6/21/15

Update 6/22/15 930p - Conflicting Air Masses of "Dynamite" Potential Set for Monday Into Early Tuesday Morning

Update 930 P

Round -2 The Cold Front Action

Fasten you seat belts; it's gonna be a bumpy night!!!

http://www.spc.noaa.gov/products/watch/ww0338.html
 URGENT - IMMEDIATE BROADCAST REQUESTED
   TORNADO WATCH NUMBER 338
   NWS STORM PREDICTION CENTER NORMAN OK
   915 PM EDT MON JUN 22 2015

   THE NWS STORM PREDICTION CENTER HAS ISSUED A

   * TORNADO WATCH FOR PORTIONS OF 
     NORTHEAST ILLINOIS
     NORTHERN INDIANA
     SOUTHERN LOWER MICHIGAN
     NORTHWEST OHIO
     LAKE ERIE
     LAKE HURON

   * EFFECTIVE THIS MONDAY NIGHT AND TUESDAY MORNING FROM 915 PM
     UNTIL 300 AM EDT.

   * PRIMARY THREATS INCLUDE...
     A COUPLE TORNADOES POSSIBLE
     SCATTERED DAMAGING WINDS AND ISOLATED SIGNIFICANT GUSTS TO 75
       MPH POSSIBLE
     SCATTERED LARGE HAIL AND ISOLATED VERY LARGE HAIL EVENTS TO 2
       INCHES IN DIAMETER POSSIBLE

   SUMMARY...THUNDERSTORMS ARE LIKELY TO INCREASE IN COVERAGE AND
   INTENSITY THIS EVENING AS A STRONG UPPER JET AND COLD FRONT APPROACH
   THE REGION FROM THE WEST. A WARM AND VERY MOIST AIRMASS ACROSS THE
   WATCH AREA WILL FUEL ROBUST STORM UPDRAFTS AMIDST INTENSIFYING
   DEEP-LAYER WIND FIELDS. THIS SHOULD SUPPORT BOTH SUPERCELL AND
   FAST-MOVING LINE SEGMENTS WITH DAMAGING WINDS...LARGE HAIL...AND
   POSSIBLY A COUPLE TORNADOES.

   THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 70 STATUTE
   MILES NORTH AND SOUTH OF A LINE FROM 35 MILES NORTH OF MOUNT
   CLEMENS MICHIGAN TO 45 MILES NORTH OF CHAMPAIGN ILLINOIS.  FOR A
   COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
   UPDATE (WOUS64 KWNS WOU8).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
   TORNADOES AND 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.

   &&

   OTHER WATCH INFORMATION...CONTINUE...WW 335...WW 336...WW 337...

   AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
   SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE
   WIND GUSTS TO 65 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
   500. MEAN STORM MOTION VECTOR 27035.



Update- 145P
Round -1 Warm Front Action

As discussed yesterday, as the warm front approaches this afternoon and early evening, the old meso-complex of storms ignited overnight ahead of the front will continue to advance into Southeast Lower Michigan. The air mass ahead of the complex is moderately to strongly unstable along with upper wind Bulk Shear in the neighborhood of 50 knots. This has weakened from earlier readings of 75 knots and is depicted by a general weakening of the storm complex as of early afternoon. Non-the-less as the old storm complex/outflow moves into more favorable conditions it's identity should be maintained enough and thus the issuance of Severe Thunderstorm Watch. #333

Reasons for the watch from SPC:

...GREAT LAKES/MIDWEST REGION...
   A LARGE -- BUT GRADUALLY WEAKENING -- MCC CONTINUES MOVING ACROSS
   THE GREAT LAKES/MIDWEST ATTM...CENTERED OVER SRN WI/NRN IL AND LK
   MI.  STORMS HAVE INTENSIFIED OVER THE PAST HALF HOUR IN THE SRN LK
   MI/SWRN LOWER MI AREA INVOF A SHARPENING WARM FRONT...AND EXPECT
   POTENTIAL FOR STORM REDEVELOPMENT ACROSS THIS AREA -- AND SWD INTO
   ADJACENT NRN IL/NRN INDIANA -- AHEAD OF THE MAIN MESOSCALE LOW
   ASSOCIATED WITH THE MCC.  ALONG WITH RISK FOR STRONG/DAMAGING WINDS
   AND HAIL...A COUPLE OF TORNADOES WILL ALSO BE POSSIBLE -- GIVEN
   PRESENCE OF THE AFORMENTIONED WARM FRONT AND STRENGTHENING FLOW
   ALOFT WITH TIME.

No change in blog through tonight!
_______________________________________________________________________________
6/21/15

In my Summer Outlook; I stressed the likelihood of impressive jet stream conflicts along with their attending surface air masses outcomes with wetter, stormier conditions for most of the region at least part of the summer depending on air jet stream/air mass dominance. It's been notably active to our south and west all season.

