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Rainfall warnings and possible widespread thunderstorms Fri 19 July 2019
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18-07-2019 8:02pm#1Will start a thread as tomorrow Friday could become an active day with high rainfall amounts and possible widespread thunderstorms.
Fair spread in predicted rainfall levels. Could expect Met Eireanns warnings to get upgraded if necessary as the day unfolds and more models fine tune. Impossible to predict where the heaviest convective rain might fall, for this reason if it takes off they might issue a blanket warning.
EDIT : Updated warnings.
Met Eireanns Warnings
Status Yellow - Rainfall warning for Ireland
Heavy thundery downpours will give high totals of rainfall in short spaces of time today/early tonight leading to localized spot flooding.
Valid: Friday 19 July 2019 06:00 to Saturday 20 July 2019 03:00
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http://www.convectiveweather.co.uk/forecast.php?date=2019-07-19
Day 2 Convective Outlook
VALID 06:00 UTC Fri 19 Jul 2019 - 05:59 UTC Sat 20 Jul 2019
ISSUED 20:07 UTC Thu 18 Jul 2019
ISSUED BY: Dan
A broad upper trough will linger to the northwest of the British Isles on Friday, with strong southwesterly flow aloft on its forward side. A pronounced shortwave will approach the Celtic Sea late in the afternoon, swinging across Ireland during the evening and England/Wales overnight. This forecast period is rather messy, and so pinning down the local detail is rather tricky and nowcasting will play a key role.
... S IRELAND / CELTIC SEA / SW WALES: MORNING ...
A complex pattern will evolve during Friday, as a rather elongated and slack surface low drifts northeast across Ireland towards SW Scotland / NW England during the forecast period. Embedded elevated convection with some sporadic lightning is possible first thing on Friday morning over the Celtic Sea / S Ireland / SW Wales, but any lightning will tend to reduce with time as the intensity weakens during the morning hours.
... IRELAND: AFTERNOON / EVENING ...
In the wake of any morning activity, provided sufficient cloud breaks occur over central and southern Ireland, a notably unstable airmass (600-1,000 J/kg CAPE) will be possible here by midday and through the afternoon hours given heating of a warm, moist low-level airmass. Wind convergence, local topography and a differential heating boundary may all contribute to the development of scattered thunderstorms during the afternoon and evening hours, in an environment with 30kts DLS and forced ascent on the leading edge of the approaching shortwave.
Hail up to 1.5cm in diameter and an isolated tornado cannot be ruled out, given locally backed surface winds to the northeast of the surface low. The exact location of the narrow corridor where low-level shear will be maximised (along the convergence zone) is a little uncertain, and heavily dependent on the shape / elongated nature of the surface low - and nowcasting will be essential for detecting this risk. The convergence zone will tend to extend across the Irish Sea towards NW England, and so scattered heavy showers and isolated thunderstorms will also be possible over these areas.
One main concern is the close proximity to the wrap-around occlusion and the potential therefore for cloud cover to limit the amount of insolation0 -
Approaching system off the W coast with the frontal triple point giving the heaviest of the rain set to pass over Ireland in the areas highlighted by Met Eireann although the ECM would suggest other counties could be added.
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A level 1 is issued for Ireland and England mainly for excessive convective precipitation and tornadoes.
Level 1 areas are issued for various parts of central Europe, SE Europe, the Georgian and Russian Caucasus region and NW Russia mainly for excessive convective precipitation and to a lesser degree for large hail.
A level 1 is issued for the E Black Sea mainly for non-supercellular tornadoes (waterspouts).
SYNOPSIS
A broad, weak to moderate westerly flow stretches across Europe. Two mature cyclones are located between Iceland and Scotland and over NW Russia, respectively. The tails of their largely occluded frontal systems fan out into a main frontal zone that runs between 50 and 55N and sharpens somewhat to the west, where a frontal wave crosses Ireland and Scotland.
A subtropic high pressure systeme with very warm air covers the S half of Europe.
DISCUSSION
... Ireland and England ...
Warm and very moist air is advected into Ireland and England in the warm sector of the frontal wave. Despite poor lapse rates, daytime heating will allow around 500 J/kg of CAPE over Ireland, while this buildup will be slower and weaker over England. Moderate to strong vertical wind shear (0-3 km: ~15 m/s, 0-1 km: ~10 m/s) overspreads the unstable air. Vertical wind profiles are strongly veering near the warm front with 0-3 km storm-relative helicity on the order of 200 m^2/s^2, before they straighten to some degree in the warm sector.
The rain shield of the warm front, which might already include a few embedded thunderstorms, will largely clear Ireland by 12 UTC and England by 15 UTC. Scattered thunderstorms will then initiate in the warm sector in the late morning to afternoon, aided by daytime heating, sea breeze fronts and strong synoptic lift ahead of a short-wave trough, and will organize into multicells and perhaps a few supercells. Possibly training storms and high precipitation efficiency in the very moist air could support some heavy rain events with a possibility of flooding. In addition, one or two tornadoes could spin up, especially if clearing skies and insolation follow soon after the warm front passage, while wind profiles are still most supportive. The hail and wind risk is limited by poor lapse rates and very moist air, though marginally large hail or a hail cover are not ruled out in case of a supercell.
Storms will gradually decay when they move offshore onto the North Sea. The cold front may push new rounds of (partly embedded and weakly electrified) convection SE-ward into S England and the Channel region overnight, but they will struggle to stay surface-based. The severe weather risk decreases overnight, though plentiful rain could still accumulate.0 -
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Some hours out yet before the main body of thunderstorms reach the SW it would seem if they are still firing by then. ECM and ICON showing thunderstorms reaching and moving into the SW by about 04.00 or 05.00
Rapid Developing Thunderstorms SEVIRI v2018
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Meteorite58 wrote: »ECM has shifted it's highest rainfall amounts somewhat.
That would correlate with what we are seeing on the current radar. I don’t see big totals at my station in Waterford City. 6.1mm overnight0 -
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