Severe Weather Discussion for November 21 – 27, 2011

Severe Weather Discussion for November 21 – 27, 2011.
Issued:  11/20/2011.
Highlights;
–  Severe thunderstorms are possible in southeast Oklahoma on Monday.  Primary threats are large hail and damaging winds, but a few tornadoes seems probable. Widespread showers and thunderstorms are likely elsewhere.
–  Thunderstorms, maybe a severe one or two, are possible Friday across the eastern 1/3rd of Oklahoma.  Primary threat is large hail.
–  Temperatures will be in the mid 40s on Monday, near 60F Tuesday, mid 60s Wednesday, upper  60s Thursday – Friday, mid 50s Saturday, and near 60F Sunday.
– Happy Thanksgiving!
Probabilities:
–  Severe Thunderstorms in Oklahoma:  15%
–  Storm Chase:  < 5%
–  Winter Precip:  5%
Discussion:
Southern stream shortwave trof will move into the region late Monday and move across during the afternoon hours.  A synoptic cold front is currently held up over north Texas this evening with mid/upper 60s dewpoints to its south.  To the north, temperatures are commonly in the 40s.  As the upper system approaches, the boundary is expected to drift northward, allowing for warm/moist air to shift northward into southeast Oklahoma.  Models disagree as to how far north the warm front will move, but for now I am siding with the farther north NAM.  Where ever the front ends up, severe thunderstorms are likely near and to the south of this feature.  Favorable shear will pose a tornado threat.  Isentropic lift will increase in earnest Monday afternoon, allowing for numerous showers and thunderstorms across much of Oklahoma.  Beneficial rainfall looks on-tap for eastern Oklahoma where a flash flood watch is currently posted.  Given that some of these areas are in a D0-D1 drought, some parts of Oklahoma maybe cleared of drought conditions.  After the system passes early Tuesday, a cool day is expected with a warming trend through Friday.  Models are in good agreement with this pattern and Thanksgiving is likely to be very pleasant across Oklahoma and Texas.
Next system moves towards the region late Thursday into Friday.  18z GFS took a radical departure from prior runs and the 12z ECMWF.  It cannot be ignored given that the prog valid 126hrs is similar to the current incoming system.  There are differences in the overall forecast from this change but nothing significant.  The main change was to move rain changes back west and add thunder for eastern Oklahoma.  Models indicate decent moisture return, dewpoints in the 50s, ahead of the dryline and eventually cold front.  Currently there seems decent potential for eastern Oklahoma/Texas to pick up another 1/2 to 1 inch of rainfall.    Systems moves on by for a cool Saturday and Sunday across Oklahoma.
Followed NAM for temperatures through Tuesday and then the GFS in-general through Sunday.  12z NAM has mid 40s tomorrow and given expected isentropic lift/clouds, see no reason to disagree.  OUN followed the same.  SPC outlook for tomorrow also looks good.
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