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Displaying AFOS PIL: AFDFWD Received: 2018-08-10 04:57 UTC

FXUS64 KFWD 100457 AAB

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1157 PM CDT Thu Aug 9 2018

/06Z TAFs/

Undaunted by nightfall, a cluster of thunderstorms was able to
feed off an inordinate amount of instability on the northern
fringes of the Metroplex, surviving deep into the evening. 
Although the activity was primarily to the north and northeast of 
the big airports in the Metroplex, it caused considerable 
disruptions to commercial operations. A few sprinkles of light
rain will still be possible from the remaining mid clouds, but the
updrafts will no longer be supportive of lightning.

A low-level trough will remain draped across the Metroplex
overnight. This will promote some continued upglide, but the main
corridor of warm/moist advection will be oriented through Central
Texas into East Texas. Despite being worked over late this 
afternoon, this buoyant inflow beneath steep lapse rates aloft 
will promote the redevelopment of thunderstorms across Central 
Texas. Late in the evening, some precip-bearing updrafts had
already returned to areas west of I-35 and south of I-20. This 
activity should steadily increase in intensity and areal coverage 
during the early morning hours, eventually producing some embedded
thunderstorms with steep lapse rates aloft. Morning showers will 
be possible as far north as the Metroplex, but the environment 
across North Central Texas will be less favorable for thunder.

The wind field has been governed by outflow, but with the
proximity of surface troughing, light easterly winds should take
hold across the Metroplex, veering to the southeast by daybreak.
Outside of renewed outflow, south flow will prevail through

With a moisture-rich boundary layer still in place on Friday
beneath weak troughing aloft, some redevelopment of thunderstorms
should occur at peak heating. The weak surface wind field will
allow residual boundaries to linger. With much of the forcing on 
the mesoscale, initiation will be largely dictated by the location
of these boundaries, which may be determined by the nocturnal 
activity that has yet to occur. Despite the uncertainties in
placement, the timing of this convection would be focused yet
again during the typical peak heating period. As a result, will 
introduce some late afternoon/early evening thunder in the TAFs.



.SHORT TERM... /Issued 347 PM CDT Thu Aug 9 2018/
/This Afternoon and Tonight/

The main challenge in the short term forecast period will be the
location and coverage of precipitation. For the rest of this
afternoon, it appears that locations south of I-20 will stand the
best opportunity for showers and thunderstorms. A few storms will
be possible near the Highway 380 corridor this afternoon as well.
Overnight tonight, storm chances will increase quite noticeably
across the Concho Valley and into Central Texas. 

This afternoon, there has been a relative lull in convective
activity from about noon through the 3 PM time frame. A broad
surface trough continues to slide southward through the forecast
area with an mesoscale convective vortex or MCV noted across the
Concho Valley. Agitated CU was noted from near a Gatesville to
Athens line and I've nudged PoPs into the 50 percent category
here. There will be a risk for strong to near severe downbursts
given large amounts of DCAPE and a very hot and well-mixed
boundary layer. A small thunderstorm cluster was noted just north
of the Highway 380 corridor in response to just daytime heating.
The cessation of this convection will be interesting, but in
general, it should decrease after sunset.

Overnight tonight, showers and thunderstorms should blossom 
across Central Texas and the Concho Valley. RAP and NAM guidance 
continue to support strong isentropic ascent along the 305K theta 
surface. As noted yesterday, the NAM has done a pretty good job of
handling the overnight LLJ and I see no reason to disregard its 
output tonight. 925mb winds will climb into the 30 to 35 knot 
range and glide atop the surface trough. There may be some 
additional assistance from the aformentioned MCV and this should 
help fuel widespread to numerous convection across Central Texas. 
HREF members concur with this assessment and mean QPF values are 
quite aggressive across this area with rain totals in excess of 
4". I'm not completely sold on this potential, but given the very 
moist regime (characterized by 2" PWATs) and the unseasonably 
strong LLJ, it's not out of the realm of possibility. I've 
inserted "heavy rain" wording into the western portions of Central
Texas tonight and there could be a low end flood threat, 
especially across some of the more flood prone areas in Central
Texas. Elsewhere, there will be a chance for a lower coverage of 
showers and thunderstorms. Overnight low temperatures will fall 
into the 70s areawide. There may be a low potential for some 
patchy fog along the Red River where skies.



