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Area forecast discussion
National Weather Service Fort Worth Texas
922 PM CST Tue Jan 16 2018

quick update this evening to account for current temperature
trends now that skies have cleared and winds are becoming light.
These conditions will allow for rapid cooling overnight as
dewpoints across the area range from -5 across the north and west
to around 10 in the southeast. Notoriously cold spots in low
terrain will easily see temperatures plummet into the single
digits (eastland AWOS is already down to 4f as of 9pm) while more
urbanized areas are expected to stay around 10-14f. The hard
freeze warning remains in effect area-wide through Wednesday
morning. Since winds will be light, wind chill values will remain
mostly in the single digits, or just a few degrees below the
actual temperatures. This will be the coldest night in quite some
time (as much as 20-30 years for some locations), so remember the
4 p's: people, pets, pipes, and plants.



Aviation... /issued 540 PM CST Tue Jan 16 2018/
VFR conditions will prevail through the taf period. While dfw area
airports are mostly clear, a deck of mid/high clouds continues to
move south through central Texas, but will clear the Waco taf
site in a few more hours. Breezy north winds of 10-20 kts will
subside this evening and become NE at 5 kts or less; they will
remain light and variable into Wednesday. Light southeast winds
are likely to resume late Wednesday afternoon or evening.



Short term... /issued 414 PM CST Tue Jan 16 2018/
/tonight through Wednesday evening/

The deep upper trough that brought winter weather to much of the
central and southern U.S. The past couple of days will continue
moving towards the East Coast tonight. Dry and subsident air on
the back side of the trough will continue to filter into Texas and
result in clearing skies tonight. As skies clear and wind speeds
decrease, temperatures will rapidly fall with nearly all of north
and central Texas cooling to around 10 degrees or lower.
Therefore...we will issue a hard freeze warning for the entire
County Warning Area. For some locations this will approach or break daily record
lows, including Waco (record low is 11 set in 1930). However, it
does not appear that dfw will reach the current record of 2
degrees set back in 1930. Either way it will be very cold with
even lower wind chills. The only good news is that wind speeds
will decrease through the night so wind chills will not be
appreciably lower than the actual air temperature. Since we will
already have a hard freeze warning out, we will not issue a
separate Wind Chill Advisory but will highlight the wind chills in
the hard freeze warning.

By mid morning Wednesday, temperatures will warm up steadily as
a weak upper ridge builds in from the west and the full strength
of the January sun is put to work. This will help temperatures
finally climb above freezing by afternoon with highs in the lower
and middle 30s.



Long term... /issued 414 PM CST Tue Jan 16 2018/
/Wednesday evening through Sunday/

Generally quiet weather is anticipated in the long term forecast
period with a warming trend through the forecast period. There
will be a couple of opportunities for rain chances, especially
near and east of I-35 late this week and into the weekend.

While widespread single digit overnight low temperatures are not
expected across the area Wednesday night into Thursday morning,
it'll remain cold during this time period. Clear skies and the dry
airmass will allow temperatures to fall into the teens areawide,
with the exception being across the more urban sites in the d/fw
metroplex. Thursday will be warmer with temperatures climbing into
the low to mid 40s across a majority of north and central Texas. A
slightly greater southwesterly component to the surface winds for
areas near and west of the Highway 281 corridor will allow
temperatures to warm into the low to possibly mid 50s.

A low-amplitude upper trough is expected to dive southward across
the Concho Valley on Thursday afternoon. There may be some lift
along the northern periphery of this feature, but it'll likely
remain too meager to overcome the copious amounts of dry air at
the surface to result in nothing more than some mid-clouds, mainly
south of I-20. If lift is stronger and sufficient saturation can
occur, I wouldn't rule out a few sprinkles or perhaps a few sleet
pellets. For now this potential looks low and i'll continue with
silent 10 pops across central Texas. Increasing low level winds will
usher in greater low level moisture helping to keep overnight lows
into Friday morning greater than the previous night. Readings
will generally be in the upper 20s and low 30s. Some of the
sheltered sites may fall into the mid 20s, however. There will be
the potential for some patchy drizzle/fog on Friday morning across
the Brazos River Valley as this warmer and more moist airmass
lifts northward into the cooler air. If the gradual ascent is a
bit more robust, I wouldn't be surprised to see a few sprinkles
early Friday morning.

Above normal conditions should return on Friday as stronger
southerly flow ramps up. A larger part of the area should warm up
nicely as southwesterly low level flow overspreads much of the
area. Areas near and west of I-35 will should easily climb into
the low to mid 60s, with even a few upper 60s possible across far
western zones in accordance with ec MOS output. Areas to the east,
however, may remain entrenched in low level clouds, fog/drizzle
such that temperatures struggle to climb out of the low 50s. Low
level isentropic ascent along the 310k Theta surface may be
sufficient enough to produce a few rain showers down across
extreme southeastern parts of the Brazos River Valley during the
afternoon hours and i've maintained a 20 pop here.

More impressive low level warm air advection is expected Friday
night into Saturday morning. A strong southerly low level jet of around
35-40 knots should develop across the central and Southern Plains
as the low level height gradient tightens. The mixed planetary boundary layer should
allow overnight low temperatures to remain well above seasonal
norms with most areas in the 40s and 50s. There will be the
potential for some sprinkles across east TX, but measurable
rainfall should be hard to come by during this time period (friday
night into Saturday morning). With that in mind, i'll only
advertise a 15 pop with a mention of rain showers.

Saturday will be well above normal with regards to daytime high
temperatures, especially across the western two-thirds of the
area. Strong south to southwesterly winds will induce decent
compressional warming. This should allow temperatures to soar into
the upper 60s into the mid-70s, especially out across western
zones. Out east, cloud cover may linger through a good portion of
the day, but the southerly winds will still allow temperatures to
climb into the low to mid 60s. The moisture depth does increase a
little during this time and i've elected to continue the mention
of a few sprinkles/rain showers out across far eastern zones.
Without a focus for large scale lift, it's possible that most
areas remain precipitation-free.

Another warm night will be on tap Saturday night into Sunday
morning as another nocturnal low level jet ramps up. Some of the models
indicate that 925mb winds could crank as high as 45 to 50 knots.
While mechanical mixing isn't as efficient at night, with this
amount of flow, I wouldn't be surprised if some areas flirt with
Wind Advisory criteria---especially across far eastern zones. The
one certainty, however, is that overnight conditions will be very
mild by mid-January standards, with some sites across East Texas
falling to just under 60 degrees for lows!

Sunday presents a challenge to the wx/pop forecast. While north
and central Texas will have been under the influence of a good
warm/moist advection regime, there are still some questions about
the quality of moisture return northward and thus rain/storm
chances. Models do agree that a very Stout upper level low,
characterized by nearly 200 meter height falls, will overspread
the NE New Mexico. The subsequent Lee-side trough should develop
out across southwest Kansas. Given these dynamics, this system should
be efficient at drawing up a good plume of low level moisture. A
moisture discontinuity should develop and give birth to a Pacific
front/dryline type feature across the Big Country on Sunday. The
true cold front will likely be oriented east-west and slide
southward across the Front Range of the Rocky Mountains. Long term
deterministic model guidance still remains split with regards to
the timing and placement of the surface features, however. The 12
UTC GFS continues to be one of the faster pieces of guidance and
slides the front through the area relatively quickly on Sunday.
The 12 UTC ECMWF, however, is a little slower and is the preferred
model given that the upper trough may dig a bit further to the
south. The southwesterly flow aloft should result in some capping.
Even with the 12 UTC ecmwf's position of the upper low, it's
probable that most of the good forcing for ascent will remain
northwest of our area. Moreover, surface flow actually veers a bit
which should limit convergence along the Pacific front/dryline, so
i'll keep pops at or below 50 percent.

While instability and shear will be in place, lapse rates
generally appear quite poor. In addition, there are still some
questions regarding the quality of low level moisture return
northward. As I mentioned yesterday, we'll keep an eye on this.
Despite the passage of the first Pacific front/dryline, west to
northwest winds will be ideal for downsloping and so we will
actually remain quite warm on Sunday with highs in the mid to
upper 60s with some low 70s possible. This could also result in
an elevated fire weather threat as well across the western zones.



Preliminary point temps/pops...
Dallas-ft. Worth 12 33 21 49 32 / 0 0 0 0 0
Waco 9 35 18 45 32 / 0 0 0 0 5
Paris 9 31 18 43 27 / 0 0 0 0 5
Denton 7 32 15 49 27 / 0 0 0 0 0
McKinney 7 31 19 44 27 / 0 0 0 0 0
Dallas 12 33 23 49 32 / 0 0 0 0 5
Terrell 9 32 19 44 28 / 0 0 0 0 5
Corsicana 12 32 19 43 29 / 0 0 0 0 5
Temple 11 35 18 45 32 / 0 0 0 5 10
Mineral Wells 6 35 12 50 30 / 0 0 0 0 0


Forward watches/warnings/advisories...
hard freeze warning until 10 am CST Wednesday for txz091>095-

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