Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Houston/Galveston Texas
556 am CST Wednesday Nov 25 2015
12z taf discussion in aviation section.
ongoing moisture return will support overcast 6000ft ceilings this
morning. Will likely keep VFR ceilings through the afternoon. Ceilings
should begin to lower tonight into Thursday am as higher low level
moisture arrives over southeast Texas. Models also hinting at possible
shower activity off the Gulf so added vcsh for tafs except for
kcll/kuts/kcxo. Will need to monitor kgls for fog development
overnight. Again think models are too aggressive with IFR ceilings
overnight into Thursday morning.
Previous discussion... /issued 443 am CST Wednesday Nov 25 2015/
a weak warm frontal type boundary could be made out at 4 am over
the southwestern set of counties and into the Gulf. Temperatures
were in the upper 60s south of the boundary from gls to vct and in
the lower 60s to the north. The boundary also delineated dewpoints
in the middle 60s to the south from dewpoints in the 50s and lower
60s to the north. Isolated showers were along the boundary about
40 nm offshore of High Island. The nam12 moves the front northward
today with the best chances for isolated showers along the front.
However...am expecting isolated showers also over the coastal
areas due to strong warm air and moisture advection at least
through this morning.
The main item of concern for later this week and over the weekend
will be rain chances and amounts. A building ridge over the Gulf
and a deepening upper level trough over the northern plains and
central/southern rockies will bring a southwesterly flow aloft
across Texas by late today. A cold front will then approach the
forecast area late Friday into Saturday. The models were coming
into better agreement with a slower approach and passage of the
front. Moisture from Hurricane Sandra in the eastern Pacific is
forecast by the models to move over Mexico into Texas late this
week and over the weekend. This will help push precipitable water values to over
2 inches along and ahead of the front.
The limiting factor for rainfall over southeast Texas will be the
presence of the downstream upper level ridge over the Gulf and the
surface high pressure ridge extending into the area from the
eastern Seaboard. Because of this...the higher rainfall amounts
over the weekend are expected to be north and west of the forecast
area. Rain chances in the forecast reflect this with likely probability of precipitation
over the northwestern and northern set of counties starting Friday
and persisting into Sunday. Elsewhere the rainfall coverage will
depend upon the strength of the ridge. The upper level trough is
forecast by the models to stay over The Rockies and northern
plains...although there are differences between the GFS and European model (ecmwf)
after Sunday. A model consensus keeps chances for rain over the
area Monday and Tuesday as upper level shortwave troughs interact
with tropical moisture streaming overhead from the Pacific.
Rainfall totals vary widely by the model solution. However...liked
a combination of the GFS and European model (ecmwf) which kept the higher amounts
to the north and west. A model consensus is for rainfall amounts
through midnight Saturday night to range from 1 to 2 inches along
and north of a line from Edna to Navasota to Groveton. Amounts of
one half an inch or less are currently expected for this time
period along and south of a line from Cleveland to Houston to Bay
City. Needless to say...these expected amounts will likely change
as the model solutions converge over the next couple of days.
southeast winds have increased last night into this morning. Seas
have built up to 5-6ft across much of the Upper Texas coast. Small
craft exercise caution will continue through the morning. Winds are
expected to drop below 15 knots later this morning. This will allow
for seas to decrease slightly. Winds are expected to increase again
tonight with higher seas so caution flags may be needed again.
Long southeast fetch should support rough seas into Friday. Cold front
will push off the coast late Saturday with offshore winds
developing through Sunday with decreasing seas.
Sea fog has the potential to be an impact starting late this
afternoon through the end of the week for portions of the Upper Texas
coast and Galveston Bay. There is still low confidence in dense sea
fog developing but it remains possible. Shelf waters are still in
the low/middle 60s. Surface dewpoints are expected to reach upper 60s to
near 70 on Thursday. The differences between the shelf waters and
moisture may be enough for fog formation.
Tides...continue to exceed astronomical tide levels and are running
1 to 1.5 feet above normal due to east to southeast winds. As winds
veer to the southeast and increase the tide levels should stabilize. Total
water level around 3 feet may be possible at high tide times for
beach flood prone areas such as Bolivar Peninsula. Rip currents will
likely be elevated through Sunday.
Preliminary point temps/pops...
College Station (cll) 75 65 76 67 75 / 10 20 40 30 70
Houston (iah) 75 66 77 70 77 / 10 20 20 30 50
Galveston (gls) 74 68 75 69 75 / 10 20 20 20 30
GM...small craft should exercise caution until noon CST today for the
following zones: waters from Freeport to the Matagorda Ship
Channel 20 nm to 60 nm...waters from Freeport to the
Matagorda Ship Channel out 20 nm...waters from High Island
to Freeport 20 to 60 nm...waters from High Island to
Freeport out 20 nm.