Today’s highs in the low-to-mid 40s marks the coldest day of fall (and it feels even colder with the wind chill), so far in Washington, D.C. But next Tuesday, following a reinforcing shot of polar air, highs are likely to be held in the 30s for the first time.

If you compare the atmospheric flow pattern (approximating the jet stream) this morning with next Tuesday morning, it’s fairly easy to see why it’s cold today, and why it’s going to be noticeably colder on Tuesday.

Today (see below), the air flow reaching the D.C. area originates from the Arctic, but flattens somewhat over the north central U.S. before reaching us – allowing it to moderate some.  That’s why – over the past few days – the truly frigid conditions have focused in the northern Rockies and northern Plains.

But Tuesday (See image below), the flow of Arctic air is steeper and deeper, and more directly targets the Eastern U.S. And so, we have more penetrating cold in the D.C. area.

The evolution in the temperature difference from average between today and Tuesday reflects the change in the flow pattern.

This afternoon, temperatures in the Mid-Atlantic are forecast to be about 10 degrees below average.

By next Tuesday afternoon, they will be closer to 20 degrees below average.

The GFS model forecasts highs on Tuesday afternoon only near 30 (see below) versus just above 40 today (not shown).

While GFS forecasts are sometimes too cold (model has a cold bias), even if it’s off by 5 degrees, a high of 35 is impressively chilly for mid-November.   We’ll experience the peak of the cold snap late Tuesday night and early Wednesday morning, when the GFS forecast lows in the upper teens in our coldest suburbs (see below).

BRRR. Temperatures are forecast to moderate, however, by late next week, as Wes Junker discussed yesterday.