PAR operations underway…
Kevin and Eric will begin Phased-Array operations centered on the Altus, OK, supercell. Mark and Brad will practice interrogating WSR-88D data using WDSSII while being on standby for either CASA operations or a CASA archive case later this evening.
Patrick Burke (EWP Weekly Coordinator, 27-30 May)
Western OK…IOP begins 5 PM
Forecasters completed PAR and CASA Training, and are now learning WDSSII using live data of a supercell near Altus, OK. There is a second severe storm near Elk City. Both storms are moving very slowly…seemingly balanced by southeasterly low level inflow and southwesterly mid level steering flow. They may also tend to propagate into the instability axis…which is unfortunately just west of the CASA network. With some luck, however, we could see storms reach the western parts of CASA later this evening. PAR operations will begin at 5 pm.
Patrick Burke (EWP Weekly Coordinator, 27-30 May)
Training Continues…3pm
The SPC has placed southwest Oklahoma, including most of the CASA domain, under a Severe Thunderstorm Watch until 03 UTC. The outflow boundary has zipped up with a pre-frontal trough from Shattuck to Mangum, OK. Scattered CBs have formed off and on in this zone…but none have quite taken hold, as convergence and lift remain quite shallow. Other thunderstorms have begun to sustain themselves farther south along the trough axis into Texas. Opportunity for more robust convective initiation should increase up into Oklahoma with additional heating/destabilization. Water vapor imagery also hints at the influence of a short wave ridge exiting western Oklahoma…with a more diffluent upper flow pattern approaching from eastern New Mexico/West Texas.
The forecaster/evaluators have switched places so that both sets of two will receive training on both the PAR and CASA experiments. The Oklahoma IOP will either begin at 4pm (WDSS training on the fly) or 5 pm (WDSS traning at 4pm).
Patrick Burke (EWP Weekly Coordinator, 27-30 May)
Our four forecaster/evaluators (Eric Stevens, Brad Colman, Mark Melsness, and Kevin Brown) arrived at the NWC early this afternoon, and are ready to hit the ground running in this Holiday-shortened week. Today should be our best chance for a central Oklahoma IOP, so we have split the forecasters among PAR and CASA for training on those programs through 3 pm. After checking the weather… we may be able to swap and allow the groups to train on both programs. If weather dictates that operations begin prior to 5 pm, however, we will forego WDSSii Training. Kevin has WDDS experience, and other scientists are available to either drive WDSS or train the other forecaster “on the fly.”
The forecast is for thunderstorms to initiate near the intersection of a cold front and outflow boundary in northwest or west central Oklahoma. Other storms may initiate farther south along the outflow boundary toward southwest Oklahoma and western north Texas. Storms should then move east and southeast toward the PAR and CASA domains, although some southward propagation may occur within the instability axis. The northeastward extent of this activity toward central Oklahoma is somewhat in question…as that area was overturned by an MCS earlier today. At worst…we expect a few severe storms at long range but within the PAR domain. At best…we could have severe storms in both the PAR and CASA domain by early to mid evening. The Shear/CAPE combination is sufficient for rotating storms…and even a tornado threat just east of the outflow boundary…although weak mid level winds may lead to a quick transition toward high precipitation character.
Patrick Burke (EWP Weekly Coordinator, 27-30 May)
Experimental Warning Program Blog Entry: 4/23/08
Between 3 and 5 pm today, Angelyn Kolodziej and I ran through an archived event, using PAR data as the basis for mock severe weather warnings. We both noted the utility of rapid-update radar data in catching the onset of low-level mesocyclogenesis. It was also enlightening to interrogate storms as a team viewing the same data. This forced us to state our reasoning aloud, and resulted in a verbal exchange of conceptual models and warning philosophies. I felt that we arrived at more accurate and timely warning decisions than either one of us could have accomplished alone. When the 1.5 hour simulation concluded, it was fairly obvious from my five plus years of NWS warning experience that we had issued more warnings over a small area than we would have issued using WSR-88D data. Angelyn and I suspect the PAR scan strategy captured certain features that tipped the scales toward issuing a warning, and which may have fallen between traditional WSR-88D volume scans.
Shortly after 5 pm, we had intended to begin probabilistic warning operations, but paused to observe the supercell that came up to the south and east of Norman. All eyes were fixed on the live updating PAR data and the SADS. Oklahoma City television crews delivered video of a low hanging wall cloud with rising scud, but weak rotation. The circulation never quite tightened up, and the storm had trouble maintaining supercell structure for any length of time.
The Norman storm was at the southeast extend of an extensive cluster of multicell thunderstorms that spread northward across Oklahoma through mid evening. Between 6 and 8pm, Mike Magsig worked this activity from one of the probabilistic warning desks. Meanwhile, at the second desk, I shifted my attention to an ongoing high-end severe weather event in north Texas. A long-lived, high-precipitation supercell moved eastward into the Fort Worth WSR-88D domain. This storm expanded in size, forming a classic bow echo anchored by a broad mesocyclone at the northern end. An exceptionally intense rear inflow jet presented 90 to 100 knot ground-relative velocities at times. Out ahead of this complex, another large supercell formed and approached the southern sides of Fort Worth. This storm quickly took on the appearance of a classic, tornadic supercell. Eventually, the bow echo overtook the tornadic storm in the vicinity of the KFWS radar. With the advantage of near range sampling at low levels, the radar detected several small-scale vortices along the leading edge of the storm outflow.
The variety of storm modes and storm motions in the two operational domains fostered a productive discussion between myself, Mike, and Greg Stumpf. Mike had difficulty drawing probabilistic grids for the transient multicell hail storms taking place in Oklahoma. One potential approach may be to outline a broad area of low probability severe hail, and then embed shorter duration, higher probability warnings for particular cores that show some persistence or organization. Whatever the warning philosophy, the actual grid preparation could benefit from some type of automated routine or suite of routines for defining a threat area. For instance, a tool that outlines the 55 dbZ contour with attention to echo overhang might be a good starting point for drawing a hail threat area.
The Texas storms brought up a host of even more complex issues, including personal tornado warning thresholds expressed as a percent chance of tornado, detailed spatial resolution of tornado threats (e.g. high probability surrounding a TVS and lower probabilities along the RFD gust front), and how to emulate longer lead-time information in a probabilistic way (e.g. drawing a 2-hour probability swath to mimic a special weather statement that WFO Fort Worth issued to raise awareness in the metropolitan area).
Much of our conversation stemmed from large scale design issues, using examples from the evening’s data to explore probabilistic warning strategies. In general, we concluded that in designing a probabilistic warning system, researchers may begin with an idealized philosophy, and then incorporate forecaster preferences that have been gained through experience. Many of these preferences will hopefully become evident throughout the course of the EWP spring activities.
Patrick Burke (WFO OUN Forecaster, EWP Weekly Coordinator-in-Training)