Severe Weather Discussion for May 21-24, 2011

Severe Weather Discussion for May 21-24, 2011.
Issued:  05/21/2011.


–  Severe thunderstorms are possible later today across the eastern 1/4 of Oklahoma.  Primary threats are large hail and strong winds, but a tornado or two is possible.

–  Active severe weather day is likely across the eastern 1/3rd of Oklahoma on Sunday.

–  Severe thunderstorms are possible across western Oklahoma on Monday.

–  Active and potentially significant severe weather day is possible on Tuesday.


12z models continue prior trends of maintaining severe weather potential across parts of Oklahoma through Tuesday.  Recent GFS/ECMWF indicate that Wednesday is likely out, so will drop that day from the discussions.

For Today, a dryline is located just west of I-35 per the Oklahoma Mesonetwork.  Temperatures are in the upper 70s to low 80s to the east of this feature with dewpoints generally in the upper 60s.  18:30z SPC analysis shows CAPE values @2000 J/Kg between I-35 and HWY 169, although CIN is -25 to -50 J/Kg ATTM.  Satellite imagery shows a few CU just west of Tulsa and southward, indicating the return of 805mb moisture.  Additionally, stratus is noted in far southeast Oklahoma.  NAM and some runs of the HRRR keep the area dry through tonight while the GFS develops convection.  Tough call on what will happen, but the potential is good enough to warrant a slight risk from SPC.  Currently, expect storms to develop after 4pm in eastern Oklahoma with a large hail and wind threat.  A tornado or two could occur given directional shear, although low-level winds aren’t great.

Going into Sunday, the severe weather trend continues and should push slightly west.  However, the primary threat will again be in eastern Oklahoma.  Winds aloft improve and instability is again present owing to surface temperatures in the 80s and dwepoints in the 60s.  CAPE values again approach and likely exceed 3000 J/Kg across eastern Oklahoma.  Severe thunderstorms are likely across this area and SPC has hinted at a possible upgrade to a moderate risk.  This all looks good and certainly appears things could get lively tomorrow afternoon.

By Monday the dryline should have shifted west to the TX/OK border with recent models showing a shortwave trof ejecting eastward into the state.  Severe thunderstorms would again be likely in an atmosphere characterized by mid/upper 60s dewpoints and temperatures in the 80s.  Wind fields are very good across the state with good turning.  Models are different regarding QPF with the NAM much more convective than the GFS.  GFS waits to near 00z with the NAM developing ongoing convection during the day, but doesn’t seem to modulate the threat at this point.  Tough call as the models haven’t done a good job convective wise the past few days.

Surface through 850mb environment remains generally the same as a well-timed 500mb shortwave trof ejects eastward into the state Tuesday afternoon.  A dryline will likely be near Weatherford attached to a surface low in northwest Oklahoma to southwest Kansas.  Wind fields will be very good and support supercells.  NAM and GFS both develop convection near I-35 late Tuesday afternoon, although I do think we’ll see this shift westward.  The orientation of SPC Day 4 outlook reflects going thinking.  Expected CAPE values of at least 3000 J/Kg, limited early morning convection, and seasonably strong wind fields all point to at least a medium-end event.

Quick look at 12z ECMWF maintains prior thinking for Monday and Tuesday.

SPC has risk areas for all four days and there is good potential for severe thunderstorms each day.  The higher-end days look to be Sunday and Tuesday.  We may consider a chase tomorrow but, the threat is a little east.  The likely days for chasing are Monday and Tuesday.  I doubt SPC will do a moderate for Day 3, but it sure looks like we’ll end up with one at some point so I’ve gone 75% for it.


Risk area for any part of OK (valid:  05/22 Day 1, Day 2, Day 3):

Slight:  100%, 100%, 100%
Moderate:  75%, 5%, 75%
High:  0%, 0%, N/A

Chase Status:

Level 3 – Monitoring Monday for a chase.

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