244 FXUS62 KRAH 200813 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 412 AM EDT Sat Aug 20 2022 .SYNOPSIS... A weak surface boundary will hold across the eastern Carolinas through the weekend. A series of upper level disturbances will cross the region late Sunday into Monday. && .NEAR TERM /TODAY THROUGH TONIGHT/... As of 330 AM Saturday... Water vapor satellite showed a deep upper low centered across the Midwest, a ridge off the coast near Bermuda, and a weak shortwave moving east across NC. At the surface, a front was stalled along the coast of the Carolinas. Radar displayed light showers developing across the NE Piedmont and Coastal Plain associated with the upper wave, and a large area of showers and thunderstorms along the coast associated with the surface front. Mostly light showers will remain possible early this morning east of U.S. Hwy 1 as the upper wave moves east out of the area. Today will be the driest day out of the weekend, with mostly isolated diurnal showers and thunderstorms possible this afternoon. Dry air moving in aloft behind the departing wave will limit convective coverage, however the eastern half the of the region may see more scattered showers and storms develop were moisture and instability increases. Shear and CAPE are low, and no severe weather is expected at this time. Highs in the mid-80s will feel more like the upper 80s to low 90s thanks to higher dewpoints moving into the region. Lows tonight will be in the upper 60s to low 70s. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 400 AM Saturday... Moisture aloft quickly rebounds early in the day on Sunday as an upper wave moves east from the TN Valley across NC throughout the day. Showers will first develop across the west early in the morning, and move east into the Coastal Plain by early afternoon. Then, another shortwave will move across the region for the second half of the day, generating an additional chance of eastward moving showers and thunderstorms for the late afternoon into overnight. There may be a few stronger storms that develop in the afternoon as BL shear slightly increases, however local flash flooding from heavy rain may be the greater threat as precipitable water values increase to near 2.25" by the afternoon. As of now, most showers/storms look to move quickly enough for most areas to avoid the flood threat, however urban areas that have training storms and more slow-moving storms will have a higher chance at local flash flooding. The stalled surface front to our east may help strengthen convection across the Coastal Plain, although the front will being to wash out by the end of the weekend. Although confidence in areas observing precip Sunday is high, confidence in the timing of precip is on the low side due to disagreement in the high-res models. Increased cloud cover and precip will keep highs slightly lower compared to Saturday, with areas near the VA border reaching the low 80s by the afternoon, and areas to the south reaching the mid-80s. Lows will again be in the upper 60s to low 70s. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 400 AM Saturday... A mid/upper trough will slowly push east from the OH Valley and extend from Upstate NY down the spine of the Appalachians on Monday and Monday night. A jet streak will also be across the northern mid- Atlantic on Monday, placing central NC in the right entrance region of the jet. Upper divergence from this feature, along with 10-20 m height falls from the approaching mid/upper trough and shortwave energy rounding the base of the trough, will result in good forcing for ascent. At the surface, a weak boundary will reside over the NC Piedmont or Foothills. Deep southwesterly flow and good moisture transport ahead of this boundary will result in PW values of around 1.75-2.25" (or 1-2 standard deviations above normal) across most of central NC, highest SE. Thus fairly widespread showers are expected across central NC on Monday, particularly in the south and east where forcing and moisture will be maximized. The one exception may be the NW Piedmont where the flow aloft should begin to turn more westerly, shutting off the best moisture transport and shortwave energy, especially by the afternoon and evening as the trough axis approaches. So cut down POPs to high chance there. Instability looks marginal (500-1000 J/kg of CAPE) but still enough to have a chance of storms in the afternoon/evening. The widespread clouds and precipitation will keep high temperatures below normal on Monday, in the upper-70s to lower-80s. A secondary stronger cold front looks to move through at least part of the region on Tuesday morning before getting hung up somewhere near or over central NC. Drier air will filter in behind the front, but it is unclear exactly where the front will set up. Regardless, it does still appear from the GFS and ECMWF that there will be a fairly strong gradient in PW values across central NC on at least Tuesday and Wednesday, lowest NW and highest SE. Thus the greatest POPs (high chance) are in the SE and the lowest POPs (slight) are in the NW on these days. POPs increase a bit areawide on Thursday and Friday as the flow aloft turns more southwesterly again and PW values increase. However, compared to Monday, the rest of the workweek should have storms that are mainly diurnally-forced and less widespread. This is due to the main part of the mid/upper trough lifting NE into eastern Canada, while only weak troughing over the Eastern US remains. High temperatures from Tuesday through Friday should be near normal (generally in the 80s), while lows will be slightly above normal (generally mid-60s to lower-70s). && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... As of 130 AM Saturday... LIFR/IFR ceilings and VIS will continue to develop early this morning across most of the region. Scattered -RA/DZ will also continue overnight, mainly along and east of HWY-1. Rain and low CIGs/VIS will improve to VFR conditions by mid to late morning. Isolated TSRA will develop this afternoon near KRWI, then diminish by the evening. Looking beyond 06z Sun, scattered showers and storms are possible Sunday, with rain chances increasing for Sunday night through Monday night, along with areas of fog late Sunday night/Mon morning. After these high rain chances and likely sub-VFR conditions Sun night through Mon night, it'll turn a bit drier for Tue through Thu, although a few afternoon storms will remain possible, esp over eastern sections. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...JJT/Hartfield NEAR TERM...JJT SHORT TERM...JJT LONG TERM...Danco AVIATION...JJT/Hartfield