Wednesday, January 30, 2013

Timing Tonight's Front

We go from fog to warmth to wind in a 24 hour window around here today.  Once the morning fog lifts and the warm front that lurks nearby pushes north later on today, temperatures will nudge higher in advance of tonight's cold front passage.  This front means business, having produced a litany of severe weather reports across the Mid South and Ohio Valley through the night as it has steadily marched eastward.

The Storm Prediction Center has portions of the region in a slight risk for severe criteria winds with the front itself -- the thunder aspect of severe weather is not likely but strong winds are possible around the region later today.  The best chances for severe criteria gusts from the front's squall line are along the Shore (pre-front) and to our west and southwest across South Central PA down towards DC (with the front).  It's important to note the differences here -- the severe risks to our west and southwest will be expected with the squall line while our wind threat locally and at the Shore is due more from the robust low level jet that will zip overhead tonight (winds 5000 feet up modeled to gust to over 90 mph).

Winds will ratchet up this afternoon and tonight throughout the region -- and wind advisories are high wind warnings are out for various portions of the region this evening and tonight as pre-front winds could gust to 40 mph or higher after 6 PM this evening.  The highest winds from the pre-front aspect of the storm are expected east of I-95, with winds that could gust to 60 mph or even higher at the Shore.  In the city and in immediate South Jersey, I think those winds could gust to 50.  The low level jet does not position itself to bring as strong a wind gust to the north and west burbs but even there winds should gust to 40 mph or perhaps a notch higher after 6 this evening.

The front's timing has slowed a little bit compared to prior predictions, which means that the lion's share of rain and wind with this storm system looms for tonight after 7 or 8 PM.  A few showers or a band or two of rain will probably pass through Central into Northeast Pennsylvania during the day but the city and points southeast should remain drizzly at worst but avoid shower activity until after dinner.  Those showers will push in from the west in advance of the front, with the squall line passing through the region after Midnight from west to east.  The squall will feature a quick shot of gusty wind but heavy rain with it...and the lion's share of rain with the storm system probably falls with the front as it moves through.

Rainfall has nudged a bit less rainy in the last 24 hours in modeling but the region is on track for three-quarters of an inch to an inch of rain on average, with perhaps two inches in spots northwest.  Runoff into the usual suspect streams remains an issue due to frozen ground but we may see a bit less rain than what was modeled prior.  We'll see on this part of things.

In terms of the storm itself, it is more an issue for tonight for the region, not for today in our area.  We'll provide another update on this this evening.