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Area Forecast Discussion (AFD)

Issued by Norman, OK (OUN)

                            
747 
FXUS64 KOUN 200125 AAA
AFDOUN

Area Forecast Discussion...UPDATED
National Weather Service Norman OK
725 PM CST Mon Feb 19 2018

.UPDATE...
Front moved further south than previously forecasted so have made
some adjustments to grids to account for this further south
position. It does appear that the front has stalled or at least
very nearly stalled. Front is forecast to lift back north
overnight the question is how far north. The 18Z NAM12 seems to
have the best handle on current front position, etc. This model
shows the front moving north to a line near Stillwater to
Cheyenne. This position is not as far north as other models.
Moisture will also spread back northward which could lead to an
area of fog development. 

Showers/storms will remain possible the rest of this evening and
overnight. It appears that the better chance for precipitation
will increase overnight,especially in SE parts of the fa. Some
freezing rain may also be possible in far northern parts of the
fa. Temperatures could drop to around freezing in this area and
with the front not forecast to move that far north then
temperatures have a chance to still be freezing when precipitation
moves into the area. However, if the front moves further north
than forecasted freezing rain will not occur. 

So adjusted temperatures, winds, and dewpoints to account for the
current and forecast position of the front. Lowered PoPs in some
areas for this evening. Also added a mention of fog and a chance
for freezing rain.



&&

.PREV DISCUSSION... /issued 527 PM CST Mon Feb 19 2018/ 

DISCUSSION...
Aviation discussion for the 00 UTC TAFs is below.

AVIATION...
Have very low confidence in the TAFs. 

At KOKC and KOUN, believe conditions will generally bounce 
between MVFR/VFR before 12 UTC. IFR conditions and a wind shift 
to the north will likely occur 1-6 hours behind a cold front 
passage 12-21 UTC. Went with a later time of -TSRA (09-12 UTC), 
but storm timing, if -TSRA happens at all, remains very uncertain.

AT KSPS, KLAW, KHBR, and KCSM, generally think VFR conditions will
occur, though MVFR conditions are possible, mainly after 06 UTC. 
Went with a later time of -TSRA (07-11 UTC) at KSPS and KLAW, but
storm timing, if -TSRA happens at all, remains very uncertain. 
Chances for -TSRA remain too low to mention near KCSM and KHBR. 
Surface winds at KCSM and possibly KHBR remain tricky before 
06 UTC near a front, though they should shift to the 
south/southeast. A wind shift to the north will occur with cold 
front passage 12-21 UTC.

At KPNC, worsening conditions are expected now through 15 UTC with
IFR/LIFR conditions expected. Airport minimums may be met as well
03-15 UTC. Improving conditions are expected after 15 UTC. 
Kept TEMPO -RA mention 05-09 UTC, though confidence of occurrence
is decreasing.

At KWWR and KGAG, surface winds remain tricky before 12 UTC, but
generally think they will shift to the southeast. MVFR conditions
will likely become IFR and possibly LIFR near KWWR 03-15 UTC. 
KGAG may have IFR/LIFR conditions 03-15 UTC as well. Surface 
winds will become northerly by 12 UTC. Improving conditions can 
be expected after 13 UTC.

MBS

PREV DISCUSSION... /issued 318 PM CST Mon Feb 19 2018/ 

DISCUSSION...
A shallow cold airmass has moved across the northern half of 
Oklahoma (western half) today behind a cold front. The front may 
move as far south as Hobart, Norman and Chandler before becoming 
stationary by late afternoon/early evening. Overnight, most high 
resolution models lift the frontal boundary northward during the 
evening and overnight. The front may lift back to around a 
Stillwater to Woodward line. Areas of fog and drizzle may also 
develop along and north of the boundary. So far the NAM has done a
decent job with the frontal position and post frontal 
temperatures. Therefore, will follow its frontal timing as the 
front moves southward on Tuesday. Expect this timing may be a 
little slow however. 

On the warm side of the front, widely scattered showers and a few
storms have developed over the past hour or so. Widely scattered 
storms will remain possible through the afternoon mainly elevated 
in nature. There is enough instability and effective shear for 
some hail. 

Better shower and thunderstorm develop will arrive this evening 
and overnight as part of the western trough lifts northeast into 
the central and northern Plains. A weak shortwave trough will also
approach western Texas this evening. Overall not very confident 
how convection/precipitation will evolve tonight, but will keep 
higher rain chances mainly along and east of Highway 81.

Precipitation chances will diminish from north to south on Tuesday
as the cold front pushes into northern Texas by late Tuesday 
afternoon/early evening. Rain and storms should linger across 
parts of southeastern Oklahoma Tuesday night. Some of the rain may
be heavy which may result in areas of minor flooding. 

On Wednesday, a shortwave trough will approach the southern Plains.
This may result in more precipitation with a risk of freezing 
rain and maybe sleet. How quickly the cold air erodes is still 
uncertain, but some ice accumulations seem possible Wednesday and 
Wednesday night. Surface winds during the period are not expected 
to be very strong. 

At least two more opportunities for rain and storms will arrive
Thursday into Friday/early Saturday. 

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  42  68  27  37 /  50  60  10  30 
Hobart OK         52  66  25  35 /  30  20   0  30 
Wichita Falls TX  66  72  32  38 /  50  50  20  50 
Gage OK           36  47  15  33 /  20  10   0  30 
Ponca City OK     33  49  22  37 /  50  60   0  20 
Durant OK         63  66  38  42 /  80  90  70  60 

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...None.
TX...None.
&&

$$

25/17