Saturday, November 23, 2013

Forecast For Sunday, November 24, 2013

An arctic cold front will pass through the region this evening. Gusty northwest winds will develop in the wake of the frontal passage. Skies will be mostly cloudy, gradually turning partly cloudy after the front passes through. There could be a few snow flurries or even a snow shower this evening. Wind gusts to 35 MPH are possible after 10 P.M.

A strong arctic airmass will take hold behind this front as Canadian high pressure builds in. Temperatures on Sunday will struggle to rise above freezing. Strong northwesterly winds will develop as the pressure gradient tightens in the wake of the arctic front. Sustained winds between 20 to 25 MPH can be expected with wind gusts up to 40 MPH. A few gusts above 40 MPH are possible, especially in the Poconos and along the coastline. The strong northwest flow could create a few lake effect snow flurries in our area as the fetch off the lake may reach into our region. You will need to bundle up if you plan to be outdoors tomorrow. Our forecasted high temperature of 32 degrees in Philadelphia with a 25 MPH wind equates to a wind chill factor of 18 degrees. In the Poconos, the high temperature is expected to be around 23 degrees and combined with a 25 MPH wind you have a 6 degree wind chill value.  The wind may also enhance fire danger for Sunday given the low relative humidity, dry ground, and low fuels. A red flag warning has been issued for much of the area. 

The urban heat island effect and a continued breeze will probably mean that Philadelphia doesn't drop below 20 degrees early on Monday Morning for a minimum temperature. Right now, it appears the minimum will fall between 20 to 23 degrees. However, most of the suburbs surrounding the city will likely drop into the teens.

On Monday, highs are expected to be in the mid-thirties. However, the wind will be less making it feel a bit better. In fact, winds will probably turn to the southwest later in the day.  At this point, an area of low pressure will be developing in the Gulf of Mexico. How quickly this area of low pressure turns to the northeast and where it does turn to the northeast will make all the difference in the weather conditions in our region for Tuesday through Thursday. The 12z guidance was all over the place. The NAM has a low pressure system moving northeast across the interior. The GFS has a low pressure system moving northeast, but far enough offshore where it only brushes New Jersey and Delaware with showers. The EURO is somewhat of a compromise between the two American models. Temperatures would be directly impacted by the track of the low pressure system. The NAM would be mild…the GFS would be chilly…and the EURO would be in-between the two American models.

Given that we will be coming off of a cold airmass, some sleet is possible at the onset of any precipitation in some portions of the area. Most of the upcoming event will probably be in the form of liquid rain. The rain may briefly end as snow showers with little or no accumulation. The forecast is of low confidence given the lack of model consensus.  Further adjustments in the forecast may be necessary and we will post more about the upcoming storm throughout the next few days. If a low does get close to the region, it will likely turn chilly and windy in its wake on Thanksgiving. The wind may present a problem for any parade balloons.