Archive for August, 2012

Monsoon Moisture to Remain in Place Through Friday with a Persistent Forecast of Afternoon Thunderstorms this week….Drying Begins Next Weekend…….

Quick Update Thursday AM;

 

Thunderstorm action was isolated in the southern Mono County area. Today the air-mass is similar, however a surge of moisture is moving NNW from SE Ca then turning NW at 36 north.  It is expected to push up into Mono County tonight and continue northward through Friday and Saturday.  An especially juicy surge is expected Friday into the Friday night some of which includes some of the remains of Hector now SW of Cabo San Lucus.

The NWS has isolated Thunder today Thursday, then Scattered TSRWs Friday and Friday night then Isolated Saturday and Sunday.  Some of the newer guidance is suggesting that the action may continue a bit longer into the weekend.

Will update in the Morning…..

Next Week looks dry at the moment and sensibly cooler beginning about mid-week.

 

The Dweeber………………..:-)

 

__________________________________________________

Wednesday Am Madness…..

The Dweebs this morning were looking for a trigger that would initate deeper convection today.  Water Vapor Loop showed the old upper low off shore at about or just west of 125west/36.5N.   SSE Flow over Mono County and debris clouds still in the loop from yesterdays Sierra storms mostly to the north. To the southeast, a strong MCS developed over Sonora, Mex. There was plenty of convection still occurring over the Sea of Cortez and South Central AZ as well.

At the moment….there appears to be a subtle area of dryness or some kind of dry slot over the southern San Joaquin valley then SE into SOCal that should move into Mammoth late this afternoon or this evening. (Possible VT center?) This may keep the convection going into the evening hours beyond diurnal expectations over Mono County.  Otherwise the main action looks to be mostly further north today like yesterday, with the exception of that dry area in the wave loop that will arrive sometime late today.   The NAM has Thursday more stable so storms will be more widely scattered.

Next big question will be what happens Friday. 12NAM has area of 70%Rh moving rapidly NW into California and moves up into the pacific NW as well. The Subtropics south of US/Mex border is loaded with Tropical moisture from a combination of Monsoon Moisture and moisture from TS Hector. This moisture moves rapidly northward through California Friday into Early Saturday before getting blown off to the east Saturday PM.  Thoughts this morning about Friday range from the moisture coming in too early so that conditions become over developed with nothing much happening,  to deep convection with Rain and Thunder that continues well into the night Friday.

As far as the weekend goes…..If storms do develop Saturday during mid to late morning…..they should get blown east later in the afternoon as SW flow increases with rapid drying occurs from west to east during the PM…..due to the ejection of the off shore upper trof.

Next week looks dry for the most part with highs in the 70s in Mammoth and lows in the upper 30s to mid 40s.  Afternoon and evening Zephier winds will develop Saturday PM and continue into next week.

 

Temps over the next 5 day will range from 75 to 80 with lows near 50…then night time lows cooling well down into the 40s early next week.

 

The Dweeber…………;-)

——————————————————————————————————————————————————–

Tuesday Am Update:

Heavy Showers and Thunder roared across the Mammoth area yesterday afternoon. Mammothweather.com picked up .19 hundreds yesterday while some RAWs stations in Mammoth had up to .33 hundreds.

Today lots of Monsoon moisture remains in place. However, the Cap is a bit lower today so showers may start a bit later in the day.  Outlook is the same with subtle differences in the make up of the atmosphere over the Southern Mono county area. IE the little waves are hard to see in models that trigger possibilities. Overall, Terrain induced RW’s is the rule with the high elevated heat sources providing lift and pulse type storms.

Scattered showers and Isolated thunderstorms are once again in the forecast with a good 50% probability of .01 of an inch in anyone’s rain tip bucket for Mammoth Lakes.

Still keeping an eye out for the moisture remains of TS Hector over the weekend when the upper low now currently near 130W gets the boot across the Northern Sierra.  It could get interesting Saturday when some of the remains of Hector get lifted over the Sierra ahead of the upper Trof that comes through to the north Later Sunday.  More later………..>>>>>>

The Dweeber……….

