Update: Saturday 6:35am
EARLY IN THE PERIOD...
THE MAIN SHOW WILL PROBABLY WAIT UNTIL LATE AFTERNOON OR EARLY EVENING AND BE MORE TIED TO LOW LEVEL CONVERGENCE ALONG THE APPROACHING COLD FRONT. AGREE WITH SPC DAY 2 OTLK WHICH HAS ALL OF OUR AREA IN A SLGT RISK.
The first two images show the bulk shear and MLCAPE parameters that they refer to in their discussion. The last image is a Supercell Composite parameter which factors in a combination of other severe weather parameters. Looks pretty ugly over Lincoln.
Convective Available Potential Energy. A measure of the amount of energy available for convection. CAPE is directly related to the maximum potential vertical speed within an updraft; thus, higher values indicate greater potential for severe weather. Observed values in thunderstorm environments often may exceed 1000 joules per kilogram (J/kg), and in extreme cases may exceed 5000 J/kg. Mean Layer CAPE - CAPE calculated using a parcel consisting of Mean Layer values of temperature and moisture from the lowest 100 mb above ground level.
SBCAPE (Surface-Based Convective Available Potential Energy) is a measure of instability in the troposphere. This value represents the total amount of potential energy available to a parcel of air originating at the surface and being lifted to its level of free convection (LFC). No parcel entrainment is considered. The CAPE and CIN calculations use the virtual temperature correction.
A multiple ingredient, composite index that includes effective storm-relative helicity (ESRH, based on Bunkers right supercell motion), most unstable parcel CAPE (muCAPE), and effective bulk wind difference (EBWD). Each ingredient is normalized to supercell "threshold" values, and larger values of SCP denote greater "overlap" in the three supercell ingredients. Only positive values of SCP are displayed, which correspond to environments favoring right-moving (cyclonic) supercells.
Update: Friday 6:03pm
Here is an update to the Sunday forecast. Most storms should be later in the day. The image below shows the Lincoln area in a Slight Risk area according to the Storm Prediction Center. Click that link for the full 3 day outlook from the SPC.
ALTHOUGH ELEVATED CONVECTION COULD PERSIST INTO SUN AFTN AIDED BY LOW LEVEL JET...PER NAM/GFS...12Z ECMWF GENERALLY KEPT AREA DRY UNTIL 00Z MONDAY WHEN STRONG UPPER JET PUNCHES INTO REGION ON SOUTH SIDE OF THIS NEXT UPPER TROUGH. DUE TO UNCERTAINTY IN AMOUNT OF ELEVATED CONVECTION PRECEDING MAIN LATE AFTN/EVENING DEVELOPMENT LEFT IN MORNING POPS NW 2/3RDS AND DID NOT BREAK UP THE AFTN PERIOD TO ACCOUNT FOR POSSIBLE HIGHER CHANCES LATE IN THE AFTN. DID BOOST MAX TEMPS A FEW DEGREES SOUTH ON SUNDAY AS THAT AREA DID SEEM THE LESS SUSCEPTIBLE TO IMPACT OF MORNING WARM ADVECTION CLOUDS PSBL PRECIP. STRONG/SEVERE STORM CHANCES APPEAR HIGHER THAN PAST SEVERAL DAYS AS 0-6KM SHEAR IS STRONGER AND MAX TEMPS NEARING 90 SHOULD INCREASE MLCAPE VALUES. ALTHOUGH HEAVY RAIN WILL LIKELY OCCUR WITH THE ACTIVITY AS WELL...VERY HARD TO PIN DOWN WHERE AXIS OF HEAVIEST WILL OCCUR AS A CASE COULD BE MADE FOR IT SETTING UP JUST ABOUT ANYWHERE IN OR EVEN POSSIBLY JUST OUTSIDE THE FA.
Beginning to become a little more concerned about instability during the day and afternoon on Sunday as a shortwave rotates through the base of the trough. It now appears that there will be the possibility for some thunderstorms to popup. The majority of the bad weather should remain to the east and north, but the severe parameters are worth noting. Here is an except from this mornings AFD from Omaha NWS. I bolded the important part.
.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY)
Even more important, this from the Storm Prediction Center this morning in their 4-8 day outlook:
BOTH MODELS DEPICT THE ADVANCE OF A FAIRLY STRONG UPPER TROUGH INTO THE CENTRAL U.S. DAY 4 /SUN 8-31/...ALONG WITH AN ASSOCIATED/SHARP COLD FRONTAL PROGRESSION.
This is a 6 hour accumulated precipitation map above. What that means is this is what the GFS expects to happen from 2pm until 8pm in the evening. Obviously the bulls-eye for rain isn't too far away so this is something to be watched.
This is vertical velocity and vorticity, the lift and twist to the air as it rises. These are from two different levels. The left is an 850mb view (~5000 feet) and the right is a 500mb view (~18,000 feet). Note that they only line up to the north of the state, meaning the most likely area for severe is to the north.
The parameters exist for some High Precipitation (HP) supercells, this is 11am Sunday. Again, something we'll be watching for as we get closer to Sunday.
Updated 9:17 pm, Thursday