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

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FXUS64 KFWD 170445
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1145 PM CDT Tue May 16 2017

.AVIATION...
Only minor changes made to previous TAF package as most of the
forecast is still on track regarding overnight convection and MVFR
cigs.

Stratus has been slow to advance northward ahead of the newly-
developed QLCS currently progressing toward North and Central TX.
As a result, have pulled the brief mention of MVFR in advance of
the anticipated convection. In addition, have bumped up the
timing by around an hour from previous TAFs based on latest
guidance, with the line expected to reach Metroplex airports
around 08z or 09z and Waco an hour or two later. The main concern
other than lightning will be gusty winds in the vicinity of this
convection. The line`s intensity by the time it reaches the I-35
corridor is still in question, although most signals suggest that
convection will be sub-severe with outflow rushing ahead of the
storms in a strongly capped environment. Have maintained VCTS but
it is also possible that no thunder occurs depending on how
quickly the QLCS meets its demise.

An hour or two of MVFR stratus may follow the decaying line of
storms early Wednesday morning, but most of the day will feature
clearing skies with breezy southerly winds. A deck of cigs around
5-6 kft should be positioned across eastern portions of TX and
may remain situated over eastern Metroplex airports as well.
Another surge of low MVFR stratus is expected around midnight
Thursday morning and have introduced low cigs at all airports for
this time frame.

-Stalley

&&

.UPDATE...
Our anticipated line of storms formed within the last hour in West
Texas and is already progressing east. The storms ignited along
the dryline as the upper level trough continues to swing through
New Mexico. A Severe Thunderstorm Watch has been issued for our
western and northwestern counties through 5 AM, but tracking the
storms still places them in our western counties around 6-7
UTC/1-2 AM CDT.

Overall, not much has changed in our thinking of evolution. The
00Z FWD sounding indicates a cap remains in place and should
remain in place overnight. A strong 45-55 kt low-level jet will
fuel these storms tonight, with elevated instability of 1000-2000
J/kg and near 40-50 kts of shear. The storms are expected to
remain elevated as they move into North and Central Texas. The
highest severe weather threat will be along and west of Interstate
35/35E with mostly a damaging wind threat and possibly some hail.
However, we still cannot completely rule out an isolated tornado
threat, especially if storms redevelop along a forward surging
outflow boundary. These storms would likely be surface based with
strong southeast flow ahead of the line, and a brief tornado is
possible.

JLDunn

&&

.PREV DISCUSSION... /ISSUED 321 PM CDT Tue May 16 2017/
An upper level low is currently moving east across the
Arizona/New Mexico border and will continue eastward into the
Texas Panhandle this evening. At the surface, a moist and unstable
airmass has become established across much of the Southern Plains
ahead of this system, setting the stage for an active evening and
night across much of TX and OK. Thunderstorms have already begun
to erupt along a dryline over the Texas Panhandle. As the upper
low progresses east, the dryline will also shift eastward with
thunderstorms continuing to develop. Thunderstorms will remain
fairly isolated this afternoon to the west of the forecast area,
but will increase in coverage this evening as stronger forcing for
ascent arrives.

Convective mode will likely be linear by the time storms reach our
western-most counties, which is expected to be around midnight.
Damaging winds should be the primary threat along with marginally
severe hail, though an isolated QLCS-type tornado or two cannot
be ruled out. Convection should begin to decrease in intensity as
it approaches the I-35 corridor during the overnight hours, due
to diminishing lift as the upper low lifts northeastward into the
Central Plains, and a capping inversion strengthens. However, the
presence of a strong low level jet tonight may keep at least a
damaging wind threat in place as far east as I-35. Convection will
continue to weaken as it pushes farther east during the morning
hours, eventually dissipating Wednesday morning. A break in the
weather is expected for the rest of the day Wednesday as
subsidence develops in the wake of the upper level system.

On Thursday, another upper low will have dropped southeast from the
Pacific Northwest, becoming quasi-stationary near the Four Corners
region. Thunderstorms are expected to develop to the west of the
region again along the dryline Thursday afternoon as a lead
shortwave lifts northeast across West Texas. Storms will lift
northeast across roughly the northwestern half of the forecast
area Thursday evening where the strongest forcing will reside.
There may still be isolated storms farther east where strong
warm/moist air advection will persist, and we will keep at least
low POPs going across all of the region. Convection will quickly
lift out of the area along with the initial shortwave late
Thursday night.

A second and stronger shortwave will round the base of the upper
low on Friday, generating another round of dryline activity to our
west Friday afternoon. Storms will become possible across the
western counties Friday afternoon, then increase and spread east
Friday evening as the shortwave continues east into West-Central
Texas. Also, by evening, a cold front will begin moving southeast
into the northwestern zones. The front will continue to provide
focus for additional development overnight Friday night and into
Saturday as it continues to progress slowly southeast. The main
focus will shift from severe weather to locally heavy rain and
flooding by Saturday due to the slow-moving front and persistent
ascent associated with the shortwave. The front will eventually
move into South-Central and Southeast Texas on Sunday as the upper
low ejects northeast and the shortwave moves east of the region.
This should bring an end to precipitation during the day Sunday,
with drier weather continuing into Monday.

A strong shortwave trough will drop southeast from the Rockies
into the Southern Plains late Monday into Next Tuesday. An
attendant cold front will provide focus for another round of
showers and storms Monday night into Tuesday as the shortwave
continues to drop southeast. This will help shift the upper level
pattern to troughing in the southeast CONUS and northwest flow
aloft across North Texas. This type of pattern can be somewhat
unsettled this time of year, so we should continue to see at least
a chance of showers and storms through the middle of next week.

30



&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    70  90  75  90  71 /  70  10   5  20  40
Waco                69  90  74  90  71 /  70  30   5  20  30
Paris               68  83  71  86  70 /  50  20  10  20  40
Denton              68  89  71  90  69 /  70  10   5  20  40
McKinney            69  87  71  88  70 /  70  20   5  20  40
Dallas              71  92  76  91  72 /  70  20   5  20  40
Terrell             70  86  73  88  69 /  70  20   5  20  30
Corsicana           70  88  75  89  70 /  70  20   5  20  20
Temple              69  88  74  89  70 /  70  40   5  20  30
Mineral Wells       65  90  67  90  66 /  80   5   5  20  50

&&

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

$$

26/82



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