Monthly Archives: December 2018

Winter Weather

INTERESTING FORECAST FOR SUNDAY NIGHT

[su_box title=”Forecast update Sunday 11pm” box_color=”#defcdc” title_color=”#000000″]Too warm for snow tonight and the NAM has reduced the QPF in Phladelphia to zero. [/su_box]

First, will the Eagles win again with Foles?  Yes.

That said, let’s turn to tonight’s forecast which may be a more difficult call. A front will pass through tonight between midnight and daybreak.  Weak low pressure is predicted to move along the front.  Each model run has increased the intensity of this wave of low pressure.

The models are consistent with low temperatures being above freezing (36 degrees in Blue Bell).  The latest NAM has several critical temperatures of the atmosphere supporting snow, except for the lowest level.  QPF values are now 0.07 inches water.  Currently the models have a general consensus of light snow with a slight grassy coating in the areas in blue –

P-Type
Current Model P-type prediction after midnight Sunday.

If there is further strengthening of the low, dynamic cooling may move this area of snow closer to the city.  Right now, the areas shown are the best bet, but it wouldn’t surprise me if there’s some very light snow falling closer to the city.  Since it will occur before daybreak, we’ll have to see if anything is left on grassy surfaces.  This is the best we can do this year for a white Christmas.

[su_note note_color=”#d9f2da”]Of more interest is the period around New Years Day.  For almost a week,  the GFS and FV3-GFS have been showing some sort of major storm (rain, ice or snow) in the Jan 1-2 timeframe.  Something I’m watching. [/su_note]

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

[su_box title=”Forecast Update Saturday 11pm” box_color=”#defcdc” title_color=”#000000″]Little change in the forecast for Sunday; Mostly sunny with high 44. A cold front moves through after midnight Sunday. A weak impulse will bring light rain showers before daybreak Monday.

Some of the thermal profiles suggest this may fall as light snow showers or flurries, especially northwest of the city. There’s some evidence that this impulse may strengthen slightly, so stay tuned.

UPDATE Sunday 7 AM:  Last night’s NAM shows it will be a bit too warm in the immediate PHL area for light snow tonight. (Despite the upper atmosphere having temperatures that support snow.)  Here’s the current precipitation type (PTYPE)  forecast for this evening into Monday. We would have to get much more intensification and dynamic cooling for any accumulation here.

NAM forecast
NAM forecast 11 PM tonight

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High pressure will slowly build in this weekend behind the departing low pressure system that brought the heavy rains today.

On Saturday, according to the GFS, there will a significant amount of low level instability cloudiness – stratocumulus should be prominent with occasional breaks of sunshine possible, more sun possible later in the day.  It will be windy with gusts approaching 30 mph.  High 45

The high builds in Saturday night and begins to depart on Sunday as another secondary cold front moves through Sunday night. Sunday will be mostly sunny and seasonably chilly, but still above average. Winds will be lighter, out of the southwest.   High will be about 44.  (Average high is 41.)

The secondary front moves through Sunday night with light rain showers possible. UPDATE Fri 11 pm : There’s a slight chance of it falling as snow showers or flurries after midnight.

Monday, Christmas Eve, will be mostly sunny and colder.  High 41.

[su_note note_color=”#d9f2da”]The medium range outlook through New Years maintains the pattern of near average temperatures with some warmups and rain.  Little possibility of snow, although the long range shows cold air building in Siberia, Greenland and the polar areas. Expect a change to colder and stormer conditions the first week in January. [/su_note]