Lower Dewpoints = More Snow and Ice
January 20, 2012
www.DCstorms.com
- Dewpoints are running in the single digits. I will stress that the dry air will produce a much stronger evaporational cooling effect causing snow and sleet to hang on longer before a change over to freezing rain.
- Immediate Washington Area: 1 to 2″ of snow is likely across Northern Virginia, downtown Washington, & central Maryland before a change over to sleet and freezing rain Saturday morning. A glaze of ice accretion (freezing rain) is likely on top of the snow in the immediate Washington Area. Western Fairfax county, upper Prince William County and upper Montgomery county could see ice accretion of a quarter inch if the cold air hangs tough through mid morning Saturday (hence a Winter Storm Warning may be needed).
- Northern Maryland: I think snow will hang on longer… and upwards of 3 to 4″ will fall in Frederick and Baltimore. As you get closer to the Pennsylvania border, I see 4 to 5″ accumulating before a change over to sleet and freezing rain Saturday afternoon.
- Southern Pennsylvania: you will remain snow for 90% of this system before possibly mixing in with a bout of sleet towards the end… 5 to 7″ with sweet spots of 8″ is possible here.
- Areas in pink on the map (Fredericksburg, Quantico, Stafford, Culpeper, over to southern Maryland): Expect a period of snow (coating to 1″) that will switch over to sleet… and freezing rain early Saturday morning. A glaze of ice on untreated roads will make for extremely hazardous driving on Saturday morning. Temperatures should warm into the middle to maybe upper 30s by afternoon… I say should b/c the air is so damn dry… this will be a nail biter.
- DEWPOINTS are low… teens and single digits! This air is dry and a rapid warm up at the lower levels of the atmosphere is extremely unlikely as evaporational cooling slows mid-level warming. I think some folks need a Winter Storm Warning versus a “Winter Weather Advisory” due to the threat of Freezing Rain holding on in the Northern Shenandoah Valley and even across the Interstate 66 corridor of Northern Virginia and parts of Maryland.
- Don’t be surprised if you wake up to Winter Storm Warnings in the northern and western suburbs as the cold air hangs on tough.
Advertisement
No comments yet
