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snowlover2

July 17-19 Severe Weather

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SPC has expanded the moderate risk area into northwest WI and the enhanced across the rest of north WI into the UP of MI. They even say in the disco that a derecho appears possible.

Quote
Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1121 AM CDT Fri Jul 17 2020

   Valid 171630Z - 181200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   THROUGH TONIGHT ACROSS PARTS OF THE NORTHERN PLAINS AND UPPER
   MIDWEST...

   ...SUMMARY...
   A significant severe weather event is possible this evening and
   tonight over parts of North Dakota, northern Minnesota, and
   northwest Wisconsin.  Widespread damaging winds are possible.

   ...ND to WI/Upper MI...
   Morning water vapor loop shows fast westerly flow across the
   northern tier of states, with an embedded low-amplitude shortwave
   trough over eastern MT.  Southerly low-level winds are present
   across the Dakotas, with local VADs showing 20-30 knots at 1-2km. 
   These winds are helping to transport 70s surface dewpoints
   northward, yielding an axis of MLCAPE exceeding 4000 J/kg later
   today from central ND into western MN.  Thunderstorms are expected
   to form early this afternoon as forcing overspreads the returning
   moisture, with a few supercells capable of large hail, damaging
   winds, or perhaps a tornado over western/central ND.  All guidance
   lends confidence that these storms will congeal into one or more
   bowing structures by this evening over eastern ND.  Storms will
   track rapidly eastward at 40-50 knots across parts of MN and into
   northern WI and upper MI overnight.  

   Given the very favorable thermodynamic profiles in place, the strong
   westerly flow aloft, and the consistent model guidance, it appears
   possible that a derecho will occur this evening and tonight from ND
   to WI - with the threat of a corridor of widespread and significant
   damaging winds.  Have expanded the MDT/ENH risks eastward into parts
   of WI/Upper MI where the bowing complex appears most likely to track
   late tonight.  Have also expanded the ENH southward into more of
   central MN due to uncertainty of how far south the MCS might
   develop.

 

day1otlk_1630.gif

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Just now, CheeselandSkies said:

Miss north FTL.

Saturday night is gonna be a dead on hit.  Like the Summer nighttime MCS of yore.

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Solid support for a weakening MCS to move in very early Sunday morning around here. However, I'm not sold on anything more than a marginal worthy severe threat.

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^

ugh. a thundershower around breakfast and than clouds to spoil the heat. Hoping this thing is racing so it maintains some intensity and than clears MBY.

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No real change on the updated day 2 but they do mention that an enhanced area will likely be needed.

Quote
Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1239 PM CDT Fri Jul 17 2020

   Valid 181200Z - 191200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
   THE UPPER MIDWEST AND GREAT LAKES REGION...

   ...SUMMARY...
   Scattered severe storms should occur Saturday across portions of the
   Upper Midwest and Great Lakes vicinity. Damaging winds and large
   hail appear to be the main hazards with these storms, some of which
   could be significant. A few tornadoes are also possible.

   ...Upper Midwest through Great Lakes areas...

   An MCS will likely be ongoing over a portion of the Great Lakes
   region, most likely from upper MI into WI, with trailing outflow
   boundary extending farther southwest into southern MN. Meanwhile,
   farther upstream, a progressive shortwave trough will reside over
   the northern Plains with accompanying cold front likely extending
   from eastern ND southwestward through western SD. This front will
   continue east and likely extend from northern MN through eastern SD,
   central NE into northeast CO by early afternoon. The atmosphere in
   vicinity of and south of the outflow boundary and east of the cold
   front will likely once again become very unstable with 3000-4000
   J/kg MLCAPE supported by rich low-level moisture and steep lapse
   rates. Initial thunderstorms will most likely develop near
   intersection of the cold front and remnant outflow boundary from
   southeast SD into southwest MN. This region will reside within belt
   of stronger mid-level winds supporting 35-40 kt effective bulk
   shear. Discrete supercells will be likely with a threat for large to
   very large hail and a few tornadoes possible as well. Eventually
   storms should evolve into an organized MCS with an increasing threat
   for damaging wind, some of which could be significant. 

   Considerable uncertainty still exists regarding where tonight's MCS
   and outflow boundary will have the most impact on Saturday's
   pre-storm environment. Will therefore leave as SLGT risk for now.
   However, an upgrade to enhanced will probably be needed for a
   portion of this region in upcoming day 1 outlooks.

   ..Dial.. 07/17/2020

 

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8 minutes ago, RyanDe680 said:

Borderline meh for the metro

 

I'd agree with that at this point.  Timing not great (could be even worse I guess) and also some indications of any heavier activity missing to the west.

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this mornings 3km NAM has a good handle on the current storms, just about an hour or 2 late with the development

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3 hours ago, madwx said:

I'm ready for the 2 straight hours of strobe like lightning

injectthis.PNG

Bring it. If that timing is right, I'll be going to work in the trailing stratiform precip region, which if any luck will have some lightning I can catch on-air with our skycams.

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Got the very rare PDS T-storm watch for a good chunk of MN.

Quote
  URGENT - IMMEDIATE BROADCAST REQUESTED
   Severe Thunderstorm Watch Number 380
   NWS Storm Prediction Center Norman OK
   535 PM CDT Fri Jul 17 2020

   The NWS Storm Prediction Center has issued a

   * Severe Thunderstorm Watch for portions of 
     Northern and central Minnesota
     Southeast North Dakota
     Northern South Dakota

   * Effective this Friday afternoon and Saturday morning from 535
     PM until 100 AM CDT.

