Area Forecast Discussion
Issued by NWS Lake Charles, LA

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FXUS64 KLCH 220126

Area Forecast Discussion
National Weather Service Lake Charles LA
826 PM CDT Mon Aug 21 2017

KLCH radar shows sctd showers and tstms moving west acrs the
Atchafalaya Basin, with activity extending fm eastern Avoyelles
Parish south to central Vermilion Parish. Activity so far appears
to be maintaining intensity although loss of daytime heating
should allow convection to diminish in strength and coverage over
the next few hours, and this is reflected in recent hi-res
guidance as well. Updated POPs based on these trends, bumping POPs
up slightly acrs eastern portions of the area for early this
evening. Remainder of fcst appears to be in good shape at this



.PREV DISCUSSION... /issued 424 PM CDT Mon Aug 21 2017/

Latest water vapor satellite imagery/upper air analysis showed a
deep layer ridge axis across the Southeastern States, with an
upper low spinning over the North Central Gulf of Mexico. At the
SFC, high pressure extended from the Carolinas into Central TX.

Radar imagery late this afternoon showing most convection
continues to be tied to a slowly northward moving sea breeze and
subsequent outflows over the southern third or so of the inland
forecast area, though some isolated cells have also managed to get
going over Central LA. While most of this activity is expected to
wane with the loss of diurnal instability, have left a small PoP
over ERN zones as the upper low over the NC Gulf continues to
track slowly WWD.

This feature is progged to continue WWD on TUE while weakening
over the NW Gulf Coast Region, while a robust upper trof digs into
the ERN CONUS, eroding and shunting southward the ridge over the
Southeastern States. Consequently, a little more in the way of
convective coverage is expected tomorrow. Greater coverage is
expected WED thru FRI as a frontal boundary is progged to drop
into the area and subsequently stall near the coast.

Meanwhile, the remnants of Harvey, currently over the NW Caribbean
Sea, are forecast to emerge into the Bay of Campeche TUE night
into early WED, then subsequently track NW TWD the NE MX or S TX
coast, coming ashore on FRI. While there is generally good
agreement on some degree of regeneration and the subsequent track
as laid out above, the global models diverge wildly beyond this
point on where the remnants of Harvey will eventually go owing to
differing depictions of the relevant steering mechanisms. The
stalled frontal boundary and moist onshore flow alone argues for
at least chance PoPs for the weekend and into early next week
until better clarity/higher confidence emerges.


Light southeast winds and low seas will continue through Wednesday
as surface high pressure ridges west across the Gulf States. This
high is forecast to breakdown late Wednesday as the region is
squeezed between an approaching cold front to the north and what
is likely to be a regenerated Harvey over the Southern Gulf of
Mexico. Elevated winds and seas are possible Thursday and Friday
over the Gulf waters west of Cameron pending the eventual track
and strength of this system, which at this time is forecast to
move ashore near the Texas and Mexico border late Friday.



AEX  74  92  74  91 /  30  20  10  50
LCH  77  91  76  91 /  20  40  10  40
LFT  76  91  76  91 /  30  40  10  40
BPT  76  91  76  92 /  10  30  10  30



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