Forecast Discussion
Summary
SYNOPSIS
... Moisture with cloudy and cool conditions will linger into Thursday but expect some sunshine on Thursday. We can expect a slow warm up and drier conditions beginning Friday and continuing into next week.
NEAR TERM /THROUGH THURSDAY/... As of 2:15pm EDT Wednesday: Most areas remain overcast or broken this afternoon as northeast surface flow keeps cooler air up against the mountains. Dewpoint depressions of around 10 degrees this afternoon mean that the few light radar echoes are unlikely to be reaching the ground. Over some of the Southern Appalachians, clouds have mostly cleared and afternoon heating is allowing a smidgen of CAPE to develop. High-res models develop some light and shallow convection in these areas this afternoon and evening. Relatively warm air aloft will keep any convection quite shallow.
Synoptically, region is in the midsts of a large-scale Cold-Air- Damming pattern, with a parent surface high in Eastern Canada. This pattern looks to persist through the near term and into the rest of the forecast week. Upper low moves across the Great Lakes region Thursday, but does little to alter the low-level pressure/wind pattern. Highs today are expected to come in 5 or so degrees below normal due to cool advection in northeast flow and cloud cover. Highs will increase to near normal tomorrow as cloud cover is not expected to be as thick, letting in a little more solar energy. Given some uncertainty in cloud cover, there is some potential for highs to be warmer than forecast. In the mountains, which is outside the CAD, calmer winds and some breaks in clouds could lead to fog Thursday morning in the typical fog-prone areas. Winds will remain persistently northeasterly to easterly at 5 to 10 kts outside the mountains through the period, day and night. Winds in the mountains will be weaker at night and more variable.
SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... As of 130 PM EDT Wednesday: Closed upper low situated over the Great Lakes region at the beginning of the Thursday night into Friday will gradually weaken and open up as it traverses across Northeast/Mid-Atlantic through the period. The general consensus is for this upper feature to shift offshore the Northeast Coast by sunset Saturday, where it's shown regaining momentum and closing off once again. Persistent low-level northeasterly component will continue to filter in thanks to Canadian High Pressure over New England and a coastal low riding underneath the aforementioned closed low offshore helping to reinforce the northeast wind. Model trends have come in drier during the short term due to the lack of forcing and moisture. Best chance will be in the higher terrain near the NC/TN border during the first half of Friday. Once the upper trough axis slips through the area Friday afternoon/evening, all precip chances will go away through Saturday. Temperatures will begin to rebound decently from Friday into Saturday as an upper ridge amplifies over the east-central CONUS. At the same time, a longwave upper trough will dig over the western CONUS, while the closed upper low continues to meander offshore the Northeast over the weekend. With this synoptic setup, an omega blocking pattern will be underway this weekend as our CFWA ends up on the eastern peripheral of the upper ridge. With rising heights and better insolation, temperatures will end up at or slightly above normal for Friday and up to 5 degrees above normal on Saturday, especially in the Upstate and northeast GA.
LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... As of 220 PM EDT Wednesday: Omega blocking pattern will continue to control the overall synoptic pattern through a good chunk of the period as ensembles and global models keep this intact going through the early part of next week. Surface high pressure will slither southward as a result and set up shop over the heart of the Appalachians. Expect the CFWA to maintain a northeasterly component through much of the period due to stout surface ridging. The longwave upper trough over the western CONUS will gradually propagate eastward and breakdown the omega block, but will take time in doing so. As a result, precip chances are pretty much nonexistent through the medium range as deep layer subsidence remains in place with upper ridging firmly over the eastern-third of the CONUS by the end of the period. Temperatures will remain at or up to 5 degrees above normal through the middle part of next week.