Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Brownsville Texas
1149 am CST Sat Dec 20 2014
Discussion...updated for latest aviation discussion below.
Aviation...latest observation shows low level clouds covering
south Texas region with northerly winds prevailing behind the
front that moved through the area yesterday. North wind will
continue but the main issue will be patchy fog and low ceilings.
Expect the ceilings to fluctuate between 700 to 1000 feet with
drizzle through the day. Ceilings improve for a short period of
time by the evening but conditions deteriorate into tonight as
moisture surges northward increasing light rain and drizzle
potential through the morning. Ceilings return to IFR overnight
and begin to improve to MVFR by middle day Sunday.
Previous discussion... /issued 922 am CST Sat Dec 20 2014/
Discussion...marine conditions continue to improve with north
winds gradually decreasing and seas lowering over the Lower
Texas Gulf waters. Therefore...allowed for the Small Craft Advisory for the Gulf
waters to expired.
Previous discussion... /issued 621 am CST Sat Dec 20 2014/
Discussion...updated for latest aviation and marine discussions
Aviation...a mix of low ceilings this morning...from IFR near
the coast to MVFR at mfe. A strong low level inversion is in place
with a relatively saturated layer up to six or seven kft above the
inversion. Overcast skies and moderate decreasing to light north winds
will continue today...though ceilings may slowly improve by this
afternoon. A middle level trough will approach from the west...keeping
southwest winds in place aloft tonight and Sunday while maintaining
a lid on the saturated layer. Meanwhile...aviation conditions may
deteriorate Sunday with some coastal troughing or weak convergence
just offshore. The NAM is more aggressive with low ceilings for Sunday
than the GFS.
Marine...expired the nearshore Small Craft Advisory and
continued the offshore advisory until 9 am. Conditions will
slowly improve as high pressure settles over the area.
Previous discussion... /issued 348 am CST Sat Dec 20 2014/
Short term /today through Sunday/...a more neutral middle level flow
will sit atop high pressure and cooler air filtering southward over
the County Warning Area today. The result will be cloudy skies and slightly cooler
than normal high temperatures ranging from about 60 to 65 across the area.
Light north to northeast winds will prevail.
Tonight...a middle level trough will develop and amplify over new mx...
West Texas and north central Mexico today...resulting in a more
southwesterly upper flow over the County Warning Area tonight. That will bring a
layer of middle level moisture in at around 7 kft...with a warming
bulge just above that. Light north to northeast surface winds will
prevail under cloudy skies...with overnight low temperatures from
around 50 to 55...just a bit above normal. A coastal trough will
develop due to the stronger northeast winds offshore interacting
with lighter winds over land...and rain chances over the Gulf waters
will increase. The GFS is keeping rain chances limited...but the
more aggressive NAM is suggesting a chance of light rain right along
the coast Sat night. Patchy fog will also be in the mix late
Saturday night...extending into early Sunday.
Sunday...while pressures fall over the High Plains...high pressure
will retreat from south Texas...but enough of a presence will remain
on Sunday to continue a light north to northeast wind. Rain chances
along the coastal trough will be greatest during the morning hours
of Sunday...but will definitely begin to fade by afternoon as winds
start to veer with the shifting synoptic pattern. Skies will still
be cloudy to mostly cloudy...with high temperatures a little warmer
than Saturday...but still in the middle 60s. Though a weak middle level
trough will remain over north central Mexico...the effects will be
benign...with dry middle level air moving in on a westerly flow aloft.
Clouds will thin over the Upper Valley on Sunday.
Long term /Sunday night through Saturday/...
Sunday night into Monday an upper trough axis will still be draped
over central and southern Texas but the best upper divergence will
be to the northeast. The broadly diffluent southwest flow at
250/500mb will promote some residual coastal troughing however and
kept low end probability of precipitation over the immediate coast and Gulf areas through
daybreak Monday. Drier air in the 850mb layer and above should help
promote breaks in the cloud cover over land through the day but
clouds may persist over the water until a more persistent southerly
wind develops in the afternoon. Mild temperatures are forecast with
highs in the middle 70s.
The main weather story through the upcoming week will likely be the
passage of a strong cold front during the day Tuesday. GFS/European model (ecmwf) and
ensemble members are in pretty good agreement on timing and strength
of the front as well as the overall synoptic picture. A relatively
broad but large and slow moving trough is sharpened up by an
advancing Pacific northwest jet maximum Tuesday morning. The added
momentum also sends the trough into motion and the result is a
cyclone centered over the Great Lakes region which is accompanied by
a deep and fast moving front...with very strong 850/700mb support.
Strong middle level convergence behind the front also adds further
momentum to the system as surface high pressure forms over the
plains. The source airmass region for this front looks to be the
front ranges of Colorado and eastern New Mexico so a cooldown...but
not a plummet to near freezing temperatures...is forecast.
The primary impact of this frontal passage will be wind. The current
forecast calls for wind gusts approaching 35 to 40 miles per hour during the
day Tuesday over land with gusts over water well above gale force.
GFS/dgex cross sections show 45 to 48 knots winds at 925/850mb over 25
to 30 knots surface winds. The lack of cold advection with the
relatively warm source airmass region may prevent all of that
gustiness from reaching the waters surface...but a closer flirtation
with storm force gusts than is normally seen along the Lower Texas
coast cant be ruled out. The pressure gradients are quite
impressive. Would not be surprised to see Wind Advisory conditions
over land either...especially near the coast. Precipitation/cloud
cover will likely be limited by the very sharp and fast moving
frontal slope with drying all the way up to 500mb moving through
very quickly Post-frontal. Some showers right along the boundary
will of course be possible however.
It appears the area will remain breezy to windy through the
overnight and into early Wednesday morning. North winds continue
through the day Wednesday...albeit backing down from tuesdays levels
with highs in the middle 60s.
Modest ridging reestablishes over the Gulf of Mexico on Christmas
day with winds shifting to the south amid festive high temperatures
in the middle 70s. Upper ridging and relatively dry air aloft should
keep rain chances at near zero. South breezes keep up through Friday
before another front...this one looking a little weaker...pushes
through Friday night into Saturday. This front does look a little
more shallow though...with a more favorable coastal troughing setup
so kept a longer period of low grade shower chances along the
coast...and can see where those might need to be raised as the week
today through Sunday...winds and seas are diminishing as high
pressure settles over south Texas and the northwest Gulf of Mexico.
Will be able to drop the Small Craft Advisory within the next 12
hours for the Gulf waters. Seas will slowly lower to around three
feet by Sunday. Northeast winds will continue across the marine
areas...becoming light to moderate on Sunday. The development of a
coastal trough will result in a chance of light rain on Sunday.
Sunday night through Wednesday...
favorable conditions are forecast Sunday night into Monday with
light east winds building out of the south through the day Monday
amid low seas. Conditions will remain relatively favorable through
early Tuesday morning. A strong cold front is expected to arrive
Tuesday producing a prolonged period of very strong winds and very
rough seas. Frequent gale force gusts appear likely during this time
period and at least Small Craft Advisory winds and seas appears
likely through Wednesday evening. Seas will likely peak in the 10 to
12 foot range Tuesday night with higher values possible.
This product is also available on the web at: