Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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345 FXUS62 KRAH 190013 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 812 PM EDT Sun Apr 18 2021 .SYNOPSIS... A weak surface low pressure center will drift slowly east-northeast over South Carolina and southeast North Carolina through tonight. An upper level disturbance will cross our region late tonight through Monday, then push off the coast late Monday. Weak high pressure will settle over the area Monday night, then move off the coast early Tuesday, setting up a warm southerly flow for Tuesday through early Wednesday. A cold front will cross the area Wednesday afternoon, bringing cooler weather starting Wednesday night. && .NEAR TERM /THROUGH TONIGHT/... As of 305 PM Sunday... Our next weather-maker is a mid level shortwave trough now tracking E into MO/AR. This wave will dampen a bit as it crosses TN into W VA and W NC overnight. Baggy/weak surface low pressure centered just to our S over SC will track slowly to the ENE over E SC and across the SE tip of NC through tonight, keeping our surface winds variable and light. A southwest mid level flow along with an area of upper level moisture noted on GOES WV imagery (Band 8 in particular) E of the mountains has helped support mid level cloud streets and a shroud of high clouds, respectively, over central NC. As this relative moisture plume shifts E through this evening with a narrow slightly drier depth moving in, we should see a period of fair skies before the clouds spread back in late as the wave aloft approaches. Timing this wave and its attending batch of mid-upper moisture just ahead of it places a few showers moving into the Triad/Roxboro areas after midnight, before spreading into the N and NE sections during the predawn hours, although coverage should still be patchy with low amounts. While moisture will increase above about 5k ft, it should not be saturated and should not extend well into the upper reaches of the column through tonight, as PW holds under 0.75" with no opportunity for moisture return in the low levels. Thus, will keep any chances for measurable precip late tonight low. Expect a slightly milder night than last night as clouds increase with slowly rising dewpoints. Lows in the mid 40s to mid 50s. -GIH && .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 320 PM Sunday... The shortwave trough will continue moving E across VA/NC Mon, re- amplifying as it gets into eastern VA/NC by mid to late afternoon. The surface low, meanwhile, will track just off the S NC coast and push offshore, and the weak mainly N and NE flow around this low will mean continued limited to absent opportunity for saturation in the low levels, thus keeping QPF low. But while the forecast soundings show somewhat dry air in the upper levels, increasing forcing for ascent as the deepening wave moves through with dynamic cooling may be sufficient for isolated to scattered showers, more coverage N and E of Raleigh and very low to no pops in the SW. We may see a few storms in the NE if we can manage to moisten up the mixed phase region, and our NE sections will see the best overlap of increasing DPVA and elevated PW. Either way, this will overall be a low-QPF event for the vast majority of the area, with scattered coverage at most. Pops will end W to E in the afternoon, with skies clearing out by dinnertime. Highs in the mid 60s to mid 70s and lows in the 40s to around 50. -GIH && .LONG TERM /TUESDAY THROUGH SUNDAY/... As of 322 PM Sunday... The region should be relatively dry on Tuesday and Tuesday night as low pressure moves from the Plains to the northeast and another low pressure system moves across Florida into the Atlantic Ocean. Both of these systems could clip central North Carolina, allowing for a slight chance of rain Tuesday after midnight. By Wednesday morning, low pressure will be east of Lake Erie, with a cold front extending to the south along the Appalachian Mountains. Models have wavered back and forth a bit with how strong the dynamics along the front will be in North Carolina. Slightly reduced inherited pops, which were chance north of I-64 and a narrow stripe of slight chance south of that, leaving southern counties dry. The warmest temperatures of the week will come Tuesday and Wednesday in advance of the cold front. In all likelihood, the bigger impact from the front will not be rain on Wednesday, but much colder temperatures for the next 36 hours. Between the two nights, Wednesday will have lower thicknesses, but Thursday will have lighter winds. Have continued to undercut guidance through this time period, and the need for a frost/freeze headline across some locations looks likely at this point, although it`s a little too far out to pinpoint exact locations. Highs will range from the upper 50s to mid 60s on Thursday, but rebound 5-10 degrees on Friday as high pressure will dominate the Southeast. Low pressure will develop across the Plains and move east for the weekend. However, the GFS and ECMWF diverge widely by this time. The 12Z GFS shows the low moving across the Great Lakes by Sunday morning, with a second low developing along the Gulf Coast Sunday. Meanwhile, the 00Z ECMWF has the low track south of the Great Lakes more slowly and has Miller B cyclogenesis develop along the Atlantic coastline. With WPC following the European solution, have moved the forecast in this direction. Regardless of the model choice, the weekend appears to be the most likely period for rain this week. The temperature drop behind the weekend system should be much less dramatic than the mid-week front. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... As of 812 PM Sunday... High confidence in VFR conditions to start the TAF period. A surface wave of low pressure will bring in low-level moisture from the coast overnight, resulting in IFR/MVFR CIGs at FAY/RDU/RWI prior to 17Z. Confidence is not high at the moment but guidance has trended in that direction. There is a chance of light rain showers, possibly briefly MVFR, between 15 and 18Z in the Triad and 16 to 19Z at RDU/RWI. Confidence is medium. Outside of any showers, VFR should prevail. Calm winds will become north-northwesterly between 5 and 8 kt during the aft/eve. Outlook: A strong cold front will bring a chance of showers and isolated storms producing sub-VFR conditions on Wednesday. Gusty winds from the west and northwest will also be in place Wednesday night and Thursday. VFR conditions will take over Thursday and Friday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Green AVIATION...Kren/KC

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