Archives For nor’easter

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The UKMet analysis chart for today shows a building ridge in the Mid-Atlantic and a complex large LOW over Scandinavia.  This is dragging down a cold Arctic airmass, which will usher in progressively colder upper air each day through to Thursday.  The low NW of the Azores is drifting ESE but filling and can be ignored for now.

Air at 850hPa, roughly 1500m up, is used to judge airmass characteristics because, at this height, the airmass is not affected by diurnal and surface changes like sea, forest, mountain, towns, which can create big temperature variations near the ground.  The 850hPa temperature by Thursday could dip as low as -8C over Reigate.  Whilst this is not extra-ordinary it is about the coldest and most sustained chilly dip we have seen so far this winter.  Skies will be mostly clear and nights will turn frosty with day Tmax struggling to 5-6C. Wind chill will make it feel more like freezing for most days this week.

High pressure nudging in from the Atlantic will keep any precipitation light and restricted to coastal areas.  Friday sees things get interesting and unusual.

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A southerly diving jetstream gets into action on Friday and is set to amplify the 500mb trough and deepen a low off the west coast of the UK and develop it further into Biscay into Saturday and create a cut-off feature by Sunday.

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The Atlantic / Biscay LOW is unlikely to impact us in the SE much directly but, as it passes south of us through the weekend into Europe it will drag in cold easterly and then NE winds.  Our own mini-Nor-Easter!

Nor-Easters are famous powerful winter storms in the USA.  Our own version this weekend is a rather tame feature in comparison but notable because it is relatively unusual and has potential to bring a more sustained wintry feel to the SE through the weekend and maybe into next week.

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This southerly tracking LOW will move NE through the continent and will set up a cool Easterly then NE wind over the SE. Nothing outrageously cold for us because the coldest air is likely to stick further to the north east in Russia and Scandinavia.  Nevertheless, by Sunday a brisk NE wind with upper air of -8C or so will continue to make it feel chilly, after a cool week.

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The winds over the SE will therefore swing from  Northerly mid-week through to Southerly on Friday and thence to Easterly and finally Nor-Easterly / Northerly by Sunday. This anti-clockwise rotation is called backing and often ushers in cold air.  This is despite the wind turning through a seemingly mild southerly direction.  Remember we are sitting well north of the jetstream this weekend, which is somewhere in the Mediterranean, thus all airmasses are relatively cold and polar.

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Pressure stays relatively high throughout this “mini-nor-easter” episode and so this will limit chances of any snow unless the low decides to track further north nearer the UK OR we pick up sea effect snow as winds turn NE over a relatively warm North Sea.

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Snow showers are theoretically possible near the North Sea coast if Sea Effect / Lake Effect snow can be kicked off.  Such sea effect snow occurs when (very) cold air masses cross warm sea surfaces.  This can trigger lines of convective showers that dump lots of snow in places like the Great Lakes in the US.  Sea Effect snow occurs best when there is a temperature contrast of at least 13C between 850hPa (which must be well below freezing of course) and a warm sea surface.

The charts above show the North Sea is anomalously warm at more than 8C across a large area, although cooler near UK shores.  The upper air temps this weekend are around -8C, making a potential 16C contrast in temperature, theoretically sufficient to trigger showers. Unfortunately the airmass seems to be dry and, at this stage at least, rather stable. Looking ahead the cold spell could last into next week. Check our twitter account @rgsweather for local updates but always check professional weather forecast providers for decision making, of course.

A “potentially historic and crippling snow storm” is imminent for the USA NE seaboard especially New York State with cities from New York to Boston being warned by weather agencies of a potentially life threatening blizzard lasting some 48 hours.  Update Tues 27: whilst the worst of the blizzard missed New York heavy snow occurred further North.  The system tracked further east than modelled.

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New York escaped worst, but Boston hit as expected with record snow in New England

 

Watch unfolding live pictures on webcams here:

http://player.theplatform.com/p/2E2eJC/NBCNewsIE8?guid=nbcnewslive_nyc1

http://www.earthcam.com/usa/newyork/timessquare/?cam=tsstreet

Potentially 36 inches (3 feet) of snow could fall in places (that’s waist deep!) as a Nor’Easter (NorthEasterly) wind buckles round a rapidly deepening low tracking NW up the coast over the next 48 hours. All weather agencies are busy getting the news out to people in the regions likely to be impacted.

