How common for a 970mB or so depression to affect the English Channel in
September? Is there a general way of searching for such statistics?
All 6 of 6 met models are going for that prediction middle of this week

On Sunday, 13 September 2015 16:17:31 UTC+1, N_Cook wrote:
How common for a 970mB or so depression to affect the English Channel in
September? Is there a general way of searching for such statistics?
All 6 of 6 met models are going for that prediction middle of this week

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More common in late autumn in my experience, when the polar vortex spins up and the polar ice pattern sets itself for winter. Equinoctial gales were associated with this when there was more Arctic sea ice.

But this is early for any polar ice influence so something else must be the driver. Tropical storm Henri (now dead) might have had an influence in firing up the baroclinic zone, together with the negative SST anomaly in the N. Atlantic.

Len
Wembury, SW Devon
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On Sunday, September 13, 2015 at 5:17:06 PM UTC+1, Len Wood wrote:
On Sunday, 13 September 2015 16:17:31 UTC+1, N_Cook wrote:
How common for a 970mB or so depression to affect the English Channel in
September? Is there a general way of searching for such statistics?
All 6 of 6 met models are going for that prediction middle of this week

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More common in late autumn in my experience, when the polar vortex spins up and the polar ice pattern sets itself for winter. Equinoctial gales were associated with this when there was more Arctic sea ice.

But this is early for any polar ice influence so something else must be the driver. Tropical storm Henri (now dead) might have had an influence in firing up the baroclinic zone, together with the negative SST anomaly in the N. Atlantic.

Len
Wembury, SW Devon

Equinoctal gales (at least in September) seem the thing of myths. Were they ever very common? In my 24 year record only May, July & August have had less gales than September. Certainly vVery different near the Spring equinox.

I've recorded at least 4 occasions when the pressure has dropped below 980mb
in September over the last 24 years, I'm not able to say the absolute minimum achieved. Here's one example (the low's not at it's deepest - it's just the nearest archive chart I can find) http://www.wetterzentrale.de/archive...ka19980930.gif

Graham
Penzance (where it managed to stay dry until 16:00, contrary to predictions. Still quite sunny at 14:00.)





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On 13/09/2015 17:28, Graham Easterling wrote:
On Sunday, September 13, 2015 at 5:17:06 PM UTC+1, Len Wood wrote:
On Sunday, 13 September 2015 16:17:31 UTC+1, N_Cook wrote:
How common for a 970mB or so depression to affect the English Channel in
September? Is there a general way of searching for such statistics?
All 6 of 6 met models are going for that prediction middle of this week

--------------------------------------------------------------------------
More common in late autumn in my experience, when the polar vortex spins up and the polar ice pattern sets itself for winter. Equinoctial gales were associated with this when there was more Arctic sea ice.

But this is early for any polar ice influence so something else must be the driver. Tropical storm Henri (now dead) might have had an influence in firing up the baroclinic zone, together with the negative SST anomaly in the N. Atlantic.

Len
Wembury, SW Devon

Equinoctal gales (at least in September) seem the thing of myths. Were they ever very common? In my 24 year record only May, July & August have had less gales than September. Certainly vVery different near the Spring equinox.

I've recorded at least 4 occasions when the pressure has dropped below 980mb
in September over the last 24 years, I'm not able to say the absolute minimum achieved. Here's one example (the low's not at it's deepest - it's just the nearest archive chart I can find) http://www.wetterzentrale.de/archive...ka19980930.gif

Graham
Penzance (where it managed to stay dry until 16:00, contrary to predictions. Still quite sunny at 14:00.)





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That fits the bill ,so far, 17 years back, but the models are putting
this weeks one to be a bit deeper

On 13/09/2015 17:17, Len Wood wrote:
On Sunday, 13 September 2015 16:17:31 UTC+1, N_Cook wrote:
How common for a 970mB or so depression to affect the English Channel in
September? Is there a general way of searching for such statistics?
All 6 of 6 met models are going for that prediction middle of this week

--------------------------------------------------------------------------
More common in late autumn in my experience, when the polar vortex spins up and the polar ice pattern sets itself for winter. Equinoctial gales were associated with this when there was more Arctic sea ice.

