Area Forecast Discussion

WHAT HAS CHANGED

* Rainfall amounts and the potential for storms have increased slightly more for Friday.

KEY MESSAGES

As of 400 AM Wednesday...

1) Scattered showers and perhaps a few storms are possible from Wednesday night into Thursday night. Temperatures will be well above normal through this period.

2) The chance of showers will maximize ahead of and along a cold front on Fri, with a few thunderstorms possible especially late morning through afternoon.

DISCUSSION

As of 400 AM Wednesday...

KEY MESSAGE 1... Scattered showers and perhaps a few storms are possible from Wednesday night into Thursday night. Temperatures will be well above normal through this period.

A broad mid/upper trough will approach from the west through Thursday, with an embedded weakening shortwave that moves from the Deep South into the Southern Appalachians on Wednesday night. Deep- layer moisture will increase with deep SW flow bringing in plenty of Gulf moisture. PW values are modeled to be as much as 200-225% of normal. This will result in a chance of showers beginning on Wednesday evening/night, with the western Piedmont being the most favored area, but the best forcing will still go to our west and north. So forecast rainfall amounts are less than a quarter inch.

There is also a chance of showers during the day Thursday, and isolated storms are possible given about 500-1000 J/kg of CAPE. But coverage should be more isolated given a relative minimum in forcing. Shower and storm chances increase again late Thursday night as a more potent shortwave tracks into the lower MS Valley and a slow-moving cold front approaches from western NC.

Due to the southerly flow ahead of the cold front, temperatures will be very warm today and tomorrow, with highs in the mid 70s to lower 80s (10-15 degrees above normal). Lows will be in the lower-to-mid- 60s.

KEY MESSAGE 2... The chance of showers will maximize ahead of and along a cold front on Fri, with a few thunderstorms possible especially late morning through afternoon.

The models indicate a mid/upr-level cyclone now over the cntl Great Basin will progress ewd and reach the mid MS Valley and Mid-South by Friday morning, then pivot ewd and across the OH and TN Valleys Friday and the nrn Middle Atlantic and Northeast Fri night. Related modest, 40-60 meter 500 mb height falls, and 35-45 kts of swly 500 mb flow, will overspread cntl NC on Fri, as the strongest flow and forcing for ascent otherwise pass just to the northwest and along the cntl Appalachians.

At the surface, a synoptic cold front that will have slowed and possibly stalled over the southern Appalachians by early Friday will move slowly ewd and across the srn Middle Atlantic and Carolinas through early Friday night, then offshore Sat morning. The front may be preceded by a pre-frontal trough or differential heating/outflow boundary from elevated early morning convection Fri, which may serve as the principal focus for deeper, surface-based convection by late morning-early afternoon. Mesoscale uncertainties regarding the location and extent of early morning convection will have ramifications on where subsequent convection may develop and deepen with diurnal heating later Fri, and where the corridor of heaviest rain may align.

Regarding that rainfall potential, there has been a slight increase in QPF across physics-based and AI guidance and ensembles since 24 hours ago. Specifically, the 50th percentile of each in 00Z/4th guidance depict 0.5 to 0.75" amounts, up by about a quarter inch and what may be considered the "best guess" at this time. 10th percentiles range from around 0.25", while 90th percentiles range from 0.75 to 1.5", highest in EPS and GEFS guidance and lowest in their AI counterparts. While the availability of hi-resolution, convective allowing guidance may increase forecast confidence in most likely amounts as time draws nearer, the aforementioned mesoscale uncertainties will probably remain through Fri morning.

Values in forecast instability fields are also slightly higher relative to 24 hours ago, which suggests a greater potential for thunder mainly with the expected deeper convection from late morning through afternoon Friday. With slightly greater instability of ~750 J/kg forecast, and amid strengthening swly flow aloft, a low-end risk for strong to locally damaging wind gusts may result.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

As of 120 AM Wednesday...

Patchy fog has begun to develop across parts of central NC, and it is likely to get more widespread overnight before lifting by mid- morning. Some MVFR stratus is also possible this morning, especially in the west, before VFR returns everywhere in the afternoon. Winds will be mostly calm tonight, increasing to 5-10 kts during the day and veering to the S/SE.

Outlook: Increasing moisture combined with a series of upper level disturbances and a cold front will result in in increasing chances of showers and possibly a thunderstorm Wednesday night into Thursday and especially on Friday which may result in adverse aviation conditions. Improving conditions are expected for Saturday and Sunday.

CLIMATE

Record High Temperatures:

November 4: KGSO: 83/1946 KRDU: 84/1946 KFAY: 86/1974

November 5: KGSO: 82/1914 KRDU: 85/2003 KFAY: 86/2003

Record High Minimum Temperatures:

November 5: KGSO: 65/2003 KRDU: 66/1977 KFAY: 67/2003

RAH WATCHES / WARNINGS / ADVISORIES

None.