Wednesday, December 07, 2005

Forecast Call #1 for Event #4

Well, folks, another storm on the horizon. The crack team of media hypers are in full effect, giving you the low down on every angle of the impending snow.

Here's the straight scoop you need and then the more technical discussion comes afterwards:

I feel confident that Philadelphia, the PA suburban counties, Trenton, up towards North Jersey are going to be in the bullseye for the 4-8" accumulation range. You may have a little more in your hood especially if your neighborhood tends to be snowier, a little less in another, but expect about that much to fall. Lehigh Valley and Berks should expect 3-6". Poconos/I-81, about the same. South Jersey is a different story and could be more, could be less, based on much ice and sleet mix into the equation. I talked about that this morning and I feel freezing rain is at play in places especially west of the Garden State Parkway, east of 295, and south of 195. That's why you guys are in the 3-6 range at this point. Delaware can expect similiar icing south of Smyrna.

I expect the snow in from WSW to ENE with this event. Philadelphia should have the snow by 1-4 AM. Allentown between 2-5. Lancaster between 12-2 AM. North Jersey between 3-6 AM. If anything changes, I will update with a final call on Thursday AM before 9 AM.

Now on to the technical.

We've got two camps. The NAM model, which has continued to show the westward bias and a more precipitated bias in recent days, continues to show its wonder at work. The NAM model wants to give Philadelphia 3/4 of an inch of ice, mostly because it takes the storm a good bit to the left of the GFS model. The GFS gives us about 5.5 inches of snow assuming 10" of snow to 1" water ratio...I would imagine it might be closer to 12 to 1 given a possibility of lower dewpoints at the start of the event, then we're looking at 6.6" at the airport.

The NAM is still trying to pop out multiple low pressure systems in its model run and still is having trouble, in my opinion, kicking this system to the east. It keeps the mid-level feature we talked about in prior discussions back less so than the GFS. Given the fast flow in the upper levels (I discussed that 200 mb map this morning that highlights a 150kt jet), I don't expect any lag time by the mid level low.

The GFS handled the last system better than the NAM did -- not great by any stretch. Given its relative consistency with the European model, which held firm for several days with this system's track, it makes sense to lean towards the GFS but not completely buy it as it paints snow to the coast and gives AC close to 9". Not going to happen. With an onshore flow coming in off of 45 degree water, I would expect some sleet and or freezing rain to develop within 20 miles of the coast. I extended the ice potential further inland towards 295 just in case it gets a touch warmer, but I would expect the outer burbs in South Jersey to stay more snow and less ice.

Confidence in this forecast at this point is higher than the last one but still not dramatically high because we are dealing with a mid-level feature transfering energy to a developing coastal low. If the low doesn't develop fast enough, it will more further east and be weaker, resulting in less snow. If the low develops too fast and bombs quickly, the ice solution could play into the I-95 corridor at times with some sleet because it will pump warmer air in off the ocean.