   ...THIS IS A PARTICULARLY DANGEROUS SITUATION...

   * Primary threats include...
     Widespread damaging winds expected with scattered significant
       gusts to 90 mph likely
     Scattered large hail and isolated very large hail events to 2.5
       inches in diameter possible
     A couple tornadoes possible

   SUMMARY...An intense linear-type complex of storms is expected to
   evolve into a derecho this evening and produce
   widespread/significant damaging winds as it accelerates
   east-southeastward across the region. Isolated large hail is also
   possible, and a tornado risk cannot be ruled out, particularly near
   the warm front.

   The severe thunderstorm watch area is approximately along and 85
   statute miles north and south of a line from 85 miles north of
   Mobridge SD to 45 miles east of Brainerd MN. For a complete
   depiction of the watch see the associated watch outline update
   (WOUS64 KWNS WOU0).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   REMEMBER...A Severe Thunderstorm Watch means conditions are
   favorable for severe thunderstorms in and close to the watch area.
   Persons in these areas should be on the lookout for threatening
   weather conditions and listen for later statements and possible
   warnings. Severe thunderstorms can and occasionally do produce
   tornadoes.

 

ww0380_radar.gif

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4 hours ago, Hoosier said:

I'd agree with that at this point.  Timing not great (could be even worse I guess) and also some indications of any heavier activity missing to the west.

I dunno, most guidance suggests whatever is left moves through Chicago/N IN Sunday morning...pretty much the least favorable time for severe wx, climatologically. 

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2 minutes ago, purduewx80 said:

I dunno, most guidance suggests whatever is left moves through Chicago/N IN Sunday morning...pretty much the least favorable time for severe wx, climatologically. 

Guess it depends.  If it can get in at like 4 am, I'd consider that marginally better than 7 am.

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Just now, Hoosier said:

Guess it depends.  If it can get in at like 4 am, I'd consider that marginally better than 7 am.

agreed. as others have pointed out, there are positives to MCS maintenance that time of night.

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strong llj really helping to sustain what remains of overnight MCS into N. IA right now but it should crap the bed here as the jet fades

 

 

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Thread should probably be extended to include the 19th, for the Eastern GL and OH Valley.

I wouldn't be surprised if the slight risk area gets expanded back NW to Detroit and Toledo, although it is contingent on how tonight's activity evolves.

image.thumb.png.92dc3cd54f825b652a36786376b94c57.png

   SPC AC 180558

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1258 AM CDT Sat Jul 18 2020

   Valid 191200Z - 201200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   NORTHERN OH INTO NORTHWESTERN PA AND WESTERN NY...

   ...SUMMARY...
   Isolated strong to severe thunderstorms may occur Sunday from
   portions of the Great Lakes/Ohio Valley regions into the mid
   Mississippi Valley and parts of the Plains. Damaging winds and large
   hail should be the main threats.

   ...Great Lakes into the Ohio Valley and Western New York...
   An MCS may be ongoing at the start of the period Sunday morning
   across parts of Lower MI, with additional convection possible
   farther south into northern IL/IN. This MCS should decay quickly
   across Lower MI and vicinity as it encounters substantial convective
   inhibition with eastward extent across the Great Lakes region.
   Depending on its organization, it may still pose an isolated threat
   for damaging winds before it weakens/dissipates.

   In the wake of this morning activity, an upper trough is forecast to
   move east-northeastward from the Upper Midwest/Great Lakes into
   Ontario and Quebec through the period. A surface low should likewise
   develop northeastward across Ontario/Quebec through the day. A cold
   front trailing southwestward from this low across the Great
   Lakes/Upper Midwest should shift east-southeastward. Diurnal heating
   of a rather moist low-level airmass will likely foster moderate to
   potentially strong instability ahead of the front by Sunday
   afternoon. The stronger large-scale ascent associated with the upper
   trough should remain in Canada. Regardless, low to mid-level
   westerly flow is forecast to strengthen through the day across parts
   of the OH Valley into western PA/NY. A corresponding modest increase
   in effective bulk shear to around 25-35 kt will probably be
   sufficient for storm organization.

   Current expectations are for scattered storms to develop along/ahead
   of the front Sunday afternoon across northern IN/OH. Additional
   convection may advance eastward from southern Ontario across Lakes
   Erie/Ontario, and into northwestern PA and western NY by early
   Sunday evening. Clusters/small bows should the main storm mode. With
   steepened low-level lapse rates and enhanced low/mid-level flow
   across these areas, at least isolated damaging wind gusts may occur.
   Isolated instances of marginally severe hail also appear possible.
   Confidence has increased enough regarding this scenario to include
   15% severe wind probabilities and a corresponding Slight Risk from
   northern OH into western NY. Storms should gradually weaken Sunday
   evening farther east into central PA/NY as they encounter less
   instability.

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43 minutes ago, A-L-E-K said:

strong llj really helping to sustain what remains of overnight MCS into N. IA right now but it should crap the bed here as the jet fades

 

 

We’ll see, definite signs the last half hour of disorganization but still tons of lightning with the MCS.

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23 minutes ago, A-L-E-K said:

Still hanging 

Struggling to maintain, with shear lacking and best flow north.

This is probably the best it'll get.

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