>1 May, 2011

Written by on May 1, 2011 in Rest of Europe with 0 Comments

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TODAY’S TOP WEATHER STORIES
On Weather & Climate Through the Eyes of Mark Vogan

Latest News From Devastated South

From the Networks

Another EF-5 Declared From Wednesday’s Outbreak
ACCUWEATHER.COM

Thousands Mourn Southern Tornado Victims
FOX NEWS

Tornado Outbreaks Then and Now – Apples and Oranges?
THE WEATHER CHANNEL

TODAY’S WEATHER ACROSS UK & EUROPE By Mark Vogan

Continued wet & unsettled across Iberia, spreading eastwards across the Mediterannean. UK remains settled, warm and mostly sunny

As an upper low drifts northwards out over the Bay of Biscay, this opens the southwestern door to more rainfall across much of Iberia, holding temperatures in the upper teens and low 20s C. Dissapointing to many who may have chosen to vacation across the region at what would be considered a ‘nice and comfortable’ time of year. Unfortunately modelling would suggest a degree of persistency across much of the Portugal-Spain landmass in the unsettled, showery and relatively cool weather through certainly the first half of the new week.

As for the southern Europe-Mediterannean region, this unsettled, low pressure influenced weather will push hefty, persistent rains across much of Italy and across Greece and all the way into Turkey. This will hold highs to perhaps only 22 or 24C at best for typically warmer Rome and Athens.

UK holds on to some of the best weather in all of the continent

The UK and northern France as well as the low countries of Belgium and the Netherlands into Germany will enjoy mostly sunny weather and temperatures ranging from 18 to 24C (66-75F) and this looks set to hold for the forst half of the week before a trough drops into central European, bringing cooler, breezier and more wetter weather into Germany, Poland on eastwards. The UK may hold onto the more sunnier, milder weather despite the dissapointing turn in the weather over the central continent.

TODAY’S WEATHER ACROSS AMERICA By Mark Vogan

Huge cooldown across much of US, arrives into north Texas today, Storminess to slowly creep further east, eventually providing flooded areas with a break

The strong storm that’s now spinning across western Ontario which produced 6-12 inches of snow, a blizzard and gusts to 80 mph has send a cold front down into central Texas today, shoving the intense heat east into the Southeast today and bringing a refreshing, cool and dry air flow in, all the way from Canada. Highs throughout north Texas won’t get out of the 50s, a HUGE contrast to what this state has seen the the last month with 80s and 90s dominating. Far south and southeast Texas will remain hot as the strong cold front won’t reach as far as this until tomorrow and Tuesday, therefore highs in the lower Rio Grande Valley will reach the low 100s once again while a hot, stickly 90 degrees should be reaches in Houston this afternoon. Areas to the north over Dallas and across to San Antonio and Austin may see showers, thunderstorms and these may turn severe as the heating process kicks in and the due to the fact this is a strong cold front with a very substantial thermal contrast this boundary is seperating. Afterall, 50 degree air and low dew point air lies just behind it, while 90s and 100s remain ahead of it…

The above graphic, shows the huge area of the country this front has carved out and dropped cool, dry air into. As you can clearly see from the current position of the front, that South and Southeast Texas awaits it’s arrival, thus heating and incoming humidity off the Gulf won’t be held back, but note the low that’s formed, this may energize those upper-levels and therefore this is why the risk is there for thunderstorms turning severe, especially around 4pm onwards. I would’nt be surprised to see a few tornadoes touchdown in areas such as around San Antonio, Austin and even up into the Shreveport area of Louisiana.

This cold front lies in the same spot unfortunately where most of those fronts have be stalled out over. A primary reason behind the ‘training storms’ and the resulting flooding from Arkansas up through Missouri and into western and central Tennessee and Kentucky. More heavy showers, thunderstorms and potential severe weather is likely through today and tonight. You know the drill if you live here. Keep checking back to the your weather information provided by your TV, Radio and internet….

