July 17th-21st Severe Thread

[andyhb]

Latest D4-8 has outline large areas of potential with a vigorous southeastward progressing upper trough dropping out of the Hudson Bay region. The pattern appears favorable for at least enhanced MCS activity as mid level flow increases given the large reservoir of strong instability built up by the East-Central US ridge.

 

DAY 4-8 CONVECTIVE OUTLOOK     NWS STORM PREDICTION CENTER NORMAN OK   0356 AM CDT SUN JUL 14 2013   VALID 171200Z - 221200Z   ...DISCUSSION...   MULTI-DAY SEVERE EVENT POSSIBLE D5 /THU JUL 18/ THROUGH D7 /SUN JUL   20/   MEDIUM RANGE GUIDANCE FROM THE GFS...ECMWF AND CMC GLOBAL MODELING   SYSTEMS HAS BEEN CONSISTENT WITH THE LARGE SCALE PATTERN EVOLUTION   DURING THE D4-8 PERIOD SHOWING DEVELOPMENT OF BROAD LONG WAVE TROUGH   MOVING ACROSS SERN CANADA...THE GREAT LAKES AND NERN STATES.  AS   THIS OCCURS A SURFACE LOW...INITIALLY OVER THE NRN PLAINS...WILL   MOVE ENEWD ACROSS THE NRN GREAT LAKES AND SERN CANADA WHILE A   TRAILING COLD FRONT EXTENDING SWWD FROM THE LOW ADVANCES SEWD ACROSS   GREAT LAKES AND NERN STATES.  ALTHOUGH THE ECMWF DETERMINISTIC RUNS   AND ENSEMBLE SYSTEMS HAVE EXHIBITED MORE RUN-TO-RUN CONTINUITY THAN   THE GFS IN THE HANDLING OF THE SHORT WAVE FEATURES AND ASSOCIATED   WIND FIELDS ASSOCIATED WITH THE LONG WAVE TROUGH...A SIMILAR LARGE   SCALE SIGNAL FROM MULTIPLE MODELING SYSTEMS SUGGESTS PATTERN   PREDICTABILITY IS RELATIVELY HIGH DURING THIS PERIOD IN THE REGION   OF INTEREST.   A VERY MOIST AND UNSTABLE AIR MASS IS LIKELY TO BE PRESENT OVER THE   NRN PLAINS/UPPER MS VALLEY AND INTO THE NERN STATES ON D4-5 IN   ADVANCE OF THE SURFACE LOW AND COLD FRONT.  THIS WILL INCREASE THE   POTENTIAL FOR WIDESPREAD DAMAGING WIND GUSTS AND OCCASIONAL HAIL TO   OCCUR WITH SEVERE STORMS ALONG AND AHEAD OF THE COLD FRONT.    ALTHOUGH PRIMARY THREAT AREAS MAY BE MODULATED BY EFFECTS OF PRIOR   CONVECTION/OUTFLOW BOUNDARIES...OVERALL SYNOPTIC SCALE FORCING   APPEARS SUFFICIENT TO DELINEATE REGIONS OF ENHANCED SEVERE POTENTIAL   DURING THIS PERIOD.     D5 /THU JUL 18/...SEVERE STORM POTENTIAL IS EXPECTED TO INCREASE BY   LATE AFTERNOON/EVENING OVER THE UPPER MS VALLEY ALONG/NORTH OF A   WARM FRONT...WITH SEVERE STORMS POSSIBLY SPREADING EWD DURING THE   OVERNIGHT HOURS TOWARD THE GREAT LAKES.  THIS WILL OCCUR AS THE   SURFACE LOW MOVES EWD AND THE LOW LEVEL JET VEERS...STRENGTHENS AND   BECOMES COUPLED WITH A STRONG WNWLY MID/UPPER LEVEL JET POSITIONED   IMMEDIATELY TO ITS NORTH.     D6 /FRI JUL 19/...THE ELONGATED COUPLED LOW/MID LEVEL JET STRUCTURE   IS EXPECTED TO PROGRESS EWD ACROSS THE GREAT LAKES AND INTO THE NERN   STATES AS THE SURFACE LOW MOVES ACROSS SRN CANADA...AND THE COLD   FRONT MOVES SEWD ACROSS THE GREAT LAKES.  SEVERE STORM POTENTIAL IS   EXPECTED TO CONTINUE EWD/ESEWD ALONG AND AHEAD OF THE COLD FRONT   FROM THE GREAT LAKES INTO NRN PARTS OF THE NERN STATES.   D7 /SAT JUL 20/...THE COLD FRONT AND STRONGER WINDS ALOFT WILL MOVE   ACROSS THE REMAINDER OF THE NERN STATES AND NRN MIDDLE ATLANTIC   REGION MAINTAINING A SEVERE THREAT OVER THIS AREA.   ..WEISS.. 07/14/2013

