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The February 2012 exceptional snowfall along the Adriatic side of Central Italy

October 2012
Meteorologische Zeitschrift 21(5):503-508

DOI:10.1127/0941-2948/2012/0536

Authors:

Carlo Bisci

University of Camerino

Massimiliano Fazzini

University of Camerino

gérard Beltrando

Univesité Paris Diderot Paris 7

Antonio Cardillo

Regione Molise

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Between the end of January and mid February 2012, the Italian peninsula has been subject to the influence of many advections of arctic-continental air generating a series of cyclogenesis over the central Mediterranean Sea. This caused widely spread mainly snowy precipitation, often persistent, mostly affecting the central-southern Regions, as well as Rome and Naples. Snowfalls and low temperatures caused some sixty casualties, besides huge damage to economic and productive facilities. The analysis of a large number of nivometric monitoring points, belonging to different institutions (Meteomont, Military Aviation, Civil Protection and Universities) allowed evaluating the spatial distribution of total snowfall. Comparing these figures with those referring to past perturbation phases similar in length - recorded in the winter of 1929, 1956, 1985 and 2005 - demonstrates that the 2012 event can be considered exceptional being characterized by a higher total thickness of snow cover almost everywhere along the hills and low mountains of the Adriatic side of Central Italy.

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THE FEBRUARY 2012 EXCEPTIONAL SNOWFALL ALONG THE

ADRIATIC SIDE OF CENTRAL ITALY

ISCI

, M.

AZZINI

with collaboration of

G.B

ELTRANDO

CARDILLO

and

V.R

OMEO

University of Camerino, School of Environmental Sciences, Camerino, Italy.

University of Ferrara, Department of Physics and Earth Sciences, Ferrara, Italy.

Université Diderot – Sorbonne Paris Cité, UMR 8586 du CNRS, Paris, France.

Regione Molise – Department of Civil Protection – Campobasso, Italy.

Ministry of Agriculture and Forestry – Servizio Meteomont – Rome, Italy

Corresponding author: Massimiliano Fazzini, University of Ferrara - Department of Physics and Earth Sciences – Via Saragat, 1 –

44100 Ferrara; email: fzzmsm@unife.it

Abstract – Between the end of January and mid February 2012, the Italian peninsula has been subject to the

influence of many advections of arctic-continental air generating a series of cyclogenesis on the central

Mediterranean Sea. This brought to diffuse mainly snowy precipitation, often persistent, mostly affecting the

central-southern Regions, as well as Rome and Naples. Snowfalls and low temperatures caused some 60

casualties, besides huge damage to economic and productive facilities. The analysis of al large number of

nivometric monitoring points, belonging to different institutions (Meteomont, Military Aviation, Civil

Protection and Universities) allowed to evaluate the distribution of total snowfall. Comparing these figures

with those referring to past perturbation phases similar for length - recorded in the winter of 1929, 1956, 1985

e 2005 - it was possible to realize that the 2012 event can be considered exceptional being characterized by a

higher total thickness of snow cover almost everywhere along the hills and low mountains of the Adriatic side

of Central Italy.

Zusammenfassung - Zwischen dem Ende von Januar und der Mitte von Februar 2012, wurde die italienische

Halbinsel von der Ankuft der artische-kontinentale Luft getroffen, die ein Cyklogenesis im Raum des

zentralen Mediterran bewirken. Es folgen verbreitet, schneeige und andauernde Niederschlaege, die am

meistens die suedliche Regionen Italiens sowie die Staedte von Rom und Neapel treffen.Der Schneefall und

die niedrige Temperaturen haben etwa 60 Personen getoetet und die gesamt Produktionswirtschaft

beschaedigt. Von der Analysis von vielen nivometrischen Kontrollpunkte, die zu verschidenen

Forschungaemte gehoeren (Meteomont, Aeronautica Militare, Protezione Civile, Universitaet), hat man die

gesamte Schneeakkumulation rechnen gekoennt; von dem Vergleich der bestehende nivometrische Daten und

der historischen Winterdaten der Jahren 1929, 1956, 1985 und 2005, hat man beobachten gekoennt, wie das

neue Ereignis im Raum des Huegelgebietes des mittleren adriatischen Hanges “aussergewoehnlich” erklaert

koennte.

