Severe Thunderstorm Warning 159, NWS Fort Worth, TX

Area Forecast Discussion
National Weather Service Fort Worth TX
342 PM CDT Sun Jul 1 2018

.SHORT TERM...
/Late Afternoon and Tonight/

An MCV aided by a series of southward propagating gravity waves
is generating an area of scattered thunderstorms across the
northwest corner of the CWA this afternoon. This activity will be
mainly mesoscale-driven, so any outflow boundaries kicking south
will need to be monitored for additional development later this
afternoon and this evening. The brunt of this activity will remain
across the northwestern third of the region based on the slow
northeastward drift of the MCV, but slight chance POPs will
continue to be carried as far south as the Interstate 20 corridor
to account for any southward moving outflow. Conditions are right
for a few storms to produce strong downburst winds, and a low-end
severe wind threat will exist in the strongest storms. Subsidence
increases the farther south you go, so it would be very difficult
for any storms to survive south of I-20.

Activity will diminish this evening as instability wanes, giving
way to another warm and humid night. Surface winds have already
weakened compared to the past several days due to a broader
pressure gradient, and will likely remain around 10 MPH or less
during the overnight hours. Lighter and more veered low level
flow should hold off the stratus invasion tonight.

30

&&

.LONG TERM...
/Monday Through Next Weekend/

Winds will be noticeably lighter Monday and Tuesday, but with
thinner boundary layer moisture, dew points should effectively
fall each afternoon. Triple-digit temperatures may be more
widespread, but heat index values should remain below heat
advisory criteria. With drought-stressed (or otherwise dormant)
vegetation, this decrease in moisture could increase the number
of potential fire starts, but the reduced wind speeds should aid
in containment and limit wildfire spread.

Although the heat will persist on Tuesday, ridging aloft will be
steadily losing its grip, giving way to tropical easterlies. The
unsettled weather in the northeastern Gulf will become a deeply
etched trough as it drifts westward early this week. Its
associated cloud cover will begin spilling into East Texas on
Tuesday, but it will be until after dark before any showers and
thunderstorms impact our eastern zones.

Now that this initial easterly wave is only a few days away, some
of the subtle differences among available guidance are becoming
more clear. One of the more significant discrepancies is the
diminishing amplitude of the feature as it approaches our meridian
on Wednesday. The operational GFS maintains cyclonic curvature
into southern Oklahoma though an increasing number of ensemble
members are limiting the northward extent of the wave. The
consensus of synoptic guidance is trending toward a drier forecast
for our north and west. The sharp northwest edge of the
precipitation may be within our CWA, but the clouds should envelop
the entire region, reducing daytime temperatures in all zones.

Precipitable water values will soar over 2 inches, approaching or
exceeding record values for early July. This will greatly enhance
the precipitation efficiency with the convective cells on
Wednesday, and slow storm motion could result in some isolated
flooding concerns. For now, mean areal QPF will remain
conservative. While precip-loading could yield some downbursts,
weak shear and gentle lapse rates should limit the severe threat.

After the midweek wave passes to our west, easterly flow will
prevail during the latter half of the week. This will mean above
normal cloud cover and precipitation chances with near normal
daytime temperatures. More significant troughing may arrive next
weekend.

25

&&

.AVIATION... /Issued 101 PM CDT Sun Jul 1 2018/
Broad cyclonic flow across the northern half of the country is
compromising our upper ridge across its northern flank, allowing
convection to persist ahead of a weak front draped across
Oklahoma. Satellite imagery reveals what appears to be a gravity
wave originating from earlier convection and progressing south,
as well as an MCV north of KABI lifting slowly northeast. These
two features will combine to generate additional thunderstorms
around the Bowie area this afternoon and will likely affect the
UKW arrival gate for the next several hours. Slow southward
development of these storms will become possible associated with
the gravity wave and potential outflow, a few of which may get
within the 25 mile range ring around DFW, so the current TAFs have
maintained the VCTS at DFW, along with AFW and FTW. Adjustments
in timing may be required in later amendments depending on how
convection evolves, and VCTS might even need to be removed if
activity remains to the north. Otherwise, VFR conditions and south
winds are expected area-wide.

30

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    79 102  79 101  80 /  20   0   0   5  10
Waco                75 101  75 101  77 /   0   0   0   0  10
Paris               75  97  75  98  75 /  20   5   5  10  20
Denton              77 102  76 102  77 /  30   0   0   5  10
McKinney            76 101  76  99  77 /  20   0   0   5  10
Dallas              80 103  81 101  80 /  20   0   0   5  10
Terrell             74 101  77 100  77 /  10   0   0   5  20
Corsicana           74 101  76  99  76 /   0   0   0   5  20
Temple              75 101  74 100  75 /   0   0   0   0  10
Mineral Wells       75 103  74 103  75 /  30   5   0   0   5

&&

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

25/30

Hazardous Weather Outlook
National Weather Service Fort Worth TX
345 PM CDT Sun Jul 1 2018

TXZ091>095-100>107-115>123-129>135-141>148-156>162-174-175-021100-
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-
345 PM CDT Sun Jul 1 2018

This Hazardous Weather Outlook is for North and Central Texas.

.DAY ONE...This Afternoon and Tonight.
Thunderstorms are possible through this evening along and north of a
line from Comanche to Dallas to Paris. Downburst winds will be the
primary hazard, and an isolated threat for severe damaging winds will
exist with the strongest storms.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.
Fire weather conditions will become elevated west of Interstate
35 each afternoon Monday and Tuesday.

Thunderstorm chances will return to the area late Tuesday and
continue through next weekend. The peak chances for thunderstorms
will be across Central Texas on Wednesday.

.SPOTTER INFORMATION STATEMENT...
Limited spotter activation may be needed through this evening for
areas north of the I-20 corridor.

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