Sunrise 6:12 AM   Sunset 8:07 PM Moonrise 4:09 AM   Moonset 5:43 PM

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FXUS62 KRAH 061839 AFDRAH

Area Forecast Discussion National Weather Service Raleigh NC 239 PM EDT Mon May 6 2024

SYNOPSIS
A series of mid to upper-level disturbances will interact with an unseasonably moist airmass as they move across NC through Thursday, while sub-tropical high pressure will otherwise extend across the South Atlantic states. A cold front will move across the region on Friday.

NEAR TERM /THROUGH TONIGHT/
As of 1055 AM Monday...

The gridded morning forecast update was sent with just minor tweaks to what should be another day of warm and unseasonably humid conditions, with scattered to numerous convection that will come in waves and may last through the night.

Both the GSO and MHX 12Z-observed soundings sampled minimal convective inhibition and an already weakly unstable environment over NC this morning. Showers and storms are consequently expected to become numerous in coverage with additional diurnal heating and destabilization through the afternoon, probably first associated with ongoing clusters and weak MCVs moving newd from w-cntl SC/ern GA and into the srn NC Piedmont.

PREV DISCUSSION
/ISSUED 330 AM EDT Mon May 06 2024/

A shortwave trough over the middle MS Valley will deamplify as it advances eastward, progged to reach the central and southern Appalachians this evening and then across NC and the mid-Atlantic States tonight. A weak area of low pressure is expected to develop over Va during the afternoon and evening, with a surface trough taking shape in the lee of the mountains. Renewed SWLY moisture advection ahead of this trough will lead to a resurgence of anomalous moisture into the region with PWATs 1.6-1.8, near record daily maximum.

A parade of upper disturbances will move through the region during the period. And based on upstream radar observations, there is a high probability that a prominent MCV or two will emerge to support a west to east moving band of deep moist convection(DMC), potentially multiple bands, through the afternoon and evening.

Compared to previous days, more robust instability of 1000-1500 J/Kg should develop across the area, likely maximized east of US 1 where strongest insolation is expected. Shear will increase slightly, with models indicating a pocket of enhanced shear of 25-30kts into western NC late this afternoon and evening. Thus, cannot rule out an isolated severe cluster or two Monday afternoon and evening. As we've seen the past few days, the anomalous high moisture in place will also support an isolated flooding threat, primarily in urban and poor drainage areas.

Rain chances should decrease by the late evening, though some lingering isolated convection overnight owing to the dampening upper trough moving through the region.

Highs ranging from upper 70s/near 80 north to lower/mid SE. Lows in the lower to mid 60s.

SHORT TERM /TUESDAY AND TUESDAY NIGHT/
As of 330 AM Monday...

The aforementioned dampening trough will move off the mid-Atlantic coast during mid to late morning. Synoptic scale subsidence will overspread the area in it's wake, with a westerly downslope component noted over the area. However, moisture/PWATS will remain exceptionally high as strong insolation fuels moderate instability during the afternoon. Discernible forcing is weak, limited to daytime heating, weak sfc convergence along a lee side trough across the area, and quite possibly a subtle upper perturbation with the back/anticyclonic side of the exiting trough. If storms do develop, sufficient deep layer shear of 30-35 kts could support an isolated severe storm, with damaging winds the primary threat. Warmer with highs ranging from mid 80s north to upper 80s/near 90 south.

Convection will dissipate after sunset. Lows 65-70.

LONG TERM /THURSDAY THROUGH MONDAY/
As of 202 PM Monday...

Thursday/Friday: There is good consensus amongst models supporting an upper trough moving east from the Great Lakes/Midwest across the eastern seaboard Thursday into Friday. This feature will promote increasingly swly flow and deep moisture advection into the southeast with PWAT rising to 150 to 200 % of normal.

At the sfc, a weak low initially over IN/OH Thursday morning, will deepen some as it progresses east into the Mid-Atlantic through Thursday night. An associated cold front will approach the Southern Appalachians Thursday night, before passing through central NC on Friday. Given high humidity and temperatures reaching the upper 80s/lower 90s on Thursday, moderate instability is expected to develop across our area ahead of the approaching front.

Aloft, increasing mid-level height falls and associated perturbations will help to generate widespread pre-frontal showers and storms which should grow in coverage/intensity Thursday afternoon. Additionally, severe parameters including bulk-layer shear (30 to 40 kts), 0-1 km shear (15 to 25 kts), mid-level lapse rates (>7 C/km), and even helicity (200 to 300 units) will all be elevated. As such, there still appears to be a good chance for severe weather (potentially widespread) Thursday and Thursday night.
Damaging wind gusts, large hail, and isolated tornadoes would all be possible. The SPC has outlined our entire area with a 15% chance for severe storms four days in advance, increasing confidence that Thursday could be a complex severe weather day.

Depending on the eventual evolution of the cold front, some guidance does show instability forming ahead of the front as it moves through our area on Friday. As such, maintained thunder in the forecast for those south of Raleigh on Friday. Additionally, the upper trough will swing through on Friday which could generate additional showers/storms into the evening period. Highs on Friday may be a bit tricky given uncertainty wrt to the advancing cold front. For now, highlighting mid to upper 70s north to lower to mid 80s south.

Saturday through Monday: The cold front will have pushed east of the area by Saturday morning, behind which considerably drier and cooler air will filter across central NC. An additional weak perturbation aloft will pass over later Saturday which may generate a few showers across our northern areas, but overall the area should stay mostly dry. Similar conditions are expected Sunday through Monday, with dry and cooler temps in the upper 70s.

AVIATION /18Z MONDAY THROUGH SATURDAY/
As of 235 PM Monday...

Patches of MVFR ceilings from earlier lower ones may linger for another hour or two but otherwise lift to VFR this afternoon.
Scattered to locally numerous showers/storms --and associated brief downpours, flight restrictions, and gusty surface winds-- will then pose the primary aviation concern through early tonight.
Continued unseasonably humid air will also favor the redevelopment of areas of IFR-MVFR stratus late tonight-Tue morning. Associated ceilings should then lift and scatter and yield to a gusty swly surface wind by ~14-16Z Tue.

Outlook: There will be a chance of mainly afternoon-evening showers and storms throughout cntl NC through Thu, then ahead of a passing cold front, mainly at FAY, on Fri.

CLIMATE

Record High Minimum Temperatures:

May 8: KGSO: 66/1938 KRDU: 68/1930 KFAY: 70/2003

May 9: KGSO: 68/2002 KRDU: 70/1936 KFAY: 71/2009

RAH WATCHES/WARNINGS/ADVISORIES
None.

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