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Colder Sunday
Update Sat 11/12 @ 6:13 PM —
A cold front moves through after midnight tonight (Saturday) with showers. Colder air moves in Sunday and especially Sunday night. A mix of clouds and sun with highs 50.8º sd 1.8º NBM model, Blue Bell. (Average high this week is 54º-55º)
NBM temperature meteogram for Blue Bell, PA (Click on image for a larger view.)
The long term outlook is for temperatures to be at or below normal for the next 10 days or so.
It will be fairly windy and gusty—
NBM winds and wind gusts for Blue Bell PA (Click on image for a larger view.)
BTW, how much rain did we get on Friday? Not as much as it seemed—
MRMS rainfall estimates for Friday. Contours are in mm (25.4 mm = 1 inch) (Click on image for a larger view.)
Where’s the Sun?
Update Sat 11/12 @ 5:26 PM —
Well, my ‘experiment’ with relative humidity didn’t work. The models were correct and we had mostly sunny skies. I do realize what I had overlooked— there was too little moisture at upper levels. Anyhow, I always like to see what parameters connect with sensible weather and this is what makes it fun for me.
We might have a chance to try the same technique tomorrow. 🙂
Update Sat 11/12 @ 9:31 AM — I was curious about the amount of sunshine today. For a reason. The models’ cloud algorithms are still pushing clouds to dissipate with sunshine, but a look outside suggests otherwise.
The latest GFS and HRRR all show little to no cloudiness at this hour. Not correct and not the first time their cloud algorithms under-forecast cloudiness.
What the models all show is significant moisture at about 3000 feet (925 mb height). Here’s the GFS current model—
GFS 925 mb Relative Humidity and 500 mb Vorticity (contours) for noon today. Significant low level moisture with vorticity providing upward motion may keep the clouds in place longer. (Click on image for a larger view.)
Water Vapor shows upper air disturbance (vorticity)—
As is often the case, the latest Water Vapor satellite image shows the area of vorticity. This is expected to move in around noon, according to the GFS and move out about 2-3 PM. (Click on image for a larger view.)
So if we use the model’s cloud algorithms, we have sunshine shortly. If we use ‘my technique’ of relative humidity at specific levels combined with voriticity, we have clouds lasting until about 2 PM or so. ‘My technique’ has let me down in the past, so it’s an interesting experiment.
Updated Fri 11/11 9:41 PM — Tonight’s models are pushing more sun, little cloudiness on Saturday.
Previously Posted Fri 6:21 PM —
The remnants of what was Nicole will depart around daybreak Saturday and we will likely wake up to a mix of clouds and sunshine.
We can see the remnants of Nicole plainly visible on the current water vapor satellite image, but also note a developing disturbance (white circle) that will affect our weather Saturday night—
Water Vapor image showing the remnants of Nicole. A disturbance has developed at the base of the jet trough (white circle) and this may move in to our area late Saturday night (GFS model) or early Sunday morning (ECMWF model) It will be fast moving, as it’s embedded in a very strong jet streak.
Saturday
A mix of sun and clouds in the morning, but there may be periods of considerable cloudiness later in the afternoon as a secondary cold front and the disturbance approaches. It will be mild in the morning (upper 60s), but temperatures will be dropping slowly to near 60 after 2 PM. Windy in the morning, but winds should slowly decrease during the day.
High temperature 68.1º sd 1.1º NBM model Blue Bell, PA (this high will be in the morning.)
Some showers moving in late evening.
Sunday
Showers should depart early morning. A period of sun in the morning will give way to instability cloudiness in the early afternoon. The sun may break out again late afternoon. Winds breezy and somewhat gusty.
High temperature 50.6º sd 1.8º NBM model Blue Bell, PA
Areas of temps at or below freezing Sunday night in areas north and west of the city.
The latest HRRR has reverted back to a wetter and stormier forecast for the immediate PHL area. Rainfall amounts now forecast to be in the 1-2 inch range here—
Latest HRRR (17z) showing 1-2 inch rains in a band through Philadelphia. (Click on image for a larger view.)
Indeed, the 2-5 PM time frame (mentioned in last night’s update) may include some very strong thunderstorms and rain, as CAPE values are currently approaching 600 J/kg2—
Current Radar with RAP model MUCAPE (“most unstable” CAPE) yellow contours approaching 600 J/kg2 moving into the PHL area.
