Marginally Severe Storm just south of the CWA

 Just before 20Z, storms have developed and the Throckmorton storm looks to be close to severe threasholds. Confidence is high that a warning will be needed for the storm. Prob severe has reached 99% with estimated hail size around an inch. Growth rate and glaciation are strong.

The storm weakened a bit as it entered the CWA, but then strengthened quickly. Growth rate and glaciation was strong. A warning was issued.

Scott Rudge.

Formerly Tornadic Storm in CO moving into CYS area

Storm moving into our area out of Weld Co., CO.  Seems to have lost its rotational signature, but is already cycled a couple of times…and at the least has exhibited some signs of strong downdraft wind wrapping around.   Jared issuing SVR for wind at 2115ZCYS

of interest…total lightning has been relatively steady on this storm over the past 15 minutes.  

Only some ebbs and flows…nothing notable…

ltg

db

Severe Weather over Colorado

With the fast and furious pace of severe weather over the Central US today some posts need to be condensed.  Below is an image of three severe storms over Colorado--with storms of interest labeled with 'A', 'B', and 'C'.

Figure 1.  NOAA/CIMSS ProbSevere and MRMR composite reflectivity at 2044 UTC 7 May 2014.  Storms of interest are marked with yellow A,B, and C.

The NOAA/CIMSS ProbSevere model had probabilities in excess of 50% with varying lead-time for these storms.  The first ProbSevere > 50% for these storms occurred at 2020, 2024, and 2034 UTC and the first NWS warnings on these storms occurred at 2101, 2026, and 2055 UTC, respectively (A, B, C), which translates into 41, 2, and 21 minutes of lead-time.

-Sieglaff

Thunderstorm activity expected in western Oklahoma

Upper level analysis has ridge shifting east with trof entering the four corners region. Upper flow is west to southwest across the southern plains with 120 knot jet across central Texas.

NAM/RAP 500/700 Heights/Vorticity not showing any strong upper waves coming through this afternoon and evening.

Satellite and surface data show some mid level cloudiness moving through the southwest portions of the CWA. Dry line resides across far western portions of OK. Moist southerly BL flow continues across central and eastern portions of the area.

Nearcast moisture fields indicate increased PW’s and higher Theta E moving into the area by late afternoon and early evening.

Convection has initiated just south of the forecast area and just east of the dry line.

Scott Rudge.

Value of GOES data in ProbSevere Model

The NOAA/CIMSS ProbSevere model uses five predictors--two environmental fields (MUCAPE and effective bulk shear), two satellite growth rates, and one radar hail size estimation.  When any piece of data is not available, the model simply runs without that data.  So in cases were storms are developing in regions of opaque clouds, the satellite growth parameters are not available and the model defaults to environmental variables and MRMS MESH.  However, the ProbSevere model is most skillful when the satellite predictors are available.  A storm in far north central Texas from today demonstrates the value of GOES storm growth rates.  Figure 1 shows the ProbSevere output before the growth rates were available at 1958 UTC 7 May 2014.  The storm of interest has a probability of 6%.

Figure 1.  NOAA/CIMSS ProbSevere and MRMS composite reflectivity valid 1958 UTC 7 May 2014.

And the following time, 2000 UTC 7 May 2014, the satellite growth rates became available (both strong) and the MRMS MESH value also increased.  The probability jumped from 6% to 70%.

Figure 2.  NOAA/CIMSS ProbSevere and MRMS composite reflectivity valid 2000 UTC 7 May 2014.

-Sieglaff

Prob Svr Trend

I was focused on a storm south of Cheyenne that was developing just west of I-25. The first few scans showed some potential with the storm. The Prob Svr was indicating smaller values (~30% range) around 1930Z. I utilized the all-tilts and dual pol products to see the extent of the storm height and magnitude of the reflectivity. It was apparent that 60+ dbz were up to around 19,000 AGL at the time. A freezing level of around 4,000 AGL gave confidence that some type of hail was falling. It was only about ten minutes later than the Prob Svr jumped from the 30% range to the 70% range. This would have had a decent influence on any warning that was issued. Soundings depicted plenty of dry air aloft, which would have supported some wind associated with this storm. Approximately 15 minutes time passed before velocity returns showed interest features that may have signified some decent wind gusts.

