Area Forecast Discussion
Issued by NWS Lake Charles, LA

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FXUS64 KLCH 051737
AFDLCH

Area Forecast Discussion
National Weather Service Lake Charles LA
1137 AM CST Mon Dec 5 2016

.AVIATION...Showers and a few thunderstorms will be ending through
the day west to east as low pressure advances across the forecast
area. IFR ceilings will persist.

&&

.PREV DISCUSSION... /issued 1035 AM CST Mon Dec 5 2016/

UPDATE...
Surface low off the Southeast Texas coast along a frontal boundary
that is located about 40 miles off the Southwest Louisiana coast
to just off the Southeast Louisiana coast. This surface low will
move east during the afternoon hours. At this point it looks like
the land areas of the forecast area will stay in the cool sector
reducing any risk for severe weather. An upper level low moving
into Southwest Texas will also continue to move off to the east-
northeast. Dry slot looks to be moving around the upper level low
and up the Texas coast. Chances for heavy rain will occur ahead of
the dry slot. Therefore, the best chance for heavy rain will be
from now until about 05/21Z, and mainly over Southwest and South
Central Louisiana. Southwest Louisiana could see an additional 1
to 3 inches, while South Central Louisiana could see an additional
2 to 4 inches.

Will keep the Flash Flood Watch as is for now. However, may be
able to cancel it early over portions of the forecast area,
especially Southeast Texas once the dry slot moves through, and
rainfall rates will be greatly reduced. Also, lowered the pops
somewhat for areas that are expected to be dry slotted this
afternoon.

Rua

PREV DISCUSSION... /issued 541 AM CST Mon Dec 5 2016/

DISCUSSION...
12Z TAFS

AVIATION...
Showers with a few embedded thunderstorms streaming in off the
gulf this morning in advance of a currently stationary warm front
situated approximately 80-100 miles offshore. This warm front will
slowly lift onshore throughout the day today but will quickly be
displaced by an advancing cold front that will push through the
area by this evening. The practical results of these interactions
will be numerous showers and increasing thunderstorms as well as IFR
to VIFR CIGS throughout the morning and into the afternoon.
Guidance is spread with regards to timing of the activity finally
moving out of the area so have maintained showers and
thunderstorms in the package until 00Z Tue. This may be a bit
pessimistic especially for BPT and LCH but it allows for the
current spread in guidance and will be refined as the day
progresses.

In addition to large swaths of showers and general thunderstorms,
there will be a brief period as the warm front moves onshore late
this morning into early this afternoon where strong to severe
thunderstorms could develop. This threat will exist primarily
across eastern TAF sites including LFT and ARA.

PREV DISCUSSION... /issued 415 AM CST Mon Dec 5 2016/

DISCUSSION...
Early morning sfc analysis shows low pressure developing over the
wrn Gulf off the cntl TX coast with a quasi-stationary front
continuing to drape over the waters off the wrn Gulf Coast...while
high pressure remains centered over the Mid-South. Water vapor
imagery shows a mid/upper-level low crossing the mountains of nrn
Mexico with a deep srly flow persisting over the nwrn Gulf and wrn
Gulf States region. Regional 88Ds show showers continuing to
blossom over much of the forecast area at this time...along with a
few storms...as isentropic lift ahead of the approaching storm
system increases.

Not much to add to the inherited grids/zones this morning. The
combo of deep Gulf moisture, frontal boundary and lows both
sfc/aloft will continue to lead to the formation of showers into
the afternoon. For now the storm activity showing up on radar over
the nwrn 1/2 of the forecast area is assumed to be elevated in
nature, but this could change later in the day, mainly closer to
the coast in better proximity to the warm sector. The sern 1/2 of
the forecast area is included in SPC`s day 1 marginal/slight
outlooks as dewpoints are progged to climb back into the 60s with
the passage of the front...and low-level shear is thus expected to
improve especially in the afternoon. However SPC`s probability
charts maintain best shot at severe stays well off to our east...
thus for now will leave any severe wording out of the grids/zones.
Forecast QPFs for today remain high with areal averages of 1 to 2
inches the norm for most areas...thus have not made any changes to
the inherited Flash Flood Watch given the current saturated
conditions ongoing across the region. Short-range high-res models
are in agreement with all of the heaviest convection moving east
of the area by late afternoon.

Mid/upper-level low is expected to open up as it lifts newd
through tonight...taking its sfc reflection with it and allowing a
drier wrly flow to develop in its wake. This is in turn will finally
shunt all the precip out of the area during the evening hours. The
drier conditions will persist into early Wednesday before weak sfc
high pressure moves east of the area and a light return flow sets
up...while the flow aloft begins to take on a little more of a
srly component as a shortwave moves out of the Rockies. Combo of
this moistening with weak energy spilling over the region should
allow for a few showers to develop mainly over the nwrn zones
during the afternoon on Wednesday. Rain chances will increase
Wednesday night as moisture further increases and a strong cold
front sweeps across the area. Slim rain chances lag on into
Thursday morning across lower Acadiana before the front finally
clears and much drier air fills in behind it.

Strong Canadian high pressure is progged to build over the
forecast area for late in the week with the coldest temperatures
of the season expected. Lows across the nern zones are forecast to
drop to the mid 20s for Friday and Saturday mornings...with most
of the rest of the area seeing freezing temps both mornings (the
coastal areas should remain just above freezing for now). Highs on
Friday will fail to get out of the 40s as of now. A warmup looks
on tap beginning later Saturday as high pressure moves east of the
area and a srly flow ushers in warmer air off the Gulf.

With a progressive pattern in place, another round of precip looks
possible late in the weekend as another disturbance aloft crosses
the wrn Gulf region and works with increasing moisture.

MARINE...
Elevated srly winds over the outer waters this morning will
diminish a little this afternoon before the low passes and a
strong wrly flow develops in its wake...thus SCA headlines for
tonight were inserted this package. Elsewhere strong offshore flow
is again expected behind the mid-week fropa...with SCA conditions
expected at that time.

&&

.PRELIMINARY POINT TEMPS/POPS...
AEX  51  48  59  46 / 100  30  10  10
LCH  58  50  65  51 / 100  20   0   0
LFT  65  53  66  51 / 100  30   0   0
BPT  59  48  68  52 / 100  20   0  10

&&

.LCH WATCHES/WARNINGS/ADVISORIES...
LA...Flash Flood Watch until 3 PM CST this afternoon for LAZ027>033-
     041>045-052-053-073-074.

TX...Flash Flood Watch until 3 PM CST this afternoon for TXZ180-201-
     215-216-259>262.

GM...Small Craft Advisory from 6 PM this evening to 6 AM CST Tuesday
     for GMZ450-452-455-470-472-475.

     SMALL CRAFT EXERCISE CAUTION until noon CST today for GMZ450-452-
     455-475.

     Small Craft Advisory until noon CST today for GMZ470-472.

&&

$$


AVIATION...23



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