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Friday and the Weekend

Posted Thursday 04/04/24 @ 5:35 PM — Showers developed in Delaware and Chester counties early Thursday afternoon and moved northeastward. The clouds and showers are the result of instability from cold air aloft and a cyclonic flow around the deep low pressure system that affected our weather earlier this week.

For Friday, the cold cyclonic flow will continue with sunshine in the morning and some sun with instability cloudiness in the afternoon. Showers may wait until evening to move in from the northwest. High upper 40s to about 50º

For Saturday, the effects of the deep low will slowly diminish. A mix of sun and clouds but a light sprinkle can’t be ruled out Saturday in areas far northwest of the city. Gradually moderating temperatures.

For Sunday, more sun than clouds, but some instability cloudiness still possible.

Wednesday night through Thursday

Posted Wednesday 04/03/24 @ 5:30 PM — We’ve had a lot of rain and we’re not quite done with it. Rainfall over the past 72 hours has been in the 2-4 + inch range —

More showers tonight with the actual cold front moving through around midnight.

We may actually see some a bit of sun (with plenty of clouds) Thursday morning, but an upper air low will move directly over us resulting in thicker clouds and scattered showers developing early to mid afternoon—

A similar scenario for Friday.

Wednesday Looking less Wild

Posted Wednesday 04/03/24 @ 9:02 AM — Last night’s models have backed off on the northern extent of the approaching warm front. That means that thermodynamic energy/instabliity (CAPE) will be significantly less than had been forecast, making thunderstorms and tornadoes less likely.

Vertical Shear and Helicity values remain highly elevated from 11 AM through the early afternoon. Since CAPE values are expected to be low, it’s unclear how that energy will come together into sensible weather. I would expect strong wind gusts during that period, along with heavy rainfall.

Wild Weather Wednesday

Update Tue 4/02 9:58 PM — Tonight’s models are increasingly forecasting the possibility of some severe weather Wednesday afternoon (3-4 PM) into the evening. This is especially true of areas from Philadelphia southward. Extremely high shear and helicity values coupled with moderate CAPE may allow some severe thunderstorms to form. High winds expected. Even tornadic activity is possible. Stay tuned.

Wednesday-Thursday Outlook

Posted Tuesday 04/02/24 @ 4:40 PM — I’ve been “doing the weather” for more years than I want to admit, but I don’t recall as many days of rain where 1-3″ accumulation has become the norm.

I’ve been able to access the MRMS rain accumulation data for the past two days, through 3 PM. (I’m not sure how accurate it is since the radar for Philadelphia, located in Fort Dix NJ, has been down for repairs.) —

Additional rainfall, probably the heaviest of this week, will be on Wednesday as a warm front moves across. Perhaps another 1.5- 2″!

We had some low level thunderstorm activity Tuesday afternoon and the possibility exists for additional thunderstorm activity on Wednesday and especially Wednesday evening when thunderstorms may be moderate to strong as the cold front moves through.

It would not surprise me if a severe thunderstorm watch is issued for the period 5 PM through 10 PM Wednesday.

The latest water vapor image shows the current weather well—

Look for updates Wednesday morning if severe weather looks more likely.

Monday into Tuesday

Posted Monday 04/01/24 @ 7:50 PM — The forecast is unchanged. The latest GFS (which tends to slightly under-forecast rainfall) has 3 plus inches of rain by late Thursday.

Tuesday– An additional 0.8 -1″ of rain expected, especially north of the city.

Wednesday— Even heavier rainfall on Wednesday into Thursday.

By Friday—

I’d like to post today’s rainfall, but the server I connect to is down.

Posted Monday 04/01/24 @ 9:45 AM — Last night’s models continued with a little-changed forecast. Several low pressure systems will move through our area from today (Monday) through Thursday, culminating in a closed low over Ohio and a developing Nor’easter for New England off of our coast by Thursday morning—

The trend has been for slightly higher rainfall totals in our area (now over 3″ expected by Thursday.

As is almost always the case, the upper low will trail the surface low. The upper low will track over our area on Friday, still with a chance of showers and considerable clouds at times.

Originally Posted Sun 7:49 PM —A series of low pressure systems will move across the country into our area over the next few days. The latest GFS shows these disturbances—

The first of these systems will bring rain to our area Monday. The trend has been for the heaviest rain to remain to our south. Rain starts about daybreak and continues through about 2-3 PM. Most of the immediate PHL area will get only 0.25″ to 0.35″ of rain, but areas in southern Chester and Delaware counties will have heavier rainfall.

The second two systems will merge into a deeper low that moves to the Great Lakes, bringing heavier rain Tuesday.

This same low will spawn a coastal low bringing rain again on Wednesday. An upper closed low will slow the departure of the Great Lakes low.

A cold front moves through early Thursday.