*SEVERE WEATHER POSSIBLE FRIDAY INTO EARLY SATURDAY FOR MUCH OF ARKANSAS*
The focus on this period will be on the severe weather threat on Friday. Severe weather threat has increased from 24 hours ago but there are still questions regarding the overall threat. This update 3 things have changed: (1) multiple rounds of thunderstorms. (2) Highest severe threat location. (3) Flooding threat has increased. Let's dive in.
During the day the trough will be moving towards the state and becoming rapidly negatively tilted. As the base of the trough crosses the Rockies, rapid cyclogenesis will take place with a 990mb low developing and situated along the Kansas and Oklahoma border. This will cause a tightening pressure gradient across the state that will increase wind speeds and with a warm front stalled in the northern parts of the state, this will lead to backing of the wind profile across the state. With a Gulf air mass in place with dew points in the 60s, cape values near 1500 j/kg. One thing to note is the cloud cover forecast and the possibility of pre frontal precipitation. If its higher, then this will negate any higher instability. If the clouds are less and the precip dosent occur, then the instability levels increase significantly. For this reason, there remains a bust potential either way. Higher equals a larger severe threat, lower equals lesser threat. This should be refined by early to mid morning Friday.
Guidance is starting to give us the idea of multiple rounds of thunderstorms. The first wave would be during the afternoon and evening, starting near the I-20 corridor and moving into Central by the evening. This round could move in prior to the main dynamic forcing meaning greater instability could be used up before the best dynamics get here but uncertainty does exist in this scenario. These phasing issues between the thermodynamics and the atmospheric dynamics cast a lot of uncertainty on mode and hazards with the first wave. Given the atmosphere dynamics in place this would be the initial severe threat with a cellular event most likely with this round.As the evening progresses, the main system will move into the west with rapid high falls aloft, increasing jet stream patterns and an increasingly enlarged hog graph on forecast soundings, indicating a favorable environment for tornadoes. However, the cape values normally decrease with the setting sun, so therefore this could lead to a somewhat lower threat. While there are some questions in the event, a few tornadoes are possible with the environment across the state. Higher instability values would yield a higher tornado threat than currently forecast and this will be fine tuned during the day tomorrow.
As we go into the overnight hours, the cold front will move through the state with a line or broken line segments along it. This will be the second severe threat. This will be a damaging wind threat with embedded tornadoes also possible. The line will swiftly move east of the state with ending any rainfall and severe threat.
A very complicated forecast in store for the day tomorrow. One ingredient could change the whole forecast. Stay weather aware and stay tuned for updates all day long.
Cold air will be slow to arrive behind the system so we will see clearing skies and temps in the 70s Saturday and Sunday, but a cooling trend starting on Sunday.
CURRENT CONFIDENCE LEVELS ON STORM HAZARD:
HIGHEST SEVERE THREAT FT SMITH TO LITTLE ROCK TO EL DORADO TO TEXARKANA
On Monday a disturbance will move through aloft with a slight chance of rain. Guidance indicates some snowflakes are possible in the northwest, however I do not buy that set up at this time. This will be monitored through. The rest of the period will be dry and colder than average with sunny days and clear nights. As we head into late next week into the weekend, things get interesting. All 3 operational members indicate a storms system moving through the state with cold air in place. It also indicate a multitude of precip types as well. This is the first time that all 3 have indicated this so it has caught my attention. There has been a lot of flip flopping going on as well on the system so confidence is low at this time. But if trends hold, then winter weather chances will return to the forecast but for now will go 20% to account for the uncertainty this far out.
~Chief Forecaster Derek