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FXUS62 KRAH 070541 AFDRAH

Area Forecast Discussion National Weather Service Raleigh NC 140 AM EDT Tue May 7 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 935 PM Monday...

An area of showers and isolated thunderstorms that tracked across much of the northern half of the forecast area is currently falling apart around Rocky Mount, while another broken line of showers and thunderstorms extending from Myrtle Beach to Charlotte and eastern Tennessee is now approaching from the west. An increasing low-level temperature inversion should reduce the amount of instability for thunderstorms, but still think that thunderstorms will be a possibility through the night, although severe potential is minimal.
The observed precipitable water value from the 00Z GSO sounding was 1.18 inches, just over the 75th percentile for the date, meaning that the showers/thunderstorms could be efficient rain makers as well. Expect another muggy night with overnight temperatures in the low to mid 60s.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/
As of 340 PM Monday...

Tuesday and Tuesday night: Aloft, as the s/w moves east and off the mid-Atlantic coast, a brief period of omega blocking will set up as the sub-tropical ridge builds northward through the Southeast US, central Appalachians, OH Valley and western Great Lakes. To the east of the block, a low will progress eastward through Quebec and Newfoundland Tue, then out over the northern Atlantic Tue night. To the west, a large low will sit over the northern Plains as several s/w disturbances rotate around it. The eastern low progressing eastward Tue night will weaken the block, allowing a leading s/w moving through the OH Valley around the western low to push the ridge slightly eastward and suppress it southward. At the surface, a warm front will lift newd through the area early Tue, with a Piedmont trough setting up east of the mtns and strengthening through Tue night as a low develops over the southern Great Lakes.
Expect continued advection of warm, moist air into the area, with PWATS starting the day around 1.7 inches, decreasing slightly with daytime mixing, but remaining largely in the 1.4-1.6 inch range. The 12Z NAM and 12Z GFS both have MLCAPE values of about 1000-2000 J/Kg (GFS lower than the NAM) across all of central NC Tue aft/eve, with effective shear around 30 kts. The SPC has included just about all of central NC in a marginal risk for Tue. The big question will be the presence of a forcing mechanism to get storms firing. Look for showers/storms to largely form along the developing lee trough and/or differential heating boundaries if they are present. An isolated strong to severe storm is possible, with the primary threat of damaging wind gusts and possibly hail. As for temperatures, highs should top out in the mid to upper 80s, while lows in the mid 60s to around 70 degrees are expected.

Wednesday and Wednesday night: Aloft, the leading s/w will continue eastward through the Northeast US toward the eastern low, while the western low finally begins to migrate slowly eastward. A second s/w will swing through the Plains and the MS Valley Wed/Wed night. At the surface, the surface low will move slowly eastward through the Northeast US Wed and offshore Wed night. Another low will develop along the front over the southern Plains early Wed, lifting newd into the upper MS Valley through Wed eve before drifting eastward into the OH Valley Wed night. The trough over central NC will weaken and lift northward out of the area as the low move east and offshore Wed night. The frontal zone between the two lows should generally remain north of the area through Wed night, with continued swly flow over the area. Expect continued advection of warm, moist air into the area, with PWATS largely in the 1.4-1.7 inch range. The 12Z NAM and 12Z GFS both have MLCAPE values of about 1500-2500 J/Kg across all of central NC Tue aft/eve, maximized over the eastern Piedmont and Coastal Plain, with effective shear again around 30 kts. The SPC has included all of central NC in a marginal risk for Wed. The forcing mechanism will likely be the lee trough as it moves eastward through the area. An isolated strong to severe storm will once again be possible. As for temperatures, highs should be about a category higher than Tue, topping out in the upper 80s to low 90s. Lows should be in the upper 60s to low 70s.

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 /06Z TUESDAY THROUGH SATURDAY/
As of 140 AM Tuesday...

Several small clusters of showers and thunderstorms extend from the NC mtns to the western and central Piedmont.
The general model consensus is for the convection to drift east into central and eastern NC overnight and into the early/mid morning hours. While associated MVFR to IFR restrictions will be possible at just about any of the TAF sites, confidence is the exact timing and location is low.

Additionally, continued unseasonably moist/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.

Some additional convection is possible this afternoon and evening, but should be more isolated/widely scattered in nature and potentially limited INVOF KINT and KGSO.

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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