"Summer as a rule can be one of the more difficult seasons to forecast for because of the lighter, variable upper wind jet dominance. This summer that general trend may not apply as much as two dominant upper wind patterns via for center stage; a relatively strong polar jet that has had no trouble visiting the Great Lakes throughout the spring along with the sub-tropical/tropical jet aided by an ever increasing El Nino. Overall; I look for temperatures to average around normal but with notable swings as the upper low and troughing in eastern Canada via for dominance against upper ridging, aided and at times, even suppressed by El Nino affected winds across the south. This is a difficult forecast as we dealing with two distinctive upper wind patterns, not always present in such fashion in the summer." 



Both the GFS and  NAM Models have been strongly suggesting we have the above to contend with - in spades- Monday into early Tuesday morning while the European has been somewhat weaker with the overall system. Latest 12Z guidance of the Euro now intensifies the low center to 988MB by the time it reaches Ontario Tuesday morning.

Thus far; this severe weather season has been intermittent and on the slow side as Southeast Michigan has remained much of the time in the more stable air masses, aided at times by the cold to cool Lakes and easterly fetch as systems approach from the southwest.The dynamics, upper and lower strong wind jets along with the instability, deep layer shear and CAPE/LI's projected this time are further north over Wisconsin and Lower Michigan and are quite strong. In fact, this time around the worst (or best depending on your point of view) severe weather dynamics look to be coming together just to our west and northwest Monday night and Tuesday morning, then advecting into our region during the very early morning hours of Tuesday. One caveat to limit severe weather after warm frontal passage and before the cold front approaches in the overnight hours will be the warmer air pulled north aloft into the strong system to our northwest and thus, this will provide a temporary cap against the development of severe weather. At this time, it looks as though the dynamics of the system along with cooler air aloft (both advected in and slight overnight cooling aloft) with aid in eroding any cap that does form by the time the cold front approaches Tuesday morning. All severe weather risks are here, including strong damaging winds and tornadic cells and may be realized for at least some. At this time, we have two general periods of severe weather potential - warm frontal and cold frontal.

Warm Front Risk

Never trust a warm front! I learned that early on back in the some of the stormy 70's summers and a even more notable case was the Frankenmuth tornado and flash flooding. Ironically,  the Frankenmuth Tornado occurred on this date; June 21st, back in 1996. I remember it well as I was working along with two other METS and the newly installed Doppler Radar was still in its infancy having been installed in the early 1990s. While leery of the warm front draped over Southeast Lower Michigan, most eyes were watching the cold front and severe weather possibility over Wisconsin with a watch box issued for that region. As the atmosphere cooled aloft, thunderstorms and very heavy flash flooding rains popped like popcorn in the proximately of the warm front. Helicity values and instability were notable along the warm front and thus, helped spawn the infamous tornado.

Therefore; this is definitely something that has to be watched with this aforementioned system with both the warm front and cold front as helicity/EHI values are extremely high promoting tornado risk! The biggest negative is while all this "dynamite" exists, will it become lit or realized? It could become negated if part or all of Southeast Lower Michigan becomes too warm aloft which inhibits thunderstorm growth. At this time, with the warmer air rushing in aloft and best dynamics northwest, the risk of severe weather with the warm front will be marginalized (become capped) but can not be ruled out and bears watching until the warm front clears the area!

GFS Maps:






 SPC's Take


Jun 21, 2015 1730 UTC Day 2 Convective Outlook
Updated: Sun Jun 21 17:32:26 UTC 2015 (Print Version | 20150621 1730Z Day 2 shapefile | 20150621 1730Z Day 2 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Probabilistic
 Population  Cities  CWAs  Interstates  Counties  ARTCC  FEMA Regions
 
Categorical Day2 0600Z Outlook
Day 2 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 129,731 27,151,847 Chicago, IL...Detroit, MI...Milwaukee, WI...Toledo, OH...Madison, WI...
SLIGHT 143,283 14,682,662 Cleveland, OH...Minneapolis, MN...Buffalo, NY...St. Paul, MN...Fort Wayne, IN...
MARGINAL 190,594 20,003,960 Indianapolis, IN...Columbus, OH...Kansas City, MO...Pittsburgh, PA...Rochester, NY...
 Forecast Discussion
   SPC AC 211732

   DAY 2 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1232 PM CDT SUN JUN 21 2015

   VALID 221200Z - 231200Z

   ...THERE IS AN ENH RISK OF SVR TSTMS GREAT LAKES AND UPPER MS
   VALLEY...

   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER MIDWEST TO LOWER
   GREAT LAKES...

   ...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF THE N-CNTRL/NE
   STATES...

   ...SUMMARY...
   SCATTERED SEVERE STORMS ARE LIKELY ACROSS PARTS OF THE UPPER
   MISSISSIPPI VALLEY AND GREAT LAKES REGIONS...SOME OF WHICH SHOULD BE
   INTENSE...MAINLY FROM MIDDAY THROUGH THE EVENING ON MONDAY.