Jared Maples

ProbSevere adds confidence to EWP warning

The NOAA/CIMSS ProbSevere model is also being evaluated by the Cheyenne area EWP team on Wednesday.  Forecasters were monitoring a developing storm in far northern Colorado.  The forecasters were examining all radar tilts and noticed 67 dBz near 20,000 feet.  The ProbSevere value at 1936 UTC 7 May 2014 was 36%, while not high, the forecaster noticed this value was much higher than any nearby convection.  Over the next 4 minutes the ProbSevere increased to 56% and then 74% (Figure 1).  The combination of all radar tilts, some dual polarization fields, and the ramp up of ProbSevere resulted in the forecaster to  issue an experimental severe thunderstorm warning at 1944 UTC.

Figure1.  NOAA/CIMSS ProbSevere and MRMS composite reflectivity valid 1936-1940 UTC 7 May 2014.

-Sieglaff

ProbSevere and Severe Convection along Texas Dryline

More active severe weather is beginning on Wednesday afternoon.  A thunderstorm developed in the northern San Angelo, Texas CWA.  The developing storm was in a favorable environment, exhibited strong normalized vertical cloud growth rates and strong glaciation rates.  The rapid development of this storm resulted in the initial ProbSevere values of 50% at 1914 UTC 7 May 2014 (due to favorable environment and GOES-EAST RSO scanning, capturing the satellite growth of this storm faster than what would have been in routine GOES-EAST scan mode).  The ProbSevere increased to 99% by 1930 UTC as the precipitation core and MRMS MESH values increased.  The San Angelo WFO issued a severe thunderstorm warning for this storm at 1945 UTC--29 minutes after the first ProbSevere value in excess of 50%.

Figure 1.  NOAA/CIMSS ProbSevere and KFDR 0.5 degree reflectivity valid 1914-1945 UTC 7 May 2014.  The NWS severe and tornado warning polygons are also included.  The text read out is for the storm of interest.

EWP forecasters have been looking at other testbed products largely in this region, but they have been monitoring the ProbSevere and were pleased to see high probabilities early on in this storm.  The first severe report with this storm occurred at 2020 UTC 7 May 2014--half dollar sized hail in Baylor county, Texas.

-Sieglaff

Early Afternoon Set-Up for WY, CO, NE

Severe t-storms are a possibility through the afternoon in the High Plains around WY, CO, NE.

NAM, GFS agree on a low on the E. Colorado/W. Kansas area strengthening some through the afternoon, increasing the easterly, upslope flow into the area.  This will also serve to advect higher moisture content from the east…something we see in the Nearcast precip. H2O analysis

Ongoing convection in WY in combination with plenty of cirrus over the area of concern has limited for now the use of the CI product.  Plenty of clearer air farther southeast in KS outside of the area of immediate concern.

The Nearcast vertical theta-e difference product shows a band if instability along the WY, CO border and on into western NE.  The model forecast shows a maximum in instability near the WY, NE border at 22Z.

As ongoing convection in WY emerges into warmer, ore unstable air to the east, there is an expectation that storms will intensify.  Also need to be on the lookout for any thinning in the cirrus shield over the next few hours in NE as we could see more development out here.

Storm motion should be to the northeast.  Low freezing levels may lead to very large hail.  Looking at the 22Z Nearcast forecast difference in PW between the low and mid-levels, higher values are seen in the area of concern…drier air aloft could assist in downdrafts and damaging wind production.

Will monitor impulses rounding the upper trough to the west for increased vertical motion through the afternoon/evening.-db

Cu field in NW Texas

CI tagging cu field in western north Texas with 90 percent development. A few storms have already formed with strongest storm approaching Knox county with 27% on prob severe model.

BT