textproduct: Columbia

WHAT HAS CHANGED

Updates to aviation section for the 18z TAFs. Any rainfall amounts on Wednesday are trending light with drier weather expected Thursday. Confidence increasing in more widespread rain chances to end the weekend.

KEY MESSAGES

- 1) Warming trend through mid-week with near normal temperatures Thursday and into the weekend.

- 2) First rain chance moves in on Wednesday with additional chances late in the week, but especially this weekend.

DISCUSSION

KEY MESSAGE #1: Warming trend through mid-week with near normal temperatures Thursday and into the weekend.

The strong upper ridge currently positioned over the central CONUS will continue to move in through today and especially on Tuesday. This will bring temperatures near average this afternoon but as 850 mb temperatures reach the NAEFS 90th percentile on Tuesday, highs will begin reaching into the low to mid 70s. A cold front moves through the region on Wednesday with associated rain chances, but temperatures are expected to remain fairly mild post FROPA with highs only dipping a bit compared to Tuesday, into the upper 60s to lower 70s. Cooler/drier air likely moves in for the late week as weak troughing moves into the FA, but temperatures currently are expected to remain near normal during the extended period, though uncertainty still remains for this weekend especially due to timing discrepancies for a system progged to move in during this time period.

KEY MESSAGE #2: First rain chance moves in on Wednesday with additional chances late in the week, but especially this weekend.

There has not been significant change for the outlook into the midweek as the Baja low will slowly shift eastward with PWAT's in the region increasing toward 1-1.25" on Wednesday ahead of surface cold front from a surface low in southern Quebec. Scattered rain chances are expected to move in early Wednesday before ending sometime Wednesday afternoon as the front moves through. In general, very light QPF is expected with the latest GEFS probabilities for greater than 0.10" being less than 50% for much of the FA. The latest deterministic guidance has trended Thursday drier as high pressure briefly builds into the area but greater uncertainty remains for Friday through Sunday.

Through the latest cluster analysis, it is revealed that much of this uncertainty stems from discrepancies in the evolution of the Baja low's progression over the south-central US and thus it's impact on a upper low that will be shifting toward New England. In general, a faster moving Baja low would allow shortwave ridging (as shown in the 06z ECMWF) to build in on Friday and into Saturday, bringing drier conditions while a slower progression (12z GFS) may allow a weak disturbance associated with the New England upper low, to near the region bringing rain chances. Despite this uncertainty on Friday and Saturday, there is general consensus amongst all clusters that the greatest chance for widespread rainfall comes Sunday as the deepest moisture moves into the FA with strong upper support from the southern upper low and maturing surface low pressure moves in.

AVIATION /18Z MONDAY THROUGH SATURDAY/

High confidence in VFR conditions continuing through the period. Surface high pressure continues to shift eastward across the Carolinas, with surface winds slowly but surely shifting out of the east and southeast. Mid-level cloud deck from earlier this morning has cleared, with all TAF sites reporting clear skies. This is forecast to continue for the most part throughout the period despite moisture beginning to increase a bit tonight. Winds will likely veer closer to southerly this afternoon before becoming light and variable overnight tonight. While there is a bit of a low-level jet tonight, it looks to set in after the inversion does overnight. As a result, the slight increase in low-level moisture may result in some MVFR ground fog late tonight at our fog prone locations. By tomorrow, stronger winds out of the southwest are expected as the pressure gradient tightens ahead of an approaching front. Look for wind gusts during the afternoon hours between 15 and 20 knots across the area.

EXTENDED AVIATION OUTLOOK...No anticipated aviation concerns through early this week. Restrictions possible moving into mid-week as another system pushes into the region and brings rain potential along with it.

CAE WATCHES/WARNINGS/ADVISORIES

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