andyhb Posted October 7, 2013 Share Posted October 7, 2013 SPC has highlighted a risk area in the most recent D4 highlighting the High Plains with the upcoming passage of a strong negatively-tilted shortwave. As they mention, this system won't have nearly the moisture return to work with as with the one last Friday, but strong wind fields should promote rotation with any storms that do become more robust. DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0357 AM CDT MON OCT 07 2013 VALID 101200Z - 151200Z ...DISCUSSION... MODELS ARE IN GOOD AGREEMENT IN DEPICTING A POTENT NEGATIVELY TILTED SHORTWAVE TROUGH MOVING INTO THE CNTRL PLAINS LATE ON THU/D4...THEN INTO THE NRN PLAINS ON FRI/D5. THE OVERWHELMING MITIGATING FACTOR TO A MORE SIGNIFICANT EVENT WILL BE THE BOUNDARY LAYER MOISTURE MAGNITUDE. WITH SUCH A DRY ANTECEDENT AIR MASS UPSTREAM...DEWPOINTS ARE ONLY EXPECTED TO RISE INTO THE MID 50S BY THU EVENING AND IN A RELATIVELY NARROW PLUME. CONDITIONALLY...WIND PROFILES WILL BE VERY STRONG AND FAVORABLE FOR SUPERCELLS OR SEVERE LEWPS. DUE TO THE NARROW ZONE OF INSTABILITY...AND CAPPING POTENTIAL FARTHER E INTO THE LOWER ELEVATIONS AND WHERE COOLER AIR WILL EXIST...THE THREAT AREA WILL BE LIMITED TO WRN PORTIONS OF NEB AND KS...AND PERHAPS EXTREME ERN CO GIVEN THE MERIDIONAL NATURE OF THE UPPER FLOW WHICH WILL KEEP LOW LEVEL WINDS BACKED. Link to comment Share on other sites More sharing options...
Stebo Posted October 7, 2013 Share Posted October 7, 2013 The concern with this one will indeed be the moisture return, the wind fields and forcing are pretty good maybe even a bit better than last Friday. I just don't think we will be able to get the moisture to return in sufficient time, the Western Gulf of Mexico was scoured out pretty well with the last front that just came through. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted October 7, 2013 Share Posted October 7, 2013 Great shear again, moisture as said going to be a problem. 12z NAM gets 55 dews up to the OK Panhandle. Link to comment Share on other sites More sharing options...
andyhb Posted October 7, 2013 Author Share Posted October 7, 2013 Either way, good to see strong systems ejecting out over the Plains again. Link to comment Share on other sites More sharing options...
brettjrob Posted October 7, 2013 Share Posted October 7, 2013 The concern with this one will indeed be the moisture return, the wind fields and forcing are pretty good maybe even a bit better than last Friday. I just don't think we will be able to get the moisture to return in sufficient time, the Western Gulf of Mexico was scoured out pretty well with the last front that just came through. My thoughts exactly. Dew points of 55 F can sometimes be sufficient for a significant supercell/tornado threat on the High Plains, but this time of year, it's not that likely. For the region affected, just as a sanity check when discussing potential setups with meager moisture, the benchmark I like to use is 2007-04-21 (Tulia/Channing/Cactus). Dew points were 53-55 F that day along the I-27 corridor, which may be repeatable Thursday. H5 temperatures were -12 to -14 C; Thursday looks a touch warmer, but not much. The H5 pattern and kinematic profiles modeled for Thursday do have some interesting similarities. If it were anywhere further east, I'd be completely ready to declare Thursday DOA. At 3000-4500 ft. elevation, I'd say the odds still strongly favor a benign frontal squall line evolution, but it does bear watching. Link to comment Share on other sites More sharing options...
