Our teams are working in the North Platte CWA. They have sectorized, with Matthew and Mike taking storms west of the longitude of the radar, and Rob and Les taking those to the east. Matthew/Mike have issued one warning, using base data in conjunction with MESH, POSH, and max height of 50 dbZ. Their cell is elongated and straddling the east to west oriented fontal zone. Rob and Les have observed numerous microbursts near the radar. They feel the storms are not severe, but if they had the option – they would issue a Special Weather Statement.
Patrick Burke (EWP Weekly Coordinator, 18-22 May 2009)
Mike and Matthew would very much like to see a MRMS product depicting the max height of the 60 dbZ echo to use in concert with or in place of the 50 dbZ echo product.
Patrick Burke (EWP Weekly Coordinator, 18-22 May 2009)
The cells in far NW Nebraska have weakened. Other multicell storms were located west of North Platte, and satellite showed some vertical development to the congestus located all along the stalled front in north central Nebraska. We have relocalized the workstations, and will begin to simulate warning operations in the North Platte, NE, County Warning Area.
Patrick Burke (EWP Weekly Coordinator, 18-22 May 2009)
Matthew has worked diligently to track down phone numbers of people who live beneath the storm near Harrison, NE, where MESH indicated golf ball size hail earlier. His calls were mainly unsuccessful in reaching people, but one person reported 0.25 inch diameter hail, the same as a recent LSR from the Cheyenne WFO.
Patrick Burke (EWP Weekly Coordinator, 18-22 May 2009)
Both teams have been issuing warnings for hail in far northwest Nebraska. These storms appeared to be in the best environment, taking advantage of moderate mid level flow seen on the Medicine Bow profiler, and somewhat backed northeasterly surface flow just north of the slow moving cold front. Forecasters have been using the Max Estimated Hail Size (MESH) product, which reached near 1.75 inch. They have also been very interested in reflectivity at the 0 and -20 degree C level. They have looked at echo tops products, but mostly for completeness. The echo tops have not influenced warning decisions.
Patrick Burke (EWP Weekly Coordinator, 18-22 May 2009)
Since about 4:15 PM CDT, forecasters have been analyzing data in the Cheyenne CWA, while NSSL scientists provide more in-depth explanation of the various MRMS products. One team has already issued a severe thunderstorm warning for hail. We suspect the event will peak later this evening, however, once the forecasters are fully familiar with the MRMS tools available to them, and when storms move into the North Platte, NE, area.
Patrick Burke (EWP Weekly Coordinator, 18-22 May 2009)
Forecasters have finished with an LMA archive case. Timing couldn’t be better, as the SPC has issued a mesoscale discussion citing a severe weather watch possible in the central High Plains. Forecasters are listening to an end-of-day discussion from the Experimental Forecast Program. This will serve as at least the beginning of a “shift change” type briefing, while we bring the machines up into the Cheyenne, Wyoming, CWA.
Patrick Burke (EWP Weekly Coordinator, 18-22 May 2009)
Forecasters are currently working an archived LMA event, viewing lightning data associated with a number of supercells. Starting at 4 pm CDT, we will initialize the machines to our central High Plains target region for the MRMS IOP. This should give forecasters plenty of time to become familiar with navigating and interpreting the MRMS products as storms develop in Wyoming, before we begin intensive warning operations from 5-9 pm.
Patrick Burke (EWP Weekly Coordinator, 18-22 May 2009)
For the first and likely only time this week, we have Slight Risk areas in the Day1 Outlook from the SPC. We will use our time this afternoon to prep the HWT systems for a MRMS IOP to take place in Wyoming/Nebraska. The Florida Slight Risk is also intriguing, with several slow moving storms acting at times like supercells. Lapse rates are not very steep, so the main hazard is tornadoes. This event was ongoing early in the afternoon, however, and the risk area on the central High Plains syncs better with our operations and the availability of technical support in the HWT.
Categorical Day 1 Convective Outlook Issued 1630Z on May 20, 2009
Surface analysis revealed low pressure along a cold front in the eastern Dakotas. A pre-frontal trough extended through central Nebraska. Our focus for convection, though, will be the front and a deeply mixed boundary layer just south of the front in southeast Wyoming.
18 UTC surface map from the HPC
Models are consistent with a QPF signal developing in southeast Wyoming…and progressing along the stalled or slowly moving cold front in northern Nebraska and far southern South Dakota late this afternoon and this evening.
NAM Radar Reflectivity Valid at 03Z 5/21/09
This looks to be our best opportunity for a real-time IOP this week. VORTEX2 will also be operating in our target area.
Patrick Burke (EWP Weekly Coordinator, 18-22 May 2009)
Early on, forecasters commented that they enjoyed viewing LMA data from an early spring case in the southeast U.S. This was their first chance to navigate the data in a hands-on fashion. Technical problems delayed our intended MRMS IOP. Forecasters eventually viewed some MRMS data from radars near Salt Lake City and Glasgow. This was a good exercise in familiarization, but there were still some questions about the product labels in Google Earth, and what exactly the radar images represent. These questions will be answered on Wednesday. Technical problems were solved by the time we moved our IOP into the Glasgow area, but the weather did not cooperate. Storms were not continuous in time, and were not very threatening when they did exist. We decided to cut our losses, and spend the last two hours of the evening swapping yesterday’s teams between the CASA and PAR archive cases. I have heard a lot of good discussion as the teams viewed these cases, and we will discuss this further to begin the day on Wednesday.
Patrick Burke (EWP Weekly Coordinator, 18-22 May 2009)
