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Rainshadow

February 14th & 15th, Coldest Air Mass Of The Season?

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It doesn't work every time or maybe not here every time (graph), but the -NAM doesn't hurt and February 14th & 15th may be the coldest two days of the season. 

Even four to five days out there are operational model differences.  The GFS is so busy plow driving the cold air in (only the ICeisON is colder at 1 pm Friday) that it doesn't give a Norlun Trof a chance to form.  Granted placement is an unknown, but the Op Euro has it within Mt. Holly's CWA, the GGEM up in New England.

Suburban locations because of radiational cooling might have had a colder night, but PHL's lowest temperature so far this season is 19 degrees on January 21st & December 19th.  That is only four degrees lower than the 23F reached on November 13th.

 

1.JPG

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This is not the you've been NAMMed NAM btw, brief summary from Colorado State U:

A Brief Introduction to the Annular Modes and Annular Mode Research
David W. J. Thompson

 

The following text is designed to introduce scientists from outside the climate dynamics community to the annular modes and current topics in annular mode research. The text is updated and improved regularly. In the interest of being inclusive, I have not cited individual papers, but rather refer broadly to the most relevant subset(s) of papers contained on this site. Please send any comments to David W. J. Thompson (davet@atmos.colostate.edu)

 

What are the annular modes?

 

The annular modes are hemispheric scale patterns of climate variability. Another more popular example of a large scale pattern of climate variability is the El-Nino/Southern Oscillation (ENSO). But whereas ENSO owes its existence to coupled ocean/atmosphere interactions in the tropical Pacific, the annular modes owe their existence to internal atmospheric dynamics in the middle latitudes. ENSO is the most important (in terms of variance explained) pattern of large scale climate variability in the tropics; the annular modes are the most important patterns of climate variability in the Northern and Southern Hemisphere middle and high latitudes.

There are two annular modes in Earth's atmosphere: a Northern annular mode (NAM) and a Southern annular mode (SAM). Both annular modes explain more of the week-to-week, month-to-month, and year-to-year variance in the extratropical atmospheric flow than any other climate phenomenon. For example: the NAM and SAM explain on the order of ~20-30% of the total variance in the geopotential height and wind fields of their respective hemispheres, depending on the level and timescale considered.

The annular modes describe variability in the "anomalous" atmospheric flow, that is, variability not associated with the seasonal cycle. In the pressure field, the annular modes are characterized by north-south shifts in atmospheric mass between the polar regions and the middle latitudes. In the wind field, the annular modes describe north-south vacillations in the extratropical zonal wind with centers of action located ~55-60 and ~30-35 degrees latitude. By convention, the high index polarity of the annular modes is defined as lower than normal pressures over the polar regions and westerly wind anomalies along ~55-60 degrees latitude.

To first order, the time series of the annular modes are consistent with a normally distributed red-noise process with an e-folding timescale of ~10 days. This means that: 1) the annular modes vary on timescales as fast as weeks; and 2) the high and low index polarities of the annular modes do not reflect two distinct states of the climate system, but rather the wings of a normally distributed frequency distribution. However, not all aspects of the time series of the annular modes are consistent with a red-noise process with a 10 day timescale: e.g., the annular modes exhibit enhanced variability on monthly timescales during seasons of rigorous stratosphere/troposphere coupling (see section on Stratosphere/troposphere coupling, below); and both annular modes have exhibited trends over the past few decades towards their high index polarities (see section on Climate Change, below).

 

 

What's the difference between the NAM, the Arctic Oscillation, and the North Atlantic Oscillation? And what's the difference between the SAM, the Antarctic Oscillation, and the high-latitude mode?

 

The short answers : none and none.

Through most of the 20th century, the NAM was referred to exclusively as the North Atlantic Oscillation. That's because both the data coverage and the amplitude of the NAM are largest over the Atlantic sector of the hemisphere. When the polar scale of the northern pressure center of the NAO was identified in the late 1990s, the name Arctic Oscillation was introduced to highlight the fact that the pressure anomalies associated with the NAO span most of the Arctic. But 'oscillation' is something of a misnomer, as neither the northern or southern annular modes oscillate regularly in time (see text on What are the annular modes?, above). For this reason, in recent years the NAO/AO nomenclature has been increasingly supplanted in the dynamical literature by the phrase Northern Annular Mode (NAM). Annular denotes the longitudinal scale of the pattern, and annular mode suggests the NAM reflects dynamical processes that transcend a particular hemisphere or, for that matter, planet.

Likewise, the leading mode of variability in the Southern Hemisphere has been referred to as the High Latitude Mode and the Antarctic Oscillation, but is most commonly labeled the Southern Annular Mode in the recent literature.

