textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated for 12Z TAFs.

KEY MESSAGES

- 1. Beautiful weather continues through the end of this week, with rain chances continuing to lower this weekend. Uncertainty in the forecast remains next week.

DISCUSSION

Key Message 1: Beautiful weather continues through the end of this week, with rain chances continuing to lower this weekend. Uncertainty in the forecast remains next week. A rinse and repeat forecast remains in place for the next few days, even potentially extending into the weekend. We remain within the grips of strong high pressure that extends from the northwestern Atlantic over the eastern CONUS. While dry air is firmly in place, there has been a bit of an erosion of the dry air that was so staunchly holding court across the area. Cumulus began developing yesterday within more eastern 925-850 hPa flow and the stratocu continues tonight. PWs are near 1" and dewpoints have slowly crept back up into the mid to upper 50s across the area. So our long streak of high diurnal ranges looks to be taking a break, at least for today and Friday. Afternoon cumulus is likely to persist both days with highs approaching 80F again both afternoons.

"Cooler" (low 70s is not too dissimilar from what we have been seeing) weather is expected to push back in this weekend as reinforcing high pressure settles into the region. Guidance has really shifted pretty starkly towards a much drier forecast this weekend, with AI ensembles showing low probabilities for any rain at all and the physics based models & their ensembles catching up to this idea. This owes to the pattern upstream from our forecast area being A) very complex, and B) amplifying quite a bit. The trend over the last 24 hours is to show more phasing between the northern and southern stream shortwaves across the western CONUS by Saturday which them amplifies the pattern overall. This is acting to weaken and stretch the shortwave that was previously forecast to approach on Sunday and Sunday night. The result is far less isentropic ascent than the suite of guidance from 10/27 12z & 18z was showing. There were signs then but the whole of guidance has completely shifted towards a dry forecast all weekend.

So another nice, autumnal weekend looks on tap. Dry, cool air should be in place both Saturday and Sunday, with an increase in mid-level clouds expected as the weak, stretched trough does pass through the area. Highs should be in the low to mid 70s, with lows in the low 50s. This will likely persist into early next week, though uncertainty is high in the forecast towards the middle of next week. The pattern over North America is looking increasingly complex by this point, with a very meridional northern and southern stream of the jet stream expected. The phasing of these two will be critical to the actual weather impacts that we'll see. Given the rapid change in the forecast for this upcoming weekend within the guidance over the last 36 hours, this should prove a useful example for how difficult it will be to ascertain anything other than coarse forecast details beyond a few days given the overall pattern complexity.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Mainly VFR conditions expected.

Little change in the current forecast thinking. High pressure moving off to the east has allowed an easterly wind off the surface to begin bringing Atlantic moisture back inland. This has helped to produce an moist upslope flow over top of a weak northerly surface flow, which will continue to bring a mixture of scattered to broken mid-level clouds across the forecast area today. Cloud bases around 5-6 kft are indicated on satellite and radar, and those are forecast to continue this morning. By late morning and into the afternoon, better mixing should bring more scattered mid-level cloudiness for the remainder of the forecast period. Winds will continue to be north to northeasterly, with speeds light through sunrise, and then increasing to between 5-10 kts through the day and afternoon. The light winds and cloud cover should combine to help inhibit any fog formation through sunrise.

EXTENDED AVIATION OUTLOOK...Significant restrictions will be possible this weekend as moisture surges into the Southeast and rain chances also increase.

CAE WATCHES/WARNINGS/ADVISORIES

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