Sat/Sun, July 2/3.11

[Derecho]

Too early to start speculating?

Latest DTX AFD for SEMI

SATURDAY LOOKS TO BE THE MORE INTERESTING DAY. A WEAK COLD FRONT
WILL SLOWLY SAG SOUTH ACROSS THE AREA ON SATURDAY. LATEST 12Z GFS
BUFR SOUNDINGS SHOW SBCAPE VALUES CLIMBING TO NEARLY 4000 J/KG.
ALTHOUGH THIS IS LIKELY TOO HIGH GIVEN THE 75+ SURFACE DEWPOINTS
FORECASTED BY THE GFS...MODIFIED SOUNDINGS WITH A 71F SURFACE
DEWPOINT STILL GIVE SBCAPE VALUES AROUND 3000 J/KG WITH CIN VALUES
AROUND 100 J/KG. THIS CAP...ALTHOUGH WEAKER IN THE NORTHERN CWA...IS
SOMEWHAT CONCERNING GIVEN VERY LITTLE SYNOPTIC FORCING WITH THE MAIN
SHORTWAVE WELL NORTH OF THE REGION IN ONTARIO. CHANCES FOR
CONVECTION MAY DEPEND ON UPSTREAM MCS DEVELOPMENT IN ORDER TO
OVERCOME THIS CAP. IF CONVECTION DOES MANAGE TO INITIATE...IT WILL
NOT BE DIFFICULT TO ORGANIZE GIVEN 40+ KNOTS AT 500MB AND 25+ KNOTS
AT 850MB IN A LARGELY UNIDIRECTIONAL WIND PROFILE. DEEPER MIXING AND
A SLIGHTLY WARMER AIRMASS WILL ALLOW HIGH TEMPS ON SATURDAY TO MAKE
A RUN AT THE LOWER 90S BUT THIS IS LARGELY DEPENDENT ON THE TIMING
OF POSSIBLE CONVECTION.

[davefootball123]

Ya ive been watching the models very closley... Deffenitley a very unstable environment with lots of CAPE and Lifted indicies down to -10 in areas. Shear is also quite favourable. The one thing that i am still watching is 850 mb/surface winds are out of the WSW at 18z and 0z on Saturday. If this is the case im not entirley sure we will have enough forcing along the short wave trough for a large severe weather event. None the less...severe weather seems quite possible with linear segmants/clusters and possible MCS seems to be the probable convective mode if anything were to happen. Also if you take a look at the QPF forecast at 00z Saturday it indicates some fallen precip through much of southwestern ontario and into the GTA....wonder if it thinks there will be some storms too. As for Sunday, I dont expect much. If you look at the forecast MLCAPE and Lifted Indices the best instability is in the States on Sunday towards the east coast.

[Smokin Joe]

any updates on the situation?

[Derecho]

Originally Posted by davefootball123

The one thing that i am still watching is 850 mb/surface winds are out of the WSW at 18z and 0z on Saturday..

Cold front passage around mid-afternoon according to the SREF

[davefootball123]

Originally Posted by Derecho

Cold front passage around mid-afternoon according to the SREF

The cold front looks to pass between 12 and 2 on the 15z SREF...NAM is a little later with it coming through after dinner....There now looks to be some 850 mb forcing along the front which is good. Airmass is still looking to be pretty unstable over the southwest with MLCAPES AOA 1500j/kg with lifted indices between -2 and -8 however further east into the Golden horseshoe it appears instability will be less facourable. Shear isnt looking as good as it was but 30-40kts still looks to be reasonable. Main threat appears damaging winds with these storms if any were to form.

[Derecho]

Looks like my jinxing powers are still going strong

Only extreme SW Ontario is in the current day 3 "see text" risk.

[Smokin Joe]

I'm holding out hope that the risk area will fatten up for sat. over the next couple of days and creep over the border.....but man this is depressing if nothing comes this weekend

EC has Windsor reaching 35c now on saturday from 32 yesterday.......i'm going down if there is any hope

[davefootball123]

Saturday still could be interesting for a possible line of thunderstorms. Instability is looking fairly good on the latest NAM, GFS and SREF. These models bring the cold front through between 5pm and 12am...Temps and dewpoints still look quite favourable... along with PW values of 1.5 inches or greater, however there isnt alot of favourable shear looks to be about 30kts. And the GFS and NAM hint at a possible cap(warm air aloft between 850 and 700mb limiting storm formation) however if the cap erodes storms are deffeintley possible given the MUCAPES of around 2000j/kg or greater. Still needs to be watched. At the moment i wouldnt be suprised if we got in a slight tomorrow but i may have just jinxed it so ya


EDIT: 18z NAM run gets rid of the cap almost entirley also a little more favourable 0-700mb shear is starting to show up hinting at some possible damaging winds with a line that may form...have to watch this one for sure

[Derecho]

A great AFD from DTX, it sounds promising.

UPPER LEVEL WAVE SEEN ON WATER VAPOR IMAGERY OVER UTAH/COLORADO WILL
LIFT THROUGH THE UPPER MIDWEST ON FRIDAY NIGHT AND INTO ONTARIO ON
SATURDAY. WITH THIS FEATURE PASSING NORTH OF UPPER MICHIGAN IT ONLY
SUPRESSES 500MB HEIGHTS TO BETWEEN 586-589DM ON SATURDAY. GIVEN THE
WEAK UPPER LEVEL FORCING...PREFERENCE IS TOWARDS THE SLOWER FRONTAL
TIMING GIVEN BY THE 12Z NAM/UKMET/ECMWF. THIS PLACES THE FRONT NEAR
OR SOUTH OF THE I-69 CORRIDOR BY THE MID-AFTERNOON/PEAK HEATING TIME
FRAME. LOCATIONS SOUTH OF THE FRONT WILL LIKELY STILL BE SOMEWHAT
CAPPED LEAVING SOME UNCERTAINTY IN CONVECTIVE POTENTIAL.
HOWEVER...WITH A WEAK FRONT IN THE VICINITY(POSSIBLY RECEIVING A
BOOST FROM LAKE BREEZES OFF LAKE HURON)...PUSHING SOUTH INTO THE
INCREASINGLY UNSTABLE AIRMASS(92/72 PARCEL) MAKES SEVERE WEATHER A
CONCERN ON SATURDAY AFTERNOON/EVENING. WHAT WE MAY LACK IN SHEAR
AND LARGER SCALE FORCING...WE WILL BE ABLE TO COMPENSATE FOR GIVEN
THE HIGH INSTABILITY...PROVIDING A THREAT FOR SEVERE STORMS WITH
STRONG WINDS BEING THE PRIAMRY THREAT. DEPENDING ON FRONTAL TIMING
A HEAT ADVISORY MAY ALSO NEED TO BE CONSIDERED GIVEN HEAT INDICIES
IN THE UPPER 90S TO NEAR 100 FOR THE GREATER DETROIT AREA AND
LOCATIONS FURTHER SOUTH.

[davefootball123]

SREF and NAM are starting to come into decent agreement with the passage of the front. They both agree that we will be very unstable...Looks like some good dynamics are setting up. I think saturday could be interesting. Only thing that still isnt looking great is shear along and ahead of the coldfront.