On to December...

[csnavywx]

Update on post 28.

Nov 13th (old) post below....

Lots of changes going on right now, and I've heard some rumbling in the threads about the clipper-type system coming up next week, but I have a strong feeling that system (and the ongoing one) is simply an appetizer to a much more active regime.

But how and why?

Some of this has to do with the tropics (and recent -dAAM/dt trend wrt mountain torques) as mentioned in HM's thread. This should allow the recently raging Pacific Jet to buckle and cause a -EPO pattern. It's been very obvious that the models have been pointing to a very strong -EPO ridge, and this appears to be in the beginning stages of materializing. Both the GFS and EURO (Euro shown here) are in fairly good agreement, with some variance on the strength of the ridges in later frames, though the agreement is rather exceptional for this time range.

Current setup:

48 hr:

Note how quickly the EPAC ridge is strengthening. Another low-height ridge is moving towards the Bering Straits, which should eventually phase with the mean longwave ridge over the EPAC and amplify. It initially sets up a Rex-type block, but then quickly transitions into a full blown classic omega block.

96 hr:

By this point we're in a full -EPO omega blocking pattern and the PV has begun to drift towards the NW Territories/Nunavut. Pressures have risen significantly over NW canada and AK where a major dome of cold arctic air is building. The mean longwave position should still be in the plains/off the front range of the Rockies at this point (after smoothing out s/w trofs). Heights are beginning to gradually build in the W Atlantic in response to the longwave and PV digging in over Canada and the CONUS.

144hr

-EPO block is maturing, and the PV continues to drift slowly southward. The beginnings of cross polar flow can be seen between these two features and some seriously cold air is built up over Canada at this point. Meanwhile, the response over the NW Atlantic has been to gradually build heights and this is reflected in a large and growing longwave ridge pattern there.

192 hr

EPO block still in place, and this ridge doesn't really look to go anywhere. True cross-polar flow is developing at this point, with another low-height ridge pattern similar to the first couple of frames developing over Siberia/E Asia. Persistent height building/WAA aloft has allowed the W Atlantic ridge to build into an incipient blocking pattern. Also notice the Nina-induced SE ridge attempting to make a comeback. This is important, as it tends to keep cold air surges from scouring the GOM, keeping our moisture source in play.

240 hr

Monster (582+ dam) -NAO block over Greenland on this run. Previous runs had something similar, and the ensembles show generally good support for strong ridge/block pattern here. It remains to be seen whether or not it will actually get that strong, but if it does, watch out. Meanwhile, the EPAC ridge looks to get another boost with a possible repeat phasing scenario, and the PV is solidly locked on our side of the hemisphere... for now. Ridging over the far SE states and GOM is still present on both ensembles in some form, keeping the moisture supply in play.

What does this mean for folk in the plains and Midwest/GL?

Patterns like this tend to feature rather extreme gradients, and I don't think this will be an exception. This pattern would also keep a fresh supply of cold air coming, but if the flat SE/GOM ridge materializes, I think we'll be in for a lot of overrunning events. We've seen somewhat similar setups in the past few years, and each one has lent one or more widespread ice/mix/snow events.

A few pointers:

-This pattern favors repeated shallow arctic air intrusions.

-Careful using 850s and 1000-500mb thickness charts! Shallow intrusions do not tend to show up well using these measures.

-A persistent and sharp baroclinic zone is likely to be present. These tend to set up over the Ohio or TN valleys, but can move north and south based on the strength of the s/w trofs round the base of the western Longwave.

-This type of pattern is also favorable for inverted-trough type scenarios. Watch out for these.

Having said all of that, check out some of the 180 hr/240 hr ensemble frames:

EC 192/240 hr 850 temps/MSLP:

GFS 192/240 hr 850 temps/MSLP:

All in all, some remarkably good agreement from the ensemble means there. Note the favorable positions of the SE ridge and cold/arctic High. Like I said before, don't get to caught up on the specific 850s here, the SFC temps are likely to be way different (look at the separation of the surface trough and 850 thermal ribbon-- HUGE).

[Hoosier]

Good post. This type of pattern is often favorable for model busting cold, as in the shallow cold being underestimated. It seems like the biggest errors tend to occur in the Plains states. IIRC, the first part of December 2007 had a pattern like this and it was very stormy.

[JoMo]

This usually leads to SW Flow over the top of cold (arctic) air at the surface which leads to freezing rain/sleet type scenarios. The main issue is how far SE the cold air makes it and if the moisture will flow over the top of it or if it will be farther SE in the 'warm' sector.

