Area Forecast Discussion
Issued by NWS Oklahoma City, OK
FXUS64 KOUN 232003
Area Forecast Discussion
National Weather Service Norman OK
303 PM CDT TUE AUG 23 2016
A challenging pattern to forecast continues with regard to timing
and coverage of precipitation chances. Our best success has been
identifying waves in southwesterly mean flow via Water Vapor loop
and adjusting based on other observational data. Short term model
guidance has been reasonable, although some timing issues have been
noted with these small difficult to resolve shortwave troughs.
One of the more significant wave seems to be fairly well resolved
in the latest guidance.
Later this afternoon through early evening there should be a
window for diurnally driven isolated to scattered thunderstorms
primarily across the northwest portion of the area. This is
supported by most CAMs. There is some discrepancy in guidance
with timing and magnitude of the brief period of subsidence in the
wake of this first shortwave trough but we have attempted to add
more spatial/temporal detail into the night. The most likely
scenario is for storms to initiate near a weak confluence zone
roughly along line from roughly Woodward to Alva and move east.
The combination of warming mid levels and subsidence as mid level
ridging briefly builds in later this evening should limit
longevity of storms. So there is some question how far east they
will move or at least how numerous they will be into north-central
Oklahoma late this evening and early tonight.
Latest surface obs show upper 60 to low 70 degree dew points across
the western portion of the area where satellite has shown a
clearing trend and developing cumulus field. The greatest depth
with cumulus is over the southern Texas Panhandle and west
Central Texas and this should be where an increase in convection
will be most notable later this afternoon. Further northwest into
our area, abundant low level moisture and diabatic heating have
contributed to moderate MLCAPE values of at least 2,500 J/kg.
Within a zone of weak low level confluence across the north, at
least isolated convection should form later this afternoon. VWPs
show respectable mid-level flow for August contributing to around
30 to 40 knots of deep layer shear into early evening, supporting
Later tonight, strengthening low level jet and ascent from another
approaching shortwave should support showers and thunderstorms
continuing northeastward from west central Texas into western
north Texas and western Oklahoma. This activity will probably
continue spreading northeast into north central Oklahoma
throughout the early morning. Later in the day with diurnal
heating of moist low levels, instability will increase and
thunderstorms should become more numerous along and near a weak
surface front that should be positioned over southwest Kansas and
perhaps far northwest Oklahoma. Marginally severe storms will be
possible given at least modest instability and anomalous westerly
mid level flow for mid August contributing to around 30 knots
0-6km bulk shear.
Through late Wednesday the southeastern upper high will retrograde
to near the Mississippi River with building heights across the
eastern part of the state. Continued mean troughing to our west
with occasional shortwave troughs traversing the area will result
in precipitation chances continuing into the weekend each day.
Timing of individual waves of convection is difficult enough in
the short term and becomes even more difficult later in the week
through the weekend as spread in deterministic guidance grows with
regard to timing and amplification of shortwaves.
We kept low probabilities into next week but there seems to be
less opportunity for forcing given the evolution of the synoptic
pattern. Mean mid level height rises and relaxing flow aloft is
seen in medium range guidance, but a moist and conditionally
unstable atmosphere remains.
.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK 74 93 71 92 / 10 20 20 20
Hobart OK 73 93 70 92 / 30 20 30 20
Wichita Falls TX 74 95 71 95 / 20 20 10 10
Gage OK 71 91 65 84 / 30 30 50 40
Ponca City OK 75 93 72 90 / 20 30 50 40
Durant OK 73 94 71 95 / 10 0 10 10