Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Houston/Galveston Texas
338 am CST Wed Dec 19 2018
some pockets of dense fog have developed out over The Hill Country
where skies have cleared, west of the trough axis this morning.
Patchy fog can be seen in the observations across southeast TX, mostly
occuring west of I-45 and north of I-10. As of 315 am, radar
imagery showed showers and isolated thunderstorms continuing to
develop mainly north of I-10. The trough axis is moving to the
east at a decent speed, faster than what some of the short term
guidance has indicated in the most recent runs. As a result, it
looks like our best chance for showers and isolated thunder today
will be mainly before noon, as subsidence takes hold across southeast Texas
by this afternoon and the showers shift east of the region. Storm Prediction Center
also has the best chance for thunderstorms outlooked for 12-16z
today. Within this time frame, we should see our best moisture
with precipitable water values (pws) between 1.5-1.25 inches, but
not as much in the way of instability, with forecast soundings
only indicating the potential for elevated convection, if that.
With little in the way of cape in the low levels and lapse rates
fairly stable within the surface to 3 km layer, sticking with
isolated thunder for now. The GFS does bring the best vorticity
through the area this afternoon between 18-00z and low level lapse
rates and instability do become more favorable, but by then the
better moisture will be east of the region.
Cloud cover should hold tight through much of the day today, before
the clearing line moves across southeast Texas from west to east tomorrow
morning. As a result high temperatures today will rise into the
upper 50s in the northern zones to low 70s closer to the coast.
Winds will be out of the northwest behind the front between 5 to 10 kts
inland. Tomorrow, with mostly clear skies overhead, temperatures
will be slightly below seasonal normals in the mid 50s to 60s.
Winds pick up substantially by early tomorrow morning as the
pressure gradient quickly tightens behind the passage of today's
frontal boundary. Winds will be out of the NE between 18 to 25 kts
and gusty, and a Wind Advisory may be needed specifically along
Winds remain elevated Friday morning but start to weaken in speed
throughout the day as high pressure builds in across East Texas. With a
warm air advection pattern returning Saturday, moisture will be
on the rise and skies will transition from clear to partly cloudy.
Saturday will likely be our warmest day of the week, with high
temperatures in the mid 60s to low 70s.
Still plenty of variability amongst the global models in the
extended portion of the forecast. Remaining fairly consistent
with the previous forecast package at this time, but did lean
closer to the European model (ecmwf) and Canadian solutions as they have been a
bit more consistent with the timing of the front Sunday into
Monday. GFS is the fastest with this boundary, with the front
reaching the coast Sunday afternoon. On the other hand, the
Canadian looks to be about 12-18 hours behind the GFS, with the
front not reaching the coast until 06z Monday, and the European model (ecmwf)
almost looks to stall the front out just slightly inland, with
winds never turning out of the northwest at the coast. The models are in
agreement that this should be a fairly weak and dry frontal
passage, with strong capping at 850 mb. The upper-level forcing
is just not very supportive of a progressive front, with 500 mb
heights staying rather zonal and parallel to this feature. As a
result, high temperatures behind this boundary at this time only
look to lower by about five degrees Sunday and Monday.
lack of observations off Matagorda Bay make it a challenge to
resolve where any type of coastal low or trough has developed.
Based on the obs we do have it looks like there is a weak area of
low pressure between Matagorda Bay and the 42019 buoy. This low
should track up the coast today as a result of an upper level
trough moving over the area. There should not be any hazardous
marine conditions but that will change with a frontal passage
tonight into Thursday.
A gale watch will be issued for the offshore waters of the Upper
Texas coast. It may be that the 20-60nm waters will be the areas
that see gale force winds, but still possible for the near shore
waters. Advisories will for sure be needed and likely a Gale
Warning for the offshore waters beginning Thursday afternoon through
A low water advisory will also be likely for the bays as the strong
northerly winds will drive tide levels to around 2 feet below MLLW
especially for the upper portions of each Bay. Low water advisory
may begin Thursday afternoon with low tides and may still be needed
through low tide on Friday afternoon. This could very well be a
prolonged low water event making navigation through the Houston Ship
Channel and Galveston Bay problematic.
Conditions should improve over the weekend with southerly winds
developing again with return flow Saturday and a weak front possible
Preliminary point temps/pops...
College Station (cll) 63 48 59 41 61 / 80 10 0 0 0
Houston (iah) 65 49 59 42 60 / 90 10 0 0 0
Galveston (gls) 67 53 60 47 59 / 80 10 0 0 0
GM...gale watch from Thursday afternoon through Thursday evening for
the following zones: coastal waters from Freeport to
Matagorda Ship Channel Texas out 20 nm...coastal waters from
High Island to Freeport Texas out 20 nm...waters from Freeport
to Matagorda Ship Channel Texas from 20 to 60 nm...waters from
High Island to Freeport Texas from 20 to 60 nm.