Temperatures to trend slowly toward more seasonal norms the next week to 10 days as a series of weak trofs effect the central west coast
Monday May 13, 2013
Posted at 3:07 pm by Howard
Tuesday Morning Update:
Latest guidance points to a Vort max that has recently moved on shore just south of Monterrey Bay at 15Z. You can see the dark area of that Vort center plainly on shore in the water vapor loop. Although the timing of the dynamic forcing will not be perfect as the dynamic lift for the Sierra will come too early for the diurnal heating…..there will nevertheless be some buildups and some Thunder/RWs over Eastern Ca. No cooling is expected now from this system. A stronger trof will move into our region Thursday, bringing about 8 degrees of cooling along with gusty SW breezes during the PM hours. A few showers are possible Thursday Evening.
A NW flow aloft with higher heights at 500MB will finish off the weekend promoting high temps back into the upper 60s and low 70s Sunday and Monday. The next note worthy weather system will develop the 2nd half of next week. It is a colder trof bringing the chance of showers. Stay tuned on that one. A long wave trof may develop and hang around for quite a while there after.
Its springtime in the Sierra!….and the Maps show it!
If you think that it has been warmer then normal the past several days…you are correct. Seasonal highs at the 8000 foot level should be more in the low 60s this time of the year while lows are expected in the low 30s. The past week, mammoth experienced highs in the low 70s and lows in the 40s. With the positive height anomaly shifting to the east, a slow cool down will take place the next few days along with an increase of afternoon breeze. However, with all said, highs will still average some 5 to 8 degrees above normal until stronger trofing develops later next week. Daytime Highs may then return to the low 60s or possibly lower.
North American height anomalies in the 6 to 10 day outlook show positive height anomalies over North Central Canada and Southern Ca with lower heights north of AK and the pacific NW. The polar vortex is set up north of AK. So a split in the westerly’s and a southern branch will develop off the west coast pushing marine air into the coastal areas beginning Thursday. The longer range shows even lower height anomalies later next week. All in all its still spring. The Dweebs would not be surprised to see another dusting over the higher elevations by the following weekend.
Dr Howard and the Dweebs…………………………………..:-)
Mid Springtime Showers And Thunder still On for the High Country this Weekend with Showers, Thunder and even some snowfall Monday-Tuesday over Upper Elevations….Fair Weather Returning by….Or Just after Mid Week…….
Friday May 3, 2013
Posted at 9:21 am by Howard
The GFS has done an excellent job so far in forecasting the coupling of a short wave now over the Northern Rockies that will ultimately diverge to the Rt and pick up the old cut-off low, now located at about 139W and just north of the Tropic of Cancer. All models have this scenario now over the next 48 hours.
Current Weather as of 5-3-2013: From the 12Z Friday WRF Model
The Subject short wave is located From Coeur D’Alene, SW to the CA/OR border. As the upper ridge off the NW coast builds north due to upstream amplification, it becomes positive tilt allowing the short wave to diverge to the Rt, forcing it to spin up a closed center over Northern Ca Saturday afternoon. Saturday PM will be the first opportunity for showers over the Sierra from the northern system only. At the same time, all this SW digging has picked up the Old Cut off as it begins to move toward the Southern Ca coast Saturday. This old cut off is the system that carries the moisture. By Saturday/night, the cut off opens up and spins up a 70….then 90knot upper jet that transports moisture into Southern Ca. During the day Sunday…..Moisture and UVV increase for Southern Ca and so does the rain and possible thunder, especially Sunday afternoon and night.
By Sunday evening, the cooler system to the north is well off the San Fran Coast and the short wave that was once the old cut off is moving on shore early Sunday evening. Rain should be in progress by Sunday afternoon and this is great news for the fire fighters that are battling fires in the mountains NE of LA. As the upper low at 500mb continues to spin up off San Fran coast, subtropical moisture gets pulled up through the Owens Valley, Southern Sierra, reaching the Mammoth Area then late Sunday night into Monday morning. The moisture then continues to flow up into the Northern Sierra and remains until the offshore cut off low makes its move inland….Monday night into Tuesday.
