Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 132027

Area Forecast Discussion
National Weather Service Houston/Galveston TX
327 PM CDT Tue Apr 13 2021

.SHORT TERM (Through Wednesday Night)...

A messy and complicated 36 hours is on tap for the region as a
weak front hovers over the area. Satellite derived PW fields show
around 1.60 to 1.70 inches over SE TX this afternoon. Convective
temperatures have been met but convection has been slow to develop
but the potential is still there for late afternoon and evening
shra/tsra. Water vapor imagery shows a weak short wave over
northern Mexico and this should provide some forcing around mid
evening and that`s when the TT WRF develops some tsra over the
central zones near the weak surface boundary. Have leaned a bit
toward the TT WRF mid evening and the HRRR for late night. The
HRRR develops a burst of precipitation along the boundary and
quickly shunts it off to the east. Most areas should get some rain
and the stronger storms should be capable of producing a quick
burst of 1-2 inches of rain overnight. SPC still has a large
portion of SE TX in a Marginal to Slight Risk for strong/severe
storms tonight. CAPE values are lower than progged yesterday but
still reach around 1000 J/Kg, LI values are between -4 and -8 and
mid level lapse rates remain steep at 7.5 C. Parameters are in
place to get a few strong to severe storms tonight but much is
dependent on the position of the front and the timing of the weak
s/wvs over Mexico. FWIW, a quick word about the ECMWF which has
been eerily consistent with bringing the wind shift toward the
coast by 12z Wednesday. It has been consistent with bringing a
line of storms across most of the CWA between 09-15z. It is also
the strongest with a short wave embedded in the 500 mb flow and
again, water vapor does show a couple of disturbances upstream so
it may be on to something. MinT values will again remain very
warm with cloud cover and very moist low level air in place (dew
points near 70 degrees). Most locations will probably stay above
70 degrees yet again tonight with the exception being those
getting some rain and rain cooled air. SREF favors the southern
Gulf waters for more sea fog so we will need to watch the southern
counties for dense fog and another possible advisory.

The boundary hangs around the CWA on Wednesday with additional
shra/tsra possible. Much will be dependent on what happens
tonight, and if the air mass gets worked over, there probably
won`t be much activity on Wednesday. 850 mb temps don`t show much
cooling and MaxT values should warm into the lower and possibly
mid 80`s south. PW values are progged to remain near 1.70 inches
so with the boundary and surface heating, it seems reasonable that
additional shra/tsra will develop. CAPE values are actually a bit
higher on Wednesday and should reach around 2000 J/Kg but jet
dynamics remain less than stellar. That said, there could be a
couple of strong storms again due to some steeper lapse rates. SPC
has placed the coastal sections of SE TX in a Marginal Risk for
strong storms on Wednesday.

Additional showers and isolated storms will be possible Wednesday
night as the front finally sags into the coastal waters. MinT
values will trend cooler in the wake of the boundary. 43


.LONG TERM [Thursday through Tuesday]...

On Thursday, Southeast Texas will be in predominantly zonal flow
aloft as it is sandwiched between two upper-level lows, with one UL
low located over The Great Lakes and the other located near Utah. A
weak frontal boundary will be positioned just offshore of our coast
as well. Small and embedded shortwaves will push through this zonal
flow which will be just enough upper-level support to invigorate
showers and isolated thunderstorms on Thursday around the frontal
boundary. Forecast soundings show significant dry air aloft during
this time frame, so convection should be relatively shallow.

By Friday, the upper-level trough over Utah will begin to push
southeast. Leeside cyclogenesis will help strengthen a surface low
and its associated cold front as this front approaches SE Texas.
Moistening mid-levels from WAA and Gulf moisture will help saturate
forecast soundings and increase PWATs to around 1.9" across our
region. This combined with some instability and a frontal lifting
mechanism will increase our chances for showers and thunderstorms on
Friday. This front is expected to stall near the coast again with
the GFS showing it stalling offshore and the ECMWF showing it
stalling in our southern CWA. Therefore, rain chances Friday and
onwards depends on where this front stalls. However, in the wake of
Friday`s front, NE flow resumes along with CAA and slightly cooler
and drier conditions. This intruding dry air will help limit the
coverage of these showers as well.

From Friday night onwards, surface winds will remain N-NE and skies
will be partly cloudy. Daytime highs will struggle to reach the 70s
this weekend. Partly cloudy skies will slightly enhance radiational
cooling, so overnight lows this weekend will struggle to reach 50
north of I-10 whereas areas south will hover in the low 50s. As a
high pressure builds in further south on Monday and washes out most
rain chances, winds become light and variable, slowing down that CAA
and allowing temps to climb back up to the mid-70s on Tuesday.  KBL



A couple of issues will affect mariners tonight. The first, is
dense sea fog affecting the southern Gulf waters adjacent to
Matagorda Bay. Visibility at platforms over the Gulf have wavered
between 1/4 and 1/2 NM. Will extend the Marine Dense Fog Advisory
for the 0-20 NM waters from Freeport to Port O Conner through 06z.
It may need to be extended and expanded to include the bay. Over
the eastern Gulf waters, the pressure gradient is expected to
tighten significantly this evening as the gradient tightens in
response to a developing coastal trough and as the inflow into a
developing convective complex over NE TX increases. A SCEC has
been issued for the eastern waters for tonight. Winds will become
east on Wednesday as low pressure develops over South Texas. The
low will meander over South Texas and surface winds will be SE
ahead of the next cold front that will move into the coastal
waters on Friday night. A strong N-NE flow will develop Saturday
and Sunday and a SCA will likely be required over parts of the
coastal waters. 43


College Station (CLL)      82  67  77  58  71 /  40  60  50  50  30
Houston (IAH)              83  69  82  62  74 /  60  70  70  60  30
Galveston (GLS)            80  71  80  67  75 /  30  50  40  60  30


GM...Dense Fog Advisory until 7 PM CDT this evening for the following
     zones: Coastal waters from Freeport to Matagorda Ship
     Channel TX out 20 NM.



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