National Weather Service Raw Text Product

960 
FXUS64 KHGX 030357
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
957 PM CST Fri Dec 2 2016

.UPDATE...
The well-advertised rain event for Southeast Texas has begun
today, with the first wave of rain showers moving through. The
most intense rain has come over the offshore waters, and is where
a small handful of CG strikes have occurred. Mesoanalysis has
shown significant low level shear and helicity, and this has
largely been reflected in the resultant cells, as even small
showers have shown weak rotation, particularly over the waters
closer to the surface trough axis. Whether or not this has
translated to waterspouts is unknown, with no reports received.
But as a result, there has been a sensitivity to potential for
landfalling waterspouts/tornadoes right on the coast this evening.
However, to this point, this threat has not seriously emerged.
This may be shown by examining effective SRH, rather than defined
0-1km or 0-3km SRH, which has been significantly lower. Despite
the favorable kinematic environment, it does not seem to translate
well to the inflow layer of our cells this evening.

Rainfall so far has been relatively light, despite isolated cores
of 1-2 inch per hour instantaneous rain rates. These cores are too
small and moving too quickly, and thus precip so far does not
appear to exceed half an inch. Still, there is a long weekend with
plenty of rain ahead, and the expectation was already for this
evening to be a relatively low contributor to the total rainfall.
Thus, the potential for eventual excessive rainfall is not
changed at this time.

Changes to the forecast have been relatively minimal, as the focus
has been more on mesoanalysis and radar meteorology. Fortunately,
the forecast from this afternoon has been tracking relatively
well. The biggest changes have been to PoPs, in an attempt to
blend current rainfall with hi-res, short term guidance in the
near term. Into tomorrow, the forecast weights to the more broad-
brushed previous forecast, as confidence in CAMs highlighting the
true areas of heaviest rainfall decreases.

Luchs

&&

.PREV DISCUSSION... /ISSUED 554 PM CST Fri Dec 2 2016/ 

AVIATION...
Low forecaster confidence level on the 03/00Z TAFS. Looking for mainly
periods of SHRA possibly embedded with TSRA this evening, with activity
becoming more widespread/numerous during the overnight hours and on
into tomorrow. Majority of the 00Z TAFs have MVFR ceilings overnight
with IFR conditions possible during the day tomorrow. IFR/LIFR ceilings
and visibilities are likely with any hard to time strong SHRA/TSRA.
Winds (both speed and direction) will be tricky and will depend on
when/where any boundaries set up. Generally have gusty east winds for
much of the area tonight through tomorrow morning becoming northeast
inland and east to southeast near the coast tomorrow afternoon.  42

PREV DISCUSSION... /ISSUED 346 PM CST Fri Dec 2 2016/ 

DISCUSSION...
All of the ingredients for what is setting up to be a high
rainfall event are coming into place. The coastal surface trough
axis is currently just offshore...with the greatest rain coverage
occuring over the northwestern Gulf this afternoon. Bands of
precipitation are coming onshore and these bands will continue to
increase in areal coverage through the evening hours. The main
threat with these bands will be isolated tornadoes embedded within
them as lower level winds significantly turn within the lowest
couple of kilometers. A developing warm frontal boundary moving up
towards the upper Texas coastline through the weekend will maintain
the isolated tornado threat through Saturday...or until the lower
level winds back more northeasterly with this boundary's north(east)ern
approach. The main threat throughout the weekend will evolve from
isolated (near coastal) tornadoes and locally heavy bouts of rain
leading to minor flooding issues to more areawide flooding.

Antecedent dry soils and rivers well within banks will keep the
immediate flash flooding threat at bay but...by Saturday afternoon
or evening or once soils become more saturated...the flooding
threat will move to the forefront. Thus...a Flash Flood Watch may
need to be issued for the remainder of the weekend into Monday.
Once all of the forecast meteorological parameters were analyzed
in relation to flash flooding...from the near 2 inch pw offshore
air mass being efficiently pumped in on moderate mid-level flow/
location of theta E axis in relation to the vicinity warm frontal
boundary as well as well as decent upper level forcing going into
Sunday (e.g., better jet positioning of RRQ/LFQ as the upper low
enters the Big Bend region)...there is a good potential for an
eventual regional flash flooding event.

The coastal trough will shear out with the upper low's northeastern
passage Monday...ending precipitation from west to east through
the day. Moderate northwest to westerly winds in the wake of this
low will scour out skies and advect in a much drier air mass
across the region early Tuesday. Early week diurnal temperatures
in the morning interior 40s/coastal low to mid 50s will still warm
into the daytime 60s under a weakening northwest wind Tuesday...onshore
breezes Wednesday. Rain chances (primarily showers) will briefly
increase through Wednesday and peak pre-sunrise Thursday downstream
of a late day into morning cold frontal passage. A continental-in-
origin cold...dry air mass will descend into eastern Texas late
next work week and significantly chill the weather out. Late period
winter-like conditions under clear skies...north to east breezes
with minimum Ts in the 30s and days slowly warming into the low to
mid 50s. 31

MARINE... 
At 3:00 PM the coastal warm front was located from near the Sabine
to the Upper Texas offshore waters to the Lower Texas coastline. The
high resolution models move this boundary slowly toward the coast
overnight tonight. There is a chance that some isolated strong
storms may produce isolated strong wind gusts and waterspouts later
this afternoon through tonight mainly east of the frontal boundary.
Other impacts for tonight include winds gusting between 20 and 30
knots and seas approaching 10 feet (mainly beyond 20 nm).

Winds and seas should diminish on Saturday as the frontal boundary
moves onshore. Periods of showers and thunderstorms will continue to
be a hazard through Monday. Moderate winds may approach advisory
levels on Monday as the main storm system moves east of the area. 40/08

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      51  53  48  55  50 /  90 100  80  80  70 
Houston (IAH)              53  61  54  61  54 /  90 100  90 100  90 
Galveston (GLS)            63  68  65  67  61 /  80 100  90 100  90 

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Coastal Flood Advisory until 6 AM CST Saturday for the following 
     zones: Brazoria...Chambers...Galveston...Harris.

GM...Small Craft Advisory until 6 AM CST Saturday for the following 
     zones: Coastal waters from Freeport to the Matagorda Ship 
     Channel out 20 NM...Coastal waters from High Island to 
     Freeport out 20 NM...Galveston Bay...Matagorda Bay...Waters 
     from Freeport to the Matagorda Ship Channel from 20 to 60 
     NM...Waters from High Island to Freeport from 20 to 60 NM.

&&

$$

Discussion...25