Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 191512

Area Forecast Discussion
National Weather Service Norman OK
Issued by National Weather Service Tulsa OK
1012 AM CDT Wed Oct 19 2016


Only minor tweaks to Pops and Wx have been made to the grids for
this afternoon. See discussion below.



Latest HRRRX data has been pretty consistent in developing
convection this afternoon mainly after 21Z along the frontal
boundary, which lies roughly along the I-44 corridor as of 14Z.
Convection should then increase in coverage and spread southeast
with the front going into the evening. The current grids have
this scenario handled pretty well and only some minor tweaks were
made. Sufficient shear and instability in place to warrant at
least isolated severe hail/wind potential, but the better chances
will be to the east of the forecast area.



.PREV DISCUSSION... /issued 501 AM CDT WED OCT 19 2016/


AVIATION.../For the 12z TAFs/
A weak surface trough oriented southwest to northeast across the
area will separate light north winds to its north from light
southwesterly winds to the south. Exact wind direct today will be
difficult to forecast at KOKC, KOUN, and KLAW, but speeds will be
light leading to little aviation impact. Stronger northerly winds
will arrive behind a cold front tonight. The cold front will move
south across the area moving through northern terminals late in
the afternoon and the southernmost terminals by early evening.
Thunderstorms should be confined to a band that will be positioned
south of all terminals except possibly SPS. Probabilities are too
low to prevail at SPS so we have included a PROB30 for thunder.
MVFR stratus is possible for a few hours behind the front at just
about any of the terminals, but confidence in this occurring is

PREV DISCUSSION... /issued 248 AM CDT WED OCT 19 2016/

A low amplitude shortwave trough evident in water vapor channel
imagery over the central Rockies will emerge onto the central
Plains today. This trough will amplify/dig southeast late today
and tonight forcing a cold front southward through the area.
Residual surface boundary/inverted surface trough will focus
convection later today as moderate surface based instability
develops. We feel more confident on time/space details and have
attempted to convey a more specific spatial and temporal forecast
regarding precipitation chances today and tonight. Convection
should increase markedly in a band near this zone of surface
convergence by mid to late afternoon. The highest probabilities
late this afternoon and evening will be focused near and south
of a line from near Holdenville to Ardmore, with lower
probabilities extending possibly as far north OKC/Norman, but
confidence in convection over the metro is low. As the advancing
cold front will bring cooler more stable air mass southward
probably undercutting convection early tonight. Convection will
diminish or shift south of the area before sunrise Thursday

Moderate instability and weak deep layer shear may support
brief/marginal severe episodes with initial convective development
late in the afternoon. Character of forecast soundings do not
suggest a greater probabilities of one hazard over another (equal
wind and hail threat). Dry mid levels may result in favorable
min/max theta-e differences for severe microbursts, but absence of
a deep well mixed sub cloud layer should keep the wind threat from
being to prolific. Mid level lapse rates are not particularly
steep and this, along with the lack of persistent/well-organized
storms, should limit hail size. Consolidation and expansion of
convection during the early evening should be coincident with an
overall decrease in intensity and waning severe potential,
particularly once convection is undercut by the cold front.

The post frontal cooler air mass will be near or slightly below
normal for mid October. We will need to monitor trends closely for
Thursday night and early Friday morning as a surface high pressure
moves over bringing a period of very light or calm winds and
allowing for temperatures in favored/low lying areas to drop into
the upper 30s. We again went on the cooler side of model guidance,
closer to statistical guidance and bias corrected short term
ensemble guidance.

A warming trend commences late this week and continues into the
weekend. Medium range deterministic and ensemble guidance has been
persistent at showing fairly significant 500 mb height anomalies.
Trends in recent runs have been for a slightly less amplified
expansive mean ridging and a shift further east. This would place
our area in favorable northwest portion of the ridge and allow for
low level veering/downslope and a favorable pattern for anomalous
warmth. We have nudged temperatures upward from a consensus blend
Friday through Monday given this pattern.

On the western periphery of the ridge, models generally agree on a
surge of low level moisture reaching Oklahoma by Monday night or
Tuesday. Large scale ascent may gradually increase by Tuesday as
the ridge shifts east and weakly cyclonic mid level flow
strengthens across the Southwest into the central Plains. Subtle
mid level height falls atop a low level theta-e axis was enough to
broad brush low probabilities Tuesday and Tuesday night across the



Oklahoma City OK  81  53  69  43 /  10  10   0   0
Hobart OK         81  52  70  41 /   0   0   0   0
Wichita Falls TX  86  56  72  45 /  20  30   0   0
Gage OK           77  42  68  38 /   0   0   0   0
Ponca City OK     78  48  68  38 /   0   0   0   0
Durant OK         90  58  73  48 /  40  70  10   0




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