Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Brownsville Texas
239 PM CST Sat Dec 27 2014

Short term /now through Sunday night/...combination of factors
expected to lead to a good drenching rainfall for the valley
now into late Sunday. Cold front currently is on a lrd/vct
alignment...and is progressing steadily southward. It is beginning
to bottle up the surface moisture across deep south Texas...with dew point
values ranging from 55 at apy to 70 across Cameron County.
Aloft...southwest flow is bringing elevated moisture into the
region...with some light rain activity being sparked. Rainfall
activity along the cold front will likely become more widespread
when the front can tap more of these moisture pools. The front
should arrive at bks and hbv about 6pm...and should clear the
valley by 9. Midlevel shortwave still hanging back a
lifting energy will not be enough to spark thunderstorms along the
front. Once the front is through...brisk north winds will begin to
undercut southwesterly flow aloft...with good overrunning setting up
areawide. Expect most of the area to see rainfall tonight into
tomorrow...with accumulations ranging from 1/2 to 1 inch. Cold air advection will
bring the cold pool into the region overnight...with temperatures falling
into the 40s by sunrise. With dense cloud cover and rainfall
continuing tomorrow...temperatures will have trouble rising into
the 50s. The rainfall and cloud cover will continue until the
large scale 500 mb trough sweeps through Texas tomorrow. Once the axis
passes...upper winds shift more to the west and northwest...bringing
drier air aloft and ending the overrunning pattern. There may be
just enough thinning to get temperatures in the far western valley
into the upper 50s tomorrow briefly. Tomorrow night...the core of
the surface high will be along the Texas coast. Winds will be
decreasing to near calm...and skies will be mostly clear. These
factors will help temperatures fall into the upper 30s and lower
40s. Temperatures may fall even further is skies clear earlier than
forecast...which will need to be watched closely tomorrow.

Long term /Monday through Friday/...winds will veer to east
Sunday night into Monday as surface high pressure shifts
east...bringing some Gulf moisture and increased cloudiness back
into the area from east to west later Monday...but no active
weather. A zonal middle level pattern will be in effect. High temperatures
Monday will rebound into the 60s and thus fairly close to
normal...with low temperatures Monday night recovering into the upper 40s
north...and middle to upper 50s around the Lower Valley. The latest
guidance hints at somewhat lower temperatures Monday night.

The next front will push south Tuesday...powered by 1050 mb or more
high pressure spilling out of the Canadian rockies into the northern
and then central and southern High Plains. East northeast winds will
arrive in deep south Texas and the rgv Tuesday...keeping high temperatures
near normal for the day around the Lower Valley...but perhaps a bit
below normal across the ranchlands. A very positive tilt middle level
trough will pinch into the base of the wnoam ridge over central
California Tuesday...while The Rockies split the cold air moving
south...diverting some south toward Texas and another portion west
of The Rockies into the Great Basin. Low temperatures will trend
down into the 40s and 50s Tuesday night under mostly cloudy skies
and with an increasing threat of overrunning light rain. Moderate to
breezy north winds may produce some upper 30s feels like temperatures
across the ranchlands.

By Wednesday strong high pressure will be situated over North Texas
with moderate north winds filtering into deep south Texas and the
rgv...with cloudy skies and high temperatures ranging from the 40s
over the northern ranch lands and brush country to the 50s across
the Lower Valley. Temperatures Wednesday will not increase much from Tuesday
night. Overrunning with light precipitation accumulation will continue
Wednesday night under mostly cloudy to cloudy skies and light winds
as high pressure settles over the area. Low temperatures Wednesday
night will be the coldest of this episode...and will be mainly in
the 40s with some upper 30s possible across the northern tier. Feels
like temperatures will be mostly in the 30s with light north winds.
A coastal trough or weak surface low may set up at this time which
would help maintain the cloudy...colder...drizzly weather Wednesday
night into Thursday. Thursday high temperatures inched up a few degrees
from the previous forecast due to the influence of the coastal
weakness...which will wrap around warmer Gulf air while maintaining
the light precipitation.

The West Coast middle level feature will kick out on Thursday and move
over the southwest United States...while the flow downstream over
deep south Texas turns more southwest...or favorable for over running
and capping. The low will lift north and east over North Texas on
Friday...bringing drier air to much of Texas...though deep south
Texas and the rgv...or at least the Lower Valley...may remain
stubbornly under mostly cloudy skies. Either way...the return of
south winds Thursday night into Friday will support warmer temperatures...
with peeks at the sun for the Upper Valley.

&& through Sunday abrupt chance is
approaching as the front reaches the northwest Gulf this evening. Winds
will shift to the northwest this evening...with winds increasing to 20 to
25 knots. Seas will Jump Up to 6 to 8 feet...being inhibited from
further rises by the due offshore direction of the winds. Small
craft advisories have already been hoisted for all marine zones
starting at 6pm and run through the day tomorrow. Once the front
arrives...expect light rain and shower to continue through the
night and most of the day tomorrow before the surface high pressure
arrives late. Winds will then quickly go nearly calm with seas
subsiding to around 2 feet.

Monday through Wednesday...winds will remain light to moderate
from the northeast and then east Monday...but will shift to east-northeast
again and begin to increase Monday night into Tuesday as colder
air pushes south and out into the northwest Gulf. MDT to breezy
east northeast winds will develop Tuesday in the wake of a high
pressure air mass moving out over the Gulf. Middle day Tuesday is a
reasonable time to delineate a frontal passage as winds
increase...with lowering cloud decks and increasing chances for
light rain. Small Craft Advisory conditions appear very likely
late Tuesday through Wednesday as the gradient remains tight and a
weak coastal trough develops. Wave heights will respond to the
persistent and favorable fetch by increasing to between 8 and 10
feet on Wednesday as high pressure continues to move into the area.

Preliminary point temps/pops...
Bayview/Port Isabel 43 52 45 62 / 90 70 10 10
Brownsville 45 54 43 65 / 90 70 10 10
Harlingen 44 53 43 64 / 90 60 10 10
McAllen 47 57 43 65 / 100 40 0 10
Rio Grande City 46 58 42 65 / 80 20 0 10
South Padre Island 49 54 50 62 / 90 70 10 10


Bro watches/warnings/advisories...
GM...Small Craft Advisory from 6 PM this evening to 6 PM CST Sunday
for gmz130-132-135-150-155-170-175.



This product is also available on the web at:


National Weather Service Glossary of Abbreviations