OceanStWx Posted May 5, 2012 Share Posted May 5, 2012 Quite the EML being advected northward over Nebraska this morning. Probably going to make for a pretty sharp cut off between areas that go and areas that don't on the southern end of the slight. Link to comment Share on other sites More sharing options...
RCNYILWX Posted May 5, 2012 Share Posted May 5, 2012 New Day 1, hatching added to the 10% TOR (certainly justified when looking at the sounding for FSD below): ...N CNTRL STATES TODAY/TNGT... REGION INVOF AFOREMENTIONED FRONT AND OUTFLOW BOUNDARIES OVER SRN SD....NRN/ERN NEB...NW IA...AND SW MN WILL BE BECOME VERY UNSTABLE AS 60S SFC DEW POINTS OVERSPREAD REGION BENEATH STEEP MID LVL LAPSE RATES...WITH LATE AFTN SBCAPE EXPECTED TO RANGE FROM 2000 TO 4000 J/KG. CONTINUED EWD ADVANCE OF LEAD UPR LVL DISTURBANCES AHEAD OF MAIN WRN STATES TROUGH...AND SUBSTANTIAL DEGREE OF VERTICAL VEERING IN THE WIND PROFILES...WILL RESULT IN HODOGRAPHS VERY FAVORABLE FOR ROTATING STORMS...ESPECIALLY E OF THE TRIPLE POINT LOW ALONG THE QSTNRY/WARM FRONT. AT LEAST ISOLD TSTM DEVELOPMENT APPEARS LIKELY THERE...AND ALSO FARTHER W INTO THE BLACK HILLS DURING MID-LATE AFTN. RAPID GROWTH INTO SUPERCELLS CAPABLE OF VERY LARGE HAIL AND TORNADOES MAY OCCUR...ESPECIALLY OVER NERN NEB/SE SD INTO PARTS OF NW IA AND FAR SW MN. AS THE COLD FRONT ACCELERATES E/SE ACROSS THE NRN/CNTRL PLNS TNGT...UPSCALE DEVELOPMENT INTO ONE OR MORE MCSS APPEARS LIKELY. THESE MAY POSE A GRADUALLY DIMINISHING SVR THREAT EWD IN THE UPR MS VLY AND SWD INTO THE MID MO VLY EARLY SUN. 06z NAM Sounding at 00z for FSD: Link to comment Share on other sites More sharing options...
OceanStWx Posted May 5, 2012 Share Posted May 5, 2012 New Day 1, hatching added to the 10% TOR (certainly justified when looking at the sounding for FSD below): Early visible satellite shows a pretty sizable OFB moving south through Nebraska (subtle, but you can see it moving through the fog bank). So I'm wondering if maybe those parameters end up a touch south of KFSD in the end. But either way, looks like some nasty conditions setting up along the boundary. Link to comment Share on other sites More sharing options...
Jim Martin Posted May 5, 2012 Share Posted May 5, 2012 Much better. 12z NAM Sounding for Sioux Falls SD at 4pm cdt this afternoon. Link to comment Share on other sites More sharing options...
RCNYILWX Posted May 5, 2012 Share Posted May 5, 2012 Early visible satellite shows a pretty sizable OFB moving south through Nebraska (subtle, but you can see it moving through the fog bank). So I'm wondering if maybe those parameters end up a touch south of KFSD in the end. But either way, looks like some nasty conditions setting up along the boundary. Yup good point, definitely very subtle but there. Completely agreed about the nasty conditions- even if south of FSD, that sounding should be fairly representative of what the storms have to tap into. Another thing, based on the trajectory of the morning convection and the short wave producing it, the border area of NE/SD/IA looks like it won't be worked over, so if I were chasing today, I'd probably head there and assess upon arrival. Link to comment Share on other sites More sharing options...
OceanStWx Posted May 5, 2012 Share Posted May 5, 2012 Yup good point, definitely very subtle but there. Completely agreed about the nasty conditions- even if south of FSD, that sounding should be fairly representative of what the storms have to tap into. Another thing, based on the trajectory of the morning convection and the short wave producing it, the border area of NE/SD/IA looks like it won't be worked over, so if I were chasing today, I'd probably head there and assess upon arrival. I agree, something like sit around Norfolk and wait. Easy access north, east, and west from there. Link to comment Share on other sites More sharing options...
RCNYILWX Posted May 5, 2012 Share Posted May 5, 2012 Much better. 12z NAM Sounding for Sioux Falls SD at 4pm cdt this afternoon. Pretty incredible sounding for tornado and very large hail potential, though the low level speed shear at 21z is somewhat lacking (with great directional shear on the other hand). If initiation holds off towards ~00z, which is roughly what the latest HRRR is showing, that'll give some time for the LLJ to ramp up and increase the 0-1km shear magnitude. Link to comment Share on other sites More sharing options...
OceanStWx Posted May 5, 2012 Share Posted May 5, 2012 It really looks like low level advection is beating back that OFB, especially for central and eastern NE. Link to comment Share on other sites More sharing options...
OceanStWx Posted May 5, 2012 Share Posted May 5, 2012 59/59 at Ainsworth, NE and 78/69 at Norfolk, NE right now. Very tight thermal/moisture gradient across this boundary. Link to comment Share on other sites More sharing options...
Buckeye05 Posted May 5, 2012 Share Posted May 5, 2012 Are these currents storms going to enhance (boundaries?) or negate tonight's threat? Lot of widespread clouds and precip right now. Link to comment Share on other sites More sharing options...
OceanStWx Posted May 5, 2012 Share Posted May 5, 2012 Are these currents storms going to enhance (boundaries?) or negate tonight's threat? Lot of widespread clouds and precip right now. They are currently sharpening the boundary greatly in Nebraska. This will return northward during the day some (I'm currently thinking around the SD/NE border). This will create a significant tornado threat along and near the boundary, but any storm north of the boundary will still have the capability to produce significant hail. Link to comment Share on other sites More sharing options...
RCNYILWX Posted May 5, 2012 Share Posted May 5, 2012 1620Z Update to SWODY1 (key part bolded, explains shifting of 10% hatched TOR a bit south from 13z, placing Norfolk, NE area OceanSt suggested in the crosshairs): ...NRN PLAINS/UPPER MS VALLEY INTO MID AND LOWER MO VALLEY... ELEVATED SUPERCELLS ARE ONGOING THIS MORNING OVER SERN SD/SWRN MN WITHIN THE EXIT REGION OF 20-30 KT LLJ WHERE WAA AND ISENTROPIC ASCENT ARE BEING ENHANCED. 12Z OAX SOUNDING IS LIKELY A PROXY FOR THE INFLOW AIR MASS THAT IS BEING LIFTED ABOVE COMPOSITE BOUNDARY...FEATURING A MOIST BOUNDARY LAYER AND STEEP MIDLEVEL LAPSE RATES WITH MUCAPE OF 2000-3000 J/KG. GIVEN THE GRADUAL INTENSIFICATION AND BROADENING OF THE LLJ TODAY...EXPECT ONGOING ELEVATED STORMS TO PERSIST ACROSS PORTIONS OF SRN MN WITH A CONTINUED RISK FOR LARGE HAIL. BASED ON LATEST SURFACE OBSERVATIONS...IT APPEARS ACTIVE COLD POOL ASSOCIATED WITH SD STORMS MAY DISPLACE EFFECTIVE SURFACE BOUNDARY A BIT FARTHER TO THE S INTO NRN NEB THAN MODEL GUIDANCE SUGGESTS. TO THE S OF