Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 181303 AAA
AFDOUN

Area Forecast Discussion...UPDATED
National Weather Service Norman OK
803 AM CDT Tue Apr 18 2017

.UPDATE...
Removed a few counties from the Dense Fog Advisory in parts of
western and northwestern Oklahoma.

&&

.DISCUSSION...
Dense fog with visibilities 1/4 mile or less in some locations
will continue this morning mainly east and southeast of a Hollis,
Oklahoma to Anadarko to Enid to Ponca City line.

Fog has lifted into a low level stratus cloud layer west of the
line mentioned above due to increasing low level winds. Thus,
dense fog is no longer expected in these locations.

Products have been updated.

MBS

&&

.PREV DISCUSSION... /issued 640 AM CDT Tue Apr 18 2017/

AVIATION...
18/12Z TAFs.
LIFR/IFR conditions will prevail through at least 15Z at most
terminals with main restriction being FG central/southwest
Oklahoma and KSPS. Cigs/vsby will improve after 15-17Z with
increasing flow and mixing especially northern and western
Oklahoma. VFR should be in place by 18Z. There are signs of
IFR/MVFR conditions again after 09Z tonight but confidence not
high enough for inclusion this forecast.

PREV DISCUSSION... /issued 354 AM CDT Tue Apr 18 2017/

DISCUSSION...
Primary forecast focus is on fog this morning and thunderstorm
chances returning late Wednesday continuing through Friday.
Highlighting heavy rainfall and severe storm potential.

Through this morning, developing areas of dense fog will continue
to be a challenge. Scattered to broken cirrus, the result of
convection across portions of eastern Texas, will continue to
slowly exit eastward through sunrise. West and along the western
edge of this shield, areas of fog and stratus have persisted since
early this morning, building quite a wide swath from north Texas
into western and central Oklahoma. Visibilities and cloud heights
have varied greatly at times, but since 2 AM, many sites have
started to tank, to 1/2 to 1/4mi visibility. A dense fog advisory
is in effect through the morning for all of western north Texas
and most of central and western Oklahoma.

Fog should begin to dissipate late in the morning through Noon.
Brief ridging building in from the southwest across the region
will result in warmer than average temperatures, highs in the
upper 70s/lower 80s, along with clearing skies in the afternoon.

Wednesday, positively tilted 500mb ridge will continue to promote
warmer temperatures, with boundary layer flow tapping into the Gulf,
keeping bumping already moist dew points, in the upper 50s/lower 60s
to the mid 60s across most of central and eastern Oklahoma by the
afternoon. Through the day, a frontal boundary will drop south
across Kansas, interacting with the dry line over western Kansas,
moving into a well mixed boundary layer with an axis of 1500 to 2000
J/Kg MLCAPE forming along the boundary by the late afternoon/early
evening. Expect thunderstorms to develop along the front, in Kansas,
gradually building south into north central and northeastern
Oklahoma as an MCS, laying down a cold pool to help reinforce the
cold fronts push southward into Oklahoma by day break.

Thursday, expect the remnants of overnight convection to be
ongoing across portions of eastern into central Oklahoma, along
the cold front, which will slow, becoming near-stationary by the
late afternoon nearing the Red River as a mid-level trough
approaches off the western high plains. As Vivek alluded to in the
Monday afternoon AFD, increasing isentropic ascent across the
region will combine with impressive precipitable water values
>=1.20in, resulting in widespread shower and thunderstorm
development along and north of the frontal boundary. Given the
stationary boundary locally heavy rainfall is possible, which may
lead to an increased flooding risk, especially overnight into
early Friday across portions of northern Oklahoma. Bufr profiles
across portions of western and northwestern Oklahoma reveal steep
mid-level lapse rates, along with elevated instability; combined
with modest effective shear values, some updrafts may be capable
of large hail development Thursday night. Hence the SPC day three
marginal drawn up by Joey and Brian.

Friday morning, scattered showers and thunderstorms will likely be
ongoing across portions of the region and this will play a major
role in how things evolve through the day. At present, the GFS
remains more bullish with the progression and strength of the
500mb trough as it digs off the Rockies compared to the ECMWF.
Either solution, the risk of heavy rainfall will continue across
portions of Oklahoma, but given the variability, the exact
location and axis of heaviest rainfall remains hard to pin down.
At the moment, it`s looking likely 2.00 to 3.50 inches of rain,
widespread, could result from Thursday through Friday across
portions of central and north central to northeastern Oklahoma,
with locally higher amounts more than possible. Given recent
rainfall, flooding concerns remain elevated on Friday.

As for severe storms, Friday, the impact of the ongoing convection
through the morning hours will have an obvious impact on where, if
any, suitable warm sector will reside and the potential for severe
thunderstorms. At present, given the various solutions, it appears
some recovery may occur along and near the Red River Valley,
including far southern Oklahoma into north Texas, with storms
primarily developing along the front as it advances south/southeast
overnight into early Saturday.

Kurtz

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  78  61  80  60 /   0   0   0  10
Hobart OK         78  61  82  59 /   0   0   0  10
Wichita Falls TX  80  60  84  63 /   0   0   0   0
Gage OK           85  61  87  54 /   0   0   0  20
Ponca City OK     79  61  82  58 /   0   0   0  50
Durant OK         78  61  81  65 /   0   0   0  10

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...Dense Fog Advisory until 10 AM CDT this morning for OKZ008-012-
     013-017>020-023>048-050>052.

TX...Dense Fog Advisory until 10 AM CDT this morning for TXZ083>090.

&&

$$

17/10



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