[IWXwx]

Great analysis. I like overrunning events. It leads to interesting weather over a wide area. I'd take this over a couple of lame early season clippers.

[JoMo]

Good post. This type of pattern is often favorable for model busting cold, as in the shallow cold being underestimated. It seems like the biggest errors tend to occur in the Plains states. IIRC, the first part of December 2007 had a pattern like this and it was very stormy.

Yeah, this was the ice storm that happened here Dec 8th-10th 2007. As you can see on the upper air maps, the 850 MB freezing line (upper left panel) was way NW of where the precip was occurring in SW Missouri.

However, the surface maps clearly show the cold air cutting under the warmer air aloft:

Continued through to the next morning:

The end result:

The shallow cold air has a tough time making it through the Ozarks so that's why there was a sharp cutoff where the ice stopped to the SE.

[Mallow]

Especially for what it might mean for us here in the western lowlands of the Pac NW.

[Srain]

This is one of the best discussions from a local WFO I have seen in a long time regarding all the players and the effects felt downstream...

Dodge City, KS...

DAYS 3-7...

TROPICAL THUNDERSTORMS REMAIN ACTIVE IN THE INDIAN OCEAN, BUT

ACTIVITY HAS DECREASED IN THE MARITIME CONTINENT IN RECENT DAYS.

ATMOSPHERIC RELATIVE ANGULAR MOMENTUM HAS DECREASED TO NEARLY TWO

STANDARD DEVIATIONS BELOW CLIMATOLOGY, AND TENDENCIES STILL ARE

NEGATIVE. HOWEVER, MOUNTAIN TORQUE HAS BEGUN TO INCREASE LARGELY DUE

TO A POSITIVE CONTRIBUTION FROM THE ANDES IN SOUTH AMERICA. THE

WHEELER-HENDON MJO PHASE SPACE DIAGRAM SUGGESTS THAT THE REMNANTS OF

A MJO OSCILLATION MAY BE PROGRESSING RAPIDLY EASTWARD ACROSS THE

WESTERN HEMISPHERE. THIS FEATURE LIKELY WILL ENHANCE CONVECTION IN

THE INDIAN OCEAN LATE THIS WEEK INTO NEXT WEEK. THE ATMOSPHERE

APPEARS TO BE OSCILLATING THROUGH PHASE 1-2 TOWARD PHASE 3-4 OF THE

BERRY/WEICKMANN GLOBAL WIND OSCILLATION. PHASES 3 AND 4 FAVOR

RIDGING IN THE WESTERN UNITED STATES AND UPPER LEVEL HIGH PRESSURE

AROUND 160W WITH A MEAN TROUGH IN THE EASTERN PACIFIC.

THE NUMERICAL MODELS TODAY ARE IN GOOD AGREEMENT ON THE EVOLUTION OF

THE LARGE SCALE FLOW THROUGH LATE NOVEMBER. THE UPPER LEVEL RIDGE

NEAR 135-140W WILL BUILD INTO THE WESTERN UNITED STATES WHILE A

SHARP UPPER LEVEL RIDGE BUILDS AROUND 160W BY 18 NOVEMBER. A SLOWLY

PROGRESSIVE LONG WAVE PATTERN SUPPORTS PROGRESSION OF A LONG WAVE

TROUGH TO THE CENTRAL PLAINS BY 22-23 NOVEMBER. A LOBE OF THE POLAR

VORTEX WILL DEEPEN IN CENTRAL CANADA BY THE WEEKEND, AND A STRONG

TROUGH ROTATING AROUND THE VORTEX WILL MOVE ACROSS SOUTHERN CANADA

22-23 NOVEMBER. THIS WILL OPEN THE DOOR FOR AN INVASION OF

SHALLOW ARCTIC AIR IN THE CENTRAL UNITED STATES AROUND 22

NOVEMBER, ALTHOUGH CONFIDENCE IN SYNOPTIC SCALE DETAILS THAT FAR OUT

IS LOW. THE ECMWF IS MORE PROGRESSIVE WITH THE CENTRAL UNITED STATES

TROUGH THAN THE GFS AND PROBABLY IS MORE REASONABLE.

IN THE DAY 4-7 PERIOD, THE NUMERICAL MODELS AGREE REMARKABLY WELL.

