textproduct: Columbia

WHAT HAS CHANGED

Rainfall forecast remains on track. Potential for thunderstorms slightly elevated across the southern Midlands this afternoon and this evening.

KEY MESSAGES

- 1) Widespread rain and a few thunderstorms expected most of today, with rainfall totals of 0.5"-1" still expected for much of the forecast area.

- 2) Potential increasing for well above normal temperatures mid to late next week.

DISCUSSION

KEY MESSAGE #1: Widespread rain and a few thunderstorms expected most of today, with rainfall totals of 0.5"-1" still expected for much of the forecast area.

A quick-hitting low pressure system remains on track to move through the Southeast states today. This is expected to bring much needed rainfall over the next 24 hours. While some echoes are starting to show up on radar early this morning, surface conditions remain too dry with RH values between 50% and 65% for much of the area, and any rain trying to fall is likely evaporating. That said, isentropic lift will begin to increase over the next several hours as southwest flow aloft continues to strengthen and moisture increases through the column. This will result in increasing shower coverage through the morning hours ahead of the upper trough and deepening surface low. HREF members remain in good agreement with the timing and potential for moderate rainfall with this initial area of precip moving through the state. QPF totals from this initial batch of rain should be around 0.5", with higher amounts possible toward the north and west of I-20 and lower amounts toward the south and east. Around 18z this afternoon, a warm front will push north through the forecast area ahead of the approaching cold front. We'll likely then see at least marginal instability develop, with the potential for 100-300 J/kg of SBCAPE possible in the CSRA and southeast Midlands by later this afternoon. As such, there will be a slightly elevated potential for some thunderstorms to develop, particularly in this region. Additionally, SPC is carrying general thunder for our forecast area, with a Marginal Risk (1/5) nosing in the CSRA and southern Midlands.

Questions remain as to any severe potential with storms that are able to develop along and ahead of the cold front. South of the warm front, hodographs look favorable and 0-3km SRH approaches 200 m2/s2, so it would appear instability and moisture availability will be the limiting factors. A low-end tornado threat is therefore plausible across the southern Midlands should all of these ingredients come together at the right time. That said, the absence of one or more variables will limit the overall threat as the cold front moves through this evening. This second batch of rain will probably be a bit shorter-lived in nature, but pack a higher potential for some heavier downpours and quick accumulations. HREF members move the bulk of rain east of the forecast area after 00z tonight, with a few showers then possible through the remainder of tonight into early Monday morning. The upper low will be weakening overhead into an open wave as it moves eastward and eventually offshore tonight. Event rainfall totals of 0.5"-1" with localized higher amounts up to 1.25" look to be reasonable for the majority of the area.

KEY MESSAGE #2: Potential increasing for well above normal temperatures mid to late next week.

Medium range guidance continues to indicate the potential for well above normal temperatures later this week. Global deterministic models and their ensembles all favor upper ridging building over the central to eastern CONUS behind the departing upper trough. NAEFS and GEFS climatological percentiles continue to be close to the maxima for 700mb temps for the latter half of the week, with values greater than the 90th percentile at 850mb. This persistent signal increases confidence that well above normal temperatures will settle in from at least Wednesday through Friday. NBM highs are around 70 by Tuesday, then will likely be in the 70s for the next several days as a gradual warming trend occurs. NBM QMD probabilities are >90% southeast of I-20 for >75 degrees on Friday, with still impressive 50%-80% probabilities northwest of I-20.

AVIATION /07Z SUNDAY THROUGH THURSDAY/

VFR conditions continue but restrictions likely move in after 12-15z today as rain begins to move into the area.

Cirrus continue to stream into the region ahead of the incoming system with some mid level clouds being noted in observations just west of the area. This likely continues most of the night with ceilings that gradually lower after 09-10z with winds that remain light out of the southeast. As rain pushes in between 12-14z, MVFR ceilings are expected to develop, continuing much of the period with visibility restrictions also likely, especially later in the morning after 15-17z. Guidance remains fairly aggressive in bringing in possible IFR ceilings as well mainly for the Augusta and Columbia terminals after 15-17z as the bulk of the rain pushes in while there is a bit more uncertainty toward OGB. Winds generally shift out of the south to south-southwest at 5-8 kts through the day as rain pushes through the terminals where a couple thunderstorms cannot be ruled out near AGS/DNL/OGB, but confidence remains too low to add into the TAF at this time. The center of the surface low with a shot of "drier" air is expected to move over the area and thus recent HRRR, HREF, and LAMP guidance suggests brief improvements in ceiling restrictions may be seen early Sunday evening before falling back down on the backside of the low, bringing back possible IFR ceilings through the end of the period. The low moving overhead also will bring a sharp wind shift toward the west and eventually northwest during the evening hours. Rain is expected to move out toward the end of the period, but ceiling and visibility restrictions likely remain. EXTENDED AVIATION OUTLOOK...Restrictions are expected to remain into early Monday before drier air moves in and VFR conditions return much of the extended period.

CAE WATCHES/WARNINGS/ADVISORIES

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