Two days dry before a significant rain event
Enjoy a pleasant weather ride into the weekend because the second half is looking like a washout!
Today and Tonight: Friday will bring lower humidity, full sunshine and warm afternoon temperatures in the mid 80s. Winds will be light and westerly. Skies stay clear and winds remain light overnight with low temperatures returning to the mid 50s.
Up Next: Another nice afternoon is in store for Saturday with mostly sunny skies and highs in the mid 80s. Clouds will begin to increase overnight with low temperatures holding in the mid 60s. Big changes are expected for the second half of the weekend. An area of showers and thunderstorms is expected to develop late Sunday and rain could fall heavily at times through Monday morning. Temperatures will stay in the 70s. While a few more ingredients would still need to come together for severe weather, that is a possibility still on the table. Right now though, our main concern will be with heavy rain as 3-6” can be expected, and locally higher amounts are possible. Both flash and river flooding will be a threat. CLICK HERE for more details.
THE SCIENCE: A cold front has moved through the area and lower dew points are resulting in lower humidity. In fact, drier air is noted all the way into the upper levels and with a ridge moving overhead between now and Saturday, mainly clear skies are anticipated. With the ridge and drier air combining, high temperatures will continue to run warmer than average by 5-10 degrees. The weather will once again turn active by the second half of the weekend. A strong shortwave trough will move from the Four Corners into the Lower Mississippi River Valley. Forecast models show a complex surface setup on Sunday morning with an area of low pressure in south Texas and an associated warm front across the northern Gulf. Another surface low will be positioned near the Texas/Oklahoma border. These features are expected to merge as the warm front lifts into the Southern U.S. and the upper trough deepens and becomes negatively tilted near the Texas/Louisiana border. Strong positive vorticity advection and frontal lift will cause a shield of rain to develop by Sunday Afternoon. PWATs (atmospheric moisture) will quickly increase to 2” or two times the normal for this time of year allowing thunderstorms to be very efficient rain makers. Periods of heavy rain are then expected through at least the first half of Monday with the Weather Prediction Center (WPC) forecasting 3-6” of rain for Southeast Louisiana and Southwest Mississippi. The area is now included in a “slight risk” in the excessive rain outlook which means there will be a 15 percent chance of flash flooding. There is also a “slight risk” for severe weather for the western half of the forecast area per the Storm Prediction Center (SPC). Forecast models depict a situation worth watching closely. The track of the surface low raises some concern as it will position near the Louisiana/Arkansas border by Sunday Night with screaming low level winds on the order of 40-60 knots. 0-3km helicity (spin) could top out between 250-450 m/s, plenty sufficient for rotating storms. CAPE (instability) could be between 1,000 – 2,000 j/kg which is supportive of strong updrafts. Vertical speed shear is somewhat lacking though which could be a primary limiting factor to severe weather. However, a saturated atmosphere with lower column evacuation aloft would likely lean toward heavy rain being the biggest threat. Areal and flash flooding will be the main concern with this event though the situation will need to be monitored for severe storms. Runoff will also cause significant rises on area rivers—possibly above flood stage at some locations on the Amite, Comite, Tangipahoa and Tickfaw. Once that trough kicks through the region, quieter weather is expected for Tuesday. Another wave will trek across the U.S. on Wednesday which may send a cold front through our region. However, it looks as though the more northern position of the upper trough will keep the threat for high impact weather lower.