--A heat wave seems to have locked in over the South American mid-continent with every likelihood that it will hold through at least Saturday.

Metsul say that this heat wave set a record for electrical demand in the southernmost Brasil state of Rio Grande do Sul on Tuesday.

On Tuesday, Porto Alegre, Rio Grande do Sul, Brasil, topped out 37C, or 99F. And with apparent temperature to at about 44C, or 110F. Normal high would be 30C. Overnight, the low was about 27C, or 80F, versus normal of 21C.

The night was even more sultry at Santa Maria, in the heart of RGS. The overnight low here was 29.6C, or 85F.

Already, as of 1600 UTC on Wednesday, the temperature at Porto Alegre has reached 37C. Farther south, Pelotas has seen 38C, or 100F.

-Flip side of the big heat wave is the strong, drenching thunderstorms that will erupt along its southern rim. Already, as of early Wednesday, thunderstorms have poured 50 to 100 mm of rain over much of Buenos Aires, the heart of Argentina`s Pampas, through the southern half of Uruguay. I reckon that high amounts in heaviest cloudbursts would be about 150 mm.

So, the southern rim of the heat (one may call it a cold front) will alternately swell northward and back southward right through the weekend. Fueled from the north by steamy tropical heat, this weather boundary will continue to spark heavy, inundating thunderstorms. Storms will trigger flooding downpours and high winds, even hail.

Once or twice through Saturday, the northern reach for thunderstorms will cross into southernmost Rio Grande do Sul, Brasil, but it seems unlikely that any such storm would reach Porto Alegre.

--Another winter storm followed a big warm-up over northwestern Turkey early this week. At Yesilkoy airport, near Istanbul, snowfall was about 4 cm. Snow fell at the tail end of the storm, most of which yielded rain. The cold rain and snow followed three warm days having highs of 12.8C to 15.6C.

It looks to as though the next winter storm for western Turkey and the Aegean Sea region as a whole will happen between Sunday and Tuesday.

Image Credit: COLA--www.wxmaps.com

--More on the Black Sea storm. It is forecast to translate eastward to Central Asia sparking heavy snow and high winds in the greater Caucasus. Western Iran should get some soaking rain and mountain snow, too. Significant rain could invade the desert of central Asia with snow in nearby mountains.

What I want to underscore, however, with respect to this storm, is the potential for its Western Disturbance to shed badly needed rain and snow along the Himalaya and its foothills as far east as Nepal. Pakistan and India would benefit mightily, were this to happen.

Other areas from Yemen to Oman to Afghanistan and southwestern Pakistan could also see meaningful, even abnormal, rain in the wake of this weather system between Friday and Monday.

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Tuesday afternoon, the temperature rose above freezing at Istanbul (Yesilkoy) airport for the first time since Saturday morning, local time. Thus brings to an end the coldest stretch of weather so far this winter. A few highlights here:

--Coldest was -6.6 C early Tuesday morning.

--Snowfall of about 12 cm, spread over Saturday through Monday.

--Winds reached 80 to 100 kph back on Saturday as the core of the cold swept in from the north.

--Wind chill dipped to -10 C on Saturday.

Elsewhere, snow fell widely over northwestern Turkey along with interior highlands across the full breadth of the nation. Near the shores of the Black Sea, heavy rain fell ahead of heavy snow. Rain and snow had water equivalent of about 10 cm in both Giresun and Hopa. Snowfall at Giresun topped 30 cm through Tuesday morning.

--Here is how this all came about. First, a cold outbreak settled southward over the Ukraine and Russia to the Black Sea and eastern Balkan Peninsula. Low pressure was set over the Black Sea owing to the contrast between arctic chill and the sea's relative warmth. Strong northerly winds shunted between the Black Sea low and the Balkan Mountains. Moisture to trigger snow came both by way of the Mediterranean and Aegean seas, and directly from the Black Sea.

--Elsewhere, cold and snow have had a much harsher impact than that in Turkey. In Bulgaria, the aftermath of two windswept snowstorms, the former being more severe, left 25 to 50 cm snow depth along the Black Sea coast. On Monday and Tuesday mornings, cold spots in Bulgaria reached -20 C to even -25 C.

