September 9th-10th Severe Threat

[andyhb]

Certainly fuelled by the developments in the most recent Euro run, SPC has highlighted a D5 region for much of the sub-forum as a series of strong impulses rotate around the base of a developing longwave trough/ULL over Central US this coming week. Flow at all levels looks to be strong, with the LLJ on the Euro increasing to over 55 kts by 00z 9/11. The Euro was actually quite close to a full phase of the CA shortwave and the upper low dropping south, which would likely induce a very strong surface cyclone/rapid deepening (it already is 991 mb at 120 hrs as depicted by the 00z run).

 

As mentioned below, quality of lapse rates/WAA strength is certainly a potential caveat, as it appears that the tropical activity off the Baja currently may have a say in this, contaminating lapse rates since it partially is absorbed by the ejecting California wave. Regardless, this is a setup to watch given the relative rarity of a system of this potential magnitude in September.

 

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0400 AM CDT SAT SEP 06 2014

VALID 091200Z - 141200Z

...DISCUSSION...
WHILE SUBTROPICAL RIDGING REMAINS PROMINENT ACROSS THE SOUTHERN TIER
OF THE U.S. THROUGH THIS PERIOD...THE MEDIUM RANGE MODELS CONTINUE
TO SUGGEST THAT A SIGNIFICANT CLOSED LOW WILL DEVELOP WITHIN THE
MID-LATITUDE WESTERLIES...WHICH WILL LIKELY DIP SOUTH OF THE CENTRAL
CANADIAN/U.S. BORDER AREA DURING THE MIDDLE TO LATTER PORTION OF THE
COMING WORK WEEK. ON THE SOUTHERN THROUGH EASTERN PERIPHERY OF THIS
DEVELOPING CYCLONIC CIRCULATION...IT APPEARS INCREASINGLY PROBABLE
THAT AN IMPULSE...EMERGING FROM UPPER TROUGHING OFF THE CALIFORNIA
COAST...WILL CONTRIBUTE TO SIGNIFICANT SURFACE CYCLOGENESIS EAST OF
THE MIDDLE MISSOURI VALLEY THROUGH THE GREAT LAKES REGION.

ALTHOUGH IT APPEARS THAT MID-LEVEL LAPSE RATES BY THIS TIME MAY NOT
BE PARTICULARLY STEEP WITHIN THE WARM SECTOR OF THE DEVELOPING
LOW...THE RETURN OF SEASONABLY HIGH MOISTURE CONTENT SEEMS LIKELY
AND SHOULD CONTRIBUTE TO AT LEAST MODEST CONDITIONAL INSTABILITY.
THIS...COUPLED WITH STRENGTHENING OF LOWER/MID TROPOSPHERIC WIND
FIELDS TO SEASONABLY STRONG LEVELS...SUGGESTS INCREASING POTENTIAL
FOR A REGIONAL SEVERE WEATHER EVENT...WHICH COULD INCLUDE SUPERCELLS
AND THE EVOLUTION OF AN ORGANIZED CONVECTIVE SYSTEM...ACCOMPANIED BY
THE RISK FOR DAMAGING WIND GUSTS AND A FEW TORNADOES. GIVEN THE
CONVECTIVE SIGNAL EVIDENT IN THE MODEL OUTPUT...CONFIDENCE IS
SUFFICIENT TO DELINEATE A SEVERE RISK AREA ACROSS SOUTHERN PORTIONS
OF THE GREAT LAKES REGION AND OHIO VALLEY FOR WEDNESDAY.
HOWEVER...ORGANIZED SEVERE STORMS APPEAR AT LEAST POSSIBLE AS EARLY
AS TUESDAY EVENING ACROSS PARTS OF THE MID MISSOURI AND MIDDLE
MISSISSIPPI VALLEYS.

..KERR.. 09/06/2014

[Stebo]

We were looking at this last night especially with the 00z Euro, it won't take much instability to get things really active for Wednesday with that low and subsequent wind fields. I will say I am surprised about the day 5 being issued though.

[wisconsinwx]

We were looking at this last night especially with the 00z Euro, it won't take much instability to get things really active for Wednesday with that low and subsequent wind fields. I will say I am surprised about the day 5 being issued though.

