was characterized by a mainly wind and hail event.The thunderstorms across MO prove that constant analysis of the atmosphere becomes vital, especially with nearby frontal boundaries, that play significant roles in the thermodynamic layout of the atmosphere.

Pertinent Images From Today

 

11/24/10 12z 500mb Analysis

 

11/24/10 12z Sfc Analysis

 

SPC Storm Reports 11/24/10

Norman, OK Special 18z Sounding

Springfield, MO Special 18z Sounding

 

18z Vis Sat Imagery

(Note the clearing along the I44 Corridor)

22z SBCAPE

22z 0-3km CAPE 

(note the MAX near the storms in MO)

18z HRRR 4hr Forecast.. Valid 22Z

Severe Weather to Return to the Southern Plains Tomorrow (Forecast 11/24/10)

It's November, but believe it or not, we are looking at the threat for a severe thunderstorm event across Oklahoma. Though quick moving storms, and less than favorable terrain may add some challenge to the forecast, the ingredients are coming together for a severe thunderstorm event tomorrow. Lets look into the setup!

Currently, a stationary front is draped across Central Texas into Southern Arkansas. A few elevated showers and storms are occurring on either side of the front, and may continue through the overnight hours. As low pressure deepens across Oklahoma tomorrow, this stationary front will be lifted north as a warm front. In the upper levels a powerful trough will continue to dig into the southern plains, with nearly 80kt of WSW flow at 500mb.. Deep layer shear values 65+ kts will provide more than adequate support for organized thunderstorm activity..

There is some discrepancy between Numerical models in the amount of instability that will be able to develop in the warm sector tomorrow afternoon. Latest High Resolution short term models are less generous with instability across the area, with SBCAPE values less than 500 j/kg across the area.. Morning precipitation and cloud cover likely are the causes for these discrepancies. With the moist airmass in place, any localized clearing would lead to rapid destabilization. If destabilization would fail to occur as the RUC/HRRR suggest, the amount of shear available would probably be "too high" to support powerful long lived updrafts.

Regardless, I would probably start near McAlester, OK as a beginning target..I believe convection should initiate and move rather quickly to the Northeast across the area. I would expect damaging winds to be the primary threat with the upper level energy in place, and freezing levels too high for a large hail threat.. Tornadoes will also be possible, especially in northeast OK into MO, where low level shear will be enhanced..

Forecast and Analysis Images

 

 Current SFC Map 06z 11/24

Current 500mb NAM 21 hr Forecast 21z 11/24

 

12am Wednesday (11.24) Radar, SFC Obs, Frontal Boundaries

Model Discrepancies - 21z CAPE Values

RUC - Top - Low Instability

NAM - Bottom - Favorable Instability

Allentown, PA Thurs Nov 4th Forecast

Synopsis: A complex flow pattern exists across the central US, as a trough continues to carve its way eastward toward the area. A moist airmass is being advected northward, in response to an upper level low found in the gulf of Mexico, and further aided by an easterly surface component, from a ridge centered off the coast. This moisture combined with increasing ascent ahead of the approaching upper level energy, will yield a rainy day across the forecast area!

Current 500mb Map
http://w1.spc.woc.noaa.gov/exper/mesoanalysis/s19/500mb/500mb.gif?1288826605859

Current 700mb Map
http://w1.spc.woc.noaa.gov/exper/mesoanalysis/s19/700mb/700mb.gif?1288826623865


Forecast: The atmosphere should saturate from top down in the early overnight hours across the area, as moisture is advected northward across the area. Precip should be ongoing by morning Thursday, and will continue for much of the day, as low pressure deepens, and moves eastward. On the backside of this system, winds will shift to the north, and usher in cooler temperatures. Extensive low clouds and moisture laden air will prevent significant cooling in the overnight hours. With that said, the temperature may reach its minimum near the end of the period, depending on the extent/duration of precip. Here is an image created, that shows the amount of 1hr precip (green bars), clouds (white) and temperature(red) as well as dewpoint (green) . CAPE (red/green/yellow line at bottom) is also plotted here, but as you can see, it is rather negligible. Meaning that there will not likely be any convectively enhanced precip.

http://www.wickedwindmedia.com/KABEOverview.jpg

Thus, looking at tomorrows data, highs should be confined to the mid 40's, as rain and clouds will likely hold temperatures down. Winds will be tricky with the precip, but it should be safe to assume that they will certainly be stronger than the previous few days, with low pressure deepening in the area, and any added momentum transfer from precip loading. This precipitation event should be more of a strati-form rain type event, with little in the way of thunderstorms to yield locally enhanced precipitation amounts. It's likely that much of the area will see over 1/2 inch of precipitation tomorrow. I encourage you to look at the latest model data, to look at the speed and timing of features, in determining the amount of total precip that will fall. Min temperatures, in addition will be tricky. It appears rain may be ongoing during the favored low temperature time frame. This may hold temperatures up slightly in the early morning hours. Models do indicate some cool air behind this system, so depending on when precipitation ends Thursday evening, the low may actually occur, once again, near the end of the period, as seen in the image posted above.
 
-Brandon Sullivan-
University Of Oklahoma
School Of Meteorolog