Author: Chris Dzombak

The storm system that swept across northern Indiana late this afternoon/early this evening is moving our way, and while Ann Arbor is not under a severe thunderstorm watch, some strong storms currently south/southwest of Jackson are headed our way.

These storms have weakened somewhat in the last two hours and are not severe, but are expected to bring 40+mph winds, brief moderate downpours, and occasional lightning, so the usual storm safety advice applies: best to be indoors.

The full special weather statement from NWS Detroit follows:

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1019 PM EDT MON JUN 24 2013

MIZ075-082-250315-
LENAWEE-WASHTENAW-
1019 PM EDT MON JUN 24 2013

...SIGNIFICANT WEATHER ADVISORY...

AT 1015 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 24 MILES WEST OF
CHELSEA TO 19 MILES SOUTHWEST OF HUDSON...MOVING EAST AT 45 MPH.

WINDS GREATER THAN 40 MPH...OCCASIONAL CLOUD TO GROUND LIGHTNING...
BRIEF MODERATE DOWNPOURS...ARE POSSIBLE WITH THESE STORMS.

* THUNDERSTORMS WILL BE NEAR...
  ADDISON BY 1025 PM EDT...
  HUDSON AND CEMENT CITY BY 1030 PM EDT...
  CLAYTON BY 1035 PM EDT...
  ONSTED AND MORENCI BY 1040 PM EDT...
  CHELSEA AND MANCHESTER BY 1045 PM EDT...
  CLINTON AND ADRIAN BY 1050 PM EDT...
  DEXTER AND TECUMSEH BY 1055 PM EDT...

GUSTY WINDS MAY CAUSE SMALL OBJECTS SUCH AS TRASH BINS TO BLOW
AROUND. STAY AWAY FROM HIGH OBJECTS OUTDOORS SUCH AS TREES. SEEK
SHELTER IN A STURDY STRUCTURE UNTIL THESE STORMS HAVE PASSED.

$$

MANN

Per MD 1212

A severe system responsible for several severe thunderstorm warnings (mostly due to long swaths of damaging winds) in eastern IL and across northern IN is weakening, but continues moving across the upper midwest at 35-45mph. The current severe thunderstorm watch (WW358), in effect until midnight for northern IN and SW/south central MI, may be extended to include SE MI depending on how the storm develops or weakens over the next half hour or so. The system appears to be weakening now, and will continue as temperatures cool; it’s a question of how quickly the system weakens.

Additionally, a new thunderstorm outlook issued at 9:10pm EDT, effective through 8am Tuesday, places us squarely in the 40% probability area for thunderstorms.

The 9pm convective outlook, valid until 8am Tuesday, places us in the “Slight” risk area for severe weather:

The primary threat from these storms will be damaging wind. We have a 15-30% chance of damaging wind through 8am Tuesday, along with a 5% risk of hail, and a very small tornado risk.

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.