FXUS64 KOUN 261135

Area Forecast Discussion
National Weather Service Norman OK
635 AM CDT Wed Apr 26 2017

The April 26-27, 2017 12 UTC TAF discussion follows:


Overall, a low confidence aviation forecast through early this
afternoon. MVFR to IFR ceiling restrictions associated with low
stratus are expected to continue across most terminals through
this morning. The exception might be southwest Oklahoma and
adjacent north Texas where generally VFR ceilings are expected.
Periods of light rain may impact terminals across western and
northern Oklahoma this morning as well. Ceilings are expected to
transition toward VFR from west to east this afternoon.

Gusty northerly winds will continue through this afternoon before
weakening this evening. Winds will become southerly toward the end
of the TAF period as a surface ridge shifts eastward.



.PREV DISCUSSION... /issued 423 AM CDT Wed Apr 26 2017/

Primary forecast challenge is the potential for severe weather and
heavy rainfall late Friday into Saturday.

For today, showers and thunderstorms will remain possible this
morning across southeast and south central Oklahoma as a cold
front shifts southeastward. Strong cold air advection and limited
solar insolation behind the cold front will result in a rather
cool day with temperatures around 20F below average. Some remnant
showers will be possible, especially across west central and
northern Oklahoma through this morning as the upper-level trough
shifts eastward.

For Thursday into Thursday night, a fast-moving shortwave trough
will pass by the Plains. Some showers and isolated storms will be
possible near the Kansas/Oklahoma border in association with the
wave. The attendant cold front is expected to shift southward into
Oklahoma through Thursday night.

For Friday, model consensus indicates >=65F dewpoints will advect
northward to at least south central and southeast Oklahoma in
association with a warm front. This will result in moderately
unstable airmass, along and south of the warm front, with MLCAPE
>= 3000 J/kg by late afternoon. Effective bulk shear is forecast
to be >50 knots. The combination of shear and instability will
provide a parameter space that will be favorable for supercells
with all potential hazards in the warm sector.

The 26/00Z GFS, NAM, and ECMWF still indicate quasi-steady or
even slight mid-level height rises late afternoon/early evening,
which results in some uncertainty on whether surface based
convection will initiate late afternoon. Even so, guidance
indicates a the triple point may develop as the remnant cold
front intersects the dryline/warm front intersection either in
north Texas or southern Oklahoma. Near and northeast of this
triple point will be the most likely area for surface-based
convective initiation.

There also continues to be uncertainty on the northern/western
extent of the warm sector. The the 26/00Z ECMWF has the 65F
isodrosotherm to near I-44 at 00Z, while the NAM and GFS keep the
boundary/greater moisture a couple counties farther south. The
location of the warm front will modulate the northern extent of
surface-based convection, so its eventual location is critical
for any attendant tornado risk.

By late evening into the overnight, increasing isentropic ascent
(augmented by a strengthening low-level jet) will result in
widespread showers and thunderstorms, along and north of the warm
front. Elevated instability/effective bulk shear will result in
severe weather potential even north of the front with large hail
being the primary hazard. Flooding will become an increasing
hazard Friday night into Saturday--especially across southeast
Oklahoma where precipitable water values will approach 2.00" by
Saturday morning.

Significant precipitation should come to an end by Saturday
evening; however, wrap-around showers will be possible across
northern Oklahoma into Sunday. Abundant cloud cover and lingering
showers will keep temperatures well below average for Sunday
afternoon. This will lead to a cold night with lows in the 30Fs
and 40Fs by Monday morning. Another cold front may approach the
area Tuesday into Wednesday of next week.



Oklahoma City OK 55 42 71 54 / 20 10 10 10
Hobart OK 61 43 78 52 / 20 0 10 10
Wichita Falls TX 63 45 83 58 / 10 0 0 0
Gage OK 60 43 74 46 / 20 0 10 20
Ponca City OK 56 39 65 50 / 30 10 20 40
Durant OK 64 43 74 60 / 60 0 0 0




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