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andyhb

Central/Western Medium-Long Range Discussion

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Figured I'd create another one of these since the old one got locked.

 

Might be potential for a severe wx episode next week if some of the medium range model solutions are on the right track. Looks like a rather sizable upper trough for August dropping through the Pacific NW, then ejecting in some form towards the Northern/Central Plains.

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Environment for Wednesday 8/20 in the mid-Missouri Valley should be very impressive for August. I haven't delved into the guidance enough to assess the likelihood and possible timing of CI, but the parameters certainly grabbed my attention.

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00z GFS/NAM soundings are still really impressive on Wednesday afternoon/evening in (you guessed it) north central/northeast NE and south central/southeast SD with steep mid level lapse rates and strong directional shear in the lowest km. The area is very weakly capped at 21z so there should be a window for storm initiation in there, and with a well-timed shortwave impulse passing through the area, it screams a good August chasing opportunity as it looks now (who woulda thunk it) and does have several similarities to the June 16th/17th setups. It likely will come down to mesoscale placement again, but any supercell that goes up there will have good possibilities for significant severe given the parameters in place with a feed of 70 Tds along a corridor on either side of the NE/SD border.

 

I would think that SPC has to revise that "no severe area" in the D3 with the upcoming D2. There seems to be increasing potential here.

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00z GFS/NAM soundings are still really impressive on Wednesday afternoon/evening in (you guessed it) north central/northeast NE and south central/southeast SD with steep mid level lapse rates and strong directional shear in the lowest km. The area is very weakly capped at 21z so there should be a window for storm initiation in there, and with a well-timed shortwave impulse passing through the area, it screams a good August chasing opportunity as it looks now (who woulda thunk it) and does have several similarities to the June 16th/17th setups. It likely will come down to mesoscale placement again, but any supercell that goes up there will have good possibilities for significant severe given the parameters in place with a feed of 70 Tds along a corridor on either side of the NE/SD border.

 

I would think that SPC has to revise that "no severe area" in the D3 with the upcoming D2. There seems to be increasing potential here.

Some similarities to June 17th especially, at least given the slow/lazy storm motion and proximity to the NE/SD border.

 

00z NAM and GFS are still onboard. They're actually in fairly good agreement with the severe parameters near the warm front in southeastern SD by mid to late afternoon.

post-533-0-13117700-1408508596_thumb.gif

Strong turning in the lowest 1-1.5km, a weakening cap and plenty of instability - assuming there's at least some clearing during the day. Both the GFS and NAM are showing >200 m2/s0-3km and >100 m2/s0-1km helicity. This combined with 30-40 knots (or more) of shear and as mentioned, there could be significant severe.

 

I'm very interested to see the HRRR come into range. The 4km NAM simulated reflectivity shows a somewhat messy storm mode firing around 7-8 p.m. Will the window be that narrow/will initiation be that late? We'll see how the high resolution models trend.

 

Either way, it's looking very interesting from far northeastern Nebraska into southeastern South Dakota, up to about or just north of I-90. Even the forecast soundings for KFSD look impressive with enlarged hodographs. Intriguing for any time of the year, but especially for August.

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Well after Wednesday went to a non-event rather quickly due to leftover clouds/etc, there appears to be a decent amount of potential near the WF on Saturday, especially on the 00z Euro, with a relatively strong/backed LLJ and good upper support over the E Dakotas and perhaps W MN. Again, leftover convection is going to be a question mark, since this evening could have relatively widespread storms ongoing.

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AS it has been a common theme this year, the NAM looks great a day out and the RAP decides to stomp all over it lol. Was rather impressed with the models until this morning, however we still could see some isolated tornadoes up in SD.

Not exactly the best looking surface flow/theta E look to things attm though. Upper level flow is relatively marginal but it is doable.

One thing to note is the 700s where there is a moderate influx of flow leading to enhanced surface-700mb shear which could be enough for a tornado or two today, though given the dynamics right now this looks to be mostly a wind and hail event.

