Two Short/Easterly Waves on the move from the south to influence weather over Mono County this weekend…
Thursday July 30, 2015
Posted at 5:02 pm by Howard
Moisture, mainly high level is increasing from the southeast where PWAT values are close to 2.00 in some areas. Over Southern Mono County at the moment PWAT is running about .7 so it has a long way to go before we get into the Soup…. Two short waves rotating around the Continental high will provide the extra lift for not only the possibility of daytime precipitation and thunderstorms but nocturnal precip as well. The lower levels are still pretty dry this afternoon. So the air mass is still in the moistening phase from the bottom up….then later tomorrow, from the top down… By Saturday, it will be pretty juicy out there. However, any heavy rain during the day will still be dependent upon how much sun we get early in the day. The first short wave is headed up tonight…there will be another wave coming through tomorrow night into early Saturday AM.. If these waves were timed in the afternoon, Heavy rain would be almost guaranteed…. But that is not the case.
If you are a camper, be prepared for some rain late tonight and a better chance again later Saturday night.
During the day, the sun will be the driver along with CAPE*
*CAPE is Convective Available Potential Energy and can be found on a Skew -T diagram by lifting a parcel from its initial surface temperature and dew point to either the CCL (convective condensation level) by heating or to the LCL (lifted condensation level) by mechanical lift (ie frontal or kinematic forcing). If the parcel continues to ascend at the wet adiabatic rate it will reach the LFC (level of free convection) where the parcel is warmer than its environment and become positively buoyant such as a hot air balloon. The difference in temperature at 500 MB or roughly 18000 feet between an ascending saturated parcel and its environment is the LI (lifted index). the LI is negative for positively buoyant parcels. The CAPE is the total amount of buoyant energy in joules/KG calculated above the LFC to the tropopause or the integrated area between the moist adiabatic trajectory of the ascending parcel and environmental sounding. CAPE is directly related to updraft velocity and correlated to hail size and other severe thunderstorm characteristics. A weak high based thunderstorm will have CAPE values between 50 and 500 joules/kg while severe thunderstorms that produce large hail and tornadoes can have CAPES in the 3000-5000 joules/kg range. A thunderstorm in a high CAPE environment with strong updrafts can survive in the stronger wind shear needed to create a mesocyclone or tornado. CAPE is strongest is areas of steep lapse rates and abundant low to mid level moisture. Any process that increases lapse rates such at strong surface heating in the summer or cooling aloft by vertical motion will increase CAPE. Likewise any process that increases low and mid level moisture from the ground up primarily through vertical motion or from the cloud base down as a shower or outflow boundary will feed back into increasing CAPE values. CAPE is like gasoline for convection and without it, deep convection will not exist. To ignite the CAPE, some sort of trigger or lifting is needed for the parcel to reach the LFC . This trigger can be any type of low level convergence usually coupled with an area of upper level divergence.