[Quincy]

The setup certainly has potential and it might just be one of those rare times this summer where a large part of the northern United States including the Northeast has a string of severe thunderstorm days.

 

I'm particularly focused on Friday at this point, although there are plenty of timing and other details to sort out. Historically we've seen some impressive heat waves end with a bang. Prior to a shortwave digging south, we will have a very hot, humid and unstable air-mass in place. As wind fields ramp up through the amplification process, that's when things may really ignite.

 

Here's what I'm talking about, it's the Euro forecast (00z Mon run) for Friday evening, courtesy PSU E-Wall:

[andyhb]

New D4-8 maintains three consecutive days outlined.

 

DAY 4-8 CONVECTIVE OUTLOOK     NWS STORM PREDICTION CENTER NORMAN OK   0313 AM CDT MON JUL 15 2013   VALID 181200Z - 231200Z   ...DISCUSSION...   PATTERN FCST TO BECOME FAVORABLE FOR CORRIDORS OF ENHANCED SVR   POTENTIAL BETWEEN UPPER MIDWEST AND MID-ATLC/NEW-ENGLAND REGION.    THIS MAY INCLUDE SWATH OF DAMAGING WIND ON ONE OR MORE DAYS WITHIN   DAY-4 TO DAY-6 TIME FRAME...AND RELATIVELY DENSE DIURNAL    CONCENTRATIONS OF MULTI-MODAL SVR CONVECTION OTHERWISE.  TO SOME   EXTENT...SVR THREATS ON DAYS 5-6 DEPEND ON EACH DAY PRIOR...HOWEVER   GIVEN OVERALL FAVORABLE PATTERN AND PROBABILITY OF STG BUOYANCY IN   PRECONVECTIVE AIR MASS...WILL MAINTAIN 30% AREAS FROM PREVIOUS FCST   WITH ONLY MINOR ADJUSTMENTS.  BEYOND THAT...POTENTIAL BECOMES TOO   CONDITIONAL FOR OUTLOOK.  OPERATIONAL SPECTRAL/ECMWF...AS WELL AS   ENSEMBLES OF EACH...HAVE BECOME REMARKABLY CONSISTENT WITH EACH   OTHER AND FROM RUN TO RUN WITH PATTERN EVOLUTION DISCUSSED BELOW.   IN MID-UPPER LEVELS...ANOMALOUS COLD-CORE CYCLONE NOW OVER OK WILL   MOVE SWWD TO SONORA AND GET ABSORBED INTO BROADER SUBTROPICAL   TROUGHING BY DAY-4/18TH-19TH.  RIDGING WILL DOMINATE MOST OF CONUS   TO ITS N AND NE...EXCEPT FOR CORRIDOR FROM NRN PLAINS ACROSS GREAT   LAKES TO NEW ENGLAND.  EXPECT INCREASE IN CYCLONIC CURVATURE AND   STRENGTH OF FLOW OVER THAT BELT DAYS 4-7 WITH ACCOMPANYING SEWD   MOVEMENT OF SEASONALLY STG COLD FRONT.  FAVORABLE LOW-LEVEL MOISTURE   IS ALREADY IN PLACE OVER MUCH OF MIDWEST/NERN STATES AND SHOULD   REMAIN SO PRIOR TO FROPA OR MCS USAGE.  AS CYCLONE NOW OVER GULF OF   AK DIGS SWD...PORTION OF INITIALLY CUT-OFF LOW OFFSHORE CA WILL   EJECT NEWD THROUGH MEAN RIDGE OVER PAC NW AND BC DAY-3...THEN ESEWD   ACROSS SRN PRAIRIE PROVINCES TO NRN MN DAY-4/18TH-19TH.  SFC   CYCLOGENESIS OVER DAKOTAS AND RESULTING MASS RESPONSE BENEATH SRN   RIM OF FAVORABLE WNW FLOW ALOFT SHOULD CONTRIBUTE TO SVR THREAT   INCLUDING SUPERCELL RISK...POTENTIALLY EVOLVING UPSCALE INTO MCS   OVERNIGHT AND MOVING EWD ALONG BAROCLINIC ZONE INTO UPPER GREAT   LAKES REGION.     SYNOPTIC AMPLIFICATION ALOFT AND PERHAPS OUTFLOW SHOULD SHUNT   LOW-LEVEL FRONTAL ZONE AND CORRIDOR OF ORGANIZED SVR THREAT SWD   DAY-5/19TH-20TH INTO VERY MOIST AND LIKELY HIGH-CAPE AIR MASS...WITH   MID-UPPER WINDS NEARLY PARALLEL TO FRONTAL ZONE OVER MUCH OF AREA.    CONTINUED MID-UPPER AMPLIFICATION/SWD SHIFT OF CYCLONIC FLOW ALOFT   SHOULD OCCUR DAY-6/20TH-21ST...WITH SVR THREAT SHIFTED ACCORDINGLY   EWD AND SEWD.  ANY ORGANIZED SVR-WIND EVENT THAT DEVELOPS MAY   OVERLAP PARTS OF TWO OUTLOOK-DAYS.   ..EDWARDS.. 07/15/2013

