MU's Current Conditions: (at 15:18) Temp: 82 F | Dew Point: 81 | Wind: ENE - 5 mph
SPECIAL WEATHER DISCUSSION (Updated twice weekly, but more often when storms threaten.)

* Bipolar Weekend -- Cooler into Early May *

2:00pm Friday, April 28:
A summer preview of sorts is upon us today and Saturday with temps in the 80s both days...and muggy dew points in the 60s for Saturday making for a Heat Index near 90. If clouds and showers hold off Saturday, then we'll have a shot at reaching the record of 87 degrees (1974). However, debris from today's convection in the OH Valley (which may arrive here with a shower after midnight tonight) and scattered pop-up storms Saturday afternoon may yield enough clouds to hold temps below the record.

Either way, there's a sneaky backdoor cold front that will try to nose into the area from the Northeast around daybreak Sunday. It's not a for-sure that it will succeed at moving through here, but it looks more likely than it did earlier this week. In the worst case, a chilly East wind and low clouds would hold temps in the low 60s Sunday...whereas if the front fails to move through we could reach the 80s again! My sense is that the outcome will be between these two extremes as peeks of sunshine partially negate the cooling effects of the East which case temps may top out in the upper 60s or low 70s Sunday.

Beyond that, unseasonably warm conditions will return Monday (low 80s) ahead of a cold front approaching from the West. Scattered showers or a T-storm are possible Monday afternoon or night as this front moves through. The middle and end of next week then look cooler; perhaps even colder-than-normal with highs holding in the 60s for a few days...and perhaps even in the 50s one day later next week if we experience a steady rain. Details are uncertain, but a jet stream trough will develop along or East of the Appalachians--a set up that will yield lots of clouds and cooler conditions...and quite possibly a low pressure system and a soaking rain late in the week or next weekend. --Horst

Noon Monday, April 24:
After a gorgeous Sunday, the work week begins with overcast and cool conditions as Easterly flow off the Atlantic brings a shallow maritime polar air mass into the region. Temperatures will hold in the 50s today and Tuesday, as there will be little or no sunshine either day. In terms of rain, a few sprinkles or a band or two of light rain will skirt by today into tonight; but there's a better chance for a few hours of steadier rain Tuesday into Tuesday night, as a slow-moving upper-level low lifts up the coast.

Wednesday will be a transition day as a cloudy, damp start should yield to peeks of afternoon sunshine and a late-day high temp in the upper 60s to near 70. Thursday will be sunny and much warmer with highs in the upper 70s to near 80. A jet stream disturbance may pass by to our west and north on Friday, perhaps touching off a stray shower/storm; however most of the day should be partly sunny with afternoon highs in the low 80s.

Believe it or not, the weekend will likely be even warmer! As a broad jet stream trough holds over the nation's midsection, a ridge will sharpen along the East coast...into almost a Bermuda high pressure configuration by late Sunday. This set up will likely yield the first 90 degree readings of the year in some spots to our eastern MD, VA, and NC. Here in Lancaster, weekend highs will likely reach the mid to upper 80s...and just maybe touch 90 Sunday afternoon given sunshine from start to finish. Our Summer preview may continue into Monday (highs in the 80s), before a cold front moves in with showers/storms sometime Monday afternoon or night.

One caveat: Spring is the season of the backdoor cold front--pesky shallow cold air that drops down from eastern Canada, often with surprising results. Such a front will drop into northern New England this weekend...holding high temps there in the 40s and 50s, while the Mid-Atlantic is baking. There's an outside chance (20%) this front will try to sneak some shallow cold air down the Hudson Valley and into the Lehigh Valley--if so, then some clouds and cooler temps could spoil part of our three-day Summer preview. But the odds are strongly in our favor for the warmest temps of 2017 so far, occurring here by Sunday and/or Monday. --Horst

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