QPF: The GFS put more precipitation in the Sierra then LA…the WRF has more in the LA area. WRF has .75 inches over next 72 hours with the Sierra .50
The GFS has a lot more in the Sierra. At this time, the Dweebs are looking at light snowfall for the Mammoth area with any where from 1 to 6 inches over the higher elevations above 9000 feet. The snow level will be as low as 8000 during the Monday/Tuesday time frame. As the upper low ejects east between Tuesday and Wednesday…..Shower chances diminish mid week, lending to a fair warm following weekend with above normal temps….
This is the Dweebs last update until Mothers Day…….Adios!!!
Dr Howard and the Dweebs…………………………..:-)
Warming Temps on the Way Thursday into Friday….Developing Closed Low to Bring First Widespread Spring Thunderstorm Outbreak as early as Sunday into Tuesday….Westerlies may Make a Run for the Coast by Mid Month…..
Wednesday May 1, 2013
Posted at 10:08 am by Howard
The Dweebs are pretty excited about the prospects for some Spring Time Thunder and showers beginning Sunday, then into Tuesday. This mornings 12z GFS deterministic run has an upper cyclonic center developing off the Northern Ca coast as early as Sunday morning. As it slides SW…It couples with an older Cut Off, currently trapped underneath an upper high to the north. (REX BLOCK) The old cut off should offer some additional moisture as it phases with the cooler, quasi continental short wave headed through the pacific northwest this Friday.
As the over land upper jet of 90knots rolls off the Northern Ca. coast….it spins up a new quasi cutoff which then couples, and thus opens the old cut-off low to release its moisture. Again as explained below in my old discussion, the high May sun angle along with good upper divergence aloft and our elevated heat source should all help to put on a pretty good show between Sunday PM and Tuesday. The upper jet is expected to be positioned into the South Central Ca. coast…favorable for good upper divergence over the Central Sierra. The upper low is expected to eject through Ca Tuesday.
However, you can never trust a cut off with it timing out of here so stay tuned!
Longer Range: Anomalous positive heights will develop over the pacific NW later next week while the wave length open up a bit across the CONUS. Will have to keep an eye out for the westerly’s making a run for the west coast later week 2.
Dr. Howard and the Dweebs………………….:-)
Upper Air Pattern to change the following week for the possibility of Showers and Thunder.
A developing REX block is occurring out at 140W. The REX is highlighted by an upper level low below “latitude wise” an upper high to the north. This pattern, at this Longitude, this time of the year, keeps the westerly’s to our north and often times our weather fair. However, the block is expected to break down late next weekend with the upper cut-off drifting toward California. At the same time, a short wave dropping SE from the pacific north west may either diverge to the Rt, thereby coupling with it, or eject it through Southern Ca to our south. The position or exact track of the upper low will be important to the forecast for our weather next week.
At this time, confidence is low because of the distance in time. However, with antecedent warmth of the upcoming weekend and the possibility of increasing divergence and cooling aloft, an unstable atmosphere may very well develop over the elevated heat source of the Sierra. Showers and thunder for the high country is a good possibility beginning Sunday PM the 5th through the 7th or 8th of May.
Longer Range Thoughts:
The Dweebs note that the QBO is still very neutral in its index and as is often the case, blocking over near the Greenland area persists. The current forecasts of the more significant teleconnections of the AO and NAO are neutral to negative and the PNA index forecast is of a weakly positive sign into May. So more of the same weather is expected for some time to come. Warmer than normal over the Far west and southwest and Colder than normal over most areas of the Midwest and wetter then normal over parts of the east and southeast. Will the Midwest have a slower start to their growing season?
Dr Howard and the Dweebs……………………………….:-)