Update 4/18/13; Severe Weather Reported

 Severe Weather April 18 2013 From the NWS


A strong cold front moved through Southeast Michigan on Thursday, April 18th. The front produced severe thunderstorms, heavy rain and
damaging winds.



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4/17/13 - 130 PM: Update
Little change to yesterday's blog as ingredients are progged to come together for the risk of strong to severe storms Thursday into early Friday. As we move closer to the time; a few important items have begun to become clearer.

12z 8am Thursday 4/18 -  Friday 12z 8am Fri 4/19
The highest severe threat for strong to damaging severe winds appears to be midday Thursday into Thursday evening. Refer to narrative and maps below for Thursday as confidence in modeling of the atmosphere is increasing with each successive run. Winds will average 20 to 30 mph with gusts possible in excess of 55 mph in the strongest of thunderstorms. Wind criteria for a severe thunderstorm is 58 mph along with 1" hail. At this time; the main threat from these storms would be wind damage. Because of the strong dynamics and shear in the atmosphere a risk of a few tornadoes can't be rule out.

In addition; also indicated below is concern for strong winds with the passage of the cold front around dawn Friday and moderate to strong gusty prevailing winds on Friday behind the front. Wind gusts of 40-50 mph are possible around frontal passage and after on Friday.

The Storm Prediction Center has now /130 PM Wed/ included all of Southeast Lower Michigan in it's severe threat for the above time period; 8AM EDT THU-8AM EDT FRI.

< Day 1 Outlook

Day 3 Outlook >

Apr 17, 2013 1730 UTC Day 2 Convective Outlook

Updated: Wed Apr 17 17:17:50 UTC 2013  (Print Version)

Probabilistic to Categorical Outlook Conversion Table

Categorical Probabilistic  Population  Cities  CWAs  Interstates  Counties  ARTCC  FEMA Regions Categorical Day2 1730Z Outlook

Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area MODERATE 98,699 13,128,064 Chicago, IL...Memphis, TN...Joliet, IL...South Bend, IN...Decatur, IL... SLIGHT 348,105 52,217,566 Houston, TX...Indianapolis, IN...Columbus, OH...Detroit, MI...Nashville, TN...

Forecast Discussion

SPC AC 171715 DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1215 PM CDT WED APR 17 2013 VALID 181200Z - 191200Z ...THERE IS A MDT RISK OF SVR TSTMS FOR SWRN LOWER MI...ERN/SRN IL...WRN/NRN IND...SERN MO...FAR WRN KY/TN...ERN AR...NWRN MS...FAR NERN LA... ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE GREAT LAKES TO THE WRN/CNTRL GULF COAST... ...SIGNIFICANT SEVERE WEATHER EPISODE CONSISTING OF POTENTIALLY WIDESPREAD DAMAGING WINDS AND SEVERAL TORNADOES APPEARS INCREASINGLY LIKELY ON THU... ...SYNOPSIS... AN AMPLIFIED UPPER-LEVEL TROUGH CENTERED FROM THE NRN PLAINS TO THE SOUTHWEST AT 12Z/THU WILL PROGRESS EWD ACROSS THE UPPER MS VALLEY TO THE SRN PLAINS THROUGH EARLY FRI. A VIGOROUS SHORTWAVE IMPULSE WILL EJECT FROM THE CNTRL PLAINS TO WI/IL WITH AN INTENSE AND STRENGTHENING MID-LEVEL SPEED MAX /AOA 100 KT/ OVERSPREADING THE MIDWEST. AT THE SURFACE...CYCLOGENESIS WILL CONTINUE FROM THE IA/IL BORDER NEWD TOWARDS NRN LK MI. AN ATTENDANT COLD FRONT WILL SWEEP EWD LIKELY REACHING LK MI TO THE LOWER MS VALLEY BY THU EVENING. A WARM FRONT WILL ATTEMPT TO ADVANCE NWD IN LOWER MI...WITH LOWER CONFIDENCE IN HOW FAR N IT WILL EXTEND WITH ABUNDANT CONVECTION EXPECTED N OF THE BOUNDARY. ...GREAT LAKES TO THE WRN/CNTRL GULF COAST... FAIRLY EXTENSIVE BANDS OF CONVECTION SHOULD BE ONGOING AT 12Z/THU ALONG BOTH FRONTAL ZONES. DIURNAL HEATING WITHIN A RICHLY MOIST AIR MASS FROM THE WRN GULF INTO THE MIDWEST CHARACTERIZED BY 60S TO LOWER 70S SURFACE DEW POINTS AMIDST A REMNANT EML PLUME EMANATING N/NEWD ACROSS THE S-CNTRL CONUS...SHOULD RESULT IN A MODERATELY UNSTABLE WARM SECTOR WITH MLCAPE REACHING 1000-2000 J/KG. LOWER-LEVEL SHEAR/HODOGRAPHS WILL BE IMPRESSIVELY LARGE WITH NRN EXTENT ACROSS THE BULK OF THE WARM SECTOR. THESE FACTORS COMBINED WITH STRONGLY FORCED ASCENT WILL LIKELY YIELD AN EXTENSIVE QLCS THAT WILL INTENSIFY AND INCREASE IN FORWARD SPEED DURING THE LATE MORNING THROUGH THE AFTERNOON. BOWING SEGMENTS AND EMBEDDED SUPERCELLS WILL BE FAVORED...ESPECIALLY WITH NRN EXTENT GIVEN THE DEGREE OF SHEAR. POTENTIAL WILL ALSO EXIST FOR DISCRETE SUPERCELLS DEVELOPING AHEAD OF THE QLCS AS MLCIN BECOMES MINIMAL. THIS WOULD SEEM TO BE MORE PREVALENT WITH SRN EXTENT WHERE LARGE-SCALE ASCENT WILL BE PROGRESSIVELY WEAKER. SWATHS OF WIDESPREAD DAMAGING WINDS APPEAR PROBABLE ALONG WITH A ROBUST TORNADO RISK /SOME OF WHICH COULD BE SIGNIFICANT/. THE OVERALL SEVERE THREAT WILL LIKELY DIMINISH BY LATE EVENING/OVERNIGHT AS THE SURFACE MOISTURE PLUME IS PINCHED OFF WITH NRN EXTENT GIVEN DOWNSLOPE DRYING OFF THE SRN APPALACHIANS INTO THE CNTRL/UPPER OH VALLEY. ..GRAMS.. 04/17/2013

