Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 262316 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 715 PM EDT Tue Mar 26 2024 .SYNOPSIS... High pressure will extend southward across the region through this evening. As a front approaches from the west and southwest, an area of low pressure will lift northeast through the Southeast states and eastern Carolinas Wednesday through Thursday. The cold front will move eastward through central North Carolina Thursday night. Dry and warming weather is expected Friday and Saturday. && .NEAR TERM /THROUGH TONIGHT/...
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As of 715 PM Tuesday... Early evening update included adding thunder to portions of the region as there is limited instability which is resulting in a few rumbles of thunder of the line of precipitation moving across the region. As this line of precip moves across the region over the next few hours, instability is expected to be near zero, thus chances for thunder of the next few hours diminish slowly. Rain will be mostly light as is moves across the region, but there are a few moderate to heavy showers developing along the line. A short lull from rain is expected after this first round moves out, before another round of more active weather is expected later tonight and continue through the overnight hours. As of 330 PM Tuesday...Water vapor imagery depicts a subtropical ridge axis along the East Coast, sandwiched between a closed mid/upper low meandering near Bermuda and broad troughing over the central US. Within this broad troughing, one shortwave and occluded surface low are currently centered over the upper peninsula of MI, which will continue to push NE into southern Ontario through tonight. This system is dragging a cold front to its south that will slowly push east through the TN Valley and reach the Appalachians tomorrow morning. A period of rain will be possible over the western Piedmont from late this afternoon into early evening, particularly over the Triad. But kept POPs at only slight to low chance as model soundings show the low levels staying fairly dry and high-res guidance depicts the rain fizzling out as it heads NE. GLM satellite data and surface obs even show isolated thunder over western NC, but not expecting it to get this far east. Otherwise it will be dry across the rest of central NC through this evening as the best forcing and moisture stay to our west, and surface ridging noses down the Mid-Atlantic coast from a high over the Canadian Maritimes. However, clouds will continue to thicken and lower, becoming overcast in the west and mostly cloudy in the east. A surface low or inverted trough has developed over the northern Gulf of Mexico today and will slowly lift NE, pushing a warm front that begins to push into southern NC overnight. The main NE-SW oriented axis of widespread showers will begin to enter the Triad after about midnight, slowly spreading east into the rest of the Piedmont overnight, where POPs are likely to categorical. As the warm front lifts north, there could be enough instability for an isolated storm especially south, but confidence is not high enough to include in the forecast at this time. Low temperatures tonight will be mild, ranging from mid-40s far NE to mid-50s far SW.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 245 PM Tuesday... Confidence remains high in a somewhat prolonged and briefly moderate to heavy rainfall event, as a polar low over N MN and a large upper level longwave trough over central NOAM (with embedded shortwaves) early Wed lumbers eastward into and through E NOAM by Thu night. One noteworthy player, a shearing vorticity lobe now diving through the Desert Southwest in the southern portion of the longwave trough, swings over the Gulf Coast through Wed evening and through the Carolinas late Wed night through Thu, taking on a neutral to slight negative tilt in the process. Our PWs will steadily ramp up, peaking at 150-200% of normal over our area (approaching daily record maxes) and over coastal NC Wed afternoon through early Thu before the anomalously high values push further E. The highest rain amounts will fall through the heart of central NC Wed and over the Coastal Plain Wed night, coincident with peaks in upper divergence generating bursts of greater large-scale ascent. At the surface, low pressure over the Gulf will lift NNE through GA/SC through Wed, with a cold front extending southward from it and a warm front edging into our SE sections, while a weak inverted trough extends NNW through W NC, keeping our NW sections in the cooler/more stable air attached to a weak cool mesohigh centered near and off the Mid Atlantic coast. By Wed night into Thu, the approaching mid level shear axis deepens the surface frontal low (or lows, most likely) to our S/SE as the frontal zone it sits along is kicked eastward, resulting in a trend toward cool and more stable low levels areawide Thu as high pressure begins to ease into the area from the lower Miss Valley. An increasing MSLP gradient between this high and the slowly exiting front should lead to brisk gusty winds late Wed night through Thu. Most models are in fairly good agreement on this pattern, although vary a bit with front and low tracks, contributing to greater uncertainty with temps Wed, esp through the Hwy 1 corridor which could end up on the cooler or milder side of the low/front. Forecast confidence is trending a bit higher with storm total amounts through the heart of the precip area, topping out around 3- 3.25" surrounded by a 1-2" buffer, although important model variations in placement persist. Last night`s traditional and AI models as well as ensemble systems have trended further E with the band of heaviest rain as compared to yesterday, although they most recently have nudged back slightly west. Overall, we think that the heaviest totals will be from Hwy 1 E, and possibly aligned along the I-95 corridor where the greater moisture transport and longer residence time of high PW will coincide with the peak upper