Keywords:, February 2012, exceptional snowfall, Central Italy

Introduction –

This study aims at

analyzing

descriptive and dynamic climatologic features

of the atmospheric events which caused diffuse

snowfalls on most of Italy, and particularly the

central portion of its Adriatic side, during the

first two weeks of February 2012 These

phenomena, defined as “never occurred in living

memory” by almost every mass media, have

been sided by strong northern winds and a

definitely severe thermal scene, even though not

as much as in February 1956 and January 1985.

They caused some 60 casualties and economic

damage for ca. 1’000 million Euros, besides

roof collapses in more than 400 buildings and

long lasting seclusion of more than one hundred

villages in the hilly and mountainous sectors.

The Adriatic side of Central Italy every winter

is affected even at low elevations by often

abundant snowfalls. Notwithstanding this, until

a few years ago the monitoring of snowfalls has

been limited to the higher portion of the

Apennines; as a consequence, studies on

climatology of snowfalls and related synoptic

observations are very rare and mostly deal with

the mountain area (Fazzini et al., 2005 il y a

deux Fazzini 2005, precise ex 2005a, 2005 b;

Fazzini, 2007; Fazzini & Romeo, 2011).

The study area –

The study area almost

exactly corresponds to the Adriatic side of

central Italy, including (from the North to the

South) the Emilia-Romagna, Marche, Abruzzo

and Molise Regions. It covers more than 35’000

sq.kms and is characterized by the presence of

the Central Apennines, a rather well organized

mountain belt siding to the West the Adriatic

Sea running almost in parallel at a distance

generally ranging between 40 and 60 km; this

distance becomes progressively larger to the

north (where the narrow coastal lowlands give

way to the wide Po Plain). To the south, the two

major reliefs of the Apennine are included: the

Gran Sasso d’Italia (2’912 m, where remnants

of the southernmost glacier of Europe, the

Calderone, are still present) and the Majella

(2’795 m).

Synoptic weather conditions on the

period –

After a first half of winter

characterized by a rather mild and really dry

climate, at the end of January the synoptic

circulation dramatically changed as a

consequence of a moderate episode of polar

stratwarming. This caused a marked expansion

towards Scandinavia of the Azores anticyclone

which thus formed a Wejkoff bridge with the

Russian-Siberian anticyclon. Accordingly,

pressure fields on the Mediterranean

progressively yield and the baric contrast

activated intense fluxes of polar air (alternately

intermediate and continental) which in turn

originated continue and repeated cyclogenesys

on the Central Mediterranean area. As a result,

weather was continuously perturbed, with

diffuse instability phenomena.This atmospheric

event can be split into two phases, separated by

a period of relatively weak snowfalls.

The first phase (January 31

February 4

)

– During the last day of

January 2012, intermediate polar air currents

connected to a well-structured low pressure

system coming from the British Isles reached

the Mediterranean through the Rhone valley;

this caused rapid cyclogenesis in the lee of the

Maritime Alps, along the Ligurian Gulf; the jet

at altitude determined a strong advection of

potential vorticity (APV). Orographic and

synoptic features brought the cyclonic structures

to move very slowly Southeastward, attracting

gradually colder and rather unstable currents

from the East on the Adriatic sectors. These

additional thermal contrasts determined the

typology of precipitations (even thunderstorms),

which reached their peak on February 1

and 2

along the hills and low mountain area between

the Romagna and Marche Regions and on

February 2

and 3

in the high valleys of

Abruzzo and in the upper Molise (Sangro,

Aterno).During this phase, snowfalls

sporadically affected the coast, particularly

because of the strong northern winds stirring

atmospheric layers near the ground and bringing

heat from the sea, whose temperature was

around 12 C. Between February 3

and 6

currents came from southwest at altitude and

from northeast at the ground, where the freezing

level dropped to the sea level. This induced a

secondary but significant phenomenology in the

whole study area, especially in February 4

with snowfall down to the coast and significant

accumulations on the ground along hills and

foothills exposed to the first quadrant, as a

consequence of an intense stau effect.

