Scaly Mountain Weather

Summary

SYNOPSIS

... Warm high pressure will persist across the region through the middle of the week with a few showers and storms possible each afternoon over the mountains. Rain chances increase Thursday and remain in the forecast each day through Tuesday, as multiple weak waves of low pressure move out of the south central states and pass through our area. Temperatures will remain above normal.

NEAR TERM /THROUGH TONIGHT/... As of 300 AM EDT Tuesday: Similar conditions to yesterday look on tap for today, as a positively tilted upper ridge axis remains atop the forecast area. The ridge will work to keep the atmosphere fairly suppressed. However, strong heating across the mountains will likely overcome mid-level warm temps to produce scattered showers and possibly a couple of isolated garden-variety thunderstorms. Steering flow will be weak, so convection will have potential to dump locally heavy rainfall. But the isolated coverage should limit the flood potential. Otherwise, a fair wx cu field can be expected across the Piedmont with light winds thanks to associated sfc high centered over the area. Highs are expected to be about a category warmer than yesterday, 4-5 degrees above normal.

Like last night, convective outflow will be capped by mid-level temps and likely spread east of the mountains in the evening and take a while to thin out. But whatever convective activity that does develop should wane fairly quickly after sunset. Mid-level flow is expected to tick up slightly out of the NW overnight, which may help clear out the clouds. So a slightly higher potential for mountain valley fog is expected. Lows will be a few degrees above normal.

SHORT TERM /WEDNESDAY THROUGH THURSDAY/... As of 130 AM Tue: Upper ridge will persist over the Southeast coast Wednesday. Cold front will push slowly past the Ohio River, having limited dynamic support with parent low occluding north of Lake Superior. The front looks to remain west of the Appalachians thru Wed night. Max temps will trend warmer, both at the sfc and at around 700 mb. Any uptick in low level instability looks to be stifled despite good lapse rates developing above 700 mb; we also lack much of a trigger, so deep convection looks questionable even over the mountains.

Vort lobe encircling the Canadian low will rotate past the Great Lakes Wednesday night, and RR quad of associated jet streak will promote development of a weak, possibly convectively enhanced shortwave. This may result in some convection in East TN and remnants thereof could reach the mountains in the very early morning. The shortwave itself is likely to push across the Appalachians near peak heating Thursday, flattening the ridge a bit. 700mb temps cool slightly and although this may not totally erode the inversion it makes convection more likely than Wednesday. Storm motion will be a bit faster and steering flow westerly, so small PoPs are warranted in the upper Piedmont in addition to the high chance to likely values over the mountains. The better flow will also translate to a bit better deep layer shear, perhaps above 30 kt. However the column may be too moist for the level of severe threat than we would typically see with convection this time of year, or for strong cold pool generation, thus not especially concerned for severe. Locally heavy rain may be of greater concern. Although increased cloud cover may knock temps back a little in the higher terrain, the Piedmont will trend a little warmer Thursday.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 200 AM Tue: An unsettled medium range period is in store, initially as a result of an expansive but low-amplitude trough centered over the southwest CONUS, through which multiple shortwaves will pass Friday and the weekend. By early next week some of the waves will phase, amplifying the pattern and leaving a deep trough over the East. Temps are expected to remain above normal with strong height anomalies over the western Atlantic and persistent west to southwest low-level flow. PoPs will run above climo each day and the frequency of the passing shortwaves makes it difficult to say at this forecast range that any appreciable dry period will occur.

Friday still looks to bear severe wx risk, with the shortwave tracking from the lower MS Valley toward the Mid-Atlantic coast. This will not only offer a convective trigger but also enhance deep shear and likely better low level moisture advection resulting in more CAPE in the late afternoon.

Cyclogenesis looks to occur in the Miss and lower Ohio valleys Sunday night or early Monday, effectively activating a warm front over our area and resulting in a sharp increase in PWATs and perhaps posing the greatest threat of heavy rainfall for the period, with soils possibly being primed in some areas by repeated rainfall over the previous few afternoons.