SCCA Solo Nationals Weather - Sunday

Update: Saturday 6:35am

When you are in the midwest, you never like to hear about severe hail and tornadoes... but we are. Once we get through Sunday, the weather will improve considerably. It's late afternoon and evening Sunday and into the early morning hours of Monday (midnight to 3-4am) that is the concern. If you have enclosed trailers for your car, I would certainly use them on Sunday. 

This is from the Storm Prediction Center this morning in their Day 2 Outlook:

Probabilistic Outlook

EARLY IN THE PERIOD...
ELEVATED THUNDERSTORMS MAY BE ONGOING ALONG THE NOSE OF LLJ (Low level Jet) ACROSS THE UPPER RED RIVER VALLEY. THIS ACTIVITY SHOULD BE ROOTED AOA (at or above) 850MB (~5000 feet) AND THE GREATEST THREAT WITH THESE STORMS SHOULD BE MARGINALLY SEVERE HAIL BEFORE THEY PROPAGATE INTO SRN MANITOBA. 

HOWEVER... 
GREATER SEVERE RISK WILL OCCUR ALONG THE COLD FRONT DURING THE LATE AFTERNOON AS BOUNDARY LAYER WARMS... FORCING SBCAPE IN EXCESS OF 3000 J/KG FROM CNTRL MN...SWWD INTO KANSAS. LATEST THINKING IS FRONTAL CONVECTION SHOULD DEVELOP AFTER 21Z (5pm) WITHIN AN INCREASINGLY SHEARED ENVIRONMENT THAT SHOULD INITIALLY SUPPORT SUPERCELL STRUCTURES. ACTIVITY ACROSS CNTRL KS MAY BE SOMEWHAT HIGH-BASED AS TEMPERATURES SOAR INTO THE 90S. HOWEVER...UPDRAFTS THAT EVOLVE ACROSS NEBRASKA INTO MN WILL BE CONSIDERABLY LOWER AND MULTIPLE HP SUPERCELLS COULD DEVELOP ALONG THE FRONT BEFORE STORM MERGERS RESULT IN AN ELONGATED MCS-TYPE COMPLEX. 

LARGE HAIL IS LIKELY WITH THIS ACTIVITY AND DAMAGING WINDS MAY ALSO BE NOTED. A FEW TORNADOES CAN NOT BE RULED OUT WITH EARLY DISCRETE SUPERCELL STRUCTURES. FRONTAL MCS SHOULD PROGRESS INTO THE MID-UPPER MS VALLEY DURING THE OVERNIGHT PERIOD.

Click image for full size

This is from the Omaha NWS Area Forecast Discussion this morning:

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Click for full size - Saturday Morning Water Vapor Image. Note the drier air (darker color) that will be moving into Lincoln today. Also note the blob over Montana, that is Sunday evenings weather maker.

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. 


ML CAPE VALUES ARE EXPECTED TO REACH 3000 TO 4000 J/KG IN THE AFTN AND LINGER INTO THE EVENING. 0 TO 6 KM BULK SHEAR VECTORS IN COMBINATION WITH EXPECTED CAPE SHOULD BE SUFFICIENT FOR STORM ORGANIZATION. INITIALLY DISCRETE STORMS WILL LIKELY MERGE INTO ONE OR MORE CLUSTERS AND/OR A LINE. 21Z SUNDAY TO 06Z MONDAY  (5pm until 2am ) SEEMS TO BE THE MOST FAVORED TIME BASED ON FORECAST SOUNDINGS AND OTHER CURRENT MODEL DATA. IN ADDITION TO THE SEVERE THREAT...LOCALLY HEAVY RAIN IS PROBABLY GOING TO BE AN ISSUE DUE TO THE RECENT ISSUES WITH SOME STREAMS/RIVERS.

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.

0-6 km Shear - Shear is the change in wind direction with height.

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.

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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.

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Previous Post

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)
ISSUED AT 327 AM CDT THU AUG 28 2014
THERE IS A BREAK IN THE STORMY WEATHER SATURDAY NIGHT... HOWEVER THUNDERSTORM CHANCES INCREASE SUNDAY AFTERNOON AND SUNDAY NIGHT. DO MAINTAIN LIKELY POPS DURING THIS TIME WITH A SHORTWAVE TROF PUSHING THROUGH THE PLAINS AND HIGH PWATS RETURN AHEAD OF THE FRONT. HAVE A DRIER PERIOD FORECAST MONDAY 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.

THE MOST SUBSTANTIAL SEVERE RISK THIS PERIOD REMAINS APPARENT DAY 4 FROM THE CENTRAL PLAINS NEWD TO THE UPPER MS VALLEY...AS THE UPPER TROUGH SHIFTS INTO/ACROSS THIS AREA. AS THE ASSOCIATED COLD FRONT ADVANCES INTO A MOIST/DESTABILIZING AFTERNOON AIRMASS...VIGOROUS THUNDERSTORM DEVELOPMENT IS EXPECTED TO OCCUR. WITH A BELT OF 40 TO 50 KT SWLY FLOW PROGGED TO SPREAD ACROSS THE MID MO VALLEY VICINITY THROUGH THE DAY ATOP LOW-LEVEL WARM-SECTOR SSELYS...SHEAR WILL BECOME FAVORABLE FOR ROTATING STORMS. AS A RESULT...A RISK FOR LARGE HAIL AND LOCALLY DAMAGING WINDS -- AND POSSIBLY A FEW TORNADOES -- SEEMS LIKELY TO MATERIALIZE...PARTICULARLY WITHIN A ZONE FROM NRN KS NNEWD INTO MN/WRN WI DURING THE AFTERNOON AND EARLY EVENING HOURS...AND THEN INTO IA/NWRN MO THROUGH THE EVENING HOURS.

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