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Area forecast discussion...updated 
National Weather Service Brownsville Texas
541 PM CST Monday Mar 2 2015

Discussion...surface observations and in-situ webcams suggest
that dense fog is moving farther inland this evening. Therefore
the dense fog advisory is now also in effect for inland Cameron
..inland Willacy...And Hidalgo County until 10 am CST Tuesday
morning. No other forecast adjustments made.
&&

Aviation...LIFR conditions are expected through the overnight
hours due to dense fog and low ceilings. The most uncertain aspect
of the current taf package will be how often visibilities and
ceilings change due to the fog and low clouds. Tomorrow...surface
winds increasing from the southeast will scour the fog away...
with a return to VFR conditions.
&&

Previous discussion... /issued 259 PM CST Monday Mar 2 2015/

Short term.../now through Tuesday night/...stationary boundary
continues to be draped to our south with light northerly surface/near
surface flow underneath southerly flow which continues to lead to
overcast skies today. Clouds have not budged today and in fact drape
most of the state of Texas currently. With no insolation reaching
the surface and virtually no mixing...visibilities continue to be
restricted as well with patchy to areas of fog. Temperatures
continue to underachieve...especially in the ranchlands where lower
50s reside...mid/upper 50s in the valley.

Areas to widespread fog can be expected across all of deep south
Texas tonight. Dense fog may reside to the immediate coast and
coastal sections with a light east flow there. Over land...a light
north to nortwest surface wind will prevail which should keep the dense
fog at the coast. With no radiational fog due to cloud
cover...widespread 1/2 to 2 miles should be common. Dense fog
advisory currently at the coast and coastal waters will be
extended through the night as conditions do not change through
Tuesday morning. With low clouds in place expect light drizzle and
light rain especially overnight.

Lee troughing across the Sierra madres will strengthen Tuesday which
will replace ridging nosing into the area and help lift the
lingering coastal troughing out of the area. Surface winds become
southeasterly and gusty...especially at the coast. This should help
mix some of the clouds out with peaks of the sun by early afternoon.
Southwesterly middle level flow will also increase which should help
mix down drier air and warm temperatures into the low 80s out west
and upper 70s along the coast.

Tuesday night will be warmer with increased temperature and moisture
advection and higher dewpoints. Cloudy skies return early but with
stronger low level winds believe fog will not be an issue. Winds
will remain southeasterly with lows in the 60s.

Long term.../Wednesday through Monday/...highly advertised major cold
front still on tap for Wednesday night into Thursday. Sharp
positively tilted trough over the western half the U.S with a highly
amplified ridge off the West Coast to surge Arctic air through
the plains and into Texas. Deep south Texas to see the front
shortly before or after midnight Wednesday with the front
clearing the Lower Valley before sunrise Thursday.

Models remain in good agreement with the front timing and strength
with cold air becoming entrenched over the region thusday and
Friday with little relief expected until next Sunday. The
northern and southern branch of the jet stream initially phase
together Wednesday allowing for the Arctic air to surge south. The
northern branch then lifts out NE while energy remains across the
Desert Southwest and off Baja California California with the southern stream. Its
this southern stream energy take will determine our rain chances
in wake of the front. A lot of uncertainty in the probability of precipitation with
guidance holding onto good to likely chances but very low quantitative precipitation forecast. A
blend of the 12z model package and the inherited forecast keep the
best chances in the middle and Lower Valley through much of the
period.

As for temperatures...the big plunge/fall of 30-45 degrees takes
place all within a 9 to 18 hour period Thursday morning. Wind
chills will be a factor dropping between 25 and 35 degrees by
Thursday sunrise...sustained winds of 15 to 30 miles per hour...and not
recovering until later Friday. Models are doing their darnest
keeping temperatures rather low Friday and Saturday and even
Sunday with no real southerly return flow expected. Future
forecast may have to lower temperatures some more if the cold air
does not modify...very similar to what took place this past weekend.

Too early and highly uncertain if any freezing precipiation develops
over the northern ranchlands late Thursday night and Friday morning.
Wet bulb zero temperatures approaching freezing on forecast
soundings and atmosphere indicates an 8000 foot deep saturated layer.
The low quantitative precipitation forecast signal would suggest freezing drizzle at best but at
this time will keep liquid until we get closer to the appointed
time.

Marine...now through Tuesday night... dense fog advisory with
visibilities at a quarter mile or less and rapidly changing will
remain in effect through the night. Easterly winds tonight will give
way to southeasterly winds and gusts to 20 knots by middle morning.
This should mix out any fog and low clouds by middle morning. Small
craft may need to exercise caution beginning tomorrow with the
increase in southerly winds.

Wednesday through Saturday/...moderate southerly flow persist
through Wednesday evening then a major cold front surges into the
coastal waters by midnight Wednesday. Marine conditions deteriorate
rapidly Wednesday night and remains adverse Thursday and probably
through Friday. Gale conditions from Wednesday night through
Thursday morning are becoming more likely as models are now
indicating sustained winds approaching gale force. In any
case...gale force gusts will likely be obtained with seas rapidly
exceeding 10 feet by sunrise Thursday. Coastal troughing sets up
later Thursday and persist into early Saturday keeping the Gulf and
nearby Laguna Madre under a northerly flow at moderate to strong
levels with periodic Small Craft Advisory conditions warranted.
&&

Bro watches/warnings/advisories...
Texas...dense fog advisory until 10 am CST Tuesday for txz251-253>257.

GM...dense fog advisory until 10 am CST Tuesday for gmz130-132-135-
150-155-170-175.
&&

$$

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