THIS BOUNDARY...THE EROSION OF LOW CLOUDS WILL ALLOW FOR STRONG DIABATIC HEATING TO OCCUR. WHEN COUPLED WITH BOUNDARY LAYER DEWPOINTS IN THE MID 60S-LOWER 70S AND THE STEEP MIDLEVEL LAPSE RATES...EXPECT AFTERNOON MLCAPE VALUES TO APPROACH 2500-3500 J/KG. PERSISTENT LOW-LEVEL WAA...CONVERGENCE ALONG THE FRONT AND WEAK MIDLEVEL HEIGHT FALLS ARE EXPECTED TO CONTRIBUTE TO SURFACE-BASED TSTM DEVELOPMENT THIS AFTERNOON OVER THE MID-MO VALLEY WITHIN A KINEMATIC ENVIRONMENT CHARACTERIZED BY A VERTICALLY VEERING WIND PROFILE AND STEADILY STRENGTHENING LOW AND DEEP-LAYER SHEAR. AS SUCH...SETUP WILL BE QUITE CONDUCIVE TO SUPERCELL EVOLUTION WITH AN ATTENDANT RISK FOR TORNADOES...VERY LARGE HAIL AND DAMAGING WINDS. UPSCALE GROWTH OF STORMS INTO AN MCS OR TWO APPEARS LIKELY TONIGHT WITH A CONTINUED THREAT FOR DAMAGING WINDS AND HAIL. Link to comment Share on other sites More sharing options...
OceanStWx Posted May 5, 2012 Share Posted May 5, 2012 I like what I'm seeing in northern Nebraska right now. The OFB is just northwest of a line from KBVN-KOFK-KSUX. However, the low level clouds are eroding faster than the wind shift is retreating. This means you'll get equal diurnal heating on either side of that wind shift, and that will have a residual effect on the atmosphere into the afternoon. Look no further than Broken Bow, winds shift from SE to NE over the last hour but have BKN to SCT clouds. That zone between Norfolk and O'Neill should be primed for something big, especially with storm motion progged to be roughly parallel to that effective boundary. Link to comment Share on other sites More sharing options...
baroclinic_instability Posted May 5, 2012 Share Posted May 5, 2012 Latest Rapid Refresh is catching on too...drops the boundary farther S, but also has a stronger differential diabatic heating zone, which may act to enhance the warm front locally in that region. Latest RAP is maxing out the EHI's at 10+ already at 20z. Link to comment Share on other sites More sharing options...
OceanStWx Posted May 5, 2012 Share Posted May 5, 2012 The RAP mesoanalysis forecast appears to be off by 20-30 miles at least on placement of effective boundary at hour zero. It thinks that the entire southeast corner of SD is still south of the OFB. Link to comment Share on other sites More sharing options...
andyhb Posted May 5, 2012 Author Share Posted May 5, 2012 Sioux City could have some problems later on considering it is south of the OFB (and close to being right on it)... Link to comment Share on other sites More sharing options...
brettjrob Posted May 5, 2012 Share Posted May 5, 2012 The southward shift of the expected WF placement does not excite me, given the tight N-S gradient in mid-level flow near the Missouri. We'll see what we can manage with great low-level, but questionable deep-layer, shear. Link to comment Share on other sites More sharing options...
Indystorm Posted May 5, 2012 Share Posted May 5, 2012 Northeast Nebraska still looking prime to me for svr action later this evening. Quite the contrast in temps and dews from there northward to southeast S.D. Deep moisture convergence in the area. Shear could be better but helicity is higher than I expected. Gonna be fun to watch the derby and then radar later on. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted May 5, 2012 Share Posted May 5, 2012 84/73 at LCG and 90/70 at SUX, boundary looks to be just north of HWY 20 in northeast NE. Link to comment Share on other sites More sharing options...
