Convective Outlooks 2016

Convective Outlook 20.07.2016

deutsche Outlook-Kurzfassung (aufklappen)
CategoricalHeavy RainHailWind GustsTornado

Risk Area (sq. km) Population Larger Cities in Risk Area
20 % 675.883 94.888.203
50 % 433.026 120.283.549
Severe Threat 1 169.910 65.748.556
Severe Threat 2 18.400 8.702.991

bei Fragen zu den
Convective Outlooks hilft unsere
Forecast FAQ

 

A Severe Threat 2 has been issued for e Netherlands and extreme NW Germany mainly for large hail, excessive precipitation and to a lesser degree for severe wind gusts

 

A Severe Threat 1 surrounds the Severe Threat 2 mainly for medium-size to locally large hail, excessive precipitation and severe wind gusts

 

A Severe Threat 1 has been issued for N Spain and S France mainly for large hail

 

Synoptic Setup

A deep vortex south of Iceland remains stationary during the forecast period, while a cut off takes place over Eastern Europe. In-between, ridging at first strengthens from N Africa over Spain to Germany. On Wednesday, the ridge gets gradually narrow, and synoptic forcing from the Atlantic-Vortex can easily encroach on wrn and crtl Europe. Within a subtropical airmass at lower levels, an active day concerning convection is expected primarily over Germany and Be-Ne-Lux.

Mesoscale Discussion

…N-France, Be-Ne-Lux and NW Germany…

The most prominent feature will be a secondary trough/PV anomaly, that pivots from GB to the North Sea on Wednesday. As it interacts with a lower positive theta-anomaly over S England, the PV Thinking teaches, that baroclinic development occurs. The resulting sfc cyclone encourages the LL transport of a moist and hot airmass mainly to N France and the Be-Ne-ux countries. Here, sfc temperatures around 35 °C and mixing rations near 15 g/kg are forecast. The highest moisture will be concentrated in the wake of a moisture flux convergence, that ranges from the the centre of LL cyclone over GB to the south-east, as indicated by a tight and linear theta-e maximum. Within a moderate SWly diffluent mid level flow, an EML is advected over the moist boundary layer, yielding potential instability and ML CAPE of 1000-1500 J/kg. As the WLA caps the instability, CI is suppressed until the early evening. We anticipate the first DMC at the northern part of the convergence somewhere between Antwerpen and the Ruhr. This is by two reasons:

1. The most convenient position of that area relative to the surface low with generally maximized cyclonic stream lines
2. Additional forcing via strong upper lvl divergence at the left exit region of a 300 hPa jet-streak, that stretches from the Pyrenees to W Germany

All in all, there is a substantial overlap of all three ingredients over the highlighted area. Besides this fact, shear conditions are not that favourable with 0-6 km DLS between 15 und 20 m/s, disordered hodographs and only weak pre-storm environmental helicity (0-3 km ~ 100 J/kg).
Hence, we expect mostly multicellular storms, but also a supercell is possible, primarily at the tail end of a developing cluster. Large hail up to 5 cm is the dominant hazard in any well organized storm and will be most likely near the German border. Later on, as storms may cluster into a more ore less organized system, the threat switches to severe wind gusts (delta theta-e around 24 K) and local flash floods. Due to high cloud bases and low LL helicity/shear, the tornado risk is negligible.
During the night, additional storms may form further to the south over E France and Luxembourg and move into SW Germany. One or two severe reports are possible here as well, but overall severe potential will weaken due to lowering instability.

…N-Spain, S-France…

Steep lapse rates but less pronounced LL moisture result in 500-1000 ML CAPE. With orographic lift and 15-20 m/s DLS, one or two well organized, high-based storms may develop along the Pyrenees in the evening. The main risk will be large hail up to 5 cm.

Model consistency, additional remarks

Besides the fact that CI is likely over N France, Be-Ne-Lux and W Germany, there are still uncertainties concerning instability-amount and the spatial-temporal evolution of the convergence. As GFS tends to overestimate the BL moisture, we think that the predicted 2k J/kg are unrealistic. Nevertheless, we introduced a small Severe Threat 2 over the region where we estimate the best overlap of moisture, lapse rates, deeper lift and wind shear and where a supercell with large hail is most likely.

Convective Outlook 23.06.2016

deutsche Outlook-Kurzfassung (aufklappen)
CategoricalHeavy RainHailWind GustsTornado


Risk Area (sq. km) Population Larger Cities in Risk Area
20 % 661.260 93.117.157
50 % 343.873 90.318.295
Severe Threat 1 337.988 84.496.076
Severe Threat 2 111.647 35.799.168

bei Fragen zu den
Convective Outlooks hilft unsere
Forecast FAQ

 

A Severe Threat 2 has been issued for N France, parts of Be-Ne-Lux and NW Germany mainly for large to very large hail, severe wind gusts (isolated damaging wind gusts possible), excessive precipitation and a tornado event

 

A Severe Threat 1 surrounds the Severe Threat 2 mainly for large hail, severe wind gusts and excessive precipitation

 

A Severe Threat 1 has been issued for the western Alpine region mainly for large hail

 

A Severe Threat 1 has been issued for S France mainly for large hail

 

Synoptic Setup

An amplifying upper trough over the E Atlantic will be the prominent feature during the forecast period. On its eastern fringe, southerly winds support the influx of warm subtropical air masses towards West and Mid Europe. In the lower troposphere, homogeneous pressure fields with weak gradients prevail across the forecast region. The anabatic sfc cold front, that corresponds to the trough, is presently situated west to the the European coastline and will slowly be displaced to east. Prefrontal pressure falls may induce one or several convergence lines within the subtropical air mass. Regarding severe weather, a potentially dangerous set-up will be unfolding over Be-Ne-Lux and W Germany.