Just look at the shear strength of the chilly airmass flowing all the way down and into the Southern Plains from Canada. The mid-20 degree departures from normal is most impressive considering the hot month and a half it’s been in this drought and fire stricken region. It’s a complete flip from just 24 to 36 hours ago. Also note the 5 to 10 degree above normal temps to the south/southeast of the boundary.

TEXAS COOLDOWN: Highs range from upper 40s/low 50s in north to upper 90s/100s in south

WEATHER TALK
By Mark Vogan

SPECIAL ARTICLE

THE PHYSICAL NORTHWARD MIGRATION OF THE SUB-TROPICAL HIGH, ITZC/EASTERLY AFRICAN JET & TRANSITION FROM DRY SEASON TO WET OVER AFRICA

Today’s upper pattern over Africa, note the trough off Morrocco, suppressing heights across north Africa & Sahara. 

North Africa still somewhat cool, Sahel & Sub-Sahara is hottest for now and to get hotter through this week.

ITCZ still over the Equator at the moment as the pper-level sub-tropical high migrates northwards with the hot, dry season continuing across the Sahel/Sub-Saharan belt. As for the Sahara, well it’s still spring with mostly comfortable temperatures with low’s still managing to soak area, bring clouds, wind and cool air in off the North Atlantic and down from southern Europe as pressures remain relatively low still.

The hottest temperatures across Africa are centered over the Sahel and Sub-Sahara region with the strongest pressures overhead.

The hottest period of the year is right now over the countries SOUTH of the Sahara Desert, while days for most of the Sahara Desert and north African Mediterannean coastline is warm and sunny for the most part with areas of rain, cloud and cooler temps where lows are nearby, this is the pleasant and comfortble time to visit the countries stretching from Morrocco, Algeria, Libya and Eqypt with daytime highs generally reaching 25-32C (77-90F) and if you don’t mind the odd shower or two. With the core of heat further south, the north awaits the true blow torch that’s imminent now through the next 30 to 40 days.

Upper pattern over Africa for Tuesday (May 3rd), note pressure height rises expanding over Sahel/Sub-Sahara region. Libya & Eqypt to get warmer but core remains to the south!

ITCZ CURRENTLY BRINGING THUNDERSTORMS EAST TO WEST OVER EQUATORIAL AFRICA

It’s part of the seasonal northward progression of the high which is strongest further south at this time of year with March through May the hottest time as the high is too strong for clouds and rains to form. Those form along the low pressure belt (ITCZ, underneath the high pressure belt). The March through May period sees the ITCZ/low pressure belt focus close to or directly over the Equatorial countries with temperatures by night staying way up in the very uncomfortable 27-32C (80-90F) thanks to a moist air mass which the PM storms create throughout the overnight. This moisture hanging in the air holds temperatures up. By day temperatures rapidly push towards 38C (100F), the strong surface heating and this moisture rises into powerful tropical downpours which help keep a lid on the heat.

APRIL/MAY IS HEART OF THE HOT/DRY SEASON IN THE SAHEL-SUB-SAHARA REGION

In a Sahel/Sub-Saharan belt, roughly 12-18 degrees north of the equatorial belt where the ITCZ is currently, it’s the heart of the hot/dry season across the Sahel and Sub-Sahara. This encorporates the countries stretching from Senegal, Mali, Niger, Chad, Sudan and Ethiopia and at present the hottest air is overhead. This is right in the heart of this region’s hottest period of the year with average daily highs ranging from 30-43C (86-109F) along this belt.

Up next for this gruelling high pressure cell will be North Africa’s Sahara Desert and Mediterannean. While pressures remain low enough for low pressures to spin just to the north and bring rain, some of which is heavy across the Med Sea and into the Saharan region, the hot/dry air focusing on the Sahel/Sub-Sahara will over the next 2 months migrate with the sun north.

Niamey, Niger (Courtesy of Wikipedia) currently in it’s hot/dry season, will be transitioning to it’s wet season into June and July.

