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Area forecast discussion 
National Weather Service Norman OK 
602 am CDT Friday Mar 19 2010 


Aviation... 
cold front is into east OK Panhandle with apparent pre-frontal wind 
shift and pressure pulse into northwest OK. Will use latest NAM for 
timing of main front/windshift. Showers/T-storms likely becoming 
more numerous near front after 20-21z followed by rain changing 
over to mix/snow 6-10hrs after frontal passage. Conditions deteriorating to 
MVFR then IFR by end of period as low/middle levels saturate behind 
the front. 


&& 


Previous discussion... /issued 359 am CDT Friday Mar 19 2010/ 


Discussion... 
March madness at its best. Or worst. Increasing concern that the 
upcoming event will be another major one for parts of the area... 
and we will kick things up another notch or two and enhance the 
wording in the npw/hwo/sps, et cetera. We are going to stay with a 
watch at this time since the worst will arrive in the 2nd or 3rd 
periods... but we will move up the start time to 00z this evening 
in west/northwest OK and we will add a few more zones to the watch in east/southeast 
OK. It is not out of the question that we could go ahead and 
upgrade to a warning later this morning if the 06z model runs 
provide sufficient confidence in doing so. 


Intensifying upper low takes a southern track into southeast OK or even 
NE Texas per most of the models. This is a potentially worst-case 
scenario for central/east OK. Latest HPC guidance shifts the maximum snow 
accumulations east as well... into east OK but with 8-10" from ncentral 
OK to east/southeast of okc along the east border of our County Warning Area. Typically our 
heaviest snow falls while surface winds are north or north-northeast in these cases... 
and amounts begin to taper off once winds back more to the northwest. 
This would be in the absence of rapid deepening of the surface low... 
and in this case the low gets going over Arkansas but deepening rates 
are not forecast to be too extreme. This and the fact that southeast OK 
will likely be the last to cool enough for a changeover leads US 
to go with somewhat lower totals than HPC in southeast OK... but we 
still have enough to justify a watch as far S/southeast as Ada/Coalgate 
areas. On the other side... we will go for a little more than HPC 
in northwest OK into parts of the panhandles... where March climatology 
and all recent NAM runs supprt some 4-8" amounts where the colder 
air will be around longer. Tough call in central OK and the okc 
area... where our current storm totals range from 3-6" but easily 
could end up less or could end up much more. Winds will make this 
another tough one to measure due to blowing/drifting... which will 
become more and more inevitable as surface temperatures fall to near or below 
freezing for most of Saturday in central/north OK. Winds likely to 
average at least 20-35mph as supported by 0-1km speeds in the 
30-40kt range. At least near-blizzard conditions are likely 
again... and there is some potential for an eventual upgrade to 
another Blizzard Warning at some point. 


In the meantime... cold front has entered the OK Panhandle and 
will sweep southeast into northwest OK by 15z... reaching I-44 corridor 00-03z. 
We have used the nam12 to capture the sharp windshift and 
decidedly non-diurnal temperature drop behind the strengthening front. 
Limited Gulf moisture return ahead of it will be offset by diurnal 
heating and strong frontal convergence/lift to allow for 
convective development along front by middle-late afternoon. A few 
strong to marginally severe storms will be possible given the 
strong low-level forcing... but weak instability and limited 
large-scale forcing will lower the potential. 


One good thing about late-season March snowfall events is that the 
snow usually doesn't stay around very long. We will adjust the 
temperatures down for a couple days afterward to account for probable 
snow cover... then bring temperatures back up by Tuesday ahead of another 
system swinging through Wed-Thu. This one looks to be weaker and 
farther north... and so for now we will remain optimistic and keep 
it as rain/T-storms Wed-Thu. 


This just in - 06z NAM hits much of central/NE OK with 15-25 
inches of snow before all is said and done on Sunday. Not buying 
that much yet... but we will be looking very closely at this run. 


&& 


Preliminary point temps/pops... 
Oklahoma City OK 69 31 34 25 / 30 100 80 40 
Hobart OK 68 31 34 23 / 30 100 60 20 
Wichita Falls Texas 72 35 41 30 / 20 90 60 20 
gage OK 52 27 33 14 / 30 100 50 10 
Ponca City OK 69 30 34 29 / 40 100 80 50 
Durant OK 69 44 49 30 / 10 70 90 50 


&& 


Oun watches/warnings/advisories... 
OK...Winter Storm Watch from Saturday morning through Sunday morning 
for okz007-008-012-013-017>020-022>032-042-043. 


Winter Storm Watch from this evening through Sunday morning for 
okz004>006-009>011-014>016-021. 


Texas...none. 
&& 


$$ 


06/24/24