FXUS64 KLIX 250929

Area Forecast Discussion
National Weather Service New Orleans LA
429 AM CDT Sun Aug 25 2019


Main focus in the short-term will continue to be flash flooding
concerns today stretching into early this upcoming week. A quick
overview of the synoptic set up reveals a persistent low to mid-
level low, slightly tilted in height across far eastern Texas into
the NW GOMEX. With SE LA and southern MS being on the western
edge of this weak low, ongoing southerly winds continue to pump
deep moist Gulf air across the region, with RAP13KM analysis
indicating a large area of 2.3 to 2.5 inch precipitable water
values in place. Beginning with this morning, similar to
yesterday, a large outflow boundary will continue to slowly drift
NE across western areas, keeping shower/storm chances in place
early this morning generally west of I-55. HRRR/NAM3KM guidance
suggests this boundary to aid in enough dynamic convergence to
help develop shower/storms generally across all of SE LA later
this morning through the afternoon and evening. While storm
motions this afternoon will generally be somewhat progressive in
and around 200/10 knots, boundary orientation/evolution may pose a
risk for some back building/training cells in a few areas. With
such anomalously high PW's across the region, have decided to go
with a Flash Flood Watch today for all of SE LA, with the threat
extending north and east later this evening through tomorrow for
southern MS counties.

One additional note for later this afternoon through early
tomorrow is with this slow eastward movement of the mid to upper-
low, some reflection may begin at the surface with a weak
surface/meso low developing across NW areas. Depending on just
how prominent this feature becomes, some slight backing of surface
winds may develop, with in conjunction with persistent southerly
winds in the low-levels, SRH 0-3km values peak up around 200-300+
m2/s2 close to the low position. This may lead to a few isolated
quick spin ups in shallow cells that do develop and may need to be
watched, with the main area of this focus being along and west of
I-55 tomorrow evening/night, spreading east across coastal MS on

The latest 00Z SUN 36hr extended run of the HRRR did illustrate a
potential issue that was first noticed last night, which is with
this low eventually drifting north and east across southern MS/AL
on Monday, tropical banding may set up anywhere across SE LA and
southern MS due to unidirectional SW to WSW flow from the surface
to the mid-levels. This means flash flooding issues may likely
persist into the day on Monday, with the greater risks east of
I-55, where the WPC maintains a Slight risk for excessive
rainfall. Main idea here is there is a possibility for locally
enhanced regions of flash flooding potential, but narrowing down
small mesoscale features responsible is nearly impossible this
far in advance. Watch for later forecast updates to reflect this
potential with time.

By Tuesday, this system finally stretches out in the mid-levels
and becomes absorbed by a passing weak trough and we return back
to more of a typical summertime pattern with afternoon hit-or-miss
shower/storm chances. Temperatures also build back into the lower
90's for inland locations, helping build heat indicies back into
the lower to mid 100's. There is a possibility for some at or near
advisory criteria heat indicies Tuesday and Wednesday, but this
risk and /or extent will be determined by how much surface
moisture remains in place across the region. Additionally, long-
range guidance still is on track about a passing "cold" front by
late-week, which may help bump temperatures down a bit. However,
just how much dry air works in is still not too clear, but a nice
relaxing break from the heat will be much welcomed! Time will
tell for now. KLG



An ongoing unsettled weather pattern will continue to keep high
rain/storm chances in place through the day today and into early
this upcoming week. Main threats with any one storm will be gusty,
erratic downdraft/outflow winds in excess of 25 to 35 knots,
dangerous lightning and a few isolated waterspouts, especially
late tonight and into the day on Monday for near coastal areas of
SE LA and southern MS. Conditions return back to a normal
summertime pattern on Tuesday and Wednesday before a late-week
cold front possibly dips into the northern GOMEX, shifting winds
from the north and lowering rain chances. KLG



Mostly VFR conditions are expected to prevail early in the day, but
occasional MVFR is likely to mix in this morning, especially during
periods of SHRA/TSRA. Prevailing MVFR conditions with briefly lower
IFR due to lower CIGS and occasional VSBY restrictions in SHRA/TSRA
is then expected to develop during the 17-21z period for the
airports along and west of a KMCB-KNEW-KGAO line, and then either
during late afternoon or tonight for KASD and KGPT. Prevailing IFR
conditions due to lower CIGS is expected to develop around 03z
Sunday night at KBTR and KMCB 22/TD



DSS code: Yellow.
Deployed: None.
Activation: None.
Activities: Marginal to Slight Risk of Excessive Rainfall.

Decision Support Services (DSS) Code Legend
Green = No weather impacts that require action.
Blue = Long-fused watch, warning, or advisory in effect or high
visibility event; Marginal risk severe or excessive rain.
Yellow = Heightened impacts with short-fused watch, warning or
advisory issuances; radar support for slight risk severe
or excessive rain.
Orange = High Impacts; Enhanced risk severe; nearby tropical
events; HazMat or other large episodes.
Red = Full engagement for Moderate to high risk of severe and/or
excessive rainfall, or direct tropical threats; Events of
National Significance.


MCB 84 71 85 72 / 70 80 60 10
BTR 83 74 88 75 / 90 70 50 10
ASD 86 73 86 74 / 70 80 70 30
MSY 85 76 87 77 / 80 70 70 20
GPT 86 74 84 75 / 30 80 80 40
PQL 89 73 85 74 / 30 80 80 50


LA...Flash Flood Watch through Monday morning for LAZ036-037-039-040-

MS...Flash Flood Watch from this evening through Monday morning for


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