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4/16/13 - 330 PM
As mentioned in my previous blog; I'd keep my eye peeled for any potentially rough weather in our near future and Thursday into midday Friday may fit the bill at this early stage. In addition and partly because of our recent flooding; some local lowland and river flooding may again be realized with heaviest rains.
 
Discussion
A powerful jet stream aloft, instability at the surface all wrapped around a deep low pressure system and sharp cold front spell trouble for much of the mid part of the country and into the Great lakes and Ohio/Tennessee Valley mid to late week. What really has me concerned in the strong jet aloft; we're talking 70 knots - 100 knots of wind just off the surface to around 18,000 FT /500 MB/. Even if the instability is marginal and the fronts push through at lesser favorable times; this system STILL looks potent, take a look..

First off; Thursday afternoon with out first system>>>

As modeled by the GFS as of 12z Tuesday; a strong upper wind max/80k-500 mb/ will help usher in the elevated thunderstorm complex expected to develop Wednesday night and push through Southeast Lower Michigan Wednesday night into Thursday afternoon. The right-rear quadrant of this max jet is projected to cross this region sometime Thursday afternoon. This will give storm development an added "kick" along with instability which is projected to rise with daytime heating with lifted index's ranging in neighborhood of -3 > -6. Caution; remember this is model projected and you know where that sometimes leaves us! Actual instability will largely depend on several factors; surface heating (i.e. sunshine), colder air present aloft at the time just to name a few. These periodic thunderstorms will primarily be elevated (not surface instability based) as they advance through the region Wednesday night into early Thursday. Severity will depend largely on available instability aloft and potential surface based instability thrown into the action along with projected wind max "kicking -in"!  Negatives include; time of day, little added surface instability along with the max leaving the region a bit earlier which would help negate severe potential.

                                                                                                Thursday Midday

Then on Friday early in the day (below maps); the main surface system along with wind max is slated to storm through the region. Again; the yellow highlighted discussion of model projected above applies here, also. Timing of the system and limited instability is unfavorable for "classic severe weather". However, with the powerful cold front being aided by a 70 knot - 100 knot jet core just aloft; this still would have the potential for a potent squall line of wind were the winds realized by any decent updrafts along the front, thunder or not! Strong gusty winds look favorable later also behind the system as it wraps up to the north.
                                                                                                      Friday Forenoon

Again this is two to three days out and this atmosphere and attending severe weather is yet to be better sampled. In any event; stay tuned for updated info on this potential first notable severe weather event of the season.

For the latest on severe weather potential for the US click here!
 

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