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Area Forecast Discussion (AFD)

Issued by Houston/Galveston, TX (HGX)

                            
000
FXUS64 KHGX 160442
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1142 PM CDT Mon Apr 15 2019

.AVIATION...
A patch of MVFR ceilings developed earlier this evening and
although this area of cloud cover has dissipated, it's a signal
that low level moisture is returning at a faster pace. Winds won't
fully decouple overnight but think there will still be enough
mixing to limit the threat for ground fog. Best chance for some
fog by morning will be near KCXO. The ECMWF cloud product and MAV
guidance suggests that MVFR ceilings will develop over the 
western third of the CWA and move east during the morning. Current
thinking is that MVFR ceilings will impact area TAF sites between
13-19z with VFR ceilings for the rest of the afternoon. A tight
pressure gradient will foster strong S-SE winds and will maintain
a gust group for inland TAF sites. Saturation beneath a building 
cap will yield MVFR ceilings areawide on Tuesday night. Although 
PW values reach 1.50 inches by 12z Wednesday, moisture profiles 
still look too dry to mention VCSH. 43

&&

.PREV DISCUSSION... /ISSUED 632 PM CDT Mon Apr 15 2019/ 

AVIATION...
VFR conditions expected for most of the night with some increase
in clouds after 09z, especially over western TAF sites. Might get
a brief window of MVFR ceilings at KCLL toward morning but the 
air mass is dry and feel most of the area will probably remain 
VFR. Winds will not fully decouple tonight and will increase again
on Tuesday. Fcst soundings show a saturated layer developing 
between 00-03z Wednesday night and would expect MVFR ceilings to 
develop by 03z. 43

PREV DISCUSSION... /ISSUED 353 PM CDT Mon Apr 15 2019/ 

NEAR TERM [Through Tonight]...

Fairly nice spring day with temperatures in the upper 70s to low
80s in a few areas. Southerly winds over the area remain in place
due to a surface low pressure in the lee of the Rockies with high
pressure to the east. Upper level pattern has become more zonal
with only a strong trough over the Great Lakes. Upper level low
off the southern coast of California and another one off the
Pacific NW coast should cause the pattern to amplify the next few
days up stream.

Tonight should have fairly quiet weather with low temperatures in
the low 60s and a decent southerly breeze. Gulf moisture will be
returning tonight into Tuesday so cloud cover should increase with
warm air advection pattern setting up over the area.

SHORT TERM [Tuesday Through Wednesday]...

Upstream upper level lows should phase together over the Desert 
SW on Tuesday and Tuesday night. This should allow for pressures 
to continue to drop over the High Plains and more southerly winds.
Upper level ridging will also develop over Texas which should 
keep conditions dry for Tuesday but with warm air advection 
increasing we expect there to be a few showers Tuesday night into 
Wednesday. Models hit rain chances harder during the day Wednesday
but we are backing off a bit on this since strongest lift is not 
until Wednesday night and there will be stronger forcing over 
north Texas. SPC has enhanced risk of severe for central and north
Texas based on this with slight/marginal risk over SE Texas 
mainly for the possibility of severe weather developing southward 
overnight.

LONG TERM [Wednesday Night Through Monday]...

Wednesday night into Thursday morning the atmosphere becomes more
primed for supporting severe weather. Upper level trough advances
towards the area with PVA being more channelized. Upper jet 
dynamics look favorable with another left exit region moving into 
the area. This is more apparent in the NAM but the GFS/ECMWF both 
show a southern jet streak like the NAM but coupled with another 
jet streak moving SW to NE over N Texas into W Missouri. Both 
divergence and diffluence will be enough for strong lift by 
Thursday morning. LLJ at 850mb does shift east more ahead of the 
line of storm into LA/MS and veers over SE Texas. Linear forcing 
should be strong enough for a squall line to form an push through 
the area Thursday morning. Problem will be whether there is enough
instability to remain overnight and if forcing will be enough for
the cap to erode. Quite possible to get a line of storms to form,
become strong/severe but then weaken only to re-develop later in 
the day over LA/MS as the cold front pushes east. Right now think 
SPC's slight risk looks on track for much of the area given the 
overnight nature of the event and questionable thermodynamics.

Overpeck

MARINE...

Not a lot of change from previous thinking with onshore winds begin- 
ning to increase tonight. We could approach SCEC criteria overnight. 
Otherwise, we are still looking for the next cold front to push off- 
shore early Thurs. Scattered showers/thunderstorms to accompany its 
passage. Generally moderate offshore flow to prevail in its wake.
41

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      60  81  68  79  62 /   0   0  10  50  80 
Houston (IAH)              61  81  68  79  66 /   0   0  10  40  80 
Galveston (GLS)            67  76  71  76  68 /   0  10  10  30  60 

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 7 AM CDT Tuesday for 
     the following zones: Coastal waters from Freeport to 
     Matagorda Ship Channel TX out 20 NM...Coastal waters from 
     High Island to Freeport TX out 20 NM...Galveston Bay...
     Matagorda Bay...Waters from Freeport to Matagorda Ship 
     Channel TX from 20 to 60 NM...Waters from High Island to 
     Freeport TX from 20 to 60 NM.

&&

$$

Discussion...25
Aviation/Marine...43