divergence and mid level DPVA. Confidence with overall timing is fairly high, although models vary quite a bit with timing the departure of the precip Thu into Thu evening. Think that the NBM/LREF mean timing remains a bit too slow with the surge in NW and N flow behind the front, so have sped up the precip exit a bit Thu. Given that this precip will be spread out over 30+ hours in most spots, the excessive rainfall outlook is maintained over our E half this afternoon at a marginal risk. Our Coastal Plain areas should be able to mostly handle these amounts, particularly given the existing drought conditions there and long duration, so no plans for a flash flood watch at this time. I could certainly see the potential need for a few flood advisories esp in poor drainage areas, with an uptick in river levels across the board, but there is high uncertainty of any situation more dire than that occurring, and the latest river forecasts keep our points just below flood stage at the worst. The overall rainfall timing is to bring likely to categorical pops eastward through the CWA Wed, then move these higher pops to just the E half Wed night into Thu morning before sweeping pops E and out Thu afternoon. Some embedded thunder is likely within this system, including a few short bows, focused on Wed into Wed night in the S and E. Lapse rates stay rather muted overall until Thu, when upper level clearing moves in from the W, and despite mid level SW flow increasing to 40-50 kt Wed, the early rain arrival will limit instability Wed, esp across our N and W. Certainly, though, an isolated strong wind-maker is possible over our SE. Expect highs 56-72 Wed, including mostly 50s across the far N and NW Piedmont that will be NW of the low track, holding in the cooler and more stable air with high rain chances through the day. Lows 44-53 Wed night, highs 53-64 Thu, and lows 36-42 Thu night with clearing skies. Given the complexity of the expected surface pattern, confidence in the details of these temps is not high. -GIH && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 250 PM Tuesday... Dry and windy conditions Friday. Warming temperatures through the weekend. Rain chances increase early next week, although uncertainty exists. Friday: Surface high pressure centered over the Tennessee Valley will slowly shift over the Southeast and off the Florida/Georgia coast by early Sat morning. A tight pressure gradient will exist over central NC between this feature and the deepening low pressure as it migrates into the Canadian maritimes. Surface winds will increase Fri afternoon through the early evening as the boundary layer mixes up into 25-35 kts of 925-850mb WNW flow. Momentum transfer from point soundings range from the low 20 kts (SW) to upper 20 kts (NE) with the top of the mixed layer suggesting up to low 30 kts may perhaps be possible, but will likely depend on coverage/thickness of afternoon stratocu that may prevent deeper mixing and lower gusts. A dry downsloping component through the mixed layer will also favor warming and drying downsloping winds and have trended the forecast towards a drier (mid/upper 30s dewpoints) and warmer (upper 60s to low 70s for highs) scenario through central NC. This will result in RH falling into the 30s to mid/upper 20s during the afternoon and may result in increased fire concerns if soil moisture is able to recover from rainfall from Wed through Thurs. Sat through Tues: The remainder of the forecast is mostly dry through Sun night. Zonal flow aloft and deepening return warm low- level flow will continue to moderate temperatures into the 70s to low 80s by Sun with weak disturbances bringing wisps of upper level cloudiness. By Mon, surface high pressure ridging down from eastern Canada into the Mid-Atlantic will push a cold front into the Mid- Atlantic and would provide the focus for some light rain as strengthening WAA at 850mb rides over top of the cooler air along and behind the cold front (best chances across the NC/VA border). The better shot at precipitation comes potentially Tues into early Wed when there will be better H5 height falls from a northern-stream trough as it dives out of central Canada and pivots across the Great Lakes and northern Mid-Atlantic where PWATs ahead of the trough are around 1.5 inches. Highs will be tricky early next week and will entirely depend on the cold frontal placement and associated rain chances behind it; highs will likely be in the mid 60s behind the front to low/mid 80s to its south. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... As of 230 PM Tuesday... Mostly VFR conditions will continue across central NC through this evening. However, brief periods of MVFR ceilings have already been observed and can`t be totally ruled out across the far west (including INT and GSO). Patchy light rain also can`t be ruled out there later this afternoon into the evening. Elsewhere, it will just be dry with thickening and lowering clouds. The main NE-SW oriented axis of widespread light to moderate rain will begin to enter the Triad after about 03z, slowly spreading east into the rest of the Piedmont and Sandhills (including RDU and FAY) overnight, then the Coastal Plain tomorrow morning. This rain will be accompanied by widespread MVFR then IFR ceilings, with LIFR even possible at INT and GSO. A separate area of low stratus could bring MVFR ceilings into RWI sooner (after midnight tonight), but IFR may not reach there until after the end of the TAF period. Outlook: Rain showers and IFR/LIFR conditions will persist across most areas through Thursday morning. Isolated TSRA are also possible Wednesday and Thursday. VFR conditions will return from west to east Thursday afternoon and evening and continue into Sunday. Gusty winds of 20-30 kts are expected each day from Thu into Sat, from the N on Thu, from the W/NW on Fri, and from the SW on Sat. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Danco SHORT TERM...Hartfield LONG TERM...Swiggett AVIATION...Danco/JJT

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