[Stebo]

New D4-8 maintains three consecutive days outlined.

 

The part that concerns me, is that the winds might become parallel to the front, which could mean a slow frontal progression and training across the area. This would be very bad for the region considering we are already very waterlogged.

 

 

 

Needless to say, it isn't going to take much to get things to flood, especially if some of these areas receive isolated convection between now and Thursday to Saturday.

[IWXwx]

The part that concerns me, is that the winds might become parallel to the front, which could mean a slow frontal progression and training across the area. This would be very bad for the region considering we are already very waterlogged.

 

Needless to say, it isn't going to take much to get things to flood, especially if some of these areas receive isolated convection between now and Thursday to Saturday.

 

 

After a week of humid 90's, that rain will be quite the relief. But, yeah, training rains could be a concern in some areas.

[WestMichigan]

The part that concerns me, is that the winds might become parallel to the front, which could mean a slow frontal progression and training across the area. This would be very bad for the region considering we are already very waterlogged.

What a tale of two sides of the state.  My area is dry and the grass is brown.  The east side of the state and down into Ohio is very wet.

[TimChgo9]

Looking to possibly be a wet stretch for this subforum, but the the eastern ones as well.

 

06z GFS showing the rain potential for Friday around the GL region.

 

And then, by the 23rd, the GFS is showing this, although how well this works out, is probably going to be dependent on what  goes before.

 

However, being a week out, this will change.

 

Not looking forward to the high humidity this week.  The A/C is struggling here, and the landlord has not responded to requests to look at it.......

[Brewers]

The models seem to be hinting at an active NW/zonal flow after this weekend. Something to keep an eye on.

[Stebo]

The models seem to be hinting at an active NW/zonal flow after this weekend. Something to keep an eye on.

Yeah the nodels continue that trend through the end of the cycle. Should be interesting to see how things trend after this weekend because the boundary isn't going to push too far South, so I would expect episodic convective systems to run along it after this weekend as a low sets up shop in the Northern Plains.

[A-L-E-K]

I don't expect high coverage...at all but I think we could see some powerhouse cells across the northeaster cwa.  Definitely some quality supercell over the lake photo op potential.

[harrisale]

Quiet thread. Getting into NAM range now for the S. ON/MI threat. Promising cold front should pass over Friday afternoon/evening. Thinking mixed storm modes with potential for some embedded rotation in any line segments or rotating storms out ahead of the MCS in the earlier evening hours. Of course we will need to see how tomorrow and more importantly Thursday's convection play out but this should help stir the pot:

 

 

Good looking helicity with about 2000-3000 J/kg SBCAPE to work with yields healthy EHI's from Chicago into eastern Quebec:

 

[YHM Supercell]

