Update Sun 8:51 AM— The clouds from that predicted upper air disturbance have started moving in. The cloudiness mid-day may be considerable and last into mid to late afternoon today.
Saturday Forecast Review —
HRRR 8 AM (12z) Saturday forecast for 11 AM Saturday -Hail parameter showing 0.9 inches (red/orange) (Click on image for a larger view.)
Stan in Collegeville had commented that he had some brief hail late Saturday morning. I was curious if the models had predicted this. Indeed, yes. Here’s the HRRR model “hail parameter” from Saturday’s 8 AM model run (12z).
FYI, NOAA’s Severe Storm Site defines hail as being greater than 0.2″ in diameter. Otherwise it’s still ‘sleet’ or ‘ice pellets’, even if it’s created from low level convective or thunderstorm activity.
Update Fri 10:49 PM— Based on tonight’s early models, HRRR, NAM-NEST, I’ve updated Saturday’s forecast below. It’s more optimistic about some sunny breaks. Sunday’s forecast unchanged.
This coming weekend will be influenced by an influx of colder air and a dip in the jet stream to form an upper air trough, pushing a cold front through. Disturbances rotating around an upper low will bring showers on Saturday.
GEFS upper air wind forecast (250 mb- jet stream level) for Saturday 8 PM. The dip in the jet winds and the upper air low in upper NY State will bring enough moisture and lift to create cloudiness and light showers on Saturday. The tropical jet (2) is just visible. (Click on image for a larger view.)
Saturday
A mix of sun and clouds early, then mostly cloudy with very light scattered showers starting mid to late morning. Showers should be light (about 0.08-0.15 inches). A mix of sun and low dark clouds in the afternoon, with another chance of scattered showers, especially 4-6 PM. Windy. High 52.7º ± 1.6º (NBM model Blue Bell)
This afternoons’s HREF 1 hour precipitation forecast for 2 PM Saturday. The HREF is similar to the ECMWF forecast. The NAM-NEST forecast (not shown) is more optimistic about some sun early and clearing after 3 PM. (Click on image for a larger view.)
Previously Posted Fri 4:56 PM —
Sunday
Mostly sunny, some periods of instability cloudiness late morning into early afternoon. WINDY and chilly. High 45.5º ± 2.6º NBM model Blue Bell)
Winds
NBM wind forecast (Click on image for a larger view.)
This coming weekend will be influenced by an influx of colder air and a dip in the jet stream to form an upper air trough, pushing a cold front through. The disturbances rotating around an upper low will bring showers on Saturday.
GEFS upper air wind forecast (250 mb- jet stream level) for Saturday 8 PM. The dip in the jet winds and the upper air low in upper NY State will bring enough moisture and lift to create cloudiness and light showers on Saturday. The tropical jet (2) is just visible. (Click on image for a larger view.)
Saturday
Mostly cloudy with very light showers starting mid to late morning and lasting into early afternoon. Showers should be light (about 0.05 inches). Some models have some clearing in the mid afternoon, but most maintain the chance of light scattered showers until 3-4 PM. WINDY. High 54.2º ± 2.2º (NBM model Blue Bell)
Sunday
Mostly sunny, some periods of instability cloudiness. WINDY and chilly. High 46.3º ± 2.4º NBM model Blue Bell)
Winds
NBM wind forecast (Click on image for a larger view.)
Update Thu @ 10:07 AM — The rain is exiting, but cloudy damp conditions will linger throughout the day. Rain redevelops Thursday night.
Friday looks good as we’ll be in-between systems, specifically a strong cold front that moves through Friday night.
Saturday looks unsettled, windy, with scattered showers especially northern suburbs. An mid-level disturbance and upper trough will bring the showers.
Sunday looks partly sunny, still breezy and unseasonably cold.
Update Wed @ 10:22 PM — Tonight’s early models have the rain ending Thursday morning from the city westward. Very cloudy. Rain redevelops Thursday evening.
Update Wed @ 11:23 AM — With such a complex system to affect our weather over the next several days, expect changes in the forecast. As an example, today’s rain, originally expected to move in after noontime, now appears to move in after 3-4 PM.
Rainfall amounts tonight will be over 1 inch and areas in NJ will see higher amounts, lingering through Thursday.
Much of the rain Thursday will be just east of Philadelphia, but some showers are still possible in our immediate area.
The forecast for Friday looks better as some clearing is expected behind a cold front.
Saturday still looks unsettled with possible scattered showers due to an upper air trough moving through.
The complex weather pattern discussed in earlier posts starts Wednesday afternoon, with several areas of low pressure moving through. The first will be Wednesday into Thursday, then Thursday into Friday. The current timing shows the heaviest rain falling during the nighttime hours, Wednesday night and Thursday night.
There may be daytime periods Thursday and again on Friday where things temporarily partially clear. Unfortunately, Saturday is looking unsettled and showery due to an upper air low—
GEFS statistical mode forecast for Saturday 2 PM. The main low in Quebec Canada will have several surface lows (black L) rotating around it. An upper air low (Blue L) will bring showers to our area on Saturday. Green blue shading is rain and up north, snow. Note that the red540 thickness line is south of our area indicating chilly weather on Saturday. (Click on image for a larger view.)
Update Mon 10:43 PM— Not much change in the forecast. The complex system in the Midwest will move north of the Great Lakes while disturbances develop and move up over us from Thursday through Saturday. The complexity of this setup will prove difficult to forecast the rain and dry periods accurately. The best day looks to be Sunday, but it will be chilly. Stay tuned.
Previously Posted Sun 7:06 PM —
A gradual warmup in store for us on Monday and Tuesday. Highs just above 60º
A large storm in the upper Midwest will bring rain to our area on Wednesday.
GEFS forecast for Wednesday at 2 PM. Rain expected as a southwesterly moist flow develops. (Click on image for a larger view.)
Thursday, we’ll likely have more rain as a secondary coastal low is spawned off of the main low—
GEFS forecast for 11 AM Thursday. Possibly heavy rain from this secondary low. (Click on image for a larger view.)
After a quieter day on Friday, the weekend looks to be unsettled with possibly more rain.
