Thursday 14 July 2016 Severe Weather Discussion

GEEK ALERT..A TECHNICAL DISCUSSION. I JUST WANT TO "SHOW" FOLKS WHAT GOES INTO BOTH THE CREATION OF AND PREDICTION OF SEVERE WEATHER.

I hope you find it interesting.

SATRAD AND TEMPS FOR NY AND NEW ENGLAND

Map of satellite/radar/temperatures  (MAP ABOVE) Indicates that the low clouds of last night and early this morning are beginning to thin or dissipate. Where this occurs sunshine breaks out and the air is quickly warming with temperatures in the low and mid 80s. The more sun, the more the air warms and the more UNSTABLE the atmosphere becomes.

Below is the “sounding” from this morning’s balloon launch from Albany, NY. A sounding or rawindsonde is snapshot of weather conditions aloft over Albany. It’s a measurement of temperatures (red line) and moisture (green line) and wind speeds and directions (wind barbs on right side of diagram) – all this data is plotted on a diagram with the vertical axis being height above the ground and the horizontal axis being temperature. This data is very useful in many areas of local weather forecasting including convection and in gauging the possible intensity of it.

14 JULY 2016 12Z/8AM EDT SOUNDING FOR ALBANY NY

The sounding has been “modified” by “warming” it to this afternoon’s expected maximum temperature (and the expected dew point at that time). The pink area is the indication of the expected instability this afternoon, it is the Convective Available Potential Energy or CAPE. The higher the value of the cape the more unstable the atmosphere. another cape parameter is the downdraft cape or DCAPE. The higher this value the greater potential for strong downdraft/microburst winds. Other data is also calculated from the sounding including other storm motion (direction and speed), as well as, instability indices as well potential rainfall that could occur.

Looking at the modified sounding, if the atmosphere warms enough and the high CAPE values are reached then severe thunderstorms will likely occur. The high DCAPE values of > 1000 j/kg would favor strong winds. The mode of convection, (that is either supercell, clusters, pulse or lines) would likely be in the form of storm clusters or line segments based on the the BRN parameter or Bulk Richardson Number, as well as a hodograph which is a wind speed and direction analysis of the winds aloft. Below is the expected storm intensity analysis and hodograph.

FORECAST STORM MODE

STORM STRENGTH

HODOGRAPH/HODOGRAM FOR ALBANY NY FROM 8AM EDT 14 JULY BALLOON LAUNCH

A “long and nearly straight” hodograph like the one above, is supportive of cluster and/or linear convection.

In addition the storm motion from SW to NE at 15-25 mph could favor convective cells moving over the same area; this is called training. combine the possibility of l for training cells along with relatively slow storm motion and the higher than normal moisture content of the air over the region today,  very heavy rainfall could occur with today’s storms. The risk for local flooding is possible in areas of poor drainage, perhaps even flash flooding; as well as, ponding of water on roads. There is the potential for a quick 1.5-2.5 inches of rain in a very short time in any storm; maximum rainfall potential could exceed 3”, especially in slower moving cells or if training occurs.

So there you have it, how this weatherman prepares a severe weather forecast.