--Harsh cold has also been felt since last Saturday over the Ukraine and Poland. The last two mornings have seen lows down to -25 C and even -30 C in Poland to the western Ukraine.

--Looking forward, it is fair to say that the brunt of cold will lift northward from the Black Sea with moderation in the cold for Turkey. Farther west, however, the weather is going to become unsettled with persistent cold over the heart of Europe southward as far as Italy and Greece and westward into France and the United Kingdom.

--I understand from Noman, writing from Pakistan, that the lack of winter rain and mountain snow is raising fears of drought in the north of his country. This drought is related to the behavior of Western Disturbances. I cannot say whether this is a flat-out lack of WDs or a lack of moisture with an otherwise normal number of such weather systems.

Image Credit: COLA/www.wxmaps.org

During the next few days, a WD related to the latest Black Sea storm will bring some rain and mountain snow to the far northwest of the Subcontinent. It will even trigger spotty rain along the Makran Coast to near Karachi. Yet, if the drought is as serious as implied, it will take many more such weather systems to break it.

--Another weather hot spot to watch through the week will be Queensland, where the former Tropical Cyclone Olga has become a remnant tropical low stalled over the south shore of the Gulf of Carpentaria. This low is shown by numerical forecast models to persist and even strengthen before drifting southward and southeastward late in the week. A swath through Queensland striking southeast from the Gulf to the east coast will be prone for localized rainfall of 25 to 50 cm through Friday. Southeastern Australia could become involved in this weather setup at the end of the week.

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--Winter has been slow in coming to Turkey and Greece, notwithstanding the cold outbreaks that have chilled the rest of Europe. At Istanbul airport, west of city center in nearby Yesilkoy, average monthly temperature for December was 2.4 C above normal. Through Monday, January was warmer than usual by 4.1 C with no measurable snowfall.

As of Tuesday, however, the first shot of wintry cold struck northwestern Turkey. Cold, windswept rain Monday night yielded to wet snow on Tuesday. The temperature slipped to near freezing during the afternoon.

Elsewhere in the northwest, snowfall was 13 cm at Edirne and 5 cm at Tekirdag. However, amounts were much higher in Bulgaria with nearly 30 cm on the Black Sea at Varna.

Indeed, Varna was near the heart of the parent storm which set up over the Black Sea as of early Tuesday. Varna was hit, first with rain, then with sleet followed by heavy snow. Strong northern winds shunting cold out of Russia and the Ukraine squeezed between the Black Sea storm center and the Balkan mountains. Caught in the path of these winds, Varna was hit with much blowing and drifting snow.

--Unsettled weather will persist for a few more days along with stubborn low pressure, both in Turkey and the Black Sea region overall.

Things will become more "interesting," for weather enthusiasts, come Friday and Saturday. At this time, another low by way of the Ionian and Aegean seas will renew the Black Sea low, triggering another northerly cold outbreak down the western shore to western Turkey and Greece.

Being colder than the last, this coming shot will spark snow farther south and east. For Istanbul itself, this coming outbreak will have stronger, harsher winds. After starting as a cold rain, precipitation will become snow that will be heavy enough to settle over the city. Snowfall will depend in part upon proximity to the still-warm Black Sea, the frost (sub-freezing temperature) being stronger and beginning sooner westward from the city center.

Snow will lay elsewhere in western Turkey and in northern Greece, albeit with details of where and how much being beyond to the scope of this column. Bulgaria`s coast will withstand a harsh shot of biting cold wind and snow, and maybe heavy snow.

Here is a look at the 1200 UTC, Tuesday, GFS numerical forecast near-ground wind field for 1200 UTC, Saturday. The streamlines indicate a low pressure center hugging the shore east of Istanbul. Between the low and the eastern Balkan Peninsula lie forecast 30-knot winds--near gales. And strong northerlies (cold!) into northwestern Turkey through the Aegean Islands of Greece.

At the following morning, 0600 UTC on Sunday, this would be the surface temperature pattern, based upon the same, as above, GFS model run. What stands out here is the cold tongue (below -10 C) poking southward over northwestern Turkey (west of Istanbul) from the "mother lode" over the Ukraine and Russia. Well shown here is the far warmer Black Sea, including leeward shores eastward from the Bosporus.

