... Canadian high pressure will continue to shift toward coastal New England tonight while wedging cold air southwest down the east side of the Appalachians. Meanwhile multiple weather systems look to parade across the region from the Mid-South. As a result we see a wintry mix today in the mountains with rain elsewhere. By the weekend and early next week it's the concern for flooding as additional heavy rain pushes into the region.
NEAR TERM /THROUGH TONIGHT/... As of 1032 AM EST
...Wintry weather for some this afternoon and evening with a cold rain elsewhere...
Subtle changes in regards to warmer temperatures this morning as the wedge sets in and a delay in precipitation onset for more of an afternoon/evening arrival.
Still looking at a fairly complex forecast today as a southern stream wave approaches the region from Tennessee and western North Carolina. Radar continues to indicate weak echoes from Roanoke east to Lynchburg and Dillwyn as well as off to our south around Wise/Bristol. Most of the precip is in the form of liquid this morning with temperatures in the mid to upper 30s and low 40s. A few instances of graupel and sleet though have been noted around the US- 460 corridor from Roanoke to Lynchburg by local media and mPING reports. Precipitation will continue to overspread the area from south to north overrunning what looks to be an "in-situ wedge" setting up shop due in part to blocking high pressure in central Pennsylvania.
With the wedge in place temperatures look to stand pat if not drop a few degrees as a result of wet bulbing as precipitation moves in. Confidence on this is highest over the higher terrain west of the Blue Ridge Parkway and in elevations above 3500 feet. Elevations below this point the confidence is lower for little to if any wintry weather concerns.
Areas along and west of the Blue Ridge will remain in a Winter Weather Advisory through this afternoon for parts of the NRV/Mountain Empire south of US-460 and through Saturday morning for the Greenbrier Valley/Alleghany Highlands regions west of the I-81 stretch. These location locations are likely to see a dusting to 1 inch of snow with a light glaze of ice. Places such as Mountain Lake, western Greenbrier County, Mountain Grove, Mount Rodgers, and Peaks of Otter could see amounts on the order of 2 to 4 inches with a light glaze of ice. Minor travel impacts are expected but most roads should remain wet based on the recent warmth the last few days. Winds will also not be an issue with gusts of 20-30 mph over the mounts and 10 to 15 mph down low. Mountain areas will likely change to rain though as the warm nose wins out early Saturday morning.
As for rainfall amounts many locations look to remain between a 0.50 to 0.75 inch areawide. Localized heavier amounts are possible although most of the precip looks to be light to moderate this afternoon and into the overnight hours. No flooding concerns are expected at this time.
Rain will taper a bit mid to late Saturday morning into the afternoon hours as the back edge of the rain pulls out and next front starts to lift in. As a result we look to at least get a 12 hour window with drizzle and fog or no precip at all. Beyond this period the flooding concern increases as our next round of heavy rain returns.
Confidence remains moderate to high in precip and wind probabilities. Low to moderate confidence on temperatures and wintry precip based on the strength of the wedge.
As of 445 AM EST Friday...
Minimal Winter Weather Event Expected Today Impacting Mainly the Higher Terrain of the Western Mountains...
A difficult and complex forecast in place today from the standpoint of winter precipitation. After unseasonably warm temperatures the past couple of days and lots of sunshine, we return to the winter weather problems today at least in a minimal fashion. The complexity is that confidence is low in winter precipitation type, supporting temperatures, and accumulations. Certainly this event does not rival any of the high impact events we have had in recent weeks this February. Feeling is that this is a minimal impact event at best and almost entirely confined to higher terrain, mostly above 3000 ft.
Temperatures this morning are still well above freezing in most areas this morning, generally in the upper 30s to mid 40s with dewpoints in the 20s, so clearly some room for evaporative cooling as the precipitation arrives later this morning, currently moving northeast from Middle TN and northern AL/GA. However, the timing of this precipitation into the area mid to late morning allows for some additional warming this morning. Current advertised temperatures grids do not even show temperatures throughout the vast majority of the CWA, especially elevations below 2500 ft., even reaching freezing today or tonight. Even with the wedge, largely "in-situ" confidence in temperatures dropping low enough to support accumulations of snow/sleet/freezing rain across the majority of the area remains low to very low as we proceed further into the day as the precipitation spreads further northeast.
