Hail and Damaging Wind in Texas, April 21, 2018

Area Forecast Discussion
National Weather Service Fort Worth TX
659 AM CDT Sat Apr 21 2018

.AVIATION...
/12Z TAFS/

Morning satellite and surface observation data show that low
clouds continue to spread north and east with MVFR/IFR cigs/vis
now located from Mineral Wells to Waco and back to the southwest.
We can expect these lower cigs to continue to spread into the
region as low level moisture is pulled northward. Radar imagery
shows a large area of mainly showers to the northwest of the major
airports but there are some embedded thunderstorms as well.
Through the remainder of the morning, there should be an increase
in the coverage of showers across much of North Texas and we'll
show an abrupt deterioration in conditions around 14Z. For now,
we'll keep mainly showers through the morning, although they may
be accompanied by a period of IFR cigs through midday into the
early afternoon hours.

Later this afternoon as the whole storm system moves east, a cold
front will begin to move into the region. Scattered thunderstorms
are expected to develop by 21-22Z to the northwest of the major
airports and should consolidate into a broken line into the
evening hours. We'll include a VCTS in the Metroplex at 23Z with a
TEMPO for TSRA from 23-01Z. Convective chances will be 1-2 hours
later at Waco. The afternoon/evening thunderstorms will be
accompanied by a cold front and wind shift to the northwest. MVFR
cigs are expected to persist through the overnight after the
precipitation has ended with some clearing expected later in the
day on Sunday.

Dunn

&&

.SHORT TERM... /Issued 257 AM CDT Sat Apr 21 2018/
/Today and Tonight/

After a couple of fantastic days across North Texas to end the
week, changes are rapidly occurring to start the weekend.
Water vapor imagery shows a large upper low moving out of the
4-corners region and into the Plains early this morning. As it
does, strong low level warm moist advection is helping an already
large cloud shield expand north and east. Most areas will be
overcast by sunrise with cloud heights falling through the
morning.

Regional radar imagery shows that most of the ongoing showers and
thunderstorms are still mainly across Oklahoma, but as stronger
warm advection spreads south and east beneath an increasingly
diffluent upper jet, we should see an expansion southward of the
showers and thunderstorms through the morning hours. The best
combination of moisture and lift will persist across North Texas
through early afternoon as a surface low over West Texas starts to
move eastward. The exact track of this low will have implications
mainly on our temperature forecast, as the warm sector will remain
to the east and south of the track. We should see temperatures
warm into the upper 70s across our southwest counties while areas
north of I-20 to the Red River will likely stay in the 60s.

Highest rain chances through midday should be across the northern
half of the CWA closely tied to the strong low level warm
advection. As the upper low continues eastward, this initial wave
of precipitation will also begin to shift east. A cold front will
begin to slide southward into the region this afternoon, and will
likely serve as a focus for additional showers and a few
thunderstorms into the evening hours. Given the extent of the
cloud cover currently observed, it appears unlikely that we'll see
significant breaks and destabilization this afternoon ahead of the
cold front. That being said, several of the high-resolution
models do show thunderstorms developing along the cold front late
this afternoon into the evening. There will be an axis of
instability, aided by steepening lapse rates in vicinity of the
upper low, along and ahead of the cold front late this afternoon
across our northwest counties into the I-35 corridor. Scattered
thunderstorms that develop along the front could become semi-
organized given the strong deep layer shear although there should
be a tendency for them to quickly become elevated. These would
pose mainly a low- end severe hail risk. If any storms can
actually become surface based ahead of the front then they would
have an attendant damaging wind threat.

Precipitation should end from west to east tonight with slightly
cooler air spilling into North Texas along with breezy northwest
winds. Low level moisture will linger through the night with
cloudy conditions persisting.

Dunn

&&

.LONG TERM... /Issued 257 AM CDT Sat Apr 21 2018/
/Sunday Onward/

While showers and thunderstorms will have exited the forecast area
by Sunday morning, cloud cover will linger through much of the day
as moisture wraps around the departing low. Our western zones may
begin clearing out by midday, but expect our northeastern areas
to remain overcast into the afternoon. Have kept temperatures
cooler in these areas with highs likely struggling to reach the
mid 60s, but temperatures will climb into the 70s to the west and
south where some sunshine will occur in the afternoon. Breezy
northwest winds at 15-25 mph will prevail through much of the
day.

It will be a dry start to the week with a gradual warm-up as upper
ridging occurs between systems. Highs will climb into the 70s on
Monday with some 80s likely by Tuesday. Moisture however, will be
slow to return during this time without a favorable southerly
fetch, and dewpoints are expected to hold in the 50s. Moisture
return will not be aided by the next approaching shortwave which
will be pivoting through northwest flow aloft over the Central
Plains late Tuesday. This storm track is quite unfavorable for
pulling moisture back into the region which will limit the extent
of rain and thunderstorm chances as it arrives on Wednesday.

