Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Fort Worth Texas
1133 am CST Sat Mar 8 2014
Concerns...strong...gusty northwest winds and MVFR conditions.
A cold front has just passed through kact with winds going northwesterly.
Northwest winds will be increasing across the metroplex taf sites
within the hour while kact may not fully increase until 20-21z.
Northerly winds of 10-15kt will prevail overnight and then around
10kt on Sunday.
Will be maintaining MVFR conditions /mostly for ceilings/ across all
taf sites this afternoon and overnight as moisture remains trapped
below the frontal inversion. Conditions will improve late Sunday
morning through early afternoon.
Radar and models indicate light rain and some drizzle will be
moving northwest across the metroplex sites through middle afternoon
and across kact later in the day. The rain should taper off across
the metroplex sites by this evening while a threat continues over
kact during the evening and overnight hours. Do not expect more than
several hundredths of an inch across the metroplex...but kact
might see one or two tenths. Visible and ceilings could fall a category
during any period of moderate precipitation. 75
Previous discussion... /issued 424 am CST Sat Mar 8 2014/
Early morning water vapor imagery shows a complex collection of
shortwave troughs located over/around the southern Continental U.S. Rockies.
09z surface observations showed a cold front racing south-
southeast across the southern High Plains and into the far western
portions of the County Warning Area. Winds 1-2 hours behind the front were
stronger than expected with observations around the Wichita Falls
area showing winds of 25 to 30 miles per hour gusting to 40 miles per hour at 09z. These
strong winds had been relatively short lived overnight...lasting
only 2 hours or so. However...these stronger than expected winds
are at least somewhat indicative of a stronger and faster moving
front than what had been forecast the past couple of days in model
guidance. Regional radars showed a band of rain showers extending
from Graham north-northeast towards Oklahoma City...more or less
located just behind the cold front. There were some isolated
lightning strikes observed across central and northern Oklahoma
this morning...but nothing closer to Texas at the time of this
Today and tonight...the speed of the front makes the high
temperature forecast difficult today. Wherever the front winds up
at 13z/7am...those locations will be observing their daytime high
temperature at that time as temperatures will fall behind the
front throughout the day today. Have this just west of the
metroplex at this time...meaning the metroplex may climb a few
degrees before the front arrives. Either way...highs in the middle
50s are likely...which is just a few degrees above 09z
temperatures for most locations in the dfw area. Temperatures are
expected to remain above freezing behind the front today...so no
wintry precipitation is expected behind the front across North Texas
at this time.
Taking a closer look at precipitation chances...forecast soundings
continue to indicate good low and upper level saturation with some
middle-level dry air holding in place as the front moves across North
Texas this morning. Lapse rates from the middle to upper troposphere
are expected to be moist adiabatic...meaning that there is a low
potential for free convection and lightning to be associated with
any rain shower activity today...so left thunder out of the
forecast. An isolated lightning strike or two would not be a big
surprise...but largely we should be thunderstorm free today.
Dynamic lift acting upon the middle-level dry air could steepen lapse
rates more than expected...however the bulk of large scale forcing
for ascent is expected to be north of the County Warning Area...at least for this
With most of the large scale forcing for ascent holding north of
the County Warning Area this morning...the likelihood of significant precipitation
occurring along the front is greatly reduced. That said...the
mesoscale forcing for ascent associated with the front should be
sufficient for at least a narrow band of rain showers to develop
behind its leading edge...much like what was observed on regional
radars early this morning. Think that scattered to numerous rain
showers will develop along the front as it moves southeast across
the County Warning Area this morning...resulting in a fairly high chance for
measurable rainfall. As a result went ahead and bumped probability of precipitation into
the 50 to 60 percent range from the dfw area northward where the
forcing for ascent associated with the front and a shortwave
trough aloft overlap. Rainfall amounts will likely be very
light...struggling to exceed one tenth of an inch for most
For this afternoon and evening...the front will push southeast
across the entire County Warning Area...then slow down or stall near the Texas Gulf
Coast. The frontal slow down is more or less in response to
cyclogenesis associated with a strong piece of upper level energy
digging into the backside of the complex upper trough upstream.
With the front slowing down or stalling...this next piece of
energy will induce lower to middle-tropospheric return flow over the
frontal inversion. This is easiest to see by looking at winds at
the 850 mb level on the NAM. Winds initially veer along/over the
cold front as expected...then suddenly back around to the south
between 21 and 03z as the upper trough begins to have a large
impact on the mass fields in the model. At any rate...assuming
this pans out...this would result in good isentropic lift/warm air
advection over the frontal inversion from late this afternoon to
this evening. This favorable uptick in forcing for ascent should
result in more efficient rain shower development and precipitation
production. This process looks to benefit locations mainly along
and southeast of a line from Killeen to Corsicana to Canton...so
went ahead with 80 probability of precipitation and around a quarter inch of rainfall in
the forecast for these locations. Again...no thunderstorms are
expected at this time...so overall this is a low impact forecast.