THE STRONG UPPER LEVEL TROUGH NEAR 165W WILL PROPAGATE OVER THE

WEAKENING EASTERN PACIFIC RIDGE AND MOVE ACROSS THE CENTRAL PLAINS

TUESDAY NIGHT AND WEDNESDAY MORNING. LOW LEVEL OFFSHORE FLOW WILL

CONTINUE ALONG THE GULF COAST THROUGH WEDNESDAY, AND LOW LEVEL

MOISTURE WILL BE EXTREMELY LIMITED IN THE CENTRAL PLAINS AS THE

UPPER LEVEL TROUGH RIPPLES THROUGH THE FLOW. INSTABILITY WITH THE

UPPER LEVEL COLD POOL AND UPPER LEVEL DIVERGENCE IN THE EXIT REGION

OF THE JET STREAK MAY BE SUFFICIENT TO SUPPORT LIGHT PRECIPITATION

IN NORTHERN KANSAS AND SOUTHERN NEBRASKA LATE TUESDAY NIGHT AND

EARLY WEDNESDAY, BUT THE POTENTIAL FOR MEASURABLE PRECIPITATION IS

VERY LOW SOUTH OF INTERSTATE 70. TEMPERATURES IN THE LOWER LEVELS OF

THE ATMOSPHERE WILL BE WARM ENOUGH THAT PRECIPITATION SHOULD FALL IN

LIQUID FORM.

AS THE LONG WAVE TROUGH DEEPENS IN THE EASTERN PACIFIC LATE THIS

WEEK, INCREASING FLOW PERPENDICULAR TO THE ROCKIES WILL SUPPORT

STRONG TROUGHING IN THE LEE OF THE MOUNTAINS THURSDAY AND FRIDAY.

TEMPERATURES SHOULD WARM BACK INTO THE 60S NEAR THE COLORADO BORDER

THURSDAY, AND HIGHS NEAR 70 CAN BE EXPECTED IN FAR WESTERN KANSAS

FRIDAY. DEWPOINTS WILL BE IN THE 20S IN MOST AREAS, AND RELATIVE

HUMIDITIES WILL APPROACH RED FLAG CRITERIA BOTH THURSDAY AND FRIDAY.

AN UPPER LEVEL TROUGH WILL MOVE THROUGH SOUTHERN CANADA TO THE GREAT

LAKES BY SATURDAY MORNING, AND A SHALLOW SURGE OF COOL AIR WILL WORK

ACROSS KANSAS FRIDAY NIGHT. THERE WILL BE A SUBSTANTIAL TEMPERATURE

GRADIENT IN WESTERN KANSAS SATURDAY WITH TEMPERATURES IN THE UPPER

60S AND LOWER 70S WHERE THE SHALLOW COLD AIR MIXES OUT AND NEARLY 20

DEGREES COOLER NORTH OF THE BOUNDARY. ANOTHER UPPER LEVEL TROUGH

WILL MOVE FROM THE SOUTHWESTERN UNITED STATES TO THE NORTHERN PLAINS

SUNDAY. THE SHALLOW COLD AIR WILL RETREAT NORTHWARD SATURDAY NIGHT

AND MAKE ANOTHER SURGE SOUTHWARD ON SUNDAY. CONFIDENCE IN THE

STRENGTH AND TIMING OF THE TROUGHS RIPPLING THROUGH THE STRONG

SOUTHWEST UPPER LEVEL FLOW IS NOT HIGH, AND THE PRESENCE OF A SHARP

LOW LEVEL BAROCLINIC ZONE WALLOWING BACK AND FORTH IN KANSAS MAKES

TEMPERATURE FORECASTS HIGHLY SUSCEPTIBLE TO SIGNIFICANT ERRORS

DURING THE WEEKEND. THE ECMWF SEEMS TO HAVE A TENDENCY TO SCOUR OUT

SHALLOW COOL AIR TOO QUICKLY, AND THE GFS LARGELY WAS USED AS A

FIRST GUESS ON FRONTAL POSITIONS SATURDAY AND SUNDAY.

[Hoosier]

This is one of the best discussions from a local WFO I have seen in a long time regarding all the players and the effects felt downstream...

Dodge City, KS...

The DDC long term discussions are very informative. They go into detail that most other offices don't.

[Thundersnow12]

Excellent and detailed discussion sir. Have been watching the LR ensembles for about the past week and have been noticing the same thing. Think it was 05' but not sure, we got a nice 5" snowstorm right around turkey day, wouldn't mind that again.

Hopefully there will be enough cold air around for a sizeable system to tap along with sufficient moisture.

[Hoosier]

Excellent and detailed discussion sir. Have been watching the LR ensembles for about the past week and have been noticing the same thing. Think it was 05' but not sure, we got a nice 5" snowstorm right around turkey day, wouldn't mind that again.

