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

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FXUS64 KFWD 201147

Area Forecast Discussion
National Weather Service Fort Worth TX
647 AM CDT Fri Apr 20 2018

/12Z TAFS/

An upper level storm system to the west will continue to send a
steady stream of high clouds across the region today. Meanwhile,
surface high pressure will slowly move to the east allowing winds
to become a little more southerly. VFR conditions should prevail
through most of the period, although later tonight better moisture
will begin to spread northward. Showers and a few thunderstorms
will likely be ongoing late tonight across parts of West Texas
and Oklahoma. These will steadily advance eastward into Saturday.
As the main surge of moisture arrives during the mid morning
hours, we should see ceilings begin to rapidly lower. Widespread
MVFR cigs are expected by 14Z across North Texas along with
scattered showers and a few thunderstorms. Rain/storm chances will
persist through much of the day Saturday before ending from west
to east during the evening.



.SHORT TERM... /Issued 323 AM CDT Fri Apr 20 2018/
/Today and Tonight/

Morning water vapor imagery shows a large upper low spinning over
the southwest U.S. with subtropical moisture streaming northeast
into Texas. This system will spread into the Plains later tonight
with rain/storm chances increasing into the weekend.

At the surface, high pressure is centered over the upper
Mississippi Valley leaving our region on the southern periphery
with light east-northeast winds and relatively dry air in place.
This surface high will shift to the east later today allowing
winds to become more southerly and better moisture to be
transported northward. Dewpoints currently in the upper 30s and
lower 40s should steadily climb through the day. With a steady
stream of high cloudiness expected today, highs will top out in
the upper 60s to near 70 degrees.

By tonight, as the upper low gets closer, large scale forcing for
ascent will increase across the southern Plains. The strongest
lift will be centered to our northwest across parts of Oklahoma
where scattered showers and a few thunderstorms are expected to be
ongoing through the night. Some of this activity will likely
spread into our northwest counties after midnight with rain
chances continuing to increase into Saturday.



.LONG TERM... /Issued 323 AM CDT Fri Apr 20 2018/
/Saturday Onward/

The main focus through this portion of the forecast is the
potential for widespread rain/storms on Saturday, including a low
potential for strong/severe storms and some minor flooding.

On Saturday morning, a swath of rain with embedded thunderstorms
will be in progress across parts of North Texas, spreading in from
the west. This first wave of activity will be due to strong
isentropic ascent ahead of a potent upper trough moving eastward
from the Rockies. The highest rain chances through the morning
will be across North Texas, while areas in Central Texas will see
more isolated to scattered coverage. Rain rates aren`t expected to
be very high, and robust convection should be difficult to come
by during this time frame with relatively limited instability.

Later in the afternoon, a surface low will deepen to our west with
a dryline draped south and an advancing surface cold front
entering our northwestern zones. Increasing lift along these
boundaries and increasing dynamic ascent as the upper trough moves
closer should result in a second wave of new convection developing
within the forecast area. This activity will be the main concern
for a few stronger storms, although the strong/severe threat will
depend on the location/speed of the surface boundaries and
available instability. A slower advance of the cold front would
allow more time for southerly winds to usher in higher surface
dewpoints and SBCAPE up the I-35 corridor. If morning activity is
not as widespread as thought, the environment would be able to
destabilize more quickly in the afternoon. While skies are
expected to be mostly cloudy through the day, MUCAPE could still
increase to around 1000-1200 J/kg due to warm/moist advection
within the lowest 1 km. In addition, large bulk shear from a 50+
kt mid-level jet would be supportive of organized thunderstorms. A
threat for marginally severe hail and strong winds would exist
with any storms in this environment from Saturday afternoon
through Saturday evening. While heavy rain is not expected to be
long-lived at any given location, prolonged rainfall throughout
the day could result in some rises along rivers and streams.
However, the threat for flash flooding and rapid water rises
appears relatively low at this time. Overnight, activity will
taper off from west to east as the cold front clears the forecast
area and the upper trough axis shifts east.

Sunday will be mild and dry following the passage of the cold
front. Some post-frontal stratus will linger through the morning
hours, and possibly through much of the day across our
northeastern zones as moisture wraps around the departing low.
Have decreased forecast highs in these areas, but maintained 70s
farther southwest where clearing is expected. We`ll remain between
systems through Monday with upper ridging in place. Temperatures
will be a bit warmer, but still a few degrees below seasonal
normals to begin the week.

A northern stream disturbance will dive southward through the
Central PLains on Tuesday. The orientation of this system will
make it terribly inefficient for moisture recovery across Texas
prior to the arrival of its associated cold front during the
middle of the week. Clear skies and the return of E/SE winds will
cause temperatures to warm into the 80s for most areas Tuesday
afternoon, but dewpoints will hold mostly in the 50s. The
aforementioned cold front is expected to arrive sometime on
Wednesday with chances for showers and thunderstorms accompanying
its passage. Will keep PoPs in the 20-30% range right now from
Tuesday night through Wednesday night until there is better
agreement on timing with this system. With limited moisture and
instability, activity may be relatively scattered and
disorganized. This shot of cool air will knock temperatures back
to below normal for most areas on Wednesday and through Thursday
as well. By late in the week, model solutions diverge
substantially with large deviations in ensembles. Will keep
temperatures near the mean solution with a dry forecast to end the
week at this time.



Dallas-Ft. Worth    69  53  64  49  69 /   5  30  80  70   5
Waco                71  52  68  51  71 /   5  20  60  60   0
Paris               65  50  61  50  62 /   0  20  90  80   5
Denton              68  52  60  47  67 /   5  40  80  60   5
McKinney            67  50  60  49  65 /   5  20  80  70   5
Dallas              69  54  63  50  70 /   5  20  80  70   5
Terrell             68  49  64  50  67 /   5  20  80  80   5
Corsicana           69  50  65  51  69 /   5  20  70  70   5
Temple              71  52  71  51  73 /   5  20  50  50   0
Mineral Wells       70  52  63  46  69 /   5  50  70  40   0



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