Plains Weather Discussion

[trapperman]

Eoro is a lot colder than the 12z GFS. Threat would be more supressed. The old GFS was too progressive with almost every southern stream shortwave in the medium range. Moisture return maybe a problem if the low is as far NW as the 12z GFS.

And it actually sped up instead of slowed down...

[Amped]

And it actually sped up instead of slowed down...

The GFS was upgraded in the spring, the one downside to that is it may change the model biases. However it also may slow system down in future runs.

[brettjrob]

Bleh. Both 12z models trended toward a faster ejection that lifts as it progresses through the Rockies. Shades of 2012.

[trapperman]

Bleh. Both 12z models trended toward a faster ejection that lifts as it progresses through the Rockies. Shades of 2012.

Still some potential, Brett. Euro took it a bit south so maybe it picks up more moisture???

[baroclinic_instability]

Something I am not sure we saw all of last year. Deep cold front and sharp return upslope flow through the plains and into the Rockies.

[andyhb]

Still some potential, Brett. Euro took it a bit south so maybe it picks up more moisture???

I'm not so sure it took it south, although it is slightly slower than the GFS, which also may have more of an influence on the day following the ejection (Saturday), the Euro has more breadth to the warm sector than the GFS on Saturday, owing to the fact that the Gulf coast high has progressed further east.

Regardless, these things will change as we move closer, as always.

[brettjrob]

Currently trying to determine which limbs I'd sever to lock in the 00z GFS for next Sat.

[andyhb]

That's pretty nice regarding the kinematics. Fairly classic low amplitude s/w (similar to things we'd see in May, aside from the thermos). If (and this is a rather big "if") we can get 12-15 degree C dewpoints at H85 and 60-65+ degree F sfc dewpoints into OK/KS like the 00z GFS seems to be suggesting (ignoring the CAPE progs because the GFS could be underestimating BL temps), with a setup like that, we could be in business.

00z Euro is faster by nearly a day than the GFS.

[Amped]

00z Eruo western Nebraska day7 12z gfs eastern Nebraska Day 7. It's gonna be boring winter if that is the extent of the disagreement models show.

Shear and SRH will be plentiful. The variables in question are dew points and daytime heating.

[brettjrob]

For now, it looks like the GFS and ECMWF are converging on a more progressive solution that results in threats both Fri (southern High Plains) and Sat (Midwest). I think the best chance for a headline event would be a slower ejection that focuses the threat entirely on Saturday farther west near the I-35 corridor. If the current timing stands, I don't like Saturday's potential as much, because the quality and width of the warm sector will start to fade as it encounters resistance over IL/IA/MO from the influence of the east coast high. Friday could be interesting for areas like the Panhandles and W KS, but it would take a lot going right to manage a "significant" event from that.

[andyhb]

I think the models should continue to change the timing at least until the rex block clears and that closed low enters the upper air network more completely.

[andyhb]

Several of the WFOs in the region have begun to mention this system in their AFDs.

OUN:

REST OF FORECAST WILL GO PRETTY MUCH UNCHANGED. INCREASED CHANCES

FOR SHOWERS AND STORMS LATE IN THE WEEK AND THE FIRST PART OF NEXT

WEEKEND. SEVERE WEATHER APPEARS POSSIBLE FRIDAY AND SATURDAY...

STAY TUNED.

TSA:

NOT MUCH HAS CHANGED WITH REGARDS TO FORECAST THINKING FOR THE

UPCOMING WEEK. A WARMING TREND WILL COMMENCE MONDAY...WITH A

TEMPORARY SETBACK TUESDAY NIGHT AND WEDNESDAY AS A WEAK COLD FRONT

PASSES. WILL REMOVE POPS TUESDAY NIGHT AND WEDNESDAY AS CHANCES

APPEAR TO BE LESS THAN THE 20 PERCENT THRESHOLD TO INCLUDE A

MENTION. RAIN CHANCES WILL INCREASE MARKEDLY BY LATE

WEEK...ESPECIALLY IN THE NORTHERN PART OF THE FORECAST AREA AS

GULF MOISTURE SURGES NORTH AND MEETS A STALLING FRONTAL BOUNDARY

NEAR THE KANSAS/OKLAHOMA BORDER. A STRONG UPPER SYSTEM WILL ALSO

LIFT NORTHEAST INTO THE PLAINS BY EARLY NEXT WEEKEND WHICH MAY

BRING A THREAT OF SEVERE WEATHER AROUND SATURDAY. SLIGHTLY

COOLER AND DRIER WEATHER WILL FOLLOW IN THE WAKE OF THIS SYSTEM

NEXT SUNDAY.

SGF:

AFTER A BRIEF COOL DOWN...MEDIUM RANGE MODELS CONTINUE TO BRING

STRONG UPPER LEVEL ENERGY OUT OF THE SOUTHWESTERN UNITED STATES FROM

FRIDAY INTO THE EARLY WEEKEND. AN INCREASINGLY DIFFLUENT FLOW ALOFT

ALONG WITH A DEVELOPING BAROCLINIC ZONE SHOULD MAKE FOR A RATHER WET

END TO THE WORK WEEK. WE HAVE MAINTAINED HIGH CHANCE TO LIKELY POPS

STARTING ON THURSDAY. THE LONG WAVE PATTERN CONTINUES TO SUPPORT

THIS ENERGY PASSING TO OUR NORTHWEST...WHICH WOULD EVENTUALLY PUT

THE OZARKS INTO THE WARM SECTOR OF A RATHER VIGOROUS STORM SYSTEM.

WHILE THIS SETUP WOULD INITIALLY APPEAR FAVORABLE FOR STRONG/SEVERE

STORM POTENTIAL...ONE MAJOR QUESTION MARK WILL BE THE RETURN OF

QUALITY MOISTURE FROM THE GULF OF MEXICO. WE WILL HAVE PLENTY OF

TIME TO FIGURE THAT ONE OUT THROUGHOUT THE UPCOMING WEEK.

EAX:

The cut-off low will head into the central Plains on Friday, kicking

the warm front northward through the region and spreading a chance

of thunderstorms across the entirety of the forecast area. Timing

and placement are relatively consistent between the longer-range

models through this period, lending confidence to higher-end

precipitation chances going into the weekend. The dynamic system

becomes stacked by early Saturday, then sweeps a strong cold front

through the Plains by Saturday afternoon. Moisture, deep layer

shear, instability, and the timing of frontal passage still looks

supportive of a chance for severe weather, especially across

southeastern portions of the CWA. Any precipitation should push out

quickly Saturday night, leaving a quiet forecast for Sunday.

TOP:

THURSDAY NIGHT THROUGH SATURDAY...RAIN AND THUNDERSTORM CHANCES WILL

INCREASE ACROSS THE ENTIRE CWA FROM THURSDAY NIGHT INTO SATURDAY

MORNING AS THE H5 TROUGH ACROSS THE SOUTHERN HIGH PLAINS LIFT

NORTHEAST ACROSS WESTERN KS INTO EASTERN NE. THE SURFACE WARM FRONT

ALONG THE KS AND OK BORDER WILL LIFT NORTHWARD ACROSS THE CWA FRIDAY

AFTERNOON AND FRIDAY NIGHT. ISENTROPIC LIFT AND ASCENT AHEAD OF THE

H5 LOW LIFTING OUT ACROSS WESTERN KS WILL CAUSE PERIODS OF SHOWERS

AND THUNDERSTORMS FRIDAY THROUGH SATURDAY MORNING. AN ENVIRONMENT

CONSISTING OF STRONG VERTICAL WINDSHEAR...DEEP MOISTURE ADVECTION AND

INCREASING INSTABILITY ACROSS WESTERN OK...NORTHWARD INTO WESTERN KS

WILL PROVIDE THE CHANCE FOR SEVERE THUNDERSTORMS FRIDAY AFTERNOON

AND EVENING. THERE IS A CHANCE THAT SOME OF THESE STORMS MAY

REMAIN STRONG TO SEVERE AS THEY MOVE INTO THE WESTERN COUNTIES OF

THE CWA LATE FRIDAY EVENING.

AS THE UPPER LOW LIFTS NORTHEAST ACROSS EASTERN NE A DRYLINE/PACIFIC

FRONT WILL PUSH EAST ACROSS THE CWA. THE ECMWF HAS THE PACIFIC COLD

FRONT PUSHING EAST OF THE CWA AFTER 18Z SAT...WHICH WOULD CAUSE THE

REDEVELOPMENT OF AFTERNOON THUNDERSTORMS EAST OF THE CWA. IF WE

GET INSOLATION EARLY SATURDAY AFTERNOON TEMPERATURES MAY WARM UP

TO INTO THE UPPER 70S TO AROUND 80 ACROSS EAST CENTRAL KS BEFORE

COLDER AIR MOVES IN BEHIND THE PACIFIC FRONT.

[Disc]

Some pretty impressive wind shear values showing up on the 18z GFS run.

[andyhb]

Instability notwithstanding, that is a nasty LLJ (50-70 kts at H85) on the 00z GFS for Saturday. Seems like it wants to place its axis over E KS, NE OK and W MO at this juncture. 90 kts at 500 mb to boot.

[brettjrob]

Instability notwithstanding, that is a nasty LLJ (50-70 kts at H85) on the 00z GFS for Saturday. Seems like it wants to place its axis over E KS, NE OK and W MO at this juncture.

