Sun 7:33 PM — Forecast Review — Overall a beautiful day and nicer weather than forecast. The clouds moved in later than had been predicted. The rain made it a bit further into Philadelphia than forecast this afternoon, but did diminish in intensity as forecast. Yesterday’s ICON and Canadian GEM did better than the GFS with forecasting the late arrival of the showers.
More showers expected later this evening and after midnight.
Update Sun @ 8:28 AM — Despite the early sunshine, clouds are expected to move in by late morning. Last night’s late models (06z) continue with the forecast of showers dissipating as they move into Philadelphia this afternoon.
Most of the eastern area will be dry today (until this evening). Here’s last night’s high resolution HIRESW model forecast showing the eastern extent of the showers this afternoon at 4 PM; they aren’t expected to move much more eastward this afternoon—
Why does the rain dissipate? The reason is a sharp mid level (500 mb) ridge that doesn’t allow vertical upward motion eastward—
Update Sat @ 10:40 PM — Tonight’s models have the rain in far western suburbs Sunday afternoons, but struggling to move into the city during the afternoon as it hits a sharp mid-levelupper air ridge. Much of the eastern area remains dry during the day. Still a lower confidence forecast.
Update Sat @ 9:15 AM — There’s still some uncertainty about the onset of showers Sunday. The GFS, GEFS, SREF and ECMWF have showers moving in from the west by 12-2 PM. The Canadian RGEM and ICON have a later onset, towards evening. I’m leaning towards the GFS group—
Update Fri 10:13 PM— Tonight’s models suggest an even earlier start with the showers on Sunday, possibly late morning to noontime. The NBM still holds the showers off until evening. So forecast uncertainty remains for Sunday.
The forecast for the weekend has clarified since posting yesterday’s outlook. High pressure will be with us for Saturday. The timing of an approaching warm front on Sunday will occur earlier than many models had been forecasting— the warm front will bring some showers as early as Sunday afternoon. (Most models have joined the GFS and ICON with the earlier showers.)
High pressure will influence our weather on Saturday. It will still be somewhat windy mid-day. Highs 65º ± 1.0º NBM model, Blue Bell
High pressure moves off as a warm front associated with a deep low in the Great Lakes region approaches. Today’s models have joined yesterday’s GFS and ICON models—w showers move as early as 2- 4 PM, especially west and southwest of the immediate PHL area. Highs 66.3º ± 3.0º NBM, Blue Bell (large spread due to uncertainty in cloud cover.)
High pressure will be with us for most of the weekend. An approaching warm front will bring some showers late Sunday afternoon or Sunday evening.
High pressure will influence our weather on Saturday. It will still be somewhat windy mid-day. Highs near 65º.
High pressure moves off as a warm front associated with a deep low in the Great Lakes region approaches. Today’s GFS and ICON models have showers moving in about 4 PM, but today’s ECMWF, SREF and Canadian RGEM hold off the showers until Sunday evening. So there’s uncertainty with the speed of this system. Highs 69 to 70º
Weekend Weather & This Week’s Weather returns April 30th.
Thu 5:30 PM Forecast Review— We had the wind gusts and some areas had strong storms. The HRRR did pretty good forecasting the stronger storms north of Philadelphia.
Update Thu @ 10:15 AM — Some changes in the forecast with the latest HRRR just available. Timing of the frontal passage today is about 5 PM ± 1.5 hours in the immediate Philadelphia area with thunderstorms, then passing into NJ.
A rapid change in pressure with the frontal passage will result in high wind gusts, as the winds shift from southwest to northwest. Depending on the model, gusts from 30-50 mph possible.
Previous model runs showed shear and helicity to be low with severe thunderstorms unlikely. Despite this, the HRRR is showing an elevated hail parameter with the storms with strong vertical motion being present.
Update Wed @ 6:08 PM — A cold front moves through Thursday afternoon with thunderstorms. Current timing is between 2:30 and 5 PM depending upon the model. Here’s the NAM-NEST forecast for 4 PM—
Forecast helicity and vertical shear remains low and CAPE values remain in the respectable moderate range. No severe weather expected although some strong thunderstorms are possible.
Update Tue @ 8:08 PM — Very warm weather for Wednesday and Thursday with high temps 80-84º. (Average high is 64-65º.)
A cold front moves through Thursday afternoon, with current timing about 5 PM according to the latest NAM-NEST. Thunderstorms are expected.
A low helicity and low shear environment is currently predicted, so severe weather is unlikely, although some strong storms always possible since CAPE values are forecast to be in the respectable low moderate range of 600 joules/kg range.
Update Mon @ 6:50 PM — A review of the latest GFS and Canadian RGEM are more optimistic than the high resolution models that the showers tomorrow morning will be light and depart mid morning. Huge difference here, so I guess we’ll see.
Warm temps and sun in the afternoon.
Update Mon @ 5:11 PM — The low pressure system that gave us the showers and clouds over the weekend will rotate yet another weak disturbance and front through on Tuesday. (The center of this low is still near Nova Scotia.)
The forecast has changed from yesterday— what had been forecast to be a light sprinkle moving through early to mid morning Tuesday now looks to be a several hour period of showers, possibly lasting a bit past noon time. Total QPF is on the order of 0.15 inches.
Originally Posted Sun 7:32 PM —
Our weather will turn more spring-like this week as we come under the influence of an upper level ridge with warm air moving up from the south—
We’ll have temperatures in the 70’s by mid-week and possibly higher. The cold front that will be causing severe weather in the middle of the country is expected to weaken considerably as it approaches us Friday.
No major storms expected this week for our area. Some showers Monday night will move out by Tuesday.