Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Fort Worth Texas
547 PM CST Wednesday Nov 25 2015
cloud cover will be on the increase as strong southerly flow
continues to stream Gulf moisture into the region ahead of the
potent storm system expected later this week. Current VFR ceilings
will drop to IFR near sunrise Thursday morning across all taf
sites. South-southeasterly winds will remain breezy overnight around
13 kts and increasing to 15 kts with higher gusts during the day
Thursday. Patchy drizzle will be around Thursday morning as well
but expect intensity and coverage of rain to increase by early
Thursday afternoon and remain in the forecast beyond the current
taf forecast period.
Previous discussion... /issued 342 PM CST Wednesday Nov 25 2015/
Watches... Flash Flood Watch for much of North Texas late
Thursday night into early Sunday morning.
Total rainfall... widespread 4 to 7 inches of rain with heaviest
north of I-20. 1 to 3 inches of rain across the southeast counties
outside of the watch.
Potential for winter weather... none at this time but
temperatures near or just above freezing across northwest counties
Saturday and Sunday mornings. No winter weather travel impacts
expected in north/central Texas through Sunday.
Afternoon water vapor imagery shows a large upper level low
pressure system over California and Nevada this afternoon. This
system is in the process of cutting off over the western U.S. And
will be responsible for several rounds of moderate to heavy
rainfall through the weekend and a strong cold front on Friday.
For the remainder of today and tonight...warm southerly flow will
continue to transport moisture northward as a Lee side surface
cyclone persists across southeast Colorado. Farther north...cold
Canadian air is spilling southward through the High Plains. Skies
across north and central Texas should remain mostly cloudy through
the overnight hours with only a few spotty showers developing in
the strengthening warm advection regime.
Thanksgiving day...a northern stream shortwave will dive southeast
out of Canada and give a southward push to the Canadian cold
front while the main upper low remains well to the west. This
favors continued strong southerly flow across North Texas but also
should allow the colder air to accelerate down the Front Range of
The Rockies into western Oklahoma and the Texas Panhandle by
midday. Increasing large scale forcing from the upper low to the
west and strengthening upper jet diffluence across the Southern
Plains will help support widespread showers and a few
thunderstorms along and ahead of the southward surging cold front.
Across North Texas...mainly warm advection showers are expected on
and off through the day Thursday...although an isolated storm is
not out of the question. Model guidance indicates about 200-500
j/kg of instability to work with. While locally heavy rain will be
possible during the day Thursday...better rain chances come later
Thursday night into Friday.
Late Thursday night as the front gets closer...isentropic ascent
will strengthen as warm moist air is forced up over the relatively
steep frontal slope. While the actual cold air is fairly
shallow...there will be an area of strong forcing right along the
front which should result in a line of heavy rainfall as the front
moves south. This should occur along the Red River and generally
be located north of I-20 through early Friday morning. As the
front continues south...considerable moisture will continue to
stream north atop the front resulting in continued rain through
the day across much of north and central Texas. Friday will be a
cold day with northerly winds behind the front around 20 miles per hour and
temperatures falling 20 to 30 degrees in a short amount of time.
Highs on Friday are likely to be in the morning with temperatures falling
into the 30s by afternoon.
There may be a brief break in the rain activity late in the day
Friday as the front continues southward but the main upper low
will still be off to the west. On Saturday...Hurricane Sandra is
expected to make landfall in central Mexico. While the hurricane
itself will be of little direct impact to North Texas...its upper
level wind fields will enhance an already strong jet stream across
the region. This should result in another uptick in the rainfall
activity across the region. Forecast soundings during this time
show precipitable water values around 1.6 inches which is still quite high for
this time of year. Deep warm advection continues above the colder
air and the 850-700mb frontal boundary is located right across
North Texas. All of this points to continued moderate to
occasionally heavy rainfall through Saturday.
Things should finally begin to taper off on Sunday as the main
upper low begins to pull off to the northeast and a fast moving
shortwave swings through the Southern Plains. This will usher in
some drier low and middle level air and should push the bulk of rain
off to the east.
Concerning temperatures and potential for any freezing rain...
The airmass is cold but not exceptionally cold and temperatures
will fall to near freezing both Saturday and Sunday mornings. Our
overall concern for freezing precipitation is low at this time
given the exceptionally deep warm layer of air above the cold
front. With precipitation rates expected to be moderate to heavy
some of this warmer air will get pulled down. Also...there will be
a lack of significant cold advection during this time. So while
temperatures may quickly fall to 33-35 degrees...they will
struggle to fall any lower. In addition...the process of actually
freezing water releases a significant amount of heat. In the
absence of any strong persistent cold advection...temperatures
will remain just above freezing.
Beyond Sunday...the forecast will remain dry.
Preliminary point temps/pops...
Dallas-ft. Worth, Texas 63 71 51 51 37 / 10 50 90 100 90
Waco, Texas 63 72 64 67 40 / 10 60 60 90 90
Paris, Texas 60 69 59 62 41 / 10 40 80 100 90
Denton, Texas 63 70 41 41 36 / 10 50 100 100 90
McKinney, Texas 62 70 49 49 37 / 10 50 90 100 90
Dallas, Texas 63 70 59 59 38 / 10 50 90 100 90
Terrell, Texas 63 71 64 65 40 / 10 40 70 100 90
Corsicana, Texas 63 73 64 68 42 / 10 40 60 90 90
Temple, Texas 63 72 64 68 40 / 10 60 60 90 90
Mineral Wells, Texas 63 70 41 41 34 / 10 60 100 100 90
Flash Flood Watch from late Thursday night through late Saturday
night for txz091>095-100>107-115>123-129>135-141>146.