A Closer Look At Friday's Frontal System

iWeather Online synoptic forecaster Fergal Tierney says: Looking to tomorrow, Friday's band of precipitation moving eastwards across the country it really looks like being the biggest snowmaker yet. 

Conditions could be the worst we've seen so far as abundant precipitation falls through the cold slab of Arctic airmass in place over the country. The midlands and east could get 10-15cms of snow in a short period of time ahead of the front, turning increasingly to rain as the front passes. This rain instantly freeze on the cold surface, causing extremely hazardous conditions for both drivers and pedestrians alike, with roads and footpaths be covered with a glaze of black ice. With a severe frost setting in Friday night, venturing out is not recommended unless totally necessary.

Looking at the GFS Forecast Sounding for Dublin Airport for midday Friday there is a perfect snowy profile. The red curve is the forecast temperature throughout the atmosphere (vertical axis) and the green curve is the dewpoint. The red diagonal lines are isotherms, marked in degrees on the top and right-hand side. We can see that the whole profile lies to the left of the 0°C isotherm, therefore confirmation that any precipitation will be frozen. 

With an almost vertical profile and saturated mid levels (from 800-600hPa), there will be abundant precipitation present and falling as snow through the cold dry lower atmosphere. Model precipitation rates of up to 2mm/hr mean this could translate into snow accumulations of 2-4cms/hr - more than enough to grind things to a halt. The precipitation will be weakening all the time as it crosses the country, so I'd expect midland counties to see the higest snowfall.

 TOP IMAGE (c) Meteociel