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

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FXUS64 KFWD 210434
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1134 PM CDT SAT AUG 20 2016

.AVIATION...
Decaying area of rain/storms associated with a departing MCV
continues across parts of Central TX tonight. Additional isolated
showers and thunderstorms have developed in its wake which should
continue overnight with the aid of the low-level jet. This
activity is expected to affect the Waco TAF site for at least a
few hours early Sunday morning but should not progress northward
to the DFW Metroplex sites. As a result, have removed all mentions
of showers from DFW area TAFs and have also backed off on the
amount of time that Waco should be affected based on the latest
trends.

Otherwise, calm surface winds will persist overnight in the
vicinity of the stalled front. At the Metroplex sites, some brief
lowered vsbys due to mist will be possible overnight (and has
already been noted at FWS and CPT), but should not persist long
enough to warrant a mention in the TAFs. MVFR cigs may affect the
Waco site around the time that rain may be occurring, but low cigs
are no longer expected at DFW area airports. Winds will increase
during the morning hours and will initially be out of the
northeast before veering to the east or even southeast by Sunday
evening.

-Stalley

&&

.UPDATE...
Recent surface analysis places a slowly moving frontal boundary
from about Texarkana, southwestward to near Hillsboro to Lampasas,
although its exact location is hard to define at this point. To
the north and west of this boundary, drier air continues to advect
towards the Red River, with dewpoints now in the 50s across parts
of Central Oklahoma. Farther to the south, a persistent Mesoscale
Convective Vortex continues to track steadily towards the east
amidst 15-20 kt 850-300 mb flow. Recent IR satellite imagery
reveals cloud tops associated with this feature are now warming
somewhat, and we`ve seen a recent downtrend in reflectivities
from regional radars.

The near term forecast remains complicated--thanks to the
abundance of mesoscale features that will be driving our
precipitation chances overnight. Given the aforementioned 15-20 kt
cloud-bearing flow per recent RAP analyses along with radar
trends, it appears as if the MCV will continue to make steady
eastward progress over the next few hours. This feature should
remain in close enough proximity to our CWA to throw embedded
moderate to heavy rainfall across our southeastern most zones
through midnight.

As the low-level jet begins to increase tonight and overtops a
remnant outflow boundary laid out across the Texas Hill Country,
we should see an expansion in the precipitation coverage. Just how
far north this next round of rain makes it is still in question,
however, with varying solutions afforded by various high-
resolution guidance. For this update, made some significant cuts
to the PoP grids from near the Metroplex and points northwest, and
confined the greatest chances basically southeast of a Palestine
to Temple line. Given the tropical nature to the airmass, any
cells will still be capable of producing hefty rainfall amounts,
although at this time it appears the highest flash flood threat
has shifted just southeast of our CWA. Given the considerable
uncertainties lingering tonight and subsequent impacts on the
evolution of tomorrow`s precip chances, we have elected to leave
the Flash Flood Watch as it is for now, although reduction to the
area may be warranted on the next shift.

Carlaw

&&

.PREV DISCUSSION... /ISSUED 345 PM CDT SAT AUG 20 2016/
Even though the radar has been fairly quiet this afternoon and
the heavy rainfall threat has been minimal so far, the threat for
heavy rainfall continues through Sunday and may be maximized
overnight tonight. The combination of a front, an outflow
boundary, and a MCV are all complicating the rain forecast for the
next 24 hours.

The front is finally making its way southeast across North Texas.
It is expected to stall this evening south of Interstate 20 but
north of Waco and possibly north of Hillsboro, too. Very isolated
convection is currently developing along the front in our area,
but better convection has developed ahead of the front across the
Concho Valley. An outflow boundary from this morning`s rain is
still moving south through Central Texas and is close to exiting
our CWA. This outflow boundary will collide with an MCV over the
Hill Country in a few hours, and its impact on the MCV will need
to be closely monitored. The MCV is currently moving northeast
along a track towards our southern counties of Bell and Milam. The
collision with the outflow boundary could under cut the convection
occurring with the MCV but there may be a short-lived enhancement.
If this MCV is able to persist, it will likely have a significant
impact on our rain chances this evening and tonight and could
increase the threat for heavy rain and flash flooding somewhere
across our south and/or southeastern counties. Keep reading for
additional possibilities and additional information on amounts and
impacts.

