Update Sat 10/08 @ 5:43 PM — Latest NBM model shows low temperatures tonight to be the coldest so far this season—
Today’s 19z NBM model forecast mean minimum temperatures for tonight. The standard deviation is 2.5º-3º so it might be higher or lower than these temps. I’m betting on lower. (Click on image for a larger view.)
While we’ll see moderating temperatures through Wednesday, a sharp dip in the jet flow expected Thursday-Friday with a cold front moving through probably before daybreak Friday—
NAEFS model jet stream winds (250 mb) Thursday morning. Strong in the Dakotas impulse rounding the bend will trigger low pressure development. Associated strong cold front comes through before daybreak Friday. (Click on image for a larger view.)
Previously Posted Fri 8:13 PM —
A cold front will pass through this evening (somewhat later than forecast yesterday) with a shift of winds to the north. Cooler air will filter into the area. Some light scattered sprinkles are showing on radar (as forecast by yesterday’s HRDPS) and this afternoon’s GFS is forecasting some additional sprinkles around midnight. Most areas dry.
The weekend will be sunny and cool. (Seasonal average high temperature is 67-68º this week.)
Saturday
There’s still a chance of brief period of clouds early afternoon Saturday, but otherwise quite nice.
High temperature 57.7º sd 1.9º NBM model Blue Bell, PA
Saturday night will feature fairly chilly temperatures, into the mid to upper 30s in some areas outside the city.
Sunday
Sunday will continue with fair skies and slightly warmer temperatures.
High temperature 61.7º sd 1.9º NBM model Blue Bell, PA
Outlook: Monday through Wednesday moderating temperatures. A strong cold front later in the week will bring much colder temperatures.
Updated Thu 10/06 9:29 PM —A cold front moves through late Friday afternoon, preceded by an increase in winds early afternoon. There isn’t much moisture associated with this front and its passage will be marked by only minimal cloudiness and a wind shift. The Canadian high resolution model shows a few light widely scattered showers/sprinkles about 7 PM Friday evening after the front moves through.
A cool but beautiful weekend. Mostly sunny but a few hours of cloudiness moves in about noontime Saturday.
A nice weather weekend
Update Wed 10/05 @ 9:01 PM —The low pressure system that’s been with us for days is departing tonight. High pressure builds in Thursday and Friday. A cold front moves through Friday afternoon with possibly some clouds and an increase in wind speed.
Cold high pressure moves down from Canada for Friday and Saturday, but quickly departs—
Today’s 18zGEFS forecast for 5 AM Saturday morning. Somewhat cold high pressure sinks down (as indicated by the red 540 thickness line.) but quickly retreats northward for Sunday.
There may be some instability cloudiness mid day on Saturday as an upper air disturbance moves through. Otherwise sunny Temperatures may go to the low 40s Friday night and Saturday night with some upper 30s northern and western suburbs. Highs upper 50s to near 60º.
Update Wed 10/05 @ 7:35 AM — The latest GFS this morning shows light showers and clouds lingering until about 4-5 PM today.
06z GFS shows light showers lingering at 4-5 PM today. (Click on image for a larger view.)
Rain moves out Wednesday evening
Updated Tue 10/04 10:01 PM — Some showers may linger into early evening Wednesday.
Update Tue 10/04 @ 6:01 PM — Current water vapor image captures what’s going on in the atmosphere—
The upper low over Virginia will merge with the coastal low Wednesday afternoon and will move away Wednesday night. The upper low in South Dakota will push a cold front through our area on Friday. Rather strong high pressure in Canada will drop down over us over the weekend with rather chilly conditions. Right now little or no precip from this expected, but I wouldn’t be surprised if we have considerable instability cloudiness on Saturday with light scattered showers especially northern areas. (Click on image for a larger view.)
Rain Continues into Wednesday Afternoon
Update Tue 10/04 @ 11:50 AM — The latest models show the rain continues into at least Wednesday afternoon. Here’s the latest HREF model forecast for Wednesday at 2 PM—
This morning’s 12z HREF shows the upper low and surface low becoming vertically stacked off the Delaware coastline on Wednesday at 2 PM. Rain continues into our area at that time. Rain should taper late Wednesday afternoon with possibly some breaks in the clouds towards evening. (Dark blue is low cloud cover) (Click on image for a larger view.)
Update Mon 10/03 @ 6:05 PM — This afternoon’s models are in good agreement that an additional 2 – 3 inches of rain will fall before it tapers some time Wednesday afternoon. That’s on top of the amounts shown in the MRMS graphic below.
Here’s additional rain prediction from the Canadian High Resolution —
Latest Canadian 18z HRDPS 48 hour additional rain accumulation forecast through Wednesday 2 PM (Click on image for a larger view.)
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.
Previously 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.
