Monthly Archives: April 2016

Weather Updates

Weather Update

A quick update- No significant changes since yesterday, except the NAM has been trending towards colder surface level temperatures.   QPF values still about 0.80.  Timing of precipitation still looks on schedule, with snow starting about 8 AM or so and ending a around sunset.

The unknown is how much dynamic cooling will occur if precipitation rates are high.    Still likely to be only grassy surface accumulations, except where elevations are higher and except where bursts of heavier precipitation allows for dynamic cooling.    Either way, interesting weather for April.

10AM: This morning’s NAM model has brought the QPF way down to 0.40 inches water. With less precip, there will be less dynamic cooling and even less likely for there to be accumulation.

Philadelphia Area Weather Forecasts

Philly Weekend Weather Forecast

An interesting weekend weather forecast for the beginning of April…

See my posts earlier this week for the synoptic details.

Previous weather outlooks for the snow this Saturday appear to be supported by the latest weather model runs.  Both the GFS and NAM crank out a QPF between 0.65 and 0.80 inches of water.

(If this were February, we’d have a significant snowstorm on our hands.  But it’s April and that’s  going to make a huge difference.)

Sun angles are high and the effects of solar insolation through clouds is prominent, preventing much, if any, accumulation on dark asphalt roadways.  Additionally, near-surface temperatures won’t be at or below freezing until late in the day.   So accumulations won’t really be a concern.

That said, it will be cloudy on Saturday, with wet snow mixed with rain, heavy at times, becoming all snow later in the afternoon.  Very windy! Highs near 40, but dropping to 32 late afternoon.   Grassy accumulations possible with icy conditions possible Saturday evening.   Greater accumulations north and west of Philadelphia.

Looks to be partly sunny and  unseasonably cold on Sunday.

Friday 6 PM Update: Latest NAM model really cranks out the precipitation, with a QPF of over 1 inch water.  The NAM has also dropped the temperatures into the 30s.  It’s possible this could become a freak spring snowstorm with accumulation!  Updates later tonight.

Friday  10:40pm Update: No significant change.  The forecast above captures everything well.  Maybe less windy and maybe a midday transition to rain before changing back to snow.

Philadelphia Weather Outlook

Spring Snow

The models continue to show an area of vorticity to cross our area on Saturday and induce development of a coastal low.  Precipitation is expected to develop Saturday morning and now continue into the afternoon.  Temperatures are expected to fall during the day.

The upper air profiles suggest wet snow is possible at the onset, despite temperatures too warm to allow accumulation.  But as temperatures fall during the day, some grassy surface accumulation is possible in the afternoon and icy conditions are possible Saturday night.

Friday 7 AM Update:  Last nights models show earlier surface development and greater intensification of this coastal system expected to to form from a clipper-type vorticity passing over us.

The. NAM cranks out a QPF as much as 1.00 inches water  during the daytime hours of Saturday. This high QPF is likely over-done, but it does suggest a cold windy day with rain/wet snow for much of the day on Saturday.   Impossible to determine snow accumulation, but expect some snow accumulation on grassy surfaces during the afternoon hours with possible icy conditions Saturday night. If precipitation rates increase, temperatures may fall below those predicted by the models.  Areas north and west may truly have a significant snow accumulation.