For now, at least, these summer thunderstorms are just north of downtown Ann Arbor, extending north past Flint and west past Lansing. These storms developed relatively quickly late this afternoon, and we can expect development to continue into the evening as the air cools.
A severe thunderstorm watch, effective until midnight EDT, extends into the western third of Washtenaw County; at closest, its border is 10 miles from A2, so I would expect to see some thunderstorms here at some point tonight, some of which may be severe. (Within the severe thunderstorm watch area, which includes the northern half of Indiana and the southwest/south-central portion of Michigan, primary risks are significant damaging winds, large hail, and a few tornadoes.)
Looking forward, we can expect thunderstorms across the area Tuesday morning. (The SPC puts us in the 40% probability area for thunderstorms from midnight through Tuesday morning.) Some of these storms will be severe, with the primary threats being damaging wind, large hail, and brief heavy downpours.
As on any hot, humid summer day, we can expect thunderstorms to develop across SE Michigan and northern Ohio today. It is difficult to predict accurately & specifically whether any will hit an area as small as Ann Arbor.
Severe weather is not generally expected, but isolated thunderstorms could be strong, with 50-60 mph wind gusts and briefly heavy rainfall.
The relevant part of today’s severe weather outlook from NWS Detroit:
THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND TONIGHT FOR THE CENTRAL GREAT LAKES REGION. WIDESPREAD SEVERE WEATHER IS NOT ANTICIPATED BUT AN ISOLATED THUNDERSTORM MAY PRODUCE WIND GUSTS TO 50 KNOTS AND BRIEF HEAVY RAINFALL. STORM MOTION WILL BE WEST TO EAST BETWEEN 15 AND 20 KNOTS.
As of 1:20 pm, a small cell has popped up just north of Ann Arbor; this cell is tracking east-northeast and will continue to develop while moving away from the city. We can expect similar pop-up thunderstorms across the area this afternoon.
The SPC puts us at 10%-30% probability of thunderstorms until midnight; and only a 5% probability of damaging wind or large hail.
We have a chance of thunderstorms scattered across the area later this afternoon into tonight. These will be typical summer thunderstorms and are not expected to be severe.
THERE IS A CHANCE OF THUNDERSTORMS THIS AFTERNOON AND TONIGHT...MAINLY ACROSS THE SAGINAW VALLEY AND NORTHERN THUMB REGION. THESE STORMS ARE NOT EXPECTED TO BE SEVERE...WITH STORMS CAPABLE OF PRODUCING BRIEF HEAVY DOWNPOURS AND WIND GUSTS TO 30 MPH. STORM MOTION WILL BE FROM WEST TO EAST AT 20 MPH.
The Michigan DEQ has declared today an action day for elevated levels of ozone.
People should try to avoid activities which lead to ozone production, and those with respiratory issues should limit prolonged outdoor exertion.
Details follow, from NWS Detroit:
MIZ063-069-070-075-076-083-220115- ST. CLAIR-OAKLAND-MACOMB-WASHTENAW-WAYNE-MONROE- INCLUDING THE CITIES OF...PORT HURON...PONTIAC...WARREN... ANN ARBOR...DETROIT...MONROE 203 PM EDT THU JUN 20 2013 ...AIR QUALITY ALERT FOR FRIDAY JUNE 21ST... THE MICHIGAN DEPARTMENT OF ENVIRONMENTAL QUALITY HAS DECLARED FRIDAY...JUNE 21ST...TO BE AN ACTION DAY FOR ELEVATED LEVELS OF OZONE. POLLUTANTS ARE EXPECTED TO BE IN THE UNHEALTHY FOR SENSITIVE GROUPS RANGE. THE ACTION DAY IS IN EFFECT FOR THE FOLLOWING MICHIGAN COUNTIES... MACOMB...MONROE...OAKLAND...ST CLAIR...WASHTENAW...AND WAYNE COUNTIES. PEOPLE AND BUSINESSES ARE URGED TO AVOID ACTIVITIES WHICH LEAD TO OZONE FORMATION. THESE ACTIVITIES INCLUDE...REFUELING VEHICLES OR TOPPING OFF WHEN REFUELING...USING GASOLINE POWERED LAWN EQUIPMENT...AND USING CHARCOAL LIGHTER FLUID. POSITIVE ACTIVITIES INCLUDE...CAR POOLING...DELAYING OR COMBINING ERRANDS...AND USING WATER BASED PAINTS. IT IS RECOMMENDED THAT ACTIVE CHILDREN AND ADULTS...AND PERSONS WITH RESPIRATORY DISEASES SUCH AS ASTHMA...LIMIT PROLONGED OUTDOOR EXERTION. FOR FURTHER INFORMATION...PLEASE SEE THE MICHIGAN DEPARTMENT OF ENVIRONMENTAL QUALITY PAGE ON THE INTERNET AT... HTTP://WWW.DEQMIAIR.ORG $$ BT
We have a chance of isolated strong, possibly severe, storms this afternoon through midnight, with an associated slight risk of damaging wind or large hail. Little-to-no tornado risk.