Nicole Update
Update Fri 11/11 @ 10:24 AM — Current radar is consistent with the previous forecast of the heaviest rain moving off to our west—
Radar and RAP Model at 10 AM Friday. Yellow “theta E” contours are far west of us; the heaviest rain will be far west of our area.
The latest HRRR does NOT show any of the severe helicity and elevated vertical shear between 3-5 PM as it did last night.
However, the latest HRDPS shows the possibility of some heavier showers/thunderstorms between 1 and 5 PM, especially in New Jersey.
Winds increase during the afternoon and evening, but the NBM is not showing as strong wind gusts as it had forecast previously (about 35 mph) .
The HRRR has reduced its rainfall totals, but the NBM and especially the NAM-NEST has somewhat higher local totals.
Total rainfall based on the latest HRRR (which may be a on the low side)—
Update Thu 11/10 @ 8:13 PM — The basic trend has been for the heaviest rain and activity to be west of the immediate Philadelphia area but close enough that areas of Chester county and upper Montgomery county may be affected by higher rainfall.
As the system departs after midnight and before daybreak Saturday, highest winds will be from Philadelphia, eastward into NJ.
I’ve been looking over this afternoon’s models and two interesting periods stand out Friday into Saturday, based on the HRRR and Canadian HRDPS model.
First is an area of very high helicity and relatively high vertical shear around 3-5 PM Friday in our western suburbs—
Today’s 18z HRRR shows very high helicity and elevated vertical shear around 3 PM in the western suburbs. Ordinarily, this would be a likely time for severe weather, but CAPE values are low. Honestly, I’m not sure what to make of this. (Click on image for a larger view.)
Combining this model with the Canadian High Resolution model suggests some heavy weather between 3 and 5 PM Friday.
Another period to keep an eye on is 2 AM Saturday morning—
Today’s 18z HRRR showing elevated CAPE and elevated helicity. Low vertical shear. Some isolated thunderstorms with strong winds possible. (Click on image for a larger view.)
Tonight’s 00z NBM just became available. It shows increasingly windy conditions through the afternoon until about 4 AM Saturday—
Tonight’s 00z NBM winds wind gusts and standard deviation. (Click on image for a larger view.)
Less Rain from Nicole here
Update Thu 11/10 @ 9:49 AM — The timing for the arrival of the rain from Nicole is essentially unchanged. Rain starts here about 7-8 AM Friday morning (earlier to the south and west) and ends about 7 AM Saturday morning. Sun breaks out Saturday, but some cloudiness increases during the afternoon as a secondary front moves through.
Wind gusts are expected to peak during Friday evening and the over-night hours. Peak wind gusts 35-40 mph.
As is almost always the case, the distribution of the rain has changed [considerably], with our area now forecast to receive less than 1 inch—
Today’s 12z NAM total precipitation by Saturday morning. This will likely continue to change in either direction, but the trend is downward in our area. (Click on image for a larger view.)
Nicole Remnants to move Faster
Updated Wed 11/09 9:45 PM — Tonight’s NAM-NEST continues to show an earlier arrival of the rain from Nicole. Some showers as early as daybreak Friday, and the system exits before daybreak Saturday with sunshine early morning.
Tonight’s NAM total accumulated rain forecast has moved closer to the NBM model forecasts of recent days—
Tonight’s 00z NAM accumulated rain forecast by Saturday morning. (Click on image for a larger view.)
Nicole Remnants to move Faster
Update Wed 11/09 @ 8:47 AM —
The remnants of Tropical Storm Nicole (or remnants of possible Hurricane Nicole) will move up the Appalachians and affect our weather Friday morning. Rain moves in between 7 and 10 AM here and will end early morning Saturday as late as 10 AM, but possibly earlier. Some sun possible around noon Saturday.
Currently, there are large differences in the rainfall totals here for Nicole. The model blend (NBM) continues to crank out 2.5 inches, but the NAM and GFS show much lower amounts here, with greater amounts far western areas.
Latest NAM model rainfall totals by Saturday morning. (Click on image for a larger view.)
It will be windy. Here’s the NAM wind meteogram for Blue Bell, PA
Today’s 06z NAM wind meteogram for Blue Bell. Wind gusts near 40 mph late Friday into Friday night. (Click on image for a larger view.)
