Papa Lazarou
Living in a De Zerbi wonderland
That site seems to suggest that the temperature will remain below 0oC for a week, which clearly isn't the case... Or am I looking at it wrong?
That's the 850hpa temp - so at a fixed pressure level in the atmosphere. With low pressure, that's closer to the ground than otherwise. It's a way of taking diurnal variations out of measuring the true temperature of an airmass.
On the chart, there's a yellow bar - click on the Temp 2M to get the true surface temperature.