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Warming Up; Strong/Severe Storms Possible Sunday

First, terrible news. We were temporarily relocated this morning:

No word on where Memphis went. (This was later fixed. We all make mistakes. Let’s give The Weather Channel a break).

Tonight – 43 by 9 pm

Today was the last really cold morning we’ll have for the next several days.

The weather will be clear for tonight’s Titans game at LP Field. Expect mid-40s with a light south breeze. Wind won’t be a factor in the kicking game.

Friday – Mostly Cloudy, Chance of Rain – Morning Low 35, Afternoon High 58

6am 36 . 9am 45 . Noon 55 . 3pm 57 . High 58 . 6pm 52 . 9pm 51

Chilly (not cold) morning, warmer afternoon, and winds out of the south. Some weather models are also picking up rain showers beginning mid-morning.

Saturday Warmer – Morning Low 48, Afternoon High 68

6am 49 . 9am 57 . Noon 65 . 3pm 67 . High 65 . 6pm 64 . 9pm 61

The southerly winds will increase through the day: 5-10 mph in the morning, to 10-15 mph by the afternoon (with gusts up to 25).

Slight rain chances arrive late Saturday night, but the real weather will happen Sunday.

Sunday Rain. Strong/Severe T’Storms Possible – Morning Low 57, Afternoon High 71

Early this morning, the Storm Prediction Center shifted the strong/severe storm outlook from west Tennessee into middle Tennessee:

Storm Checklist: So you want to make a strong/severe storm? Here’s an oversimplified list of the ingredients you need, and what we currently expect to see Sunday:

1.  Warm, Moist Air

Unseasonably high temps (70s) and dew points (low 60s) will be in place ahead of an arctic cold front arriving Sunday night. This will be the fuel we need for thunderstorms to develop.

gfs_dew2m_east_29

The approach of the cold front will, at minimum, create rain showers, and probably also thunderstorms, beginning around noon. Timing isn’t certain, but we do not look dry Sunday afternoon. (Sorry, neighbors!).

The GFS model spreads rain into middle Tennessee through Sunday afternoon, then brings in a squall line around 6 pm. The European (ECMWF) model generally agrees with this timing.

2.  Energy/Moisture

This is very difficult to forecast this far away. The unit of measure for energy/moisture is “CAPE” (Convective Available Potential Energy). It’s the “stuff” you need to make a big storm.

Not that CAPE.

CAPE is abundant in the spring/summer, but it’s generally lacking in the fall. CAPE can be surface based, or just hanging out overhead.

Sunday’s CAPE is expected to be relatively low, but enough to cause trouble. Again, this is hard to forecast, but you don’t need much to cause strong/severe weather if the other ingredients are there.

3.  Instability

Unstable air occurs when the air above is increasingly colder. Storms feed on it. It’s too far away to know how unstable it’ll be Sunday. Too-early indications are there will be marginal instability.

4. Shear

There are many types and forms of shear, but for our purposes think of it as the wind changing speed and direction the further up in the  atmosphere you go. This supports any existing thunderstorm updrafts, and can create very broad rotation from which severe weather may develop.

Sunday’s shear looks much more impressive north of us in the Ohio River Valley, but the up-to 60 knot shear we’ll see Sunday isn’t bad:

We will be watching this very closely tomorrow and through the weekend. Right now, conditions look marginal for severe weather. However, much can change with this forecast. Those of you with Sunday afternoon plans should keep an eye on it.

Rainfall totals through Monday morning are estimated around 0.70″:

hpc_total_precip_se_17

Questions? Ask us on Twitter @NashSevereWx.