Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 172335

Area Forecast Discussion
National Weather Service Norman OK
635 PM CDT Wed May 17 2017

The May 18-19, 2017 00 UTC TAF discussion is below:


Unrestricted ceilings are expected to become restricted (MVFR) at
some terminals as stratus develops from south to north late
tonight. Greatest confidence for stratus is from I-44 south and
east. Opted not to include in KHBR/KCSM, where confidence is
lower; however, stratus could impact terminals this far west.

Thunderstorms--potentially strong to severe--are expected to
develop toward the end of the TAF period across central and
western Oklahoma. Gusty, eratic winds will be possible within any
thunderstorms. Otherwise, southerly winds should weaken this
evening before becoming gusty by mid-morning.



.PREV DISCUSSION... /issued 410 PM CDT Wed May 17 2017/

Primary forecast focus is on Severe Thunderstorms Thursday and
chances on Friday.

This afternoon, stout southwest/west winds will continue into the
early evening as the surface low continues to lift north/northeast
across the Mid-Missouri valley of Nebraska/Iowa. Winds will relax
through sunset.

Briefing ridging overnight will open the plains to increasing
boundary layer return flow after midnight into Thursday morning.
GOES-16 (Formerly R) low level Water Vapor paints a fairly clear
picture, with the hefty western trough churning over the inter-
mountain west. A diffuse dry line will set up through the day,
with mid-60s, nearing 70s, dew points advecting and pooling across
portions of southern and central Oklahoma and portions of western
north Texas. I prefer not to Re-hash the excellent SPC Day Two
Outlook from Mr. Kerr, so I`ll try to keep this brief. With the
large scale trough anchored near the Four Corners, expect one or
two weak 500mb short wave perturbations to shift eastward over the
panhandles and West Texas plains by midday, with several of the
latest convective allowing models (CAMs) suggesting developing by
mid-afternoon, east of the dry line, within the warm sector,
forced by a noticable 700mb jet and subsequent trough. The latest
Experimental HRRR and Texas Tech WRF have been consistent with
this trend. Although this outcome is less certain, the fact that
it`s been consistent lends some thought to such an outcome. Better
overall certainty in initiation will be nearer the exit region of
the 500mb jet axis over the northeastern Panhandles across
northwestern Oklahoma into southwestern Kansas. The proximity to
the trough allows for greater height falls and steep low level
lapse rates focused near the dry line and frontal boundary
interaction. This suggests far western and northwestern Oklahoma
could see rapid supercell updraft growth, supported by sufficient
deep layer shear and copious amounts of instability. Large
damaging hail, up to baseballs, damaging wind gusts over 70 mph
are possible. Backing surface winds through through 00Z will
increase 0-1km helicity values over 300 m^2/s^2 through 00z, near
initiation. Paired with modest LCLs, tornadoes are possible with
this initial development.

Overnight, storms will grow upscale as the frontal boundary pushes
southeastward into the region, with a line of broken
thunderstorms developing and pushing eastward across central
Oklahoma through the early morning hours, Friday, with damaging
winds and hail the primary concerns.

Friday, not much of a reprieve, with lingering showers in the early
morning before quick recovery ahead of the deepening 500mb trough
over the southern Rockies through midday. Conditions point toward
early afternoon development along the frontal boundary across
central Oklahoma. Hail, wind, and flooding will be the big concerns,
Friday. Given the warm air advection ahead of the front and it`s
orientation, training thunderstorms could easily become an issue,
exacerbating flooding potential. Additionally, low level shear and
lapse rates, along with low LCLs could point toward a narrow window
for a few tornadoes. However, the focus is on the widespread 2 to 4
inches of rainfall that is expected across central into southern
Oklahoma and western north Texas, along with locally higher amounts
resulting in flooding.

Heavy Rainfall and Flooding don`t usually get the headlines, but
it`s nothing to scoff at, and Friday would be a good day to pay
attention to rainfall amounts and to be careful if you are
traveling. Remember, when you come to a flooded roadway, Turn Around
Don`t Drown.



Oklahoma City OK  64  86  66  77 /   0  20  50  60
Hobart OK         59  86  65  80 /   0  60  30  60
Wichita Falls TX  64  89  68  82 /   0  60  40  60
Gage OK           55  84  56  78 /   0  60  60  40
Ponca City OK     61  85  65  77 /   0  20  60  70
Durant OK         72  85  69  82 /   0  20  40  40




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