Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

afdbro 

Area forecast discussion...updated
National Weather Service Brownsville Texas
1228 am CDT Friday Oct 31 2014

Discussion...updated for latest aviation discussion below.

&&

Aviation...light winds and mostly clear skies early will lead to
light ground fog and low cloud development toward dawn. Deep
moisture is limited...but some moisture is available near the
surface. The sounding exhibits no appreciable cap and is
conditionally unstable. Low clouds may act against thicker fog
development...however. Model guidance suggests MVFR conditions
from a ceiling/visibility combination through dawn...but more from
ceilings after dawn through early afternoon. Winds will shift to
northeast toward dawn as well...with the approach of a frontal
boundary now over central Texas. The front will wash out over the
County Warning Area this afternoon...but upper energy above the system could help
initiate a few showers. High pressure and drier air will overtake
the area by this evening...with a disappearance of clouds.

&&

Previous discussion... /issued 624 PM CDT Thursday Oct 30 2014/

Discussion...updated for latest aviation discussion below.

Aviation...VFR conditions will prevail through midnight before
MVFR conditions begin to develop as patchy fog develops across
the Rio Grande Valley with a weak front approaching the area.
Tempo groups were included indicating the best time for fog and
light rain/drizzle develops as the front moves through the area.
Expect a light northeast flow into Friday behind the front and
increase in winds no more than 15 knots by Friday afternoon.

Previous discussion... /issued 319 PM CDT Thursday Oct 30 2014/

Short term /tonight through Friday night/...500mb ridge across the
western United States and 500mb trough across the eastern United
States will bring surface high pressure over the northern plains
southward into the central and Southern Plains tonight into Friday.
This will allow a weak cold front to move through the Rio Grande
Valley Friday afternoon. Before the front arrives Friday...light winds
and relatively clear skies across the County Warning Area tonight will allow patchy
fog to develop. Low to middle level moisture will increase across the
area tonight into early Friday as the front approaches from the
north and isolated showers and thunderstorms are expected to develop
across portions of the County Warning Area Friday as the front moves into the area.
Drier and cooler air will filter into the Rio Grande Valley Friday
night as high pressure builds into the area in the wake of the
front.

Long term /Friday night through Thursday/...
Friday night into Saturday northeasterly flow shifts to more
easterly flow as surface ridging emerges over the northwestern Gulf
of Mexico. This movement is forced by sharp middle level ridging that
should aid in keeping the column dry. Slightly cooler and less humid
air will also be continuing to filter into the area through the day
as the aforementioned ridging shifts a cooler Continental airmass
poleward.

Sunday and Monday still look breezy to windy as strong ridging over
the southeast United States...and northeastern Gulf of Mexico
interact with Lee troughing over northern Mexico and the central
US...forced by a strengthening and broadening upper level jet
maximum ahead of ad digging southwestern US trough. Wind gusts of 30
to 35 miles per hour look like a pretty good bet both days. Low level
southeasterly winds will be advecting in moisture...which may help a
few coastal showers crop up...but 20 to 30 knots southwesterly 700 mb
flow will keep the chance for deeper showers and storms limited.

12z guidance suite shows better agreement on Tuesday-Thursday cold front
evolution. Although it is noted the 12z GFS ensemble appeared to
show a larger number of members going with a slower solution than it
had in previous runs. Forecast went with the operational GFS/European model (ecmwf)
consensus which provides strong southwesterly middle level winds on
Tuesday...which would continue to keep drying/capping in place
through the day. Overnight Tuesday night the broad jet maximum ahead
of the slowly moving trough catches what is currently dew point 21-east and
rapidly advects it northeastward. This results in an appreciable
increase in column moisture ahead of the trough. Went with the
operational GFS/European model (ecmwf) consensus for the forecast with a frontal
passage Wednesday morning. Rain chances increase close to and
immediately along/behind the front before cold advection and
negative vorticity advection cut off lift. Kept the probability of precipitation a little
below guidance consensus again mainly over timing concerns. May be
able to start ramping up probability of precipitation in the next cycle or two with the new
found guidance consensus. Marine impacts looking more likely as well
with strong northwest winds building in behind the front. Forecast
highs fall about 8 to 10 degrees from previous days maxes. /68-jgg/

Marine...
tonight through Friday night...seas were near 1 foot with
northeast winds near 4 knots at buoy020 early this afternoon.
Light east winds will prevail across the coastal waters tonight
before a weak cold front moves through the Lower Texas coast Friday
morning. Winds will shift to the northeast and increase Friday
afternoon as the pressure gradient increases in the wake of the
front. Small craft exercise caution conditions will prevail
offshore the Lower Texas coast Friday into Friday night as a result.

Friday night through Monday...
northeast winds shifting to more moderate east winds on Saturday
should produce relatively low seas and favorable marine conditions.
Stronger southeast winds increase to at least exercise caution
levels Sunday and Monday with advisory conditions possible. Seas
will be at least moderate and possibly locally rough.

&&

Bro watches/warnings/advisories...
Texas...none.
GM...none.
&&

$$

This product is also available on the web at:
http://weather.Gov/rgv

54/55

National Weather Service Glossary of Abbreviations