Tuesday, January 15, 2013

Advisories Nudged, Icy Rain Possible In Outer Burbs

Winter weather advisories are nudged south into the upper halves of the suburban counties for tonight (in the purple shading on the graphic above).  It's going to be a dicey and very close call across the outer suburbs on whether temperatures get below 32 degrees but erring on the side of caution is always prudent...and given modeling is hinting at the possibility of freezing rain in some parts of the counties, putting out a winter weather advisory across those areas is very much justified.

The threat across the outer burbs is icy rain.  It's snow north of I-78 and our projections of two to three inches up in the Poconos, Schuylkill County, and in Northwest Jersey remain on track.  Across the Lehigh Valley and the outer burbs, the potential for icy rain and sleet (with snow in the Lehigh Valley mixing in as well) are all on the table.

The mid afternoon run of the NAM, below, shows that fine line and how precipitation will vary quite a bit over a short distance.  This is the 4 AM precipitation output -- showing rain up to Telford and Soudertown but icy rain north of that to the Lehigh Valley.  Don't get fixated on the specific location, just be aware that those in the outer burbs run the risk of dealing with freezing rain overnight.

Other runs of the NAM from earlier today nudge things a degree or two colder in Pottstown and Doylestown, which makes all the difference between 32.5 and rain and 31.5 and icy rain...there isn't much modeling difference in temperature but that degree or two makes all the difference with what happens at the surface.  Pottstown, as the NAM's earlier run projects, could be below freezing tomorrow morning with icy rain falling.

The city and immediate burbs will likely be rain although it won't be the mildest of rains -- temperatures will be in the middle 30's tomorrow morning.  Rain will move in over the next several hours from the southwest, falling into the morning hours in the city.   Rainfall totals in the city and points south will average out to between a half and an inch.