3/23/2021 - 3/24/2021 Heavy Rain, Severe, Flood Discussion

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.