Possible Severe Weather Tomorrow

 There is a possible severe threat tomorrow for most of our region. The SPC has issued a marginal risk(for severe thunderstorms), and a general risk of thunderstorms for our western and northern areas. Most of MoCo is in the marginal risk. The main threat is for damaging winds. Pea sized hail is also possible with these thunderstorms, but it's mainly wind. A cold front moving through the area will create the potential for strong, and potentially severe thunderstorms. After the cold front has moved through and temps have dropped enough, there is some possibility of; SNOW?! Say it isn't so?? Yes, in all seriousness, there is a chance for some very isolated, localized snow showers/flurries while temps are close to freezing. This is mainly for very late Wednesday night - Thursday morning (any chances after 7 am has a much less chance of happening due to sun angle and temps rising, it's still possible though, just much less likely). However, don't bet on it. It has a pretty good chance of not happening. Even if it does, it may be mixed with rain or another type of precip. It won't stick to anything, except mainly grassy areas, if there is stickage in the first place. The highest chance of stickage will be in Northern MD, but even there, the stickage will be on the grass. More into that later.

The dark green is the marginal risk for severe weather. Most of our region is in the dark green, while our western and northern areas are in the TSTM risk(general risk of non-severe thunderstorms).

Areas in the green area have a 5% chance to see 65+ mph winds 25 miles away from any point. Isolated strong thunderstorms, some possibly being severe possibly producing damaging winds and maybe evens small hail.

From the SPC: "Convective development is forecast to occur in lee of the Appalachian crest relatively early in the period, from eastern PA southward across central VA. Only modest instability (at or below

500 J/kg mixed-layer CAPE) is expected ahead of the advancing front, with storms to remain relatively low-topped across the region. Still, with linear forcing along the front, and fairly strong

west-southwesterly flow through the cloud-bearing layer, a few stronger -- possibly damaging -- wind gusts may occur within what should evolve into a semi-continuous band/line of convection. This convection should move off the Mid Atlantic Coast and into southern New England by late afternoon, weakening as it crosses MA/CT/RI and vicinity through the evening." For those who don't understand what they are saying, although theres not much instabillity in the atmosphere(key ingredient in severe weather), linear forcing along the front + somewhat strong (south)westerly flow through the cloud bearing layer may cause stronger, maybe even damaging wind gusts.

This is the NAM(12km, 18z run) at hour 27(5 PM Wednesday), and it shows a good amount of shear in the atmosphere. Most of the region is above 60kt(around 69 MPH) (except for western Maryland), and a lot of our region is also over 65kt(75 mph) in shear, and some of our region is even reaching around 70kt(80 mph) or higher! This is in terms of shear in the atmosphere. There is a good amount of shear in the atmosphere. At this time, all of the region is under 50 CAPE(instability) and there isn't much lift + moisture(<50% for a lot of the region) either. You need a good amount of these ingredients for severe weather. This map proves that this is mainly a wind threat.

This is the NAM(12z run, takes in data) sounding does indeed show snow for Northern MoCo at hour 45, around 4 AM EDT. This is a good sounding, with north/northwest winds  up until around 500 mb into the atmosphere, where it switches to more west. The dew point is below freezing. The dew point is the measure of moisture in the atmosphere, and doesn't determine whether or not snow will fall. However, it is a small indicator. It is also an indicator that the air is somewhat dry, and that snow showers/flurries will be isolated. The dew point starts to get around 30-34 around 700-900 mb, before lowering at 700 mb. The temp is 34 at the surface, but is a good amount below freezing for the rest of the atmosphere. The atmosphere would be cool enough the whole time that it would be able to snow on the ground, even above freezing. There is no sun angle concerns at this time(4 am), plus if it snows, the temp can quickly drop. Since the temp here is so close to 32, I wouldn't be surprised if places reach 32 or maybe even lower due to dynamic cooling, if the isolated bands set up. Don't count on it, since its so isolated. No model can really pick up on this. Close range HRRR may be able to help, but even then, the only way we can be sure is using radar. All there is is a chance for some flurries/snow showers. Don't get your hopes up for snow. Severe weather is also likely to be isolated.