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Image credit: COLA--www.wxmaps.org

I cannot recall seeing so much rain forecast by a numerical forecast model for Egypt and northwest Arabia. I am talking about highest rainfall of 10-15 cm in an area from south of Cairo east to Sinai, also the Nile Delta. Amounts to at least 5 cm along the northern Red Sea coast of Saudi Arabia to the desert of southern and eastern Jordan. Frame of time would be late Sunday through late Monday, local time.

So, what is the trigger for so much rain? In short, a strong wave-cyclone (mid-latitude storm) tracking east along the north shore of Africa. As of Saturday, this storm is whipping up coastal rain and strong winds over Libya and Tunisia. The low pressure center is forecast to track east along the coast. But the upper trough supporting the storm is forecast to dip sharply southward over the Sahara as the whole package shifts eastward.

It is the sharp southward dip in the trough and winds aloft that is key to the forecast of extreme rainfall. The resulting southerly wind flow will tap equatorial moisture to feed the downpours, although Red Sea moisture will likely factor in, too.

Upon reaching the Nile Delta, the storm center is forecast to hook northeastward to Cyprus and central Turkey. This turn will aim the core of its heavy rain northeast through Palestine/Israel, Lebanon and Syria into much of Turkey. This would include substantial rainfall for northern and western Iraq as well as the desert of eastern Syria, northeastern Jordan and even northernmost Saudi Arabia.


An interesting aspect of this storm is its potential to snow upon some unusual spots. Among these would be the mountain spine (I do not know its name) of eastern Egypt. Another would be the highlands of Sinai such as Gebel Musa. The cold at the core of the trough could "catch" the trailing edge of the rain, leaving tops above 1,500 meters whitened with snow.

OTHER ASPECTS OF THE STORM...

Thunderstorms will contribute to the rain output. I see potential for severe thunderstorms with high winds and hail on the plains of northwest Iraq, east Syria and eastern Jordan, to name but a few.

Then there is the wind itself. Reaching 60-100 kph over wide areas, these winds would raise widespread clouds of thick dust over deserts of Egypt to northwest Arabia, Iraq and eastern Syria.

Oddest, maybe, of the likely aspects of this storm would be wind-set high tides (flooding?) on the northern Red Sea; most of all, the Gulf of Suez and the Gulf of Aqaba. For not knowing better, I would have to wonder whether high tides on the Gulf of Suez would drive a substantial northward flow of water through the Suez Canal.

By wind-set, I mean tides raised by the long fetch of strong southerly winds over much of the Red Sea. Add to this the effect of strong south-to-north pressure gradient over the Red Sea.

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--A broad and well-marked atmospheric trough (Western Disturbance or W.D.) will track out of Iran and northeastern Arabia to the northern Subcontinent during the next two to three days. In so doing, it will trigger scattered outbreaks of rain, even a thunderstorm here and there. Coverage of rain will tend to thin towards the east.

Through Sunday, tropical moisture flowing towards the W.D. from the south will also trigger hit-or-miss downpours along the Western Ghats.

--The GFS numerical forecast model is once again hinting at anomalous wet weather during the second week of January beginning at about the 7th. This would start in Sri Lanka and the state of Tamil Nadu, then expand to Kerala and Andhra Pradesh.

Coincident with the forecast rainy outbreak over the South East would be some kind of cyclonic disturbance, maybe a tropical cyclone. Too early for me to have any confidence here.

--December's cold wave in Europe yielded during the last week of the month to moderating Atlantic winds that broke through from the southwest. Yet it kept a stronghold over the British Archipelago and Scandinavia.

Now, look for arctic cold to regain ground over Europe such that Iberia to Italy and the western Balkan Peninsula will become solidly cold in time for early next week. Daily temperatures 5C to 10C/10F to 20F below normal will spread widely.

Along with the Europe cold wave will be widespread light falls of snow. Localized heavy falls will happen along the Atlantic-Mediterranean storm track, suppressed as it be by the south-flowing cold.

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