Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Fort Worth Texas
1243 PM CDT Monday Sep 22 2014
main concerns for the 18z taf cycle will be wind speed/direction for
the metroplex tafs and ceilings across Waco taf site.
For the metroplex tafs...persistent east northeasterly winds
continue this afternoon in the wake of a weak frontal boundary
that moved through the metroplex early this morning. Latest hrrr
model guidance is handling near term very well...but still
probably turns winds too quickly to the NE later this afternoon. As a
result...have carried east-northeast winds through this evening. 10 to 15
knot winds should eventually decrease and will become more east
and southeast in response to the Lee trough across Colorado. VFR
ceilings and visby should prevail throughout the entire taf cycle with
just some high level cirrus overspreading the region.
For the Waco taf...the weak cold front continues to slide to the
south. A few isolated showers cannot be ruled out...but overall
confidence remains low and does not warrant inclusion into the taf
at this time. Relatively drier air should move into central Texas
later this afternoon and will result in decreasing rain chances
and improving ceilings. Some high based cumulus will still linger through
late afternoon into the evening with some high level cirrus moving
main change to the forecast this morning was due to slightly
varying wind direction...sky coverage...temperature and dewpoint
from the previous package.
Most coarse and even hi-resolution model guidance has winds a tad
bit more backed /more northeasterly/ than actual observations
show...and have adjusted wind speeds/directions to reflect more of an
easterly direction through the middle afternoon. 12z forward radiosonde observation
revealed that the depth of the easterly winds extended up to
around 925 mb...likely demarcating the top of the mixed layer.
With about 20-25 knots aloft...have increased wind speeds at the
surface to account for some momentum Transfer. Also...with the
more easterly winds...we have slowed the progression of the
magnitude of the dry air advection across the southern zones. This
should help to curb the diurnal range of temperatures across this region
and as a result have nudged maximum temperatures down a degree or two as well.
Despite the relatively more moist conditions across the southern
zones...have removed mention of thunder due to poor lapse rates
The rest of the package appeared in fine shape and no other
changes were necessary.
Previous discussion... /issued 400 am CDT Monday Sep 22 2014/
a cold front has pushed south of the I-20 corridor and will
continue moving southwestward across north and central Texas
today. Showers developed during the predawn hours in the vicinity
of the lagging 850mb front...along which a moisture discontinuity
will intensify today. Despite meager lapse rates above 850mb...the
steepness of the frontal slope 5-10kft above ground level is enhancing the
mechanical forcing to the extent that updrafts have been able to
produce a few cloud-to-ground lightning strikes. The primary
convective Mode today will be showers...albeit isolated...but a
few thunderstorms will be possible along the advancing elevated
front into the afternoon hours. As such...the arrival of drier air
at the surface will not mean an end to rain chances.
Sunshine will offset weak cold advection in the low-levels. Though
several degrees cooler than Sunday afternoon...high temperatures
today will still be near normal. Pleasant Post-frontal dew points
may dip below 50 degrees this afternoon. Lee troughing at the
surface will gradually develop through midweek...but a middle-level
ridge building into the Ohio Valley will keep the autumn-like
surface high in place across the eastern states. As a result...
easterly surface flow will persist across north and central
Texas...recycling mild and dry air throughout the week. This will
keep temperatures near normal and prevent Gulf moisture from
The upper low...now swinging through the intermountain west...will
separate from the polar flow as it moves into the northern plains.
The unseasonably strong ridging from the prairie provinces into
the Canadian Arctic will race eastward...leaving behind the trough
south of the 49th parallel. Although ridging aloft will dominate
Texas early in the week...guidance is in fairly good agreement
that this feature in the plains will effectively split the upper
ridge. Troughiness over Texas late in the week is prognosticated to
intensify into the upcoming weekend...but any forcing associated
with this is unlikely to result in precipitation. With a dry
boundary layer and even drier mid-levels...precipitable water values will remain
unseasonably low across north and central Texas.
our equinox cold front is nothing compared to the Arctic air that
invaded the region in September 1983...resulting in a remarkably
early first frost. On the morning of September 22...temperatures
plunged into the 30s throughout our northern and western zones.
The chilliest spots were Bridgeport and Lampasas...both of which
dipped to 35 degrees.
The autumnal equinox is at 929 PM CDT this evening.
Preliminary point temps/pops...
Dallas-ft. Worth, Texas 87 63 85 62 87 / 10 0 0 0 0
Waco, Texas 88 61 86 60 87 / 20 5 0 0 0
Paris, Texas 82 58 82 56 83 / 0 0 0 0 0
Denton, Texas 86 59 84 58 86 / 10 0 0 0 0
McKinney, Texas 85 56 84 56 85 / 10 0 0 0 0
Dallas, Texas 87 63 85 62 87 / 10 0 0 0 0
Terrell, Texas 85 59 84 58 85 / 10 0 0 0 0
Corsicana, Texas 88 61 85 59 86 / 10 0 0 0 0
Temple, Texas 89 61 86 61 88 / 20 5 5 0 0
Mineral Wells, Texas 86 59 85 58 87 / 10 5 0 5 0