Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 250915

Area Forecast Discussion
National Weather Service Norman OK
415 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 conda little itions
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 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
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.



Oklahoma City OK  85  51  54  41 /  10  40  40   0
Hobart OK         88  50  61  43 /  10  30  40   0
Wichita Falls TX  93  57  63  45 /  10  20  20   0
Gage OK           80  43  60  42 /  10  50  30   0
Ponca City OK     83  49  53  37 /  10  50  50  10
Durant OK         84  65  68  43 /  10  30  40  10




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