.LONG TERM... /Issued 347 PM CDT Thu Aug 9 2018/
/Friday through next Thursday/

Showers and thunderstorms may be ongoing at the start of the long
term period Friday morning, forced by robust isentropic
ascent/warm advection over-topping a diffuse remnant outflow
boundary/wind shift across Central Texas. Recent hi-res guidance
is in decent agreement in depicting fairly high precipitation
coverage across Central Texas and up to about the I-20 corridor
through the morning hours, and this seems reasonable given the
anticipated magnitude of lift and copious amounts of moisture.
We've increased PoPs to 70% across a good chunk of our Central
Texas counties Friday morning. PWATs are forecast to push 2" in 
spots here, so heavy rainfall will be possible. In addition,
upwind corfidi vectors of less than 5-10 kts or so, becoming
increasingly boundary-parallel portend some risk for
training/backbuilding cells. Relatively high 1 and 3-hour flash 
flood guidance across Central Texas reduce our concern for
widespread flash flooding at this juncture, but some localized
hydrological concerns may arise generally south of I-20 through
the morning hours. 

This initial round of convection should diminish into the early-
afternoon as the initiating ascent peters out as the low-level
wind field relaxes. Given the anticipated convective coverage
across Central Texas, re-development of showers and storms during
the afternoon is in question, so we've reduced PoPs a bit across
the last few rows of counties. Additionally, if this complex
exhausts a robust enough outflow, it could even hamper convective
chances north of I-20 later in the day. High temperatures will
also obviously hinge on the placement of left over cloud cover and
mesoscale boundaries. The warmest conditions should occur near the
Red River, while locales south of I-20 may have a hard time
getting into the 90s. 

A similar scenario may unfold Friday night into Saturday morning
as moist upglide gets cranking once again, and so high-end chance
PoPs will be advertised across much of North and Central Texas.
These may need to be increased as confidence in the placement of
pertinent mesoscale features increases. Over the weekend, upper 
level troughing will become more established across parts of West 
Texas. This will keep a persistent fetch of deep southerly flow 
and associated moisture transport going across the western half of
Texas. The brunt of large scale ascent looks like it will remain 
just west of our forecast area by the end of the weekend and into 
early next week, and a fairly tight PoP gradient has been 
introduced from west-to- east starting on Sunday. Both the GFS and
ECMWF show some pretty dry air punching into our southeastern and
eastern counties during this time frame, and today's mid-range 
ensemble guidance is similarly advertising the lowest 
precipitation chances east of the I-35 corridor. Assuming this 
upper low doesn't pivot any farther west than currently 
advertised, some of our far western counties may benefit from 
decent wetting rains Sunday-Tuesday. 

By the middle of next week, the persistent upper troughing and
associated broad cyclonic flow overhead may begin to break down as
the southwestern US subtropical ridge attempts to build back
eastward. Temperatures should rebound into the mid and upper 90s
Wednesday and Thursday, and PoPs will quickly trend downward
through this period. 



Dallas-Ft. Worth    77  92  73  89  74 /  50  50  50  30  60 
Waco                75  93  72  90  74 /  70  70  50  50  60 
Paris               74  93  72  89  71 /  20  30  30  30  30 
Denton              75  93  70  88  72 /  40  40  50  30  50 
McKinney            74  93  72  89  73 /  40  40  40  30  50 
Dallas              77  93  75  91  75 /  50  50  50  30  60 
Terrell             76  93  73  90  73 /  40  50  50  30  40 
Corsicana           75  91  73  90  73 /  50  70  50  50  50 
Temple              75  93  74  91  72 /  70  70  50  50  60 
Mineral Wells       73  91  70  86  71 /  50  50  50  40  60