   ...UPPER MS VALLEY/GREAT LAKES...
   STRONGLY CONSIDERED AN UPGRADE TO MODERATE RISK WITH POTENTIAL FOR
   CLUSTERS OF INTENSE SEVERE STORMS WITH ALL SIGNIFICANT SEVERE
   HAZARDS POSSIBLE. BUT WILL DEFER GIVEN ENOUGH UNCERTAINTY WITH
   REGARD TO EVOLUTION OF LATE D1 CONVECTION WITH ITS SUBSEQUENT EFFECT
   ON THE DEGREE OF DOWNSTREAM DIURNAL DESTABILIZATION...ALONG WITH
   TIMING OF THE PAIR OF MID-LEVEL SHORTWAVE IMPULSES WITH RESPECT TO
   PEAK HEATING.

   GUIDANCE IS CONSISTENT IN DEPICTING STRENGTHENING
   LOW/MID-TROPOSPHERIC FLOW IN RESPONSE TO A CONVECTIVELY-GENERATED
   MCV FROM LATE D1/EARLY D2 AND APPROACH OF AN UPSTREAM SHORTWAVE
   TROUGH CURRENTLY OVER THE SRN CANADIAN ROCKIES. THESE FEATURES WOULD
   ENHANCE LOW-LEVEL WAA OF THE RICHLY BUOYANT AIR MASS CURRENTLY
   PRESENT OVER THE LOWER MO VALLEY. AVAILABLE CAMS VARY MARKEDLY WITH
   THE DAYTIME EVOLUTION OF AN MCS EXPECTED TO BE ONGOING ACROSS PARTS
   OF SRN MN/NRN IA. IT SEEMS PLAUSIBLE THAT THIS ACTIVITY SHOULD
   PERSIST THROUGH THE DAY WITH AN ORGANIZED SEVERE RISK ON THE EDGE OF
   A ROBUST PLAINS EML. THIS TYPE OF SCENARIO MAY RESULT IN LEAD
   CONVECTION OUTPACING THE MORE FAVORABLE THERMODYNAMIC ENVIRONMENT
   CHARACTERIZED BY RATHER STEEP MID-LEVEL LAPSE RATES AND VERY LARGE
   BUOYANCY. 

   AT LEAST SCATTERED UPSTREAM TSTM DEVELOPMENT SHOULD OCCUR BY LATE
   AFTERNOON ALONG THE COLD FRONT FROM CNTRL/ERN WI SW TO THE IA/IL
   BORDER AREA AS CONVERGENCE ALONG THE FRONT AND DIABATIC HEATING
   OVERCOME INHIBITION DUE TO THE INITIALLY STOUT EML. SUPERCELLS ARE
   EXPECTED IN INITIAL STAGES OF DEVELOPMENT...WITH SOME OF THIS
   CONVECTION GROWING UPSCALE DURING THE EVENING. WITH LOW-LEVEL FLOW
   BECOMING INCREASINGLY VEERED IN THE WAKE OF THE LEAD MID-LEVEL
   IMPULSE...MAIN HAZARDS WITH SW EXTENT SHOULD BE VERY LARGE HAIL
   TRANSITIONING TO PREDOMINATELY SEVERE WIND. WHERE 850 MB WINDS CAN
   REMAIN QUITE STRONG WITH ENLARGED LOW-LEVEL HODOGRAPHS /MOST LIKELY
   IN ERN WI TO LOWER MI/...A RISK FOR STRONG TORNADOES AND/OR
   SIGNIFICANT SEVERE WIND GUSTS MAY DEVELOP.

   ..GRAMS.. 06/21/2015


Part Two: The Cold Front

The second villain in the piece (and possibly the worst) will be the strong cold front as it sails east-southeast at 45 to 50 mph through lower Michigan during the overnight hours of Monday into early Tuesday. As the storms approach, the intense wind max moving through the region at all upper levels will help push any storm development and line eastward of upwards of 50-60 mph aiding some very turbulent storm downdrafts creating scattered high wind damage. The risk of tornadic cells will gradually decrease with time as wind directions at all levels align with straight line high winds remaining the main risk.

This entire system reminds me of a few of our stronger squall lines including bow echoes and derechos; May 31st, 1998 (which is also an analogue), also July 7th 1991 and July 2nd 1997 because of the tornado threat. I'm sure there are others, too numerous to mention. Again the dynamite appears to be there and whether of not the extreme weather conditions materialize will be an up to the minute realization. Models are predicting one of the stronger severe weather events in recent times as the dynamically driven system runs rudely into explosively unstable air mass. I wouldn't be surprised in SPC upgrades some of the area to a moderate risk if these parameters continue in successive model outputs. Keep tuned to NWS web page/NWR and other weather mediate outlets during the day Monday into Tuesday morning!

I will update any notable changes as usual through the period.

GFS Maps:










Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian