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Plains May 27-30 severe weather threat?


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That's certainly a nice jet streak getting ready to nose into the western High Plains:

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The 12z sounding from LBF shows there is obviously an impressive cap in place over the warm sector which won't break until the 500mb jet streak moves over the region, but looks nice once you cool those mid level temps some and speed up the mid level winds like will happen later.

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The lack of turning between the surface and 500mb is a bit concerning, though, so it will be somewhat important for the surface winds to back later.

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The RUC really cranks up the low-level jet early this evening over Nebraska. A nice wide swath of 60kt+ winds straight out of the south at 850mb! I'm still favoring the area north or northwest of Grand Island, maybe near Broken Bow.

18Z sounding about to go up here. I am heading to BBW shortly after I get off at 1.

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17Z SMART Severe Analysis showing the highest instability in and around Norfolk, NE to Brookings, SD to Broken Bow, NE and Red Wood Fall, MN, with Norfolk, NE in the highest threat for Tornadic potential. Seeing values at this hour of SFC CAPE: 2739 j/kg, 0-3KM Shear 57.5 knots, LI's -8.2, 0-1KM SRH 283. Also Potential for convective winds of 83 knots, and hail 1.2" in diameter. Detailed analysis at http://smartwxmodel.net

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Best of luck to the chasers. From what SPC said, sounds like the window for tornadic activity will be brief, but possibly intense.

Considering the strength of the low level wind fields I would say so. It will line out quickly, but the initial supercells are playing with a lot of S/SSE winds gusting to 30 knots over eastern Nebraska/S. Dakota.

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MESOSCALE DISCUSSION 1029

NWS STORM PREDICTION CENTER NORMAN OK

0140 PM CDT MON MAY 30 2011

AREAS AFFECTED...CENTRAL NEB/EASTERN SD INTO SOUTHEAST ND/WESTERN MN

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 301840Z - 302015Z

SEVERE/TORNADO THREAT IS EXPECTED TO INCREASE THROUGH LATE

AFTERNOON/EARLY EVENING...PERHAPS INITIALLY ACROSS

WEST-CENTRAL/NORTH-CENTRAL NEB INTO SOUTHEAST SD. ONE OR MORE

TORNADO WATCHES WILL BE NEEDED BY MID AFTERNOON /LIKELY BY 20Z/.

18Z SUBJECTIVE SURFACE ANALYSIS REFLECTS A 996 MB SURFACE LOW ACROSS

EASTERN SD BETWEEN HURON AND ABERDEEN...WITH A COLD FRONT EXTENDING

SOUTHWESTWARD FROM THE LOW INTO WESTERN NEB NEAR/WEST OF NORTH

PLATTE...WITH EARLY AFTERNOON VISIBLE SATELLITE IMAGERY REFLECTING

AN INCREASING SURFACE BASED CU FIELD NEAR/JUST EAST OF THE COLD

FRONT /ESPECIALLY ACROSS NEB/. WITH STRONGER DPVA/IMPLIED ASCENT NOW

BEGINNING TO OVERSPREAD THE NORTH-CENTRAL HIGH PLAINS...AN INCREASE

IN DEEP CONVECTION IS EXPECTED IN VICINITY OF THE FRONTAL ZONE BY

MID/LATE AFTERNOON...WITH AN ASSORTMENT OF NUMERICAL GUIDANCE

/INCLUDING EXPERIMENTAL HRRR/ INDICATIVE OF DEEP CONVECTION AS EARLY

AS 20-21Z.

AFOREMENTIONED ASCENT COUPLED WITH AMPLE PRE-FRONTAL HEATING AND

MIDDLE/UPPER 60S F SURFACE DEWPOINTS WILL CONTRIBUTE TO WEAKENING

CINH AMID MODERATE INSTABILITY. IN CONJUNCTION WITH A

STRENGTHENING/BUT LARGELY UNIDIRECTIONAL WIND FIELD...INITIAL MODAL

SUPERCELLS CAPABLE OF SOME TORNADOES/LARGE HAIL ARE LIKELY. STORMS

SHOULD ULTIMATELY CONGEAL THROUGH EARLY/MID EVENING...WITH MORE OF A

WIDESPREAD DAMAGING WIND THREAT EVOLVING AS WELL.

..GUYER.. 05/30/2011

Literally right as I hit enter on my last post.

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Yeah I am just heading out right now! Good luck!

Same to you! I'm stopped in Ansley now, pondering hedging a bit more N toward Taylor-Chambers. Tough balance trying to avoid moisture mixing issues S and more meridional flow N. Really pulling for the RUC's consolidated secondary sfc low locally backing winds and enlarging hodos in this general area.

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Blah, hopefully these Cu can keep stewing for another couple hours before initiation... I never like tornado potential much on days when initiation is before ~20-21z, except in the most dynamic setups

EDIT: Too late, I guess... time to work with what we've got.

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Shear is still somewhat unidirectional...

post-525-0-91382500-1306785654.jpg

Things look a little better a bit north of NE, towards the far eastern Dakotas into MN closer to the warm front/surface low, but things don't quite look ready to go there yet as the cap appears stronger.

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The strong tornado threat will probably peak in a few hours when surface winds start to back and the low level jet picks up, assuming things don't go linear too fast.

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