textproduct: Raleigh

SYNOPSIS

A mid and upper-level trough and accompanying surface cold front will move slowly eastward across the Middle Atlantic and Carolinas through Wednesday.

NEAR TERM /THROUGH TONIGHT/

As of 400 PM Tuesday...

* Convection will become increasingly-numerous, and slow- moving/backbuilding with a primary threat of heavy rain/flooding, over the Piedmont and wrn Sandhills this evening

A positive tilt mid/upr-level trough stretching this afternoon from ON to the mid MS Valley will migrate ewd and reach the vicinity of the cntl and srn Appalachians by 12Z Wed. It will be immediately preceded by a plume PWs around 2.25" and also a convectively- amplified mid-level trough that includes this afternoon a few MCVs and areas of pre-frontal convection over cntl PA, the srn OH/WV border, and ern TN/KY, respectively. The latter and srn-most feature, and another that may develop from growing convection over the wrn Carolinas, will focus mesoscale forcing for ascent as it/they progress slowly east and across the NC Piedmont tonight.

At the surface, a Piedmont trough will remain over cntl NC, downstream of an outflow-reinforced and modulated front that will approach from the northwest and extend from the nrn Middle Atlantic coast to the srn Appalachians by 12Z Wed.

Diurnal convection, minimal in coverage and intensity along the Piedmont trough, will become increasingly-numerous over the Piedmont late this afternoon through evening, as the aforementioned upstream convection/aggregate outflow and MCVs from the wrn Carolinas to ern TN/KY, edge ewd. Swly, 15-25 kts of lwr to mid-tropospheric flow and mean wind evident on the 12Z MHX and RNK RAOBs will support multi- cell development and individual cell motion to the northeast at similar speeds this afternoon. However, a nocturnal acceleration of a modest, ~25 kt low-level jet will become anti-parallel to the mean wind and cause upwind propagation vectors to decrease and support slow-moving/backbuilding convection tonight. While a threat of a few strong to tree-damaging wet microbursts will increase with the increase in number of cells over especially the nw Piedmont through early evening, flash flooding, especially in urban areas, will pose a greater concern. Low temperatures will be in the 70s.

SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/

As of 215 PM Tuesday...

Upper level trough will shift across the Mid-Atlantic region Wednesday. At the surface, a cold front extending from Maine down across the Appalachian Mountains into the deep south will slowly move across our region beginning early Wednesday and exiting our region sometime Thursday morning. Showers and storms early Wednesday morning will be scattered becoming more numerous/widespread by the mid/late morning. As the front progresses east, increased chance of storms will be along and east of the US1 corridor in the afternoon and evening hours. Most of the precipitation will clear west to east late evening and continue the eastward drying trend into the early overnight hours.

While stronger storms will have some gusty winds, the main threat with these storms will be heavy downpours resulting in flash flooding. WPC has portions of central NC in a slight risk (level 2 of 4) for flash flooding for Wednesday, mainly across the NE, near the VA border and coast. While it only extends a few counties into RAHs region, this could later be extended further inland. Generally everywhere else is in a marginal risk for flash flooding (level 1 of 4). Thus, everyone across the region should be aware of stronger thunderstorms with quick heavy downpours, especially in low lying and poor drainage areas. Rainfall amounts from this afternoon through Thursday morning will vary from 0.50 to an inch in the south 0.75 to 1.50 across the north. Some models are showing localized amounts of 1.50 to 2.50 inches possible in areas across the northern Piedmont.

Temperatures will be very dependent on when the rain moves in but expect highs in the low 80s north and mid 80s south. Overnight lows will range from upper 60s to low 70s.

LONG TERM /THURSDAY THROUGH TUESDAY/

As of 215 PM Tuesday...

Following this trough associated with the front, a weak ridge will build in for the weekend. Due to this, moisture flow into the Carolinas will be weakened and reduce temperatures and dew point temperatures slightly. Thus, overall reducing precipitation chances through the weekend.

The only area of interest for precipitation over the weekend will be in the Sandhills and Southern Coastal Plain. Recent GFS and ECWMF model runs continue to have low confidence with the development of a tropical system off of an old frontal boundary west of Florida. Current ensembles have the system remain disorganized as it crosses the Florida peninsula and up along the Mid-Atlantic coast. With the low confidence of the track, PoPs remain low with isolated showers through early next week.

Daily temperatures will range from the low to mid 90s during the day with overnight lows in the upper 60s to low 70s.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

As of 830 PM Tuesday...

A slow-moving, broken band of convection associated with an upper trough over eastern TN and western NC is beginning to move east into the NW Piedmont, including around INT and GSO. Any storms embedded within the band could result in brief MVFR to IFR conditions along with gusty winds, such as the line currently moving through GSO. The band likely won't reach RDU until the overnight hours, but some isolated showers will be possible anywhere in central NC out ahead of it. Furthermore, the band will be associated with widespread MVFR to IFR ceilings from late this evening into the overnight hours over the Piedmont. Even some LIFR ceilings can't be ruled out especially around the Triad. The band will then push farther east into FAY and RWI on Wednesday morning, but by this point, it will be in a weakened state, and ceilings may largely be MVFR there instead of IFR. Ceilings should lift to VFR everywhere by the afternoon, but scattered to numerous showers and storms are expected to develop across central NC once again, particularly in the south and east.

Outlook: Morning stratus and fog will be possible amid a lingering, unseasonably moist airmass Thu morning, especially at ern sites, ahead of a slow-moving and weakening cold front. Isolated showers and storms may linger in the south and east on Thursday, before dry weather and VFR conditions largely prevail from Friday into the weekend.

RAH WATCHES/WARNINGS/ADVISORIES

None.