Flooding rain may follow record warmth

* Flood watch through Monday afternoon *


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9:34 p.m. update:  The flood watch has been expanded west to include Loudoun and Fauquier counties.

From 6:13 p.m.: For a second straight day, Reagan National Airport achieved record warmth, soaring to 72 degrees.   The tropical air over the area is moisture rich, setting the stage for possible heavy rain into Monday and prompting a flood watch from the National Weather Service.

The NWS cautions:

PERIODS OF MODERATE TO HEAVY RAINFALL ARE EXPECTED TO AFFECT THE WATCH AREA AFTER MIDNIGHT TONIGHT AND CONTINUE THROUGH MONDAY AFTERNOON. 1 TO 3 INCHES OF RAINFALL…WITH LOCALLY HIGHER AMOUNTS CAN BE EXPECTED DURING THIS TIME.

High resolution NAM model simulates 1-3" of rain across area through 4 p.m. Monday (WeatherBell.com)

High resolution NAM model simulates 1-3″ of rain across area through 4 p.m. Monday (WeatherBell.com)

Some of the heaviest rain may fall between 1 a.m. and 7 a.m. Monday morning, when thunder and gusty winds may accompany some of the rain bands moving through – from southwest to northeast. That’s when some flooding of urban areas and small streams could occur. The flood watch excludes Loudoun, Frederick and Fauquier counties, as the heaviest rain is expected near the I-95 corridor and to the east.

A lighter, steady rain may fall during the daylight hours Monday, tapering off in the afternoon.

Temperature Map

Temperatures: Latest D.C. area temperature map. See interactive map on our Weather Wall.

The likely downpours follow a historic surge of winter warmth. Record highs were broken or tied at all three airports. Surprisingly, the warmest temperatures of the day occurred early in the morning before a band of showers cooled the air by 5-10 degrees.

Reagan National’s 8 a.m. reading of 72 tied the record high for the date set in 1889 (at 24th and M St). Dulles hit 71 at 7:20 a.m., shattering the record of 67 from 1984. And BWI 71 a.m. reading broke the record of 70 from 1889.

Today’s low temperatures were also likely record-setting (assuming they don’t fall markedly prior to midnight) – not only for the day but also for the month at Dulles and BWI.

Reagan National only fell to 57 – and will likely smash the record high minimum of 49 from 1923 (set at 24th and M; due to the rain and cool river influence, it just missed the monthly record high minimum of 59 from December 5, 1973). Dulles has only dipped to 62, 13 degrees above its previous record high minimum (49 from 1990) for the date and one above December’s record high minimum of 61 from Dec. 23, 1990. BWI’s low of 62 would likewise break the previous record high minimum for the date (48 from 1931) and month  (59, from 1990).

Also on Capital Weather Gang

D.C. area forecast: Abnormal warmth, gusty showers and a Christmas chill