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BLOG: Mild Weekend

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Tim Williams

A lot has changed over the past 24 hours. After most maximum temperatures for the day were established very early in the morning (including the 69 degrees at BWI at 12:21 a.m. EDT) while widely-separated showers and drizzle were occurring, some cooler and drier air arrived during midday yesterday. The winds, which were primarily out of the southwest, also began to pick up. This was in response to the passage of a front that had some noticeably cooler air behind it. The sun managed to come out for at least a while, which started mixing the air between several-thousand feet above ground level and the boundary layer quite a bit. And therefore, most area thermometers “bounced around” in the upper 50s yesterday before dropping even further well after sunset.

Now, as an upper-level low pressure system continues to lift to the north and east, destined to slowly weaken over eastern Canada, the weather will still be influence by an upper-level trough axis. This trough axis, or “dip in the jet stream” will remain in place over the Northeast and the mid-Atlantic states during the next 36 hours. Because of this, it won’t be getting warmer (or, if you prefer, “milder”) any time soon. But temperatures are expected to be within a few degrees of the seasonal averages today, tomorrow and Sunday. While a gusty breeze should be returning to the area today, once it slackens off tonight, it won’t be returning this weekend. However, a good deal of sunshine WILL BE returning, probably each day. This makes the temperature forecast our “biggest challenge” moving forward… 850-millibar temperatures are being forecasted by most of the models to be around zero degrees Celsius this morning and only between +1.5 and +2.0 Celsius this afternoon. So, if there’s sufficient mixing that occurs during midday and this afternoon (after a modest temperature inversion gets broken), the dry adiabatic “magic chart” would imply that some places (mostly north and west of Baltimore) may have a very tough time seeing their temperature cracking the 60 degree mark.

Tonight, with total clearing expected and a diminishing wind, many outlying areas will either wind up in the upper-30s or the lower-40s. Meanwhile, most larger cities and towns will be in the upper-40s at daybreak tomorrow.

A high pressure ridge will be building into the Northeast tomorrow and tomorrow night, which will bring an end to the “breezy”, or “windy” scenario, and we think that how high temperatures can get tomorrow afternoon will be largely dependant on where things start off in the morning. We’re about a third of the way through astronomical fall now, and even if the day is fairly sunny with very little wind, if the temperatures start out in the mid 40s during the morning, it’ll be difficult for them to be get any higher than 63 in the afternoon.

Sunday is looking pretty good, with bright sunshine early probably dimmed by some high, thin clouds later in the day. At this juncture, the models do seem to be handling the timing of the next shortwave disturbance differently as it cruises through the Eastern Region early next week. Therefore, we may start off Monday “cloudy, with a couple of showers around in the afternoon”, or “increasingly cloudy, with a couple of showers… mainly in the afternoon or at night.” The timing element, in turn, may determine just how quickly the sun comes out on Tuesday. These details should get ironed out over the next 48 hours.

Have a good weekend !!!

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