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fxus64 koun 251735 

Area forecast discussion
National Weather Service Norman OK
1235 PM CDT Tue Apr 25 2017



Aviation... /for the 18z tafs/
VFR conditions will prevail into the evening. A cold front will
sharpen and move south through mid-late evening. Thunderstorms
will form near and just behind the cold front, first over
southeast Kansas and northeast Oklahoma, and eventually further
south by mid-evening, possibly as far southwest as okc/oun. We
have introduced a period of vicinity thunder and although
confidence is not all that high we also added a tempo group for a
few hours after about 02z. For gag/wwr, showers and possibly a
thunderstorm may move in from the panhandles behind the front
later tonight. For pnc, thunderstorms are most likely east and
south of the Airport, but we did include vicinity thunder. Post
frontal showers seem possible into the night around pnc. MVFR
ceilings will form at most taf sites behind the front and persist
through at least mid-morning.


Previous discussion... /issued 616 am CDT Tue Apr 25 2017/

the April 25-26, 2017 12 UTC taf discussion follows:

no ceilings or visibility restrictions are expected through this
afternoon. Winds across western Oklahoma and adjacent North Texas
will gradually shift to the southwest/west this morning.

A cold front with a northerly wind shift will enter northwest
Oklahoma this afternoon and will progress southeastward through
the evening and overnight hours. Showers and thunderstorms may
develop along the front this evening near kpnc and may build
southwestward toward kokc/koun.

Additional showers/storms will be possible overnight at any
terminal; however, opted to include only at kgag/kwwr/kpnc, where
probabilities are currently the highest.


Previous discussion... /issued 421 am CDT Tue Apr 25 2017/

the primary forecast concerns are the potential for severe
weather this evening and for severe weather/heavy rainfall Friday
into Saturday.

For today, very warm to hot temperatures are expected across the
area. Veering low-level flow and a low-level thermal ridge (850 mb
temps +24c in western north texas) behind a dryline will result
in temperatures well into the 90fs across western North Texas and
adjacent parts of southwest Oklahoma.

Ahead of the dryline, temperatures will still warm well into the
80fs, coincident with the nose of the low-level/850 mb thermal
ridge. The exception will be across far northwest Oklahoma, where
a cold front is expected to enter in the afternoon.

Strong to severe thunderstorms are expected to develop along the
cold front mid to late evening. Initial storms are expected to
develop across southeast Kansas and build southwestward into
northern/northeast Oklahoma. These storms may build as far
southwest as central Oklahoma. Environmental conditions will be
favorable for large hail and perhaps damaging wind gusts with any
linear segments. Additional showers and perhaps isolated
thunderstorms will be possible as the shortwave trough shifts
eastward Tuesday night into Wednesday--especially across the
northern half of Oklahoma.

For Wednesday, expect significantly colder air to advect behind
the front. Strong low-level cold air advection, limited solar
insolation, and lingering showers (associated with the shortwave
trough) will result in high temperatures only the 50fs for many
locations--around 20f below average. There may even be some upper
40fs across the northern Oklahoma.

Another shortwave trough will eject into the plains late
Thursday. Showers and thunderstorms will be possible across
northern Oklahoma as this wave passes by. Limited moisture (due to
wednesday's front) should mitigate any risk for severe weather.

For Friday, the potential severe weather risk and location will
be modulated by 1) moisture recovery northward (i.E., The location
of the warm front) and 2) timing of ascent/surface cyclogenesis.

Currently, it appears the preceding shortwave troughs on
Wednesday and Thursday will mitigate the northern extent of the
moisture recovery/warm sector for Friday. Model consensus would
suggest the warm sector would be confined across
southern/southeastern Oklahoma and adjacent North Texas where
dewpoints may recover to >= mid-60fs. The 25/00z GFS is farther
north and west than the European model (ecmwf) with the placement of the warm
sector (northern extent near I-44).

With regard to timing, significant forcing is offset from peak
heating/instability in the late afternoon. The 25/00z GFS and
European model (ecmwf) even have subtle mid-level height rises across southern
Oklahoma/North Texas Friday afternoon/evening. This brings some
uncertainty on convective initiation. The slower/offset timing of
the forcing also delays surface cyclogenesis and the attendant
low-level wind response. Consequently, low-level hodographs have
a slight weakness around ~1-3 km.

Though these factors may temper the potential for a higher-end
severe event, the overall environmental conditions (effective
bulk shear and instability) in the warm sector will be more than
sufficient for supercells with all potential severe weather
hazards. Any changes in the aforementioned factors will affect
any subsequent forecasts.

By Friday night, increasing isentropic ascent will result in
widespread showers and thunderstorms, even north of the frontal
zone. Sufficient elevated instability/effective bulk shear will
result in the potential for severe storms with a threat for large
hail. Heavy rainfall may lead to flooding during this period--
especially across central, southern, and southeastern Oklahoma.
Precipitable water values are forecast to be >=1.25" Friday night
and are forecast to increase to near 2.00" across southeast
Oklahoma by Saturday morning. Therefore, the zone of heavy
rainfall is expected to shift into southeast Oklahoma on Saturday.

Any significant precipitation is expected to end Saturday evening
(though lingering, wrap-around showers will be possible across
northern oklahoma). Cooler weather is expected in the system's
wake for Sunday before a warming trend into early next week.



Preliminary point temps/pops...
Oklahoma City OK 85 51 54 41 / 10 40 40 0
Hobart OK 88 50 61 43 / 10 30 40 0
Wichita Falls Texas 93 57 63 45 / 10 20 20 0
gage OK 71 43 60 42 / 10 50 30 0
Ponca City OK 82 49 53 37 / 10 50 50 10
Durant OK 84 65 68 43 / 10 30 40 10


Oun watches/warnings/advisories...

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