Focusing on next Tuesday through Thursday morning right now.
LONG TERM (Tuesday through Friday)...The first in a series of shortwave troughs will likely move northeast across the mid Mississippi valley Tuesday night as a broad upper level trough develops over the western U.S. due to a digging shortwave trough over the Desert Southwest. A belt of stronger southwest winds in the mid to upper levels will set up from northeast Mexico and the western Gulf coast across the lower Mississippi Valley and southeast U.S. Tuesday through Thursday. Ripples of weak shortwave troughs will move through the flow before the strong shortwave trough moves through the forecast area on Thursday. A combination of a low level frontal boundary and/or low level convergence and deep moisture content will linger over the area and this will be a focus for repeat showers and thunderstorms and heavy rainfall. CIPS analog guidance is also showing a strong signal for heavy rainfall, and the GFS/ECMWF operational models also have periods with 3-4+ inch plus bullseye over the central Gulf coast region Tuesday night and Wednesday. There is fairly good agreement amongst the models which leads a bit higher than normal confidence. Drier weather should finally return late Thursday into Friday as the shortwave trough moves east, however southwest flow aloft will linger over the region possibly setting the state for another round of high rain chances and heavier rainfall again by next Saturday.
Last Edit: Mar 24, 2021 14:33:11 GMT -6 by SKYSUMMIT
Regarding the severe potential for next week, per the SPC:
Some severe potential could persist near the TX coast eastward along the central Gulf coast on Day 5/Wed. However, a surface low is forecast to develop south of the TX coast over the western Gulf. This could maintain a warm front just offshore from the central Gulf coast, resulting in mainly elevated convection is a warm advection regime ahead of the next upper shortwave trough. Severe potential will largely be dependent on the position of this warm front. Medium-range guidance varies on the position of this boundary, resulting in too much uncertainty to include severe probabilities.
The low over the western Gulf should develop northeastward sometime on Day 6/Thu, as an upper trough over the Plains ejects eastward. Strong deep-layer southwesterly flow will spread across the southeastern U.S., while increasing southerly low level flow brings richer Gulf moisture further inland ahead of an eastward-advancing cold front. This could bring another bout of severe potential to much of the South, but the timing of the upper trough, strengthen of the surface low and quality of the thermodynamic environment remain uncertain.
Post by Stephanie Carpenter, WBANK JP on Mar 21, 2021 1:39:44 GMT -6
Cheshire Cat, I think they are going off the basis of a few models. Some models are saying 3" to 5" while others are saying 4" to 7". Thus the upping on their forecast of 3" to 7". That would be very manageable if that is spaced out over two to three days. If there may be a training event, which may or may not happen, for those amounts to come at one time may be problematic.
Tuesday through Thursday, a low pressure system will move through the area and stall as it progresses eastward, which will enhance rain chances for the area throughout this time period. Southerly surface winds will act to enhance the moisture availability and warm air advection into the region ahead of and during the system moving through during this time period. Due to the slow moving nature of this system, training storms will be very possible during this event. And the potential for heavy rainfall, especially Tuesday overnight into Wednedsay and Wednesday night will be a concern. Model trends have been showing better consensus today than previous days for our area. In general, looking at the models, our area could see rainfall amounts ranging from 7 to 10 inches for the next 5 days (tonight through Friday evening) with locally higher amounts certainly possible, which is consistent with the WPC 5-day forecasted rainfall. One factor that will determine the risk of heavy rainfall will be how high the rainfall rates will get / how efficient will the rainfall be. Upper level divergence will on Tuesday evening will allow for lifting in the environment, which will allow for storms to become more efficient. PW values based on the models will be around the 90% for sounding climatology ( at least 1.5 to 2 inches average every day). There will be plenty of instability and some thunderstorms may be possible during the daytime heating hours. The winds look fairly strong just above the surface, but we have often overcome strong low level winds to produce heavy rain events in the past in our area. So as a whole, models are showing favorable instability, lifting, moisture, and buoyancy. The winds may be a bit strong at the low levels, but this can be overcome, depending on the set up of the sytem. Given the parameters, it looks pretty likely that we could see some heavy rainfall and efficient rainfall Tuesday through Thursday, especially North and South of Lake Pontchartrain and along the Mississippi coastal areas.
On Thursday, there is also the possibility of severe weather for our area. This is still very uncertain and will depend on how the system develops over the next few days. There will be plenty of moisture and warm air in the environment due to the southerly surface winds leading up to Thursday, which will help enhance instability. Upper level divergence will help to enhance lifting and buoyancy in the environment. However, there is a big caveat regarding the shear. Southerly surface winds on Thursday will provide favorable helicity looking at the model consensus, but these winds are really only decent during the morning and early afternoon hours on Thursday. By the late afternoon hours / evening hours, the winds will be mostly southwesterly, which will provide lower helicity values and less favorable conditions for severe weather and more specifically tornadoes. But given the higher instability, moisture, lifting, and buoyancy, strong winds and frequent lighting will be possible with this system on Thursday. Overall, the timing of this system and how it develops will be crucial to determining our chances of severe weather and which types of weather we could see on Thursday.