_________________________________________________________________________________________________________

Thunderstorms continued each day over Eastern Ca this past weekend. Although there were reports from locals that some brief showers occurred….MammothWeather.com had nothing recorded in the rain tip bucket here near the Village at Mammoth.  The Dweebs see no change in this pattern through Friday. However drying is expected to begin Saturday and increase Sunday, as a system moving though the Gulf of Alaska gives the boot to the off shore upper low NE into the Pacific Northwest/Northern Ca beginning this weekend. This backs the upper flow from a more SW direction. (Drier upper flow pattern). In the transition, thunderstorms will become more isolated over the Eastern Sierra and end early the following week. Daytime highs will remain about 80 degrees each day, however this is increasingly above normal as climo temps head slowly south each few days.

In the meantime…..Monsoonal moisture will continue to support showers and thunderstorms mainly during the afternoon and early evening hours. This will be mainly driven by the high elevated heat sources of the Sierra and areas of surface convergence throughout Mono County. By midweek, an upper ridge moves westward from New Mexico, so that by Wednesday night/Thursday, deeper tropical based moisture moves northward Via Baja, Ca. Any slight trigger of UVM would be sufficient to bring night time Thunder to the high country at that time. The Dweebs do see such an area of UVM. Stay Tuned…….

Next week: Beginning the 20th….

An Eastern Pacific trof will swing through the state. As the thermal trof returns to Nevada, gusty dry Zephyr winds will return to the Eastern Sierra Monday through Wednesday. This is a dry pattern with temps cooling to the mid 70s..  For the time being…that puts an end to our thunderstorm pattern.  Will it redevelop again???   Stay tuned………………>>

 

 

Dr Howard and the Dweebs………………………………..:-)

 

 

————————————————-
Reference Glossary of Weather Terms
Disclaimer: I have been a hobbyist meteorologist for over 30 years here in the Mammoth area and I do this for my personal enjoyment. The National Weather Service saves lives every day . . . I do not. When making important planning decisions please use information provided by the National Weather Service as they are the most knowledgeable and accurate information source available today.

Upper High over the Great Basin at 700MB Becoming Negitive Tilt….to provide a Rush of Monsoon Moisture and Dynamics Beginning Saturday…..Wet Thunderstorms Expected Later This Weekend

Stage is set for a nice out break of convection this weekend….Upper high has really cooked our air mass and now the Upper high at 700mb is forecasted to become negative tilt allowing SSE flow up the Southern and Central Sierra this Weekend. Campers take note to expect the possibility of heavy rain and lightning in some of these storms. Temps will be in the mid to upper 80s then cool into the upper 70s as thunderstorm coverage increases.  Nighttime lows in the 50s will cool into the 40s by Sunday night…

Next week begins with scattered thunderstorms.  Then moisture lurking to our south later next week from Tropical storms west of Cabo.

Comment:

Retired NWS forecaster Reno, Tom Cylke put into perspective what happens in a “Monsoon Pattern”. The emphasis to the public has always been that its the moisture that brings the thunderstorms during SSE flow. Nothing could be further from the truth…..It is Air Mass Modification”. In simple terms, an increase of dynamics, (vertical motion induced by a change in the upper flow from SSE in which the stability of the over lying atmosphere become increasingly unstable. Although you can see moisture at times when the air is cooled to its dew point,. However, you can not see actual dynamics…..only the results thereof.

 

Here is Tom’s most simplified version of what happens when we get into a classic Monsoon Pattern as the trajectory of both impulses, moisture and quasi stationary couplets in a regional develop to produce one of the exciting phenomenons in the mid Summer here in the Eastern Sierra.

From Tom C:

In the monsoon pattern the surface thermal trough and its associated low level convergence is coupled with divergence aloft around the periphery of the 4 corners high (after all, high pressure aloft is a large area of upper divergence which becomes enhanced by embedded easterly waves and MCS induced vort maxes rotating around the periphery of the high. Southeasterly flow enhances the Surface thermal trough (convergence) with warm advection while building up CAPE , theta-e AND PW values IE (Airmass Modification). Also to the northwest of the 4 corners high, an upper level  jet max will develop in the thermal gradient over the Pacific northwest which will create upper divergence in the right rear entrance region which oftens couples with the low level convergence of the Surface thermal trough over the Sierra and Western Nevada. Tstms only require UVV(conv/div couplet) on an unstable airmass to trigger. The unstable airmass is primarily a result of the vertical redistribution of temperature (lapse) and moisture by UVV or convection.