Hopefully there will be enough cold air around for a sizeable system to tap along with sufficient moisture.

2004

[Thundersnow12]

2004

lol my bad, thank you!

[baroclinic_instability]

Great discussion CSnavywx, very informative. I definitely need to work on my long range forecasting skills after reading this.

[Stebo]

2004

Ugh don't remind me of that storm, drove from Mount Pleasant to Detroit in a blizzard, first time I ever drive in snow and its a nightmare, 2 1/2 hour drive ended up being 6.

[Guru Of Reason]

Thank you, Csnavywx. Awesome analysis.

[wxlady]

If I had to guess, I'd bet this was written by former OU grad student Jon Finch. Excellent forecaster.

Anyway, the whole set up looks great for northern Utah and Colorado snow bunnies. Fresh snow just in time for the weekend and continuing through the extended holiday. Maybe they should have a Black Friday special at Alta.

This is one of the best discussions from a local WFO I have seen in a long time regarding all the players and the effects felt downstream...

Dodge City, KS...

DAYS 3-7...

TROPICAL THUNDERSTORMS REMAIN ACTIVE IN THE INDIAN OCEAN, BUT

ACTIVITY HAS DECREASED IN THE MARITIME CONTINENT IN RECENT DAYS.

ATMOSPHERIC RELATIVE ANGULAR MOMENTUM HAS DECREASED TO NEARLY TWO

STANDARD DEVIATIONS BELOW CLIMATOLOGY, AND TENDENCIES STILL ARE

NEGATIVE. HOWEVER, MOUNTAIN TORQUE HAS BEGUN TO INCREASE LARGELY DUE

TO A POSITIVE CONTRIBUTION FROM THE ANDES IN SOUTH AMERICA. THE

WHEELER-HENDON MJO PHASE SPACE DIAGRAM SUGGESTS THAT THE REMNANTS OF

A MJO OSCILLATION MAY BE PROGRESSING RAPIDLY EASTWARD ACROSS THE

WESTERN HEMISPHERE. THIS FEATURE LIKELY WILL ENHANCE CONVECTION IN

THE INDIAN OCEAN LATE THIS WEEK INTO NEXT WEEK. THE ATMOSPHERE

APPEARS TO BE OSCILLATING THROUGH PHASE 1-2 TOWARD PHASE 3-4 OF THE

BERRY/WEICKMANN GLOBAL WIND OSCILLATION. PHASES 3 AND 4 FAVOR

RIDGING IN THE WESTERN UNITED STATES AND UPPER LEVEL HIGH PRESSURE

AROUND 160W WITH A MEAN TROUGH IN THE EASTERN PACIFIC.

THE NUMERICAL MODELS TODAY ARE IN GOOD AGREEMENT ON THE EVOLUTION OF

THE LARGE SCALE FLOW THROUGH LATE NOVEMBER. THE UPPER LEVEL RIDGE

NEAR 135-140W WILL BUILD INTO THE WESTERN UNITED STATES WHILE A

SHARP UPPER LEVEL RIDGE BUILDS AROUND 160W BY 18 NOVEMBER. A SLOWLY

PROGRESSIVE LONG WAVE PATTERN SUPPORTS PROGRESSION OF A LONG WAVE

TROUGH TO THE CENTRAL PLAINS BY 22-23 NOVEMBER. A LOBE OF THE POLAR

VORTEX WILL DEEPEN IN CENTRAL CANADA BY THE WEEKEND, AND A STRONG

TROUGH ROTATING AROUND THE VORTEX WILL MOVE ACROSS SOUTHERN CANADA

22-23 NOVEMBER. THIS WILL OPEN THE DOOR FOR AN INVASION OF

SHALLOW ARCTIC AIR IN THE CENTRAL UNITED STATES AROUND 22

NOVEMBER, ALTHOUGH CONFIDENCE IN SYNOPTIC SCALE DETAILS THAT FAR OUT

IS LOW. THE ECMWF IS MORE PROGRESSIVE WITH THE CENTRAL UNITED STATES

TROUGH THAN THE GFS AND PROBABLY IS MORE REASONABLE.

IN THE DAY 4-7 PERIOD, THE NUMERICAL MODELS AGREE REMARKABLY WELL.

THE STRONG UPPER LEVEL TROUGH NEAR 165W WILL PROPAGATE OVER THE

WEAKENING EASTERN PACIFIC RIDGE AND MOVE ACROSS THE CENTRAL PLAINS

TUESDAY NIGHT AND WEDNESDAY MORNING. LOW LEVEL OFFSHORE FLOW WILL

CONTINUE ALONG THE GULF COAST THROUGH WEDNESDAY, AND LOW LEVEL

MOISTURE WILL BE EXTREMELY LIMITED IN THE CENTRAL PLAINS AS THE

UPPER LEVEL TROUGH RIPPLES THROUGH THE FLOW. INSTABILITY WITH THE

UPPER LEVEL COLD POOL AND UPPER LEVEL DIVERGENCE IN THE EXIT REGION

OF THE JET STREAK MAY BE SUFFICIENT TO SUPPORT LIGHT PRECIPITATION

IN NORTHERN KANSAS AND SOUTHERN NEBRASKA LATE TUESDAY NIGHT AND

EARLY WEDNESDAY, BUT THE POTENTIAL FOR MEASURABLE PRECIPITATION IS

VERY LOW SOUTH OF INTERSTATE 70. TEMPERATURES IN THE LOWER LEVELS OF

THE ATMOSPHERE WILL BE WARM ENOUGH THAT PRECIPITATION SHOULD FALL IN

LIQUID FORM.

AS THE LONG WAVE TROUGH DEEPENS IN THE EASTERN PACIFIC LATE THIS

WEEK, INCREASING FLOW PERPENDICULAR TO THE ROCKIES WILL SUPPORT

STRONG TROUGHING IN THE LEE OF THE MOUNTAINS THURSDAY AND FRIDAY.

TEMPERATURES SHOULD WARM BACK INTO THE 60S NEAR THE COLORADO BORDER

THURSDAY, AND HIGHS NEAR 70 CAN BE EXPECTED IN FAR WESTERN KANSAS

FRIDAY. DEWPOINTS WILL BE IN THE 20S IN MOST AREAS, AND RELATIVE

HUMIDITIES WILL APPROACH RED FLAG CRITERIA BOTH THURSDAY AND FRIDAY.

AN UPPER LEVEL TROUGH WILL MOVE THROUGH SOUTHERN CANADA TO THE GREAT

LAKES BY SATURDAY MORNING, AND A SHALLOW SURGE OF COOL AIR WILL WORK

ACROSS KANSAS FRIDAY NIGHT. THERE WILL BE A SUBSTANTIAL TEMPERATURE

GRADIENT IN WESTERN KANSAS SATURDAY WITH TEMPERATURES IN THE UPPER

60S AND LOWER 70S WHERE THE SHALLOW COLD AIR MIXES OUT AND NEARLY 20

DEGREES COOLER NORTH OF THE BOUNDARY. ANOTHER UPPER LEVEL TROUGH

WILL MOVE FROM THE SOUTHWESTERN UNITED STATES TO THE NORTHERN PLAINS

SUNDAY. THE SHALLOW COLD AIR WILL RETREAT NORTHWARD SATURDAY NIGHT

AND MAKE ANOTHER SURGE SOUTHWARD ON SUNDAY. CONFIDENCE IN THE

STRENGTH AND TIMING OF THE TROUGHS RIPPLING THROUGH THE STRONG

SOUTHWEST UPPER LEVEL FLOW IS NOT HIGH, AND THE PRESENCE OF A SHARP

LOW LEVEL BAROCLINIC ZONE WALLOWING BACK AND FORTH IN KANSAS MAKES

TEMPERATURE FORECASTS HIGHLY SUSCEPTIBLE TO SIGNIFICANT ERRORS

DURING THE WEEKEND. THE ECMWF SEEMS TO HAVE A TENDENCY TO SCOUR OUT

SHALLOW COOL AIR TOO QUICKLY, AND THE GFS LARGELY WAS USED AS A

FIRST GUESS ON FRONTAL POSITIONS SATURDAY AND SUNDAY.

[patrick7032]

Immediately ahead of the outbreak if the current run of the GFS can verify, and the ECMWF AND CMC have hinted at it, given the history of high shear/low CAPE systems this season, and the fact that the GFS ALWAYS under forecasts LLVL thermal fields, we could have one more severe wind, weak tornado event. It's STILL WAY TOO EARLY to get hopes up, let alone start a thread....Still something to watch as current runs already show instability which is RARE for the GFS, let alone at this forecast range.

[patrick7032]

Immediately ahead of the outbreak if the current run of the GFS can verify, and the ECMWF AND CMC have hinted at it, given the history of high shear/low CAPE systems this season, and the fact that the GFS ALWAYS under forecasts LLVL thermal fields, we could have one more severe wind, weak tornado event. It's STILL WAY TOO EARLY to get hopes up, let alone start a thread....Still something to watch as current runs already show instability which is RARE for the GFS, let alone at this forecast range.

