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Area forecast discussion 
National Weather Service Fort Worth Texas
404 am CST Monday Dec 29 2014

Discussion...

Today will be a warmer day across most of the region but some
cloud cover over the far eastern counties affects the high
temperature forecast for today. Most of the area will warm into
the 50s and lower 60s under mostly sunny skies...but areas in the
east that remain under cloud cover through the morning will likely
only see afternoon highs in the 40s.

An Arctic front is currently moving down the plains and was
located near the Kansas/Nebraska border at the time of this
discussion. It is expected to arrive in north central Texas
tonight and will slowly seep its way through the region. We will
notice a more significant temperature difference Tuesday through
Wednesday as the dewpoints drop and the Arctic air continues to
usher into the area. High temperatures on Tuesday and Wednesday
will only be in the 30s and 40s. The western and northwestern
counties of the County Warning Area will barely reach 32 degrees...if at all...on
Wednesday. The coldest overnight lows are expected Tuesday night
with temperatures dropping into the lower 20s in the northwest to
lower 30s southeast. Wind chill values Tuesday night and
Wednesday morning will be in the teens across most of North Texas.

We wish we could say that confidence in if and where any winter
precipitation will occur Tuesday through Thursday morning has at
least increased some but unfortunately the latest model runs do
not offer much help to the challenge. Further challenging the
forecast is now that the NAM and sref are within the window for
precipitation chances...their aggressiveness in producing winter
precipitation causes additional concerns.

What we do know is there will be some isentropic lift across
parts of the region during the Tuesday night through Thursday
morning time frame. Most of the models indicate this lift will be
fairly weak but there are noticeable differences between each
model. We also know that there will be a dry layer of air near the
surface that any falling precipitation will have to overcome to
reach the ground. Sometime sleet is heavy enough to fall through a
near-surface dry layer...but it usually takes saturation of the
near-surface layer for any rain/freezing rain to reach the
ground.

Our latest thinking regarding winter precipitation is there
continues to be low chances for a rain/freezing rain/sleet mix
across our far western counties Tuesday night/Wednesday morning...
and then across roughly the southwestern half of the County Warning Area during
the day on Wednesday. The main challenge and question regarding if
we see any precipitation in these areas is how strong will the
lift be...and if and how long will it take for the near-surface
layer to become saturated. We still think that if any
precipitation occurs Tuesday night through Wednesday it will be
light but there could be some trace/light accumulations of ice
and/or sleet.

The chances for winter precipitation Wednesday night/early
Thursday morning are also hindered for the same reasons listed
above. We know that the lift will be increasing across the region
as southerly winds above the surface induce warm air advection but
will the near-surface layer already be saturated and if not...how
long will it take for that to happen. Have spread low probability of precipitation across
all of the region Wednesday night/early Thursday morning with a
mention of rain and/or freezing rain west of a line from Sherman
to Fort Worth to Lampasas. The models have middle level temperatures
warming under the influence of warm air advection beginning
Wednesday into Wednesday night and the profiles look too warm for
sleet at this time...but its possible some light sleet could
occur. While the hourly forecast makes it seem like there could be
several hours of freezing rain across our western
counties...expect temperatures will begin warming at some point
that night or Thursday morning with any freezing rain
transitioning over to liquid rain. If there are going to be
impacts from freezing rain Wednesday night...it would most likely
be over our western counties where temperatures are expected to be
in the 28-29 degree range. However...the ice should melt as the
precipitation transitions to liquid rain and temperatures warm.

We will be issuing a Special Weather Statement to highlight the
winter precipitation potential. As mentioned before...the NAM and
sref runs must be watched. The reason they are more aggressive in
generating winter precipitation is they return low level moisture
rather quickly into the area on Wednesday. The potential for
this to happen needs to be closely watched as this would mean a
longer period for freezing rain/sleet and thus higher impacts. The
GFS/ECMWF/Canadian have consistently kept the low levels dry for
the past couple of days now and continue to do so on tonight/S
runs.

Widespread rain is expected across the region Thursday through
Saturday. An upper level low will be moving towards the
region...inducing large scale lift...but its arrival is slower
than previous model runs. Now the upper level low does not pass
through the area until Saturday night which is the reason for the
extension of probability of precipitation into Saturday. Another front will move through
the region on Sunday.

82/jld

&&

Aviation...
/issued 1154 PM CST sun Dec 28 2014/
main concern is the likely development of a low cloud/fog bank
across East Texas tonight. Low level winds turn more easterly and
could bring this low cloud bank or fog westward during the
morning hours. Once the sun rises it will work to prohibit this
westward movement...but a lingering IFR cloud bank may impact
dfw/Dal/gky taf sites middle-late morning. Have included a tempo for
IFR ceilings at just Dal from 14 to 17z...where probability would be
highest but confidence on this is lower than usual and will need
to be monitored.

Otherwise VFR will prevail through Monday evening with generally
light S/southeast winds and just some high clouds.

Winds will turn more easterly Monday night and with higher
moisture to the east and upslope flow...this should allow for the
redevelopment of low clouds and fog...this time impacting all of
the taf sites sometime after 6z. Confidence in this again is not
high...but NAM soundings are very aggressive in low level
saturation indicative of LIFR cigs/fog.

Tr.92



&&

Preliminary point temps/pops...
Dallas-ft. Worth, Texas 56 35 42 27 35 / 5 5 5 5 10
Waco, Texas 56 34 45 29 38 / 5 5 5 5 20
Paris, Texas 46 30 43 25 37 / 5 5 5 5 10
Denton, Texas 56 28 41 23 34 / 5 5 5 5 10
McKinney, Texas 55 28 42 24 35 / 5 5 5 5 10
Dallas, Texas 57 35 43 28 35 / 5 5 5 5 10
Terrell, Texas 54 32 44 28 37 / 5 5 5 5 10
Corsicana, Texas 55 36 45 29 39 / 5 5 5 5 10
Temple, Texas 56 34 45 29 38 / 5 5 5 5 30
Mineral Wells, Texas 60 28 38 22 33 / 5 5 10 10 20

&&

Forward watches/warnings/advisories...
none.

&&

$$

79/82

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