CATEGORY 4 SEVERE STORMS
Impacts: 1. A few tornadoes 2. Wind damage, gusts over 70 mph 3. Hail up to 1.5 inches
I am very impressed with an outbreak of severe as outlined on the map below. The initial run of storms will develop across West Virginia and move quickly east-northeast with wind damage, potential tornadoes and hail. The shear values across south-central Pennsylvania are very high and can support the potential for tornadoes. After the first few hours of storms and tornado potential, we should see a linear squall line develop from Harrisburg to south-central Virginia that will move through southeast Pennsylvania, Maryland and Virginia impacting Baltimore, Washington and Philly with high winds and heavy rain. I expect to see about 10-20 reports of tornadoes and over 100 reports of wind damage.
The tornado threat will last from 2 p.m. to 7 p.m. for areas bounded by State College, Du Bois, Johnstown to Roanoke to Hagerstown and Harrisburg to State College. Within that area, shear values are high and RR model suggest that discreet storms will have rotation within them.
The dynamics are very impressive with a 100 kt jet nosing into the threat area, a deepening low pressure going to 996 mb, a 50 kt 850 mb jet, surface dew points coming up into the mid-upper 60s. Model soundings show high helicity and turning of the winds with height.
So all the parameters are coming together for a major outbreak in the part of the country that does not really see outbreaks like this.
I will be twittering information out during the day and evening. You can follow me at http://twitter.com/#!/Henry_Margusity
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The band of snow and ice that develops this weekend will be bad in Kansas but more of a nuisance through the Ohio Valley.
As milder weather moves north, it will mean snow will hit the Great Lakes and Northeast today into tonight. California will get more heavy rain.