Model guidance today has been highlighting deep convection
developing in the Hill Country this evening and overnight. At this
point, it is difficult to say if this deep convection will occur
with the northeastward heading MCV and/or develop around a
surface low currently located between Sonora and Del Rio. The
signal for heaviest rain has been consistently in the Hill Country
and just outside our CWA, but any slight movement to the mesoscale
features could place part or all of the heavy rain in our area. If
this were to happen, the most likely location for heavy rain would
be across our southern and southwestern counties, likely southwest
of a line from Hamilton to Waco to Centerville.

There are two areas of concentration for rain chances and amounts
tonight and overnight. The first will be along the stalled front
where convection is expected to develop late tonight and continue
into Sunday morning. The most likely location for this to occur
will be just south of Interstate 20, but north of a Goldthwaite
to Waco to Palestine line. It does not appear strong convection
will occur as the best dynamics will be south of that area, but
moderate to heavy rain may occur resulting in isolated areas of
flooding. The second area of concern is across the south and
southwest as mentioned above. In our far southwestern counties,
southwest of a line from Hamilton to Waco to Centerville,
significantly higher amounts could occur if the location of the
deep convection is displaced east. In this area, rainfall amounts
near 10 inches could be a possibility. Otherwise, rainfall totals
of 1-3 inches are expected through Monday. However, the rainfall
amounts are likely not to be as significant to the flash flood
threat as much as the rainfall rates which may cause flash flooding
problems.

One possibility that could deter rain chances overnight tonight
is if convection this evening moves east into southeast Texas and
therefore cuts off the moist southeast flow into our region.
Otherwise, we anticipate the heavy rain will continue into Sunday
morning with a weakening of the overall convection during the day.
What happens during the day on Sunday will affect rain chances
Sunday night into Monday. The front looks like it will start
lifting back north Sunday night and there may be scattered showers
and storms that develop in the warm, moist sector as the low level
flow increases overnight.

By Monday, an upper level ridge builds in from the east but we
maintain southwest flow aloft with a persistent upper level trough
to our west. Models indicate the southwest flow will occur down
into the lower levels of the atmosphere with a H850-700 ridge also
to our east. This will allow for some drying of the atmospheric
column. A shortwave trough will pass through the Plains on
Thursday with another trough developing in the west and moving
through the Plains over next weekend.

Regarding rain chances next week, scattered showers and storms
may develop across the region on Monday with better rain chances
across the northwestern half Monday night into Tuesday. Wednesday
looks dry but low rain chances return later in the week as the
first trough moves through the Plains and a front possibly crosses
into the region. Temperatures will warm early next week into the
lower 90s but still no triple digits in sight at this time.

JLDunn



&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    72  83  72  88  74 /  40  30  30  30  30
Waco                72  82  72  87  74 /  80  80  50  30  20
Paris               68  85  69  85  71 /  50  30  30  30  40
Denton              68  85  70  86  73 /  30  20  30  30  40
McKinney            69  85  71  86  74 /  40  30  30  30  40
Dallas              72  84  73  88  75 /  40  30  30  30  30
Terrell             71  84  72  87  74 /  60  50  30  30  30
Corsicana           72  83  72  88  74 /  80  80  50  30  20
Temple              72  83  71  87  74 / 100 100  50  30  20
Mineral Wells       68  83  69  86  72 /  30  30  30  40  40

&&

.FWD Watches/Warnings/Advisories...
Flash Flood Watch through Sunday evening for TXZ129>135-141>148-
156>162-174-175.

&&

$$

26/90



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