4/8/15

-Update 4/9/15: Stormy April Beginning To Come To Fruition: Severe Weather Potential 4/9-10

Quick Update This Evening Into Friday - 4/9/15

Very little change from yesterday's blog with timing issues and low level stability major deterrents for an organized outbreak of severe weather. If anything; all things considered now, any organized severe weather looks doubtful with the strongest weather /winds/ coming in isolated strong storm/severe, ahead of and along the cold front overnight and toward morning. Widespread strong winds are expected after cold frontal passage near sunrise (as stated yesterday, see next paragraph below). Winds on Friday look to rev-up to between 25 - 40 MPH with gusts possible 40 - 50.


-4/8/15
Review
Overall with the data I've looked at as of the 18Z GFS Wed 4/8 run, I see the best (or worst if you prefer) of the strong weather, mainly west, southwest and south of Southeast Lower Michigan. This mainly because of late timing issues and somewhat out of alignment severe weather parameters.

Thunderstorms look likely, some elevated and some strong to possibly a few severe with gusty damaging winds, mainly from late afternoon into the over night hours with the evolving squall line. However, the strongest of winds could very well be behind the line of storms, the early part of Friday.

 Any notable changes, look for updates.
______________________________________________________________________________
It was just last week when I called for a stormier April and now we have out first potential severe weather event, Thursday into early the morning hours of Friday. It's been relatively calm too long and mainly due to the the overhang of cold, Polar air over the region. This brought the colder than average March but with the change of the month, came a change in the over weather and temperatures pattern and - the springtime conflict of air masses. With the strengthening heating of the atmosphere comes the usual air mass battle and resultant storms and severe weather.

It's been relatively calm across the country this spring as the cool, stabilizing residual Polar air masses continued to slide down across Canada into the eastern half of the country while this has brought a slow start to spring across much of the Great Lakes and Northeast, it also has kept severe weather basically at bay. In addition the near freezing waters of the northern Great Lakes basically, 30s to lower 40s over the southern Great Lakes have a remarkable effect of local and downwind areas. Today is an excellent example of the contrasting low level air masses across a rather small region of the country. The combination of a cold polar high pressure in southeast Canada and its attending northeast wind across the icy Great Lakes, show the strength of air masses in this classic early spring weather pattern. Meanwhile, much warmer (some places close to 40 degrees) bubbles up from the south and southwest as warm spring-like winds push rudely northeast into this cold, stable dome of air. Below, look at the contrasting temperatures of both air masses over the Great Lakes and Northern Ohio Valley.

Water Temperatures remain in the 30s to lower 40s over the Eastern Great Lakes.
(Click on ALL maps for larger depiction and clarity)















 Great Lakes Surface Map as of 5PM 4/8/15


Outstanding, all that's needed to mix up these opposing foe's is some sort of catalyst to come along and surge one air mass into the other. Cue surface/instability maps for Thu into Fri>>>>

During Thursday:
The warm front pushes north through the lower Great Lakes by early evening along with ushering in more unstable air and decent helecity (which aids in the development of tornadoes). Storm Relative Helicity (third map) along a warm front is generally where it is best available because of the clockwise turn of the air from the colder air mass to the north and east to the warmer air mass south and southwest. Therefore, east to southeast winds gradually turn to south and southwest in the lowest layers of the atmosphere. The Storm Relative Helicity Index map relates those numbers, the higher the number the more likely of tornadic storms using the scale below (third map). One very important caveat to remember however, is that strong instability (CAPE/LI/Bulk Shear among other parameters) is also needed. Many times, one of these parameters may blow the roof off (no pun intended) but with the absence of another, severe weather fails to materialize.



 

GFS 18Z SKEWt

beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=GFS&STATIONID=DTW


DATA TABLE
    Helicity Amount of Rotation
> 100 Some storm rotation
>  250 Enough rotation to support supercell thunderstorms
    and some tornadoes
>  400 Enough rotation to support dangerous tornadic thunderstorms



5PM 4/8/15 - Helecity





 8PM 4/8/15 - Helecity


GFS 03z SKEWt

Note that while helicty remains potent, the atmosphere begins to stabilize as nightfall overtakes the region, particularity so early in the heating season. April severe weather events can be one of the most extreme events because of strong, almost winter-like dynamics (wind fields/energy) feeding the low pressure storm system. And, when strong winter-like dynamics meet up with spring or even summer-like air masses all hell can break loose.
11pm Thu - Helecity








The bulk shear here at 7AM Fri pushes through Southeast Lower Michigan just on the heels of the line of convection. Strong winds indicated aloft behind the line of storms will blast down to the surface behind the front bringing strong, gusty surface winds!


