top border

Please note, not all links may be active. This site is a snapshot of an earlier time.

10-Day Outlook: Cold and Stormy?

Josh Larson @ 1:30 PM

Today's Forecast

Today's forecast calls for partly sunny and breezy conditions with cooler temperatures only in the mid 40s for highs. A rogue flurry or sprinkle cannot be ruled out during the late afternoon and evening periods. Overnight lows, under partly clear skies, will be in the 30-35 degree range for much of the area.

Pattern Overview

What an incredibly complex and active pattern to forecast for! The main forecast challenge for the first part of the 10-day outlook is how "zonal" (or flat) the atmospheric flow pattern becomes by this weekend. If you look at the NAM's forecast 500mb height pattern for Saturday, for instance, you will see how level/west-east the flow is over much of North America. Why does this matter to the forecast? When the flow pattern is not (highly) amplified -- i.e., no strong troughs and ridges -- it is more difficult to forecast the intensity and timing of individual waves of low pressure.

This has an especially troubling impact on the forecast for upcoming week given that the models do forecast a VERY ACTIVE storm track; however, in part because of the aforementioned atmospheric flatness, they have been flip flopping all over the place and are back and forth on storm (and resultant rain and snow) potential over the next 5 days. As such, this 10-day outlook is at much lower confidence levels than normal. What I can say with relatively high confidence is that it appears that the next 5 days will average some 5-7 degrees below normal, while the following 5 days are likely to average a sizeable 8-12 degrees below normal. I do believe, too, that it is likely (66%+) that we will see snow in the immediate DC Metro area over the next 10 days.

Above image courtesy

The next 5 days (Dec 1-5)
Forecast high/low: 44/31 (normal = 51/35)
Forecast precip: above normal

Luckily the forecast for the next 72 hours is pretty clear-cut: after today's partly cloudy and seasonably cool weather, expect even slightly cooler temperatures on Friday, under mostly sunny skies; highs will be in the low to mid 40s, with overnight lows in most areas from the mid 20s to near 30. Partly sunny on Saturday, though clouds will increase as the day wears on, with temperatures near 45/33.

After Saturday, however, forecast confidence goes down precipitously (no pun necessarily intended): it appears that on Sunday a wave of low pressure will approach from the south and west; however, as hinted at above, the timing and intensity of this wave is still uncertain, as are the temperature profiles that would determine precipitation type. It seems likely that the majority of the event will be rain, though it may start off as a brief burst of snow Sunday morning, and may be mixed with snow at times over the far north and west suburbs. Otherwise, I'd plan for periods of cold rain or drizzle on Sunday under overcast skies with raw highs topping out near 40; overnight lows will likely be nearly steady.

Extreme uncertainty regarding the forecast for Monday as some models hint that another wave of low pressure may try to form close to our area and perhaps spawn a secondary coastal low. At this point it seems there are three possibilities for Monday's weather:
  • (A) overcast and breezy but dry
  • (B) overcast with a messy rain/snow mix
  • (C) overcast with an accumulating snowstorm
At this point I think option (B) is probably a little more likely than the other options, but it's still basically a toss up. Temperatures on Monday are uncertain as well, so I'll present a range of highs from the mid 30s to low 40s. (Note: this particular prognosticator believes that if a storm does develop on Monday close enough to our region, that it will not be an all-rain event; some frozen precipitation is likely.)

The following 5 days (Dec 6-10)
Forecast high/low: 39/26 (normal = 49/34)
Forecast precip: near normal

Unfortunately, considerable uncertainty still remains regarding the forecast for Tuesday and Wednesday. However, it appears that we're likely to see even colder air filter into the region with partly to mostly cloudy skies and breezy conditions with scattered snow showers possible, especially on Tuesday. Temperatures are also somewhat uncertain, but I'll call for 41/28 for Tuesday with colder conditions on Wednesday -- near 36/25.

Though we're getting further away from the current date, forecast confidence actually increases for the period next Thursday through Saturday as it appears that organized storminess will no longer affect the area. It is my belief that current model guidance is underestimating the magnitude of cold air we're likely to see during this period, so my forecast likely differs from that of other forecast outlets. I'll call for partly sunny and breezy conditions during this period with widely scattered snow showers (especially to the west) and unseasonably cold temperatures mostly holding in the mid 30s for highs with overnight lows ranging from the teens to mid 20s.

Snow Lover's Crystal Ball

Next Chance of Snow:
Event #1: Sunday, Dec 3
Event #2: Mon-Wed, Dec 5-7

Event #1: 20%
Event #2: 40%

Potential Impact:
Event #1:
Event #2:

Commentary: Sunday's wave of low pressure is likely to bring mostly rain to the area, though there are indications that some form of frozen precipitation, especially at the onset, are possible. A second, stronger, area of low pressure may bring either a rain/snow or accumulating snow event to the area during the Monday through Wednesday period. Note: an unusually low confidence forecast for both potential storms, so stay tuned to for more analysis.

Comments are closed for this archived entry | Link | email post Email this post