 

12z GFS took a big step NW towards the Euro, and hence more interesting for those in the NW part of the subforum.  Timing looks poor once again though for my local area, the dry slot coming into play by about 18-21z Wednesday.

[Stebo]

12z GFS took a big step NW towards the Euro, and hence more interesting for those in the NW part of the subforum.  Timing looks poor once again though for my local area, the dry slot coming into play by about 18-21z Wednesday.

I would say it is more interesting for everyone, as it is a stronger solution closer to the Euro with a good pocket of instability in the warm sector. We get that kind of instability with those wind fields on the GFS and thing will really explode.

[Gilbertfly]

993 SLP around 18Z on Wednesday via the 12Z GFS .... CAPE lagging a bit for MBY due to timing, but with that kind of strength it shouldn't take an incredible amount of CAPE to set things off I would imagine.

[Hoosier]

The first thing I thought of when I saw this was 9/22/2006, mainly because of how anomalous that was.  The setups themselves have differences although the surface low location is somewhat similar.  This looks more like a setup that you would see later in fall, not mid September.

[Powerball]

With 1000-500mb thickness values greater than 576dm and 850mb temps of 16*C to 20*C in the warm sector, it's very hard to believe there won't be, at least, a modest amount of instability for this system to work with.

[Gilbertfly]

Looks like this time period will also feature some heavy QPF for parts of the subforum...forecast pwats at 2+ for a decent area.  Normally not that big of a deal....but there are some waterlogged areas that stand to be impacted that could lead to issues. 

[Powerball]

Looks like this time period will also feature some heavy QPF for parts of the subforum...forecast pwats at 2+ for a decent area.  Normally not that big of a deal....but there are some waterlogged areas that stand to be impacted that could lead to issues. 

 

2" PWATS (tropical-type of moisture levels) are well above average for any time of year this far north, so I'd say it's always sort of a big deal, especially in September (typically the driest month of the year). 

[Gilbertfly]

2" PWATS (tropical-type of moisture levels) are well above average for any time of year this far north, so I'd say it's always sort of a big deal, especially in September (typically the driest month of the year).

True, i was angling a bit at the forecast aspect because i dunno if widespread 2" pwats will come to fruition...but if they do, yeah some will most def have some hydro issues

[Hoosier]

FWIW, 9/22/2006 is #8 on the CIPS analog list using the MV (well, technically it's 9/23 6z).  Several days from September, several from October, a couple from August and one from July.

[Stebo]

The Euro is very impressive with the dynamics but the instability is a bit lacking.

[Hoosier]

The Euro is very impressive with the dynamics but the instability is a bit lacking.

 

 

 

Looks like it's mainly from 500 to just over 1000 J/kg and mainly along/south of the IN/MI border but that is based on the Wunderground graphics.  Are you seeing the same thing?

[Stebo]

Looks like it's mainly from 500 to just over 1000 J/kg and mainly along/south of the IN/MI border but that is based on the Wunderground graphics. Are you seeing the same thing?

Yeah, weatherbell shows the same thing. I mean with these sort of dynamics, 500-1000 J/kg of CAPE would be enough to make things very interesting.

[Hoosier]

I should mention that I was talking about the 10th.  Instability actually looks better on the 9th farther west.

[Radtechwxman]

I agree with you guys. the dynamics really compensate for lack of greater instability. very impressive system for Sept. but you remember how instability parameters looked on Nov 17th last yr? models were showing little to no cape. and we ended up with 3000 in my area. I know this system is different synoptically in a lot of ways but in a round about way it kind of reminds me of it.

[Powerball]

The models are always stingy on the instability parameters for events this far out...

 

With the temp profiles and moisture levels progged, generating enough instability should not a problem (besides the usual cloud cover issues).

[Hoosier]

I agree with you guys. the dynamics really compensate for lack of greater instability. very impressive system for Sept. but you remember how instability parameters looked on Nov 17th last yr? models were showing little to no cape. and we ended up with 3000 in my area. I know this system is different synoptically in a lot of ways but in a round about way it kind of reminds me of it.

 

 

I'm pretty sure the models were showing a sizable area of about 1000-1500 for 11/17, maybe a bit higher in spots.   

[andyhb]

I'm pretty sure the models were showing a sizable area of about 1000-1500 for 11/17, maybe a bit higher in spots.

