Round -2 The Cold Front Action
Fasten you seat belts; it's gonna be a bumpy night!!!
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.
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!
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!
|Jun 21, 2015 1730 UTC Day 2 Convective Outlook|
|Updated: Sun Jun 21 17:32:26 UTC 2015 (Print Version | | )|
|Probabilistic to Categorical Outlook Conversion Table|
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.
Bill Deedler -SEMI_WeatherHistorian