[Srain]

Immediately ahead of the outbreak if the current run of the GFS can verify, and the ECMWF AND CMC have hinted at it, given the history of high shear/low CAPE systems this season, and the fact that the GFS ALWAYS under forecasts LLVL thermal fields, we could have one more severe wind, weak tornado event. It's STILL WAY TOO EARLY to get hopes up, let alone start a thread....Still something to watch as current runs already show instability which is RARE for the GFS, let alone at this forecast range.

I made a comment in the Texas thread last night concerning this. Certainly worth watching, IMO.

[Srain]

Dodge City, KS WFO again offers a great discussion on how things will likely play out regarding the Arctic Front and reinforcing shots of cold air as well as the forces at work...

DAYS 3-7...

TEMPERATURES WILL CONTINUE TO BE EXTREMELY DIFFICULT TO FORECAST IN

THE EXTENDED PERIOD AS SHALLOW COLD AIR SLOSHES BACK AND FORTH

ACROSS WESTERN KANSAS IN RESPONSE TO MINOR WAVES RIPPLING THROUGH

THE FLOW. CONFIDENCE IN THE OSCILLATIONS OF THE SHALLOW COLD AIR

POOL IS LOW, AND THE POTENTIAL FOR MAJOR TEMPERATURE FORECAST

MISSES IS HIGH.

STRONG RIDGING IS IN PROGRESS JUST EAST OF THE DATELINE, AND

DOWNSTREAM AMPLIFICATION OF THE LONG WAVE TROUGH IN THE EASTERN

PACIFIC WILL OCCUR AS A STRONG JET STREAK MOVES OVER THE TOP OF THE

DATELINE RIDGE AND DIVES SOUTHWARD AROUND 130W BY SATURDAY. THE

VIGOROUS UPPER LEVEL TROUGH EVIDENT ON SATELLITE IMAGERY NEAR

52N/142W EARLY THIS MORNING WILL PROPAGATE EASTWARD INTO WESTERN

ONTARIO BY FRIDAY MORNING. A RESERVOIR OF COLD AIR CONTINUES TO

BUILD IN CANADA WITH SURFACE TEMPERATURES IN THE SINGLE DIGITS AS

FAR SOUTH AS SOUTHERN ALBERTA AND CENTRAL SASKATCHEWAN. AS THE UPPER

LEVEL TROUGH MOVES THROUGH SOUTHERN CANADA, A PORTION OF THIS COLD

AIR RESERVOIR WILL SURGE SOUTHWARD INTO NORTHERN KANSAS BY FRIDAY

MORNING AND SHOULD MOVE ACROSS ALL OF SOUTHWEST KANSAS BY FRIDAY

EVENING. TEMPERATURES FRIDAY WILL BE VERY WARM AHEAD OF THE BOUNDARY

AND SHOULD APPROACH 70 DEGREES ALONG THE OKLAHOMA BORDER.

PERSISTENT UPSLOPE FLOW AND ISENTROPIC LIFTING OVER THE SHALLOW COLD

AIR LIKELY WILL SUPPORT FORMATION OF AN AREA OF STRATUS IN

NORTHWESTERN KANSAS LATE FRIDAY NIGHT INTO SATURDAY. THE MOIST LAYER

MAY BE DEEP ENOUGH TO SUPPORT DEVELOPMENT OF VERY LIGHT DRIZZLE OR

FREEZING DRIZZLE FOR A FEW HOURS, BUT THE SURFACE WILL BE WARM

ENOUGH THAT ANY FREEZING DRIZZLE THAT DOES FALL WILL HAVE MINIMAL

IMPACT ON ROADWAYS. THE SHALLOW COLD AIR WILL REMAIN ENTRENCHED

ACROSS MOST OF SOUTHWEST KANSAS SATURDAY, AND THE STRATUS WILL BE

VERY SLOW TO ERODE. SOME EROSION OF THE COLD AIR IS LIKELY SINCE

MOST OF SOUTHWEST KANSAS WILL HAVE ONLY THIN, HIGH CLOUDINESS

SATURDAY, AND THE ECMWF SOLUTION OF SPREADING WARM AIR BACK TOWARD

MORTON COUNTY DURING THE AFTERNOON LOOKS REASONABLE.

