June 26th-July 1st Severe Potential

[andyhb]

Appears the N Plains into the Upper Midwest will be heating up late this week into next (and the beginning of July). Large D3 risk area has been issued for Fri 6/27 and a D4 for Sat 6/28, but the most intriguing day currently appears to be Sunday as a strong embedded vort max rotates around the established upper low over the Prairie provinces (may spawn secondary low level cyclogenesis). Instability should be available en masse once again (as per usual this time of year) and a 500 mb jet in the 60-70+ kt range should provide ample shear for severe potential, perhaps significant, over the E Dakotas and MN.

 

Honestly, while I don't usually like throwing out top dog analogs, there are a few similarities here with 6/17/10 by the time Sunday rolls around. Previous evolution is somewhat different, though.

[andyhb]

18z GFS decided to come way south for Fri/Sat.

[Thundersnow12]

18z GFS decided to come way south for Fri/Sat.

 

Pretty interesting Sunday and then in the Midwest Mon/Tue

[andyhb]

Some phenomenal soundings in MN on Sunday off the 00z GFS, Euro doesn't look bad either.

[andyhb]

New D4-8 (kind of disagree about the 35 kt deep layer shear thing since the models are indicating in the 40-55 kt range):

 

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0330 AM CDT THU JUN 26 2014

VALID 291200Z - 041200Z

...DISCUSSION...
MODELS ARE IN GENERAL AGREEMENT REGARDING THE EVOLUTION OF UPPER LOW
AS IT PROGRESSES SLOWLY ACROSS SRN SK INTO SRN MB EARLY NEXT WEEK.
STRONG MID-LEVEL SPEED MAX IS FORECAST TO EJECT ACROSS THE BLACK
HILLS REGION INTO THE UPPER MS VALLEY BY 30/00Z WITH BOTH THE
GFS/ECMWF DEPICTING 500MB SPEEDS APPROACHING 80KT BY MIDNIGHT OVER
MN. THIS FEATURE IS EXPECTED TO ENHANCE SHEAR FOR CONVECTION THAT
DEVELOPS ALONG BOUNDARY DRAPED FROM WRN MN INTO NERN NEBRASKA. WITH
SBCAPE LIKELY IN EXCESS OF 3000 J/KG AND DEEP LAYER SHEAR ON THE
ORDER OF 35KT...SUPERCELLS ARE THE MOST LIKELY STORM MODE. LARGE
HAIL...DAMAGING WINDS AND PERHAPS TORNADOES CAN BE EXPECTED IF THE
ABOVE SCENARIO EVOLVES AS EXPECTED. ORGANIZED SEVERE STORMS MAY
REDEVELOP DURING THE DAY5 PERIOD ACROSS THE CNTRL GREAT LAKES BUT
MORE UNCERTAINTY WILL PREVENT A 30 PERCENT DEPICTION AT THIS TIME.

..DARROW.. 06/26/2014

[Thunder Road]

fun paragraph in Chanhassen's AFD this morning:

 

 

 

