BrickFielder

Excellent post Steve. Jet Streams in very simple terms are fast moving ribbons of air which seperate cold air to the north and warm air to the south and are found at the upper level of the troposphere (the troposphere is where our weather is ,above which is the stratosphere). Being to the north of the jet usually means cold weather. There is a kind of feed back mechanism between the jet and weather patterns. Where there are bursts of energy (streaks) along the jet due to high temperature differences, this is where weather systems form (both low and high pressure at entrance and exit regions). These weather systems then modify the jet by moving air so that high temperature contrasts occur somewhere else (forming a new streak). This is all tempered with surface temperatures over land and sea creating different temperature air masses which tend to direct the jet in certain directions (up around warm) This is why the azores high is a regular feature in winter out over the warm atlantic ocean with sea temperatures much slower to cool down than land temperatures. This is all further tempered by weather systems causing waves which very slowly bounce out up into the stratosphere and back down again to affect the jet and weather systems below. I will stop there before I get complicated. Just to say that ignoring the polar nightime jet that the jetstream ribbon circulates the world so the pacific jet is the same one as we get here. Probably one of us will talk later about the walker,ferrel and hadley cells the subtropical jet and polar front jets weather fronts and the jetstream how to predict high and low pressures from a jet forecast and understand ridging and troughing.

Latitude. Sort of like the diagrams below. High pressure topples over the Uk from the north.

When the GFS forecasting models run at midnight ,6am midday and 6pm a number of runs are performed, each with slightly different criteria. This means that there are a number of forecasts with slightly different outcomes. One of these forecasts is picked as the actual one. If the picked forecast is generally colder or warmer than the others then it is considered an outlier. The temperatures it forecast are outside the normal of the other runs and is considered more unlikely. We tell if a run is an outlier by looking at the ensembles which show the temperatures forecast on all the runs. Generally outliers are unlikely to be acurate forecasts, but what might be an outlier in one place (i.e. London) may not somewhere else (i.e. Aberdeen). In other words if a forecast is an outlier take it with a pinch of salt. Far too often a forecast is pronounced an outlier just because people do not like what is forecast.

5280 metres is the height in the atmosphere that pressure is 500hPa. It gives an indication of what the pressure is at low levels. The point is that it tells you something about what is happening midway up in the atmosphere and can be used as a rough guide to what is happening at low levels. 528DAM and below for an increasing chance of seeing snowfall, preferable values of 522 and below. 546DAM tends to be associated with the mild and wet conditions in winter - so isn't very popular! In the summer this line is usually close to the northwest of the country. 564DAM and above is usually found with a very warm airmass in summer, and most often in a Spanish plume affair. Very warm or hot conditions are likely. Usually we don't see much above 570DAM or much below 515DAM in the UK.

Yes I have noticed it has a tendency to do that sometimes. Rainfall can be affected by heating from the sun and warmer or dryer air moving in at mid levels. What I think you are refering to is that rain is light at 3pm, heavy at 6pm ,then light at 9pm and heavy again at middnight with no obvious reason. The answer is I don't know and it could be a problem with that particular chart or GFS or just an unusual occurance.

Same chart actually on the day.

Kinks in Isobars can often show where fronts are likely. Look at the north of Spain and up through Norway on the 500hPa chart smich posted. The difference in temperature between the 500hPa and the 850hPa (lapse rate) or any layer below is a good indicator of the stability of air. Unstable air will tend to rise and form clouds. So from smich's chart we see the -35 Degrees Air is to the south and east of the Uk and this is where cloud is likely to be thickest and so give heaviest precipitation ( you would need to check lower height charts to confirm this though). We could look at how the temperature at the center of the ridge is slightly lower at -20 Degrees C indicating cool air is descending into the ridge, so that it is unlikely to remain a ridge for a long period. Possibly hinting the high pressure could move north.

Yes thats right. Thats why we call the high pressure areas ridges and the low pressure areas troughs (i.e between wave crests). Now how does this chart help you, other than knowing where it will snow at 18,000 feet.