By Wednesday morning, the upper disturbance will be on our
doorstep along with its attendant cold front. Showers and a few
thunderstorms should accompany the front's passage as it moves
through the forecast area throughout the day. Barring any drastic
changes to the anticipated environment, strong or severe storms
appear unlikely, owing to a lack of instability due to meager low-
level moisture and unimpressive lapse rates. Models still disagree
with the timing of the front with the GFS being several hours
faster than the latest ECMWF, and these timing inconsistencies
will likely continue for a couple more days. Regardless, Wednesday
will be substantially cooler and rainy for a large portion of the
forecast area. High temperatures will likely occur in the morning
prior to the front's arrival, and many areas may spend the
majority of the day in the 50s under cloudy skies.

A lull in rain chances should occur on Thursday with a slight
rebound in temperatures, but the break will be short lived as
another northern stream shortwave dives southward by Friday.
Models have been quite variable through the extended portion of
the forecast, so confidence remains low for next Fri/Sat at this
time. However, a second strong shortwave and some lingering
moisture warrants the inclusion of some low PoPs to end the week.
Temperatures are expected to remain near or slightly below normal
during this time period.

-Stalley

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    67  52  69  50  75 /  90  30   5   0   0
Waco                71  52  71  49  77 /  50  40   5   0   0
Paris               65  52  64  50  70 / 100  80  10   0   0
Denton              65  50  67  48  74 / 100  30   5   0   0
McKinney            65  51  65  49  73 / 100  50  10   0   0
Dallas              68  52  68  51  75 /  90  40  10   0   0
Terrell             66  53  67  50  75 /  90  60  10   0   0
Corsicana           68  54  69  50  75 /  70  60  10   0   0
Temple              73  53  74  50  77 /  50  40   5   0   0
Mineral Wells       69  49  69  45  75 /  80  20   0   0   0

&&

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

Hazardous Weather Outlook
National Weather Service Fort Worth TX
258 AM CDT Sat Apr 21 2018

TXZ091>095-100>107-115>123-129>135-141>148-156>162-174-175-220800-
Montague-Cooke-Grayson-Fannin-Lamar-Young-Jack-Wise-Denton-Collin-
Hunt-Delta-Hopkins-Stephens-Palo Pinto-Parker-Tarrant-Dallas-
Rockwall-Kaufman-Van Zandt-Rains-Eastland-Erath-Hood-Somervell-
Johnson-Ellis-Henderson-Comanche-Mills-Hamilton-Bosque-Hill-Navarro-
Freestone-Anderson-Lampasas-Coryell-Bell-McLennan-Falls-Limestone-
Leon-Milam-Robertson-
258 AM CDT Sat Apr 21 2018

This Hazardous Weather Outlook is for North and Central Texas.

.DAY ONE...Today and Tonight.
An increase in thunderstorms is expected across the region this
morning. Thunderstorms will become more numerous in North Texas
throughout the day with coverage remaining more scattered across
Central Texas. The main hazard through early afternoon will be cloud
to ground lightning.

Later this afternoon or evening, a few strong or possibly severe
storms may occur along a southeastward-moving cold front. Hail near
the size of quarters and strong winds would be the main hazards if
stronger storms are able to develop. In addition, heavy rain may pose
a threat for minor flooding, especially along and north of
Interstate 20. Storms are expected to end from west to east Saturday
night into early Sunday morning.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.
Thunderstorm chances will return to all of North and Central Texas
Tuesday night through Wednesday night, and again on Friday.

.SPOTTER INFORMATION STATEMENT...
Limited spotter activation may be requested late this afternoon or
evening.

Special Weather Statement
National Weather Service Fort Worth TX
906 AM CDT SAT APR 21 2018

TXZ091-092-102-211430-
Cooke TX-Montague TX-Wise TX-
906 AM CDT SAT APR 21 2018

...SPECIAL WEATHER STATEMENT...

At 906 AM CDT, Doppler radar was tracking a strong thunderstorm near
Forestburg, or 16 miles north of Decatur, moving northeast at 55 mph.

Half inch hail will be possible with this storm.

Locations impacted include...
Gainesville, Muenster, Lindsay and Forestburg.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm. Seek
a safe shelter inside a building or vehicle.

&&

LAT...LON 3383 9718 3383 9720 3380 9721 3378 9719
      3376 9719 3372 9716 3372 9711 3375 9708
      3371 9703 3330 9758 3345 9774 3387 9729
      3386 9726 3389 9724
TIME...MOT...LOC 1406Z 224DEG 48KT 3347 9755

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Special Weather Statement
National Weather Service Fort Worth TX
945 AM CDT SAT APR 21 2018

TXZ092-102-103-211530-
Denton TX-Cooke TX-Wise TX-
945 AM CDT SAT APR 21 2018

...SPECIAL WEATHER STATEMENT...

At 945 AM CDT, Doppler radar was tracking a strong thunderstorm 9
miles east of Decatur, moving northeast at 55 mph.

Half inch hail will be possible with this storm.

Locations impacted include...
Gainesville, Sanger, Decatur, Krum, New Fairview, Callisburg, Lake
Kiowa, Ray Roberts Park Johnson Branch and Valley View.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm. Seek
a safe shelter inside a building or vehicle.

&&

LAT...LON 3363 9694 3351 9694 3309 9743 3324 9759
      3372 9712 3372 9711 3375 9708
TIME...MOT...LOC 1445Z 221DEG 46KT 3325 9743

58