Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 182143

Area Forecast Discussion
National Weather Service Norman OK
443 PM CDT Sun Mar 18 2018

...Mesoscale Update...


Overall, latest surface and satellite observations and short term
model guidance show a less than impressive severe weather setup.
Our confidence in convective initation across southwest Oklahoma
into western north Texas has declined significantly. Convection
is more likely across the northern half of Oklahoma this evening
and overnight, although its intensity is in question.

Latest satellite shows departing lead shortwave trough and
associated convection moving out of the forecast area. In its
wake, subsidence has tempered cumulus development and the chances
of convection across western north Texas and southwest Oklahoma
seem very low. Latest surface observations show sharpening
dryline across west Texas extending from just east of Amarillo to
east of Guthrie and intersecting an east-west oriented surface
front south of our area. This is where the most robust convection
and resultant severe weather threat may form later this afternoon
and early evening.

Short term model guidance still shows strengthening
southeasterly low-level flow/theta-e advection ahead of the
dryline eventually reaching northwest Oklahoma this evening. This
may result in weak destabilization up into northwest Oklahoma,
and as forcing for ascent from eastward moving compact closed mid-
level low increased, convection should develop by early evening
across the eastern Oklahoma and Texas Panhandles. These storms
will move into northwest Oklahoma early-mid evening and continue
eastward early tonight. Although kinematic fiels are fairly strong,
instability is expected to be weak. Steep mid-level lapse rates
may support marginally severe hail. Strong/severe wind gusts are
also possible, although forecast soundings show boundary layer
that is less than optimal for damaging wind. Strong forcing from
advancing Pacific front merging with dryline should result in
linear evolution fairly quickly this evening and storms will move
fairly quickly east across roughly the northern half of Oklahoma
through late evening into early tonight.



.PREV DISCUSSION... /issued 300 PM CDT Sun Mar 18 2018/

A strong storm system moving into the southern Plains will bring
rain and thunderstorms to Oklahoma and north Texas though Monday
night. There is a complex mix of elevated instability and vertical
wind shear this afternoon, and it will remain complicated into
tonight. Based on the forecasts of these parameters, plus the
output of Convection-Allowing Models (CAMs), it appears that the
most likely scenario consists of at least three separate
areas/times of convective development.

First, the existing storms over central and north-central Oklahoma
are likely to remain non-severe, as they continue to travel to the
northeast this afternoon and perhaps early evening.

Second, there is a possibility of storm development in
northeast/north-central Texas this afternoon or early evening. Any
storms that can develop in this environment would have a solid
chance of becoming a supercell storm. The risk of supercell storms
diminishes quickly with northward extent, as the surface warm
front over north Texas is unlikely to move much farther north, and
the relatively cooler/drier air under the elevated frontal surface
will adversely affect storm development. In addition, short-wave
subsidence is probably occurring in the region, which will further
limit the likelihood of storm development.

Finally, the most likely area of severe weather will be over
northwest and north-central Oklahoma late this evening and
overnight, as elevated storms are likely to develop closer to the
upper-level circulation. Wind shear will be very strong, and the
modest amounts of instability should be enough to support elevated
supercell storms. This situation would most strongly favor large
hail, but strong winds reaching the surface can`t be ruled out.

As the system moves off to the east tomorrow, brisk west winds
will turn generally northerly during the day, as cooler air moves
into the region. Sufficient moisture will continue rain chances in
northern Oklahoma into tomorrow night. A few thunderstorms will
be possible with the cool air aloft, but severe storms will be
unlikely after tonight.

A mild and "quiet" period will extend from Tuesday into early
Friday, before the next storm system arrives. There is still a lot
of difference between the medium-range forecast models, so it is
hard to say exactly what will happen from Friday into the
weekend. A "chance of thunderstorms" seems most appropriate for
most of our forecast area for most of the Friday night through
Sunday periods. As is usually the case, the rain chances are
higher east/lower west.



Oklahoma City OK  64  45  53  38 /  80  10  10  10
Hobart OK         66  46  57  36 /  60   0   0   0
Wichita Falls TX  71  50  63  39 /  40   0   0   0
Gage OK           67  41  48  31 /  20  60  10  10
Ponca City OK     61  47  53  36 /  60  70  20  30
Durant OK         65  50  67  43 /  40  20   0  10




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