FXUS64 KFWD 191227 AAA

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
727 AM CDT Sun Aug 19 2018

12 UTC TAF Cycle

Concerns---Near term windshift and convective potential this
afternoon and tonight.

Outflow from RA/TSRA will briefly interrupt southerly winds
across the Metroplex TAFs. Accompanying this windshift will be the
potential for a few instances of SHRA and I`ve included both of
these elements (windshift and SHRA) in a TEMPO group for Metroplex
TAFs. The windshift should be light enough such that area
terminals remain in a south flow. More continuous southwest to southerly
winds will likely resume during the late morning into the early
afternoon hours across the Metroplex. Southerly winds will prevail
at Waco through the entire 12 UTC TAF cycle.

The next challenge will be timing the potential bouts of SHRA
and/or TSRA at the Metroplex. This morning`s convection should
leave behind a boundary which should act as a focus for renewed
convective development this afternoon. I`ll maintain the inherited
afternoon VCTS with low confidence, but if the aformentioned
boundary is shunted south of D10 airspace and/or vanishes beneath
the ambient flow, it`s possible that little to no new TS develops
across the Metroplex this afternoon. This evening offers a better
opportunity for convective development as low level ascent
increases from the west and southwest. I`ve appended a 3 hour
window for VCTS between 03-06 UTC Monday with modest confidence.
Depending on the location of convection, south flow operations
could be briefly disrupted due to numerous convective outflows.
Confidence in timing/placement of these chaotic wind shifts is
too low to explicitly mention in the TAF. Waco will remain far
enough to the south such that shower or storms appear unlikely
through the 12 UTC TAF cycle, though the potential is non-
zero...especially between the 6 and 12 UTC Monday time frame.
Outside of rain/storms, VFR is expected at all terminals.



.SHORT TERM... /Issued 407 AM CDT Sun Aug 19 2018/
/Today and Tonight/

The main challenge in the short term will be convective trends
and consequently the high temperature forecast.

This morning, a large shield of rain with embedded thunderstorms
continues to slowly advance eastward across southwestern Oklahoma
and adjacent parts of North Texas. Regional VWP sampled 20-30
knots southerly flow around 1km this morning. Despite this flow,
convective outflow continues to race east and southeastward from
this rain/storm activity suggesting that its overall progression
through the rest of North Texas may be limited. For now, I`ll
advertise a 40-50 PoP across the Big Country and western reaches
of Texoma during the pre-dawn hours. This complex should dissipate
completely as its convective outflow becomes further displaced,
limiting the ability for the regeneration of new convective cells.
With this in mind, PoPs will decrease through noon with highest
chances for rain near and north of I-20.

Widespread cloud cover from this complex should slide southward
across much of North and Central Texas through the day. Beneath
the large cirrus canopy, low level flow late this morning and this
afternoon should once again veer some to the southwest. While the
clouds may hinder diabatic heating and keep temperatures 1-3
degrees lower than Saturday, it`ll still be another hot day with
afternoon highs climbing into the upper 90s to near 101 degrees.
The exception will be along the immediate Red River Valley where
temperatures may only climb into the low to mid 90s. Heat index
values across the area may climb into the 100 to 105 degree
range...especially across East Texas. At this time, I don`t see a
need for a heat advisory as the areal coverage of heat indices
above 105 appears patchy in nature. Regardless, please exercise
your heat safety rules!

Model derived wind fields indicate that front/convective outflow
should slide southward towards the I-20 corridor in the
evening. As a result, convection is expected to re-develop late
this afternoon and into the evening hours ahead of this feature.
There will be a risk for strong to possibly severe downburst winds
given steep 0-3km lapse rates (nearly 9 C/km) and DCAPE values in
excess of 1100 J/kg. Though the exact coverage of showers/storms
is unknown, it seems reasonable to increase PoPs during the 00-03
UTC time frame Monday (or Sunday evening) as the front/convective
outflow slides southeastward. I`ll keep a 60 PoP across northeast
Texas, but given the decent CAM consensus, I`ve elected to
increase PoPs up to around 50% further southwest towards the D/FW
Metroplex and into the eastern Big Country. Storm motion should be
a little faster today, but there will still be a heavy rain/flood
potential with showers and thunderstorms.



.LONG TERM... /Issued 407 AM CDT Sun Aug 19 2018/
/Monday through Saturday/

Although the main forcing associated with a departing upper low
will be confined to the Central Plains, the tail end of a final
spoke of energy will skirt the Ark-La-Tex on Monday. At daybreak
Monday morning, showers and thunderstorms may be ongoing along
the associated cold front within North Texas, but as the boundary
moves deeper into Central and East Texas, it will become
increasingly separated from the upper support. Minimal low-level
convergence along the boundary will both reduce compressional
warming at peak heating and limit the potential that surface
parcels will be able to overcome lingering inhibition,
particularly if morning cloudiness is slow to erode. Warming
southwesterly winds ahead of the front may help to overcome the
reduced insolation, but even with extraordinary MLCAPE values
Monday afternoon, limited shear and marginal lapse rates aloft
should prevent any updrafts from persisting long enough to become
strong. Thus, only low-end PoPs will accompany the front, with a
conditional severe threat. Strengthening northwesterly flow above
the frontal layer should assure its forward progress and preclude
any postfrontal precipitation. However, if the slower NAM/ECMWF
solutions pan out, there may be a wider window (both temporally
and spatially) for thunderstorms Monday afternoon into Monday
evening, with an enhanced severe threat. In any event, any
showers and storms should exit to the southeast Monday night.

Milder and drier air will filter into the region on Tuesday, but
with abundant sunshine, high temperatures may be within a degree
or two of normal values. But after the oppressive heat and
humidity of preceding days, the middle of the week will feel
noticeably more comfortable in comparison. The low-level advection
will wane Tuesday night, but with an unseasonably mild start to
Wednesday and weak northeasterly surface flow, similar daytime
temperatures are expected. Southerly winds will return on
Thursday, and Gulf moisture will steadily increase late in the
week. The GFS has come into agreement with other extended guidance
with late-season ridging reasserting itself over the Lone Star
State. As a result, the extended portion of the forecast will
remain free of rain chances, and temperatures will climb into the
upcoming weekend.



Dallas-Ft. Worth    97  77  93  74  93 /  20  50  10   5   0
Waco               101  78  99  74  96 /  10  40  20  20   5
Paris               91  74  91  68  89 /  30  60  20   5   5
Denton              96  74  92  69  92 /  30  50  10   5   0
McKinney            96  75  92  69  91 /  20  50  10   5   0
Dallas              99  78  94  74  94 /  20  50  10   5   0
Terrell             98  77  93  71  93 /  20  50  20  10   5
Corsicana           99  78  97  74  94 /  10  40  30  20   5
Temple              98  77  99  74  97 /   5  20  20  20  10
Mineral Wells       94  73  93  70  94 /  30  40  10   5   0





NWS FWD Office Area Forecast Discussion