[su_note note_color=”#d9f2da”]Noon Update: My optimism about clearing after the warm front passage was apparently misplaced.  This was a “low-confidence forecast” for a reason.  The warm front hasn’t really made it past Philadelphia and it won’t until later in the afternoon.  A light drizzle has also developed. The GFS model was apparently correct.  Showers are beginning to develop to our south and may move in earlier than expected.  [/su_note]

[su_note note_color=”#d9f2da”]Yet Another Update 5pm: The FV3-GFS shows lower chance of thunderstorms this evening. The warm front never made it north of Philadelphia!  Poor model performance today![/su_note]

The showers have pretty much ended after 8 AM here, so yesterday’s NAM forecast has verified.

The question is – how much clearing  and brightening skies will we get?   The NBM (National Blend of Models) has things brightening considerably about 1 PM.

Current upper air analysis shows dry air punching in from the south (see 300 mb humidity graphic below)

But lower levels of the atmosphere are pretty saturated.  So I’m not sure if the drab, cloudy conditions will improve, but I think they may.

Current analysis shows much of the dynamics for thunderstorms remain to our south:

Those dynamics supporting thunderstorms are expected to move northward by late afternoon giving us scattered thunderstorms.

So brightening skies (maybe) for much of Saturday with scattered showers and thunderstorms re-developing around 4-5 PM.

[su_note note_color=”#d9f2da”]So the rain moved in earlier than expected, closer to the GFS- based LAMPS than the NAM-based HRRR. In fact, the HRRR did poorly; one of the few times I can think of where the LAMPS did better than the HRRR. Will have to try again next weekend![/su_note]

The lack of consistency and accuracy with the model forecasts this weekend is almost enough to force me into finding a new hobby.

The 2am runs of the models has the GFS bringing rain by early afternoon.   The GFS-based LAMPS short range has rain by mid morning here.  The NAM still holds off most of the rain until late afternoon and this evening.   The NAM-based HRRR shows rain moving into PHL about 3 PM.

The further north you are from PHL, the earlier the rain starts.

So there you have it.  The HRRR did well yesterday so about 3 PM looks like a good bet here in PHL.   Areas to our north, in Bucks county, upper Montgomery counties and Trenton, already have rain or will have it starting in the morning.   Areas as close as Blue Bell might have rain starting later this morning, according to the LAMPS.