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

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FXUS64 KFWD 181714 AAB

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1114 AM CST Sat Feb 18 2017

No major changes to the current forecast other than to tweak cloud
cover across the northern rows of counties based on latest
satellite imagery. Skies are mostly sunny across a good portion of
North Texas which should allow temperatures to climb into the
upper 70s and lower 80s. Lingering cloud cover will keep highs in
the 60s near the Red River and into our northeast counties. Other
than some tweaks to the hourly major changes planned.

We are still monitoring the potential for severe convection
tomorrow afternoon/evening across parts of North Texas and an
eventual line of showers and thunderstorms that may produce some
heavy rainfall across our eastern counties. No major changes in
the short term guidance is noted...although the latest GFS does
detach the upper low a little farther south on Tuesday which is
considerably slower than its previous runs. This should have
minimal impact on North Texas weather as the main convective line
will have moved to the east. It could result in a little more
cloud cover and perhaps some wrap around light precipitation
across our southeast counties into Tuesday morning. Even if this
scenario does play is unlikely that the upper low would
become cut off as upstream flow remains progressive.



/ISSUED 538 AM CST Sat Feb 18 2017/
/12Z TAFs/

Low clouds have already cleared out of KACT and are starting to
slowly erode from west to east across the Metroplex. By 15Z,
anticipate the MVFR cigs will have eroded to the east of the DFW
Metroplex airports, but could possibly be a little slower to
fully clear KDAL. VFR conditions are expected for the remainder of
the day with south winds at 10 kts or less. This evening, the
winds will shift to the east at the DFW airports, but remain south
and southeasterly at KACT.

Another surge of MVFR and IFR cigs is expected late this evening
and tonight, but timing is a little challenging. Will return MVFR
cigs at all the airports at 05-06Z with a lowering to IFR a few
hours after that. In addition, some BR may cause minor reductions
in visibility.

Outside of the time period of this valid TAF, showers and storms
are expected to impact the airports Sunday afternoon through
Monday morning. Scattered showers are possible Sunday afternoon
but storms are more likely Sunday evening into the overnight
hours. Some of the storms in the evening hours and possibly
overnight could be severe with a threat for damaging winds, hail,
and heavy rainfall. An isolated tornado cannot be ruled out.



.PREV DISCUSSION... /ISSUED 318 AM CST Sat Feb 18 2017/
An upper low can be seen on satellite exiting the ARKLATEX region
and heading for the Mississippi Valley. Typically we would
experience veered surface winds in the wake of the system.
Instead, a southerly fetch continues across North and Central
Texas due to the development of a deeper upper level trough along
the West Coast (which has already provided excessive rainfall
across California) and its resulting lee side surface troughing.
A deck of stratus quickly spread north overnight along the I-35
corridor within the deep fetch of low level moisture. The low
clouds and breezy conditions have kept temperatures above forecast
lows in most locations, with the exception being the far west
counties where drier air still lingers.

The trend this weekend will be continued above-normal temperatures
and increasing moisture in advance of the West Coast system. The
upper trough is progged to cross the Desert Southwest and
Northern Mexico over the next 24 hours, and continue east into
West Texas on Sunday. Forcing for ascent will arrive Sunday ahead
of the trough but should be meager during the morning hours. There
may still be warm/moist advection showers and perhaps a few
storms across the western counties in the morning, where chance
POPs will remain. Convection will likely increase in coverage as
it spreads east during the afternoon due to strengthening deep
layer forcing, added moisture and the development of surface
based instability.

There are still substantial model discrepancies with regard to
convective parameters and the overall chances for severe weather.
The NAM continues to be aggressive with both CAPE and shear when
compared to other models, with the most recent run indicating CAPE
at or above 2000 J/KG and bulk shear values on the order of 60
KT. The GFS indicates about half the CAPE advertised by the NAM,
but still shows bulk shear around 50 KT. This should still be
enough for at least a low-end severe threat with both damaging
winds and large hail. The best chance for strong to severe storms
would be during the 21Z to 03Z time frame when maximum
instability is in place.

The strongest ascent will occur after 00Z in a region near the
I-35 corridor and will spread east during the evening and
overnight hours. This may allow the ongoing scattered convection
in the late afternoon to grow upscale into a linear MCS as
activity spreads east. This may also lead to a transition from a
severe threat to a locally heavy rain threat as showers and storms
affect the eastern half of the region, where PWATs are forecast
to climb into the 1.3 to 1.5 inch range.

So at this time, it still appears that the severe threat will be
highest along and west of Interstate 35 during the afternoon and
early evening, while the localized heavy rain threat would be
highest east of the I-35 corridor during the late evening and
overnight hours. That said, we are still about a day and a half
away from the event and and will refine the details as the system
evolves and fresher model data arrives. One commonality in the
latest model guidance is the progressive nature of the system.
Thunderstorms should move east of the forecast area Monday
Morning, with perhaps some lingering stratiform precipitation
Monday afternoon.

A cut-off low will then develop at the base of the trough on
Tuesday and move southeast across the Gulf of Mexico through
Thursday. This will leave North and Central Texas beneath an upper
ridge, leading to warm and dry weather Tuesday through the end of
next week.



Dallas-Ft. Worth    77  58  75  60  73 /   0   5  50  70  30
Waco                81  60  76  59  73 /   0  10  50  70  30
Paris               67  55  76  60  68 /   0   5  20  70  60
Denton              72  56  73  58  72 /   0   5  50  70  20
McKinney            68  56  75  60  71 /   0   5  50  70  40
Dallas              76  59  76  61  72 /   0   5  50  70  30
Terrell             71  58  77  61  71 /   0   5  40  70  60
Corsicana           79  60  78  61  72 /   0   5  40  70  60
Temple              82  61  76  59  74 /   0  10  50  70  40
Mineral Wells       78  55  74  55  75 /   0   5  60  70  10



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