Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 282123

Area Forecast Discussion
National Weather Service Norman OK
323 PM CST Mon Nov 28 2016

Latest upper air analysis shows a deep/broad closed low centered
over eastern North Dakota. One in a series of shortwave troughs
rotating around this closed low is departing the region and
westerly downslope flow in its wake has resulted in pleasant and
mild conditions across the area today. Relatively deep mixing into
stronger mid level flow across the southern portion of our area
has resulted in gusty winds there. This, combined with low
relative humidity values is causing elevated to near critical
fire weather conditions, mainly across western north Texas and
far southwest Oklahoma.

The weather through most of the rest of the week is expected to
be uneventful. A cold front will move through the area tomorrow
bringing cooler temperatures tomorrow and Wednesday. A slight
moderation and near normal temperatures will return for the end of
the week.

Models agree on a fairly classic warm advection/isentropic ascent
precipitation event late Friday and Friday night across much of
the area. The greatest precipitation probabilities are in western
Oklahoma and western north Texas. Elevated instability is absent
so thunderstorms are not expected. Temperatures may be cold enough
for at least a mix of light snow across northern portions of the
area. A thorough assessment of wet bulb temperatures profiles in
forecast soundings, and the top down method was not performed yet
given differences in the model guidance. The more
progressive/phased system depicted by the ECMWF and supported by
its ensemble mean is colder and remains the outlier. The GFS,
GEFS, DGEX and CMC all continue to show a deep cut off low
remaining west of our area through the weekend, and eventually
opening up ejecting northeast early next week. GEFS ensembles are
surprisingly clustered fairly well despite such drastic contrast
with ECMWF/EPS. None of the GFS ensemble perturbations resembled
the ECMWF.

This continues to be a challenging forecast given this dipole of
medium range model output, and marginality of temperatures. A
glance at GFS forecast soundings suggest wet bulb temperatures
will become sufficiently cold for at least a mix of snow and
perhaps all snow across the northern portion of the area Saturday
night. We`ve attempted to represent this in the public forecast
using crude method of using arbitrary surface temperature
thresholds, but further refinement of precipitation
type/transition both temporally and spatially will be needed as
the event nears. As model guidance comes more in line, a more
thorough analysis of the thermal profile will be done and greater
detail/certainty can be conveyed.

Uncertainty is high Saturday and Sunday as models diverge further.
In fact, when looking just at deterministic guidance, our forecast
area spends at least 36 hours between where models depict the
axis of the mid-upper trough. So, the GFS lags behind ECMWF
nearly a day and a half with when the peak period of ascent and
consequently when the highest chances of precipitation arrive.
Given this uncertainty, we have kept probabilities low Saturday
through Monday and there may be a significant portion of that
period where we can remove precipitation chances altogether once
timing discrepancies are worked out. Precipitation type remains a
challenge and our forecast was constructed in such a way as to try
to keep from alternating precipitation types based on diurnal
cycle as best as possible, but this can be difficult at this time
range with such large uncertainties. Based on subtle trends and
to a larger degree the stance of the majority of medium range
guidance (all but ECMWF/EPS), we have kept a slightly warmer
forecast with less coverage of wintry precipitation. This may
change with time, but for now there seems to be only a low
probability of an impactful winter weather event with



Oklahoma City OK  37  60  32  54 /   0   0   0   0
Hobart OK         37  58  31  55 /   0   0   0   0
Wichita Falls TX  43  64  35  57 /   0   0   0   0
Gage OK           30  54  26  53 /   0   0   0   0
Ponca City OK     35  59  31  53 /   0   0   0   0
Durant OK         45  67  38  57 /   0   0   0   0




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