fxus64 koun 221119 

Area forecast discussion 
National Weather Service Norman OK 
619 am CDT Fri Sep 22 2017 

..aviation discussion... 


for the 12z tafs: 

The only exception to VFR will be a low probability of MVFR 
ceilings at airports in southwest and central Oklahoma and 
western North Texas. Latest 10.3-3.9 micrometer satellite shows 
low stratus moving north in central Texas. Short term model 
guidance may be slightly too aggressive with bringing this stratus 
northward, so we only included a brief tempo group for broken MVFR 
at okc/oun/law/sps. Confidence isn't particularly high. Otherwise, 
gusty south winds will continue and subside at all but western 
Oklahoma airports this evening. 


Previous discussion... /issued 304 am CDT Fri Sep 22 2017/ 

gusty south-southeast winds have persisted overnight particularly 
across northwest Oklahoma. Gustiness should increase area wide by 
mid morning as mixing increases. Conditions shouldn't be too 
dissimilar to yesterday since the synoptic scale pattern will 
change little. Deep western trough will move a little closer but 
still shouldn't have much impact on our weather. Lee surface low 
to our northwest will result in continued breezy south winds 
through the afternoon and into the night, particularly across 
western portions of the area. 

For today's temperatures we went with the higher side of model 
guidance (i.E., Mav) for persistence in a relatively unchanged large 
scale pattern. This is a couple degrees warmer than the previous 
forecast and was the main short term change to the forecast. A 
modest increase in high clouds could temper insolation slightly, but 
there really wasn't much other reason to lower much from previous 
day's temperatures. 

Convective initiation is expected to occur by mid-late afternoon in 
closer proximity to the western trough, from the western side of The 
Caprock into the western end of the Oklahoma Panhandle. Mean 
meridional flow will carry this convection north-northeastward into 
southwest Kansas and will not support eastward propagation into 
our area. Most of the model forecast soundings show sufficient cin 
to prevent convective development across the entire area this 
afternoon, although where deeper boundary layer moisture will be 
present (south-central/southeast oklahoma) cin is minimal by late 
afternoon and it's not totally out of the question that an 
isolated shower/storm could form there. Confidence was not high 
enough to include in the forecast at this time. Day shift will 
need to look at the latest observational data and short term 
guidance and re-evaluate this very low probability scenario. 

There is good agreement among medium range models and their 
ensemble members into the weekend and this leads to a fairly 
confident forecast. The earlier concern was a trend toward a 
slower/deeper western trough and as a result we kept pushing rain 
chances further out in time. The last handful of runs have been 
much more consistent. Showers and thunderstorms will be close 
northwest Oklahoma through Saturday, but the majority of the 
activity will not move into our area until late Sunday and 
especially Sunday night as a shortwave embedded within the 
longwave trough swings through the Central High plains. 

Sunday night into Monday a band of deep moisture sets up across 
western Oklahoma within the core of persistent low level jet/warm 
conveyor belt. Model precipitable water and 850 hpa mixing ratio are at or 
above the 90th percentile. Convection should be extensive and 
locally heavy rainfall/potential flooding will become a 

Tuesday and beyond are less clear as medium range model differences 
emerge. Agreement generally continues with northern stream 
evolution in which GFS, most of its ensembles, and European model (ecmwf) all eject 
western trough eastward through the northern plains. This sends a 
cold front south into our area. The differences in the models are 
with upstream energy and enhancement of southern stream. The GFS 
suite is more progressive while the European model (ecmwf) is more closed off and 
holds an upper low back in the southwest through mid week. The GFS 
may be a little more favorable for another round of precipitation 
in the Wednesday-Thursday timeframe. In this scenario, warm 
conveyor belt could be lifted atop the aforementioned frontal 
slope in a statically stable environment yielding a fairly 
widespread warm advection precipitation event. We'll of course 
have greater confidence as the time nears. 

We lowered temperatures closer to raw guidance early-mid week in 
Post frontal environment with probable clouds and precipitation. 
These scenarios often turn out colder than even the raw guidance 
indicates so a further downward trend in temperatures may be 


Fire weather... 
persistent southerly winds in response to deep western trough will 
continue for the next few days, peaking during the afternoon. 
Temperatures will trend slightly cooler and boundary layer 
moisture slightly higher and so minimum relative humidity values 
won't be quite as low as seen in previous days. Nevertheless, 
elevated thresholds could be at least briefly met across western 
Oklahoma and portions of western North Texas this afternoon and 
again Saturday and perhaps Sunday afternoons. Some initial attack 
fire activity could occur given these conditions. 



Preliminary point temps/pops... 
Oklahoma City OK 90 72 90 68 / 10 10 0 0 
Hobart OK 93 72 90 70 / 10 10 0 10 
Wichita Falls Texas 92 73 92 70 / 10 10 0 0 
gage OK 93 71 88 68 / 10 10 10 10 
Ponca City OK 92 73 92 69 / 10 10 0 0 
Durant OK 91 71 93 69 / 10 10 0 0 


Oun watches/warnings/advisories... 

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