While likely not chasing this one, I will still keep an eye on it. Most likely area for tornadic development if we see it would likely be near and south a ways of Aberdeen, SD. I wouldn't be surprised to see a downgrade to a 5% tor again in the mid day outlooks.

post-4301-0-11317600-1408802230_thumb.jp

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Well after Wednesday went to a non-event rather quickly due to leftover clouds/etc, there appears to be a decent amount of potential near the WF on Saturday, especially on the 00z Euro, with a relatively strong/backed LLJ and good upper support over the E Dakotas and perhaps W MN. Again, leftover convection is going to be a question mark, since this evening could have relatively widespread storms ongoing.

 

:axe:

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The Euro indicates some severe risk for Sunday into Monday across the Plains and perhaps extending into the lower Missouri/upper Mississippi Valley regions. With an upper level trough digging, an increasing low-level jet and one or more surface lows developing along a front, there could be some potential. The GFS also points at an increasing threat at this time frame. A lot can change, but it's worth keeping an eye on.

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D5 outlook out, that's quite a substantial trough the Euro has tracking through the Central/Northern Plains late this weekend.

 

3LAQSX7.gif

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CDT WED AUG 27 2014

VALID 301200Z - 041200Z

...DISCUSSION...
MEDIUM-RANGE MODELS IN DECENT AGREEMENT THROUGH DAYS 4-5 /THE
UPCOMING WEEKEND/ IN PROGRESSING A LARGE UPPER TROUGH EWD ACROSS THE
ROCKIES WITH TIME...IN THE WAKE OF AN INITIAL/WEAKENING TROUGH
EXPECTED TO BE SHIFTING INTO THE ERN CONUS. SOME SEVERE RISK
APPEARS POSSIBLE DAY 4 /SAT 8-30/ ACROSS THE NRN PLAINS
VICINITY...AS STRONGER/DIFFLUENT UPPER FLOW SPREADS ACROSS THIS AREA
IN ADVANCE OF THE APPROACHING UPPER SYSTEM. HOWEVER...ATTM IT
APPEARS THAT SEVERE POTENTIAL MAY REMAIN SOMEWHAT LIMITED/ISOLATED
DUE TO RELATIVELY MODEST LOW-LEVEL MOISTURE/AIRMASS INSTABILITY.

GREATER RISK APPEARS EVIDENT DAY 5 /SUN 8-31/...AS THE TROUGH
CONTINUES ITS EWD ADVANCE...SPREADING ENHANCED MID-LEVEL SWLYS
ACROSS THE PLAINS STATES. AS A WELL-DEFINED COLD FRONT MOVES ACROSS
THE PLAINS...BOTH THE GFS AND ECMWF DEPICT SECONDARY LEE
CYCLOGENESIS ALONG THE BOUNDARY OVER THE CENTRAL HIGH PLAINS
VICINITY. WITH BACKED LOW-LEVEL FLOW E/NE OF THIS FEATURE BENEATH
THE INCREASING SWLYS ALOFT...SHEAR FAVORABLE FOR SUPERCELLS IS
EXPECTED. THIS COMBINED WITH RICHER BOUNDARY LAYER MOISTURE -- AND
THUS MORE SUBSTANTIAL DESTABILIZATION POTENTIAL -- WOULD SEEM TO
SUPPORT AN AREA FOR ENHANCED RISK OF SEVERE STORMS CENTERED INVOF
THE MID MO VALLEY DURING THE AFTERNOON...AND THEN SPREADING ENEWD
TOWARD THE UPPER MS VALLEY THROUGH THE EVENING.


MODEL DIFFERENCES BEGIN TO BECOME APPARENT DAY 6...AND THIS COMBINED
WITH THE LIKELIHOOD FOR RELATIVELY WIDESPREAD CONVECTION ONGOING
EARLY IN THE DAY PRECLUDE AREAL HIGHLIGHTS FOR SEVERE RISK BEYOND
DAY 5.

..GOSS.. 08/27/2014

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That spot in eastern Nebraska looks interesting on the 12Z GFS. The bulk shear is about 40 kts and nearly perpendicular to the boundary. There may be a short window of discrete supercellular activity. But the one thing that looks off is the 0-1km and 0-3km shear vectors are displaced to the east. It looks like convective activity will upscale quickly to an MCS and take advantage of an increasing nocturnal LLJ focused near or south of the NE/IA/MO border area.