Right now this disturbance looks to me like a textbook example of mis-timing what could otherwise be a major event, and how frustrating it can be to follow a phenomenon so reliant on the diurnal cycle. Any time I see a forecast H5 chart valid at 12z and think "wow, that screams outbreak," I get that sinking feeling... especially in progressive patterns outside of May-June.

Slow it down 12 hours and you have a potential doozy centered on the I-35 corridor. Speed it up even 6-10 hours and Friday might look more solid across the High Plains. As it stands, it's close to the worst-case scenario, especially for chasers. With the 00z GFS timing, I see some potential for early-day action Saturday in MO/AR and E OK/KS... and *maybe* cold core for NE/IA. Overall, though, instability would be in short supply and the low levels would be veering out faster than you can say, "is it 2013 yet?"

As you said earlier, the timing is not yet set in stone, particularly given we're dealing with a SW closed low. Kinematics and timing notwithstanding, moisture return in the Plains should be above-average for fall setups, though that will be tempered a bit by mid-level thermals (> -10 C at H5... yuck).

[andyhb]

I am also weary that the GFS might also be underdoing sfc temps as well. For the KC area, for example, on Saturday, it has around 65-67 degrees. The NWS is forecasting around 74-75 degrees.

FWIW, the 00z GFS did slow down a bit from the 12z/18z runs.

[brettjrob]

I am also weary that the GFS might also be underdoing sfc temps as well. For the KC area, for example, on Saturday, it has around 65-67 degrees. The NWS is forecasting around 74-75 degrees.

FWIW, the 00z GFS did slow down a bit from the 12z/18z runs.

There's no question the CAPE values painted on the GFS are underdone for whatever solution it shows due to a cold BL bias, as is always the case in the medium range. Even so, I still don't see a quality warm sector making it very far E into AR/MO/IA with the type of trajectories they'd be seeing.

Regarding timing, the slowing trend kind of disgusted me because I've all but written off Saturday for a good chase setup (I'd rather just put my cards on Friday for pretty-looking storms out west)... but you know my bias. I do think you're right in that a bit more slowing could allow for a significant threat Sat afternoon into the eastern edge of the Plains and western Ozarks... where CAPE values might be significantly higher than shown.

[andyhb]

There's no question the CAPE values painted on the GFS are underdone for whatever solution it shows due to a cold BL bias, as is always the case in the medium range. Even so, I still don't see a quality warm sector making it very far E into AR/MO/IA with the type of trajectories they'd be seeing.

Regarding timing, the slowing trend kind of disgusted me because I've all but written off Saturday for a good chase setup (I'd rather just put my cards on Friday for pretty-looking storms out west)... but you know my bias. I do think you're right in that a bit more slowing could allow for a significant threat Sat afternoon into the eastern edge of the Plains and western Ozarks... where CAPE values might be significantly higher than shown.

Great post, and I agree. The kinematics currently progged on Saturday would make any underestimation of the instability a potentially dangerous proposition, even if it is a relatively narrow areal coverage (yet possibly significantly populated) area.

[thewxmann]

I wouldn't bank on the instability being underdone just yet... the GFS cold bias is not as prevalent after the whole upgrade, and BL moisture could still be overdone (given the ongoing drought in the Plains).

[andyhb]

I wouldn't bank on the instability being underdone just yet... the GFS cold bias is not as prevalent after the whole upgrade, and BL moisture could still be overdone (given the ongoing drought in the Plains).

To be quite honest, I haven't noticed a lot of difference in this particular field with the GFS pre and post upgrade. Of course, this may also have to do with not following a whole lot through this period given the overall lack of activity.

In addition, the drought conditions in TX, which is obviously an area the LL moisture has to cross to penetrate north, is nowhere near the drought conditions it was in last year, just an observation.

[andyhb]

00z Euro is slower and further north than the GFS, although the warm sector is significantly wider than the GFS and it actually gets small pockets 2000 J/kg+ CAPE near the low in NE around 00z, in addition to a respectable coverage of 1000-1500+ J/kg.

[JoMo]

Wait, should I be paying attention to this?

[andyhb]

Wait, should I be paying attention to this?

I'd advise you to.

[Stebo]

Wait, should I be paying attention to this?

I'd say it is a bit early to get into specifics but this could have a potential for parts of the plains states next weekend.

[JoMo]

I'd advise you to.

Man, I was getting ready for winter, too.

Looks like WAA stuff on Thurs evening, warm front action on Friday afternoon/eve and then probably a squall line or something on Sat afternoon/eve for here this run. Oh boy :-\

[thewxmann]

To be quite honest, I haven't noticed a lot of difference in this particular field with the GFS pre and post upgrade. Of course, this may also have to do with not following a whole lot through this period given the overall lack of activity.

In addition, the drought conditions in TX, which is obviously an area the LL moisture has to cross to penetrate north, is nowhere near the drought conditions it was in last year, just an observation.

