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Short-Term Severe/Flooding Discussion


Quincy
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91/76 at TOP right now, pretty juicy to say the least.

H85 DP's of 20C right now just west of TOP according to mesoanalysis too. Maybe a tad high given that the H85 DP on the 19Z KTOP RAOB was aoa 12.2C and it currently shows it at 17C, but also there appears to be moisture transport of 20m/s, so its not out of the question I suppose... Juicy at and above the surface  :maprain:

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SPC going with higher confidence today is a potential tornado threat across South Dakota and adjacent Nebraska. Although instability and moisture return will not be nearly as favorable as yesterday, the overall timing with respect to peak heating and coverage of convective initiation should result in several strong to severe thunderstorms.

 

Forcing will be more focused with water vapor imagery showing a shortwave through moving east through Montana. Mid level temperatures are cooler, so capping is not a concern. Convection allowing model solutions include thunderstorms developing by midday to early afternoon. Combine the aforementioned setup with a weak surface low lingering across southern South Dakota/far northern Nebraska and the locally backed flow could support a few tornadoes.

 

HRRR has fluctuated a bit with respect to exact placement, however it has consistently showed convective initiation across South Dakota with at least a few more robust looking semi-discrete storms on the southern flank of the activity. 

 

...SD INTO NORTH CENTRAL/NERN NEB AND NWRN IA...
   A MOIST ENVIRONMENT WITH SURFACE DEW POINTS IN THE MID 60S F EXTENDS NWD INTO CENTRAL/ERN PARTS OF SD AND NEB.  OVERNIGHT CONVECTION HAS BEEN GRADUALLY WEAKENING DURING THE PRE-DAWN HOURS AND THIS SHOULD LEAD TO A DECREASE IN CLOUD COVER THIS MORNING WITH SUBSEQUENT POCKETS OF STRONGER ADIABATIC HEATING AND DIURNAL DESTABILIZATION OCCURRING.  
 
   MODEL CONSENSUS INDICATES STORMS WILL DEVELOP BY EARLY AFTERNOON OVER PARTS OF CENTRAL SD WHERE LOW LEVEL CONVERGENCE WILL BE ENHANCED NEAR THE FRONT AND ASSOCIATED SURFACE LOW.  STRONGER WESTERLY MID LEVEL WINDS /35-45 KT AT 500 MB/ COUPLED WITH AN EASTERLY COMPONENT TO THE LOW-LEVEL WINDS ALONG/NORTH OF THE FRONT WILL PROVIDE SUFFICIENT DEEP LAYER SHEAR TO SUPPORT SUPERCELL STRUCTURES CAPABLE OF PRODUCING LARGE HAIL...DAMAGING WIND GUSTS...AND POSSIBLY SEVERAL TORNADOES.  THIS ACTIVITY IS LIKELY TO SPREAD SEWD WITH TIME AS THE WINDS ALOFT VEER TO A MORE NWLY COMPONENT...WITH THE SEVERE THREAT SPREADING ACROSS NORTH CENTRAL/NERN NEB AND POSSIBLY NWRN IA BY THIS EVENING.  THE THREAT IS EXPECTED TO DIMINISH AFTER SUNSET WITH THE ONSET OF LOW-LEVEL COOLING AND AIR MASS STABILIZATION. 
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At least as of right now... A Seemingly disappointing period is coming mid-week for the central plains and Mid-west. Very rare to get a 50-70kt H5 trough to dig this far south in late summer... Doesn't seem to render much in the way of severe weather of severe weather though.. Likely from lack of instability due to cloud cover.

namCGP_500_spd_078.gif

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Mid-level lapse rates are just awful tomorrow. One of several mitigating factors. I do think that eastern Kansas to perhaps far southeastern Nebraska has a conditional risk for something interesting, severe-wise. The NAM is trying to keep the low-levels a bit backed, which would be more favorable than the typical cold frontal passage. Even with that said, storm mode and convection evolution looks rather messy across the board. 