Review
Overall with the data I've looked at as of the 18Z GFS Wed 4/8 run, I see the best (or worst if you prefer) of the strong weather, mainly west, southwest and south of Southeast Lower Michigan. This mainly because of late timing issues and somewhat out of alignment severe weather parameters.

Thunderstorms look likely, some elevated and some strong to possibly a few severe with gusty damaging winds, mainly from late afternoon into the over night hours with the evolving squall line. However, the strongest of winds could very well be behind the line of storms, the early part of Friday.

Any notable changes, look for updates.


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

SPC Severe Weather Outlook Issued Wednesday afternoon





 SPC AC 081730

   DAY 2 CONVECTIVE OUTLOOK 
   NWS STORM PREDICTION CENTER NORMAN OK
   1230 PM CDT WED APR 08 2015

   VALID 091200Z - 101200Z

...THERE IS AN ENH RISK OF SVR TSTMS THURSDAY AFTERNOON AND EVENING ACROSS PARTS OF SOUTHERN GREAT LAKES REGION AND LOWER OHIO VALLEY...SOUTHWARD THROUGH THE OZARK PLATEAU AND ARKLATEX REGION...

...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE ENH RISK
AREA...ACROSS THE GREAT LAKES REGION AND OHIO      VALLEY...SOUTHWARD  INTO THE SOUTHEASTERN PLAINS...

...THERE IS A MRGL RISK OF SVR TSTMS AS FAR SOUTHEAST AS THE EDWARDS  PLATEAU AND ADJACENT PORTIONS OF THE RIO GRANDE VALLEY...

   ...SUMMARY...
 SEVERE THUNDERSTORMS ARE LIKELY THURSDAY INTO THURSDAY NIGHT ACROSS  SOUTHERN PORTIONS OF THE GREAT LAKES REGION...AND MUCH OF THE MIDDLE  MISSISSIPPI AND OHIO VALLEYS INTO THE SOUTHEASTERN PLAINS.  THIS WILL INCLUDE THE RISK FOR DAMAGING WIND GUSTS AND LARGE HAIL.  A  COUPLE OF STRONG TORNADOES ARE POSSIBLE.

   ...SYNOPSIS...
A SIGNIFICANT IMPULSE...WITHIN THE SOUTHERN BRANCH OF SPLIT
WESTERLIES EMERGING FROM THE MID-LATITUDE PACIFIC...IS FORECAST TO CONTINUE AN EAST NORTHEASTWARD ACCELERATION OUT OF THE GREAT BASIN DURING THIS PERIOD.  THIS FEATURE IS EXPECTED TO REACH THE CENTRAL  HIGH PLAINS BY 12Z THURSDAY...AND THE UPPER MIDWEST BY THURSDAY NIGHT...WHERE/WHEN MODELS SUGGEST THAT IT MAY INCREASINGLY PHASE WITH A SIGNIFICANT NORTHERN STREAM IMPULSE.  AS THIS OCCURS...MORE SUBSTANTIVE DEEPENING OF AN ASSOCIATED SURFACE CYCLONE...EMERGING FROM THE CENTRAL PLAINS...IS EXPECTED TO PROCEED ACROSS AND EAST  NORTHEAST OF THE GREAT LAKES REGION.

ALTHOUGH SUBSTANTIVE DEEPENING OF THE LOW IS NOT CURRENTLY FORECAST  AS IT TRACKS FROM THE MID MISSOURI VALLEY TOWARD LAKE MICHIGAN DURING THE DAY THURSDAY...IT STILL IS EXPECTED TO BE AT LEAST MODERATELY STRONG WITH LOWEST PRESSURES AT OR BELOW 1000 MB.  A TRAILING SURFACE COLD FRONT APPEARS LIKELY TO ADVANCE SOUTHWARD THROUGH THE MIDDLE MISSISSIPPI VALLEY AND PORTIONS OF THE OZARK PLATEAU AND SOUTHEASTERN PLAINS...WHERE IT WILL GRADUALLY OVERTAKE A WELL-DEFINED DRYLINE.  A WARM FRONT EAST OF THE LOW APPEARS LIKELY TO ADVANCE NORTHWARD THROUGH THE GREAT LAKES REGION...WHILE COLD AIR REMAINS DAMMED TO THE EAST OF MUCH OF THE NORTHERN AND CENTRAL APPALACHIANS.