The second phase (February 9

February 12

)

– Between February 6

and

, the cyclonic area migrated to the Central

Mediterranean, thus favoring short weather

amelioration even though temperatures become

even lower, mostly during the night. On Friday

, a new very cold vorticity nucleus,

originated on Scandinavia and present up to

500Hpa geopotential, reached Italy deepening

on the Tyrrhenian and bringing a new

significant worsening of climate. The most

significant effects have been observed on

Saturday 11

and Sunday 12

, when the entire

study area was affected by heavy snowfalls -

more abundant once again between the

Romagna and the Marche Regions - with

summed up to some 150 cm along some

windward Apennine slopes. Progressive

reduction of the phenomena has been observed

starting from the north since the morning of

February 13th.

Observations at the snow fields

A large amount of monitoring points (about

230) located at altitudes ranging from the sea

level up to ca. 1’900 m have been taken under

observation; most of them belong to the

monitoring networks “Nevemont” and

“Meteomont”, both managed by the “Corpo

Forestale dello Stato” (State Forestry); the

“Nevemont“ network, covering hills and plains,

is mostly used by the Civil Protection. Further

observations have been collected from the

monitoring networks of the Meteorological

Services of the regional functional centers for

Civil Protection of the Emilia-Romagna,

Marche, Abruzzo and Molise Regions. The

latter have generally been created in the late

‘90s; from ca. 1920 up to their establishment,

snow cover was surveyed by the former

National Hydrographic Service (Ministry of

Public Works).Despite the change of operators

and the heterogeneity of the Institutions in

charge of the measures, surveys always

followed the same methodology, i.e. reading of

the total height of the snow cover on a vertical

graduated rod, at around 9 am each day.

Sometimes, this observation is sided by an

estimation of the amount of fresh snow

deposited during the last 24 hours, measured

over a small wooden board left clean and

horizontal every day above the snow blanket.

Unfortunately, in some places the location of

the measuring rod has been significantly

changed (sometimes bringing it to places with

an altitude that differs for several hundred

meters).Notwithstanding this lack of

homogeneity, it has been possible to compare

the February 2012 event with the most

conspicuous snowfalls of the last century, i.e.

with those having long duration and strong

intensity (Table 1; data deriving from stations

that have been significantly moved are in italics

while minor displacements have been

disregarded). Snow cover measurements in a

mild climate (such as the “almost-

Mediterranean” one of the Adriatic hills) are

always difficult to carry out and often bring to

underestimation as a consequence of fast

rearrangement processes affecting the snow in

the period comprised between the observations

(typically 24 hours) and, mostly, because of the

strong winds irregularly reshaping the blanket

during and/or after the snowfall.No significant

relationship between snow cover and altitude

(Fig. 1) has been found (R

=0.17 for linear

correlation, slightly better for higher order

interpolators, cela est fonction du nombre de

points utilizes pour faire ton calcul, mais OK sur

le fait qu’il y a peu de relation entre les deux);

also the spatial distribution of total snowfall

(Fig. 1) is uneven and difficult to describe.

Anyhow, it is important to highlight the peak

present at altitudes ranging around 500 m,

corresponding to stations located on the hills

between the Marche and Romagna, where

snowfalls were particularly abundant.The map

in figure 1 has been interpolated using GIS tools

(ESRI ArcInfo 9 and Intergraph GeoMedia Pro)

basing upon all the 228 available recording

stations, also taking into account a huge mass of

unofficial data that allowed to reconstruct at

best the pattern of snowfall distribution. It

highlights a noteworthy regularity of snowfall

distribution in the Romagna foothill area (inland

of Rimini), with isolines becoming closer

approaching the higher reliefs, thus confirming

the relevance of stau phenomena connected

with the complex orography of the sector. This

observation is confirmed by the penetration of

isolines along the bottom of some of the wider

valleys, i.e. by thicker snow cover on the low

hills close to the coast than on inner valley

bottoms. The 100 cm isoline is generally located

close to the coastline, exception made for the

wave-cut reliefs of the Ancona area, where also

along the coast higher values were recorded;

this once more testifies for orographic

precipitation, since elsewhere all along the coast

and in the terminal reach of the valley bottoms

the thickness of the snow blanket never exceeds

80 cm. Generally, on the hills closer to the sea

and along the intermediate reaches of the

valleys the overall snow cover ranges between

100 and 150 cm, to reach 150-200 cm on the

Romagna plain and on the inner hills of the

Marche, exceeding 200-250 cm in the

mountainous sector. The most outstanding

figures (250 to 340 cm) have been recorded

along the foothills at the boundary between

Marche and Romagna, with a peak exceeding

350 cm in the Mt. Carpegna (whose top reaches

1415 m) area. In this sector, noteworthy is the

snow cover recorded in the town of Urbino (426

m), where the cumulated values reached 326 cm

and 200 centimeters of snow was measured on

the ground (Serpieri Meteorological

Observatory, personal communication, fig. 3).