A MORE SUBSTANTIAL THREAT FOR SEVERE WEATHER EMERGES SUNDAY AFTERNOON
AND SUNDAY NIGHT. ANOTHER SHORT WAVE WILL PROPAGATE ACROSS THE
NORTHERN ROCKIES AND JET EASTWARD ON THE SOUTHERN PERIPHERY OF THE
LARGE CYCLONE PARKED OVER SOUTHERN CANADA DURING THE AFTERNOON.
FALLING MID LEVEL HEIGHTS/STEEPENING LAPSE RATES ATOP A HOT AND
HUMID BOUNDARY LAYER AIRMASS /HIGHS 85-90F AND DEW POINTS 65-70F/
WILL YIELD STRONG INSTABILITY WITH CAPE VALUES IN EXCESS OF 3000
J/KG. AS THE UPPER LEVEL ENERGY APPROACHES DURING PEAK
HEATING...NUMEROUS SEVERE THUNDERSTORMS MAY DEVELOP OVER MINNESOTA
AND PERSIST WELL INTO SUNDAY NIGHT OVER IOWA AND WISCONSIN.
STRENGTHENING 500 MB WINDS WITH SPEED MAXES OF 70-80 KT SUNDAY
EVENING AND A LOOPING HODOGRAPH THROUGH EARLY EVENING WILL BRING
SUPERCELLS INITIALLY CAPABLE OF ALL MODES OF SEVERE
WEATHER...INCLUDING TORNADOES...BEFORE TRANSITIONING TO MAINLY A
WIND DAMAGE/LARGE HAIL THREAT AS WINDS BECOME UNIDIRECTIONAL
DURING THE LATE EVENING. THIS LOOKS TO BE ONE OF THE BEST CHANCES
OF SEVERE WEATHER THIS PART OF THE COUNTRY HAS SEEN SO FAR THIS
YEAR.

[Quincy]

12z GFS continues to look impressive for Sunday. I'd say that much of Iowa would be game as well. Most of Iowa and southern MN are progged to have 4000-5500 J/kg SBCAPE with minimal CIN and 40-55kt shear (as previously mentioned). 

 

Edit to keep discussion for the 26th on in this thread...

 

It looks like a somewhat similar day to yesterday can be expected today with storm evolution. A few isolated severe storms could develop with large hail being a big threat. Cells may merge to form a few squall lines with damaging winds tonight. The best environments are fairly split with more moisture and great instability to the south (from SW WY into NE CO, W NE and W KS) and stronger winds/greater shear up in NE WY, E MT and the western Dakotas.

 

There was one tornado report yesterday in far NE WY and that same general area, if not further north, could see an isolated tornado today. LCLs are fairly high further south, but even to the north the shear isn't anything insanely impressive.

 

I'll probably hang back across the CO/NE border region and hope for some nicely structured storms again today. The HRRR has been consistent with blowing up a few discrete cells across NE CO by mid-afternoon. It's not until tomorrow that the severe threats become more widespread/impressive.

[Thunder Road]

12z Euro has 0-1 km helicities of ~200 m2/s2 and 0-3 km of 250-300 m2/s2 over an area of 2500-3000 J/kg CAPE in NW IA and SW MN 0z Mon.  Nothing epic, but supportive of sups at least and maybe a few tornadoes.

[andyhb]

12z Euro has 0-1 km helicities of ~200 m2/s2 and 0-3 km of 250-300 m2/s2 over an area of 2500-3000 J/kg CAPE in NW IA and SW MN 0z Mon.  Nothing epic, but supportive of sups at least and maybe a few tornadoes.

 

That's perfectly sufficient for significantly tornadic supercells.

[Stebo]

12z Euro has 0-1 km helicities of ~200 m2/s2 and 0-3 km of 250-300 m2/s2 over an area of 2500-3000 J/kg CAPE in NW IA and SW MN 0z Mon.  Nothing epic, but supportive of sups at least and maybe a few tornadoes.

200 m2/s2  0-1km helicity with 3000 J/kg of SBCAPE is pretty damn good...

[thewxmann]

12z Euro has 0-1 km helicities of ~200 m2/s2 and 0-3 km of 250-300 m2/s2 over an area of 2500-3000 J/kg CAPE in NW IA and SW MN 0z Mon.  Nothing epic, but supportive of sups at least and maybe a few tornadoes.

 

Someone is jaded from last week's setups.

[Thunder Road]

12+ EHI or bust

[Thunder Road]

Seriously though, I tend to hedge conservative but I'm getting impressed with Sunday.  Just don't look at the GEM...

[Thundersnow12]

That's perfectly sufficient for significantly tornadic supercells.

Yeah no kidding.