Mesoscale Discussion

…N France, Be-Ne-Lux, NW Germany…

Current remote sensing and sfc data represent plenty of DMC popping up from Asturias to the Channel. A supercell could also be reported over N France a few hours ago. This convection shifts further to the North and Northeast influencing primarily W France and S England in the night hours. Although most storms will become elevated, one or two well organized cells with severe reports cannot be ruled out.
Tomorrow morning the coastal regions may still see remnants from the overnight convection and THR-cloudiness, that initially could suppress insolation. To the east model-guidance only expects a few clouds so that diurnal heating can easily push 2m-temperatures to the thirties.
Within the WAA regime, a spanish-plume, that emanates from the Spanish highlands, is advected to the area of interest. As a result of abundant rainfalls during the last weeks, soils are nearly saturated as indicated by meteoam. With additional moisture advection, mixing ratios may frequently exceed 15 g/kg. With a pronounced EML around 700 hPa (500 hPa lapse rates around 7 K), a loaded gun situation is forecast to evolve from Be-Ne-Lux to NW Germany providing ML CAPE between 1500 and 2000 J/kg with peaks up to 2500 J/kg.
In the wake of a Mid-Level Jet ,1-6 km DLS of 20-25 m/s is superimposed with the highest instability, yielding conductive conditions for well organized convection. With quite linear hodographs SRH reaches 100-200 J/kg and locally higher values near the coastline. In contrast to energetics and kinematics, there are still greater uncertainties concerning the forcing mechanism. As the streamlines at upr levels are very linear/uncurved and the main Jetstreak remains over GB, there is no substantial QG Forcing, that could overcome the WAA-induced capping inversion. Nevertheless, model consensus anticipates CI in the afternoon over Belgium/Netherlands in the vicinity of the prefrontal sfc low. We are still somewhat sceptic, as the today’s CI and severeness over N France was overestimated by WRF and EURO4.
Moreover, overnight convection should be monitored as it may care for a different overall set-up development (outflow boundaries and aforementioned cloudiness). If BL-rooted CI takes place as simulated by the models, convection will rapidly become multi and supercellular bearing a risk of large to very large hail, excessive precipitation and severe wind gusts. EURO 4 and WRF 4 km both indicate clustering and an evolution of a cold-pool driven MCS with bowing segments. Such a system would move into NW Germany somewhere between the Lower Rhine and Eastern Frisia in the evening and live on in the night hours (MU CAPE > 1500 J/kg). The development of strong cold pools seems to be realistic due to high Delta-Theta-E > 20 K. In such a system, the main threat switches to severe and damaging wind gusts > 32 m/s and locally significant severe precipitation. Within a small temporal window between LCL lowering and BL stabilization, a tornado event is not unlikely especially along the coastline where LL vorticity may locally be concentrated. We decided to go with a broad and solid severe threat 2, keeping in mind the high severe potential but also the uncertainties of the set-up. We will update the Outlook or publish a Mesoscale Discussion if necessary.

…Wrn Alpine Region, S France…

CAPE between 1000 and 1500 J/kg (higher values near the Alps) and orographic lifting will result in isolated CI in the late afternoon. The main threat will be isolated large hail, especially in S France where a dry Foehn layer is present in mid levels. The latter may on the other hand inhibit convection, but we issued a severe threat 1 to point out the enhanced severe potential due to hail. In general it can be stated, that CI near the Alps/Black forest is more likely than in S France.

Model consistency, additional remarks

—see text—

Convective Outlook 02.06.2016

deutsche Outlook-Kurzfassung (aufklappen)
CategoricalHeavy RainHailWind GustsTornado


Risk Area (sq. km) Population Larger Cities in Risk Area
20 % 472.637 54.721.778
50 % 784.261 154.945.777
Severe Threat 1 520.757 88.049.675
Severe Threat 2 51.705 27.090.072

bei Fragen zu den
Convective Outlooks hilft unsere
Forecast FAQ

 

A Severe Threat 2 has been issued for W Germany and E Be-Ne-Lux mainly for significant severe convective precipitation, large hail and to a lesser degree for severe wind gusts

 

A Severe Threat 1 surrounds the Severe Threat 2 mainly for severe convective precipitation and large hail

 

——— NO FORECAST TEXT AVAILABLE ———

Convective Outlook 29.05.2016

deutsche Outlook-Kurzfassung (aufklappen)
CategoricalHeavy RainHailWind GustsTornado


Risk Area (sq. km) Population Larger Cities in Risk Area
20 % 623.832 72.583.760
50 % 734.594 175.003.064
Severe Threat 1 361.351 93.203.320
Severe Threat 2 63.571 8.153.353

bei Fragen zu den
Convective Outlooks hilft unsere
Forecast FAQ

 

A Severe Threat 2 has been issued for Mid Germany mainly for (significant) severe convective precipitation, large hail and to a lesser degree for severe wind gusts

 

A Severe Threat 1 surrounds the Severe Threat 2 mainly for severe convective precipitation and large hail

 

A Severe Threat 1 has been issued for N Italy mainly for severe convective precipitation and to a lesser degree for hail and severe wind gusts

 

——— NO FORECAST TEXT AVAILABLE ———

© Sturmjäger NRW 2011 - 2017


Creative Commons Lizenzvertrag

Dieses Werk ist lizenziert unter einer Creative Commons Namensnennung - Nicht kommerziell - Keine Bearbeitungen 4.0 International Lizenz.
Frontier Theme