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FXUS62 KRAH 021805 AFDRAH

Area Forecast Discussion National Weather Service Raleigh NC 205 PM EDT Sun Jun 2 2024

SYNOPSIS
A trough will bring a chance of showers to the area through tonight.
As we enter the week ahead, expect temperatures, humidity, and precip chances to increase through mid week.

NEAR TERM /TONIGHT/
As of 203 PM Sunday...

Slow moving mid level trough axis continues to move through the region this afternoon. Widely scattered showers/sprinkles continue primarily along and east of US-1 this afternoon, but are still struggling to amount to much as most ASOS/AWOS obs have only shown trace precip amounts. Meanwhile across western NC in closer proximity to the trough, areal coverage of showers is greater but precip amounts remain light, only a few hundredths of an inch.

For the rest of the afternoon into the evening, fairly good model agreement in the idea of additional showers developing across the western Piedmont where forcing for ascent will me maximized near the trough. Rainfall amounts will be light and while there will be at least some instability in play (100-250 J/KG), strong/severe storms aren't anticipated. Showers will dissipate as they move eastward but a stray sprinkle can't be ruled out entirely across the Triangle this evening.

The trough axis will swing through NC overnight. With continued ascent aloft and modest moist advection, additional showers are possible after midnight. Confidence in the finer details of this portion of the forecast remains low. Ingredients are in place for showers overnight, but figuring out the exact placement is a challenge. Meanwhile, CAMs are all over the place with their respective solutions (as would be expected within a weakly forced environment), so I drew in some broad 30-40 PoP values across most of the forecast area (primarily along and east of I-85). Rainfall amounts, where showers occur, should only amount to a few hundredths of an inch.

With cloud cover in place tonight, look for mild lows in the low to mid 60s.

SHORT TERM /MONDAY AND MONDAY NIGHT/
As of 155 PM Sunday...

The trough axis from Sunday will roughly be over the area to start our Mon over the central Piedmont and along the US-1 corridor. This axis will slide SE toward the coast in the afternoon to early evening, with shortwave ridging building east from TN.

The latest CAMs depict a possible leftover MCV from Sunday's convection that may move across the Triangle, Sandhills, and Coastal Plain in the morning hours. While confidence is low on this feature, there will be very little CIN and some elevated CAPE of a few hundred joules to support spotty showers into mid-morning.

As clouds start to erode by early afternoon and heating raises highs into the low to middle 80s, most guidance indicates instability of around 1000 J/kg and deep-layer shear of 10-20 kt with little to no CIN. Most high-res models suggest isolated to widely scattered storm activity could form just about anywhere in central NC with PW's near the 90th percentile of 1.6 inches.

Perhaps the more favored areas for isolated storms would be east of US-1 along lingering outflows/lift from the MCV and a sea-breeze, as well as over the northwest Piedmont where a lee trough should favor storm activity over the higher terrain and tracking ESE with the NW mid-level flow. We do not expect any storms to reach severe limits given the low-end shear. Most storm activity should wane after sunset with loss of daytime heating. Low temperatures should once again be near the middle 60s.

LONG TERM /TUESDAY THROUGH SUNDAY/
As of 205 PM Sunday...

Daily shower/storm chances will continue through much of the week within warm and humid conditions, but odds are tilting in favor of dry weather and slightly lower humidity by week's end as we undergo a pattern shift to deep low pressure over/around the Great Lakes region.

Tue: Very baggy and narrow mid level ridging will build through E NOAM Tue, resulting in a weak steering flow over our area and reduced confidence in forecast details, including exact timing and placement of convection. Surface features will be ill-defined, but there's a good chance of a weak backdoor front pushing into our N and E sections Tue, separating the high off the Southeast coast with another cooler high centered over the New England coast. PWs will continue a slow rise (to 1.5-1.8"), as will surface dewpoints, so even minor low level confluence along a weak frontal zone may help induce and/or support showers and a few storms. With the baggy mid level ridge overhead yielding warm mid levels and poor deep layer shear, any storms should be weakly organized and not strong. But slow storm motion, potentially meandering and congealing cell clusters, and rising moisture content through the column may result in locally heavy downpours. Will keep pops near or just over climatology, with a slight focus on afternoon/evening, but with perturbations trying to push E into our area Tue night as the ridge starts to exit, rain is possible at any time. Expect slightly above normal temps, with highs in the mid 80s to near 90 and lows in the 60s.

Wed-Thu: Still appears that pops should be highest these two days.
Northern stream troughing in the Upper Midwest early Wed will continue to deepen and dig strongly to the SE through the Great Lakes region and toward the Ohio Valley, leading to strengthening WNW steering flow at our latitude and, especially, to our W and NW, as a synoptic cold front slowly approaches from the WNW. Forecast PW is projected to be quite high, with models suggesting values at or above 2", nearing records. Models also hint at a pattern favoring nocturnal backbuilding MCSs in our area and just upstream over the Mid Miss Valley/Ohio Valley/Mid South, including diffluent thicknesses over KY/TN into VA/NC, an 850 mb theta-e ridge nosing into the W Carolinas from the WSW, and increasing low level SW jetting esp Wed night. This, along with anomalously high PW and the LREF's projected 750-1000 J/kg SBCAPE, would suggest considerable clouds overall and above-normal pops in the good chance to likely range. Such convection details are tough to pin down at this time range with any reasonable confidence, but will indicate that convection potential will be more equally spread throughout the day and night, instead of focused purely on the afternoon/early evening hours. Temps should be near to a category above normal.

Fri-Sun: The overall longwave pattern will shift to anomalously low heights aloft across a large swath of the Great Lakes, adjacent Canada and the Northeast as a deep northern stream low settles over or just N of the Great Lakes. Deterministic models and ensemble modeling systems are all in pretty good agreement on this, although they still differ in terms of the associated low/trough, including whether it spreads in a more W-E orientation or remains concentric and digs S and SE into the Mid South and Carolinas. In either scenario, we're likely to see the approaching surface cold front pushing well into the CWA Fri and to our SE by Sat/Sun, drawing in markedly lower PWs, slightly cooler-than-normal thicknesses, and much lower surface dewpoints. Will retain pops Fri but keep just slight chances NW and near-climo chances SE, although Fri pops may need to be reduced further if model trends of pushing the cold front through much of our area by Fri morning hold (and this dry-Fri scenario is supported by the latest EC-AIFS). Expect dry conditions Sat/Sun, with temps slightly below normal. -GIH

AVIATION /18Z SUNDAY THROUGH FRIDAY/
As of 110 PM Sunday...

Mainly light sprinkles across the area at the moment but conditions remain VFR. Additional showers are expected later this afternoon, primarily around INT/GSO and there could be brief periods of MVFR ceilings within the strongest showers. Meanwhile to the east, conditions should remain dry (outside of the aforementioned sprinkle) through 00Z although some of the INT/GSO showers may make a run at RDU right around 00Z and I included a few hours of VCSH.

Late tonight, most guidance indicates widely scattered showers across the area as a trough moves through NC. Elected to include a few hours of VCSH at RDU/FAY/RWI as this trough crosses the area although confidence in how this late night scenario will play out is low.

Outlook: Additional, mainly diurnally driven showers and storms, are expected through much of this week as we return to a more typical June pattern. Highest storm chances are likely at INT/GSO although all 5 TAF sites could see impacts in the form of non-VFR cigs/vsbys within any showers that develop.

RAH WATCHES/WARNINGS/ADVISORIES
None.

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