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000
FXUS64 KOUN 221526
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
1026 AM CDT Thu Jun 22 2017

.DISCUSSION...
Clouds from former Tropical Storm Cindy will continue to affect
parts of central and eastern Oklahoma through this evening. Rain
associated with the storm should stay east of our forecast area.
We expect afternoon showers and thunderstorms to develop over
eastern Colorado, and advance southeast toward Oklahoma this
evening, much like the last couple of days. Those storms should
again die out as they move east of the 100th meridian.

No changes are planned to the forecast this morning.

CmS
&&

.PREV DISCUSSION... /issued 354 AM CDT Thu Jun 22 2017/

..Aviation Discussion...

AVIATION...

For the 12z TAFs:

VFR conditions and light winds will prevail. Thunderstorms may
impact GAG/WWR again after about 02z this evening, followed by a
cold front that will bring stronger northeasterly winds (around 10
to 15 knots). Convection, or at least outflow from convection
causing a wind shift, may impact CSM later in the evening.
Probability is too low for inclusion at this time.

BRB

PREV DISCUSSION... /issued 338 AM CDT Thu Jun 22 2017/

DISCUSSION...
The main forecast challenge will be timing of precipitation
chances over the next several days. For the last couple of
afternoons, convection that has formed along the higher terrain of
the Raton Mesa in northeast New Mexico extending northeastward
along/near a persistent surface trough. Storms then grew upscale
into clusters and line segments eventually reaching northwest
Oklahoma in a weakened state by mid-evening both Tuesday and
Wednesday. Current radar mosaic as of this writing shows an MCV
drifting south in Ellis County, but precipitation has trended down
significantly with measurable amounts not expected for the rest of
the night.

On the synoptic scale, a ~594 decameter 500 mb high was centered
over southern Arizona and we were on its northeastern periphery
with weak mean northwesterly flow aloft. Tropical Storm Cindy`s
circulation crossed the coastline near the Texas/Louisiana border
and is now moving northward. Convection associated with Cindy
should mostly stay southeast of our area, although high clouds
will increase today.

Thunderstorms should form again this afternoon in the same areas,
near/along a surface trough that will again be oriented southwest
to northeast, and augmented by local scale terrain influences.
Furthermore, a cold front sent south by a transient closed low
over Manitoba will be moving southward. This, in combination with
slowly southward shifting and flattening upper high and attendant
subtle mid-level height falls will contribute to more forcing and
perhaps greater upscale growth of convection during the evening.
Thunderstorms should move into northwest Oklahoma after around 02z
and weaken as they progress south-southeast. Given expected storm
mode by that time, along with deep mixing and steep low level
lapse rates with fairly sizeable min/max theta-e differences in
the vertical, damaging winds should be the primary severe threat.
This threat will decrease markedly with southward/eastward
extent.

The forecast becomes less clear Friday into the weekend. A
reoriented and weaker upper high to our southwest will result in
strengthening mid-upper west-northwesterly flow aloft. The
cold front that passes by on Friday will become increasingly
diffuse to our south and low-level flow will veer to
easterly/southeasterly with deepening moisture late Saturday into
Sunday. All the while, weak cyclonic flow associated with a fairly
broad based and increasingly amplified eastern CONUS trough will
keep the potential for terrain induced convection/MCS activity
across our area. Timing these will be difficult, but we attempted
to apply some pattern recognition and climatology with this
pattern by assigning higher values each night and lower values
during the day.

On Friday, given the proximity of the remnants of Cindy, low
level flow may tend to veer ahead of the advancing cold front
limiting convergence. Furthermore, thermal structure north of the
front seen in forecast soundings would generally be unfavorable
for convection. Models tend to overdo post-frontal convection in
these scenarios. Somewhere along/near I-40 and generally east of
I-35, isolated to scattered convection will probably form near the
front. Although moderate instability is seen in the models,
effective shear (~15-20 knots) is insufficient for storm
organization and short lived perhaps briefly intense storms
should occur. An isolated microburst/damaging wind scenario may
develop for this section of the forecast area for at least a brief
time late Friday. A second area of development may be across
western north Texas where moist easterly flow and remnant frontal
convergence/weak baroclinicity will be present into the evening.
This may be enhanced somewhat by weak forcing for ascent on the
far southern end of Great Lakes transient shortwave trough.

We have lower probabilities for Saturday than the model blends
given expected relatively stable post-frontal air mass. There is a
reasonably good convective QPF signal in models initiating in the
higher terrain and moving through the Panhandles into our area
during the evening/overnight however so we have increased
probabilities during that timeframe.

Although this goes against mid/late June climatology some, we`ll
need to watch for perhaps some fog but more likely low stratus
that could persist into the morning across southern portions of
the area. Some of the models are saturated in the low levels for a
fairly significant depth and this is probably the source of
overzealous precipitation probabilities behind the front.
Saturday will be the coolest day of the next several with some
locations up to 15 degrees below normal. Temperatures may be lower
if stratus persists longer than currently expected, particularly
across the southwest portion of the area.

BRB

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  92  71  86  65 /   0   0  20  10
Hobart OK         95  72  89  65 /   0  10  30  20
Wichita Falls TX  93  72  97  67 /   0   0  30  40
Gage OK           96  69  80  62 /   0  40  30  10
Ponca City OK     92  71  82  61 /   0  10  20  10
Durant OK         89  73  94  68 /  10  10  30  30

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...None.
TX...None.
&&

$$

23/26