Definitions from AMS as it pertains to the system we are referring to:

 

1. Convergence:  An atmospheric condition that exists when the winds cause a horizontal net inflow of air into a specified region. Convergence can be have both directional and speed components. Because the earth is a solid barrier low level convergence of the wind field results in a piling up of air and upward vertical motion. Surface low pressure is an area of low level convergence.

 

2. Divergence: an atmospheric condition that exists when the winds cause a horizontal net outflow or air at a specific level. Divergence in the upper levels of the atmosphere (typically at jet stream level) above 25,000 feet causes a lowering of air density and which induces upward motion in the atmosphere to fill this vacuum.

 

3. Easterly waves. A wavelike disturbance in the tropical easterly winds that  moves from east to west. Such waves can grow into tropical depressions or MCSs.  Often seen as a vort max or inverted trough of low pressure or low level jet feature propagating westward along the southern periphery of the subtropical upper high  then at times rotates north into California and Nevada from AZ.

 

4. (MCS) Mesoscale Convective systems.  A complex of thunderstorms which becomes organized on a scale larger than the individual thunderstorms, and normally persists for several hours or more. MCSs may be round or linear in shape, and include systems such as tropical cyclones, squall lines, and MCCs (among others).  These systems representing areas of enhanced instability and usually very heavy rain.

 

5. Vort Maxes. An area of the local rotation in a fluid flow. In weather analysis and forecasting, it usually refers to the vertical component of rotation (i.e., rotation about a vertical axis) and is used most often in reference to synoptic scale or mesoscale weather systems. By convention, positive values indicate cyclonic rotation. Areas of positive vorticity advection in the upper atmosphere are associated with upper level divergence and its dynamically induced UVM.

 

6. UVM  upward vertical motion;  UVV  upward vertical velocity (rising air)

 

7. PW  Precipitable Water; (Or precipitable water vapor.) The total atmospheric water vapor contained in a vertical column of unit cross-sectional area extending between any two specified levels( surface to 250 mb), commonly expressed in terms of the height to which that water substance would stand if completely condensed and collected in a vessel of the same unit cross section. A persistant pattern of vertical motion , deep convection and thunderstorm outflows in a light wind flow will result in a build up higher values of PW with time as often seen over the desert southwest during the mid summer “monsoon pattern”. A high PW airmass has the potential to produce heavy rain if sufficient UVM is avaible to trigger deep convection.

 

8. Thermal trough;   Area of low pressure at the surface resulting from the strong surface heating of the continental land mass in the summer season.  Sometimes refered to as the monsoon trough which drive the monsoon winds and associated low level convergence pattern. The thermal trough typically found  elongated along the southern and eastern periphery of the upper level high in the desert SW where strong subsidence warming and warm advection reinforces the surface heating.

 

9. Lapse rates: The change in temperature with altitude in the atmosphere. usually the rate of cooling per thousand feet. The greater the cooling per thousand feet the more unstable the atmosphere is.  UVM will result in a more unstable lapse while subsidence with building high pressure aloft will bring more stable lapse rates or capping of convection until this subsidence cap(stable layer) is broken by either stronger surface heating or cooling aloft( from an approaching trough or UVM)s

 

10.  Couplet; usually refering to the vertical coupling of low level convergence at  levels at or below 700 mb (10,000 ft) with upper level divergence  at the jet stream level 300 mb or 250 mb( at or above 30,000 ft).  This coupling is critical to maintaining UVM for the initiation and maintanence of deep convection (thunderstorms, MCSs).  The low level convergence feeds the thunderstorm inflow while the upper level divergence results in the ventilation or chimney effect of the thunderstorm. The classic anvil top of a thunderstorm is a visible indicator of the spreading out of the high level ice crystal clouds by the upper level divergence. Strong upper level divergence in dynamic systems (upper lows, jet maxes) can often induce low level convergence and associated UVM which can result in long lived daytime and  nocturnal thunderstorms.