 

Yes, and it didn't get up to 3000 J/kg. It was around 2000 J/kg in the area of the Washington supercell.

 

I agree with you guys. the dynamics really compensate for lack of greater instability. very impressive system for Sept. but you remember how instability parameters looked on Nov 17th last yr? models were showing little to no cape. and we ended up with 3000 in my area. I know this system is different synoptically in a lot of ways but in a round about way it kind of reminds me of it.

You have to realize that 11/17/13 was one of the most volatile synoptic systems to affect the Great Lakes region in the past decade, the strength of the wind fields with that trough were in the top percentile for severe weather events. 120 kts at 500 mb is exceptionally strong, not to mention how fast the surface low deepened that day. IIRC there was a lot of damage just from the synoptic winds in that event.

 

[snowlover2]

ILN saying how it might not take much to get severe weather.

 

 

 

.LONG TERM /TUESDAY THROUGH SATURDAY/...
THE OPERATIONAL MODELS ARE IN FAIRLY GOOD AGREEMENT FOR THE LONG
TERM PERIOD IN TERMS OF LARGE SCALE SYNOPTIC SYSTEMS. THERE ARE THE
USUAL STRENGTH AND TIMING ISSUES. AS SUCH...HAVE LEANED ON A BLEND
OF THE 12Z ECMWF...12Z GFS AND WPC GUIDANCE.

ON TUESDAY...REGION WILL BE UNDER A ZONAL FLOW ALOFT. MODELS
INDICATE THAT THERE SHOULD BE A DRY WEDGE IN TERMS OF DEEP MOISTURE
AND A LACK OF INSTABILITY...SO HAVE KEPT THE FORECAST DRY DESPITE
WEAK EMBEDDED DISTURBANCES WITHIN THE FLOW. SKIES WILL RANGE FROM
MOSTLY SUNNY TO PARTLY CLOUDY. HIGHS WILL RANGE FROM THE THE LOWER
TO MID 80S.

THE UPR LVL FLOW PATTERN WILL UNDERGO AMPLIFICATION THROUGH THE
REMAINDER OF THE LONG TERM PERIOD. ENERGY FROM OFF THE CA COAST WILL
EJECT QUICKLY NE INTO THE PLAINS AND THEN TO THE WESTERN GREAT LAKES
LATE TUESDAY NIGHT INTO WEDNESDAY. THIS ENERGY WILL TRY TO PHASE
WITH ENERGY DIGGING FROM WESTERN CANADA INTO THE NORTHERN PLAINS
WEDNESDAY INTO THURSDAY. THIS SCENARIO WILL ALLOW A LOW PRESSURE
SYSTEM TO DEEPEN AS IT MOVES NORTHEAST THROUGH THE WESTERN GREAT
LAKES INTO SE CANADA DURING THIS PERIOD...SENDING AN ATTENDANT COLD
FRONT SOUTHEAST THROUGH OUR REGION. CURRENT FORECASTS SUGGEST THAT A
STRONG LOW LEVEL JET AND WAA PCPN WILL BREAK OUT TO OUR WEST AND
LIKELY SKIM OUR NW CWFA ON WEDNESDAY WITH THE REMAINDER OF THE
REGION SEEING A CHANCE OF PCPN WITH AN ADVANCING WARM FRONT. THE
BEST THREAT FOR THE ENTIRE REGION TO SEE PCPN WILL COME WEDNESDAY
NIGHT INTO THURSDAY MORNING AS THE COLD FRONT SWINGS SOUTHEAST. THIS
WILL BE A DYNAMIC SYSTEM WITH DECENT WIND ENERGY AND LOW LEVEL
FRONTAL CONVERGENCE. AS SUCH...THE POTENTIAL FOR THUNDERSTORMS TO BE
SEVERE WEDNESDAY NIGHT INTO THURSDAY MORNING WILL DEPEND ON THE
DEGREE OF INSTABILITY...ALTHOUGH WITH WINDS OF LOWER 40 KNOTS AT 925
MB AND LOWER TO MID 50 KNOTS AT 850 MB...IT MAY NOT TAKE A WHOLE
LOT. SPC HAS HIGHLIGHTED THE GREAT LAKES REGION/PARTS OF THE OHIO
VALLEY IN A DAY 5 30 PERCENT RISK FOR SEVERE STORMS. WILL
HIGHLIGHT THIS THREAT IN THE HWO...BUT WILL BROAD BRUSH IT AT THIS
POINT IN TIME. COLD FRONT SHOULD PUSH SOUTHEAST AWAY FROM THE AREA
ON THURSDAY WITH PCPN PUSHING OUT AS WELL.

