000 
fxus64 koun 241130 
afdoun 


Area forecast discussion 
National Weather Service Norman OK 
530 am CST Tue Jan 24 2017 


Discussion... 


&& 


Aviation... /for the 12z tafs/ 
VFR conditions will prevail through the taf period. Winds will 
strengthen from the southwest with gusts to 35 knots at most sites 
during the warmest part of the day. Winds will subside this 
evening and remain southwesterly until a cold front passes 
through. Timing will early evening for northern taf sites 
including gage, Woodward, and Ponca City, and around sunrise for 
Wichita Falls. 


&& 


Previous discussion... /issued 403 am CST Tue Jan 24 2017/ 


Discussion... 
primary concerns for this forecast are all in the short term. Windy 
conditions and elevated to critical fire weather conditions are 
expected this afternoon across most of the area. 


Latest water vapor loop clearly shows a broad upper low in the 
west with an increasingly well defined spin over central Wyoming. 
Model guidance is in good agreement on the evolution of the upper 
low as it tracks eastward across the Central Plains today. 
Already, this system is resulting in significant surface pressure 
falls and the latest surface analysis shows a Lee surface low has 
formed in eastern Colorado. Surface pressure gradient should 
become sufficiently tight across our area for strong west- 
southwest winds beginning later this morning. Although sustained 
speeds may be marginal for a Wind Advisory, deep mixing into 
strong mid-level wind maxima and momentum Transfer should result 
in gusts between 40 and 45 mph across much of the area this 
afternoon. Therefore, we have issued a Wind Advisory, with the 
highest confidence of criteria being reached or exceeded being 
across portions of western North Texas and western Oklahoma 
extending eastward through central Oklahoma. Wind speeds may be 
more marginal further northwest away from stronger momentum aloft 
and closer to increasingly baroclinic surface trough/strengthening 
cold front. Winds will also be slightly more conditional across 
south central and southeast Oklahoma depending on depth of the 
mixing. Adjustments to the advisory may be needed based on trends 
in observational data and short term guidance. 


Concerns over cirrus being thick enough to limit diabatic 
heating/mixing seem to be fairly low at this time. Some cirrus 
will be present given strong Cross-Mountain flow upstream but 
320-325k isentropic surfaces show only modest moistening, 
primarily to our south. It does seem given the orientation of the 
strongest winds on 1.5 pvu surface and where at least modest 
moistening occurs that the thickest cirrus would be across far 
southern and southeast Oklahoma, and to our northwest across 
Kansas. 


We have increased temperatures tomorrow to the high end of 
guidance. Statistical guidance is the warmest and is warmer than 
it was 24 hours prior. Mid 70s are possible across portions of 
the area with most locations reaching at least the upper 60s. 


A cold front will enter the northwest portion of the area from 
Kansas very late this afternoon or early evening and then progress 
southeastward across the area overnight. Cooler temperatures will 
arrive behind the front which will be near or slightly below average 
for this time of year. Mean northwesterly flow is expected to 
persist through the rest of the period and with no significant 
ridging/mid-level height rises, temperatures will change little. 
Perhaps a few degrees warmer early next week. There is high 
confidence in dry weather through the end of the forecast period. 


Brb 


Fire weather... 
downslope southwesterly 20-foot winds will strengthen later this 
morning and become sustained at or above 20 mph this afternoon. 
Additionally, deep mixing and unusually warm temperatures for 
late January will cause minimum relative humidity values to fall 
to around or just below 20 percent across much of the area. The 
exception will be across portions of south-central and southeast 
Oklahoma where low level moisture should be more extensive and 
will not mix out as extensively or as quickly as further west and 
north. We have upgraded the Fire Weather Watch to a red flag 
warning for all but the aforementioned area where low level 
moisture will be greatest, and also added Seminole County. 
Northern portions of the red flag warning near the Kansas border 
may struggle to reach criteria, or only briefly reach criteria. 
This is especially true if the faster guidance, namely the NAM 
model, are correct with a quicker progression of the front into 
northern Oklahoma. Likewise, there is some question as to how far 
south the surge of driest air will occur and some of the counties 
in south-central Oklahoma may also struggle to reach criteria. 


Mid-level winds are quite intense with 700 mb speed Max of around 
70 knots over central and southern Oklahoma around the time of 
peak heating/mixing. This will result in momentum Transfer 
sufficient for gusts over 40 mph. This speed Max will intersect 
with a low level thermal ridge that will be oriented north to 
south across central Oklahoma, roughly just east of I-35 during 
peak heating. This conceptually is a pattern recognized for 
significant fire potential. 


Our wind and dew point/relative humidity forecast is on the extreme ends of 
model guidance since models typically under-forecast winds and low 
level drying from downslope/mixing process. It is entirely 
possible that our forecast relative humidity and wind values are not quite 
extreme enough and that a longer period of critical fire weather 
conditions occur, possibly over a larger spatial area. This was 
the reason for being somewhat Liberal with the ending time of the 
red flag warning. We will closely monitor trends of observational 
data and short term guidance and make adjustments as necessary as 
the event unfolds. 


For any fires that may be ongoing during the evening, area fire 
managers need to be aware of a cold front that will move through 
the area bringing a wind shift. Current indications are that the 
front will enter far northern Oklahoma by very late in the 
afternoon and then move southeast reaching Interstate 40 by around 
midnight and the Red River by sunrise. Northwest winds of at least 
10 to 15 mph will occur behind the front. We will continue to 
attempt to refine the timing of the frontal passage. 


All locations should see relative humidity recovery to 40 percent or higher by 
around 11pm or midnight. 


Brb 


&& 


Preliminary point temps/pops... 
Oklahoma City OK 73 32 47 25 / 0 0 0 0 
Hobart OK 70 29 48 25 / 0 0 0 0 
Wichita Falls Texas 74 34 51 27 / 0 0 0 0 
gage OK 67 25 44 22 / 0 0 0 0 
Ponca City OK 71 30 45 25 / 0 0 0 0 
Durant OK 74 40 52 30 / 0 0 0 0 


&& 


Oun watches/warnings/advisories... 
OK...red flag warning from noon today to 7 PM CST this evening for 
okz004>031-033>041-044>046-050. 


Wind Advisory from noon today to 7 PM CST this evening for 
okz004>031-033>041-044>046-050. 


Texas...red flag warning from noon today to 7 PM CST this evening for 
txz083>090. 


Wind Advisory from noon today to 7 PM CST this evening for 
txz083>090. 


&& 



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