 


 

Stratosphere/troposphere coupling and the annular modes

 

The annular modes are coupled with annular variability in the stratospheric flow during the winter season in the Northern Hemisphere and the spring season in the Southern Hemisphere. For decades, the prevailing wisdom was that stratospheric processes respond to but do not impact the tropospheric flow. But recent observations and model results done in the context of the annular modes suggest the coupling is two-way.

The recently discovered two-way nature of stratosphere/troposphere coupling is important for a number or reasons, not least the fact that the timescale of variability in the stratosphere is generally longer than the ~10 day timescale of variability in the extratropical troposphere. Recent numerical simulations suggest the coupling between the stratospheric and tropospheric circulations has practical applications for weather forecasting and also implications for tropospheric climate change (see text on Climate Change, below). The mechanisms whereby changes in the stratospheric flow impact the troposphere are currently under investigation.

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House closing in Colebrook, NH Friday.   -22 on the docket that night with clouds.

Friday
Mostly cloudy and cold, with a high near 6.
Friday Night
Mostly cloudy, with a low around -22.
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6 minutes ago, iceman56 said:

House closing in Colebrook, NH Friday.   -22 on the docket that night with clouds.

Friday
Mostly cloudy and cold, with a high near 6.
Friday Night
Mostly cloudy, with a low around -22.

Congratulations on the house!   Temperatures are just a bit too cold for me.

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Single digits on the gfs now. Wooooo weeee, I cant wait 

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3 minutes ago, tombo82685 said:

Single digits on the gfs now. Wooooo weeee, I cant wait 

You might have to wait until 2021.

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24 minutes ago, Rainshadow said:

You might have to wait until 2021.

can you please stop being a debbie downer. 

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34 minutes ago, tombo82685 said:

can you please stop being a debbie downer. 

It's in my position description:

As moderator you are required to downplay every cold and snow threat while pimping every heat wave that comes along.  Failure to do so will result in termination, membership expulsion as well as loss of all 401K benefits, so there.

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2 minutes ago, Rainshadow said:

It's in my position description:

 As moderator you are required to downplay every cold and snow threat while pimping every heat wave that comes along.  Failure to do so will result in termination, membership expulsion as well as loss of all 401K benefits, so there.

but what happens when your avatar picture is riding heavily on some snow?

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1 minute ago, tombo82685 said:

but what happens when your avatar picture is riding heavily on some snow?

 Well one bets on weather, one loses.

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OP EC has same low for PHL which would make it the coldest of the season.

Couple of things not coming totally together.  Thermal trof is coming through Friday late afternoon/Friday early evening.  Winds look like they are going to stay up for most of the night.  Spots that like to decouple will (Parsley's old house) and their mins will be lower than PHL's.  Maybe Tombo gets his single number?

1.JPG.626ed31334d3326435c6bab2fcee74ba.JPG

 

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14 minutes ago, Rainshadow said:

OP EC has same low for PHL which would make it the coldest of the season.

Couple of things not coming totally together.  Thermal trof is coming through Friday late afternoon/Friday early evening.  Winds look like they are going to stay up for most of the night.  Spots that like to decouple will (Parsley's old house) and their mins will be lower than PHL's.  Maybe Tombo gets his single number?

 

 

if it's windy I won't. I'm a radiating spot, not CAA spot

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Be nice to get a low teen/single digit night  to keep down ticks and other pests

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17 minutes ago, Chubbs said:

Be nice to get a low teen/single digit night  to keep down ticks and other pests

Will one Harsh night even kill much? Seen way too much activity flying and crawling around. The unfrozen ground and near foundation warm nooks are keeping pests alive. 

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10 hours ago, Parsley said:

Will one Harsh night even kill much? Seen way too much activity flying and crawling around. The unfrozen ground and near foundation warm nooks are keeping pests alive. 

Not sure what one cold night does but it can't hurt.

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4 hours ago, Chubbs said:

Not sure what one cold night does but it can't hurt.

True. 

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This 2-day cold snap may be the highlight of winter, I have never been so excited for dry, cold air.  All part of the coping process.

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I'll have to savor my -7 tomorrow night, +2 Friday, -21 Friday night, then back up to 15 Saturday in Colebrook, NH.   3-5" of snow tomorrow to boot.     That will have to last me until next winter as I won't get back until mid-April.

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On 2/11/2020 at 5:54 PM, tombo82685 said:

if it's windy I won't. I'm a radiating spot, not CAA spot

Too bad you are not in PHL, which unlike the suburbs apparently is a great radiating site.

xcxc.JPG.912b79bb1f8572eb05525fd8a9c383f4.JPG

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NAM Barney brain freeze aside, with everything predicted to transpire faster, thermal trof now late Friday afternoon, the decoupling probabilities are increasing as are lower outlying area mins on Saturday morning.

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