AIDED BY THE PRESENCE OF MOIST AND POTENTIALLY UNSTABLE AIR IN THE WARM SECTOR OF THE CYCLONE...LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION SHOULD BE SUFFICIENT TO SUPPORT WIDESPREAD THUNDERSTORM  ACTIVITY...FROM THE MISSISSIPPI VALLEY AND SOUTHEASTERN PLAINS INTO THE APPALACHIANS...PERHAPS PORTIONS OF THE PIEDMONT TO THE EAST OF THE SOUTHERN APPALACHIANS.  IN THE PRESENCE OF MODERATELY STRONG...40-50 KT DEEP LAYER MEAN FLOW AND DEEP LAYER SHEAR...ANUMBER OF THESE STORMS MAY BECOME SEVERE.  MUCH OF THIS ACTIVITY  SEEMS LIKELY TO BE FOCUSED ON THE AFOREMENTIONED SURFACE BOUNDARIES...PARTICULARLY ALONG THE SOUTHEASTWARD SURGING
FRONT/DRYLINE ACROSS THE OHIO VALLEY INTO SOUTHEASTERN PLAINS BY  THURSDAY EVENING.

   ...GREAT LAKES/OHIO VALLEY INTO SOUTHEASTERN PLAINS...
MODELOUTPUT IS SUGGESTIVE THAT DEEPER/RICHER BOUNDARY LAYER  MOISTENING MAY BE CONFINED TO A RELATIVELY NARROW CORRIDOR IN  ADVANCE OF THE COLD FRONT.  AND CONSIDERABLE CONVECTIVE ACTIVITY MAY  BE ONGOING IN THE WARM SECTOR ACROSS PARTS OF THE MIDDLE MISSISSIPPI   AND OHIO VALLEYS AT THE OUTSET OF THE PERIOD.  BY 12Z THURSDAY...IT ALSO APPEARS THAT THERE MAY BE CONSIDERABLE STABILIZATION OF THE  BROAD AREA OF STEEP MID-LEVEL LAPSE RATES NOW PRESENT ACROSS THE  PLAINS INTO THE VICINITY OF THE APPALACHIANS.  THESE FACTORS...AMONG
OTHERS...MAY BE LIMITING FACTORS TO A POTENTIALLY MORE SUBSTANTIVE   SEVERE WEATHER RISK FOR THIS PERIOD.

  STILL...GIVEN THE LARGE-SCALE FORCING AND STRENGTH OF DEEP LAYER   FLOW/SHEAR...INCLUDING A RATHER BROAD AREA OF 40-50 KT SOUTH   SOUTHWESTERLY 850 MB FLOW DURING THE DAY...THE ENVIRONMENT WILL BE  CONDUCIVE TO ORGANIZED CONVECTIVE DEVELOPMENT...INCLUDING SUPERCELLS.  AND POCKETS OF STRONGER DESTABILIZATION COULD YIELD  SCATTERED AREAS WITH POTENTIAL FOR INTENSE SUPERCELLS CAPABLE OF   PRODUCING A STRONG TORNADO OR TWO...IN ADDITION TO VERY LARGE HAIL.

IT IS POSSIBLE THAT ONE OF THESE AREAS COULD DEVELOP NEAR THE WARM   FRONT...IN THE VICINITY OF THE SURFACE LOW...ACROSS PARTS OF   NORTHERN ILLINOIS...INCLUDING THE CHICAGO METRO AREA...
DURING THE MIDDAY AND AFTERNOON HOURS.  ANOTHER COULD DEVELOP NEAR  THE COLD FRONT/DRY LINE INTERSECTION...ACROSS PARTS OF THE OZARK  PLATEAU AND ARKLATEX REGION DURING THE LATE AFTERNOON AND EVENING.    HOWEVER...TOO MUCH UNCERTAINTY CURRENTLY EXISTS CONCERNING COVERAGE  AND AREA TO SUPPORT 10 PERCENT SIGNIFICANT SEVERE WEATHER  PROBABILITIES AT THE PRESENT TIME.   OTHERWISE...DAMAGING CONVECTIVE SURFACE GUSTS MAY EVENTUALLY BECOME  THE MOST PROMINENT SEVERE WEATHER THREAT WITH AN EVOLVING SQUALL  LINE ALONG/AHEAD OF THE COLD FRONT BY THURSDAY EVENING.

   ..KERR.. 04/08/2015

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