Buckeye05 Posted May 5, 2012 Share Posted May 5, 2012 AREAS AFFECTED...CNTRL/NERN NEB...SERN SD...NWRN IA CONCERNING...SEVERE POTENTIAL...WATCH LIKELY VALID 051909Z - 052045Z PROBABILITY OF WATCH ISSUANCE...95 PERCENT SUMMARY...TORNADO WATCH WILL BE NEEDED TO ADDRESS THE DEVELOPING SEVERE THREAT FROM CNTRL/NERN NEB...NEWD INTO NWRN IA. THIS WATCH WILL LIKELY BE ISSUED BY 21Z. DISCUSSION...EARLY MORNING MCS ACTIVITY THAT SPREAD ACROSS SD INTO MN HAS REINFORCED A BOUNDARY THAT CURRENTLY EXTENDS FROM CNTRL NEB INTO THE NWRN CORNER OF IA. WHILE THIS BOUNDARY MAY CONTINUE TO SAG SWD ACROSS PARTS OF NRN IA...STRONG HEATING OVER NEB WILL LIKELY PREVENT ANY FURTHER SWD PUSH ACROSS THE CNTRL PLAINS. WARM SECTOR CU FIELD APPEARS TO BE EXPANDING AND CHANGING CHARACTER ACROSS NERN NEB INTO NWRN IA PER DEEPENING BOUNDARY LAYER. IN ALL LIKELIHOOD THUNDERSTORMS WILL EVOLVE ALONG THE WIND SHIFT INITIALLY ACROSS NEB AS LOW LEVEL LAPSE RATES ARE SOMEWHAT STEEPER ACROSS THIS REGION. NEEDLESS TO SAY EXTREME INSTABILITY...SBCAPE IN EXCESS OF 4000 J/KG...AND DEEP LAYER SHEAR MORE THAN ADEQUATE TO SUPPORT ROTATING UPDRAFTS...WILL PROVE CONDUCIVE FOR SUPERCELLS...POTENTIALLY TORNADIC. VERY LARGE HAIL IS ALSO POSSIBLE WITH THIS ACTIVITY AND A WATCH WILL BE ISSUED BY 21Z. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted May 5, 2012 Share Posted May 5, 2012 already very impressive moisture convergence bullseye, one of my favorite things to look at. Link to comment Share on other sites More sharing options...
Buckeye05 Posted May 5, 2012 Share Posted May 5, 2012 Wonder if we could see a strong tornado or two out of this. Link to comment Share on other sites More sharing options...
andyhb Posted May 5, 2012 Author Share Posted May 5, 2012 Wonder if we could see a strong tornado or two out of this. There's a hatched area, so yes, there could rather easily be some with the more dominant supercells. Link to comment Share on other sites More sharing options...
SquatchinNY Posted May 5, 2012 Share Posted May 5, 2012 How many chasers are out there? Link to comment Share on other sites More sharing options...
jpeters3 Posted May 5, 2012 Share Posted May 5, 2012 well, me Sitting right near the CU field in NE NE, on the 81-20 junction Link to comment Share on other sites More sharing options...
SquatchinNY Posted May 5, 2012 Share Posted May 5, 2012 How is the CU field looking? Link to comment Share on other sites More sharing options...
jpeters3 Posted May 5, 2012 Share Posted May 5, 2012 How is the CU field looking? They're all topping off at some level - maybe taking a bit to break through that warm, dry 800-700 mb air. Link to comment Share on other sites More sharing options...
reber500 Posted May 5, 2012 Share Posted May 5, 2012 Jeez. the RAP doesn't really develop anything until 00Z or 01Z (7PM to 8PM) After that it gets decently active around 02Z to 06/07Z... After that TwisterData doesn't show anything for the RAP (it stops at 10-hours)... Link to comment Share on other sites More sharing options...
MnWeatherman Posted May 5, 2012 Share Posted May 5, 2012 a new town in forming west of Randolph, NE, haha! Link to comment Share on other sites More sharing options...
SmokeEater Posted May 5, 2012 Share Posted May 5, 2012 How many chasers are out there? 8,942. Link to comment Share on other sites More sharing options...
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