textproduct: Columbia

WHAT HAS CHANGED

Slight uptick in rain potential Wednesday and post frontal winds Thursday continue to trend weaker.

KEY MESSAGES

1) Rain chances increase Wednesday with a few snow showers possible early Thursday.

2) Dry, gusty winds expected Thursday with an enhanced fire danger risk.

3) Cold weather continues into the weekend. Temperatures near cold weather advisory Friday morning.

DISCUSSION

Key Message 1: Rain chances increase Wednesday with a few snow showers possible early Thursday.

Ahead of a deep digging trough across the central US, a strong cold front and associated surface low will track into the Ohio Valley, and then up the east coast throughout Wednesday and Thursday. Ahead of this front, broad but fairly weak moisture advection will overspread the area with PWAT's climbing to near 1.0". HREF members have trended a bit wetter with these prefrontal showers but still keep rain chances generally less 50% and very light QPF totals; best time period for rain showers is generally between 12-6pm Wednesday, focused along the I95 corridor. Overnight, the cold front will cross the area with notable CAA developing behind it and the upper vort max and enhanced lapse rates will pivot closer shortly after. Residual moisture, frontogenetic forcing, and very steep lapse rates below 700mb, cannot rule out some snow showers across the Midlands early Thursday morning; while the HRRR remains a major outlier, the positioning of the trough axis and frontal forcing nearly always over-performs guidance, especially when guidance shows non-zero CAPE in the near surface layer. Temps will be borderline and any showers would be brief, so impacts are expected to be minimal at this time.

Key Message 2: Dry, gusty winds expected Thursday with an enhanced fire danger risk.

Overall, not much change in the thinking for the cold advection regime on Thursday and potential fire danger. Behind the front, a very dry air mass will move into the area with rapidly decreasing dew points throughout the morning. Guidance often struggles in not dropping dew points fast enough behind strong fronts so will favor lower ends of the distribution. Therefore relative humidity will likely drop to 20-25 percent Thursday afternoon. However, the general trend continues among the blend members in weaker wind gusts Thursday afternoon. Probability of wind gusts greater than 30 mph remains around 30-40 percent. While the threat has decreased slightly, there remains potential for Red Flag Warning criteria.

Key Message 3: Cold weather continues into the weekend. Temperatures near cold weather advisory Friday morning.

After 24-36 hours of strong cold advection behind the aforementioned front, near cold weather criteria low temps are expected early Friday. With high pressure settling nearby, decent radiational cooling should enhance the advected cold airmass and drop temps down into the upper 10's in most spots early Friday; NBM members now show a 50-80% chance of sub-20 F temps in the morning, with wind chills a bit lower. It still looks borderline if we will need a cold weather advisory product for Friday but guidance should come into a clear in the next cycle or two.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

High confidence in VFR conditions.

A very dry air mass remains in place today, supporting VFR conditions. Southwest winds should continue this afternoon at 6 to 10 kts with a few gusts to around 15 kts possible. Gusts diminish after sunset with high clouds streaming across the area and CIGS gradually lowering through the night as a frontal system approaches from the west. By Wednesday morning, cloud decks of 8-10k ft MSL should precede ISOLD-SCT -SHRA, potentially affecting the terminals by late morning, but confidence remains low. Winds increasing out of the southwest again at 8-12 kts with higher gusts developing Wednesday afternoon. Confidence in fog development is low for tonight and Wednesday morning.

EXTENDED AVIATION OUTLOOK...A mid-week system moving through could bring brief restrictions late Wednesday into Thursday, although confidence is low due to limited moisture. Strong gusty winds expected on Thursday.

CAE WATCHES/WARNINGS/ADVISORIES

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