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The threat on the weekend over the N Plains towards the Upper MS Valley might be thread worthy as we get closer. Seems like another anomalously strong trough (00z Euro had an 80 kt 500 mb max with this thing) will be traversing that area come Sat-Sun with potentially a sub 1000 mb surface low and a strong LLJ response. Moisture will have recovered in all likelihood over a large area by that time too.

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7.50" of rain measured in Omaha. That's gotta flood something.

 

PRELIMINARY LOCAL STORM REPORT  NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA  1119 AM CDT TUE AUG 18 2015     .TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON     .DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE.                ..REMARKS..    1117 AM     HEAVY RAIN       OMAHA                   41.26N 96.01W   08/18/2015  M7.50 INCH       DOUGLAS            NE   PUBLIC                          MEASURED 7.5 INCHES SINCE MIDNIGHT NEAR I680 AND PACIFIC  
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SPC has upgraded the day 2 outlook to enhanced for Minnesota/Iowa including the Twin Cities. The 18z NAM predicts around 300 m2/s2 of SRH tomorrow at 21z in the enhanced risk area.

 

 

   ...UPPER MIDWEST AND LOWER MO VALLEY...   HAVE UPGRADED/EXPANDED SEVERE PROBABILITIES WITH INCREASED   CONFIDENCE IN WIDESPREAD TSTM DEVELOPMENT AND A CONCENTRATED   CORRIDOR 

 

 

INITIAL MIX OF SEVERE HAIL/WIND SHOULD   BECOME A PREDOMINANT DAMAGING WIND RISK IN MN WITH A FEW EMBEDDED   SUPERCELL/MESOVORTEX STRUCTURES CAPABLE OF TORNADOES. 
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SPC has upgraded the day 2 outlook to enhanced for Minnesota/Iowa including the Twin Cities. The 18z NAM predicts around 300 m2/s2 of SRH tomorrow at 21z in the enhanced risk area.

 

anyone with input on the severe potential for MN, please chime in.  I have family/friends at a NHRA event at Brainerd International Raceway this weekend & was wondering if I'm being too hyper-nervous about severe potential for that area.  There's a lot of campers there in tents, RVs, etc & drinking, etc...

 

http://www.spc.noaa.gov/products/exper/enhtstm/

http://www.spc.noaa.gov/products/outlook/day1otlk.html

 

many thanks in advance

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It 2015'd itself. Squalled out quick and didn't get any discrete action. Man, this year really bites severe wise.

Sent from my GT-N8010

 

Good ol' 2015

 

Oh, you have a good setup for some discrete, chasable storms? Have some junk convection.

 

Oh, there's no junk convection? Have yourself a fat, messy MCS without a single SVR warning on it.

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Well this got messy fast. NE and IA already looks like a bust.

One of the biggest flops of the year, I'd say. I don't think the models handled it all that badly. The HRRR was pretty much onboard with storms merging into a massive line fairly quickly. The parameters weren't off the charts either, so I'm not sure a 10% tornado threat over such a large area was warranted. Only two severe reports, period, north of Omaha. One in Minnesota and one in North Dakota. 

 

A prime example of #2015ing.

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Heaviest rain since mid-June at my place now. Good to finally see some water coming into the ground again. The landscape here is brown and yellow as can be after the last two and a half months of almost total dryness.

 

Barton Creek's station jumped from almost nothing to 0.53" in 20 minutes. After the massive flooding in May/June on almost all the area creeks, they're about dry as a bone now. Barely a trickle.

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  • 2 weeks later...

Today could be a pleasant surprise in parts of Kansas, if one enjoys severe weather. Agree with SPC on the big hail threat, but a brief rope or two may spin up too. Small scale set-up, enhanced by an outflow boundary OFB, was not really apparent until this morning. Dewpoints of 60 degrees are forecast to make it back to the intersection of the OFB and sagging synoptic front in west-central Kansas before mixing back out slightly. Still better moisture may be found in north-central Kansas where it won't mix out as much. Upper level winds are seasonable, and enough. LLJ has a slight response to subtle short-wave coming out of the Rockies on water vapor images. Should at least start out discrete in Kansas this afternoon. I'd favor the one or two OFB storms.

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