Heavy rain, strong winds, and potentially thunder highlight Saturday
The snow and freezing rain this morning has left the immediate area, and gave most areas a coating to 1″ of snow, and also very treacherous roads. Now that the warm front has passed the area, temperatures have risen above freezing, moisture has increased, and dense fog is beginning to develop. An extremely saturated low-level profile will continue to promote an increase in fog as the night goes on, so all motorists should be extremely careful when traveling tonight, as visibilities will be below 1/4 of a mile at times.
However, a freezing rain advisory still exists for interior Central and Northern NJ, interior southern NY, and interior southern CT, as cold air has still remained at the surface. Areas close to NYC should change over to plain rain by midnight with less than a tenth of an inch of ice, and areas a bit further inland may remain below freezing until 4:00am, as a tenth of an inch of freezing rain could fall. Travel especially carefully in these areas. For more information on these advisories, see the embedded links.
Moving forward to tomorrow, the weather will continue to get worse. A storm system will be deepening and cutting into the Great Lakes, leaving a cold front in its wake — all the way down to the Gulf of Mexico.
Today’s 18z NAM valid for tomorrow at 1:00pm shows a 988mb low in SE Canada with a cold front draped across the Appalachians.
The NAM model shows the cold front quite well. East and southeast of the 988mb low in SE Canada, winds are generally southerly and southeasterly; whereas to the south, west, and southwest of that low, the winds are generally westerly and southwesterly. Additionally, a classic indicator of a cold front is a pressure trough. The isobars are the solid black lines. In the area where the different wind directions are converging, there is a very well-defined pressure trough in Ohio and Kentucky, further proving the location of the cold front. It perfectly matches the region where the wind is changing in direction.
Today’s 18z NAM valid for 4:00pm tomorrow shows an area of very high precipitable water values streaming into the northern Mid Atlantic, an indicator of a significantly moist atmospheric column. This supports the potential for heavy downpours.
Although there is not a whole lot of cold air behind the front, the front is still powerful due to significant moisture differences, as well as an abundance of warm air and moisture out ahead of the front. The high preciptable water values shown above, as well as surface temperatures rising into the upper 50 and low 60s leads to low-density air that can easily be lifted. This warm and moist air being lifted by the cold front will help to trigger an area of heavy rain, and potentially enough convection to lead to a squall line with embedded thunderstorms.