Going to be an interesting setup. Few things that I am looking at right now. Convective debris from Thursdays storms, if we have debris from previous day storms and manage to clear out by peak heating or have no debris at all, I imagine most of southern Ontario will do okay thunderstorm wise. If we stay cloudy all day, that is a different story. From what I have seen in 12z/16 and 0z/17 guidance is that much of southern Ontario at least gets some good heating in on Friday. Parameters are looking pretty good right now, was worried about timing earlier today, but 0z guidance seems to have sped up just a bit. As was posted above, SBCAPES of around 2000-3000j/kg with a nice strong 850mb jet and good height falls could lead to some nice robust convection with damaging wind/hail potential. I'm up in the air about tornado potential, could be isolated but who knows given the potential for some storms ahead of an evening MCS or even some rotation embedded into the potential MCS given the favourable helicity values. Still lots of time for things to change but it is looking quite interesting. If things continue to look good, will hopefully be chasing on Friday. Also, NAM hi-res has some isolated to scattered storms Thursday/Thursday Evening through parts of SW/SC ON.

[harrisale]

Going to be an interesting setup. Few things that I am looking at right now. Convective debris from Thursdays storms, if we have debris from previous day storms and manage to clear out by peak heating or have no debris at all, I imagine most of southern Ontario will do okay thunderstorm wise. If we stay cloudy all day, that is a different story. From what I have seen in 12z/16 and 0z/17 guidance is that much of southern Ontario at least gets some good heating in on Friday. Parameters are looking pretty good right now, was worried about timing earlier today, but 0z guidance seems to have sped up just a bit. As was posted above, SBCAPES of around 2000-3000j/kg with a nice strong 850mb jet and good height falls could lead to some nice robust convection with damaging wind/hail potential. I'm up in the air about tornado potential, could be isolated but who knows given the potential for some storms ahead of an evening MCS or even some rotation embedded into the potential MCS given the favourable helicity values. Still lots of time for things to change but it is looking quite interesting. If things continue to look good, will hopefully be chasing on Friday. Also, NAM hi-res has some isolated to scattered storms Thursday/Thursday Evening through parts of SW/SC ON.

 

Figured you'd be watching this one and might pop by soon enough 

 

I'll be out on Friday as well, best set up in a while.

[IWXwx]

Southern MI is looking very interesting Friday. Excellent lift, good instability (obviously), and a 30+ kt llj.

 

[Powerball]

Going to be an interesting setup. Few things that I am looking at right now. Convective debris from Thursdays storms, if we have debris from previous day storms and manage to clear out by peak heating or have no debris at all, I imagine most of southern Ontario will do okay thunderstorm wise. If we stay cloudy all day, that is a different story. From what I have seen in 12z/16 and 0z/17 guidance is that much of southern Ontario at least gets some good heating in on Friday. Parameters are looking pretty good right now, was worried about timing earlier today, but 0z guidance seems to have sped up just a bit. As was posted above, SBCAPES of around 2000-3000j/kg with a nice strong 850mb jet and good height falls could lead to some nice robust convection with damaging wind/hail potential. I'm up in the air about tornado potential, could be isolated but who knows given the potential for some storms ahead of an evening MCS or even some rotation embedded into the potential MCS given the favourable helicity values. Still lots of time for things to change but it is looking quite interesting. If things continue to look good, will hopefully be chasing on Friday. Also, NAM hi-res has some isolated to scattered storms Thursday/Thursday Evening through parts of SW/SC ON.

 

One thing the models have been consistent about is showing good mid-level drying for majority of the region on Friday, especially as the front slows down. So daytime heating shouldn't be a problem.

 

My biggest fear, if anything, would be the scenario the NAM and GFS are beginning to show, which his everything developing along the pre-frontal trough versus the actual cold front. If that happens, at least here in Detroit we would have to worry about storm initiation that happens a tad too early (18z-21z) and overhead versus storm initiation upstream that propagates into the area with upscale growth. The problem, usually, with early storm initiation around here is that the activity, since still in the developing stages, won't be organized/widespread, so some of us (myself most likely, being in an area favorable for downsloping and under the lake shadow) willget jipped.

 

Now that said, given the models failed to account for the 600dm ridge that popped, I wouldn't be surprised if they are a tad too fast with the breakdown of the ridge, and as a result the frontal passage.

[andyhb]

One thing the models have been consistent about is showing good mid-level drying for majority of the region on Friday, especially as the front slows down. So daytime heating shouldn't be a problem.

