Philadelphia Weather Outlook

WEEKEND WEATHER OUTLOOK

2 Comments

Low pressure will move from south to north and pass over us early Saturday. Rain will begin Friday afternoon and evening and will continue  through much of Saturday. There was some suggestion that the rain would end in the afternoon, but the latest model runs have clouds and scattered showers continuing into the afternoon hours.

We’ll be in the warm sector Saturday and temperatures may approach 60 .

Skies clear Sunday morning and a westerly flow will bring more seasonable temps in the upper 40s  to near 50.  An upper air disturbance may bring some clouds in the afternoon.

An “over-running’ event on Monday may bring a period of wet snow early Monday afternoon before changing to rain. No accumulation currently expected.  Stay tuned.

 

Forecast Review

POST “STORM” REVIEW

Snow will be ending from west to east shortly.

Well, I’m glad I had emphasized last night that all the major model’s built-in snow algorithms had predicted only 0.35 to 0.50 inches of snow and they didn’t support my old technique and the 1.5 to 2.0 inches which I had thought possible.

Indeed, this morning,  the NAM QPF amounts look to be over-done, based on radar. (Perhaps this is why the NCEP has recently decided to stop further development efforts of the NAM.)

Radar 6:37 AM. (Courtesy of weatherTAP.com- https://weatherTAP.com )

Looking back several days, the ‘new’ GFS probably did the best in advance, the Canadian not so good.  I had not mentioned the new NBM (National Blend of Models)  in my posts, but looking back, it also did well with the snow forecast in advance.

Winter Weather

WEDNESDAY WEATHER UPDATE

[su_note note_color=”#defcdc”]Update Tues 9:45PM: The latest NAM data suggests that a wave develops along the front, increasing the precipitation and delaying the end of the snow.

Current QPF  values have increased to 0.35 inches water equivalent during a time when the precipitation type will be snow. Using my own method and accounting for melting and warmer ground temps, it seems that about 2 inches of snow are possible.  Snow flurries and showers may linger until 10-11AM.

10 :15 PM Update: The NAM built-in snow algorithms show less than 1 inch of snow. The latest WRF models are closer to the NAM, so my 2 inch total isn’t supported by the built in algorithms. We’ll see what happens.

10:45 PM Update:  Latest GFS doesn’t show the enhanced precipitation nor does it delay the snow ending. It maintains a snow total of about 1/2 inch.  [/su_note]

I’ve had a chance to review the afternoon model runs.  Both the GFS and the NAM still predict just a coating (0.30 and 0.50) of snow falling after midnight and ending about 7-9 AM, based on their built-in snow algorithms.

As mentioned in my previous post, using my old, time-tested (but not always accurate) NAM FOUS data technique, I’m coming up with 1.5 to 2 inches of snow.

I’ve never been a big fan of the built-in snow depth algorithms.

Interestingly, this afternoon’s Canadian High Resolution Model (HRDPS) has been consistently predicting ~1.6 inches of snow.

The latest RAP (Rapid Refresh) just available shows 1 inch of snow and ends with light flurries about 9 AM.

So it will be interesting to see how things turn out.    I’ll be looking at the NAM data which comes out about 9:15 and the NAM FOUS data which becomes available about 9:35 PM tonight.   Check back later for an update.

Weather… and Other Things 'Up in the Air'