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OUNWRF evolves long-lived supercells over Morgan, Washington and Lincoln counties with a rapid eastward progression. This may place highest supercell risk a bit more to the north compared to theta-e difference forecast (mentioned in the blog entry below). Despite LCLs aoa 2.5 km and increasing DCAPE towards C/E Colorado, the WRF keeps max hourly wind speeds on the lower end side. Feeling is that initiation of WRF activity may be too optimistic/early with slow BL moisture recovery still underway.
OUN-WRF updraft helicity (upper left), surface hourly column hail (upper right), surface max hourly wind speed (lower left) and surface max hourly updraft helicity (lower right)
This cell produced coin-sized hail right around the time the 3d-VAR Max Updraft/Divergence peaked. It’s hard to tell if there was lead-time or not. An interesting aspect of this storm is that fact that it passed right over the krax radar and into the cone of silence. This shows the value of having multiple radars looking at the storm.
The CIMMS cloud top cooling algorithm first detected cooling rates of approximately -10 C/15 min with a thunderstorm developing across eastern Hoke and western Cumberland counties on the 1815z image. The algorithm continued to show strong cooling rates on the next two images with accumulated CTC values of approximately -30 to -35 C/15 min before the cell was dropped from the display after 1845z. A report of quarter sized hail was received in far southwestern Harnett county with this thunderstorm at 1937z, almost an hour and a half after the algorithm first detected stronger cooling with this storm.
Accumulated CTC values for a cell that produced severe hail.
Conditions gradually improve for thunderstorm development over NE Colorado although initiation may be delayed until the 23-00 Z time frame. Surface boundary pushed through as lee depression slowly consolidated over W-Kansas. 12Z Denver soundings showed steep lapse rates with a deepening and well mixed boundary layer. Numerous weak caps present (roughly at 700, 600 and 500 hPa). CIMMS Cld top cooling product revealed numerous spots with moderately cooling tops in the order of -10 to -15 K/15 min with UAHCI CI product showing low to non existent probabilities. This may be the reason for growing updrafts before reaching one of those aforementioned caps, which suppressed further development. For the forecaster however this is already helpful to pinpoint the area, where enhanced cumulus growth occurs and where initiation may be the most likely.
Question now arises if moisture recovered since 12 Z. Surface dewpoints struggle to exceed mid to upper 30s with lower 40s now entering far NE Colorado as winds backs more to NE-erly directions in response to the consolidating lee cyclogenesis. However, products like the 780mb equiv pot temp and the theta-e diff show robust signals for available potential instability over far NE Colorado with an increasing trend during the following hours. In fact, latest HRRR forecast and the tongue of pot. instability seem to overlap nicely. Hence initiation seems possible around and south of a line Steamboat Springs-Denver-Deer Trail during aforementioned time frame. Incoming mid-level speed max pushes DLS aoa 80 kt, which is more than adequate for well organized storms.
In the 1815 UTC vis satellite image (upper right of top 3-panel), cloud-top cooling was on the order of -17C/15min with a developing thunderstorm. By 1858 UTC, MRMS MESH product reached 1″ hail size (middle image), and just over 2″ hail size by 1906 UTC. The UW-CTC product lead to 45-50 minute lead time for 1-2″ hail (as estimated by MRMS MESH). This is one of many instances we’ve noticed the CTC give decent lead time for 1″ or larger hail.
1815 UTC. Rapid convective development as indicated by -17C/15min cloud-top-cooling rates.1858 UTC. MRMS (multi-radar, multi-sensor) MESH (max estimated hail size) is estimating 1.02" hail, about 45 minutes after rapid CTC. 1906 UTC. MRMS MESH now estimating 2.13" hail, about 50 minutes after initial rapid CTC.
The MRMS MESH algorithm predicted a maximum hail size of 1.34 inches with a thunderstorm across far southwestern Harnett County on the 1930z image. A report of quarter sized hail was received with this storm at 1937z to the southwest of Pineview, NC.
MESH values for 1930z across southern Harnett County, NC.
I compared the MR/MS MESH to the legacy SCIT hail algorithm. MESH values were lower. Perhaps this is an improvement over the high bias inherent in the old algorithm…or maybe just a result of differing resolutions. Quarter-sized (1.00 in.) hail was reported with this storm.
The UAH-CI algorithm displayed two areas with high strength of signal values (64 and 92) across southern Cumberland and western Sampson counties on the 1702z image. These cells intensified quickly into two thunderstorms and a report of penny sized hail was received from the eastern storm at 1823z, more than an hour after the algorithm first detected these thunderstorms.
The CIMSS-CTC algorithm showed cloud top cooling rates of between -10 to -15 C/15min on several images with a thunderstorm developing across Sampson county in North Carolina. The CTC first appeared on the 1715z image and continued to highlight this cell through the 1815z image. As the algorithm continued to show moderate cooling rates with the cell the radar presentation became more impressive and a three body scatter spike developed with the cell. A report of penny sized hail was received with this cell 1823z 5 miles WSW of Newton Grove, NC.
Forecasters are beginning the day in NC/SC region, specifically starting in the Raleigh and Wilmington CWA’s. Storms were already going as we initialized in the area, but are expected to grow in strength and coverage over the next couple of hours. All the products and algorithms seem to working well over the region (only lacking total lightning coverage by an LMA, though this region may have coverage in future years!). Multiple storms have already been flagged by the UW-CIMSS Cloud-top-cooling product with min values as low as -26 to -27C and warnings may be issued shortly by the forecasters as they get settled in the new operations/CWAs.
VIS SAT and UW-CIMSS CTC at 1845 UTC on 23 May 2012.
We’re still watching the other SPC slight risk area for later this afternoon and early evening. It is likely we will make a switch (for at least one of the teams) to the central plains (likely Hastings/Omaha CWAs) if we start to see a CI signal. Like yesterday the high-res models seem to want to initiate convection along the front by 2100 UTC, though moisture continues to be an issue over the region with dewpoints in NE CO in the upper 30s to mid 40’s increasing to only the mid 50’s over central KS/NE. Unlike yesterday over the Dakotas where a thick cirrus shield covered the region, skies are pretty clear over KS with a bit more cloud coverage behind the front in central NE. If and when storms develop, steep lapse rates and deep layer shear point to the likelihood of supercells with large hail and damaging wind (especially with the large dewpt depressions).
