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PM Update: Rain to start before dawn, turning steadier and heavier Sunday

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PM Update: Rain to start before dawn, turning steadier and heavier Sunday


* Flood watch Sunday afternoon through night *

Hope you were able to enjoy our last prestorm day of dry and calm conditions. Partially clear and tranquil conditions for much of the night precedes showers, breezes and rain moving in by the pre-dawn hours. Steadier rain develops tomorrow with downpours becoming more likely as the afternoon turns to evening. The Capital Weather Gang team is watching many potential elements of this dynamic, multifaceted storm — a storm briefing is included below.

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Through tonight: A decent evening. Breezes and clouds start building by around midnight and the hours after. By just before dawn, we have a pretty good chance at seeing some rain showers — perhaps even some light waves of steadier rain; nothing heavy is expected. Evening low temperatures briefly dip within a few degrees of 50 before rising overnight as warmer southerly breezes perhaps gust near 20 mph a couple times after midnight.

View the current weather at The Washington Post.

Tomorrow (Sunday): Our “wet and wild washout” day begins and gains momentum with time. Wet with showers, even between waves of light rains slowly build with intensity and longer durations of steadiness into the midday hours. Heavier and steadier rain develops in the afternoon, with rumbles of thunder possible, especially nearer sunset. We’ll be monitoring the flooding threat with time. Midday and afternoon high temperatures, along with wind from the south, both peak along the same timeline. Low-to-mid 60s (possibly a record warm) may be concurrent with gusts near 30 mph.

Thunder, rain, then a wintry mix are all possible — in that order. Near and after sunset, a period of very intense rain and perhaps some rumbles arrives. An inch or more additional rain may bring some rain totals over two inches, and into flooding thresholds. Remember: Turn around, don’t drown when encountering water-covered areas ahead of you. Around and after midnight, as temperatures plunge toward pre-dawn mid-30s to around 40 degrees, snowflakes and a wintry mix may occur. Winds from the northwest could continue to gust around 30 mph.

Most, if any, accumulation is expected in the Blue Ridge and Interstate 81 corridor. Morning rush hour around the Beltway could see some flakes, though. Grassy accumulations are possible with unlikely road impacts. More below in the briefing.

Slight chances of a strong thunderstorm then a snow/slush accumulation

A bit of “potpourri” weather for everyone in this upcoming storm system. Starting with thunderstorms, Sunday afternoon and evening, we have a slight “marginal” threat for one or two severe thunderstorms, mainly for damaging wind gusts over 57 mph. So far, the CWG team isn’t too concerned (but monitoring the potential) for severe winds but with a wet ground, a few downed trees are possible.

Mixed, wintry precipitation has a chance of developing next, mainly around and after midnight. Behind the evening cold front, the atmosphere continues to cool and a few limited impacts are possible at moderate to higher elevations in our region nearer and after sunrise. Here’s a summary of possible wintry impacts:

Even in preferred, colder locations, accumulations remain fairly light. Outside the mountains, east of the Blue Ridge, a burst of sleet and/or snow could cause some localized grassy dustings — even before dawn.

The timing isn’t great if we do see some sort of wintry mix from this strong mid-level atmospheric spinning eddy (called vorticity) pictured below. This brief one- to two-hour period of wintry precipitation could occur during Monday morning’s rush. Still, despite some reduction in visibility, accumulation on roads is not currently expected and as any snow probably remains “conversational flakes.”

Winds remain high into Monday and if a wind advisory is issued, we’ll be sure to update you.

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