STRONG SOUTHWEST FLOW ABOVE THE SURFACE WILL DEVELOP SATURDAY NIGHT

AS AN UPPER LEVEL TROUGH MOVES FROM THE SOUTHWESTERN PART OF THE

COUNTRY TO THE WESTERN DAKOTAS BY SUNDAY MORNING, AND THE COLD AIR

LIKELY WILL RETREAT TO AT LAST NORTHERN KANSAS BY SUNDAY MORNING.

ONCE AGAIN SUNDAY, THE SHARP BAROCLINIC ZONE ALONG THE EDGE OF THE

SHALLOW COLD POOL WILL BEGIN TO PUSH BACK SOUTHWARD BEHIND THE UPPER

LEVEL TROUGH. VERY WARM TEMPERATURES CAN BE EXPECTED IN THE WARM

SECTOR ALONG THE OKLAHOMA BORDER, WHILE TEMPERATURES ARE ABOUT 20

DEGREES COOLER ALONG INTERSTATE 70.

YET ANOTHER UPPER LEVEL TROUGH WILL MOVE THROUGH THE SOUTHWESTERLY

UPPER LEVEL FLOW MONDAY, AND THE BOUNDARY ONCE AGAIN WILL LIFT

NORTHWARD AND SUBSEQUENTLY SURGE BACK SOUTH ACROSS WESTERN KANSAS. A

MORE SIGNIFICANT SURGE OF COLD AIR STILL APPEARS LIKELY TO INVADE

KANSAS MONDAY NIGHT AS A STRONGER TROUGH ROTATES AROUND THE POLAR

VORTEX WEST OF HUDSON BAY AND DISLODGES A BIGGER PIECE OF THE COLD

AIR RESERVOIR.

[Srain]

I’m beginning to take interest in the potential severe threat next week. The Gulf should be wide open and with noisy U/A Pattern along with a volatile Arctic Boundary nearby, a significant late fall episode may well set up...DDC snip, again...

BY TUESDAY NIGHT AND WEDNESDAY OF NEXT

WEEK...THE LARGE TROUGH CENTERED ACROSS THE INTERMOUNTAIN WEST OR

THE ROCKIES...WILL AMPLIFY AND APPROACH THE HIGH PLAINS. THERE IS

SOME INDICATION THAT MID LEVEL CYCLOGENESIS MAY OCCUR AT THE BASE OF

THE TROUGH BY MID NEXT WEEK AND WOULD OFFER THE NEXT CHANCE AT

PRECIPITATION ACROSS WESTERN KANSAS. BY THIS TIME... GULF OF MEXICO

MOISTURE WOULD LIKELY HAVE ACCESS TO ANY DEVELOPING LOW...AND VERY

COLD CANADIAN AIRMASS WILL ALSO BE CLOSE BY BEHIND THE NEARBY FRONT

DRAPED ACROSS THE CENTRAL PLAINS...SO BAROCLINIC INSTABILITY AND

AVAILABLE MOISTURE MAY FOSTER STORM DEVELOPMENT BY THANKSGIVING TIME

FRAME THAT WILL NEED TO BE WATCHED.

[Stebo]

I’m beginning to take interest in the potential severe threat next week. The Gulf should be wide open and with noisy U/A Pattern along with a volatile Arctic Boundary nearby, a significant late fall episode may well set up...DDC snip, again...

BY TUESDAY NIGHT AND WEDNESDAY OF NEXT

WEEK...THE LARGE TROUGH CENTERED ACROSS THE INTERMOUNTAIN WEST OR

THE ROCKIES...WILL AMPLIFY AND APPROACH THE HIGH PLAINS. THERE IS

SOME INDICATION THAT MID LEVEL CYCLOGENESIS MAY OCCUR AT THE BASE OF

THE TROUGH BY MID NEXT WEEK AND WOULD OFFER THE NEXT CHANCE AT

PRECIPITATION ACROSS WESTERN KANSAS. BY THIS TIME... GULF OF MEXICO

MOISTURE WOULD LIKELY HAVE ACCESS TO ANY DEVELOPING LOW...AND VERY

COLD CANADIAN AIRMASS WILL ALSO BE CLOSE BY BEHIND THE NEARBY FRONT

DRAPED ACROSS THE CENTRAL PLAINS...SO BAROCLINIC INSTABILITY AND

AVAILABLE MOISTURE MAY FOSTER STORM DEVELOPMENT BY THANKSGIVING TIME

FRAME THAT WILL NEED TO BE WATCHED.

Yeah I'd certainly be watching the potential from say Wichita south to San Antonio and points East.

