Jet-stream Cirrus from warp and weft of Atlantic air currents illustrate traditional forecast rules of thumb

One of the tricky things about meteorology is that it happens in three dimensions above the surface of a rotating sphere.  In fact, if you add in time, it is four dimensional.  Yet we only have two dimensional graphics from which to build our understanding of it; its rather like building the picture of a garden viewed only through the narrow gaps in boundary fence.

This featured picture has a stable south westerly jet-stream flow aloft, marked by cirrus which weaves itself across a lower level unstable north westerly from the direction of Cape Farewell, the southern tip of Greenland.  Such differential motion of low and high level clouds give rise to traditional seagoing forecast rules of thumb and allow an observer to detect whether they are ahead or astern of a storm.  Of course, a peek at the ships log might tell them that.

Jet stream is shown here from Earthnullschool’s 250mb streamlines.  This matches the shape of the cirrus in the satellite picture above.

250mb stream lines, 29 Mar 16, ENS.
250mb stream lines, 29 Mar 16, ENS.

Whilst below the 1000mb streamlines are:

1000 mb flow, 29 Mar 16, ENS
1000 mb flow, 29 Mar 16, ENS

In this case, cumulus at lower levels moves from the north west whilst cirrus at high levels comes from the south west.  The area does lie to the south west of the complex Atlantic low in the aftermath of storm Katie and pressure is building heralding more settled weather to come.

Open Cell Convection in the Davis Straits and Labrador Sea

Sweep of cold polar air pull down Davis Straits into the Labrador Sea by major complex depression in NE Atlantic on 28 Mar 16 forms regular pattern of open cell convection.  Convection patterns only became apparent with the advent of satellite meteorology, now they reach our desk tops every day.

This is cold air over relatively warmer sea surface.  Convection and condensation results but there is a weight of cold air above which is subsiding over a big area and the convection mixes in with this to limit vertical extent. Air descends in the open cells of the pattern.

A search for radiosonde data in this region to check the atmospheric structure is difficult.  I came up with a model ascent from Aasiaat (west coast of Greenland just to the NE of this picture).  Which does show some subsidence at about 7,000ft and is consistent with the thoughts for open cell convection.

GFS Sounding Aasiaat 28 Mar 12

Storm Katie mixes up the Atlantic air


The meteorological event of the day, storm Katie, gives a dramatic signature on all the various meteorological graphics.  MODIS channel 22 at 280230, Earthnullschool surface winds and UKMO surface analysis 280000 presented above.

Surface wind flow from Earthnullschool shows the intense wind field over SE UK, squeezed ahead of the vortex, but the NW’ly surge of air from Denmark Straits is perhaps the most striking element of this graphic.

The storm is a snag in a larger complex depression which mixes cold air from the pole to the West and warm air up to the East.  By this method, the atmosphere does its job of breaking down the temperature gradient from equator to pole and illustrates one of the keys to meteorology.

Ice Edge North of Greenland

ice edge clearly visible from space.

EOSDIS Worldview north of Greenland 27 Mar 16


NASA’s EOSDIS Worldview gives stunning pictures.  This one, of polar regions north of Greenland appears to show the ice edge with cold air streaming off over the sea forming ever deepening cumulus.  This edge seems almost too bold.

Check on MODIS (Dundee) Channel 6 (snow/cloud discrimination 1628-1652nm) and Channel 22 (surface cloud 3.929-3.989µm) seems to back this analysis up; temperatures of cloud tops over the sea being colder than the ice.  Fractures and polynyas in ice, much loved by cold war submariners, show up with amazing clarity.


Airbourne Desert Sands Mark Out Cold Front in Eastern Mediterranean

desert sands blow out of Africa on a conveyor belt of air ahead of a cold front



Cold fronts are normally identifiable from their cloud signature on satellite imagery.  Of course, air mass boundaries can exist without condensation: density changes and air flows can exist without clouds particularly in dry and hot air.  Summer front can cross the UK with just low strato-cumulus.  In the Mediterranean, cloudless density boundaries one day give potential for fierce thunderstorms the next.

The 23 Mar 2016 was a case in point.  Over the Eastern Mediterranean we note a conveyor belt of air dragging sand northwards from the African deserts.  No clouds but a cold front none the less.