tornadotony Posted October 7, 2013 Share Posted October 7, 2013 My thoughts exactly. Dew points of 55 F can sometimes be sufficient for a significant supercell/tornado threat on the High Plains, but this time of year, it's not that likely. For the region affected, just as a sanity check when discussing potential setups with meager moisture, the benchmark I like to use is 2007-04-21 (Tulia/Channing/Cactus). Dew points were 53-55 F that day along the I-27 corridor, which may be repeatable Thursday. H5 temperatures were -12 to -14 C; Thursday looks a touch warmer, but not much. The H5 pattern and kinematic profiles modeled for Thursday do have some interesting similarities. If it were anywhere further east, I'd be completely ready to declare Thursday DOA. At 3000-4500 ft. elevation, I'd say the odds still strongly favor a benign frontal squall line evolution, but it does bear watching. I generally agree with this. I just don't like the moisture return trajectories off the Gulf. With the ridging position over the eastern US, I wouldn't be shocked at all if the moisture modeled is a little overbiased, as unspectacular as it already is. Link to comment Share on other sites More sharing options...
andyhb Posted October 8, 2013 Author Share Posted October 8, 2013 New D3 maintains 30% area for NW KS and a most of west central NE. DAY 3 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0109 AM CDT TUE OCT 08 2013 VALID 101200Z - 111200Z ...THERE IS A SLGT RISK OF SVR TSTMS FROM WRN KS INTO CNTRL SD... ...SYNOPSIS... A POTENT SHORTWAVE TROUGH WILL EJECT NEWD OUT OF THE FOUR CORNERS INTO THE CNTRL HIGH PLAINS BY THU AFTERNOON...AND WILL CONTINUE INTO THE NRN PLAINS OVERNIGHT. AT THE SURFACE...LOW PRESSURE WILL DEEPEN ACROSS NERN CO/SWRN NEB DURING THE DAY...WITH STRONG CONVERGENCE DEVELOPING WITHIN THE LOW PRESSURE TROUGH FROM WRN NEB INTO THE WRN OK/TX PANHANDLES. STRONG SELY SURFACE WINDS ACROSS THE WARM SECTOR WILL BRING LOWER TO MID 50S DEWPOINTS NWWD AHEAD OF THE DEVELOPING COLD FRONT AND AS FAR NW AS NERN CO...RESULTING IN A SUFFICIENTLY UNSTABLE AIR MASS FOR SEVERE STORMS. ...CNTRL PLAINS... STRONG HEATING WILL OCCUR ACROSS THE CNTRL HIGH PLAINS...AND AS TEMPERATURES COOL ALOFT...LOW TO MIDLEVEL LAPSE RATES WILL BE VERY STEEP...NEARLY DRY ADIABATIC FROM THE SURFACE TO 500 MB ALONG THE DRYLINE. DESPITE LOW DEWPOINTS...CONVECTION WILL RAPIDLY DEVELOP AROUND 21Z AS FORCING ARRIVES. FORECAST HODOGRAPHS ARE IMPRESSIVE ACROSS THE WARM SECTOR...WITH STRONG LOW LEVEL VEERING AND SPEED SHEAR WITH HEIGHT. GIVEN THE MERIDIONAL NATURE OF THE FLOW ALOFT...STORMS WILL MOVE NNEWD AT A FAST PACE. AT THIS TIME...IT APPEARS THAT THE INITIAL STORMS WILL BE HIGH-BASED SUPERCELLS CAPABLE OF LARGE HAIL AND LOCALLY DAMAGING WINDS. A FEW TORNADOES CANNOT BE RULED OUT GIVEN THE DEGREE OF SHEAR AND STEEP LAPSE RATES ACROSS THE HIGH PLAINS. HOWEVER...AS THE WIND SHIFT ARRIVES...STORMS SHOULD QUICKLY FORM INTO A SQUALL LINE...WITH LOCALLY SIGNIFICANT WIND DAMAGE POSSIBLE AS BOWS RACE NEWD IN EXCESS OF 45 MPH. ..JEWELL.. 10/08/2013 Link to comment Share on other sites More sharing options...
Chinook Posted October 8, 2013 Share Posted October 8, 2013 The models show less than 750 CAPE for most of this area. Is the SPC convinced that CAPE will be much higher? Or low-CAPE storms will take advantage of the shear? Link to comment Share on other sites More sharing options...
AgeeWx Posted October 8, 2013 Share Posted October 8, 2013 The models show less than 750 CAPE for most of this area. Is the SPC convinced that CAPE will be much higher? Or low-CAPE storms will take advantage of the shear? My guess is that the threat is maximized more so because of the shear rather than the instability. There's more than enough forecast shear to make use of the limited instability. Link to comment Share on other sites More sharing options...
brettjrob Posted October 8, 2013 Share Posted October 8, 2013 With another 24 hours of model runs in the books, I'm now convinced the threat will be very marginal. Low-level moisture looks decidedly worse on today's 12z runs than yesterday's. Link to comment Share on other sites More sharing options...