These storms could develop as a cold front moves slowly through SE Michigan from north to south. Any storms that do develop will probably be powerful.
I wouldn’t worry just yet, but as it gets even hotter this afternoon and the front moves through the area some storms will develop across the area. It’s impossible to predict to what extent any will affect Ann Arbor specifically.
THERE IS A SLIGHT CHANCE OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EARLY TONIGHT AS A COLD FRONT SLOWLY MOVES THROUGH THE AREA FROM NORTH TO SOUTH. ANY STORMS THAT DEVELOP WILL BE CAPABLE OF PRODUCING WIND GUSTS TO 60 MPH AND HAIL UP TO ONE INCH IN DIAMETER. STORM MOTION WILL BE NORTHWEST TO SOUTHEAST AT 30 MPH.
Washtenaw County Emergency Operations Center:
ISOLATED SEVERE THUNDERSTORMS WITH 60 MPH WINDS AND ONE INCH HAIL ARE POSSIBLE BETWEEN 2 PM AND MIDNIGHT.
As predicted, a severe storm system developed west of us and moved west-southwest, with the nearest severe weather to Ann Arbor passing just south of the Michigan-Ohio border (associated with the bowing squall line in the radar image above).
Ann Arbor can expect heavy rain with thunderstorms over the next several hours, diminishing later in the morning as this system moves out of the area. These storms are not generally expected to be severe, though they will bring downpours.
The severe thunderstorm watch for our area has been cancelled (Watch County Notification [WCN] below). With the watch cancelled, we are at a slight risk of severe weather – the most severe risk is around central IN and west/central OH. The most relevant convective and thunderstorm outlook products available at this time of night show us at little risk of strong thunderstorms or other severe weather as day breaks on Thursday.
Additional reading: SPC MD 1054.
WWUS63 KDTX 130444 WCNDTX WATCH COUNTY NOTIFICATION FOR WATCH 300 NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 1244 AM EDT THU JUN 13 2013 MIC091-115-161-163-130545- /O.CAN.KDTX.SV.A.0300.000000T0000Z-130613T0600Z/ THE NATIONAL WEATHER SERVICE HAS CANCELLED SEVERE THUNDERSTORM WATCH 300 FOR THE FOLLOWING AREAS IN MICHIGAN THIS CANCELS 4 COUNTIES IN SOUTHEAST MICHIGAN LENAWEE MONROE WASHTENAW WAYNE THIS INCLUDES THE CITIES OF...ANN ARBOR...CANTON...CLINTON... DEARBORN...LAMBERTVILLE...LINCOLN PARK...LIVONIA...MONROE... REDFORD...TAYLOR...TEMPERANCE AND WESTLAND. $$ LCZ423-LEZ444-130545- /O.CAN.KDTX.SV.A.0300.000000T0000Z-130613T0600Z/ THE NATIONAL WEATHER SERVICE HAS CANCELLED SEVERE THUNDERSTORM WATCH 300 FOR THE FOLLOWING AREAS THIS CANCELS THE FOLLOWING ADJACENT COASTAL WATERS DETROIT RIVER MICHIGAN WATERS OF LAKE ERIE FROM DETROIT RIVER TO NORTH CAPE MI $$ KURIMSKI ---- GROUPJUL132013 WASHTENAWMI