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

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FXUS64 KFWD 201753 AAC

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1253 PM CDT SAT AUG 20 2016

/18Z TAFS/

Areas of rain continue across much of North and Central Texas this
afternoon ahead of a cold front that is moving into the region.
The front itself is rather weak but is accompanied by some
slightly drier air behind it. For the remainder of the
day...scattered showers and a few thunderstorms will continue to
be possible...mainly south of the front and south of the Metroplex
airports. Some light rain will persist for another few hours at
the major airports. With the rain...cigs temporarily drop to MVFR
then lift to VFR as the precipitation ends. It is looking a little
more likely that the boundary will move into the Metroplex and at
least a light wind shift can be expected. Will have winds at
33006KT after 21Z. By late this evening...these winds should go
LGT/VAR. Additional showers may develop along and north of the
boundary late tonight so will have some VCSH and -RA through early
Sunday morning.

Farther south at Waco...better rain chances are expected through
tonight. VFR cigs will generally prevail but will become MVFR in
precipitation. The front looks like it will hang up north of
Waco...keeping precipitation chances going well into Sunday.



A pretty complicated forecast is starting to develop for the next
48 hours where a few mesoscale features may have significant
impacts on where and when heavy rain occurs across North and
Central Texas.

Showers and isolated thunderstorms continue this morning across
much of the region, ahead of a cold front that is still
approaching from NW Texas and Oklahoma. Earlier this morning, the
rain generated a few outflow boundaries that helped to push the
rain south and is now focusing new convection in our Central Texas
counties. For the afternoon hours, these boundaries will continue
to aid in the development of new convection and the highest
chances for rain will be generally along and south of Interstate
20. Additional showers and storms may form near the front as it
moves in this afternoon and will keep 60-70 PoPs in our northern
counties. Heavy rainfall will continue to be a threat with
flooding the main hazard. The Flash Flood Watch remains in effect
through Sunday evening.

The next mesoscale feature that complicates the forecast is a
decaying MCS west of San Antonio. The latest MSAS analysis
analyzes a surface low between Sonora and Junction which is now
being detected in surface obs and on the mosaic radar loop.
Latest model runs are consistently highlighting the Hill Country
for the development of deep convection tonight and Sunday. This
convection may assist in the development of a warm-core low
somewhere across the Hill Country. If this happens, it could
result in a tight gradient of heavy precipitation in or near our
southern counties. Right now, the models are inconsistent with
the track and location of this system, but this is to be expected
as the resolution of the deterministic models is usually too low to
resolve these smaller scale features. Also, where the surface
front stalls could have significant impacts on our rain chances.
Will wait on the remainder of the Hi-Res guidance before
determining PoPs for tonight and tomorrow and what the rainfall
threat/totals will be for the remainder of the weekend, but still
think rainfall chances through the weekend remain fairly high.



Widespread heavy rain is expected again across a good portion of
North TX today and tonight. Additional heavy rain will be possible
again on Sunday and Sunday evening. There may be a brief respite
from the precipitation late Tuesday into early Wednesday, but rain
chances are forecast nearly every day next week.


.SHORT TERM (Today through Monday)...
The main challenge this morning will be the cessation of the
loosely-defined convective complex across western North TX and
southwest OK. AMDAR, WSR-88D VWP, and RAP model output suggest
that low level south-southwest flow at around 25-35 knots will
continue to overspread a good portion of North TX this morning.
With GPS and satellite-derived PWAT values in excess of 2" across
the area, I feel that there is a good bet for at least some brief heavy
rain with a fair amount of moisture transport, across our northern
tier of counties from about the Sherman-Denison area westward
towards Bowie. While the LLJ will likely continue to veer and this
activity will decay---there is the potential for the regeneration
of activity as the cold front, currently across northern OK,
slides southward and interacts with any residual outflow.

Current output from the operational HRRR and TTU WRF both show a
rapid uptick in convection along the I-20 corridor, a result of
what I believe to be a fair amount of mass convergence along the
front and outflow boundary. However, with the front still across
northern OK and the upper trough responsible for a bulk for the
southward progression of said front lifting off towards the
northeast, it appears possible that the front may stall a bit
further to the north than previously thought. As a result, I went
ahead and added a few of our northern most counties to the Flash
Flood Watch. Regardless--- most of the heaviest rain should be
focused near the surface front and subsequent 925/850mb surfaces.
Where these boundaries set up today and tonight is likely where
the axis of heaviest rainfall will reside. Given the very moist
environment and the potential for training convection, it will not
be out of the question that 2" per hour rainfall rates will be
possible. Unfortunately, it is conceivable that this axis
establishes itself right along the I-20 corridor.

For tonight into Sunday morning---Heavy rainfall will continue to
be a threat through tonight as synoptic scale ascent (entrance
region of the upper jet) is expected to continue to overspread the
area. There is a suggestion in the model fields that some sort of
MCV may develop across the Concho Valley. The latest run of the
NAM brings a higher swath of QPF a bit further to the north than
previous runs. The 06 UTC NAM solution is now a bit more in line
with that of the 00 UTC ECMWF brings it into better agreement with
the ECMWF. Output from the tail end of the HRRR and TTU WRF do
show slightly more impressive simulated reflectivity across this
region which adds confidence to introduce Likely PoPs along and
southwest of a Graham to Mexia line through Sunday AM.

For Monday---Rain chances will continue on Monday as the upper air
pattern remains very zonal. The resultant lee-side cyclogenesis
should result in good south flow which should lift what`s left of
the old baroclinic zone towards the north. With continued
WAA and moisture transport, chance PoPs were retained across the
entire CWA, with the better rain chances west of the interstate 35


.LONG TERM (Tuesday through Friday)...
For Tuesday---Rain chances will continue as warm/moist air
continues to be transported northward with a pretty stout lee-
cyclone across SW KS. Right now, the overall coverage looks to
really be highest across northwest zones early in the day and I
have maintained the highest PoPs across this area. For Tuesday
night, little to no precipitation is forecast across North and
Central TX as the synoptic scale lift appears displaced to the

For Wednesday and beyond---the better rain chances will return to
the forecast for late Wednesday into Thursday as another cold
front is expected to slide southward towards the region. With the
airmass across the region not being scoured out, there`s a good
chance that heavy rain will be possible, mainly along the northern
third of North TX. Into the weekend, will broad brush PoPs across
the entire CWA as there is too much uncertainty with regards to
where the front will end up.



Dallas-Ft. Worth    82  71  82  72  87 /  80  80  50  40  40
Waco                84  70  82  72  88 /  90  80  60  40  40
Paris               81  69  85  69  86 /  80  60  40  20  40
Denton              82  69  85  69  86 /  90  70  50  40  40
McKinney            82  70  85  70  86 /  80  80  50  30  40
Dallas              83  72  83  72  87 /  90  80  50  40  40
Terrell             82  71  83  71  86 /  90  80  50  30  40
Corsicana           85  72  82  73  87 /  90  80  60  30  40
Temple              84  72  83  71  87 /  80  70  70  40  40
Mineral Wells       84  67  81  68  83 /  90  80  60  40  50


.FWD Watches/Warnings/Advisories...
Flash Flood Watch through Sunday evening for TXZ091>093-100>104-


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