Breezy..Dry SW Flow to Continue Today and Wednesday….Mid Level Moisture on the Way for Thursday with a chance of some light rainfall…..At the Moment a Dry Weekend is Forcasted…..AZ Monsoon Shifts into High Gear with additional chances of rainfall later next week….
Tuesday July 9, 2013
Posted at 9:23 am by Howard
Latest modeling, Radar and Sat Maps show main action today over SE Ca with small meso-scale convective cluster near Needles, CA within PWAT of 2 inches. Not a great day to be water skiing in Parker past FOX’s. PWAT over Bishop about an inch and over Mammoth .75 Although Lot’s of Moisture today in the mid levels….No significant forcing in the Mammoth area as per SPC. Skies over-developed so not much heat to work with. Slight chance of showers remains a good forecast for Mammoth today. (20%pops)
Southerly flow slowly shifting east, so we may get some sunshine yet.
Highs today will struggle to get out of the 60s with lows tonight in the low 50s. Some gusty SW winds possible. Friday looks to be a bit warmer day……Nice weekend shaping up in a drier SW flow. Highs upper 70s Saturday and near 80 Sunday.
Tuesday AM Update:
Over the past week, its been clear that there has been a little stronger Trof (Cool Pool Aloft) in the Pacific NW then climatology. This is making for a bit stronger and persistent Zephyr in the Mammoth Area. The Zephyr is the product of the differential heating of air masses that are separated topographically from one another and become induced thermally by the differential heating of the deserts to the east, on a diurnal time scale. Trofing in the pacific NW only intensifies the differences and creates a diurnal west wind system that is highlighted by lighter winds in the AM hours as compared to the afternoon and evening hours. The warmer seasonal pattern stretches north south throughout most of the Eastern Ca, along the Lee of the Sierra.
Monsoon Moisture and Mid July:
Monsoon Moisture or SSE flow is most common From Mid July Through Early August here in the Eastern Sierra. Moisture from the subtropics is usually benign unless it is associated with some kind of dynamic lift. If there is enough daytime heating, modification of the air mass within the column occurs from elevated heat sources to produce Thunderstorms in the Summer.
However, Mammoth, topographically is situated naturally in a low spot down wind of the Zephyr. The West or SW flow is often strong enough to shift a localized convergence zone more to the east of Mammoth than many areas both North and South of us. This results in an eastward displaced convergence zone usually east of Highway 395, as compared to areas north/south of our immediate location. This often results in rainfall, in areas both north and south of Mammoth while Mammoth remains dry. This was the case during the Fourth of July Holiday Weekend where thunderstorms raged over Grant Lake near June Lake northward while Mammoth remained mostly clear. This is structurally topographically driven.
Although High pressure aloft remains strong over the Great Basin and California, an impressive looking “Easterly Wave” underneath the upper high has quite a bit of subtropical moisture associated with it. A mesoscale convective cluster raged over the Sonoran Deserts last night and is moving WNW. In addition, hurricane Eric near Southern Baja is adding juice to the mix. 700mb/rh and as well as upper level wind trajectories suggest that this moisture may begin to advect into Central Ca from the SSW after midnight Wednesday. Although moisture advection from the SW or SSW is usually benign into our area rainfall wise in the Summer……It will have to be watched for any spokes of vorticity that might create lift and dynamics from an usually stable trajectory. Timing is early Thursday into Early Friday for the Central Sierra. Showers and some isolated thunderstorm’s are a possibility. The key to the brief pattern change is whether or not any areas of dynamics are associated with this moisture. IE Spokes of vorticity.
So the advection of mid level moisture is expected Thursday morning 1st, then possibly airmass modification Thursday PM and any associated instability could ignite some rainfall in our area. Will take another look at it tomorrow and again Thursday AM.
The weekend outlook shows a drier SW flow returning…..keeping the Jazzer’s happy!! However, an influx of moisture is again possible, later next week as we get into the meat of the seasonal wind season.
Dr Howard and the Dweebs………………………….:-)