The showers today will be scattered as in past days, but total rainfall (in some areas) may be greater. Showers start about 2-3 PM and continue through 8-9 PM.
Today’s 12zHIRESW 2.5KM model total rainfall forecast for later Friday (Click on image for a larger view.)
I’ll post the Weekend Weather Forecast this evening. (The weather looks to be much improved from past days, but some uncertainty about showers Sunday. )
Friday Forecast Update
Update Thu 5/04 10:59 PM — Tonight’s models continue with a forecast of sunshine Friday morning followed by clouds and pop-up showers during the afternoon, especially late afternoon and early evening.
The big change on Friday — the showers may be more substantial than past days and a rumble of thunder can’t be ruled out. As much as this weather will be the result of the influence of the upper low finally departing, a warm front type scenario will also contribute to the mix.
Thursday Forecast Update
Update Thu 05/04 @ 9:38 AM —
The early morning sun we saw might have been the most sun we’ll see today. Already, the cold upper air pool of air is causing instability cloudiness to form. Most models continue with the forecast of light scattered sprinkles and showers developing about 3-5 PM.
In some areas, the sprinkles might be negligible; in others, as much as 0.03″ of rain may fall. High temperature will be just shy of 60º (Blue Bell, PA)
This morning’s 12z NBM simulated radar forecast for 4 PM. ( Green contours are 1 hour accumulated rainfall ) (Click on image for a larger view.)
Incredibily, the NBM shows a similar forecast for Friday, perhaps even more showers!
For a greater insight into today, the upper air flow at 250 mb (~34000 ft) around the upper low is colliding with moisture circulating a mid level low at 400 mb (~23,000 ft).
Clouds and sprinkles will be the result. Lack of precision of measurements over the ocean will result in uncertainty regarding the exact placement of the sprinkles today—
Wind flow Thursday morning at 250 mb and 400 mb heights with supimposed water vapor satellite image. (Click on image for a larger view.)
Things do dry out for the weekend.
Previously Posted Wed 7:41 PM —
We have about two more days of an upper cyclonic flow that has given us the clouds, light showers and cool temperatures.
The big upcoming change will be the transition to an upper level ridge. Temperatures will move back towards the low 70s by the weekend—
NAEFS Max Temperature forecast for late Saturday. Also visible are the 250 mb (jet stream level) contours showing the ridge that will slowly move towards us. Temperatures near 70 on Saturday and above 70 on Sunday are expected.
Thursday will be similar to today, Wednesday, although there should be noticeably fewer scattered sprinkles and perhaps some more breaks of sun.
Update Wed 05/03 @ 9:37 AM —The blocked pattern will slowly transform into another blocked pattern over the weekend. By the weekend, our part of the country will be under more of an upper ridge than the current upper low. Until that time we’ll continue with unsettled weather: clouds, some sun, scattered showers, and cool temperatures.
Today, Wednesday, we’ll likely have the most widespread shower activity, but both Thursday and Friday may have a few late afternoon showers in some areas.
Here’s what things look like by Sunday—
NAEFS forecast for Sunday at 2 PM. The red line, (540 thickness line) captures the general configuration of the jet stream. Notice the extreme extent into northern Canada indicative of a blocked pattern. The Northeastern US will now be under more of the upper ridge. The weather should become drier and milder. (Click on image for a larger view.)
Tuesday – Continued Unsettled Weather
Update Tue 05/02 @ 8:16 AM — The upper air low has moved to north of NY State and it is expected to precess and end up over our area Wednesday and Thursday.
Disturbances continue to rotate around the upper low and one is bringing light showers this morning. Another is expected to move in this afternoon with more widespread showers.
By Wednesday, the upper low is over Pennsylvania—
NAEFS for Wednesday at 5 PM. Notice the RED 540 thickness line. The 540 thickness line is usually most visible on weather maps in winter. Its appearance shows the pool of very cold air aloft associated with this upper low. This cold air aloft is resulting in instability cloudiness and showers. (Click on image for a larger view.)
Update Mon 05/01 @ 8:53 PM— The blocked pattern will remain with us through the weekend. The upper low pressure system over the Great Lakes has closed off and it will slowly move directly over Pennsylvania over the next several days. Unsettled conditions with periods of cloudiness and occasional showers expected.
That was a lot of rain!
Woo! That was a lot of rain we got this past weekend! So how much did we get? Here’s the MRMS radar/rain gauge based measurement—
MRMS 72 hour rain total for this past weekend. (Click on image for a larger view.)
Previously Posted Mon 12:00 PM —
This Week’s Weather Overview
The blocked pattern will slowly loosen over the next several days. The upper low still over the Great Lakes will continue to rotate disturbances over our area, giving us periods of clouds and some showers intermixed with some sun.
Water Vapor Satellite image Monday morning shows the low pressure system still over the Great Lakes, rotating disturbances over our area. This may continue through Thursday. (Click on image for a larger view.)
