FOG IN THE MEDITERRANEAN or How bad can weather become in CAVOKLAND FOG IN THE MED As everywhere, fog develops if three basic conditions are met – Moisture – Stability – Stagnation (fog trigger) How do these conditions work together in southern Europe? FOG IN THE MED Basic conditions favoring fog development – Moisture – no problem, it’s there in abundance, Med basin is a large water body – Stability – also no problem, area “enjoys” frequent Azores High ridging – Stagnation – the big problem, large local and regional differences under same type of ridging FOG IN THE MED Stagnation - the big problem of the area Reasons for stagnation – mountainous terrain with deep valleys keep any airmass “without escape” – airmass exchange basically by way of turbulent mixing which generally weakens in fall – once winds become generally weak, air doesn’t move except local valley/mountain winds FOG IN THE MED Stagnation - the big problem of the area Reasons for non-stagnation – mountainous terrain adjacent to open water area – airmass exchange also by way of turbulent mixing which often weakens in fall, but… – once winds become generally weak, local valley/mountain winds combine with land/sea breeze which keep area ventilated FOG IN THE MED Favorable areas for fog formation by region FOG FOG FOG FOG !! FOG FOG FOG Rough coastline in N & S Italy counteract stagnation, but some wider valleys along Tyrrhenian Sea coast favor fog formation FOG FOG Coastline counteracts stagnation FOG FOG FOG FOG FOG Coastline south of Izmir does not favor stagnation! FOG IN THE MED There is a distinct fog/no fog line in the Mediterranean region Practically no fog along the coast, if adjacent to a mountain range Very foggy in valleys of mountain ranges bordering the Med or over plainland further north and east FOG IN THE MED The beginning of the fog season Later than in northern Europe due to more solar insolation and more instability??? This is how it goes….. % Frequency cig/vis < 800 ft/ 1,000 m at Vicenza 80 70 60 50 Sep Oct 40 Nov 30 Dec 20 10 0 00Z 03Z 06Z 09Z 12Z 15Z 18Z 21Z FOG IN THE MED Frequency is already high in September! Fog is persistent from November onwards – Vicenza is typical Po Valley, frequency is highest in area, but trend in Bosnia is similar – Tuzla, Banja Luka, and valley stations in MND- N/S begin the trend 2 weeks later than Po Valley, and from thereon are short of Po Valley’s frequency FOG IN THE MED Typical synopsis that lead to the combined effects of – Moisture – Stability – Stagnation Azores High ridging into area via Alps is probably the most obvious way Other possibilities? Not cP yet, more mPmm Note moisture advection from Adriatic into Po Valley Washing cold front over Bosnia Moist air over Po Air mass mix over Balkans Valley stagnates! comes under ridging FOG IN THE MED Northeasterly flow over Balkans pretend advection of dry continental air Not in autumn ! – autumn is the Balkans and Po Valley’s prime rainy season, right after the summer dryness – Gulf of Genoa Lows moving northeast can soak the Po Valley before dumping all rain onto the Balkans, therefore, NE flow in wake of system has moisture-laden air waiting for the next ridge FOG IN THE MED Certainly, the combined effects of – moisture – stability – stagnation helps fog formation in the Balkans & Italy but state of the ground is also very important in the Med’s prime wet season FOG IN THE MED Evidently, the Med will soon be no longer CAVOK-land – however, the Mediterranean Sea also cools, but slowly – adjacent land masses cool much faster – latitude is still rather north – Camp Bondsteel is further north than Milwaukee, Wisconsin – which means think FZFG!!! FREEZING FOG IN THE MED Occurs where? – Italy (Po Valley) does affect our stations – Balkans, with highest frequency in our theater; does affect all our stations – Turkey (interior) not affecting our stations – Spain (interior) not affecting our stations FREEZING FOG IN THE MED Maximum frequency in the Balkans – Favorable area of air-mass mix – Favorable area for Azores High ridging or connection with the Siberian High – Strong cooling due to “bowl effect” (see Ramstein and Grafenwoehr) Conditions typically available by mid- November cP This synopsis will clear the Balkans initially, but will create FZFG 24 hours later as early as 15 October, even in Kosovo FOG IN THE MED There are different types of fog not all fog in the Med is radiation fog – Mixing fog – Advection fog – Upslope fog are fog types which do not require stagnation FOG IN THE MED Mixing Fog – develops locally, and instantaneously if colder air is mixed with warmer air and dewpoint temperature rises above ground temperature – happens frequently in the Balkans after a cold spell when air from the Med or Black Sea is sneaking in from SE or E – Happens in the Po Valley when Adriatic Sea air is sneaking westward FOG IN THE MED Advection Fog – Fog that has developed elsewhere is coming into a fog-free area, often with remains of a frontal system (moisture trapped under inversion, but air not yet stagnant) – Likewise, a stagnant air which is coming under motion and is expanding or being pushed out of area (losing stagnation) – Can happen anywhere at any time, but favorable areas are Aviano, Taszar, Tuzla, Camp Bondsteel FOG IN THE MED Upslope Fog – special sort of advection fog that is forced to lift (rising terrain) – also moist air short of fog which comes under upslope, but can not be further lifted due to strong inversion, air is cooled to condensation point, low stratus develops and touches the ground – favorable locations are Taszar, stations along NE side of Dinarics, also Aviano and San Vito FOG IN THE MED Conclusion Fog is a major problem in fall and winter Our Med desks handle areas that have the most fog frequency in the entire theater, some locations (Milan) are even worse than Fresno, CA Not all fog cases are radiation fog for which most of our tools have been developed!
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