textproduct: Columbia

WHAT HAS CHANGED

Chances for snow in the northern Midlands tonight into Thursday morning have diminished (but remains nonzero) with HRRR trending drier. With dry air mass likely to persist Thursday into Friday, have highlighted the potential for enhanced fire danger on Friday as well.

KEY MESSAGES

1) Rain chances increase today with a very limited chance of flurries or light snow showers late tonight.

2) Dry and breezy Thursday and Friday 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 today with a very limited chance of flurries or light snow showers late tonight.

A closed low over southeast TX is beginning to phase with a strong digging upper trough over the middle of the country and will shift eastward today and push a cold front through the region overnight. Ahead of the approaching front, deep southwesterly flow will promote some weak moisture advection with PWATs rising to around 0.8 inches, however much of this moisture will initially be in the mid levels with lots of dry air remaining in the boundary layer. Expect isolated to scattered showers to move into the area by mid to late morning and continue into the afternoon, although the lack of saturated lower levels will prevent much in the way of QPF. The main window for any accumulating precipitation should be late morning into early evening. As the upper trough axis swings into the region this evening a cold front will cross the forecast area around or after midnight with strong cold advection behind the front. Hi-res guidance shows some isolated showers along and just behind the front in the northern Midlands but forecast soundings show significant drying behind the front with northwesterly downsloping flow developing. While there remains the slim possibility of some flurries or an isolated snow shower given strong cold advection and steep lapse rates, the HRRR has trended much drier and warmer than previous runs.

Key Message 2: Dry and breezy Thursday and Friday with an enhanced fire danger risk.

Northwest flow behind the cold front Thursday will lead to significantly drier air funneling into the area. HREF probability for RH dropping below critical values (25 percent) is around 40%. Hires models typically perform better in post frontal NW flow for evaluating low level moisture. Highest probability for wind gusts greater than 30 mph in HREF is actually early in the day which may not overlap with the lowest RH. Does appear that there will be at least an elevated fire danger Thursday but uncertainty remains to if we reach Red Flag Warning criteria. The air mass that settles over the area will remain very dry, continuing into Friday. Higher confidence in RH dropping below 25 percent Friday. Surface low pressure moving into the Great Lakes will likely lead to a strengthening jet aloft, although not quite as strong mixing as Thursday with forecast soundings indicate a developing warm nose around 850mb. Breezy winds may once again support elevated fire danger Friday.

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. High pressure settles likely just south of the forecast area early with winds likely becoming light. NBM continues to show probabilities of lows below 20F around 50-80%. While winds will be relatively light, with conditions close to Cold Weather Advisory criteria already, any wind may push us to criteria. Looks like a marginal event with models consistent for several days for low temperatures. Broad troughing remains over the area through the weekend with another deep trough dropping into the Southeast Sunday. While pops remain low associated with this system as moisture will be limited, will need to monitor with at least a bit of a trend among several GEFS and EC ensemble members towards the potential for winter weather, although probabilities are still low at this point.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

Generally VFR conditions expected through the forecast period though some possibility of MVFR cigs ahead of cold front.

Satellite imagery showing some higher clouds moving over the area ahead of a digging upper trough. southwesterly flow ahead of the approaching trough and a cold front will provide moisture advection into the region and expect mid level clouds to arrive by early afternoon with a lowering to low VFR cigs by late afternoon. Some isolated showers possible but not likely to result in much vsby restrictions due to very dry boundary layer. Guidance is trending up for some MVFR cig restrictions but the lack of low level moisture lends to lower confidence but will include a tempo for MVFR cigs during the 00z-06z time frame prior to the frontal passage. Winds ahead of the front should be from the southwest and then shift to the west around 05z-06z as the front moves through.

EXTENDED AVIATION OUTLOOK...Strong gusty winds expected on Thursday but otherwise VFR conditions expected. Another system expected to impact the region over the weekend and some restrictions possible.

CAE WATCHES/WARNINGS/ADVISORIES

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