Weather Alerts For Purcellville, VA

There is a Slight Severe Storm Risk for your location. Continue reading for today's outlook from the National Weather Service's Storm Prediction Center. -------------------- National Severe Storm Outlook THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY THROUGH TONIGHT IN A CORRIDOR ACROSS THE SOUTHERN GREAT LAKES AND MIDDLE/UPPER OHIO VALLEY INTO MID ATLANTIC SUMMARY A couple of organized clusters of thunderstorms may develop across the southern Great Lakes and mid/upper Ohio Valley today through tonight, accompanied by the risk for damaging wind gusts. More widely scattered strong thunderstorms east of the Blue Ridge may also pose potential for damaging wind gusts this afternoon and evening. Discussion Mid/upper flow is forecast to undergo further amplification today though tonight across southern Canada and the U.S., downstream of positively tilted large-scale troughing which continues to evolve offshore of the Pacific coast through Intermountain West. It appears that this will include building ridging across and north of the international border, from the Rockies through upper Great Lakes, to the north of a high centered over the central Great Plains. Downstream, large-scale troughing is forecast to continue slowly digging across the northern and middle Atlantic Seaboard. As it does, it likely will suppress a prominent high initially centered near the southern Appalachians. Accompanying the eastern trough, reinforcing surges of cooler low-level air will continue to overspread portions of the Great Lakes and Northeast today through tonight. It appears that this will contribute to a slow south and southwestward progression of the primary surface front across the Mid Atlantic and through the upper into middle Ohio Valley. Southern Great Lakes into Mid Atlantic A moist boundary layer, and remnant plume of relatively steep lower/mid-tropospheric lapse rates, particularly across the Upper Midwest and southern Great Lakes vicinity into the western slopes of the Appalachians, may continue to support moderate to strong potential instability along the quasi-stationary to slow moving frontal zone. Latest convection allowing guidance suggests that this front may already be providing a focus for organizing thunderstorm development across southern Lower Michigan by the beginning of the period, beneath the favorably sheared southwestern periphery of the stronger westerlies. As the boundary-layer destabilizes ahead of it with insolation, it appears that this activity may intensify further, accompanied by increasing potential to produce strong to severe wind gusts while propagating southeastward across parts of northern/eastern Ohio into the Allegheny Plateau by this afternoon. It remains unclear whether forcing for ascent and destabilization to the immediate lee of the Allegheny Mountains and Blue Ridge will maintain this cluster. However, convection allowing guidance suggests that the initiation of at least scattered vigorous diurnal thunderstorm activity is probable downstream, closer to and across the coastal plain, where the environment is likely to be supportive of a few downbursts with strong to severe surface gusts late this afternoon into evening. Late this evening into the overnight hours, downstream of another short wave perturbation digging to the east of the amplifying mid-level ridging, there is a notable signal within convection-allowing and related guidance that forcing for ascent may support another evolving cluster of storms. This may track close to, but probably at least a bit to the southwest of, the early day cluster, from the southern Lower Michigan through Ohio and West Virginia vicinity.

Pollen Index: 10.2 Pollen Level: high Predominant Pollen: Ragweed and Grass. Based on past pollen counts and expected weather conditions, pollen levels for Saturday will remain stable in the very high range. Pollen producing plants are at a relatively steady level of pollination at this time.