FOR THE PERIOD THURSDAY NIGHT INTO SATURDAY...A PRETTY DECENT MID
LEVEL CLOSED LOW WILL TRAVERSE EAST/NORTHEAST THROUGH THE GREAT
LAKES AND SOUTHEAST CANADA THROUGH THE PERIOD. THIS WILL EVENTUALLY
ALLOW AN EXPANSIVE AREA OF SURFACE HIGH PRESSURE TO BUILD INTO THE
REGION BY SATURDAY. ANY SPOTTY SHOWER ACTIVITY APPEARS TO BE
RELEGATED CLOSER TO THE GREAT LAKES ON FRIDAY SO HAVE LEFT THE
FORECAST DRY. TEMPERATURES WILL SHOW A SUBSTANTIAL COOL DOWN FROM
HIGHS IN THE 70S AND 80S ON WEDNESDAY. HIGHS BY THE WEEKEND WILL BE
MAINLY IN THE 60S WITH LOWS DIPPING INTO THE 40S. THESE VALUES WILL
BE SOME 10 TO 15 DEGREES BELOW NORMAL FOR EARLY SEPTEMBER.

[andyhb]

ILN saying how it might not take much to get severe weather.

If you remember Halloween last year, that was a good example. There was a max of 750 J/kg of CAPE at best and yet the dynamics with that system allowed it to pull over 30 tornadoes from very poor thermos.

[Hoosier]

List of all September SPC day 4-8 risk areas since 2005.  Asterisks denote risk areas that affected any part of this subforum.  Considering that the day 5 risk area issued on 8/27 of this year only touched a small part of the subforum, you basically have to go back to 9/22/09 to find the last time that a significant portion of the area was in a day 5 risk area in the month of September. 

 

Note that some late August days are on here since a day 4 area issued on 8/28 would cover part of September (the part up to 12z Sep 1).  Same thing with a day 5 area issued on 8/27. 

 

 

*9/6/2014:  day 5
*8/28/2014:  day 4
*8/27/2014:  day 5
*9/15/2012:  day 4
9/1/2011:   day 4
*8/31/2011:  day 4
*8/29/2011:  day 4
*9/22/2009:  day 4 + 5
9/18/2009:  day 4
*9/17/2009:  day 5
9/26/2007:  day 4
9/25/2007:  day 5
9/24/2007:  day 6
9/17/2007:  day 4
9/14/2007:  day 4
*9/13/2007:  day 5 + 6
9/9/2007:  day 5
*9/3/2007:  day 4
*9/20/2006:  day 4
9/15/2006:  day 4
*9/14/2006:  day 4
*9/13/2006:  day 4 + 5
*9/12/2006:  day 5 + 6
*9/10/2006:  day 4 + 5
8/29/2006:  day 4 + 5
8/28/2006:  day 4 + 5
*9/14/2005:  day 4 + 5 + 6 + 7
*9/13/2005:  day 5 + 6
*9/8/2005:  day 4 + 5 + 6
*9/7/2005:  day 5 + 6 + 7
*9/5/2005:  day 4 + 5 + 6
*9/4/2005:  day 5 + 6 +7
9/3/2005:  day 6 + 7
9/1/2005:  day 7 + 8
 

[tornadotony]

My initial thought is potentially a tornadic QLCS.  Wind fields will be hellacious but Norbert warm/moist air in the midlevels is going to be unavoidable.  750 J/kg CAPE might be the upper limit on what we see.

