Area Forecast Discussion
Issued by NWS Dallas/Fort Worth, TX

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FXUS64 KFWD 270337
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1037 PM CDT Thu Apr 26 2018


.UPDATE...
A quick forecast update was done to increase POPs slightly across
the northwest counties where lingering convection may hold
together long enough to generate a few hundredths of an inch of
rain. Activity is expected to diminish the farther southeast it
gets as drier air is encountered (though a slight chance of
sprinkles will be maintained for any virga which manages to reach
the ground). Otherwise, a reinforcing cold front will push
southeast across the region overnight, keeping a dry and
seasonable airmass in place Friday through the weekend.

30

&&


.AVIATION... /Issued 720 PM CDT Thu Apr 26 2018/
/00Z TAFs/

North flow. VFR but with some elevated showers/virga tonight.

The tail end of a skinny upper trough will swing through North
Texas tonight. The radar echoes along the Red River Valley suggest
rain showers are ongoing within it, but with a deep layer of dry
air beneath these convective elements, this has so far been mostly
virga. The 00Z RAOB from KFWD found very dry air remained beneath
the 18kft cloud bases; the relative humidity values around 700mb
were still in the single digits. This virga will attempt to
moisten the layer, but a few sprinkles would be the extent of any
precipitation at the surface. However, some sub-cloud turbulence
will accompany the evaporation process.

A small cluster of thunderstorms has developed along the
associated surface front in western Oklahoma. As the front
approaches overnight, this complex will find inadequate moisture
downstream, and only elevated showers are expected near the
Metroplex TAF sites. The passage of the front will organize the
timid northerly winds already in place, but postfrontal wind
speeds at our TAF sites will be well below the windy conditions
currently across the Texas Panhandle and West Texas. As the upper
trough axis transits the area, skies will clear and will remain
clear through the remainder of the valid periods of the TAFs.

25

&&

.SHORT TERM... /Issued 244 PM CDT Thu Apr 26 2018/
/Tonight/

Our cold front parade will continue tonight (although this one
will bring almost imperceptible changes to the temperature and
dewpoint fields). This front will be encouraged southward by a
fairly potent upper-level disturbance which is presently tracking
into Kansas, and this feature will zip overhead tonight and into
Friday morning. While moisture has been effectively scoured out by
Wednesday`s stronger cold front, 500 mb temperatures will cool
into the -18 to -21 C range as the core of this feature
approaches, resulting in steepening mid-level lapse rates. This
will help carve out a small area of instability (less than 250
J/kg)--rooted above 850 mb or so. This will probably be good
enough to support some bubbly elevated convective plumes embedded
within an expanding mid-level cloud deck tonight. We`ve expanded
the 20% PoP mention for rain showers across much of the forecast
area late this evening and into the early-morning hours and will
leave out an isolated thunder wording given the paucity of
anticipated instability. Lingering dry air in the lowest 3-4 kft
may help to evaporate a good deal of any precipitation, hence the
lower PoP values.

Otherwise, low temperatures tonight will be in the upper 40s and
mid 50s with skies quickly clearing from northwest to southeast
Friday morning.

Carlaw

&&

.LONG TERM...  /Issued 244 PM CDT Thu Apr 26 2018/
/Friday through Thursday/

The weather over the next few days will be dominated by a high-
amplitude, upper-level ridge that is in place from Baja California
across the American West and into British Columbia. At the
surface, a 1029 mb high is centered near Yellowstone National
Park, with a cold front on the leading edge of it presently across
the Central Plains. By Friday morning, this front should be south
of our forecast area, with high pressure building in behind. This
high should weaken, and slide off to the east quickly, so we
likely will not have much in the way of sensible weather impacts
by Friday afternoon.

By Saturday, winds should return from the south, allowing for a
steady warming trend to commence. Saturday should be a very lovely
day with light southerly winds, temperatures in the upper 70s to
near 80 (i.e. near seasonal normals), dewpoints in the upper 40s,
and ample sunshine. Sunday will be slightly warmer and more humid
as southerly flow continues. Overall, North and Central Texas are
in for quite a lovely weekend, so make sure to get outside.

Heading into next week, a potent upper-level trough will begin to
dig in across the Rocky Mountains. Resultant lee cyclogenesis will
act to enhance warm air advection across the Great Plains, with
the axis of a low-level jet progged to move over our forecast
area by late Monday. The GFS and ECMWF both advertise some light
QPF in our southwestern counties near this low-level jet axis, and
it is not entirely implausible. Despite a strong cap in place (as
evidenced with forecast CINH values in excess of 100 J/kg) and a
lack of upper-level support, strong moisture return and warm air
advection may permit a few showers to develop. The chances for
thunder should be low to nil however. At the very least, we are
likely to see a marked increase in cloud cover by Monday
afternoon. Will mention light, isolated showers in the forecast
products for Monday afternoon.

The middle of next week is when the forecast starts to get a
little more complicated. Model guidance is in good agreement that
a dryline should begin to sharpen over West Texas on Tuesday,
with that dryline approaching a Vernon to Midland line by late
afternoon. Forecast soundings suggest that capping may be weak
enough to allow for some thunderstorm develop along the dryline.
While most of the convection should stay west of our area, storm
motions could bring some thunderstorms into our northwestern
counties, thus carried slightly higher PoPs as well as mentioned
thunder across our northwestern counties Tuesday late afternoon
and evening. Coverage appears it may be higher on Wednesday given
the approach of an upper-level trough, and thus more noteworthy
height falls. We would likely see another round of thunderstorms
develop along the dryline (which like Tuesday, will likely be
situated across the Rolling Plains of West Texas by late
afternoon). As is typically the case this time of the year, any
thunderstorm threat in North and Central Texas brings with it the
chance for severe weather. While it is too early to know the
precise details and location of where the greatest severe weather
threat will be, there will be a possibility of severe weather
somewhere in the Southern Plains towards the middle of next week.

Godwin

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    54  77  52  81  57 /  10   0   0   0   0
Waco                52  78  50  81  55 /  10   0   0   0   0
Paris               51  73  47  77  52 /  10   0   0   0   0
Denton              50  75  48  81  54 /  10   0   0   0   0
McKinney            50  75  48  79  54 /  10   0   0   0   0
Dallas              54  78  52  81  58 /  10   0   0   0   0
Terrell             52  77  47  80  53 /  10   0   0   0   0
Corsicana           53  75  49  79  54 /  10   0   0   0   0
Temple              52  79  51  81  55 /  10   0   0   0   0
Mineral Wells       50  76  47  82  53 /  20   0   0   0   0

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

30



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