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

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FXUS64 KFWD 180054
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
754 PM CDT Mon Apr 17 2017

.UPDATE...
Thunderstorms continue to develop farther and farther south with
time due to the southward push of a strong outflow boundary.
Activity will occur mainly south of I-20 this evening, where
localized flooding will be the main concern. We will need to keep
an eye on Freestone, Leon and surrounding counties where a
cluster of northward moving thunderstorms from a disturbance over
southeast Texas will interact with the outflow generated
convection. The resulting cell mergers could possibly lead to
exceptionally high rain rates for a short period of time. Storms
should then be on a downward trend for the rest of the evening.

Low POPs will be kept generally along and east of the I-35
corridor overnight where a weak upper trough axis will linger.
Some high resolution guidance indicates isolated convection
developing through the late night hours. Activity should remain
below severe limits, but could cause nuisance flooding.

30

&&

.AVIATION...
/ISSUED 644 PM CDT Mon Apr 17 2017/
/00Z TAFs/

Concerns...Precipitation trends the next few hours and IFR cigs
late tonight into Tuesday morning.

A complex of thunderstorms continues to push through Central Texas
this evening, currently affecting KACT. Light rain will linger at
KACT for much of the evening hours. The rain is slowly ending
from north to south across the Metroplex, but some light rain may
linger for a few more hours. Several of the hi-res guidance is
showing additional precipitation developing later this evening and
continuing after midnight. With ample moisture still in place and
the upper level shortwave still over the region, this seems like
a plausible possibility and will carry a VCSH at all the TAF sites
through 06Z at KACT and 10Z at the Metroplex airports.

As this system clears the region tonight and the skies clear, we
anticipate IFR cigs and visby will develop, as early as 10-11Z.
These conditions will likely persist into the mid morning hours,
and then a gradual improvement to VFR by 18-19Z is expected. SCT
to BKN MVFR cigs with bases between 3-5 kft may persist for much
of the afternoon hours.

Looking a little farther ahead, another MVFR or IFR stratus deck
is possible late Tuesday night/Wednesday morning.

JLDunn


&&



.PREV DISCUSSION... /ISSUED 339 PM CDT Mon Apr 17 2017/
It`s been fascinating watching numerous subtle mesoscale features
come together over the last 24 hours or so to initiate two main
areas of deep convection across North and Central Texas (much to
the chagrin of meteorologists across the region). An overnight
complex, which initiated near a stalled front across northern
Oklahoma, has managed to track all the way into the I-20 corridor
as of early this afternoon. After remaining nearly stationary for
the better part of the morning, some degree of cold pool
organization appears to be ongoing at this time, and an outflow
boundary is presently surging southward towards a Cisco to
Weatherford to Waxahachie to Athens line. As a result, while
locally very heavy rainfall leading to sporadic instances of
flooding can be expected, widespread flash flooding does not
appear to be in the cards today and tonight.

The environment out ahead of this feature is quite moist and
unstable, with dewpoints in the mid 60s resulting in MLCAPE values
in the 1000-2000 J/kg range south of I-20 with little to no
convective inhibition. From our morning sounding, sufficient CAPE
in the hail growth zone is present, so even though mid-
tropospheric winds will remain light, storms this afternoon and
into the evening will be capable of producing hail approaching
severe limits along with gusty downburst winds near 50 mph. The
primary location of concern for strong to marginally severe storms
is presently shifting to areas along and south of the I-20
corridor.

The next mesoscale feature of interest is a nocturnal MCS-induced
MCV (mesoscale convective vortex) and a mid-level perturbation
presently moving northeastward out of the Texas Hill Country.
Based on recent satellite and radar trends, it appears the present
motion should keep the brunt of this activity south of our area,
but confluence zones around this feature will act as additional
foci for storm development this afternoon and evening.

It appears that much of this activity, both from the southward-
moving MCS across the Metroplex, and any activity induced by the
Hill Country MCV, should start to wane with the loss of heating
later this evening. As a result, we`ll trend likely PoPs downwards
into the chance and slight chance categories overnight across our
south and eastern counties. One thing we will need to keep tabs
on is where this aformentioned MCV/upper-low hangs out tonight,
as this will have the potential to focus additional bouts of
moderate to potentially heavy rainfall. At this time, the
strongest signal for this appears to be relegated south of our
area of responsibility.

The next change was to add a mention of fog to the worded
forecast across the entire region. Skies will likely begin to at
least partially clear tonight. This, combined with recent rainfall
and light winds should lead to the development of radiation fog.
Some of this fog may become dense, and we will highlight this
possibility in the Hazardous Weather Outlook. Low convective
chances will linger on Tuesday, mainly along and east of I-35
given the soupy airmass and lingering features zipping around in
the mid-level flow, but these will be ending Tuesday night.

Southerly low-level flow will continue on Wednesday which will
keep the moisture in place across the region. However, with
shortwave ridging overhead, we`ll keep the forecast dry, but will
need to monitor for potential sea-breeze storms moving towards our
southeastern counties.

Our next cold front is still on track to move towards the Red
River Thursday evening. Given the departure of the associated
upper-level support into the Great Lakes, it does appear this
front should begin to stall just north of the Red River--as has
been advertised by the ECMWF for several runs now. Still,
convergence along this feature may be enough to set off a few
showers and storms north of I-20 overnight into Friday morning.

The main show will then approach Friday and Friday night. A stout
capping inversion may actually keep much of Friday dry, save for
some storms north and west of the Metroplex and perhaps some
streamer showers across the rest of the forecast area. As
significant forcing for ascent approaches and lifts and erodes
this cap, expect storms to develop along the approaching cold
front Friday evening. Additional storms may also develop behind
the front given how far back the main vorticity lobe is forecast
to be. Mid-level lapse rates of 7-8 C/km and effective bulk shear
values near 50 kts portend a risk for severe thunderstorms with
this system. Lingering uncertainties regarding the pertinent
severe threats and locations will be ironed out over the next few
days, but this will be a system to watch closely.

Strong cold advection on Saturday will result in breezy to windy
conditions with north winds funneling in cooler air, and a dry
forecast is in the cards into early next week.

Carlaw



&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    62  84  64  85  68 /  20  10   5   5   0
Waco                61  81  64  83  66 /  50  20  10  10   0
Paris               61  80  63  83  65 /  20  20   5  10   5
Denton              59  83  64  84  67 /  20  10   5   5   0
McKinney            60  81  64  82  66 /  20  20   5  10   5
Dallas              63  84  65  85  68 /  20  20   5   5   0
Terrell             62  82  63  83  66 /  20  20  10  10   5
Corsicana           64  81  64  82  66 /  50  20  10  10   5
Temple              61  80  64  83  66 /  60  20  10  10   0
Mineral Wells       58  84  63  86  65 /  20  10   0   5   0

&&

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

$$

91/30



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