Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Fort Worth Texas
1151 PM CDT Thursday Aug 28 2014
the primary aviation weather concern the first 6 hours of this
taf package will be the timing of convection and a temporary wind
shift associated with a thunderstorm outflow. A well defined
outflow boundary was along a line from Gainesville to Decatur to
Cisco at 1130 PM. This outflow will continue moving southeast at
25 miles per hour and should reach the metroplex taf sites between 06z and
07z. The passage of the outflow will temporarily turn the wind
from south/southeast to the northwest and increase speeds to
around 15 knots along with some higher gusts. Thunderstorms
forming just behind the outflow should weaken to light showers as
they move east into drier air.
The better storm chances for all taf sites will be Friday
afternoon when low level moisture increases and the atmosphere
destabilizes. Coverage of storms will be scattered since most of
the large scale forcing will be north/northeast of the region.
Therefore...we will carry thunderstorms in the vicinity between
22z and 03z at the metropolitan terminals. Thunderstorm chances will be
even less in Waco so we will not mention any storms for Friday
VFR conditions are expected through Friday evening with the exception
of some brief MVFR ceilings in Waco after sunrise Friday. Some
temporary visibility restrictions are also possible at any site
that experiences a thunderstorm.
the complex of showers and storms moving east from the Low Rolling
Plains continues to weaken as it encounters much drier air in
place across North Texas. This trend will likely continue
overnight until low level moisture can increase sufficiently. Kfws
VAD indicates that a weak low level jet is developing and this
should help with moisture advection. We will keep chance probability of precipitation in
the northwest overnight and only slight chance probability of precipitation elsewhere. The
better moisture and rain chances will not arrive unitl Friday/Friday
No major changes with the forecast package other than to lower the
evening probability of precipitation across the southeast zones.
Previous discussion... /issued 342 PM CDT Thursday Aug 28 2014/
a middle-latitude trough transiting the plains has effectively split
the upper ridge that has persisted the last several days...leaving
Texas in a col. Although the main action the next few days will
either be associated with the system to our north or with a
disturbance on the Texas coast...the weakness aloft will maintain
rain chances throughout north and central Texas into the upcoming
Weakening subsidence in the middle-levels has allowed showers and
storms to move farther inland today. The activity invading central
Texas is far from the coastal low and is largely diurnally driven.
As such...this precipitation should come to an end by nightfall...
making minimal additional progress. The approaching system to the
north might suggest a vigorous low level jet could develop tonight...but
nocturnal convection closer to the coast tonight will likely
disrupt this process. Even so...deep warm/moist advection may be
sufficient to allow the ongoing activity to our northwest to trace
across northern portions of the County Warning Area tonight into Friday morning...
primarily affecting areas north of the I-20 corridor.
This sequence of events will determine what transpires later
Friday. If the activity is widespread and persists much of the
morning...it may limit the extent of redevelopment in these areas
Friday afternoon. But in such a scenario...substantial outflow
boundaries could aid in the initiation of showers/storms farther
south. Even with more extensive cloud cover...surface heating will
be sufficient to push MLCAPE values above 2000j/kg. However...
increasingly moist adiabatic lapse rates aloft should limit the
intensity of updrafts...and weak middle-level flow will shorten the
lifespan of individual cells. The plains trough and its associated
shear/forcing will be far to the north...but adequate dcape will
allow for some gusty winds across north and central Texas Friday
As the middle-latitude low ejects into the Great Lakes Friday
night...the disturbance near the coast will get pulled
northeastward toward Louisiana. Its associated convection Friday
night into Saturday morning will again be upstream of central
Texas...limiting the extent of any warm advection activity in
North Texas. By Saturday afternoon...an extensive area of showers
and thunderstorms may be ongoing from southeast Texas into
Louisiana. Our eastern zones would on the western fringe of this.
By Sunday...this disturbance will have been absorbed into the middle-
latitude flow...but the weakness aloft will linger. With minimal
inhibition and rich Gulf moisture in place...one final afternoon
of convective activity may affect portions of East Texas.
Thereafter...the subtropical ridge should take hold. Above normal
temperatures will prevail next week...with uncomfortable humidity.
Preliminary point temps/pops...
Dallas-ft. Worth, Texas 77 94 76 93 77 / 20 40 40 30 10
Waco, Texas 75 94 74 93 76 / 20 40 30 30 10
Paris, Texas 73 91 72 90 72 / 20 40 40 30 10
Denton, Texas 76 94 75 94 75 / 30 40 40 30 10
McKinney, Texas 75 92 74 91 74 / 20 40 40 30 10
Dallas, Texas 78 93 77 92 77 / 20 40 40 30 10
Terrell, Texas 75 93 74 91 74 / 20 40 40 30 10
Corsicana, Texas 75 92 74 92 74 / 20 40 30 40 10
Temple, Texas 74 93 74 93 74 / 20 40 30 30 10
Mineral Wells, Texas 74 94 73 94 73 / 30 40 40 20 10