Area Forecast Discussion
Issued by NWS Columbia, SC

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104 FXUS62 KCAE 202335 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 735 PM EDT Tue Apr 20 2021 .SYNOPSIS... Winds ramp up ahead of and behind a dry cold front Wednesday bringing an elevated fire danger risk with already dry fuels and low relative humidity. So a Fire Weather Watch is in effect for Wednesday afternoon and evening. As cool high pressure settles in, there is a slight frost risk both Thursday and Friday mornings. The first rain chance in quite sometime starts Saturday afternoon as a strong low pressure system tracks over the area. Clear and seasonable weather fills in behind late Sunday through Tuesday. && .NEAR TERM /UNTIL 7 AM WEDNESDAY MORNING/... Short wave trough moving east of the area. Light showers from earlier have dissipated so dropped pops. Skies clearing behind the shortwave but radiational cooling does not look as favorable tonight as boundary layer winds will remain up due to a 20-25 knot low level jet. Expect overnight lows in the lower to mid 50s. && .SHORT TERM /7 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... A diving shortwave and strong low pressure system over the northeast US will swing a dry cold front through the CWA Wednesday afternoon. The synoptic setup and lack of moisture will keep the front dry, but the main story will be the strong pressure gradient that develops in front of and behind the cold front. A deep high pressure building over the central US and the strengthening low pressure over the northeast US will quickly ramp winds up. With top of mixed layer winds around 30 knots, the MOS, hi-res, and blend guidance all put sustained west-northwest winds at 15-20 mph with gusts to near 30 mph. Given the setup, stayed on the high end of guidance. High temps will reach the low 80`s ahead of the front combined with some warm downsloping behind it. More on Wednesday in the Fire Weather section. As high pressure builds into the area overnight Thursday, the strong cold advection regime will drop temperatures into the mid-upper 30`s Thursday morning. MOS and blend guidance have trended slightly colder for morning lows as winds have trended weaker. However since winds are expected to remain up as least somewhat, the frost risk is somewhat lessened but this will be monitored closely. Thanks to the strong cold advection, highs Thursday stay in the upper 60`s and low 70`s. && .LONG TERM /FRIDAY THROUGH TUESDAY/... The high pressure will move directly over the CWA heading into Friday morning. With winds consequently falling off and clear skies, a strong radiational cooling night brings a frost risk Friday morning. Ensemble, MOS, and blend guidance has bounced around a bit with the placement of high and therefore wind speeds, but temps are expected to fall into the upper 30`s or low 40`s. The NBM distribution suggests only has a few members below 40 for the Columbia metro but our northern counties have the majority of members under 40. So the northern CWA looks especially prone to the frost risk. Otherwise clear and calm with Friday with temps in the low 70`s. The main weather story of the weekend will be a potentially significant rain event as a developing low pressure and warm front cross the area late Saturday into Sunday. GEFS and NBM distributions suggest a widespread 1-3 inch type rainfall event as strong warm advection and isentropic lift develops along the warm front on Saturday, and then as the low moves over/near the CWA. NAEFS shows low level moisture transport in the highest half-percentile climatologically as a 50+ knot 850 mb develops directly over the CWA. GEFS members range from 0.2 to 3.5 inches, with consistent clustering around 0.5 and 1.5 inches. But given the trend, confidence is somewhat higher in the upper end rainfall solutions. The blend additionally supports this with a 50+% probability of the 1 inch or more across the CWA over the last few cycles. From a synoptic perspective, this appears to be much more favorable for strong moisture flow into the Carolinas compared to the last few systems. High pressure builds in behind the low pressure system for Sunday and Monday with high confidence in seasonal and dry conditions. && .AVIATION /23Z TUESDAY THROUGH SUNDAY/... VFR. Mid and high level cloudiness clearing out early this evening behind an upper shortwave. Boundary layer winds will begin to pick up out of the S to SW tonight ahead of an approaching front. Model data in BUFKIT indicating a low level flow of 20-25 kt developing late tonight and would help preclude fog. Some stratus possible, but low level air still quite dry. Most guidance not indicating much in the way of stratus, and only low probabilities in the SREF. So, for now, will not include any CIG restrictions at this time. Expect W winds to increase Wednesday as a dry cold front moves through, with breezy conditions expected. EXTENDED AVIATION OUTLOOK...Rain with CIG/VSBY restrictions possible late Friday night and Saturday. && .FIRE WEATHER... A Fire Weather Watch is in effect Wednesday afternoon through Wednesday evening. West winds at 15-20 mph with gusts to 30 mph expected and with dew points falling into the 20`s and the downslope component to the winds, relative humidity values are expected to bottom out in the mid 20%`s Wednesday afternoon/evening. Cool and dry conditions expected Thursday with the relative humidity dropping to near 20% in the afternoon and winds staying up, albeit nothing like Wednesday. So the fire weather risk continues into Thursday and even into Friday as dry high pressure settles over the area. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...Fire Weather Watch from Wednesday afternoon through Wednesday evening for GAZ040-063>065-077. SC...Fire Weather Watch from Wednesday afternoon through Wednesday evening for SCZ016-018-020>022-025>031-035-037-038-041- 115-116-135>137. && $$

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