Ian Posted October 8, 2013 Share Posted October 8, 2013 With another 24 hours of model runs in the books, I'm now convinced the threat will be very marginal. Low-level moisture looks decidedly worse on today's 12z runs than yesterday's. It's rarely great to have a low just sitting on the EC if you like moisture. Link to comment Share on other sites More sharing options...
tornadotony Posted October 8, 2013 Share Posted October 8, 2013 With another 24 hours of model runs in the books, I'm now convinced the threat will be very marginal. Low-level moisture looks decidedly worse on today's 12z runs than yesterday's. Agreed. I barely see enough justification for a slight risk at this point, let alone a 30% area. This isn't going to be a dry microburst environment, even with inverted-V soundings. It certainly isn't going to be much of a tornado environment. Link to comment Share on other sites More sharing options...
AgeeWx Posted October 9, 2013 Share Posted October 9, 2013 SWODY2 mentions a "sufficiently unstable" airmass ahead of the cold front, given the amount of forcing and shear forecast. Might be a nice night for high-based, photogenic supercells out west. Link to comment Share on other sites More sharing options...
SluggerWx Posted October 11, 2013 Share Posted October 11, 2013 Andy - do you want to extend this thread out to cover 10/10, 10/11 and 10/14-10/15? Current watch out today with 40/20 watch probs - worthy of discussion: outlines of the counties contained in it. Tornadoes Probability of 2 or more tornadoes Mod (40%) Probability of 1 or more strong (F2-F5) tornadoes Low (20%) Wind Probability of 10 or more severe wind events Mod (30%) Probability of 1 or more wind events > 65 knots Low (10%) Hail Probability of 10 or more severe hail events Low (20%) Probability of 1 or more hailstones > 2 inches Low (<5%) Combined Severe Hail/Wind Probability of 6 or more combined severe hail/wind events Mod (60%) URGENT - IMMEDIATE BROADCAST REQUESTEDTORNADO WATCH NUMBER 546NWS STORM PREDICTION CENTER NORMAN OK1215 PM CDT FRI OCT 11 2013THE NWS STORM PREDICTION CENTER HAS ISSUED A* TORNADO WATCH FOR PORTIONS OFWESTERN MINNESOTASOUTH-CENTRAL AND SOUTHEAST NORTH DAKOTANORTH-CENTRAL AND NORTHEAST SOUTH DAKOTA* EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 1215 PM UNTIL800 PM CDT.* PRIMARY THREATS INCLUDE...SEVERAL TORNADOES POSSIBLESEVERAL DAMAGING WIND GUSTS TO 70 MPH POSSIBLEA FEW LARGE HAIL EVENTS TO 1 INCH IN DIAMETER POSSIBLETHE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 90 STATUTEMILES NORTH AND SOUTH OF A LINE FROM 85 MILES WEST SOUTHWEST OFJAMESTOWN NORTH DAKOTA TO 5 MILES EAST OF ALEXANDRIA MINNESOTA.FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCHOUTLINE UPDATE (WOUS64 KWNS WOU6).PRECAUTIONARY/PREPAREDNESS ACTIONS...REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FORTORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCHAREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FORTHREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTSAND POSSIBLE WARNINGS.&&DISCUSSION...ONE OR MULTIPLE ARCING BANDS OF THUNDERSTORMS AREEXPECTED TO DEVELOP AND SPREAD NORTHEAST ACROSS THE WATCH AREA.CONDITIONS WILL BE FAVORABLE FOR LOW-LEVEL UPDRAFT ROTATION ANDTORNADOES ARE POSSIBLE...AS IS SOME HAIL AND LOCALLY DAMAGING WINDGUSTS.AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAILSURFACE AND ALOFT TO 1 INCH. EXTREME TURBULENCE AND SURFACE WINDGUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 350.MEAN STORM MOTION VECTOR 14030....MEAD Link to comment Share on other sites More sharing options...
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