[ZackH]

The 00z NAM paints quite a dangerous picture in the SE ND, eastern SD, and central to south MN region Sunday afternoon and evening if things can remain discrete. Would like to see more turning in the lowest kilometer but any deviant movers will have to be watched closely with all that SREH to tap into.

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[David Reimer]

Saturday looks interesting Central Oklahoma if the 12Z/0Z 4KM NAM is correct. 40 knots at 500MB with a 35-45 knot LLJ in place is pretty unusual here in late June. Combined with low/mid 70 dewpoints and 4000+ J/Kg of SBCAPE I'm certainly keeping an eye out for a local chase. 

[Quincy]

Today has potential, although the somewhat backed winds around 500mb may limit the tornado threat. Still, we're looking at good kinematic support coupled with strong instability by mid to late afternoon. 

 

12z DDC sounding shows the backed winds aloft: 

[nrgjeff]

Today and tomorrow are unidirectional and/or veer-back in the northern Plains. Oklahoma has better turning with height on Saturday, and a LLJ, but will be subject to convection evolution in Kansas.

 

Sunday and Monday are looking more interesting in Iowa and Illinois respectively, location subject to change depending on prior convection. Turning with height is proper for tornadoes either way. I'd expect airmass recovery near outflow boundaries both days. Short wave timing is required though. We are playing games with left front/exit and right rear/entrance targets on jet maxima. It'll take a day or two to resolve, along with LLJ responses to each.

 

Sunday and Monday look most promising at the moment. If all else fails, World Cup elimination round of 16 starts Monday. Pehaps it is a good day to take off.

[Chinook]

Mesoscale discussion 1170 is out, regarding Denver and I-70 in Colorado. RAP analysis shows that it is destabilizing with less CINH, and has much of the wind shear above the 500mb level. The wind speed increases from 20 to 50 kt from 500mb to 300mb, but 20kt or less below that. (point forecast around Ft. Morgan). Actually, shear, CAPE, and CINH vary greatly across NE Colorado right now. We have a few showers popping up near me in the foothills, Denver metro also.

 

---

 PROBABILITY OF WATCH ISSUANCE...80 PERCENT   SUMMARY...THUNDERSTORMS WILL INCREASE IN COVERAGE OVER THE NEXT 1-2   HOURS ACROSS SE WY AND NE CO...AND TRACK E/NE TOWARD WRN NEB AND NW   KS. SEVERE THUNDERSTORMS CAPABLE OF LARGE HAIL AND STRONG/DAMAGING   WINDS WILL BE THE MAIN THREAT. BUT...A TORNADO OR TWO ALSO IS   POSSIBLE...ESPECIALLY ACROSS PARTS OF CO INTO SW NEB AND NW KS.

---

[Quincy]

I'd pin-point northwest Kansas as the spot for a few isolated tornadoes thus afternoon. Decent LCLs, plenty of shear and instability and the outflow boundary in the vicinity. Colby was 82/70 last check with a wind direction of 110 degrees. The window may be relatively small before the storm mode becomes messy, but we'll see.

[andyhb]

Tornado watch out for the High Plains until 10 PM.

 

Upper level flow is backed but decently strong, in the 45-55 kt range. 70s dewpoints in place near the triple point in KS/NE.

[Quincy]

It got a little interesting near the dryline with gustnadoes and some marginally large hail, but that was about it. There were a few photos of landspouts going around and I'm not surprised. There was a supposed "confirmed" tornado near Goodland earlier, but I'm very skeptical based off of radar scans.

Definitely some impressive gust fronts too, but nothing much (if at all) in the tornado department.

[Jim Marusak]

Have to admit, here in MN, the main worries here for tomorrow as I see it will be flash flooding and wet microbursts, given the PW's according to the NAM between 1.6" to 2.0" (40-50mms), and the fairly wet profiles, even though if the NAM is close (the usual caveat with that), some hail and a tornado will be possible in discrete cells in southern/central MN, imho, even ift he shear is more speed than directional.

