Severe Weather Outlook Europe - Tuesday July 7th, 2015

Since I've been largely focused on Europe lately, I taught I'd continue with an interesting and potentially severe setup that will unfold in central Europe later in the day tomorrow. Below is the surface pressure map from Met Office for 12Z Tuesday and 00Z Wednesday, indicating the surface low pressure and frontal boundary crossing Europe tomorrow.

An extensive ridge across South-Central Europe will be interrupted by a strong trough from western Europe which will advance easterly towards the Benelux region in the afternoon tomorrow. This will provide large scale ascent for widespread storm initiation along the eastwards moving cold front. Current models show strong instability overlapping with moderate speed and directional shear. This would prove sufficient enough for rapid storm initiation, with a well organized environment for supercell storm development.

Until the evening, storms should remain discrete and bring large hail, very strong winds and the possibility of a tornado, while towards the evening hours storms should merge into a large cluster or two spreading towards southwest Poland and the Czech Republic bringing heavy downpours.

The areas of greatest interest to me, as shown above, will be parts of eastern France, central Germany and western Czech Republic where widespread severe storms with large hail, powerful winds, heavy rainfall and the formation of tornadoes, is increasingly likely to form ahead and along the eastwards moving cold front from mid afternoon into the late evening hours.

Strong QG forcing combined with a very unstable airmass: 2000-2500 J/kg of CAPE and very strong 0-6 km shear: 15-25 m/s within a persistently strong southwesterly LLJ: 15-20 kts should result in organized convection, including supercells and QLCS.

Below are the ESTOFEX GFS model and the WRF 13 km Europe model outputs from Keraunos, that further illustrate tomorrow's severe potential. The image below depicts a strong jet in place for tomorrow afternoon, where the area of divergence aloft will favour storm development from eastern France to western Czech Republic.

The Boundary Layer (BL) moisture is showing mixing ratios between 11 and 13 g/kg and dewpoints between 16 and 22 degrees C, making the airmass rich in moisture during cell development. A couple of things to note is the southwesterly low-level jet (LLJ), which will be pushing large amounts of moisture northward. As a linear line of storms emerges into the evening hours, excessive amounts of rainfall will become the greater threat. The greatest tornado threat lies in southern parts of Germany and Eastern France were the 0-3 km Storm Relative Helicity (SRH) is the highest.

Below are GFS model soundings for tomorrow afternoon. Both are depicting a very unstable airmass right from the morning to the afternoon. Given that the morning soundings showed large CAPE and no capping at the surface, leads me to believe that the afternoon CAPE values generated by the GFS model are being exaggerated. If storm initiation begins earlier in the day, less CAPE buildup will take place in the afternoon hours. Just something to keep in mind!

El Nino's Influence on Europe's Summer Forecast

There has been a lot of talk about the development of a "moderate" El Nino later on this year.

Here in North America we're begining to see a familiar pattern setting up, with strong ridging in the West and troughing in the East.

                                                                                         Courtesy of NCAR

Cliff Mass and Charlie have put out very detailed posts about the upcoming El Nino, so I will not go into detail about it myself. Links are provided below.

Cliff Mass's Post: http://cliffmass.blogspot.ca/2015/06/a-strong-el-nino-develops-what-does.html

Charlie's Post: http://charliesweatherforecasts.blogspot.ca/2015/04/an-el-nino-for-california.html

But what does this mean for Europe?

Upon diving deeper about El Nino and its effects, I was unable to find a definite answer to this question. Every El Nino plays out differently which is dependent on the rise in SST and its location in the Pacific Ocean (the distance of the "blob" from South America).

It has been noted that during El Nino events, high pressure has been seen to dominate over central and Eastern Europe more frequently over the summer months. This would mean above average temperatures and precipitation amounts to be anywhere from average to below average.

So I decided to look at the long range CFSv2 (NCEP coupled forecast system model version 2) model, to see if there is any truth to this. Here is what I discovered:

                                                                     Courtesy of NOAA

The top image shows the temperature anomalies for the months of July through to September. The CFSv2 model right now is hinting at average to slightly above average temperatures for central Europe.

                                                                      Courtesy of NOAA

The bottom image shows the precipitation anomalies for the months of July through to September. Here, the CFSv2 model is currently hinting from moderately to strongly below average precipitation for central and Eastern Europe.

So I was pretty surprised when I saw the outlook by the CFSv2 model. Mind you, this is a long range model and it certainly isn't carved in stone, but seeing similar hints in a model with comparison to other El Nino cases in the past, is always a good sign.

During my research I came across this article which explains El Nino and its impacts during the summer and winter in Europe. Thought some of you might enjoy the read:

http://www.netweather.tv/index.cgi?action=news;storyid=6648;sess=

I'm hoping to provide another update before I leave for Europe in August. Until next time!

Sharp Cold Front to Advance into Southern Ontario

A strong cold front will push its way east across Northern Ontario before arriving into Southern Ontario by Saturday. A much cooler and drier airmass will be ushered into Southern and Eastern  Ontario by Sunday.

                                                                            Courtesy of TwisterData.com

Widespread showers and thunderstorms will be possible ahead and along the cold front. The severity of some of these thunderstorms will depend on the timing of the cold front passage on Saturday.

If things play out by the GFS model, as shown above, then the front will be making its way into Southern Ontario and Eastern Quebec in the afternoon with more daytime heating to allow for an unstable environment and storms to be locally severe.

However given that some models have the cold front advancing faster on Saturday morning would diminish the threat of severe thunderstorms in Eastern Ontario and Quebec.

Behind the cold front, daytime highs will be between 17°C and 20°C on Sunday and Monday with lows in the single digits.

                                                             -------- Update ----------

I have posted two soundings for Ottawa (CYOW) to contrast the difference before and after the cold front passage. The top sounding is for 5 pm Eastern on Saturday just before frontal passage. The temperature will be in the high 20s and the dew point temperature in the high teens. If the timing of the front works out like it does on the GFS model, a thunderstorm will certainly not be out of the question.

The bottom sounding is for Sunday at 8 am Eastern well after the cold front passage, where a much cooler and drier airmass sets in. With a northerly wind and the low temperature in the single digits, Sunday will feel like an Autumn day!