Saturday, January 07, 2012

Forecast for January 8, 2012

Record warmth intruded a good portion of our region this afternoon. A cold front will pass through tonight. Current guidance indicates a dry frontal passage. However, given the unseasonable warmth ahead of the front and higher than anticipated temperatures, I feel a few isolated rain showers could potentially develop. We will include a slight chance of a sprinkle or shower, with most observing increased cloud cover.

It will be more like winter reality on Sunday with high temperatures in the mid and upper forties. It still is above normal for January. Daytime hours should be mostly sunny. We will see an increase in cloudiness on Sunday Evening and Sunday Night.

I have been a bit worried about a southern piece of energy on Monday into Monday Evening. The majority of our model guidance suppresses it to the south. However, a northward trend may develop very close to the actual event taking place, and some of southern areas may get clipped with a shot of precipitation, which may even be a wintry mix. Lows on Monday Night are around the freezing mark, even considering quite a bit of cloud cover. For now, I will include a slight chance during this time frame as well. Earlier this week, one run of the GFS had indicated a swath of precipitation coming pretty far north. But in the last 36 hours, all runs of the GFS keep the precipitation south of Delaware.

The biggest and most noteworthy storm for the forecast period arrives Wednesday and lingers into Thursday Morning. A potent low pressure area will track west of the region. This is typical of a La Nina pattern. This will flood us with moist air and warm air, making the precipitation liquid rain. Temperatures could even approach 55 to 60 degrees from the city and points south as the warm sector takes over. Once again, a cold front will approach as the low swings away and this could be associated with a narrow line of low-topped thunderstorms with little lightning…but decent wind gusts of 45 to 50 MPH. It also looks like this may end up being a windy period for the typical wind prone areas.

Colder air arrives in the wake of this departing low pressure area. It will then be worth watching a system moving up from the south late Friday into Saturday. Colder air will be in place as the system makes a close approach to the Middle Atlantic States and perhaps this could yield a shot at some snow and or a wintry mix. But should this be a strong blast of arctic air, it may suppress the system to the south which would mean a cold, but dry weekend. It is possible that a pattern change may be developing in the long term which would mean a snowier and colder second half of winter, which isn’t surprising for La Nina in Philadelphia.