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  • Location: Scunthorpe
  • Location: Scunthorpe

    I thought now that we have got the individual monthly ENSO figures in for December, January and February it would be time to do some historic pattern matching to see what it could possibly mean for us in terms of possible spring CET, weather patterns and precipitation

    First I have included this table based on the La Nina years from 1870 to 2020

    Untitled.thumb.png.3e222710cc79e725b6408287f4fe251a.png

    Next I have included the ONI figures for December, January and February as well as what strength of La Nina we got and where the cold anomalies were based

    Untitled.thumb.png.81b42c16844183e9f0ed512f477e6c4b.png

    As you can see we ended up with an average moderate La Nina which was a mixed or basin wide event overall

    CET

    What does all of this mean for the possible CET and anomalies for March, April and May as well as the overall spring

    The initial table can be narrowed down to 3 relevant rows, Overall Mixed La Nina winters, Overall Moderate La Nina winters and the more precise Moderate Mixed La Nina winters.

    Using just mixed events we come out with basically an average spring in terms of CET with anomalies very close to the long term average in all 3 spring months as well as the overall spring

    In regards to just Moderate La Nina events we also come out basically bang on average too

    However when we focus more specifically on the combination of both Moderate and Mixed La Nina's the story is a little different. We come out with milder March's with anomalies at +0.79C above the mean, colder Aprils with the anomalies around -0.54C below the mean and May around average with the cold and mild March and April cancelling each other out and the average May means the overall spring anomaly ends up close to average also

    Overall 500mb Patterns for Moderate Mixed La Nina Springs

    Time to see what the 500mb patterns come up with for each category

    Overall

    image.thumb.png.dd87556396ea3d95c89917aa0c052826.png

    This overall would look like a cold pattern but the Moderate Mixed La Nina winters tend to produce mild weather in March with cold April and average May, maybe a cold April pattern has distorted the overall 500mb pattern. Time to look at each month separately.

    March

    image.thumb.png.63eb900290aeed7e5b45e05ad21e9de0.png

    March is dominated here by average easterly winds and this at first glance looks like it would be cold but the CET anomaly for the March's would suggest a milder month so maybe more of a Mediterranean influence rather than Siberian with these easterlies

    April

    image.thumb.png.8dda39fbdebd7098a8eb5018b208ba55.png

    Overall a colder pattern showing here for April's with higher pressure near Greenland and lower pressure to the east of this placing the UK in a generally cold and unsettled pattern. A snow risk cannot be ruled out here, especially earlier in the month

    May

    image.thumb.png.e18abcee88a5e3b10f04ffb475915719.png

    A generally average CET May with the driest weather in the N and the wettest in the S. Not looking good for many European locations under that low pressure with a poor start to the late spring/early summer season

    Precipitation

    How does precipitation shape up for springs following Moderate Mixed La Nina's

    Overall

    image.thumb.png.a6aaac675d050ec621cb83a186fa5b51.png

    The overall spring signal is looking drier than average away from the far SE corner of England with the driest anomalies in the W of the UK. How do the individual months break down then

    March

    image.thumb.png.1f3d0d0fa46cbbf199c219ebc5c0bc93.png

    Looking like quite a dry signal for the March's that follow Moderate Mixed La Nina winters. A good sign if you want to avoid anymore flooding after some of the winter rain we have seen. The driest overall signal is in the NW of the UK with the least dry in the SE corner of the UK

    April

    image.thumb.png.5b3b5d3c71cd68a53810eba09e37ef66.png

    A total flip around from March's to April's. Now wetter than average features quite a bit, especially the further north you go in the UK with the wettest in NW Scotland and average to slightly below average precipitation in the south and the Channel Islands.

    May

    image.thumb.png.856d0d76444e02d7b094b8070f769d1d.png

    The May's that follow Moderate Mixed La Nina winters are a lot more mixed but generally west is best if you are after drier weather with the potential for some very wet conditions further east. SE England could see some very wet weather but other eastern areas look like they could be at risk from this too

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    See http://link.springer.com/article/10.1007/s00382-014-2155-z Huge uncertainty however, re scope of any teleconnection for UK winter 16-17 (models still yet to confidently resolve re ENSO neutra

    Indeed it did. Essentially it runs an consistent story through N-D-J-F of +ve GPH/MSLP anomalies to NW/N of UK; -ve ones to S/SW. 

    The reasons why these three key strong El Nino years, 1972/73, 1982/83 and 1997/98 differed so much in their atmospheric responses is very interesting.   Purely on ocean surface / subsurface data, a

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    Posted
  • Location: Windermere 120m asl
  • Location: Windermere 120m asl

    Thanks for this informative post - perhaps might be better located in the Spring 2021 forecast thread, as it may become a little lost in here, but equally relevant for this thread given it is about observations based on ENSO.

    Just a hunch but I feel there is some credence in the forecast of a cold April, all that bottled up cold air in the arctic through March combined with a relatively weak atlantic suggests northerly airstreams could hold sway with the cold air needing to be released into mid lattitudes and the PV goes on the wane..

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    Posted
  • Location: Ludgershall, Wiltshire
  • Location: Ludgershall, Wiltshire
    16 minutes ago, damianslaw said:

    Just a hunch but I feel there is some credence in the forecast of a cold April, all that bottled up cold air in the arctic through March combined with a relatively weak atlantic suggests northerly airstreams could hold sway with the cold air needing to be released into mid lattitudes and the PV goes on the wane..

