Archive for July, 2015
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.
Upper Trof will exit the Eastern Sierra Today followed a little cooling……Continental Upper High will expand west by Mid Week bringing a warm up 1st…..Followed by a Chance of Thunderstorms Beginning Thursday into the Weekend……..
Monday July 27, 2015
Posted at 10:17 am by Howard
A synoptic scale upper Trof will exit Western Nv today and lift NE into the Northern Rockies Tuesday. This has brought a very dry air mass to the Eastern Sierra. NW flow aloft will back to the west today then weaken Tuesday followed by rising heights and a warm up beginning Tuesday.
At the moment, the Continental High is over Arkansas near the Mississippi River in the South. It will retrograded west to the Four Corner States by Thursday and strengthen. The upper level flow begins backing from the SE along the CA/NV border by Wednesday Night. So the process of moistening will begin Thursday with Air-Mass modification Thursday into Saturday. High temperatures in Mammoth will climb into the low 80s by Wednesday and continue in the 80s through Thursday before they cool back into the 70s over the weekend.
As we are aware, this summer has been a wet one. So naturally there is concern about rainfall over the upcoming weekend festivities. The Thunderstorm pattern that will develop prior to and through the weekend seems to be a typical Monsoon set up without any extra tropical storm moisture or dynamics like the last one. The storms will begin mainly high based with mostly lightning with little rain followed by more hybrid storms Friday transiting to wet by Saturday.
The intensity of any rainfall will be dependent upon the usual.
1. The amount of sunshine we get every morning and afternoon to aid in the convective process.
2. Any organized short wave, easterly wave or Vort Center that may come over the area to enhance vertical motion.
3. Also the timing of the short waves are important as if it one comes through at night, we could have nocturnal storm’s.
Is it possible that we may have heavy rain? ……Yes However, it is not possible to know at this distance in time where or when that may happen, as although there are short waves indicated by the extended models in the upcoming pattern, the location and timing is not certain.
Will update Wednesday or Thursday for a closer look….
Dr Howard and the Dweebs………………………:-)
Tom Cylke is a retired Weather Service forecaster
and my Weather Mentor for over 20 years…
For the true weather Dweebs….
The following is an excellent example of the North America Monsoon;
Over the next few days a classic monsoon pattern will set up resulting in an outbreak of thundertorms over much of the intermountain west. The monsoon is by definition a wind pattern set up by the heating of continents(mainly elevated heat sources) in the summer characterized in North America by an upper high over the four corners area and a surface thermal trough extending from Arizona into western Nevada. When the four corners high begins to build strong subsidence creates an elevated inversion or cap which inhibits deep convection but does allow for strong surface heating and mixing up to the elevated capping inversion. the strong surface heating sets the stage for steeper lapse rates and mid level moistening under a more mixed adiabatic atmosphere. The first day or two of the monsoon pattern results in high based cumulus capped by subsidence inversion however PWs , CAPE and theta E values are increasing none the less under this pressure cooker environment. This is the air mass modification stage that is waiting for a trigger to bust the cap which can be an type of cooling aloft brought about by divergence from a short wave feature (vort max) or favorable divergent area of a jet max or deformation zone. By day three isolated high based thunderstorms will develop in areas of focused vertical motion brought about by low level convergence and upper divergence couplets along the surface thermal trough or mountain ranges often with very weak upper level features rotating around the periphery of the 4 corners high. The right rear entrance region of a jet max and a topographically force convergence zones over the central Sierra and Mountains of central Nevada are often the first to trigger the high based thunderstorms. By day four PWs have doubled due to the previous days convection allowing widely scattered to scattered thunderstorms to develop triggering earlier in the afternoon and with lowering cloud bases and thus a higher potential for heavier rain. This pattern repeats with wetter and more widespread thunderstorm activity until a drying and stablizing event or pattern sets up such as the right front exit region of a pacific northwest jet bring in subsidence and drying aloft along with a downslope southwest flow. The expansion of the 4 corner high will bring back the monsoon flow pattern as the Pacific northwest trough weaked and moves eastward. Most of the moisture and instablilty generated in the monsoon pattern develops via the air mass modification(vertical motion) process with very little input from horizonal advection except in cases of outlow boundaries from MCCs and tropical storms which tend to be limited by topography and entrainment of drier and more stable environmental air. Atmospheric moisture is more a result of convection(vertical motion) not a cause of it therefore a lagging indicator. Moisture does feedback into the convective process in subsequent days resulting in lowering cloud bases, earlier trigger times a greater potential for heavy rain. The primary drivers for deep convection (thunderstorms) are adequate CAPE and a convergence/divergence couplet to trigger that CAPE.
A dry upper Trof over the west coast this morning will continue last nights drying trend….with another transitory dry Trof for the weekend continuing the trend….Weather to turn hot prior to the Bluesapalooza Fest…………….
Thursday July 23, 2015
Posted at 10:15 am by Howard
The latest Meso-Scale analysis showed no 850/250mb couplets over Mono County. Precipitable water was down to .6 over Mammoth and outside of the Rt Rear entry region over Northern Inyo…Stability indices have increased to +1 with +2 just to the west of the crest. All this adds up to a day of very weak forcing for Mono County with the best chance of isolated thunder over the Southern Sierra and the White Mts of Mono County near the NV boarder. By Friday, conditions will be totally unfavorable for any TSRWs over our region.
So ends another period of thunderstorms in what has became a famous Wet Rainy Mammoth Summer prior to the El Nino year of 2015/2016. Drier weather is now expected through next Wednesday.
Current synoptic scale weather is highlighted by a west coast trof at 500MB that is ushering in drier air aloft as well as at the mixing level. The upper trof will also be responsible for a stronger afternoon and early evening Zephyr with gusts to 30MPH during the late afternoon hours. The Zephyr will become more moderate Sunday afternoon as the deserts heat up later in the weekend. With a very dry air mass expected this weekend, night time lows will dip into the 30s in some areas.
The Dweebs are expecting the Continental upper high to retrograde to the west again and build into California. If the Upper High is centered over the state, then it will be just hot with afternoon clouds and highs in the mid 80s in Mammoth, and 105+ in Bishop. If the position shifts a bit east a little later in the week, SE flow could develop with an increasing chance of afternoon and evening thunderstorm’s. This pattern is more typical for early August with Monsoon flow. Most likely, any showers developing would dissipate during the late afternoon hours. As of this time, it is too soon to know how extensive the Thunderstorm pattern will be for the Bluesa weekend. The Dweebs will keep you informed right here at the Dweeb Report.
In the meantime…..Enjoy the great weekend this weekend as Mammoth Best BBQ Recipe’s are up for the challenge!
Dr Howard and the Dweebs……………….:-)
Outlook Updated: 7/24/15
Both GFS and ECMWF show an increase in Monsoon moisture beginning a week from today into the following week for widely scattered afternoon and evening thunderstorm’s….