textproduct: Charleston

WHAT HAS CHANGED

Aviation Forecast Discussion updated.

204 PM Update... A Wind Advisory has been issued for the entire forecast area for tonight into Monday. Severe risk has ticked down slightly (still not zero) with even less confidence in realizing any significant instability.

KEY MESSAGES

1. A strong cold front crosses tonight into Monday morning. Damaging wind gusts are the primary threat with a line of showers. A Wind Advisory is in effect.

2. Temperatures plummet Monday, changing rain to snow. Light accumulations are possible Monday evening into Tuesday morning, potentially leading to patchy slick spots.

3. A widespread hard freeze is expected Monday night through Wednesday morning, endangering early-season vegetation.

DISCUSSION

KEY MESSAGE 1...

A potent cold front will sweep across the region tonight into Monday morning. Forecast profiles show a complete lack of conditional instability, with MLCAPE near zero. However, intense kinematic forcing is present, coupled with a robust southwesterly H850 jet of 50 to 60KTs. This strong forcing and wind field will yield a line of showers capable of producing sporadic damaging wind gusts. With a dry sub-cloud layer and non-zero dew point depressions, evaporative cooling and precipitation drag will efficiently transport high momentum air to the surface. While there is a non-zero chance for a brief spin-up tornado given the strong low-level turning (SRH values 300-500), this threat is severely limited by the absence of instability. Even a modest uptick in instability would significantly alter this threat, and trends will need to be closely monitored this evening. Given the primary threat of gusty showers rather than widespread severe thunderstorms, a Wind Advisory has been issued for enhanced messaging. This advisory accounts for tightening gradients ahead of the front, mechanical mixing/precipitation drag with frontal passage, and a sharp period of strong cold air advection immediately behind the front, which typically mixes near 100 percent of the boundary layer winds to the surface.

KEY MESSAGE 2...

Following the frontal passage, strong cold air advection will establish a non-diurnal temperature trend on Monday. Temperatures will fall from the 50s early Monday morning into the 30s across the lowlands by Monday afternoon. Rain will transition to snow on the back end of this system. Given the relatively warm ground conditions and the high March sun angle, widespread accumulating snow is not expected during daylight hours outside of perhaps the highest elevations. As synoptic moisture departs, it will be replaced by an upstream fetch off Lake Michigan. The timing of this transition to lake-enhanced upslope snow is critical, as a heavy burst of precipitation is possible on the back edge of the synoptic precipitation as the upper trough pivots overhead. Once the sun sets Monday evening, any heavier snow bands could quickly overcome the warm ground flux, dragging road skin temperatures toward freezing and allowing for quick, minor accumulations. Warm flux from deeper soil layers will likely allow skin temperatures to recover once precipitation lightens, but patchy slick spots remain a concern for Monday night into especially Tuesday morning as air temperatures fall into the 20s in the lowlands and teens in the Northeast Mountains. Current forecast snow amounts remain below advisory criteria, but trends will be monitored closely. Will continue wind advisories for the higher terrain into Monday night with continued cold advection and mixed layer winds of 40-45KTs.

KEY MESSAGE 3...

A hard and relatively long-duration spring freeze will commence Monday night and continue through Wednesday morning. This poses a significant hazard to adventurous gardeners and any early- season vegetation that has emerged during the recent warm pattern. A return to a relatively warmer pattern is expected as the region rides the baroclinic zone heading into mid-week. The details in this pattern are relatively low with any small disturbance passing atop the baroclinic zone likely to produce at least some showers

AVIATION /00Z MONDAY THROUGH FRIDAY/

Ceilings and visibilities are expected to lower to MVFR/IFR as heavy rain, and possibly thunderstorms, accompany a cold front across the area late tonight into Monday. Sub-VFR flight conditions should then persist as rain showers transition to snow showers during the second half of the day Monday.

Gusty winds are expected to continue through the majority of the TAF period, with strongest winds occurring during the frontal passage. A period of LLWS may also be possible in advance of the front.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 00Z TUESDAY... FORECAST CONFIDENCE: Medium. ALTERNATE SCENARIOS: Extent/timing of LLWS and thunderstorms may vary from the forecast. Timing of transition from rain to snow may also vary.

EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY OF WFO FORECAST TO AVAILABLE MODEL INFORMATION: H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS. L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.

UTC 1HRLY 22 23 00 01 02 03 04 05 06 07 08 09 EDT 1HRLY 18 19 20 21 22 23 00 01 02 03 04 05 CRW CONSISTENCY H H H H H H H H H H H H HTS CONSISTENCY H H H H H H H H H H H H BKW CONSISTENCY H H H H H H H M H H H H EKN CONSISTENCY H H H H H H H H H H H H PKB CONSISTENCY H H H H H H H H H H H H CKB CONSISTENCY H H H H H H H H H H H H

AFTER 00Z TUESDAY... IFR possible in snow showers Monday night into Tuesday morning.

RLX WATCHES/WARNINGS/ADVISORIES

WV...Wind Advisory from midnight tonight to 11 AM EDT Monday for WVZ005>011-013>020-024>034-039-040-515>522-524-525. Wind Advisory from midnight tonight to 2 AM EDT Tuesday for WVZ523-526. OH...Wind Advisory from midnight tonight to 11 AM EDT Monday for OHZ066-067-075-076-083>087. KY...Wind Advisory from midnight tonight to 11 AM EDT Monday for KYZ101>103-105. VA...Wind Advisory from midnight tonight to 11 AM EDT Monday for VAZ003-004.