textproduct: Columbia

WHAT HAS CHANGED

Updated 00z TAF discussion.

KEY MESSAGES

1. Significant temperature drop from Sunday to Monday as wedge conditions develop.

2. Well above normal temperatures and unsettled weather late week.

DISCUSSION

KEY MESSAGE #1: Significant temperature drop from Sunday to Monday as wedge conditions develop.

Southwesterly surface flow on Sunday will help contribute to well above normal daytime temperatures, particularly with the assistance of northwesterly downsloping at 850 mb. Temperature anomalies of 10- 15 degrees F above normal will not be out of the question, bringing highs in the mid to upper 70s and perhaps a few spots touching 80 degrees. As high pressure shifts over New England on Monday, 850 mb flow becomes southwesterly with westerly flow above. A backdoor front is progged to slide across the area from the north, setting up favorable conditions for weak CAD. While PW will increase slightly to around 0.75-1", it appears most precip will remain to our north outside of a few stray showers possible Monday afternoon across the northern Midlands. Still, cloud cover and northeast cold advection will drop temperatures by 15 to 20 degrees Monday compared to Sunday, with highs ranging from the low to mid 50s northern and western Midlands to low to mid 60s southern Midlands and CSRA. Some improvement is expected on Tuesday with the wedge breaking by Wednesday as heights increase and high pressure shifts offshore. Notably, the NBM temperature interquartile range for Monday and Tuesday remain quite large (8-10 degrees), so overall confidence in the high temperature forecast is lower than normal at this forecast range.

KEY MESSAGE #2: Well above normal temperatures and unsettled weather late week.

Forecast confidence is slightly higher for late in the week as the southeast region settles under broad upper ridging. This will push most of the storm track north of us, though a shortwave may track close to the SC/NC border by Thursday or Friday. With surface high pressure consolidating offshore, temperatures will rebound back to well above normal levels, generally topping out in the upper 70s to low 80s Thursday into the weekend. This is further evident when looking at the NAEFS temperature anomalies, with values above the 90th percentile at all levels from 500mb to 1000mb and values up to the 97th percentile at 850mb by Friday. In addition to the warm temperatures, unsettled weather is possible with moisture advection on deep southwest flow, pushing specific humidity values above the 97th percentile at 850 and 925 mb Friday into Saturday. Instability will also increase, with the potential for 500-1000 J/kg of CAPE developing Thursday through Saturday pointing to the possibility of diurnally-driven showers and thunderstorms. At this time however, the severe threat appears low with a lack of upper support or wind shear.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Low ceilings are forecast to give way to dense fog later tonight, with LIFR conditions expected.

As is usual, ceilings held on well past what guidance was showing 24 hours ago. As such, low-level moisture is still quite copious beneath very dry air aloft. The remaining ceilings are forecast to diminish over the next 1-2 hours at area TAF sites. With clear skies & light low-level winds, we are expecting widespread fog to develop between 05z and 07z tonight. It will likely take a bit to get going but guidance is pretty aggressive with HRRR/RRFS/REFS guidance suggesting a high probability of visibilities <1sm tonight, with vis down to 1/4sm possible as well. Given the high confidence in the setup, utilized TEMPOs and predominant groups to show the most intense fog occurring between 06z and 14z at all sites. Fog will probably hang around for a bit in the morning but it should dissipate by late morning as mixing commences. Once this takes place, expect VFR for the rest of the period.

EXTENDED AVIATION OUTLOOK...Nightly low ceiling or visibility restrictions will remain possible over the weekend through midweek.

CAE WATCHES/WARNINGS/ADVISORIES

SC...None. GA...None.