By Joseph D'Urso LONDON (Thomson Reuters Foundation) - Vulnerable migrants and refugees arriving in the Western Balkans are facing the onset of heavy rains and cold weather, with many unprepared for bitter winter conditions, the Red Cross has warned. Sea crossings to Greece's shores have fallen this week because cooler, windier weather is making the journey more dangerous, though numbers could pick up again if conditions improve, the United Nations' refugee agency (UNHCR) said on Friday. "The arrival of winter will push people's coping skills to their limits," Simon Missiri, acting director for Europe of the International Federation of Red Cross and Red Crescent Societies (IFRC), said in a statement on Thursday.