This is true, and it'll be interesting to see if the reduction of drought conditions, both in the southern Plains and in the mid-Mississippi Valley, will help with the low-level moisture issues. However, we still have severe drought conditions in the central and northern Plains, so any veering of low-level flow could still advect dry air from those areas.

[andyhb]

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0355 AM CDT MON OCT 08 2012

VALID 111200Z - 161200Z

..DISCUSSION

MEDIUM RANGE MODELS CONTINUE TO INDICATE THE TRANSITION TO A MORE

ZONAL/PROGRESSIVE UPPER FLOW REGIME LATE THIS COMING WORK WEEK INTO

NEXT WEEKEND. AS THIS OCCURS...A CLOSED LOW...MIGRATING INLAND

ACROSS THE CALIFORNIA COAST BY MID WEEK...APPEARS LIKELY TO RAPIDLY

ACCELERATE EAST NORTHEASTWARD OUT OF THE SOUTHWESTERN STATES. AND

IT IS APPEARING INCREASINGLY LIKELY THAT THIS WILL BE ACCOMPANIED BY

SIGNIFICANT SURFACE CYCLOGENESIS FROM THE LEE OF THE CENTRAL ROCKIES

THROUGH THE GREAT LAKES AND EASTERN CANADA. GUIDANCE HAS BEEN

SUGGESTIVE THAT UPWARD VERTICAL MOTION...DEEP LAYER FLOW FIELDS AND

VERTICAL SHEAR WILL BE MOST SUPPORTIVE OF SEVERE WEATHER POTENTIAL

IN THE WARM SECTOR OF THIS SYSTEM ON SATURDAY. THIS SEEMS MOST

PROBABLE ACROSS PARTS OF EASTERN NEBRASKA AND KANSAS...NORTHEAST

OKLAHOMA...THE NORTHWESTERN THIRDS OF MISSOURI...IOWA AND ADJACENT

NORTHWEST ILLINOIS...SOUTHWESTERN WISCONSIN AND SOUTHERN MINNESOTA.

HOWEVER...THIS TIME FRAME ALSO COINCIDES WITH A SIGNIFICANT INCREASE

IN SPREAD AMONG MODEL ENSEMBLE DATA...PARTICULARLY CONCERNING THE

SPEED OF THE UPPER IMPULSE. QUESTIONS ALSO LINGER CONCERNING THE

DEGREE OF WARM SECTOR BOUNDARY LAYER DESTABILIZATION...WHICH COULD

BE IMPACTED SIGNIFICANTLY BY PRIOR CONVECTION. TOO MUCH UNCERTAINTY

STILL EXISTS TO CONFIDENTLY ASSESS THE POTENTIAL FOR A REGIONAL

SEVERE WEATHER EVENT.

..KERR.. 10/08/2012

[Ian]

I was considering a spot chase this fall but plane tix are super expensive right now.. Sat looks like it could be more widespread but I'm not sure I like the look for a tornado event of note as per many reasons noted above. Fri might be fun.

[LocoAko]

Only did a cursory glance at the models this morning but the 00Z ECMWF seems at least moderately slower with the progression of the system. At 00Z Sunday the ECMWF has the 500 hPa low over north-central Nebraska and eastern South Dakota while the GFS has the low over the Nebraska/Iowa border. The front at that time is in eastern Oklahoma but the ECMWF still has it entering the I-35 corridor (with more CAPE to boot, too). This is my first time glancing at the Euro though so I don't know how this stacks up against its other runs.

[brettjrob]

I was considering a spot chase this fall but plane tix are super expensive right now.. Sat looks like it could be more widespread but I'm not sure I like the look for a tornado event of note as per many reasons noted above. Fri might be fun.

Committing to a $500 ticket right now for this would be bordering on insanity, IMO... good call.

Only did a cursory glance at the models this morning but the 00Z ECMWF seems at least moderately slower with the progression of the system. At 00Z Sunday the ECMWF has the 500 hPa low over north-central Nebraska and eastern South Dakota while the GFS has the low over the Nebraska/Iowa border. The front at that time is in eastern Oklahoma but the ECMWF still has it entering the I-35 corridor (with more CAPE to boot, too). This is my first time glancing at the Euro though so I don't know how this stacks up against its other runs.

The Euro is a little closer to what we'd want to see for Saturday. The dryline never makes it past W OK even into the early evening, in fact. Problem is that low-level flow still veers out along most of the DL, as the trough becomes positive-tilt and the best support lifts so far north. Course, if something like the EC occurred but with a weak secondary sfc low on the OK/KS border (possible mesoscale detail to be resolved later), that might be a different story.

The 06z GFS didn't throw us any bones, speeding up by another ~6 hrs. Blah... my track record when I don't know which day to pull for less than a week out leaves something to be desired.