As for Sunday, the models are leaning towards that low pressure being off the coast instead of giving us showers on Sunday morning. Only the ICON model has showers Sunday morning for us.
Remnants of Nicole to Affect our Weather Friday into very early Saturday
Updated Tue 11/08 9:32 PM —
A quick update. The GFS and ECMWF continue with rain starting Friday morning and ending Saturday morning. The NBM has the rain ending somewhat later, in the early afternoon. The rainfall amounts have been in the 1-2” range for the GFS and ECMWF. The NBM cranks out 3” in our area.
Another development: A weak low pressure system is now forecast to develop along a secondary cold front Sunday morning with light showers here and light snow showers in western PA.
Remnants of Nicole to Affect our Weather Friday into very early Saturday
Update Tue 11/08 @ 9:36 AM — The latest GFS and ECMWF show the remnants of Nicole taking a more western track than previously forecast.
Here’s Nicole at 1 PM Friday, with rain just entering our area—
Tuesday 06z GFS forecast for 1 PM Friday. Rain just moving in. (Click on image for a larger view.)
The latest ECMWF has a similar forecast, but a little faster with the onset of the rain —
Tues 06z ECMWF forecast for Friday 1 PM. Similar track, but faster onset of the rain. (Click on image for a larger view.)
Both models now have the heaviest rain moving off to our northwest, although we’ll still get a good soaking.
The GFS has the cold front sweep the storm into the Atlantic by 8 AM Saturday with sunshine, colder and windy conditions moving in.
Remnants of Nicole to Affect our Weather Friday
Update Mon 11/07 @ 9:17 PM — Latest models have the rain from the remnants of Nicole affecting our area on Friday into Saturday. The latest 00z NBM has rain starting as early as 10-11 AM, but others start the rain in the mid to late afternoon. Rainfall amounts look heavy, with 1.5-3+ inches of rain over our area. Speed of the system varies with some models having it linger into Saturday afternoon. Others have rain ending Saturday morning.
I’ll do an update tomorrow morning.
Wide Spread in Forecast Intensity of Tropical System
Updated Mon 11/07 11:38 AM — The storm to affect Florida and us later this week has been given the name Nicole. This morning’s NAM and GFS suggest strengthening to near or above hurricane strength likely.
Update Mon 11/07 @ 9:07 AM — Significant disagreement in the forecast regarding the strength of the tropical system to affect Florida late Wednesday with the remnants to affect our weather late Friday into early Saturday.
The ensemble forecasts (GEFS, NAEFS, SREF) and the ECMWF have all reduced the strength of the tropical system to affect Florida—
ECMWF forecast for 8 PM Wednesday. 1000 millibar central pressure. (Click on image for a larger view.)
The new GFS v 16.3 has forecast an increased strength of the system at the same time period—
GFS v 16.3 forecast for 8 PM Wednesday. 985 millibar central pressure with high winds to the northeast. The other models are less intense with only 1000 mb central pressures. (Click on image for a larger view.)
The track of the storm towards us on Friday to Saturday also varies considerably from model to model.
The general consensus is that the system will be at its peak here 1AM Saturday morning with some possible clearing during Saturday afternoon.
Previously Posted Sun 9:15 PM —
I’m still getting past Sunday’s forecast disappointment, but some interesting weather changes are in store for us this week.
The front that went through today had little upper air support, but cooler air will gradually filter in over the next couple of days on easterly and northeasterly winds.
Of great interest is a tropical system (possible hurricane) that is taking shape near Florida. Below is the scenario predicted by the latest GFS v 16.3.
I expect that this forecast scenario will change in track and timing as the week progresses but here’s the latest GFS forecast—
System approaches Florida Thursday morning–
Today’s 18z GFS shows a tropical-hurricane type system developing off Florida’s Atlantic coast Thursday morning. (Click on image for a larger view.)
By Friday morning, the GFS takes this across Florida as the system will interact with a very strong cold front that will move towards us from the Midwest—
GEFS Forecast Friday morning. Tropical Storm/Hurricane will set up to interact with approaching cold front in Wisconsin (Click on image for a larger view.)
The system moves back across Florida and the moisture moves up the coast as a strong cold front approaches. Things come together over us Saturday morning. Some wild weather possible with such great temperature contrasts and high moisture content—
GFS forecast early Saturday morning 1 AM.
Stay tuned. The forecast will undoubtedly change as the week progresses.
