Area forecast discussion
National Weather Service Shreveport la
329 PM CDT Tuesday Jun 18 2013
Discussion...
busy afternoon...as an mesoscale convective system has developed over northwest la...and has now
begun to accelerate east-southeast into north central la along the residual north central
la outflow boundary from convection earlier this morning and nearby
850mb trough axis that extends west-east from East Texas into north la. This
complex is also feeding into a more unstable air mass...as 20z
mesoanalysis indicates 2000-2500 j/kg of SBCAPE has developed over
north central la as ceilings have broken out to allow temperatures to warm into the
middle/upper 80s. Given the deep warm layer and high precipitable water noted on the
12z kshv radiosonde observation...locally heavy rainfall will also be possible this
evening...even as deep layer forcing increases with the mesoscale convective vortex now
entering ecntrl Texas. Have inserted mention of locally heavy
rainfall this evening for north central la...with the any isolated severe
and heavy rainfall threat gradually diminishing later this evening
as the complex exits the area.
Meanwhile...the mesoscale convective vortex should gradually accelerate east-southeast into central la
as the northern mx/southern rockies upper ridge begins to gradually expand north
across the plains. The aforementioned surface front should become
stationary later this evening from north central la into East Texas...and
persist through Wednesday morning before gradually shifting back north
during the afternoon. The GFS has dried out considerably but seems
to have problems handling this front...with better agreement and
consistency amongst the NAM/European model (ecmwf) in slowly lifting the front north
Wednesday afternoon and washing it out Wednesday night or Thursday.
Prefer the slightly wetter NAM/European model (ecmwf) solution with daytime
heating/instability and ample low level moisture contributing to
the development of isolated/widely scattered convection in vc of the
front Wednesday. Have maintained low chance probability of precipitation for East Texas/north la along and S
of I-20...and expanded slight chance probability of precipitation a tad farther north to the
Red River into extreme southern Arkansas should the surface front drift back north.
Any convection that diminishes should diminish around
sunset...especially as the upper ridge begins to expand NE towards
the middle MS valley late Wednesday into Thursday.
The surface boundary should wash out completely during the day Thursday...although
weaknesses aloft will round the eastern periphery of the ridge Thursday
and Friday during peak heating to warrant the continuation of
slight chance probability of precipitation for north central la/portions of deep East Texas by Friday
through the weekend. Temperatures should also warm into the middle 90s by
this time as well. See very little change in the upper air pattern
as we begin the new work week...with ridging aloft strongest from
the Southern Plains into the MS valley...and an upper level weakness
over the Gulf Coast states which could result in mainly isolated
afternoon convection over north la/deep East Texas.
Prelims to follow below...
15
&&
Aviation...
main concern for the 19/00z taf issuance will be flight hazards from
scattered thunderstorms which will continue for much of this evening. A weak
frontal boundary near a keld to ktyr line will be the dividing line
between more numerous storms to the south and only isolated coverage
north. Expect mostly VFR flight weather outside of the convective
areas...but near storms expect MVFR/IFR conditions along with
moderate to severe turbulence and surface wind gusts up to 45 kts.
The front will drift slowly south tonight and most of the convection
will remain south of the boundary. However after 08z and continuing
through 14z Wednesday....much of the area along and south of
Interstate 20 may experience MVFR to briefly IFR ceilings and visibilities
due to fog. Surface wind will be determined by frontal location...
but generally in the 5 to 10 knots range. /14/
&&
Preliminary point temps/pops...
shv 69 90 73 93 74 / 30 30 10 20 10
mlu 70 89 70 92 72 / 40 30 10 20 10
deq 64 90 68 92 72 / 10 10 10 20 10
txk 68 90 70 91 73 / 20 20 10 20 10
eld 67 90 69 92 71 / 20 20 10 10 10
tyr 69 91 74 93 74 / 20 30 10 20 10
ggg 69 90 73 93 73 / 20 30 10 20 10
lfk 71 92 73 94 74 / 40 30 10 20 10
&&
Shv watches/warnings/advisories...
Arkansas...none.
La...none.
OK...none.
Texas...none.
&&
$$
15/14
