It couldn’t last forever! Our record warm December is not going to end without a messy mixture of snow, sleet, and ice.
This storm isn’t going to drop much snow – in fact many towns may not see any! Sleet and ice on the other hand is going to be a bit of an issue.
A strong high pressure over Maine is going to send a surge of cold south into Connecticut. The low levels of the atmosphere will be plenty cold for snow. Higher up, above 7,000 feet or so it’s a much different story. In mid levels of the atmosphere there is no such push of cold air.
The above map shows that mid level warmth with the height of the 500mb surface (a proxy for temperature) way above average for the time of year.
This storm is what we call a Southwest Flow Event (SWFE) with screaming southeast flow aloft and a cold northerly flow near the ground. This one will be a warmer SWFE with warmth aloft resulting in little snow but the cold northerly drain near the surface giving us a period of sleet and ice.
As the precipitation begins most of our models show temperatures near 0c at 700 mb. The SREF sounding above shows that quite well with a tight clustering of the “spaghetti” around the freezing level at 7,000 feet up. Quickly, this layer warms further guaranteeing a precipitation type other than snow.
While the computer models all show differing amounts of warmth and precipitation type at the onset there is very good agreement in the general setup. This is a high confidence forecast.
Toward the end of the storm we see temperatures about 5,000 feet up over 10C (>50F!) but near 32 degrees at the ground. This temperature inversion will lead to sleet, freezing rain, and eventually rain.
Here’s what to expect:
- Minor snow accumulation across the state. No more than an inch or two with many towns seeing little if any snow.
- Quick change (or even starting with) to sleet across the state. Sleet will fall even at the beaches. This will lead to slippery travel for the Tuesday morning commute. Up to an inch of sleet accumulation is possible in some areas.
- As the wedge of cold air near the ground begins to shrink the sleet will change to freezing rain inland and plain rain at the shoreline. Untreated surfaces will remain slick!
- Freezing rain will not be enough to cause tree or power line issues but many areas could see a solid glaze of ice.
- Temperatures in the Hartford/Enfield areas will struggle above 32F even by midday Tuesday with the cold wedge in the valley being notoriously difficult to erode.