Here is a rough outline of what the chart heights are : 1000hPa = 0 feet 900hPa = 3000 feet 850hPa = 4750 feet 800hPa = 6000 feet 700hPa = 10000 feet 500hPa = 18000 feet 300hPa = 30000 feet 200hPa = 39000 feet At 200-300hPa which is near the top of the troposphere (The lowest level in the atmosphere where our weather is, above which is the Stratosphere) is where we find the jetstream. The jetstream is a ribbon of wind which seperates cold air from warm, which can arch and pulse as it circulates the globe. Actually there are a number of jet streams and the one which normally affects us in winter is the Polar Front Jet (PFJ) as opposed to the subtropical jet (STJ) or the Stratospheric Night Jet found in the artic circle. The question which is usually asked is why look at higher levels when we live at low levels. The answer is that we are interested in the what happens when the air rises or sinks and where air is moving to and from. Cold air above us tends to make air rise and as it rises it is likely to form clouds. The colder the air the more unstable it will be. By unstable I mean that the air will have a tendency to rise. So when we look at charts at different levels we are trying to assess how far air will rise and in effect will there be clouds and will they reach great heights like thunderstorms (25000+ feet). We also look at how quickly temperatures drop so that we can judge how strong winds will be.We also try to gage what type of precipitation (rain or snow) will fall based on the temperatures. We are also interested in dewpoints and humidity which are the temperature at which water starts to form when air is cooled and how much water is in the air. The moister the air the higher the dewpoint, the more cloud and lower cloud base we tend to have. At the minute you should probably be interested in the fact that high pressure is sinking air and in the northern hemisphere means a clockwise circulation and low pressure means rising air and an anticlockwise circulation. Remember that low pressure does not always mean low temperatures at low levels. Low pressure usually has air rushing towards it from somewhere else and if that somewhere else is the artic then it brings cold air and if it is the tropics then it can bring humid warm air. Similarly high pressure does not always mean high temperature, it does usually mean lots of sunshine, but even here if it approaches from the south, then warm moist air will be cooling and form a thin layer of cloud.If high pressure approaches from the north you should get clear skies. High pressure also means sinking air so cold air from above sinks to the ground and this quite often means overnight frosts or low temperatures (In addition to no clouds holding the warmth in). Troughs and Ridges are formed where the jetstream arches upwards or downwards. Where it arches up then a pool of warm air is swept north and this is known as a ridge. Troughs form when the jetstream arches south and a pool of cold air is swept south. The 500hPa chart that smich posted above shows a ridge up towards greenland and a trough down over the UK. The arching of the jetstream is often caused by pulses of stronger wind in the jetstream which are often caused by low pressure spining winds fastly around them.In turn low pressure systems tend to form in troughs and at the entrance or exit regions of these pulses(jetstreaks). Weather fronts also tend to form at boundaries between cold and warm air, which is also where the jetstream can be found. On the 500hPa chart above the boundary would normally be where green changes to yellow, so you might expect a band of cloud there.

You could try deleting all files and history as well, or try typing in the URL in the address bar manually. Sometimes even though you ask for cookie's to be deleted they may keep a select few ,so locate and delete them manually. Look for a directory along the lines of 'Documents and Settings\MyName\Local Settings\Temporary Internet Files' and see what is in there and delete cookies manually. I suspect though it may actually be a cached DNS address at your workplace (i.e when you put the URL in it looks in the cache on a computer/proxy server somewhere in your work place for the IP address ,which may be out of date). Try hitting the refresh button maybe that will force the cached item to be refreshed. I have a slightly different problem myself. It appears to occur when I am attaching multiple pictures to a new topic and someone else is replying to a topic within that thread at the same time, then the screen times out. If you refreash it does eventually load the picture but you end up with numerous copies of the topic started. I think it may be something to do with flood control and timeout settings.

Thanks for posting, it was interesting to read. I am not quite sure about your premise as I think different densities of rocks moving about it the earth's core have a large affect on the earth's magnetic field, so gut instinct tells me when you say that the earths magnetic fields reflect solar system magnetic fields, that this fact may reflect only part of the mechanics of what is going on. As to the nine waves I can not help feeling that they would largely be swamped out by the eddies round large mountain ranges, chemical transports in the stratosphere and any number of other affects closer to home. I will keep an open mind though as I suspect magnetic fields can play a small part and assume in the fullness of time you will address my areas of confusion in later posts. It would be nice to see the mathematics behind your theory at a later point as well so I will wait patiently.

I am not really sure about the timing lines although it may work out.I guess here we are not looking at the short term forecast where we extrapolate from curent conditions or 3 months out where we can use Sea Surface temperatures and ice coverage to forecast, but in that mid range 1 to 6 weeks. Recent research shows that the linking between stratosphere and tropishere and the effects of planetary waves(Rossby) should make forecasting in this period far less random than one would believe. I guess this is why much of the most complex modelling done in GFS is to do with the atmospheric layers in the stratosphere. We do know that as a system moves over a large mountain range the atmosphere forms a waves and effectively breaks(like waves on a seashore) and I guess the timing of these waves and breaks and the time it takes for disturbances to rise up and then descend again through the Stratosphere is predictable. We ought to be able to make a pretty good forecast of the Jetstream and hence our weather from these factors.

It does look like there is some upper level shear approaching rita and when these start to overrun then the intensity should reduce. I am still not totally convinced about the ridge over texas moving eastwards allowing rita to move north but most of the models currently seem to support it. Here is a link showing roughly what the models forecast. Model Forecasts

Weather Alert Category: Level 2 Warning Weather type: ThunderStorms and heavy Rain Affecting: Wales, South West England, Lancashire, Cumbria, North West Scotland and Northern Ireland Time and Date Valid For: 11:30am Weds 31st August - 16:00 Weds 31st August 2005 Time Of Issue: 11:30am Weds 31st August 2005. A series of heavy showers and thunderstorms are currently moving through areas of Cornwall and into Wales bringing some heavy rain and lightning.There is a risk of localised flooding , large hail and lightning strikes. These storms are expected to move further north and east and possibly intensify during the day so further warnings will probably follow. Confidence Level: 90% Note: This alert should be considered a guide and we strongly recommend you stay tuned to the Met-Office for further warnings and updates. Please note, that this alert is covered by the net-weather terms and conditions of use, which are viewable here