But this is early for any polar ice influence so something else must be the driver. Tropical storm Henri (now dead) might have had an influence in firing up the baroclinic zone, together with the negative SST anomaly in the N. Atlantic.

Len
Wembury, SW Devon
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BBC weather just referred to the coming Weds LOW having a contributor to
it being the remnants of a tropical storm, bperhaps the "ill-fated" TC
Fred mentioned here exactly 1 week ago

I'll check it out , in the "Digital Times" later this week, but 02/03
September 1883 looked bad, Reanalysis site has consistent synoptic

On 13/09/2015 17:17, Len Wood wrote:
On Sunday, 13 September 2015 16:17:31 UTC+1, N_Cook wrote:
How common for a 970mB or so depression to affect the English Channel in
September? Is there a general way of searching for such statistics?
All 6 of 6 met models are going for that prediction middle of this week

--------------------------------------------------------------------------
More common in late autumn in my experience, when the polar vortex spins up and the polar ice pattern sets itself for winter. Equinoctial gales were associated with this when there was more Arctic sea ice.

But this is early for any polar ice influence so something else must be the driver. Tropical storm Henri (now dead) might have had an influence in firing up the baroclinic zone, together with the negative SST anomaly in the N. Atlantic.

Len
Wembury, SW Devon
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The BBC met referred to residual of Henri to be a contributor to the
weds situation.
Just a coincidence that for the 1 6hour slot of the GEM model last week,
AFAIK the projection of FRED,
http://www.meteociel.fr/modeles/geme...r=6&annee=2015
the deep LOW in the south of that plot looks suspiciously like what is
to become the contributor for weds.
A week ago , for that 6hour slot, FRED was still in existence and got
projected through , and then disappeared in later projections, as he died

The deepest low in the English channel for September that I can find in recent years was at 0600 UTC on Thu, 7 Sep 1995. The low I estimate (looking at the SYNOP observations) was positioned at 49N 6W with a central pressure of 965 hPa. The MSLP on the Scillies (#03803) at that time was 966.8 hPa. That low is ranked 14th lowest (2.5° grid point) pressure from the reanalysis data back to 1948. The lowest in the vicinity of the British Isles was 963.4 hPa on 9 Sep 1970, that low being just of NW Ireland.

On Monday, September 14, 2015 at 4:17:09 PM UTC+1, xmetman wrote:
The deepest low in the English channel for September that I can find in recent years was at 0600 UTC on Thu, 7 Sep 1995. The low I estimate (looking at the SYNOP observations) was positioned at 49N 6W with a central pressure of 965 hPa. The MSLP on the Scillies (#03803) at that time was 966.8 hPa. That low is ranked 14th lowest (2.5° grid point) pressure from the reanalysis data back to 1948. The lowest in the vicinity of the British Isles was 963.4 hPa on 9 Sep 1970, that low being just of NW Ireland.

I checked my record for 7th Sept 1995. I wrote "Ex hurricane Iris brought gales, heavy rain, and some spectacular seas". I recorded a gust of 55mph and 23.0mm of rain.

Graham
Penzance

On 14/09/2015 16:17, xmetman wrote:
The deepest low in the English channel for September that I can find in recent years was at 0600 UTC on Thu, 7 Sep 1995. The low I estimate (looking at the SYNOP observations) was positioned at 49N 6W with a central pressure of 965 hPa. The MSLP on the Scillies (#03803) at that time was 966.8 hPa. That low is ranked 14th lowest (2.5° grid point) pressure from the reanalysis data back to 1948. The lowest in the vicinity of the British Isles was 963.4 hPa on 9 Sep 1970, that low being just of NW Ireland.


So perhaps once a decade.
My interest is potential of marine flooding, coinciding with spring
tides (lower springs than the ones for the end of sept though).
Earlier model outputs put the track at a more problematic path, longer
run of west to east wind component along the channel