 

Sunday, different story, as I am much more liking the possibility of all modes of severe here given the more classic predicted shotgun soundings and slightly better turning. And if the PW's recover as predicted, the downpours won't be as torrential, but it won't take much to make any flooding around here worse, especially in the Minnesota River Valley.

 

sidenote: I am in the North End of St Paul, which will more likely just see street flooding at worst given the elevation of my part of the city compared to the river, as the south end of town is much more affected being a couple hundred feet lower and right next to the Mississippi.

[Minnesota Meso]

Considering Sunday for MSP, you may as well take us off the maps for severe weather, both the GFS and Euro show winds at h85 and higher strongly out of the west as the surface cyclone over Canada will drop further south than what most models showed.  The westerly winds will bring a good dry slot over the area say from h85 to 700mb if not higher.  Far southern MN and Iowa is in play.

[andyhb]

Considering Sunday for MSP, you may as well take us off the maps for severe weather, both the GFS and Euro show winds at h85 and higher strongly out of the west as the surface cyclone over Canada will drop further south than what most models showed.  The westerly winds will bring a good dry slot over the area say from h85 to 700mb if not higher.  Far southern MN and Iowa is in play.

 

You're playing dangerously close to the boundary there to be making this call.

[Minnesota Meso]

Have to admit, here in MN, the main worries here for tomorrow as I see it will be flash flooding and wet microbursts, given the PW's according to the NAM between 1.6" to 2.0" (40-50mms), and the fairly wet profiles, even though if the NAM is close (the usual caveat with that), some hail and a tornado will be possible in discrete cells in southern/central MN, imho, even ift he shear is more speed than directional.

 

Sunday, different story, as I am much more liking the possibility of all modes of severe here given the more classic predicted shotgun soundings and slightly better turning. And if the PW's recover as predicted, the downpours won't be as torrential, but it won't take much to make any flooding around here worse, especially in the Minnesota River Valley.

 

sidenote: I am in the North End of St Paul, which will more likely just see street flooding at worst given the elevation of my part of the city compared to the river, as the south end of town is much more affected being a couple hundred feet lower and right next to the Mississippi.

 

Are you looking at the Nam? I think its showing its northern bias.

[Jim Marusak]

Considering Sunday for MSP, you may as well take us off the maps for severe weather, both the GFS and Euro show winds at h85 and higher strongly out of the west as the surface cyclone over Canada will drop further south than what most models showed.  The westerly winds will bring a good dry slot over the area say from h85 to 700mb if not higher.  Far southern MN and Iowa is in play.

just taking a look at the GFS now thru 42, I am thinking definitely south and east of the twin cities, I agree with severe likely, and definitely north of BBB, STC, and PNM not getting too much. As for the twin cities though, it will still be a close call. not writing it off yet, especially south/central metro.

[andyhb]

Are you looking at the Nam? I think its showing its northern bias.

 

And the GFS appears to be too fast, you'll notice WPC used the ensemble means/12z Euro with below avg confidence in the afternoon diagnostic discussion. In other words, timing/location/magnitude of main threat is still rather variable.

[Jim Marusak]

Are you looking at the Nam? I think its showing its northern bias.

 

yea. and I am now catching the GFS as well. The one thing I find though in not writing off the twin cities is, both models seem to recover the moisture in the atmosphere over here late in the afternoon. north and west of the 651-612 though, yea I think we could write them off.

[Minnesota Meso]

You're playing dangerously close to the boundary there to be making this call.

 

Yes, I realize that, but with strong surface highs to our NE or strong surface lows to our north/north west  I have seen this many times as westerly or easterly wind have shut us down..  The last time I saw it was last fall when many of us compared the set up to the St Peter tornado, but a strong high pressure system over northern lake Superior with it's easterly winds shut down MN.  I see the same thing happening only with the cyclonic flow this time compared to anti cyclonic flow last fall.