Weather Alert Category: Level 2 Warning Weather type: Heavy rain, thunderstorms and torrential downpours Affecting: South East England Time and Date Valid For: 14:30 Thursday 25th August - 18:00 Thursday 25th August 2005 Time Of Issue: 14:30 Thursday 25th August 2005 Lines of showers and storms are generally moving east across the country. Torrential rain, along with possible flash flooding is likely, with possible Lightning and hail. This alert will be updated as and when is necessary. Confidence Level: 90% Note: This alert should be considered a guide and we strongly recommend you stay tuned to the Met-Office for further warnings and updates. Please note, that this alert is covered by the net-weather terms and conditions of use, which are viewable here

Reports of a Tornado near York this morning. Apparently, the northern/eastern section of the York ring road ground to a halt as people stopped their cars and looked at what was described as a tornado. A farmer has said he was lifted off the ground with his cattle trailer by a tornado in North Yorkshire - the second "twister" to hit the county in a week. Albert Parker was sheltering by the trailer near the A64 just north east of York when he was lifted into the air and then dropped to the ground. BBC News Picture seems to be from last weeks Thirsk funnel.

I am sorry to report that I did not see a tornado this morning in Coventry. I did see pronounced mammatus , strong cloud striations from cell to cell and what looked like a tornado out beyond the binley area of coventry. The feature did not appear to rotate and I dismissed it as strange shaped scud. Any tornado that did appear must have been before 7:15 and in another area of coventry to me.

Occasional lightning and thunder between 7am and 7:30am.Quite a high cloud base with slow moving clouds going north east. Brief sharp downpour which has pretty much dried out now. No evidence of hail and storm was not particularly severe.

It shows up on the metoffice rain radar. Which Way is it heading do you think ? Metoffice rainfall

Yes I fancy woodward will be a good place to start today.

SPC goes for north Texas, Western Oklahoma and South East Kansas. Strongest Cape looks to be in north Texas mid afternoon. Low level Helicity looks best in Texas but depp helicity looks better in Oklahoma. 700mb Vertical Velocities look best in north Texas. JetStream position shows an on coming long wave trough which should be a region of PVA. Right Entrance to a Jetstreak is in the area and is forecast to move north but is closest to north Texas.500mb vertical velocities look best in south west Kansas.850mb vertical velocities look strongest in northe Texas.Dewpoints of 60 and temperatures of 80 look good. Cinh lokks strong in north texas and weakest in Western Oklahoma. With a possibility of a cap in Texas further north might be better although things look like being a bit cluttered. Woodward and down to roger mills looks good in Oklahoma or over to poncha city.

Looks like South West Nebraska and North West Kansas along the I-80 corridor might be good again today. Heres a couple of thumbnails of Mike HolingsHead's pictures from the Grand Island SuperCell you saw for the rest of us. StormTrack discussion picture source

It seems to be coming together quite well. The significance of wind speeds increasing with height and changes of wind direction with height still needs to be explanined. Perhaps calculating the cloud base and affects of surface heating are not quite clear as well yet. Just when I think I am getting the hang of it though I see something like this.

A few more Links to get in the mood. StormGasm Discussion Forum StormTrack Discussion Storm2K local Forecast discussions VortexTimes Links Chase One Mid West Chasers Forecast Models forecasts satelite Cyclone Road Tornadoes Kick Links with Local TV forecasts

Good Luck. Friday 6th SPC has a slight risk out right now for parts of western Kansas and for a majority of Nebraska during Friday. Low level shear will be favorable for tornadoes in parts of western KS and NE. Indicators are that the Oberlin/Colby/Goodland area, depending on the develpment of the dryline could be a good place to start due to the high instability , but the best helicity is forecast in Nebraska. Satuday 7th Three options really Texas ,South Dakota or Kansas. The latest model have a nice dry line from central Nebraska into the western panhandle of Texas. Forecast temperatures of at least 80F are located ahead of this boundary. Surface winds from the south, possibly a slight backing of the winds ahead of the dry line.The upper-air winds at 250mb are forecast to be SW and even SSW along the dryline. The best chance for rotating storms would probably be closer to Texas and the east texas panhandle. The strong upper level system up in ND/SD/MN sure looks tempting as well, but the upper level winds are sufficent but not good and the dew points could be over estimated here. Or as the SPC favours, In kansas Td's won't need to be too incredible to get some High Plains tornadoes out in Western Oklahoma and Kasas. Tuesday 10th a very potent system looks to be developing, and looks like it could produce some severe weather. A deep upper level system at 998mb centered along the KS/CO border,with upper level winds in western Kansas and south into the northern Texas Panhandle being enough to sustain severe thunderstorm/supercell development. A theta-E tongue will stretch into Central Kansas.