While it may be hot and very dry at the moment beneath the high, as this core lifts north, so too does the ITCZ zone to a possition the Upper-level Ridge is currently over, thus Senegal, Mali, Niger, Chad, Sudan and Ethiopia will end their dry season and the intense heat will ease as thunderstorms began to fire up, soaking this aid, scorched region and also the bone dry, arid air will become humid!

The problem with the high is that once it reaches it’s most northerly position and centres itself over the Sahara Desert, this is more PURE and a huge desert. Because dry ground feeds back to the atmosphere, this surface environment will force a reaction in the upper-levels of the high and will make it intensify further than what it could do over the Sahel-Sub-Sahara. The temperature at 5,000 feet we see now is generally around 24 to 30C, well once centered directly over an even more arid region, this dries out the air further and therefore the surface temperatures will be even hotter. While coastal Morrocco, Algeria, Libya and Eqypt will be very hot with not a cloud to be seen for perhaps 2 or more months and temperatures reach 38-42C (100-108F), inland and over the sands of this vast desert, high’s will on a daily basis climb to between 43C-48C (109-118F). There are always low-lying basins and valleys which will reach 49C (120F) or higher.

By next Saturday, pressure heights become much stronger than they are now from west to east across the entire sub-Sahara region, providing mid-40s C for many. Note pressure heights drop off over Sahara and particularly northeast Africa where it had got warmer in Libya and Eqypt, here temperatures likely fall back to the 80s, rather than upper 90s to low 100s.

All this is very important to the tropical Atlantic Basin, why? Well, currently there is still another month till the official start to the hurricane season, why not now? Well, the ITCZ (the thunderstorm development belt) as explained above is over the equator and always lies on the southern boundary of the sub-tropical high pressure belt. At the moment both the High pressure belt and ITCZ is too far south and even at that, these thunderstorms are over a region will minimal ‘spin’. At the latitude of the equator (0 degrees), spin is zero or minimal and that is needed for tropical storms to develop from thunderstorms that form within the ITCZ zone, The further away one goes from the equator, say 15 degrees N or more, the greater the ‘spin’ potential becomes and the reason is earth’s curvature and rotation which creates a drag or friction with the atmosphere above. Thunderstorms that form and rise off a spinning earth starts to spiral. This doesn’t happejn over the equator and the further away you go from the equator, the more spin pitential there is.

So, once the high reaches North Africa and southern Europe, this will reposition the ITCZ zone over the Sahel-Sub-Sahara region. The extreme heat produced beneath the high, creates winds to blow clockwise around the high pressure cell and thus underneath the high which is centered over the Sahara, winds blow west to east over the Sahel-Sub-Sahara region from west to east, this is known as the African Easterly Jet which is embedded within a low pressure belt in which thunderstorms can form within as pressures are strongest further north. By this stage and position, it will be around June 1st and waters temperatures off the west coast from the Cape Verde Islands westward will be a lot warmer and more sustainable for tropical systems. At the moment this water is too chilly but is warming as I write this because the high is currently overhead and heating it up.

WHAT’S ON TODAY’S WEATHERBELL BLOGS?

Sunday Snow and Severe Weather from the Atmospheric Avenger
Joe Bastardi’s Blog, Weatherbell.com

Western snowpack and precipitation trends versus modeling
Joe D’Aleo’s Blog, Weatherbell.com

THE EXTREMES OF THE DAY

TODAY’S US EXTREMES
COURTESY OF ACCUWEATHER

HIGH: 108 degrees at Laredo, TX
LOW: 3 degrees at Berthoud Pass, CO

TODAY’S UK EXTREMES
COURTESY OF THE MET OFFICE

HIGH: 70 degrees (21.2C) at Porthmadog (Gwynedd)
LOW: 23 degrees (-4.9C) at Braemar (Aberdeenshire)

TODAY’S EXTREMES HERE AT MY HOUSE

HIGH: 66 degrees
LOW: 45 degrees

Thanks for reading.
-Mark

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