[Chicago Storm]

Immediately ahead of the outbreak if the current run of the GFS can verify, and the ECMWF AND CMC have hinted at it, given the history of high shear/low CAPE systems this season, and the fact that the GFS ALWAYS under forecasts LLVL thermal fields, we could have one more severe wind, weak tornado event. It's STILL WAY TOO EARLY to get hopes up, let alone start a thread....Still something to watch as current runs already show instability which is RARE for the GFS, let alone at this forecast range.

SPC...

WITH ONE SUCH SHORTWAVE TROUGH EXPECTED TO CROSS THE UPPER MIDWEST

ON DAY 4/MONDAY...THIS SCENARIO COULD SUPPORT SOME RELATIVELY

LOW-TOPPED/FAST MOVING TSTMS ACROSS PORTIONS OF THE MIDWEST/WESTERN

GREAT LAKES ALONG/AHEAD OF A COLD FRONT. THE PRIMARY UNCERTAINTY

WILL BE REGARDING LIMITED MOISTURE/BUOYANCY GIVEN LITTLE OPPORTUNITY

FOR CONSEQUENTIAL MOISTURE RETURN. NONETHELESS...SOME STRONG/SEVERE

TSTMS CANNOT BE RULED OUT DAY 4/MONDAY ACROSS THE MIDWEST/GREAT

LAKES REGION WITHIN A STRONGLY FORCED/SHEARED REGIME.

[OceanStWx]

I'm definitely intrigued. I like the track of the surface low as the models currently depict it, and the very early returns from the SREF are increasing probability and coverage of severe weather parameters.

[Srain]

Sort of surprised that no one has mentioned the 00Z 10 day Euro...

[Powerball]

Sort surprised that no one has mentioned the 00Z 10 day Euro...

There's a good reason for that.

[Srain]

There's a good reason for that.

Perhaps...

DDC...

WORTH NOTING, THE ECMWF MODEL BRINGS A LARGE POSITIVELY TILTED TROUGH

INTO OUR WESTERN CWA ON DAY 8, OR SUNDAY NOV 28TH. PLACE LOW 13-14 PERCENT

POPS IN SUNDAY AFTERNOON. THAT FEATURE WILL HAVE TO BE WATCHED AS NEXT

SUNDAY TIME FRAME GETS CLOSER.

[csnavywx]

Well this part of the pattern is done bearing its (meager) fruit. It did leave us with a hefty -NAO block, so all is not lost. As the -EPO pattern (block) was mostly shredded, the PAC wave train has re-started. Indian Ocean convection flared over the past week near 60-100E and helped in destroying it. Positive height anomalies still exist near the Bering Sea and far Eastern Siberia, but the question is, will the EPO make a resurgence? And what happens with that -NAO?

Here's where we stand:

The MJO has pretty much died and none of the models really bring it back anytime soon (pay attention to the green/ensemble line):

The current IO convection is beginning to wane, and could be signaling a change towards another +OLR phase (like what we had earlier in Nov before the giant EPAC block). If this indeed happens, as the models suggest, then a re-establishment of the -EPO or a restrengthening of the current positive anomalies over the NPAC/Bering Sea area will likely occur.

That's great, but what does that mean for us? Strong positive anomalies in that region generally teleconnect to a western to central US troughing pattern, with a SE ridge. Given that the -NAO will not likely budge with the current upstream pattern in place (this is something the longer range models and model ensembles CAN agree on), this may set up another -EPO/-NAO pattern. We've seen several model runs where they attempt to retrograde the Greenland block or move it towards Iceland, but then quickly jump ship from that solution. This is another tell-tale sign that it isn't likely to go anywhere for a while, which is good news. A strong -NAO or -NAO/-AO combo helps suppress the SE ridge, keeping it from getting too strong. Of course, it can't save us by itself, we need a decent ridge placement upstream and/or a good PV placement across Canada.

Three things acting in our favor for the SE ridge to be shunted slowly further south with time:

1) Climo (don't forget that we're still cooling at a pretty good clip this time of year).

2) An increasingly good/expansive snowpack to the north over Canada and the northern tier.

3) Regular rains/heavy rain events will weaken the drought. This has been producing a positive feedback for ridging lately, and with it weakening, its feedback will as well.

Nevertheless, expect to see models struggle mightily with individual storms given the pattern and the changes coming down the pipe.

[Chicago WX]

Thanks for giving your analysis of the medium-long range pattern...much appreciated.

Oh and lol to the thread sub-title.

[Srain]

Excellent analysis. Thanks for taking the time to put it together and move this thread along to the next event.

[Srain]

Day and night between the Op GFS and Euro...