Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Brownsville Texas
239 PM CST Wednesday Nov 25 2015
Short term /now through Thursday night/...southwesterly middle level
flow will remain across the area through the short term courtesy of
high pressure across the western Gulf and a digging middle level trough
across the western Continental U.S.. this trough will support a deepening surface
low pressure system across the Central Plains and is backed by a
cold 1044mb Alberta high sliding across the northern Rocky Mountain
states. Persistent low level southerly to southeasterly flow will
continue underneath strong middle level capping inversion reinforced by
southwesterly drier flow from northern Mexico. Light rain and
showers continue to develop across northern Mexico and the western
Gulf of Mexico and slowly move inland and have raised precipitation
chances for the rest of the afternoon. High resolution short range
models depict the axis of higher moisture to shift inland this
afternoon towards the I 69c corridor so the McAllen to Falfurrias
corridor may experience a shower or two before ending around sunset.
Tonight appears to be dry once the afternoon showers end with a
temporary decrease in column moisture under cloudy skies. Streamer
showers will once again develop across the coastal waters late in
the night. Low temperatures will fall into the lower 70s.
Thanksgiving day will be warm with high temperatures some 8 to 14
degrees above normal. The cold front will kick out of the Central
Plains and begin moving south and eastward into the Southern Plains.
Southeast winds will once again be breezy with speeds of sustained
20 miles per hour with higher gusts. A slight chance for showers mainly along
and east of I 69c throughout the day where the best deep layer
moisture will reside and proximity to any streamer showers moving
onshore. The forecast does not mention showers west of this area as
there will be less deep layer moisture and stronger capping which
may curtail any precipitation through the day.
Thursday night should begin the influx of middle and high level
moisture from tropical cyclone Sandra but most of it will remain
west and north of the area. The capping inversion seems to weaken
based on area point soundings and precipitable waters surge to 2 inches by
daybreak Friday morning. However...other than closer to the coast
for streamer showers I do not see much forcing for showers. Given
the environment I will keep atleast slight chances area wide with
slight higer chances across the coastal counties. Low will once
again be in the lower 70s.
Concerning coastal flooding...persistent south to southeasterly
onshore flow will keep long period swells and higher wave heights
ongoing. Tide and water level data from Port Isabel show observed
levels roughly one foot above predicted which will place high tide
at 4 41 this afternoon around 2 feet above mean sea level. Tidal run
up to the dune line appears plausible at high tide and have
highlighted this in our coastal flood statement product.
Long term /Friday through Tuesday/...unsettled and warmer than
normal temperatures Friday and Saturday with coastal showers.
Middle level low over the Great Basin will move little...with upper
support staying north of the area while southwest flow aloft fails
to give an approaching cold front much extra push. GFS is stronger
and faster with the front...bringing it in Saturday night while the
European model (ecmwf) brings it through on Sunday during the day. Guidance numbers
for temperatures reflect the difference with the European model (ecmwf) not really
"catching up" until Sunday night/Monday morning....after which the
European model (ecmwf) maintains the colder air through the early part of the week. A
model blend will yield lower confidence to this forecast...but timing is
closer to the GFS. Sunday temperatures blend well with those to
the north...but can see a possible downward adjustment via later
shifts. Column moisture may approach two inches precipitable water Saturday but
shallow cold air will lift moist air slowly...and resulting lighter
stratiform rain should not produce excessive accumulation...the
five day total precipitation through Sunday night is forecast at around an
inch or less.
now through Thursday night...buoy 42020 reported southeast winds
of 21 knots gusting to 25 knots with wave heights of 7.2 feet at 1
PM CST. Winds continue to hover around 20 knots and wave heights
around7 feet and have extended the Small Craft Advisory till 4 PM.
Winds appear to slightly weaken later today but will need to be
watched for possible extension of Small Craft Advisory. Moderate to occasionally
storng southeast winds will continue through the short term period
as low pressure strnegthens across the Central Plains. Periods of
Small Craft Advisory appear likely through the next 36 hours.
Friday through Sunday...east swell will play a role through Sat...
keeping Gulf wave heights at low end Small Craft Advisory criteria
with a moderate southeast wind locally. Minor coastal flooding may
be an issue during this time as well. A cold front will move through
Saturday night...but north winds behind the front look like they
will be less than advisory strength...with conditions subsequently
improving slowly into the early part of next week.
Preliminary point temps/pops...
Bayview/Port Isabel 73 82 74 82 / 20 20 30 20
Brownsville 73 83 74 83 / 20 20 30 20
Harlingen 72 84 73 85 / 20 20 30 20
McAllen 72 85 74 85 / 20 10 20 20
Rio Grande City 72 84 73 86 / 10 10 20 20
South Padre Island 74 79 74 79 / 20 20 30 20
GM...Small Craft Advisory until 4 PM CST this afternoon for gmz150-
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