Updated Mon 10/03 12:43 PM — Latest models continue to show periods of heavy rain through part of Wednesday. Total additional rain accumulation is coming in at 1.5-3” in the immediate PHL area with the upper range favored.

Posted Mon 8:56 AM

Tropical systems and their remnants often change the weather pattern and such is the case with Ian, where we’ve gone from a near drought situation to over a month’s worth of rain in a few days.

Here’s the past 72 hour rain accumulation, according to the MRMS

MRMS rain accumulation for prior 72 hours. Color code is in inches, contours are in mm (25.4mm =1 inch) (Click on image for a larger view.)

The current weather in the upper atmosphere is best captured by the satellite water vapor image—

Water Vapor Image 8AM Monday with superimposed radar and RAP model 250 mb (jet stream) wind flows (orange) Upper low in western PA is spawning coastal low off of Virginia coast. (Click on image for a larger view.)

An upper low, the remnants of what was Hurricane Ian, is to our west. It’s energy is being transferred to a secondary coastal low that will be slow to move.

06z GFS forecast for early morning Tuesday. Upper low moves to Virginia and coastal low deepens. Until the upper low catches up with the surface low to its east, the system won’t move. (Click on image for a larger view.)

Significant moisture in the system will be thrown back towards us over the next two-three days in the form of heavy rain.

Several models show several additional inches of rain possible in some areas on Tuesday, although the trend with some models is for the heaviest rain now to be to our west.

Last night’s models had the rain stopping for the immediate PHL area today. The 06z GFS continues with some rain for today, Monday, becoming heavy after midnight, with a soaking rain on Tuesday.

Many models have the system departing on Wednesday, but it may be slow to do so. Exact timing with such systems is tough. Stay tuned.


Previous coverage of Ian can be found here.

Updated Sun 10/02 11:12 PM —Tonight’s early models are showing the remnants of Ida have become a closed upper low that will meander near our area through late Tuesday. Monday may see a reduction of the rain from Philadelphia and westward, but rain rotates back in on Tuesday.  The ECMWF is showing several inches of rain possible in some areas on Tuesday.
I’ll be updating this interesting setup tomorrow

Update Sun 10/02 @ 8:42 AM — Fascinating convergence zone has developed over us—

Radar at 7 AM shows area of converging winds (Click on image for a larger view.)

The diagram on the HRRR forecast for 8:30 AM—

06z HRRR forecast for 8:30 AM shows surface winds. I’ve added the notations of the direction of the upper air winds Also visible is the wavy light orange “500-1000 thickness line” showing a small scale ‘wave‘ over our area. This convergence and wave are causing the rain. This feature is forecast to move slowly eastward over much of Philadelphia for the afternoon. (Click on image for a larger view.)

Unfortunately, the Eagles game looks like it will be played in the rain (and wind.)

Updated Sat 10/01 10:41 PM — Tonight’s models are now forecasting that even Sunday morning will have some light drizzle or rain. Rain increases in coverage and intensity during the afternoon. It looks like a wet day at the Linc.

Update Sat 10/01 @ 4:07 PM — Today’s models suggest a dry period before noontime on Sunday, but additional rain will fill in between noon and 2 PM as upper disturbances rotate in around the upper low. The HRDPS captures this —

Forecast Review— We had the break in the rain mid to late morning, but the HRRR was overly optimistic forecasting breaks in the clouds.

Read More


The upper low in West Virginia will throw more clouds and rain towards us, so much of the same.

Several models that were showing a break in the rain Sunday afternoon have moved away from that forecast this afternoon. The NAM-NEST still shows relatively little rain in the city at 3 PM. The NBM shows more widespread on and off light rain in the afternoon.

NAM-Nest forecast for 3 PM Sunday (clouds- black) rain a1 hour accumulated (green contours) and simulated radar. (Click on image for a larger view.)

High temperature 58.4º sd 3.0º NBM model, Blue Bell, PA


Hurricane Ian has its own web page. Click here.

Update Fri 09/30 @ 8:55 AM —Updated the Tropical Storm Ian page with weekend outlook and change in timing and amount of rain.

Update Tue 09/27 @ 6:08 PM — (Updated Hurricane Ian page) We continue to be a northerly flow of dry air through Friday. We may begin to see some high clouds associated with Ian Friday.

The latest ECMWF shows some rain for us by Saturday afternoon from Ian.

Latest ECMWF forecast for Saturday at 2 PM. Rain moves in from Ian. (Click on image for a larger view.)

Posted Mon 9:32 PM

Our weather this week will be influenced by an upper air trough bringing continued cooler, temperatures. Current seasonal average highs are 70-72º. We’ll be seeing upper 60s over the next two days.

Water Vapor image shows jet stream level winds and the position of upper level systems. The trough over the eastern part of the country will combine with a southerly flow over the Carolinas and Georgia to influence the movement of Hurricane Ian. (Click on image for a larger view.)

This corresponds to the current depiction of the NAEFS

NAEFS current conditions Monday evening (Click on image for a larger view.)

The remnants of Hurricane Ian will affect us later in the week and more likely, during the weekend. I’ll be following the models.

Current indications, based on the GFS, ECMWF and ICON models, suggest that the bulk of the rain associated with this storm will move just to our south late Saturday into Sunday. With hurricanes, anything can happen and changes are likely. Stay tuned

Weather… and Other Things 'Up in the Air'

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