Scientific Forecaster Discussion
fxus64 klch 241417
Area forecast discussion
National Weather Service Lake Charles la
917 am CDT Sat Jun 24 2017
Update...numerous to widespread showers and storms are expected
today as a very moist and unstable air mass remains in place. The
previous forecast remains on target and no changes are needed at
Previous discussion... /issued 653 am CDT Sat Jun 24 2017/
24/12z taf issuance.
a mix of conditions around the area this morning, with IFR cigs at
bpt, VFR at lch/aex and MVFR cigs/vsbys at lft/Ara. Widely sctd
rain showers/thunderstorms and rain have developed early this morning, with activity
occurring near the bpt/lch terminals. Recent hrrr trends indicate
this activity will slowly move northeast, with additional
convection developing and increasing in coverage during the aftn
as a front slides south into the area through this evening. VFR
conditions should prevail for the most part today, with conditions
lowering to MVFR/IFR in showers and storms. Kept tempo groups for
the aftn although timing may need to be amended as things evolve.
A few showers and storms will continue into the evening with
coverage decreasing slightly.
Previous discussion... /issued 345 am CDT Sat Jun 24 2017/
Locally heavy rainfall possible this weekend...
a surface cold front is located as of 24/07z from roughly north
central Texas to the Louisiana/Arkansas border. South of the
front, a very muggy and tropical like air mass remains in place.
Surface dew points are from the mid 70s to lower 80s and latest
precipitable water values as of 24/06z using GPS-met plot are from
1.8 to 2.2 inches. One convective complex moving away from the
front made it into the forecast area, and has now run out of steam
from roughly Leesville to Opelousas, with isolated convection
forming along the coast moving inland. Another convective complex
is noted moving away from the front toward upper southeast Texas
and west central Louisiana.
a short wave moving down from the northern plains will help kick
surface front into the forecast area this afternoon, with front
slowly meandering down to the coast through the weekend. Air mass
ahead of the front will have elevated moisture values and tropical
like with precipitable water values from 2 to 2.25 inches and
mean relative humidity over 75 percent. Low level forcing from main surface
front, along with meso-scale outflow boundaries and sea breeze, as
well as low level instability, will bring about the likelihood of
widespread showers and storms by afternoon...with activity only slowly
decreasing after sunset.
With the high moisture content and winds at 850 mb-70h rather
light and parallel to the front, convection will be slow moving
with the possibility of training. Therefore, there will be a
chance for locally heavy rainfall. Expect totals area wide to be
in the 1-2 inch range. However, where the slow moving convection
or training occurs, rainfall amounts may reach 3-5 inches or
higher. With out much significant rainfall yesterday, flash flood
guidance has recovered some, basically 2.5-3 inches for 1 hour and
3 to 4 inches for 3 hours and 4 to 5 inches for 6 hours.
Therefore, decided not to issue a Flash Flood Watch at this time.
It should be noted that the weather prediction center does have
the forecast area outlined in a slight risk (5-10 percent) of
excessive rainfall through tonight. Will place heavy rainfall in
the grids/zones and mention in the hazardous weather outlook.
On Sunday, the threat of heavy rainfall will still exist south of
where the frontal boundary sets up. With higher pops on Monday
confined to the coast, as some drier air behind the boundary works
into forecast area.
Tuesday could be the least active day in this forecast for
convection as east-northeast flow around surface high will bring
in some drier Continental air.
However, this high will move off to the east setting up a typical
subtropical ridge with southerly flow into the forecast area and
relative weakness aloft bringing elevated chances for showers from
Wednesday into the end of the forecast.
mainly light onshore flow will persist through tonight, with the
possibility of a period of light offshore flow during Sunday into
Monday as a surface boundary tries to slip into the coastal waters
from the north. High moisture values and lift from the frontal
boundary will mean elevated chances for showers and thunderstorms
from tonight into early next week.
Preliminary point temps/pops...
aex 87 72 86 68 / 80 40 50 20
lch 88 75 86 72 / 70 50 60 40
lft 88 74 86 71 / 70 50 70 40
bpt 88 75 87 73 / 60 40 60 40