Today yields yet another slight risk over north and western portions of Tennessee, with risk for large hail and damaging winds. I took a look at the models, and the is more than enough convection to support thunderstorms today. With CAPE values of 3000 j/kg, they will be strong. However, with lack of wind shear they will be short lived pulse type storms. As one dies off, another will pop up. The SPC says we are looking at multi-cell type storms, which means we may have a few line segments with damaging straight line winds.
The tornado risk for today is nearly non existent due to lack of helicity (wind shear), and therefore the SPC doesn’t even show a tornado risk over Tennessee. I don’t know what the SPC is looking at, but they are saying that there is enough deep layer shear to sustain these multicell lines, and warrant the risk of hail and damaging winds. I sure hope they are right, because I am itching for a good storm! There are great CAPE values for the day, and I have also noticed that there is very weak capping over Middle Tennessee today. This may be beneficial in preventing the weaker storms from developing. Then again, maybe not… I am still learning a lot about forecasting, so who knows. Enough of my blabbering, here is what the SPC has to say.
…DELMARVA WWD ACROSS THE SRN LOWER OH AND TN VALLEYS…
SEVERAL FEATURES SHOULD AID IN SCATTERED TO NUMEROUS THUNDERSTORMS DEVELOPING ACROSS THE REGION THROUGH THE AFTERNOON HOURS. FIRST FEATURE IS REMNANT MCV…CURRENTLY APPROACHING WRN PA. CURRENT MOTION/EXTRAPOLATION PLACES THIS FEATURE INTO S CENTRAL PA/MD PANHANDLE BY MID AFTERNOON. WEAK CONVECTION HAS ALREADY DEVELOPED AHEAD OF THIS SYSTEM OVER WV…AND SHOULD INTENSIFY AS MOVES INTO VA/MD PANHANDLE/SRN PA THIS AFTERNOON… REFERENCE MESOSCALE DISCUSSION 784.
FURTHER WEST…ANOTHER WEAK SURFACE LOW WAS LOCATED IN FAR NWRN OH…WITH A SURFACE TROUGH EXTENDING WSWWD INTO CENTRAL MO. THIS TROUGH WILL MOVE SLOWLY SWD AND CONVERGENCE WILL BE ENHANCED AHEAD OF IT AS AN UPPER THERMAL TROUGH SHIFTS EWD ACROSS THE TN/OH VALLEYS. DEEP LAYER SHEAR AT 20-30 KT WILL BE SUFFICIENT FOR SUSTAINED MULTICELL STORMS…AND IN CONJUNCTION WITH MODERATE INSTABILITY…SEVERE HAIL AND DAMAGING WINDS WILL BE POSSIBLE DURING THE AFTERNOON/EARLY EVENING HOURS.
Right now there is a mesoscale discussion in effect for western Tn, where a Severe Thunderstorm Watch appears possible. There may be one issued for northern Mid Tn later, but for now I will post the discussion.
AREAS AFFECTED…
NERN AR…BOOT HEEL OF MO…WRN TN…KY CONCERNING…
SEVERE POTENTIAL…WATCH POSSIBLE
VALID 031758Z – 031900Z
A PRE-FRONTAL ZONE OF LOW LEVEL CONFLUENCE CURRENTLY EXTENDS FROM NERN AR…NEWD ALONG THE OH RIVER INTO NRN KY. THIS AXIS WILL LIKELY BECOME THE FOCUS FOR STRONG THUNDERSTORM DEVELOPMENT OVER THE NEXT FEW HOURS AS BOUNDARY LAYER CONTINUES TO WARM/DESTABILIZE. GIVEN THE MARGINAL DEEP LAYER SHEAR IT APPEARS MULTI-CELL UPDRAFTS WILL BE COMMON WITHIN MODERATELY UNSTABLE AIRMASS. LOCALLY STRONG DOWNBURSTS AND HAIL COULD ACCOMPANY THE MORE ORGANIZED STORMS.
So, updates will come later as things progress. I would say it is safe to assume that if you are within the slight risk area, you will
see some t-storms today. I just took a look at the SPC Hourly Mesoscale Analysis, and i see more favor in those models. As you can see, thunderstorms are already developing in western Tn. I will be sure to update if we get a severe thunderstorm watch.