Conclusions –

Comparing the records of the

2012 event with the historical ones referring to

the most conspicuous snowfalls of the last

century, collected for some 60 sites in the study

area (Table 1), it clearly emerges that this last

snowfall is indisputably to be considered as

exceptional along almost all the Adriatic side of

Central Italy, where its return time could be

considered more than centennial; as an instance,

the Serpieri Meteorological Observatory

(Urbino) evidenced that the overall snow cover

in 2012 was the most abundant from 1884,

whilst in the neighboring Republic of San

Marino it was very similar to that unofficially

measured in January 1895 (as referred by

NimbusWeb). Anyhow, as also observed in the

extremely snowy winter 2004-2005 (Fazzini et

al., 2005), the highest cumulative snowfalls

have been recorded at altitudes ranging between

400 and 800 m a.s.l., while they tended to

decrease at higher elevations. This observation

confirms that in almost all the study area a

meteoric “optimum” exists at altitudes between

600 and 900 m (Bisci et al., 2002); it could also

have been influenced by the strong action of

winds that dramatically remodeled the snow

blanket, mostly along the tops of the reliefs and

the ridges. Only locally, i.e. along the wind

exposed mountain slopes in the southern part of

the study area - in southern Abruzzo (e.g.

Pescasseroli) and in Molise (e.g. Capracotta) -

the figures recorded in February 2012 are

slightly lower than those measured during the

most conspicuous events of the last century.

Acknowledgements -

A special thank goes

to the Regional functional centers for Civil

Protection of the Emilia-Romagna, Marche and

Molise Regions, for having furnished

nivometric data and for the help given in finding

historical records, to Dott. Francesco Costanzo

for the linguistic revision of the paper and to the

many observers that gave us a huge amount of

unofficial data that were instrumental for a more

detailed regionalization of the official data.

References

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C.,

AZZINI

OCCIA

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Analyse spatio-temporelle des séries de

températures dans l’Apennin centro-

meridional italien per rapport aux

paramétres topo-géographiques. Actes XV

Colloque AIC “Application de la

climatologie aux echelles fines”, 29-30.

AZZINI

M. (2007) – Caratterizzazione generale

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AZZINI

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Figure1 – The Study area. White lines depict the distribution of total snowfall in the studied period,

while dashed gray lines follow the regional boundaries. For every station the overall recorded snow

thickness is indicated. The graph evidences poor relationship between total snowfall and elevation.

Figure 2 –500 hPa and T850 geopotential at 00:00h, February 2

(left) and February 10

(right)

(source de la carte ???)

Figure 3 – Exceptional snow cover in the neighboring of Urbino (to the left) and in the Republic of

San Marino (right). Source photos

Table 1 – Cumulated snowfall (cm) for the five most relevant events of the last century in the study

area. Maximum values are highlighted in bold. In particular, the 1929 snowfalls apply to the

period February 6 - 19, the 1956period of February 3 -19, those of 1985 to the period January 2 -

18, those of 2005, to the period 24 January -3 February

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Oct 2006

The major patterns of interannual Swiss Alpine snow pack variability were determined and their relation to local and large-scale climate variability and recent trends was investigated. The snow variables considered were the seasonally averaged new snow sum, snow depth and snow days for winter (DJF) in the period 1958-1999. Three major patterns of large-scale snow variability were identified. The first pattern explains ∼50% of total variance and extends over the entire area except the southernmost parts. The second pattern explains ∼15 % of total variance and has a dipole structure with a maximum on the northern and a strong minimum on the southern slope of the Alps. The third pattern (∼10 % of total variance) is height dependent with a strong maximum at lowland stations and a minimum at high stations. In contrast to the first and second pattern, the third pattern's time component shows a distinct trend. It is well correlated with the 0°C isotherm which increased from ∼600 m a.s.l. in the 1960s to ∼900 m a.s.l. in the late 1990s and could be related to climate change. Variability in the first new snow sum pattern was primarily related to total precipitation anomalies. In contrast, variability in the first snow day pattern was primarily related to temperature anomalies. The dominance of precipitation for new snow sums and the dominance of temperature for snow days is physically consistent with the former being controlled by accumulation only and the latter by accumulation and ablation. The surface pressure anomaly pattern linked to the first new snow sum pattern is centred over southeastern Europe, resembling the Euro-Atlantic blocking pattern. For snow days the corresponding pressure anomaly is shifted further southeastward. The second snow pattern is mainly influenced by an East Atlantic like pattern, whereas only the third (height and temperature dependent) pattern is strongly linked to the North Atlantic Oscillation index.

