Area Forecast Discussion
Issued by NWS Oklahoma City, OK

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000
FXUS64 KOUN 212001
AFDOUN

Area Forecast Discussion
National Weather Service Norman OK
201 PM CST Wed Feb 21 2018

.UPDATE...
Are in the process of changing the remaining of the warning to an
advisory. Updated POPs and weather again a little bit ago.

&&

.DISCUSSION...
The large precipitation area in the southwest had enough sleet to
limit ice accumulation from freezing rain in the areas that
experienced this precipitation. The heaviest precipitation is only
confined to Clay County in the ice storm warning area and will
be moving out shortly. Already changed the western portion of the
warning back to advisory and will do the same with the eastern
part of the warning area as the heavy precipitation clears Clay
County. We are also extending the advisory in time through the
morning commute with the persistent signal of freezing drizzle
overnight and into Thursday morning. More details to follow with
the afternoon package.

&&

.PREV DISCUSSION... /issued 1153 AM CST Wed Feb 21 2018/

DISCUSSION...
The 18Z aviation discussion follows....

AVIATION...
Widespread freezing rain and sleet will cover most of Oklahoma and
north Texas this afternoon. This will be accompanied by varying
visibilities and (generally) lowering ceilings. Indications are
that ceilings will continue to deteriorate through Thursday
morning, as moisture continues to be pushed north over the cold
airmass near the surface. In addition, freezing drizzle is likely
at most of our TAF sites overnight. Finally, forecast models show
another wave of heavier precipitation Thursday morning and early
afternoon--moving from north Texas into southwest, then central,
Oklahoma. The current best estimate for surface temperatures at
that time indicates that this precipitation will be over areas
with subfreezing temperatures (and subfreezing ground
temperatures), so freezing rain is the most likely precipitation
type.

CmS

PREV DISCUSSION... /issued 946 AM CST Wed Feb 21 2018/

UPDATE...
Added Ice Storm Warning in most of our north Texas zones, updated
POPs and adjusted weather somewhat.

DISCUSSION...
Large precipitation area is expanding northeast from the Texas Big
Country into our north Texas zones. With widespread moderate to
perhaps heavy precipitation, pulled the trigger on an Ice Storm
Warning for north Texas. One potentially limiting factor will be
the mixture with sleet as the cold low-level air has plunged
southeast, and sleet is being reported to Wichita Falls media in
Archer, Baylor, Wilbarger and Foard Counties. But with this area
of precipitation including freezing rain, expect significant
impacts in north Texas, especially on the elevated roadways
through Wichita Falls. Farther north into southwest and central
Oklahoma, more sleet will likely mix in which will limit the ice
accumulations from freezing rain, and precipitation amounts are
more uncertain in south central and southeastern Oklahoma as most
models suggest precipitation intensity decreasing somewhat. But
will keep an eye on things. .26.

PREV DISCUSSION... /issued 506 AM CST Wed Feb 21 2018/

DISCUSSION...

AVIATION...
For the 12z TAFs:

Deteriorating conditions are expected today, first at north Texas
and southern Oklahoma sites, and then spreading northward across
the rest of the area. Start times may need to be adjusted, and
there may be periods of no precipitation despite prevailing
precipitation in the TAF. Ceilings should steadily decrease to IFR
just before the precipitation begins and likely remain that way
after the precipitation ends this evening. Precipitation type may
vary, but generally should range from mostly freezing rain in the
south central/southeast portion of the state to freezing rain and
sleet from western north Texas and southwest Oklahoma
northeastward through central Oklahoma and into north-central
Oklahoma. In northwest Oklahoma, the precipitation may be
predominately snow to start, and then sleet and eventually
freezing rain will become common throughout the day.

PREV DISCUSSION... /issued 354 AM CST Wed Feb 21 2018/

DISCUSSION...
The main focus continues to be precipitation type and amounts
through early Thursday. Changes to the previous forecast were
generally minor. We did emphasize sleet over a larger area given the
depth of the warm layer in short term model forecast soundings. This
should tend to limit ice accumulation precluding a more high impact
event. We also added snow in northwest portions of the area given
wet bulb profiles.

We expanded the Winter Weather Advisory to include Bryan and Atoka
counties which are both at 32 degrees. Temperatures should be steady
for much of the day there and latent heat of fusion should limit ice
accumulation. Nevertheless, some minor accumulation and possibly
minor impacts to travel are possible, particularly in the western
sections of both counties. We added the rest of the counties in
northwest Oklahoma given a stronger signal for at least some
coverage of precipitation. This could be where rates are locally
higher given weak elevated instability supporting convective
elements. Similar to last night, brief periods of moderate to heavy
freezing rain and/or sleet can`t be ruled out

Latest radar mosaic shows a northward shift of precipitation across
north Texas with heavier precipitation now approaching the Red
River. This is due to deep isentropic ascent in response to
veering/moistening flow atop cold shallow arctic airmass.
Precipitation will continue to build northward throughout the day
impacting western north Texas and southern Oklahoma this morning,
reaching the I-40 corridor by around midday, and spreading through
northern Oklahoma during the afternoon. Temperatures will change
little through the day and tonight, but should gradually rise
late tonight into early tomorrow as low level flow responds to
deepening lee cyclone forced by ejecting shortwave trough.
Although some light wintry precip may occur at the onset of the
next round of forcing for ascent and precipitation early Thursday,
by late Thursday precipitation should be mostly rain. The wet
pattern continues into Friday as yet another wave and accompanying
round of forcing for ascent brings more rain to especially the
southeast portion of the area which should shift east during the
day on Saturday. Temperatures will be warm enough for all rain,
and some weak elevated instability could support some thunder as
well.

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  29  27  39  35 /  70  70  50  20
Hobart OK         28  24  37  33 /  70  60  30  10
Wichita Falls TX  30  29  39  34 / 100  50  50  20
Gage OK           25  22  38  31 /  50  50  10   0
Ponca City OK     29  27  38  33 /  50  90  30  20
Durant OK         36  33  46  43 / 100  40  70  90

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...Winter Weather Advisory until 9 AM CST Thursday for OKZ004>048-
     050>052.

TX...Winter Weather Advisory until 9 AM CST Thursday for TXZ083>090.

&&

$$



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