Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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FXUS64 KOUN 280438

Area Forecast Discussion
National Weather Service Norman OK
1030 PM CST Sun Nov 27 2016

MVFR ceilings at OKC/OUN/PNC are expected to become VFR by 09Z.
Otheriwse, a narrow window for thunder to impact SPS between 06Z and
09Z. Southwest to west winds will increase across much of the area
Monday morning and continue into the aftn before diminishing. Sites
in central and southern OK into north Texas will see gusts of 25-



.PREV DISCUSSION... /ISSUED 909 PM CST Sun Nov 27 2016/

Recent runs of the HRRR develop convection southwest of Wichita
Falls between 1 and 2 am with further develop to the north and
east through 7 am. However, some weak returns around Big Springs
and Synder may indicate storms may form before midnight.
Regardless, it appears south central and southeast Oklahoma will
have a good opportunity for showers and storms tonight with strong
winds and hail possible with the strongest storms. Storms will
move very quickly and storm tops should be below 30k feet.


.PREV DISCUSSION... /issued 244 PM CST Sun Nov 27 2016/

Latest water vapor satellite imagery reveals one lead shortwave
trough emerging from the Central Rockies onto the Central High
Plains, and another moving through Nevada. The first shortwave
trough has resulted in strong surface pressure falls in the lee of
the Rockies and latest surface analysis shows a 988 mb surface low
in far northwest Kansas. Strong winds have resulted across
Oklahoma and western north Texas. Maximum gusts have been around
40 mph across northwest Oklahoma. The stronger winds have been
confined to the Oklahoma and Texas panhandles where deeper mixing
is occurring and gusts over 50 mph have been common. The strongest
winds in our area through sunset will be where partial clearing
and deeper mixing has occurred across far northwest Oklahoma. As a
Pacific cold front moves east and winds veer, gusts approaching 50
mph may be possible across this area until mixing subsides early
this evening. Otherwise, low stratus has been persistent across
the entire area all day and this will continue into the night with
gradual clearing from the west.

Short term model guidance continues to show a low-level theta-e
corridor ahead of the front slowly moving eastward. As
aforementioned lead shortwave lifts northeast the front/moisture
axis will linger and slowly move eastward. Cooling aloft/ascent
ahead of the next shortwave trough (now over Nevada and moving
quickly east) will overspread this moist axis and should result in
isolated/scattered convection developing late this evening and
continuing into the night. Low level moist advection beneath
steepening mid level lapse rates should contribute to at least 500
J/kg to perhaps 1,000 J/kg MUCAPE from parcels that should
originate just above the surface. This combined with strong deep
layer shear in excess of 60 knots should lead to organized/intense
thunderstorms and a few may be marginally severe. Marginally
severe hail is the most likely severe threat given somewhat
stable boundary layer limiting the wind/tornado threat. Having
said that, given the very strong momentum aloft, a few severe wind
events are possible. Spatial details of convection are not quite
clear but it does appear the potential exists further northwest
than originally thought, possible as far northwest as north-
central Oklahoma, by late evening. Convection will probably expand
in coverage toward the south and east and be most numerous later
in the night across south-central and especially southeast

Rain chances will end early tomorrow as the second shortwave
trough departs. A period of mean westerly/downsloping flow should
result in slightly above normal temperatures tomorrow. The
combination of a drier air mass and breezy conditions may lead to
elevated to near critical fire weather conditions across western
portions of our area (see Fire Weather Discussion below).
The weather will be uneventful through Thursday with the only
notable change being a cold front forced by head another shortwave
trough rotating around large/deep Midwest closed low. This cold
front will arrive on Tuesday and keep temperatures from warming
nearly as much as is anticipated tomorrow. Highs in the 50s will
be common in all but the southern portion of the area where the
front will arrive later. Even colder temperatures are expected
Wednesday as northerly flow and cold advection keep temperatures
in the 40s across the northern portion of the area. Low amplitude
ridging aloft will bring moderating temperatures (to near late
November normals) on Thursday.

A complicated scenario develops by Friday and especially this
weekend. Inconsistencies and disagreements among medium range
guidance leads to a low confidence forecast. Beginning late
Friday and persisting through the night, most of the deterministic
and ensemble guidance shows a broad/weak isentropic ascent
scenario with sufficient moistening for precipitation. This
occurs ahead of a deepening increasingly closed off mid-upper low
that will be positioned to our west. Variances in the synoptic
scale details with the pattern across the Midwest into the
Northeast have implications for precipitation type for us. Some
solutions are more robust with a cold surge into our area early on
that would be sufficient for snow across at least the northern
portion of the area. However, the GEFS mean and ECMWF
deterministic have trended less anomalously negative with 500 mb
heights across the northeast indicated that the first cool surge
may be less significant and confined to just the northern portion
of the area. The new 12z ECMWF is the most concerning for our area
with regards to cold/snow and potential winter weather impacts. It
shows the Southwest closed low phasing with northern stream wave
and accelerating east, passing to our south. This scenario would
bring a second more defined cold surge southward coincident with
large scale ascent spreading over the area. The GFS and its
ensembles as well as the Canadian are more closed off with this
system and have it out of phase with this northern stream wave,
however. If medium range guidance trends toward the latest ECMWF,
this would necessitate higher precipitation probabilities for
Saturday and more potential for snow.


Mimimum relative humidity values are expected to fall to between
20 and 25 percent across much of western north Texas and perhaps
far southwest Oklahoma tomorrow afternoon. This may be somewhat
mismatched with when the highest winds are expected (earlier in
the day) thus limiting the fire weather concern. Still, 15 to 20
mph sustained 20 foot winds will lead to elevated to near critical
fire weather conditions across this area.



Oklahoma City OK  50  66  40  56 /  30  10   0   0
Hobart OK         45  66  38  56 /  20  10   0   0
Wichita Falls TX  52  70  45  64 /  30  10   0   0
Gage OK           37  63  32  51 /  10   0   0   0
Ponca City OK     48  64  36  54 /  40  10   0   0
Durant OK         59  70  46  65 /  80  40   0   0



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