Note:
The expiration time in the watch graphic is amended if the watch is
replaced, cancelled or extended.
Note: Click for
Watch Status Reports.
SEL0
URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 300
NWS STORM PREDICTION CENTER NORMAN OK
1050 PM CDT WED MAY 13 2009
THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
NORTHEAST ILLINOIS
NORTHWEST INDIANA
SOUTHWEST LOWER MICHIGAN
LAKE MICHIGAN
EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 1050 PM
UNTIL 400 AM CDT.
HAIL TO 1 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.
THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60
STATUTE MILES EAST AND WEST OF A LINE FROM 35 MILES NORTH
NORTHEAST OF GRAND RAPIDS MICHIGAN TO 25 MILES SOUTH SOUTHWEST OF
DECATUR ILLINOIS. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU0).
REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR 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. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.
OTHER WATCH INFORMATION...THIS SEVERE THUNDERSTORM WATCH REPLACES
TORNADO WATCH NUMBER 297. WATCH NUMBER 297 WILL NOT BE IN EFFECT
AFTER 1050 PM CDT. CONTINUE...WW 295...WW 296...WW 298...WW 299...
DISCUSSION...A BROKEN BAND OF STORMS WILL PIVOT EWD IN ADVANCE OF
THE COLD FRONT AND A STRONG MID LEVEL TROUGH MOVING EWD FROM IA/MN.
LOW-MID LEVEL FLOW WILL INCREASE AS THE MID LEVEL WAVE APPROACHES
LAKE MI OVERNIGHT. DESPITE SOMEWHAT STABLE TEMPERATURE PROFILES
NEAR THE GROUND...MODEST LOW-LEVEL MOISTENING AND THE STRENGTHENING
FLOW WILL MAINTAIN A THREAT FOR DAMAGING WINDS WITH EMBEDDED
CELLS/BOWS THOUGHT THE EARLY MORNING HOURS.
AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS.
A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. MEAN STORM MOTION
VECTOR 25040.
...THOMPSON
Note:
The Aviation Watch (SAW) product is an approximation to the watch area.
The actual watch is depicted by the shaded areas.
SAW0
WW 300 SEVERE TSTM IL IN MI LM 140350Z - 140900Z
AXIS..60 STATUTE MILES EAST AND WEST OF LINE..
35NNE GRR/GRAND RAPIDS MI/ - 25SSW DEC/DECATUR IL/
..AVIATION COORDS.. 50NM E/W /35NNE GRR - 17SSW DEC/
HAIL SURFACE AND ALOFT..1 INCH. WIND GUSTS..60 KNOTS.
MAX TOPS TO 450. MEAN STORM MOTION VECTOR 25040.
REPLACES WW 297..IL LM
LAT...LON 43348405 39498791 39499016 43348644
THIS IS AN APPROXIMATION TO THE WATCH AREA. FOR A
COMPLETE DEPICTION OF THE WATCH SEE WOUS64 KWNS
FOR WOU0.
Watch 300 Status Report Message has not been issued yet.
Note:
Click for Complete Product Text.
Tornadoes
Probability of 2 or more tornadoes
|
Low (20%)
|
Probability of 1 or more strong (F2-F5) tornadoes
|
Low (5%)
|
Wind
Probability of 10 or more severe wind events
|
Mod (40%)
|
Probability of 1 or more wind events > 65 knots
|
Mod (30%)
|
Hail
Probability of 10 or more severe hail events
|
Low (20%)
|
Probability
of 1 or
more hailstones > 2 inches
|
Low (10%)
|
Combined Severe Hail/Wind
Probability of 6 or more combined severe hail/wind events
|
Mod (60%)
|
For each watch, probabilities for particular events inside the watch
(listed above in each table) are determined by the issuing forecaster.
The "Low" category contains probability values ranging from less than 2%
to 20% (F2-F5 tornadoes), less than 5% to 20% (all other probabilities),
"Moderate" from 30% to 60%, and "High" from 70% to greater than 95%.
High values are bolded and lighter in color to provide awareness of
an increased threat for a particular event.
weather.gov 
