Update Mon @ 7:51 PM — Weak thunderstorms that began in Chester county mid afternoon have moved up and diminished significantly in strength—

Updated Mon 1:30 PM — A quick mobile update. There are 3 versions of the HIRESW model. The HIRESW-FV3 only shows one line of storms about 5-6 PM, closer to the NAM-NEST forecast. The earlier update based on the HIRESW-ARW is clearly not correct.

Updated Mon 11:14 AM — A quick mobile update. The HIREW model just available shows two lines of storms one moving through early afternoon and another about 7 PM

Update Mon @ 9:25 AM — This morning’s models aren’t available at the time of this update. There’s still a range of forecasts from the models. Some show storms developing in a more random fashion. Some show a distinct line moving through this evening.

The best forecast, based on current radar, water vapor and the NBM model suggests storms develop in mid afternoon western areas of Chester and Montgomery counties and gradually move eastward, arriving in the immediate PHL area between 6 and 9 PM.

With vertical wind shear values relatively low, I don’t see severe storms in our immediate area, despite very high CAPE values.

There is evidence that the storms may diminish in intensity just as they arrive in Philadelphia. Areas from Philadelphia and eastward may receive much lower amounts of needed rain.

I’ll be posting more about our dry current spell and some theories about it later this evening.

Previously Posted Sun 11:13 PM —

A complicated forecast for tonight into Monday as the models have a wide range of forecasts.  Some show a chance of showers tonight into early morning Monday, while others have very little in the way of precipitation tonight.

Several high resolution models show scattered storms during the day, as early as 2 PM, with additional storms late afternoon and evening.  The NAM has another line of storms around 11 PM.

So, the bottom line is an unsettled day with several chances of storms with locally heavy rain any time after 2 PM.

Adding to the uncertainty is some model suggestion that storms may fall apart as they move east into NJ.

Less Unsettled Weekend

Updated Fri 8:12 AM — An early preliminary update.

Not unexpectedly, the models are backing off on the rain for the weekend. (Dry spells are hard to break.)

For today, Friday, there’s a chance of very widely scattered popup showers/thunderstorms late afternoon, mainly from Philadelphia and eastward.

Much of Saturday looks to be just unsettled with our immediate area dry until showers move in from the west later in the day or evening. Now, much of the activity goest to our north and our south.

After some lingering showers on Sunday morning, it looks like things dry out for much of Sunday.

I’ll do a complete Weekend Weather Forecast later today.

Updated Thu 6:06 PM — We may get some much needed rain. Unfortunately, it may come this weekend. The GFS, ECMWF and the NAM all have low pressure developing in the area of the upper trough depicted in my original post graphic below, as the strong ridge in the middle of the country temporarily retreats.

The timing of the rain varies with the models. The NAM has showers moving in early Saturday. The GFS during the evening hours. The ECMWF late Saturday night and early morning Sunday. The ECMWF is notable for some very heavy rain Saturday night.

Despite these model forecasts, these dry spells are difficult to break down. Low soil moisture reduces the usual feedback loop for rain production.

Current NAM forecast for 11 AM shows showers ready to move in.

Tomorrow’s model runs will hopefully better define the timing.

BTW, all models keep unsettled conditions for Sunday, with some scattered showers. Stay tuned.

Previously Posted Wed 10:30 AM —

A persistent upper level high in the middle of the country that has been resulting in recording breaking high temperatures for central parts of the country shows signs of a slight retrograde to the west allowing the Bermuda high in the Atlantic to move slightly westward.

An upper trough will develop in the middle and affect our weekend. The caption for the graphic below explains the salient issues.

The slight pattern change, described in the caption above, will result in increasing moisture and and increasing chance of showers by Sunday.

Until then, typical summertime weather for us.

I was listening to the radio this morning…they were talking about the ‘cooler weather behind all those heavy thunderstorms we had Tuesday’.

There were virtually no heavy storms in our immediate area.

What the heck are they talking about?? Here’s MRMS precipitation summary for the past 24 hours: