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Area forecast discussion
National Weather Service Fort Worth Texas
653 am CDT Fri Oct 18 2019

/12z tafs/

Challenges and concerns: low convective chances after 06z Saturday.
Timing of a surface cold front and west/northwest wind shift after 12z
Saturday at dfw international Airport.

VFR conditions with a few cirrus are expected through 03z Saturday
with prevailing southeast winds around 10 knots. A mid level
shortwave currently moving through Arizona and into nm this morning
will arrive after 06z Saturday. In advance of this system, low
levels remain dry with moisture confined above 700-750mb.

Isolated, high-based and likely elevated rain showers/ts will be possible
at dfw Metro airports ahead of a surface cold front after 08z
Saturday. For now, vcsh wording after 08z should suffice due to
low coverage and confidence. Winds ahead of the cold front will
gradually veer S-SW 10 knots or less, before shifting to the west/northwest
10-15 knots at dfw by 15z Saturday. Later tafs may have to address
if a change to thunderstorms in the vicinity is needed late tonight, as well as timing
frontal passage into dfw Metro airports.

The better large-scale ascent with this system is expected to
remain displaced well to the north of Waco Regional Airport where
I have maintained VFR with south-southeast winds prevailing around 10 knots
through tonight.



Short term... /issued 312 am CDT Fri Oct 18 2019/
/today and tonight/

A mostly sunny, warm, and breezy day is expected for the area as
a surface ridge continues shifting east away from the area.
Surface pressure falls will occur readily across the central and
southern High Plains in response to an approaching vigorous mid
level impulse lifting out of the southern rockies. Look for
southerly winds to increase by late morning and after to between
10 to 15 mph and become gusty at times west of I-35/35w. Plentiful
insolation will result in afternoon high temperatures warming into
upper 70s and lower 80s west of I-35. This area has seen less
rainfall that areas further east in the past month with drier
than normal small vegetation. The combination of the dry fuels,
humidity values falling to around 30 percent, and breezy southeast
winds will result in an elevated grass fire danger north of I-20
and west of I-35w. A grass fire danger statement will be issued
this morning for this area for an elevated grass fire threat this
afternoon. Slightly cooler and less breezy conditions are
expected further east, but it will be pleasant with highs warming
into the lower-mid 70s.

The southern rockies strong mid level impulse will progressively
move east and arrive across the region late this evening and
during the overnight hours. A weak surface low will slide east
just south of the Red River valley tonight in response to this
system with a trailing cold front arriving before sunrise Saturday
morning. Despite the impressive lift with this mid level impulse,
low levels remain very dry with a bulk of the moisture being
confined around and above 700 mb. Nevertheless, the strong ascent
aloft will steepen lapse rates within the mid levels with MUCAPE
values less than 500 j/kg being noted on forecast soundings.
Isolated, high-based and likely elevated thunderstorms will occur
from the I-20/30 corridors to the Red River valley overnight. No
severe weather is expected. In addition, little in the way of
appreciable rainfall is expected in large part due to dry low
levels and the progressive nature of this system. Isolated
rainfall amounts of a few hundredths here and there are expected.
The cold front will do little more than reinforce the dry airmass
currently in place and shift surface winds to the northwest. Any
low level cold advection is expected to be negligible across north
and central Texas, so you will be disappointed if you were hoping
for colder temperatures moving into the weekend.



Long term... /issued 312 am CDT Fri Oct 18 2019/
/Saturday through Friday/
a weak cold front will move through north and central Texas
Saturday morning resulting in a northwesterly wind shift an
invading drier air mass. There will not be much cool air with this
front, so with the clear skies and lower dewpoints, highs will
still top out near 80 along the Red River to the upper 80s in
central Texas. The occasionally breezy northwest winds in the
morning will relax by the afternoon, and although it will be mild,
it should make for a stellar Saturday. The cold front will stall
across south central and southeast Texas during the overnight
hours and with the clear skies, low dewpoints, and light winds
over north central Texas, radiational cooling will be optimal and
send temperatures tumbling into the 50s.

On Sunday an upper level trough will rapidly deepen across The
Rockies and eject northeastward out into the plains Sunday night.
This will result in a strengthening sub-1000mb surface low that
tracks across Oklahoma during the day. Increasing southerly winds
of 10 to 20 mph with higher gusts will occur and send temperatures
climbing into the upper 80s and low 90s in the favorable warm
advection regime. These winds will precede the arrival of higher
surface moisture, so relative humidity is expected to drop below
30% west of I-35 and to near 20% in the western zones. The weather
conditions combined with dry fuels will result in elevated to
near critical fire weather danger across the western zones Sunday.

Returning surface moisture will arrive by the late afternoon
hours along and east of I-35 and with the warm temperatures it
will likely yield some modest surface-based instability before
sunset. However cooling temperatures with the setting sun, will
result in increasing convective inhibition for surface-based
convection Sunday evening. There may be a small window Sunday
evening across the eastern zones where the arrival of dynamic
forcing will coincide with the weakest cinh and allow for some
surface based convection to develop. Shear and instability at this
time would be supportive of severe convection or supercells, but
it must be stressed that this is highly conditional and only has a
small window to occur. Given that the best dynamics for upper
level forcing will be displaced to the north late Sunday as the
upper trough begins to pivot into the Midwest, am more inclined to
believe that any convection will hold off until closer to
midnight with the arrival of the cold front than spontaneously
develop over our County Warning Area ahead of any boundary.

By midnight the frontal boundary will enter the County Warning Area but become
increasingly parallel to the mid level flow and deep layer shear
vectors. This is suggestive of a lessened risk of convective modes
favorable for severe weather, as storms would primarily form in a
slow moving line forced along the cold front. Still, high values
of deep layer shear and increasing low level instability just
above the surface layer would warrant a marginal threat for severe
hail and/or wind. This line of storms will progress southeast
across the County Warning Area during the overnight hours and into Monday morning.
Model guidance continues to look favorable for rain and have
bumped up pops to categorical in the northeast zones to likely for
most of the remainder of the County Warning Area. The exception will be the
northwest zones where moisture may be too limited for convection
before the front moves across. Rainfall amounts will average a
tenth of an inch the northwest to an inch or more in the east. All
of the rain should push southeast of the County Warning Area by midday Monday
with clearing skies moving in from the northwest. Much like the
Saturday front, the airmass behind this front will be drier but
not much cooler. Despite the lack of strong cold advection, the
impacts of morning rain and clouds should keep highs Monday in the

Clear skies and light winds Monday night will once again lead to
excellent radiational cooling and lows will drop into the 40s for
most of the area. Gradually moderating temperatures, pleasant,
and tranquil conditions will prevail into Wednesday as dry
northwesterly flow aloft continues. The next upper trough will
deepen Thursday with another cold front expected late Thursday.
Although return flow will be brief ahead of this front, moisture
and lift should be sufficient for another chance of showers and
storms late Thursday and into Friday. This front will tap into
some colder Canadian air and highs Friday may only warm into the
lower 60s.



Preliminary point temps/pops...
Dallas-ft. Worth 78 60 82 57 89 / 0 20 0 0 5
Waco 78 60 87 57 91 / 0 0 0 0 5
Paris 72 53 77 53 81 / 0 20 0 0 10
Denton 77 58 82 54 89 / 0 20 0 0 5
McKinney 76 57 81 54 87 / 0 20 0 0 5
Dallas 78 62 82 58 88 / 0 20 0 0 5
Terrell 76 57 84 55 88 / 0 10 0 0 10
Corsicana 76 59 84 57 87 / 0 0 0 0 10
Temple 80 61 87 59 91 / 0 0 0 0 5
Mineral Wells 81 58 82 52 91 / 0 10 0 0 5


Forward watches/warnings/advisories...

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