With these factors in mind and mainly a rain event with temperatures above freezing, have tailored the Winter Weather Advisory to include areas only along/west of the Blue Ridge and emphasized higher elevations. Would have used elevation potion in GFE, but unfortunately it failed within GFE here, so had to include the entire county and specify the elevation in the wording. Could clearly see the WSW being cancelled early if any winter weather fails to materialize outside the highest terrain mainly in western NC, Grayson county, and southeast WV, specifically western Greenbrier county.
Rain amounts today should generally be 1/2 inch or less. While this should not result in any flooding issues, it combined with all of the recent and frequent rain/snow/sleet/freezing rain events of the past month, sets the stage for a potentially significant flooding threat going into the weekend and early next week, including rivers, creeks, and streams, as FFG values are low with very saturated ground and the potential for 2-4 inches of rainfall during the weekend and early next week.
/Confidence Levels in Forecast Elements/ Temperatures - Moderate to High, Precipitation Probabilities - Moderate to High, Winds - High, Winter Precipitation Threat - Low.
SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 230 AM EST Friday...
Heavy, potentially flooding rains possible for parts of the area this weekend into early Monday...
February has been a wet month across the region with most of our climate sites ranging from around 0.50 inch to 1.25 inches above normal. Much of this precipitation fell in the form of freezing rain, sleet or snow, that helped maintain wet soil conditions as the collective snowpack gradually melted as days warmed.
This weekend, we are looking at a pattern where low pressure heads eastward through the Great Lakes region all while a second low lifts northeast out of the mid-Mississippi valley into the Lower Ohio Valley. As this is transpiring, a warm front is expected to approach the area from the south on Saturday, cross region on Sunday, and stall just to our north Sunday night. As the Great Lakes low heads eastward, its associated cold front then is expected to sweep through the area Sunday night into early Monday.
Southwest flow south of the warm front will increase in velocity and advect a generous amount of Gulf of Mexico moisture into the region. A look at the NAEFS Standard Anomalies for precipitable water show values reaching the 1.00 to 1.25 inch range, or plus two sigma, from Saturday morning through Sunday night. The area with the most prolonged period of plus two sigma is over the southwestern sections of the region -- including parts of the Mountain Empire region and New River Valley sections of southwest Virginia and the Northern Mountains and Foothill region of North Carolina. Our latest forecast will have around two to three inches of rain over the area during the period of Saturday through Sunday night. We will need to watch for potential flooding first in the short term, especially Sunday night with heavier rain showers associated with the passage of the cold front. In a somewhat later time period, mainstream river flooding may be possible, especially within the more reactive headwaters region of the Tennessee River, including the Clinch and Holston Rivers.
Monday into Monday night, cooler and drier high pressure will build into the region. Lingering scattered showers will be possible after daybreak Monday across mainly southern and eastern sections of the region.
Temperatures during this portion of the forecast will average around five degrees above normal on Friday, around ten degrees above normal on Saturday and Sunday.
Confidence in the above scenario is moderate to high on the general synoptic pattern transition. Specifics on rainfall amounts and location of the highest amounts are still a question mark, but signs are pointing to our southwest sections for the highest totals.
LONG TERM /TUESDAY THROUGH THURSDAY/... As of 230 PM EST Thursday...
A cold front will move south into the Carolinas Monday morning. From there, guidance still remains divided on an early week system that could slip in from the southwest, bringing in an opportunity of mixed precipitation whilst cold air lingers. On the other hand, some guidance wants to park high pressure overhead and keep us dry through mid-week. For now, opted with blended guidance that reflects the first option with precipitation moving in. Following that system, a weak frontal passage is possible Thursday, but looks to lack deep moisture with it.
Temperatures through the period will run warmer than normal.