Snowfall analysis over peninsular Italy in relationship to the different types of synoptic circulation: First results

Article

Jan 2005

The time series of snow data for a sample of Italian meteorological stations have been analyzed taking into account, for the time series, an acceptable continuity and quality of meteorological data. The data set is that of the Italian Meteorological Service (UGM), and refer to the period 1982-2004. The Slovenian station of Kredarica, located in the Julian Alps, has been added for convenience. The study is composed of t wo different parts: - Climatologic analysis of the snow parameters during the last 20 years. In particular, the height of the fresh snow and the number of days with permanence of snow at the ground have been analyzed. - Evidence of the synoptic situations in which snowfalls are observed with at least a thickness of 10 cm in at least a third of the total number of analyzed stations in Central, Southern and insular Italy.

Classification, Seasonality and Persistence of Low-Frequency Atmospheric Circulation Patterns

Article

Jan 1987
MON WEATHER REV

Orthogonally rotated principle component analysis (RPCA) of Northern Hemisphere 1-month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability. The analysis is detailed and comprehensive, in that 1) a high resolution, approximately equal-area 358-point grid is used for the virtually maximum possible 35-yr period of record, 2) a positive bias in the NMC data base in the early 1950s in the subtropics is largely eliminated for the first time, and 3) homogeneous, separate analyses of each month of the year are carried out, detailing the month-to-month changes in the dominant circulation patterns. The conclusion from all considerations is that the RPCA method provides a physically meaningful, as well as statistically stable product with the simplicity of teleconnection patterns but with pattern choice and depiction superior to those of the teleconnection method. -from Authors

Spatial, Temporal and Intensity Characteristics of Heavy Snowfall Events over Austria

Article

Jan 1999

Gerald Spreitzhofer

Statistical aspects of intense snowstorms over Austria are discussed based on the daily fresh snow depth-recordings from a sample of 81 stations over a 19-year period from the 1970/71 to the 1988/89-winter seasons. The study focuses on heavy snowfall events (HSEs) defined as at least a 20 cm-intensity threshold for a 24-hour accumulation of new snow. Calculation of the geometric center of the area experiencing heavy snowfall allows for the estimation of storm spatial characteristics (e.g., its expansion, eccentricity, and the number of stations involved) and the objective assignment of storms to one of four distinct regions, located to the north and south of the Alpine main crest. Temporal characteristics investigated include the annual and seasonal frequencies of HSEs, whereas considerations of intensity put an emphasis on the average and maximum new snow-depth from intense storms. The biggest 24-hour snow accumulation within the period of study was 170 cm, measured at Sillian (Eastern Tyrol) in 1986.

Classification, Seasonality and Persistence of Low-Frequency Atmospheric Circulation Patterns

Article

Jul 1987

The seasonality and persistence of the major modes of interannual variability in the low-frequency atmospheric circulation were studied using orthogonally rotated principle component analysis (RPCA) of Northern Hemisphere 1-month mean 700 mb heights. The twice-daily data for the 1950-1984 period were used. Winter results are similar to those of other recent RPCA and teleconnection studies. The strongest summer pattern is the North Atlantic Oscillation, which is also the strongest winter pattern; it systematically contracts northward in summer and expands southward in winter, being the only pattern found for every month of the year. The robustness of the RPCA results was examined through consistency with results of other studies and of adjacent month solutions within this study, as well as by replicating the results using 3-month and 10-day means of 700-mb height. It is concluded that the RPCA method provides a physically meaningful and statistically stable product with the simplicity of teleconnection patterns but with superior pattern choice and depiction.

The February 2012 exceptional snowfall along the Adriatic side of Central Italy

Abstract

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