NUCAPS Sounding Centered on SAT

Wednesday afternoon NUCAPS soundings are in and the below image is from northwestern Bexar County (San Antonio Metro).  Overall, the soundings were not too bad, however the boundary layer came in a little cold and surface temperature modification of a few degrees was needed for both the temperature and dewpoint.  Aloft, temperatures were too warm and needed to be cooled a few degrees up to the 850 hPa layer.  This obviously led to adjustments in the cape calculations.

Development of Sig Prob Severe in the Future?

Once again prob severe provides ~10-15 minutes of lead time using ~75% over typical radar thresholds. After we issued the warning we noticed signatures suggestive of significant hail sized (e.g., persistent deep TBSS, sidelobe contamination, transient BWER). This raises the question, could criteria be adjusted in the algorithm to provide sig severe guidance? This could be very useful operationally for the most high impact events that cause the most property damage and threat to life.

-dryadiabat

First Warning in San Angelo CWA

A thunderstorm developed along a residual outflow boundary/stationary front southwest of San Angelo Wednesday afternoon.  The forecaster group issued an experimental severe thunderstorm warning based on lightning jump data, ProbSevere output, and all radar tilts examination.  Figure 1 below shows a loop of 0.5 degree KSJT reflectivity and ProbSevere contours.  ProbSevere first exceeded 50% at 1952 UTC, 60% at 2002 UTC, and 80% at 2012 UTC.  The experimental data along with all radar tilts analysis helped forecasters increase lead-time and confidence in issuing a severe thunderstorm warning.  After the warning was issued the storm again experienced a lightning jump and ProbSevere values maxed at 100%, with MRMS MESH over 3.00".

Figure 1.  KSJT 0.5 degree reflectivity, NOAA/CIMSS ProbSevere contours and experimental severe thunderstorm warning polygons valid 1948 - 2016 UTC 20 April 2016.

-Sieglaff

Severe storm near KSJT

Severe storm near KSJT (J-Money):

Lightning jump product gave a nice heads-up (on the order of about 10 minutes) to developing severe storm.  Prob Severe values were also fairly high and steady-state leading into rapid intensification.

                                     1-minute visible + Lightning jump
                                                 

                                     Prob Severe + -20C Reflectivity

CI Proability

First convection firing up near San Antonio. Comparing CI Probablily to actual radar data. Shows about 15 to 20 minute lead time with CI topping out at 75 near area of convection. Not exact location but, very near location of convection. -thunder

   CI Probability

   Radar Loop

Potential Uses for High Density Cloud Winds

The lowest level of the high density cloud winds may have two potential uses, 1.) assessing low-level shear trends, and 2.) determining low-level wind shear potential. You can see in the image below the green barbs are the high density cloud winds and the light blue obs are the actual 10m observed winds from ASOS and AWOS sites. There is a difference. Winds are more southeasterly in the actual obs and veer with height in the cloud density wind plots. The ceilometers at the ASOS/AWOS sites show bases around 3.5-4 KFT, and it can be inferred that this is approximately the level of the high density cloud winds. Although too deep to assess LLWS for aviation interests in this particular case, 0-1km shear trends can be inferred. This has potential application in severe weather forecasting by providing 0 AGL to cloud base shear values.

-dryadiabat

Amarillo Start

Going with Amarillo today.

Started today with a look at Lap products first p.w. is up in the lower levels at .55. Upper levels dry out quite a bit 700-300 .09.

Cape very low, L.I. positve 5. LP h20 .51

Water vapor shows moisture field rotating out of s. Colorado. May take all day to arrive in Amarillo.

C.I. Prob at 10 at this point.

Doesnt look like much will happen until much later in the day. Perhaps not until after 5pm. -thunder

                                  P.W. LAP 4 panel

Mesoscale Analysis as of 1830z

J-Money Mesoscale Analysis as of 1830z:

Two regional short-wave features to note in the 700-500 mb layer this afternoon, as per water vapor imagery and meso-analysis data.  The leading system was near the TX/LA border and pushing east, with associated storms being heavy rain producers, given saturated, weakly sheared environment.  Houston LMA and flash rate density products show a fair amount of lightning as well.

Through 19-22z, better convective potential may shift to central/south TX, as a subtle 700 mb short-wave over west TX moves in.  This may interact with a decelerating outflow boundary in the vicinity.  Layered PW data depicts the leading edge of mid-level dry air and presumably steeper lapse rates as well.  Main question is can strong 700 mb cap shown on 12z KDRT sounding be overcome.  Time will tell.   Maybe 19z NUCAPS could help later today?

  

18z Meso Update

Large-scale upper low continues to spin across the Central Rockies this afternoon with broad cyclonic flow prevailing over much of the Southern Rockies.  On the mesoscale, latest data from the SRSOR 1-km visible satellite imagery shows along diffuse outlow boundary remnant of last night's convection slowly sagging south across southern Texas. To its north, notable clearing ongoing this hour across much of central Texas into the Texas Hill County. Prevailing through with respect to today's convective potential involves to possible areas, with the first likely kicking off sometime around 21z as isolated cells begin to develop across the Hill County in aforementioned clearing, while another round of shwrs/storms is expected to develop across the northwestern TX panhandle after the 02z time frame as shortwave energy slides across the region. After development, high-res models to include the HRRR and 3km TTU-WRF show this secondary area of convection congealing and forming into a forward-propagating MCS as it dives southeast across the Red Rvr Vly into northeastern TX during the early morning hrs.

In terms of severe potential for the experiment, the prevailing through going forward has been swayed to the Texas Hill Country area as latest rapid-refresh soundings show a gradual erosion of the cap by mid-afternoon as shortwave energy approaches and boundary layer heating continues.  If cap is able to erode, effective bulk shear of roughly 40-45 kts will support supercell structures with large hail and damaging winds being the main threats.  Latest All-Sky LAP layered precipitable water data showing low-level moisture surging westward into the Hill County and Concho Valley regions of central Texas this afternoon.  Combine this increased low-level moisture along with better forcing for ascent and the gradual erosion of the capping inversion, this region should see an increased liklihood for developing convection later this afternoon.

torman1 

Mesoanalysis for Lake Charles Area

Latest IR loop shows a tendency for warming tops through mid morning in the MCS followed by a reinvioration of convection with cooling cloud tops evident over the past hour. This is occurring as the convective complex moves toward a low-level theta-e axis evident in RAP mesoanalysis and Layer PW extending from Southwest Louisiana north-northeastward into Central Louisiana. As diabatic heating continues over this area an increasingly unstable enviornment is developing with MLCAPE ~1,000 J/KG as of this writing. Convection has developed in this area east of the MCS this morning so far. The severe threat will be limited given loose storm organization at best due to weak deep layer shear. Isolated marginal damaging wind events may occur, but significant hail size will be difficult to acheive given tendency for short duration updrafts, limited CAPE in the hail growth zone, and limited complex storm interactions/mergers. For this experiment we will be particularly interested early on PGLM lightning data from Houston, CG lightning probability, and lightning jump since severe thunderstorms may be hard to come by. A move to another area is being discussed for later this afternoon once we examine lightning for a little while longer in Lake Charles' area.

-dryadiabat