 

My biggest fear, if anything, would be the scenario the NAM and GFS are beginning to show, which his everything developing along the pre-frontal trough versus the actual cold front. If that happens, at least here in Detroit we would have to worry about storm initiation that happens a tad too early (18z-21z) and overhead versus storm initiation upstream that propagates into the area with upscale growth. The problem, usually, with early storm initiation around here is that the activity, since still in the developing stages, won't be organized/widespread, so some of us (myself most likely, being in an area favorable for downsloping and under the lake shadow) willget jipped.

 

Now that said, given the models failed to account for the 600dm ridge that popped, I wouldn't be surprised if they are a tad too fast with the breakdown of the ridge, and as a result the frontal passage.

 

With strong instability already in place by that time, activity that does fire off of the pre-frontal trough should have a good chance of being organized, perhaps in the form of a few supercells.

[Brewers]

The timing of the trough does us no favors in SE WI but I am hoping that enough instability and possible lingering OFB/lake interaction can help us out.

[A-L-E-K]

yeah looking more like a non starter every run

[wisconsinwx]

The timing of the trough does us no favors in SE WI but I am hoping that enough instability and possible lingering OFB/lake interaction can help us out.

 

Yeah, punt on this threat right now, and the fact that now every day is basically in the 90s is making this a very crappy weather week.

[Hoosier]

GFS looks much more bullish on the threat west of Lake Michigan, while the NAM has trouble generating much at all. Seems like SPC is thinking more of a NAM type solution.

[Thundersnow12]

GFS looks much more bullish on the threat west of Lake Michigan, while the NAM has trouble generating much at all. Seems like SPC is thinking more of a NAM type solution.

 

Yeah the 12z NAM looks good if something can fire with 30kts of shear overspreading the large amount of moisture/instability, small precip signal after 0z in northeast IL 

[Hoosier]

Yeah the 12z NAM looks good if something can fire with 30kts of shear overspreading the large amount of moisture/instability, small precip signal after 0z in northeast IL

NAM in particular is advertising some really good DCAPE. Anything that goes should be an efficient wind producer with significant damaging winds possible given the magnitude of the instability and deep layer flow.

[andyhb]

Yeah, punt on this threat right now, and the fact that now every day is basically in the 90s is making this a very crappy weather week.

 

It's called summer.

[Hoosier]

8/28/1990 is #7 on the CIPS analog list. Here are the reports for the top 15 analogs.

[Powerball]

One thing the models have been consistent about is showing good mid-level drying for majority of the region on Friday, especially as the front slows down. So daytime heating shouldn't be a problem.

My biggest fear, if anything, would be the scenario the NAM and GFS are beginning to show, which his everything developing along the pre-frontal trough versus the actual cold front. If that happens, at least here in Detroit we would have to worry about storm initiation that happens a tad too early (18z-21z) and overhead versus storm initiation upstream that propagates into the area with upscale growth. The problem, usually, with early storm initiation around here is that the activity, since still in the developing stages, won't be organized/widespread, so some of us (myself most likely, being in an area favorable for downsloping and under the lake shadow) willget jipped.

Now that said, given the models failed to account for the 600dm ridge that popped, I wouldn't be surprised if they are a tad too fast with the breakdown of the ridge, and as a result the frontal passage.

DTX essentially affirmed my aforementioned concern in today's afternoon AFD.

[TimChgo9]

Not much confidence. Not punting on this one yet, but not holding out for much either.

Edit: Wow, latest NAM gives us nothing.

[wisconsinwx]

Yes andyhb, my average temp never rises above 83F and we were due for a cool summer but now I bet even this 'cool' summer will be at or above average.

[MidwestChaser]

Yeah, punt on this threat right now, and the fact that now every day is basically in the 90s is making this a very crappy weather week.

 

Dude, you're a joke. This is summer. Stop whining about heat. If you want cold that bad, go to your nearest grocery store and lock yourself in their freezers.

[TimChgo9]

Yeah, punt on this threat right now, and the fact that now every day is basically in the 90s is making this a very crappy weather week.

I don't like heat either, but I live with it, and deal with it.

[cyclone77]

A big FWIW for this.  18z 4km NAM Friday eve.  Encouraging to see it fire storms this far west but I'm not betting on it.  If anything goes it would be big though.  Really looking like a nice setup for Michigan to be sure.