Sunday through Monday...the upper low is expected to deepen as it
continues slowly east and becomes cut off from the westerly flow
aloft /jet stream/ overnight tonight. Operational models continue
to struggle with the details regarding the evolution of this upper
trough into a cut-off low.
About half of the guidance deepens the primary piece of energy
aloft into one upper low...and then moves this upper low slowly
east over south Texas from tonight through Monday night. The other
half of guidance maintains that the southern piece of energy is
strongest...but shows more of an open wave structure keeping a
piece of energy discrete to the north of the stronger southern
piece of energy. The difference in solutions does not mean much to
areas south of the County Warning Area...because either way...strong large scale
forcing for ascent will be present for an extended period of time
from The Hill Country south and southeast to the Texas Gulf Coast.
For our County Warning Area however...the evolution of this northern piece of
energy seems to be more important.
If it persists...it keeps winds in the lower to middle troposphere
veered...preventing any significant moisture return for Sunday
into Monday. This would likely support a dry forecast for much of
the County Warning Area from Sunday through Monday night...when the upper low is
over south Texas.
If the northern piece of energy weakens or become absorbed into
the southern upper low...cyclogenesis will likely extend further
north away from the Gulf Coast...allowing some better moisture
return in the h850 to h700 layer. This would result in scattered
rain shower activity for locations generally east of Interstate 35
and south of Interstate 20...likely sometime between Sunday night
and Monday night.
There is little confidence in which solution will verify at this
time because the upstream trough contains 3-4 pieces of energy
easily viewable on water vapor satellite imagery early this
morning. Went ahead with 20 probability of precipitation over the southeastern quarter of
the County Warning Area to account for this uncertainty as the previous forecast
was dry...but about half of guidance shows precipitation over
these locations on Monday.
For temperatures...in general southeastern counties are more
likely to be cloudy for Sunday and Monday while northwestern
counties are more likely to see some sunshine each day. As a
result have temperatures several degrees higher to the northwest
than over the southeast during this period.
Tuesday and Wednesday...as mondays upper low continues off to the
east over the Gulf Coast...a strong northern stream shortwave
trough is expected to push east over the Central Plains. This will
result in a relatively strong surface cyclone moving off the High
Plains southeast across North Texas during the day on Tuesday.
Depending on the exact track of this low pressure system...we may
see some high to critical fire weather danger conditions across
western portions of the County Warning Area Tuesday afternoon. The strength and
track of the surface cyclone will determine the strength of its
associated dryline Tuesday.
Temperatures are expected to be above normal on Tuesday with a
nice thermal ridge oriented just southeast of this cyclone. If we
get a good dryline punch in this environment relative humidity
values Will Tank while westerly winds pick up in strength. While
we will very likely be warm on Tuesday...the strength and position
of this dryline remain a source of low confidence in the
forecast...so will hold off on doing anything more than
highlighting some elevated fire danger potential in fire weather
products at this time.
A strong cold front is expected to push across North Texas behind
this surface cyclone...likely moving across North Texas Tuesday
night. This will result in a return to below normal temperatures
Tuesday night through the day on Wednesday. No model guidance has
sufficient moisture for precipitation along the front at this
time...so as long as the upper trough remains well to the north as
expected...this should be a dry front Tuesday night.
Extended...most guidance indicates another shortwave trough moving
over North Texas Thursday night or Friday morning. Left the forecast
dry at this time without much opportunity for moisture recovery
behind the Tuesday night front. Will have to monitor the potential
for moisture return on Wednesday or Thursday though as this
Thursday night/Friday morning upper trough is somewhat strong in
the models. Cavanaugh
Preliminary point temps/pops...
Dallas-ft. Worth, Texas 56 36 58 40 69 / 50 40 10 5 10
Waco, Texas 57 37 53 38 64 / 60 70 20 10 20
Paris, Texas 57 37 55 39 69 / 60 70 10 10 5
Denton, Texas 54 35 58 35 70 / 50 30 10 5 5
McKinney, Texas 57 35 57 36 70 / 60 40 10 5 5
Dallas, Texas 57 37 57 41 69 / 50 50 10 10 10
Terrell, Texas 59 37 56 40 68 / 60 70 10 10 20
Corsicana, Texas 59 38 54 42 65 / 60 80 20 10 20
Temple, Texas 57 37 51 39 62 / 60 80 20 10 20
Mineral Wells, Texas 47 34 58 35 71 / 30 20 10 5 10