Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Fort Worth Texas
1214 am CST sun Nov 23 2014
primary concern is a potential for low ceilings/visibility through the early
morning hours and strong Crosswinds Sunday.
rain has ended and VFR conditions prevail over the region right
now. The low levels remain nearly saturated which raises concern
that fog or low clouds will redevelop during the next few hours as
drying occurs aloft and enhances radiational cooling above the
moist layer. Will bring MVFR ceilings/visibility in at 9z/3am with a tempo
for IFR ceilings. However with surface winds becoming light
southwest...it should prevent dense fog from forming. The shallow
moisture means that any clouds/fog should clear out quickly after
sunrise. VFR and generally clear skies will prevail thereafter.
Crosswinds Sunday afternoon and evening...
momentum Transfer of stronger winds aloft down to the surface
will be responsible for the high winds. Thus we will have to wait
for lapse rates to become steep enough for this Transfer to occur.
Model guidance is now in good agreement in showing the nearly dry
adiabatic lapse rates not occurring until late Sunday afternoon
when a shot of strong cold advection moves through with a cold
front. Thus the strong winds will likely not occur until after
22z/4pm and persist into the early evening hours when they should
gradually diminish after 2z/8pm. The wind direction should also be
from about 300 degrees when the strongest winds occur which should
allow full use of runways 31r/l and at least some use of the north-S
runways. The GFS continues to be the strongest with the winds and
lamp guidance is indicating sustained 32g41kt at 0z. Since all of
the other guidance is lower than this...have instead forecast
24g34kt...but this will continue to be monitored.
During the late morning through middle afternoon hours Sunday...have
lowered wind speeds from previous forecast to 17kt due to less
steep lapse rates and more limited mixing. Wind direction during
this time will be west/SW but speeds should be just low enough to
preclude a significant flow disruption during this time frame.
activity across North Texas continues to diminish in intensity and
areal coverage. The convection of greatest intensity will remain
south of the forecast area...though thunderstorms will still
impact portions of central and East Texas. Elsewhere...have reduced
probability of precipitation and changed thunder mention to isolated.
Previous discussion... /issued 320 PM CST Sat Nov 22 2014/
we continue monitoring a strong shortwave over northern Mexico and
the West Texas Big Bend country. A strong upper jet maximum over
100 kts remained upstream of the shortwave the first half of today
and slowed the system down. However...the upper jet maximum will
round the base of the system and speed it up toward the east-
northeast the remainder of the afternoon into tonight. The best
area of middle-upper level diffluence and more persistent convective
activity has been over central Texas and The Hill Country much of
the day but is expected to move over much of north and central
Texas through this evening. Surface- based instability has remained
virtually non- existent over the much of the County Warning Area due to the cool
and damp conditions that have persisted since daybreak...though
weak MUCAPE upwards to 500 j/kg did exist across the southwest
half of the County Warning Area.
The main threat from convective activity through this evening will
be additional localized rainfall amounts between 1 and 3 inches...
increasing cloud-to-ground lightning...gusty winds greater than 40
miles per hour and small hail with stronger thunderstorms. We cannot rule a
low end risk of marginal severe weather across our central Texas
counties where the stronger large scale ascent and strong westerly
bulk shear will move overhead by tonight. Southerly boundary layer
winds have exceeded 40+ kts at times and will eventually veer with
time with the approach of the strong shortwave. This may lend to
some partial mixing of stronger winds to the surface and possibly
a linear convective system by this evening from central into
southeast Texas. These areas are where low level dew points and
ambient surface temperatures are expected to be higher as well.
Otherwise...our highest concern will be localized flooding...mostly
low lying areas and smaller creeks that can rise quickly.
The shortwave will progressively move faster tonight as the
strongest upper jet winds upwards of 120 kts shift downstream and
move it along. We held on to previous forecast trends of highest
rain chances across the eastern half of the County Warning Area this evening with
a rapid west to east end to the convective chances overnight as
the shortwave disturbance dampens and lifts rapidly toward the
lower Mississippi Valley by sunrise Sunday with subsidence
arriving into north central Texas. The clearing skies and initial
light south-southwest winds overnight should allow for the
development of some patchy fog across mainly the northeast half of
the area. With westerly winds increasing after sunrise...we do not
expect any fog to persist into the later morning hours.
Plentiful sunshine is expected on Sunday with very gusty westerly
winds and warmer temperatures. The pressure gradient is expected to
be tight with good unidirectional momentum Transfer to help bring
stronger westerly flow down to the surface. We did raise wind
speeds on Sunday and it is possible that a Wind Advisory may need
to be issued in later forecasts. How warm highs rise on Sunday is
a challenge with the saturated soils across the area. The true
cold front arrives late in the day and definitely by Sunday night
with brisk and cooler conditions Monday. Winds settle down later
in the day Monday with continue dry and cool conditions persisting
into Tuesday as another strong shortwave deepens the upper trough
over the area. Moisture will be meager and we do not expect any
additional rain chances across the area.
The larger scale longwave trough moves east of the area Wednesday
into Thanksgiving day with highs moderating back into the 60s.
Another strong shortwave will move southeast over the plains and
drive another cold front into the area late Friday with cooler and
continued dry conditions returning for the remainder of the Holiday
Preliminary point temps/pops...
Dallas-ft. Worth, Texas 58 73 43 63 38 / 20 5 0 5 5
Waco, Texas 55 76 42 64 36 / 40 0 0 5 5
Paris, Texas 58 70 41 59 36 / 30 10 5 5 5
Denton, Texas 53 72 39 62 36 / 10 10 5 5 5
McKinney, Texas 58 71 39 62 36 / 20 10 5 5 5
Dallas, Texas 58 74 43 62 39 / 20 5 0 5 5
Terrell, Texas 58 73 41 62 37 / 30 10 0 5 5
Corsicana, Texas 57 75 42 64 37 / 40 5 0 5 5
Temple, Texas 55 77 42 64 37 / 50 0 0 5 5
Mineral Wells, Texas 51 72 36 62 35 / 10 5 0 5 5