    Could well be the case this year with the late PV.  A similar April to 1989 perhaps?

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    Posted
  • Location: Windermere 120m asl
  • Location: Windermere 120m asl
    2 minutes ago, Don said:

    Could well be the case this year with the late PV.  A similar April to 1989 perhaps?

    Perhaps not as cold, but a good chance of at least one northerly episode at some stage, and not necessarily a 24 hr shot. April often brings northerlies so nothing unusual, but the depth of cold this year may be more extreme than normal.

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    Posted
  • Location: Ludgershall, Wiltshire
  • Location: Ludgershall, Wiltshire
    8 minutes ago, damianslaw said:

    Perhaps not as cold, but a good chance of at least one northerly episode at some stage, and not necessarily a 24 hr shot. April often brings northerlies so nothing unusual, but the depth of cold this year may be more extreme than normal.

    Yes, perhaps not that cold.  Maybe something akin to 1998 or 2008?

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    Posted
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet

    03MAR2021 - Nino3: -0.4, Nino3.4: -0.7, Nino4: -0.8

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    Posted
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet

    10MAR2021 - Nino3: +0.1, Nino3.4: -0.3, Nino4: -0.5

    17MAR2021 - Nino3: -0.2, Nino3.4: -0.5, Nino4: -0.4

    Sub-surface just went net positive as well so March will end flat for sub-surface and SOI despite the strong Winter values.

    It does appear the Nina is being squeezed at both ends now.
     

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    Posted
  • Location: Windermere 120m asl
  • Location: Windermere 120m asl
    2 hours ago, summer blizzard said:

    10MAR2021 - Nino3: +0.1, Nino3.4: -0.3, Nino4: -0.5

    17MAR2021 - Nino3: -0.2, Nino3.4: -0.5, Nino4: -0.4

    Sub-surface just went net positive as well so March will end flat for sub-surface and SOI despite the strong Winter values.

    It does appear the Nina is being squeezed at both ends now.
     

    What does  this mean for likely summer prospects?

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    Posted
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
    44 minutes ago, damianslaw said:

    What does  this mean for likely summer prospects?

    If a Nino actually tries to develop (doubtful for me) then actually most of our 18C+ summer months come in transition years (likely because relative AAM spikes rather than just stays stable even if high).

    If we just drop back to neutral and nothing much happens then atmospheric memory will probably produce a Nina pattern even if we get periodic amplification.

    If Nina tries to redevelop during the summer then expect it to be poor.

    Options 2 and 3 are more likely in my opinion with a persistent neutral-negative ONI strengthening again in the Autumn (SOI monthly values suggest March is MJO disrupted and we have a -PDO).

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    Posted
  • Location: Windermere 120m asl
  • Location: Windermere 120m asl

    Thanks for the above, mmm more La Nina not a good prospect then. Generally means mid atlantic heights and cool NW flow..

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    Posted
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet

    24MAR2021 - Nino3: -0.7, Nino3.4: -0.6,  Nino4: -0.6

     

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    Posted
  • Location: Scunthorpe
  • Location: Scunthorpe

    These are the daily NINO Region anomalies for the last month. These are from tropical tidbits

    Untitled.thumb.png.77f0cb374cfb546797db3c38914c7abc.png

    Using daily data it appears that the La Nina event ended on 6th March 2021 when the Region 3.4 anomaly was last at or below -0.5C

    Between 7th March 2021 and 20th March 2021 it almost looked as if we were attempting to get a Weak EP El Nino going and we did get into weak El Nino territory in Region 1+2 for a time but Region 3.4 stayed below 0C anomaly but above -0.5C and just bounced around between ENSO Neutral on the colder side and True ENSO Neutral (close to 0 anomaly)

    In the days between 21st March 2021 and today the ENSO Region has started to cool again, particularly in more eastern regions. The latest figures for 1st April 2021 show we have breached weak La Nina threshold again in both Regions 1+2 and 3 so a weak EP La Nina signature is developing

    Region 3.4 is also cooling again somewhat but hasn't reached the threshold yet. March on its own would be classed as an ENSO Neutral month but with La Nina months in January and February along with a possible return to La Nina as early as during April could this mask the ENSO Neutral month in the tri monthly anomalies and just show a weakening of La Nina in the spring before it strengthens again during the summer

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    Posted
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet

    Will have to wait until wait until Monday to find but if the 31st did provide a value of -0.3 for CPC then we would indeed end up with a monthly ONI just shy of -0.5 based from the weekly official data (albeit JFM still -0.7).  

    We have seen a stronger pressure gradiant develop over the Pacific since mid-month though with stronger trades in the east (hence the fall) and stronger westerlies west of the dateline.

    Edited by summer blizzard
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    Posted
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet

    31MAR2021 - Nino3: -0.6, Nino3.4: -0.5,  Nino4: -0.6

    ONI for March was still -0.5 rounded down and the JFM ONI is -0.9. We should (bar a positive value for FMA) still see a -0.5> value for FMA which would be our 8th tri-monthly value below the threshold, the longest since the 2010-2012 Nina. 

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