 

11. CAPE;  Convective Available Potential Energy. A measure of the amount of energy available for convection. CAPE is directly related to the maximum potential vertical speed within an updraft; thus, higher values indicate greater potential for severe weather. Observed values in thunderstorm environments often may exceed 1,000 joules per kilogram (j/kg), and in extreme cases may exceed 5,000 j/kg. However, as with other indices or indicators, there are no threshold values above which severe weather becomes imminent. Higher CAPE values are directly correlated with higher low level theta-e values and more unstable lapse rates.

 

12. Theta-E     The temperature a parcel of air would have if a) it was lifted until it became saturated, b) all water vapor was condensed out, and c) it was returned adiabatically (i.e., without transfer of heat or mass) to a pressure of 1000 millibars.  Is the 1000 mb temperature in Kelvin that results after all latent heat is released in a parcel of air. High values of theta-e at low levels indicate areas of high thermal energy from both sensible and latent heat which can be used to increase instabilty (lapse rates) and associated thermal lift components of convective systems.

 

 

 

The Dweeber………………………………..:-)

————————————————-
Reference Glossary of Weather Terms
Disclaimer: I have been a hobbyist meteorologist for over 30 years here in the Mammoth area and I do this for my personal enjoyment. The National Weather Service saves lives every day . . . I do not. When making important planning decisions please use information provided by the National Weather Service as they are the most knowledgeable and accurate information source available today.

A very warm week ahead is expected for the high country with some record highs possible by weeks end…..Isolated Thunder Returning By Tomorrow….Highs All Week In The 80s….

Warming aloft will continue the next few days as the Continental high once again builds west. Located over the Texan panhandle yesterday…it has already shifted west to New Mexico this morning and will be located over Northeast AZ by Tuesday morning. Thereafter…the GFS has it near the Utah/NV border by Thursday AM. Through the process…..SE flow will move back into SE California while the Sierra Crest of Southern Mono County remains under a dry SW flow at 500MB. By tomorrow morning Tuesday…a quick shot of south east flow at 700MB will bring possibilities of a few isolated storms to Eastern Ca. However SW flow returns that evening so positive conditions for air mass modification and moisture advection really do get get established for more then isolated Thunder.

By Wednesday, the 00z Monday GFS has an area of clockwise flow at 700mb centered over Mono Lake.  So a strengthening area of mid level capping is initiated.  Then a shot of southerly flow returns with less capping Thursday at 700MB. So Thursday may be a better day for air mass modification and TSRWS, although upper level capping is stronger at 500mb Friday into Saturday. All in all…..isolated thunderstorms will be of the garden verity this week. The big message is that it is going to get very warm again here in the high country this week with the longest stretch in very warm weather in several years expected.   The forecast models do not generate any “strong” Monsoon push and/or conditions favorable for Air Mass modification “at this time” for the High Country of Southern Mono County. The long range keeps the heat over the far west until the last week of August.

High temperatures over Mammoth will reach 80 today and slowly climb to the mid possibly upper 80s by next weekend….that is barring any change in the 700MB/500MB flow pattern from the south or SE.

A message to our locals………..

Enjoy it while you can…..the first day of Fall is only 6 weeks away!!

The Dweeber………………………………..:-)

PS: Some thoughts…..

In that last winter was painfully deficient of upper level blocking near Greenland over the Western Hemispheric, SSTAs have trended well above normal over the Davis Straits and around Greenland suggesting that there will be anomalous blocking in that area when the QBO shifts positive the end of this year. Massive Arctic outbreaks into the mid Lat’s may occur, especially over the west 1st, ( late Fall/Early-Winter),  then east of the Divide in January-March. Although strong -NAO/ -AO are associated with stronger ridging over the far west. IE (+PNA),  In a moderate El Nino winter, the cold arctic air build up is more likely to be flushed out over the Atlantic from time to time opening up the wavelength for storms for the west coast, if the subtropical jet is strong enough due to El Nino.  Hopefully…El Nino becomes at least moderate in the NINO 3.4 region this Fall!!!

————————————————-
Reference Glossary of Weather Terms
Disclaimer: I have been a hobbyist meteorologist for over 30 years here in the Mammoth area and I do this for my personal enjoyment. The National Weather Service saves lives every day . . . I do not. When making important planning decisions please use information provided by the National Weather Service as they are the most knowledgeable and accurate information source available today.