[Stebo]

Just to put this into a frame of reference as to how anomalous this system could potentially be, GRR had this to say:

 

WHILE THE CALENDER STILL SAYS SUMMER... THE WEATHER MAPS ARE SAYING
FALL IS HERE. WE HAVE ANOTHER ONE OF THOSE ANOMALOUS EVENTS (WE HAD
HAD A FEW THIS PAST SUMMER) HEADING OUR WAY FOR MIDWEEK INTO THE
FOLLOWING WEEKEND. SEVERE STORMS ARE MORE THAN POSSIBLE WEDNESDAY
(SEE DAY 5 FROM SPC)THEN IT IS LIKELY TO GET COLD ENOUGH TO
CHALLENGE SOME RECORD LOWS OVER OUR NORTHERN CWA BY FRIDAY AND
SATURDAY. LAKE EFFECT RAIN SHOWERS...WATER SPOUTS AND FROST/FREEZE
ISSUES ARE MORE THAN POSSIBLE THEN TOO.

THE GOOD NEWS IS THERE IS VERY GOOD AGREEMENT WITH THE ENSEMBLES...
THE GFS...FIM...ECMWF AND GEM ON THE STORM IN THE WEDNESDAY TIME
FRAME. THIS LOOKS TO BE AN UNUSUALLY STRONG EVENT FOR THIS TIME OF
YEAR. THE RETURN INTERVAL FOR THE MEAN SEA LEVEL PRESSURE AS THE
SYSTEM MOVES THOUGHT THE GREAT LAKES IS ABOUT 1 YEAR IN 10. THE
PRECIPITABLE WATER RETURN INTERVAL IS GREATER THAN 1 YEAR IN 30 FOR
THE 10TH-11TH OF SEPTEMBER. SIMILARLY THE 850 TEMPERATURE ANOMALIES
ON THE COLD SIDE OF THE SYSTEM (NEAR ZERO) ARE AROUND ONE YEAR IN 5
FOR THAT TIME IN SEPTEMBER.

THIS SYSTEM COMES FROM A PACIFIC STORM THAT IS CURRENTLY MOVING
THROUGH CENTRAL ALASKA. IT DIVES DOWN THE CANADIAN ROCKIES IN THE
MONDAY TIME FRAME THEN DEVELOPERS A CLOSED UPPER LOW OVER THE
MONTANA/WESTERN NORTH DAKOTA EARLY THURSDAY AND CROSSES THE GREAT
LAKES ON FRIDAY. THE SURFACE LOW OCCLUDES OVER WISCONSIN WEDNESDAY
ALLOWING A 50+ KNOT LOW LEVEL JET (ECWMF AND GFS) AIMED AT SOUTHERN
LOWER MICHIGAN WEDNESDAY DURING THE DAY WITH IMPRESSIVE 1000/850
MOISTURE TRANSPORT VECTORS WHILE WE ARE IN THE RIGHT ENTRANCE REGION
OF THE UPPER JET. IT MAKES SENSE SPC HAS LOWER MICHIGAN IN THEIR DAY
5 OUTLOOK. I WOULD EXPECT STRONG TO SEVERE STORMS AND LOCALLY HEAVY
RAINFALL WITH 1 TO 2 INCHES OF RAIN IN 12 HOURS MORE THAN POSSIBLE
ON WEDNESDAY.

 

[Hoosier]

My initial thought is potentially a tornadic QLCS.  Wind fields will be hellacious but Norbert warm/moist air in the midlevels is going to be unavoidable.  750 J/kg CAPE might be the upper limit on what we see.

I guess it's a good sign that the GFS has been advertising better than that at least for a part of the area.  The crappy mid level lapse rates are a bit of a concern but I like the rich low level moisture being progged with dewpoints in the low to potentially mid 70s in some spots... not bad going on mid-September.

[Hoosier]

To go along with what Stebo posted

 

 

[Hoosier]

Noticed that the 12z GFS was showing a PWAT of 2.23" at DTX at 00z Thursday.  The September record there is 2.20" so that will be something to watch.

[Radtechwxman]

yea no system will prolly be able to surpass the level of 11-17 for quite some time. but I was just saying maybe models are underestimating cape values. however tornadotony makes a great point. with that warm moist air in the mid levels lapse rates will be less than ideal. but maybe the wind fields will compensate. only time can tell. not a bad setup for Sept standards. maybe an early taste of Fall severe weather season. would be nice to chase further north and not in the jungles down south

[tornadotony]

I think it's very unlikely that CAPE is being underestimated.

[A-L-E-K]

looking forward to my heavy rain MCS