 

RBNm3Qv.gif

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Based on fairly good model agreement at this point, it's looking quite interesting late next week/next weekend as well. A vigorous trough across the NW... The setup is somewhat reminiscent of June 16-18th, although the southeast ridge is a bit more prominent. It's way too early for specifics, but has my attention.
post-533-0-59099100-1409257001_thumb.gif

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Looking ahead to midweek, the Euro is showing some severe potential from central North Dakota down into South Dakota for Wednesday... CAPE at or above 2,000 J/kg... 0-6km bulk shear in the 40-60 knot range... a weaker cap than yesterday's runs with some QPF breaking out late over the best environment. Decent helicity values as well (would like to see a bit more low level shear, though).  

 

GFS is a bit less progressive and seems to hint at the best threat Thursday and further south and east (however, there is also some Wednesday potential in SD as well)... there seems to be a nice axis of decent potential from central SD up into southeast ND and into MN. There's a nice belt of 0-1km helicity around 150 m2/s2 overlapping 2000+ CAPE and 40 knot bulk shear. Something to keep an eye on as we look ahead.

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Well, the parameter space is fairly impressive for Wednesday, but capping and little forcing will be an issue. But if a storm can get going, it could be a big one.

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As mentioned, the timing for Wednesday/Thursday may be a bit off, but the parameters look awfully impressive for Wednesday. If the shortwave can speed up or we can otherwise get some more forcing in, that could kick off a few monsters. Thursday is probably out of reach, unless the whole thing slowed down. As advertised, Thursday would be a relatively narrow corridor of strong instability, but the kinematic support is lacking, along with an increasingly unidirectional shear pattern.

 

It's into weenie-range, but the GFS/Euro also show a potent shortwave across the Dakotas/upper Midwest by next Monday/Tuesday.

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SREF_prob_combined_sigtor__f039.gif

 

For what it's worth, there's the SREF sig tor ingredients for tomorrow at 00z (this image is run sensitive and will update, just FYI). Even though it's a controversial product, the 60% contours are fairly rare. Capping will be a possible issue, but SPC has upgraded much of central MN with a 30% hatched risk on the latest day 2 and the 12z NAM has a fairly large area in a sig tor parameter of 10+ by 03z Thursday.

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The NAM is advertising some 5-10 EHI values for Iowa, Minnesota, and Missouri tomorrow. That's pretty high for September!

Both the NAM and GFS look highly impressive for northern Iowa into southern Minnesota. Some may discount the NAM based off how it has handled some severe events this season, but even the GFS is spitting out some pretty significant values. Just pull a sounding for north-central Iowa and the GFS is showing over 200 m2s-2 0-1km helicity with 40+ knots of shear and a 40+ knot LLJ. Even seeing some STP values over 6 there on the GFS. (NAM is maxed out over southern Minnesota with double digit STPs)

 

Caveats: Capping and lack of a trigger. The GFS/NAM combo does show a subtle piece of energy swinging through southern Minnesota, but one has to imagine that the threat near and south of the IA/MA border may be minimal to cap-busted.

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The GFS has been forecasting an upper level trough, for a few days now, moving through the northern US for the middle to end of next week.  The Euro has been also on a similar solution with the trough but there are differences (some of them large) between it and the GFS.  For the GFS, the CAPE, shear, and boundary placements have been inconsistent but this system is something to watch as we approach the middle of next week.

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Next Friday and Saturday are looking interesting for the 5 state area of North and South Dakota, MN,WI or Iowa.  Way to early to figure out where and what day. Something to keep an eye on.

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Looks like regardless of how that trough ejects, we might be dealing with E Pacific TC-contaminated lapse rates again with Odile's track.

 

This is the biggest reason why I hate the second season. So many wasted setups over the past decade I can recall due to this problem.

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I was at the Ohio Severe Weather Conference a few years back. I saw Harold Brooks talk about climatological CAPE and shear. I believe Brooks said that the fall severe weather season is partly ruined by bad lapse rates from the Mexican Monsoon. Weak lapse rates are typically advected in from Mexico, they are much closer to moist adiabatic than the EML of springtime.

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Thanks to the stubborn Upper Level Ridge NW of Hawaii, there won't be any canes nearing Central/Southern Cali. It looks like Odile is going to be the closest to the heart of the drought areas without actually putting any meaningful dent into the drought.   

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