CI Algorithm in OUN

Monitoring the CI algorithm on 5/2 in the OUN county warning area, limited value was added. Values did increase in the scans leading up to convective imitation, however, in most cases these increasing probs were not associated with storms that actually did initiate (see animation below). Many of the higher values were well ahead of the boundary where we knew storms would not go. Back along the boundary where storms did develop, CI probs were either non existent (due to cirrus cover) or very low. There were limited instances of success. The only value I would say CI did provide was showing increasing probs in general across the area prior to CI. This could tell the forecaster that initiation is close, just not exactly where.

- Bucky

ProbSevere Aids in Experimental Tornado Warning

The forecasters in the Wichita, KS CWA noted ProbSevere tornado probability rapidly increased on a supercell thunderstorm that developed just ahead of a large severe squall line.  Figure 1 shows KICT 0.5 degree storm-relative velocity and ProbSevere probability of tornado contours rapidly increasing from 13% at 2048 UTC to 70% at 2056 UTC.  The velocity data shows a very strong, tight circulation.   The jump of the probability of tornado alerted the warning forecaster and after a very quick radar interrogation, he issued an experimental tornado warning at 2100 UTC.

Figure 1.  KITC 0.5 degree storm relative velocity and ProbSevere Version 2 tornado probability, highlighting the supercell ahead of the squall line valid 2048-2056 UTC 02 May 2018.

-J. Sieglaff

GLM comparison of 2 nearby storms

Two storms within one polygon were analyzed with GLM. Storm A (northeast most) exhibited an increase in energy and flash rate and decrease in flash size from 2000-2010UTC. Storm B (western most cell in Barton Co) had a lesser increase in energy while flash size remained high (~150-200 km2) with rates only slightly increasing. Storm B had a strong mid-level rotation while storm A only achieved a weak mid level meso for a short time. I expected storm A to intensify based on GLM data but it did not. - SCOULOMB

OUN Mesoscale Analysis

GOES-16 water vapor imagery reveals a broad closed mid-level low advancing into the 4-corners region with energy rounding the eastern side of the trough through west Texas.

GOES-16 Derived Motion Winds show the southwest to northeast oriented upper-level jet shifting east into west Texas, OK panhandle, and western Kansas. Diffluent flow is apparent in the winds over south-central Kansas into the Texas panhandle on the east side of the jet where convection is already ongoing and initiating. As the upper forcing shifts east, so will the convection. Given the high cloud cover, mid-level winds are not available over the region. Winds in the 850 mb to 950 mb layer are available over much of central Oklahoma, indicating 25-35 knot low level southerly flow advecting moisture into the region. Some of the lowest level winds, below 950 mb, are indicating more backing toward south-southeast, which would imply a favorable shear environment for supercell thunderstorms.

Given the cloud cover, the LAP fields have very limited data across much of OUN. However, the all-sky product does have many cloudy sky pixels, a benefit of this product over the operational LAP product. Within these pixels, CAPE ranges from 1500 to 2000 j/kg across the CWA a reduction of close to 1000 j/kg over the GFS first guess. SPC meso-analysis indicates MLCAPE between 2500 and 3000 j/kg, implying LAP CAPE is too low. Boundaries are not easily identified in the retrieval data given the cloud cover.

MetOp-A NUCAPS soundings were available over the region for the 1630 UTC pass. The surface was adjusted to match the conditions present in the NWS Norman special 18Z sounding (surface of 78F T and 68F Td). Comparing the two, the NUCAPS sounding captures the EML, though it is with much less detail. NUCAPS tries to represent the temperature inversion, but it is too coarse to be operationally useful. The drying aloft is also present, though too high, with moistening above. The general shape of NUCAPS is on par with the raob. As for the CAPE fields, NUCAPS is a little hot with MU and SB CAPE compared to the raob, while MLCAPE is slightly too low.

Expecting all three severe threats today with convection moving through the area.

- Bucky

ProbSevere example over far Southwestern Oklahoma

Thunderstorms were developing along and ahead of the dryline over the far eastern Texas panhandle and pushing into the western Norman, OK WFO.  ProbSevere All Hazards (aka ProbSevere Version 2) showed severe hail and severe wind threats increasing between 1938 and 2000 UTC 02 May 2018 (Figure 1).  The forecasters over the Norman WFO were evaluating some other products at this time, but were keeping an eye on the ProbSevere values.  The forecasters noted the good lead-time provided by ProbSevere as the first severe hail report was received at 2010 UTC (1.00").

Figure 1. MRMS Composite Reflectivity and ProbSevere Version 2 (All Hazards) contours valid 1938 - 2000 UTC 02 May 2018.  The storm of interest very near the southwestern portion of the Norman WFO is highlighted with AWIPS ProbSevere storm attribute readout.

-J. Sieglaff

Moisture with LPW

Similar to yesterday (blog post), I'm seeing increasing low-mid level moisture just to the east of the dryline, and we're reaching a point where convection is firing on the strengthening gradient.  RAP forecast moisture cross section suggests the increasing moisture, especially in what should be the 0.7-0.9 layer, before the dryline begins moving east today.  Already seeing that underway.  Will be watching evolution today using LPW...

(RAP moisture forecast cross section W to E from Panhandle, across C Oklahoma, to western AR)

(Above:  LPW, full column, and each layer + composite radar)

(Above:  ABI Water Vapor channels + cirrus)


Just like yesterday (blog), convection is developing over the panhandle along the dry line as 0.7-0.9 PW gradients quickly increase.

-Forrest

MetOps A & B versus OUN soundings

The OUN 18Z special sounding featured a strong cap near 780mb.  The cap was also there on the regular 12Z sounding, though it was closer to 850mb.  MetOps A (near 1630Z) and MetOps B (near 1530Z) happened to have some good data points around central OK.

 (Above: 18Z sounding OUN)

(Above:  MetOps A near OUN)

(Above:  MetOps B near OUN)

The inversion is apparent in MetOps A, though weaker and higher up and more diffuse.  Inversion is not discernable in MetOps B.

Below is a loop of satellite starting near 1530Z running to beyond 18Z, including three water vapor channels, and the lower right panel is the 1.38 cirrus channel to get an idea of the cloud scene for MetOps.

-Forrest

LAP output in ICT area

The all sky LAP was underestimating the instability by 500-700 across much of KS versus the SPC analysis. Likewise the PWs were lower than the LMN sounding at 17Z. The overall shape and breadth of instability was handled well by LAP with the max in NE KS but seemed to miss the secondary max further S across TX/sw OK.

All Sky LAP CAPE vs Observed CAPE

A first look at the All Sky LAP product over central KS indicates an underestimation by around 500 J/Kg of layer CAPE (Figure 1) compared to SPC meso analyzed CAPE (Figure 2). Observed sounding at Lamont, OK (Figure 3) was south of the highest instability values.

Figure 1. Layer CAPE top left image
around 3,000 J/Kg

Figure 2. SPC Sfc based CAPE vals over 
4,000 J/Kg

Figure 3. Observed CAPE of 3,059 J/KG 

at Lamont, OK

- BO

MetOPA-B comparison

MetOPA sounding close to the LMN sounding time of 17Z was similar with EML and moisture aloft. Otherwise the sounding did not capture the deep, moist boundary layer.