NOWCAST: Latest about Today's Storm Threat
Severe Risk:
The Storm Prediction Center has increased our severe weather risk from a marginal to a slight risk for severe weather for the entire viewing area. A slight risk is defined by SPC as an area of organized severe storms, which is not widespread in coverage with varying levels of intensity.
The main threats will be damaging gusty winds, localized heavy rain and frequent lightning. The secondary threats are isolated tornadoes and hail. A few isolated strong to severe storms are possible this afternoon as a defined squall line moves through the area.
Set Up:
Temps have increased significantly in the past day. That's because there is a warm front moving through the area. But the warm up is brief. There will be a strong trailing cold front that will sweep through the area later today. Widespread precipitation will be likely ahead of the front with gusty showers and storms.
Ingredients: Summary: There is a narrow window of limited instability as storms move through the area, but there will be a ton of wind energy, that could allow for a few damaging wind gusts and storms.
WIND SHEAR:
We will have tons of wind energy today. It is already so breezy (40-50 mph) even ahead of the cold front. When it comes to severe storms, as a rule, we look for at least 35 kt winds aloft as a severe criteria.
Check out these 850 mb winds at 3 pm! Around 65-70 mph at 850 mb. This is a 50-60 kt low level jet and means there is enough mid level wind energy to mix down and cause some damaging winds even with a narrow window of instability. There is also a bit of directional wind shear that could allow a brief tornado or two.
As I mentioned, it is going to be windy, even when it is not storming today. There is a wind advisory in effect today until 10 pm. Winds will be increasing during the day and will be the fastest when the showers and storms move through. The winds will also change direction from a southerly wind to a NW wind following the front.
Instability: Heat and moisture (or dew points) both are fuel for storms. The increase of each, will in turn, increase our instability. Instability is key to severe weather development.
Temps are unseasonably warm and increased substantially in the last day. Roughly 25-30 degrees. Our temps will increase to the mid and upper 60s before the front, which is about 10 degrees above average.
Notice the dew point is also on the rise. Not overwhelming, but should get to the low 60s, which signifies moisture is being transported into the area and increasing instability.
Meteorologists often refer to "weak instability" (CAPE less than 1000 Jkg-1), "moderate instability" (CAPE from 1000-2500 Jkg-1), "strong instability" (CAPE from 2500-4000 Jkg-1), and "extreme instability" (CAPE greater than 4000 Jkg-1). Models suggest there is a narrow corridor of roughly 300-600 J/kg CAPE before the front. This is considered weak instability. This will limit the severe potential, but as mentioned above, the wind energy could overcome the lack of instability and we could still see a few rogue severe storms.
TIMING:
We are currently seeing a few light showers. Which could actually help limit instability a tad.
It looks as though the main line will arrive to our NW counties around 2-4 pm
Showers and storms will continue to push from the NW to SE through our area QUICKLY during the afternoon and early evening. There will be bursts of heavy rain embedded within the main line. Expect around .5''-1'' of rain with locally higher amounts.
Majority of the showers and storms will end by the early evening. Roughly 7-9 pm.
But there could be a few isolated showers lingering into tonight, leading to a few flurries as temps drop significantly and quickly.
Hour By Hour:
Headed the U of L Game? Prepare for a change of seasons during the game! It will be warm to start. Then stormy. Then much colder. Temps will drop from the upper 60s to the 40s and then the 30s late tonight.
My thoughts:
A few rogue strong to severe storms are certainly possible with the ingredients we have available, but this will not be an event. Here is a summary of everything we discussed. Which is a lot.
To find out the details about the rest of the weekend, and of course Thanksgiving, be sure to join Hannah this evening on WDRB News. If and when storms become severe, we will be keeping you informed in a variety of ways. One of those is on social media. The links to my pages are below!
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