Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 180039 AAB

Area Forecast Discussion...UPDATED
National Weather Service Norman OK
739 PM CDT Tue Apr 17 2018

Amended TAFs to include smoke based on recent model run. Expect
smoke to impact most sites coincident with frontal passage
potentially producing IFR to LIFR visibilities, though there is
still a lot of uncertainty in how low visibilities might go as
well as how long smoke might linger.



.PREV DISCUSSION... /issued 610 PM CDT Tue Apr 17 2018/

Gusty south winds will continue into the evening. A cold front
will move through quickly overnight bringing gusty northwest
winds. With ongoing fires in western Oklahoma, these northwest
winds are expected to bring smoke just southwest of KOKC and
KOUN. However, if winds don`t shift quite as much as expected,
KOKC and KOUN could be impacted with reduced visibilities sometime
between 6z and 12z.


PREV DISCUSSION... /issued 352 PM CDT Tue Apr 17 2018/

The main focus continues to be on Fire Weather concerns in the near
term (see Fire Weather Discussion below). Otherwise the focus is on
the potential for beneficial rain late Friday through Saturday

The strongest wind gusts today have been where the deepest mixing
is occurring, west of a sharpening dryline in western Oklahoma. A
shortwave trough traversing the central and northern Plains this
afternoon will force a cold front into northwest Oklahoma by early
evening, with a continued southeast trek across the area during
the mid-late evening. Early tonight, post-frontal northwesterly
winds sustained around 20-25 mph with gusts to around 35 mph are
expected. Current plans are to let the Wind Advisory expire at 8pm
since by then diurnally driven deep mixing will have subsided by

We added a small area of smoke near ongoing 34 complex and Rhea
fires through the afternoon, and then expanded the area this
evening with strengthening low-level inversion. For now we`ve
focused near and downwind of ongoing fire activity in limited
distance but an expansion further into OKC metro area could be
needed. Smoke could reduce visibilities and impact aviation.

Cooler temperatures (around normal for mid-April) and decreasing
northwesterly winds are expected tomorrow in the wake of the
departing shortwave and cold front. Tomorrow night, there may be a
sufficient period of light/calm winds on the southern edge of
surface high pressure passing to our north to allow for good
radiative cooling and mid-30 degree minimum temperatures, possibly
lower, across northern Oklahoma. This could cause some patchy
frost. For now, we`ve included this where confidence is highest,
over north-central Oklahoma.

Surface winds will turn southern Thursday in response to the next
approaching system. It`s much more closed off and at a lower
latitude favoring more meridional mean flow across the area, and
less opportunity for deeply mixed/downsloped plume to
significantly increase temperatures. So, near normal temperatures
and increasing deep moisture are expected. Some minor differences
in medium range guidance exists relative to the time range, but
confidence in the extended portion of the forecast is above
average. ECMWF/EPS are slower, and GFS/GEFS is slightly faster,
but each show a similar track of the closed low at 500 hPa over
our southern counties through Saturday night. This is not an
optimal track or characteristic for significant instability, and
so the severe potential at this times appears limited and
marginal, generally near and south of the Red River. It is
however, a good orientation for widespread measurable rainfall
including amounts of an inch to possibly two inches.

We adjusted temperatures much closer to raw guidance for Saturday
given expected clouds and precipitation. Further lowering of
forecast temperatures may be needed.


Critical to extreme fire weather conditions continue this
afternoon across western Oklahoma where fuels are volatile and RH,
values are very low, and southwesterly winds are strong. A wind
shift is expected with a cold front this evening. By early
evening, the cold front will bring a shift to northwesterly winds
in northwest Oklahoma (around 8pm for Woodward area, and around
9pm or just after for Dewey County). Northwesterly winds will
continue to be strong but not quite as gusty overnight, subsiding
toward morning. RH should rise to above 30 percent at most
locations during the predawn hours, but then will drop again
tomorrow morning.

RH values tomorrow afternoon could fall as low as around 12
percent across portions of western Oklahoma and western north
Texas. Meanwhile, winds should steadily be decreasing. Elevated to
near-critical fire weather conditions will result, and briefly
critical conditions may occur.

Lighter winds and higher RH are expected Thursday through the



Oklahoma City OK  51  73  40  69 /   0   0   0   0
Hobart OK         50  75  40  72 /   0   0   0   0
Wichita Falls TX  55  76  41  74 /   0   0   0   0
Gage OK           46  71  37  70 /   0   0   0   0
Ponca City OK     49  71  35  68 /   0   0   0   0
Durant OK         59  74  44  69 /   0   0   0   0


OK...Red Flag Warning until midnight CDT tonight for OKZ004>006-

     Wind Advisory until 8 PM CDT this evening for OKZ004>006-009>011-

TX...Red Flag Warning until midnight CDT tonight for TXZ083>089.

     Wind Advisory until 8 PM CDT this evening for TXZ083>085-087-088.



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