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

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FXUS64 KFWD 180030

Area Forecast Discussion
National Weather Service Fort Worth TX
730 PM CDT Sat Mar 17 2018

The main area of showers and thundestorms has moved to the east
of the Metroplex TAF sites. Some showers continue to the west
and southwest that will move east northeast during the next few
hours. Thus have kept a VCTS through 03z. Although not indicated
in the TAFs, there will be chance of showers/thunderstorms Sunday,
but confidence is not high enough to include in the TAFs at this
time. South winds will back around to the east this evening and
then veer back to the southeast overnight. Winds will veer to the
south at 10 to 14 knots by midday Sunday /17z/ and then become
southwesterly by 19-21z as a dryline approaches. Stratus is expected
to spread back into the Metroplex overnight as indicated by the
OVC015 starting at 08z. As winds become more southwesterly
the stratus will shift to the east of the Metroplex TAF sites
17-19z Sunday.

Another round of showers and thunderstorms is expected to move
across the Waco area this evening so have left a VCTS through 04z
with a TEMPO TSRA for the 01 to 03z period. As with the Metroplex
TAF sites, there will be a chance of showers/thunderstorms during
the day Sunday, but confidence is not high enough to include in
the TAFs at this time. Stratus should spread back into the
airport tonight. Have placed BKN015 OVC020 starting at 04z.

z. 58


.SHORT TERM... /Issued 222 PM CDT Sat Mar 17 2018/

Strong to severe thunderstorms are likely this afternoon and
evening. A Severe Thunderstorm Watch has been issued for much of
North and Central Texas through this evening.

A high-quality warm sector airmass is in place across much of
North and Central Texas. A surface low has deepened across West
TX and is located just west of San Angelo as of 2pm. A dryline
extends south from this low and a quasi-stationary front lies to
the ENE roughly along the I-20 corridor. Over the past hour, this
boundary has started a more progressive northward shift as a warm
front and is now draped on the northern fringes of the DFW
Metroplex. Within the warm sector, partial clearing has allowed
temperatures to climb into the upper 70s with dewpoints climbing
in to the mid 60s. These conditions have led to strong surface-
based instability of around 2000 J/kg within the warm sector with
a plume of very steep lapse rates within the 800-600mb layer.

While a few convective attempts have been made within the
forecast area near Stephenville and Comanche, the more robust
convective development will continue to be farther west near the
dryline/front triple point. Lift will be aided by a mid-level
shortwave disturbance that is most identifiable in the 600-700mb
height fields. Lift from this disturbance as well as convergence
along the aforementioned boundaries will continue to result in
convective initiation over the next several hours. We may see 2 or
possibly even 3 waves of convection initiate to the west and move
east throughout the evening as lift continue to act upon the warm
sector airmass.

Storms will have the ability to become strong or severe within
the warm sector with primarily a supercellular storm mode favored
due to large instability and 50-60 kts of deep-layer bulk shear.
Relatively straight hodographs will favor splitting supercells
with both right and left movers capable of surviving. While all
modes of severe weather are possible, hail will probably be the
most common threat through this event. This will be due to the
steep lapse rates located within the hail growth zone, updraft
rotation with primarily a supercellular storm mode, and wet-bulb
zero heights around 9-10 kft. Of course, damaging wind gusts will
also be of concern with more robust convection. The tornado
threat remains somewhat questionable due to the straight
hodographs, weaker low-level flow through about 1 km, and limited
helicity in the 0-3 km layer. In addition, winds within the warm
sector are somewhat veered. If flow was to strengthen at all later
this afternoon or back more to the east, there would be a window
of increased tornado potential. This may end up being most likely
if a supercell storm can become rooted along/near the frontal
boundary where surface winds may be locally backed.

Convection should be on a downward trend later this evening, but
some surface-based instability may last through and even a bit
after sunset. The potential for severe storms, especially severe
hail will linger after sunset and into the overnight hours. The
concern should shift east of I-35 by 9-10pm when convection will
likely have grown upscale and conglomerated into a multicellular
cluster or broken line with a continued hail/wind threat. Am
expecting most convection to have exited the area to the east
around 1-2am with a general lull expected through daybreak Sunday.



.LONG TERM... /Issued 346 PM CDT Sat Mar 17 2018/

/Sunday through Saturday/

A quasi-stationary frontal boundary is expected to extend
along/just north of I-20 at 7 AM Sunday. Some scattered warm
advection showers are possible during the morning. A dryline
is expected to approach the I-35 corridor by early afternoon.
Confidence in how much thunderstorm development we will get during
the afternoon along and east of the I-35 corridor is still not
very high given the expected cloud cover and possible morning
rain. IF storms develop, the shear and instability will be
supportive of some strong to severe thunderstorms with large hail
and damaging winds being the main threats. There would also be a
non-zero potential for a tornado especially north of I-20 where
surface winds should back.

Expect elevated fire weather conditions for areas west of I-35
Sunday afternoon behind the Pacific cold front due to southwest
winds 10 to 20 mph and minimum relative humdities in the teens and
20s. Highs will range from the lower 70s northeast to the mid 80s

Rain chances will end by sunset Sunday and a Pacific cold front
will overtake the dry line during the evening and move through the
region overnight. Winds will become westerly 10 to 20 mph area
wide by daybreak Monday. Lows will be the 50s area wide.

As a surface low moves east from northeastern Oklahoma toward the
Ohio River Valley Monday, winds across North and Central Texas
will shift from westerly to northwesterly at 15 to 25 mph with
some gusts over 30 mph likely. The gusty winds combined with
relative humidities in the upper teens southwest to lower 30s
northeast will result in elevated to near-critical fire weather
conditions Monday. Highs will be in the 70s to lower 80s.

Dry weather is expected for the most of the rest of the week as
upper level ridging builds over the Rockies early to midweek and
then moves into the Plains late week. We will have northerly winds
on Tuesday with highs mostly in the 60s. Temperatures will then
warm for the rest of the week with southerly winds returning.
Highs will be in the upper 60s northeast to upper 70s west
Wednesday, 70s to lower 80s Thursday and mid 70s northeast to the
mid 80s west Friday and Saturday.



Dallas-Ft. Worth    63  81  55  76  48 /  60  30   5   0   5
Waco                63  83  54  79  46 /  80  20   5   0   0
Paris               57  70  51  73  45 /  40  60  20   5  10
Denton              58  78  52  73  44 /  50  30   5   0   5
McKinney            60  76  53  74  46 /  50  40  10   5   5
Dallas              64  80  56  75  48 /  60  30   5   0   5
Terrell             61  78  53  75  47 /  80  40  10   5   5
Corsicana           64  80  54  77  48 /  90  40  10   5   0
Temple              65  84  54  79  47 /  60  20   5   0   0
Mineral Wells       57  83  51  73  42 /  40  20   0   0   0




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