textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated for 18z TAFs. Confidence increasing in a strong front Monday.

KEY MESSAGES

- 1. A robust, strong weather system moves in Monday. Impactful weather is expected, with severe weather and strong non- thunderstorm wind gusts possible. - 2. Below normal temperatures expected early next week, with a widespread frost or freeze possible Tuesday night.

DISCUSSION

KEY MESSAGE #1: A robust, strong weather system moves in Monday. Impactful weather is expected, with severe weather and strong non-thunderstorm wind gusts possible.

A very strong low pressure will rapidly strengthen across the Great Lakes late Sunday into Monday as a strong 250mb jet and embedded upstream jet streak digs into the central US. For our area, significant moisture advection will precede the approaching trough as strengthening southeasterly flow will push PWAT's over 1.5" by Monday morning. With very impressive height falls and steepening lapse rates aloft, the overall thermodynamic environment will be sufficient for a severe threat Monday, perhaps somewhat mitigated by poor diurnal timing, but the dynamics of the system generally offset this. Kinematics are robust with a strengthening 850mb jet around 50 knots and certainly sufficient 0-3 km shear for a severe wind and tornado threat. Overall a fairly classic HSLC setup for eastern GA and the Carolinas, hence 15-30% severe outlooks for Day 4. Guidance is generally in good agreement given the Day 3-4 timeframe with LREF joint probs of greater than 30 knots 0-6km shear and 500 J/kg of SBCAPE still sitting around 50-75%, highest across eastern SC. In terms of unfavorable features for severe weather, the low track and associated axis of strongest forcing is a bit further north than we would typically see for a severe outbreak in our area. So given sufficient, but somewhat borderline moisture and instability, an over- sheared scenario where deep convection struggles is a failure mode. Outside of inherent timing uncertainty of the convective line, the presence of deep warms sector convection and/or WAA stratus could bolster or hinder severe potential, especially across eastern GA and western SC.

Beyond the severe potential, the gradient wind field will fairly impressive with very strong jet ahead of the front and CAA regime behind the front; -3 to 5 deg C of CAA behind the front is expected along with robust frontogenesis and a well mixed layer up through 700mb. While the isallobaric flow is not quite optimized, wind gusts around 40 mph are likely starting Monday morning from the southwest, then out of the northwest lasting into the afternoon, even outside of any convection. NBM probs for over 40 mph Monday is around 50-75% and the 90th percentile is generally 40-50 mph. So a Wind Advisory is definitely on the table for Monday.

KEY MESSAGE #2: Below normal temperatures expected early next week, with a widespread frost or freeze possible Tuesday night.

Little change in the previous forecast thinking as confidence continues to increase in a mid- March cold snap early next week behind the aformentioned cold front. An airmass with arctic origins will infiltrate the central US by Monday night and Tuesday and then push towards our forecast area Tuesday night and into Wednesday. Strong cold advection should continue on Monday night, pushing temperatures into the 30s by early Tuesday morning. Guidance is in good agreement that the surface high continues shifting east of the Appalachians and actually intensifies a bit beneath strong upper level convergence, with the center of the surface high and associated surface ridge axis likely settling across the central Carolinas by Tuesday night. NBM and LREF guidance has been showing increasing probabilities of lows <32F on Tuesday night/Wed morning, and this makes sense. Near ideal radiational cooling conditions appear likely in addition to a very dry airmass in place (PWs less than the 10th percentile) favor temps falling into the upper 20s and low 30s many places. We may need a frost/freeze products both Monday night and Tuesday night, with much higher confidence in Tuesday night event at this range. There is some question about overall frost potential given how dry the airmass will be but a freeze looks increasingly possible. Beyond Tuesday/Wednesday, temps look like they'll begin to moderate closer to normal by the middle to end of next week.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

VFR Conditions through the 24 hour TAF Period.

High confidence in VFR conditions over the next 24 hours. High pressure has moved off the coast, allowing winds to turn more southeast to south. This has allow some moisture to try moving inland early this afternoon, but has only produced a few cumulus in the far eastern Midlands. Winds will turn more south to southwesterly through the afternoon, which should keep any additional moisture shunted closer to the coast through the period. Guidance has been consistent with keeping skies clear, with only a few passing cirrus expected through Saturday morning. Do not expect any widespread fog tonight, but as usual a brief period of patchy ground fog at ags/ogb can not be completely ruled out around sunrise. As for winds, as mentioned they will turn southerly to southwesterly through the afternoon, with speeds between 5-10 knots, and gusts up to 15 knots possible. By sunset winds decouple and become light and variable, with those conditions lasting through the end of the taf period.

EXTENDED AVIATION OUTLOOK...No notable restrictions expected through the weekend. A cold front moving through on Monday could bring restrictions in showers and/or storms, both ahead of and behind it into Monday night. A return to vfr then possible Tuesday onward.

CAE WATCHES/WARNINGS/ADVISORIES

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