Official warnings from NOAA and all regional weather agencies are giving these urban populations warning after the system has caught computer models napping.  The storm has rather unexpectedly “blown up” recently to become a potential threat only in the last 24 hours or so.

The charts below show the synoptic set-up that develops this system, named Juno, currently a rather benign low tracking west out of continental US.   This LOW is forecast to deepen rapidly due to it’s location in relation to a fast meridional jetstream looping round a HIGH pressure ridge in the US west.  The LOW is dragging cold air from the continent interior and, as this cold air interacts with humid air and plenty of moisture over the Atlantic, it will turn into a snow-making machine that could last 48 hours and dump feet of snow widely across many places indicated on maps above.

Here are some synoptic charts showing the development.  Note the track sliding up the NE coast.  The Nor’Easter wind itself can be seen developing on the northern edge of the low which, as it is forecast to slow and stall while it deepens (a common feature of bomb depressions) the strong NorthEasterly gales, some up to 70mph, will continue to pump snow across parts of the NE building up depths to 2 – 3 feet in places.

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Note the warm sea surface temperatures off shore which will provide enormous quantities of moisture for snow production on the NE wind.

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Here is a chart showing minimum temperatures and possible snow cover by Wednesday.

The US is more used to heavy snow and more able to cope with it than the UK because the USA has a continental climate which experiences colder winters with more regular and significant snow events.  Earlier this winter Buffalo recorded feet of lake-effect snow.  Even so, this snow storm is serious and a state of emergency has been issued for New York.  The difference this time is that this storm will dump a lot of snow in a very short space of time and more people will be impacted in a densely populated and urbanised part of the USA.

The National Weather Service and regional weather agencies and the New York Mayor have all issued weather warnings for the blizzard urging people not to underestimate the possible impacts of 2-3 feet of snowfall over the next 48 hours.

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http://www.nbcnewyork.com/news/local/NYC-New-York-New-Jersey-Connecticut-Blizzard-2015-NorEaster-Snow-Wind-Whiteout-Record-289770081.html#

Here are some tweets and information emerging on the eve of this storm:

 

More info:

Excellent write up and explanation of the evolution of this Nor’Easter storm http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2015/01/28/raging-snow-howling-wind-the-meteorological-evolution-of-the-blizzard-of-2015/

http://forecast.weather.gov/product.php?site=NWS&issuedby=OKX&product=WSW&format=CI&version=1&glossary=1&highlight=off

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2902

http://edition.cnn.com/2015/01/25/us/weather-storm/

http://www.bbc.co.uk/weather/features/30989760?ns_mchannel=social&ns_campaign=bbc_weather&ns_source=twitter&ns_linkname=news_central

http://www.climatecentral.org/news/what-warming-world-means-for-major-snowstorms-18594

http://meteorologicalmusings.blogspot.co.uk/2015/01/a-meteorologists-thoughts-on-blizzard.html

http://www.bbc.co.uk/news/world-us-canada-30996010

Quick update for Friday and Saturday:

The Arctic pool of air brought down by the Northerlies through Thursday is due to develop into a cool pool of LOW pressure over the continent which will linger and flirt with the South East of the UK for this weekend. While the North and West basks under high pressure, the South is due for some cool brisk winds and some persistent rain at times this weekend: wind then rain on Friday, rain on Saturday. This will blow the cobwebs away (and some leaves!) after the balmy start to October. Significant rainfall total over 20mm on places.

se cool wash out

The wind starts first as a brisk cool Northerly on Thursday and Friday morning and then swinging round to a cool North Easterly during Friday with gales possible in the Channel and North Sea with 30mph+ gusts for Reigate. Friday pm will see the rain setting in, possibly quite late into the afternoon for Reigate. The rain is associated with complex fronts wrapped around the LOW pressure moving unusually SW across Northern France from the Netherlands. Once the rain arrives on Friday, it is likely to remain persistent until well into Saturday. Some significant totals are possible with moderate intensities on Saturday morning.  With the wind it will feel distinctly cool and autumnal compared to last weekend when 20c was exceeded in Reigate.

A Nor’easter is actually a storm off the coast of New York / Eastern USA which brings in cold blast of NE winds on the back of a depression circulation. This is like a mini-nor’easter but is tracking the wrong way.