FYI, NOAA model data, usually available on their website called “NOMADS“, has been inconsistently available today.
NOAA, over recent days, has changed SSL certificates and has attempted to move their data over to Akamai’s CDN (Content Delivery Network).
This changeover has been fraught with difficulties over recent days. With NOMADS not working, NOAA’s backup server is overwhelmed.
It’s been difficult to get a complete download of the NAM, GFS and other models. With little data available, it’s been tough to do a forecast.
Updated Fri 8/26 8:23 AM — Many of last night’s models have significantly downplayed the chances of showers today in our area. The NAM-NEST continues with very widely scattered showers around 5 PM.
Update Thu 08/25 @ 8:11 PM — The weather has been on easy auto-pilot the past few days with increasingly warm and humid conditions.
Friday will have the warmest temperatures of this week with temps in the low 90s in many areas.
A weak front will move through Friday afternoon. Most of the US models have kept any showers to the far north of Philadelphia. But, this afternoon’s NBM, Canadian RGEM, and the ECMWF shows some light showers and thundershowers developing west of Philadelphia in the mid afternoon and moving eastward.
Canadian High Resolution (HRDPS) forecast for 4 PM Friday (1 hour Precipitation rate and 3 Hour accumulated Rain) (Click on image for a larger view.)
This is a relatively new development, since the previous days model runs had no showers in our area.
A bit of uncertainty for the weekend forecast, as the high pressure system behind the front will move off to our north creating an easterly flow here. Some degree of cloudiness and possibly some afternoon showers are possible as the models have an easterly flow converging with a westerly flow.
NBM surface winds Saturday 3 PM. The wind streams clearly show an area of horizontal wind convergence, forcing air upward causing showers to develop. (Click on image for a larger view.)
The Jersey shore may be most affected by this easterly flow. The uncertainty in the weekend forecast should clarify over the next day. Stay tuned.
Quiet and increasingly hot
Update Tue 08/23 @ 5:40 PM — The balance of the week will be influenced by a very weak upper flow. (The main jet flow is north into Canada.)—
NAEFS statistical “mode” Friday forecast jet stream level contours at 250 mb. Slow, stagnant flow over the US. The little wave in southwestern PA is a weak front. (Click on image for a larger view.)
Increasingly warm and humid through Friday. High temperatures upper 80s Wednesday and low 90s Thursday and Friday. A weak front moves through Friday evening. The long range models show little chance of rain in the coming week.
Update Tue 08/23 @ 5:38 PM — A more zoomed in version of the accumulated rain graphic—
MRMS accumulated rain. Contours are in millimeters. 25.4 = 1 inch. Color code is in inches with legend at the top. (Click on image for a larger view.)
Update Tue 08/23 @ 9:05 AM —Many, but not all areas, received significant rainfall since Sunday afternoon. Here’s the MRMS rainfall totals—
MRMS 48 hour rainfall totals. Contours are rainfall in mm. Color coding is in inches. (Click on image for a larger view.)
Yesterday afternoon’s 19zHRRR did well in predicting the additional rain and thunderstorms that evening.
Additional Showers and Storms Monday Evening
Update Mon 08/22 @ 5:56 PM —This morning’s HIRESW (high resolution models) weren’t all on-board with much additional rain this evening.
However, the 19z HRRR shows some significant rains/thunderstorms popping about 7-8 PM in the immediate PHL area.
19z HRRR showing some heavy showers/thunderstorms 7 PM (Exact location of heaviest rain shouldn’t be taken literally) (Click on image for a larger view.)
Monday showers not a drought-breaker
Previously Posted Mon 10:20 AM —
Additional showers and maybe some thunderstorms during the day today (Monday), but the latest HRRR and RAP shows much of the activity today before 1 PM, with another round this evening.
Much of the remaining rain forecast by this morning’s models will fall to our west, north and south, with only about 0.3″ additional in the immediate PHL area.
Last night’s rain was disappointing, except in some areas (not forecast).
MRMS past 24 hour rainfall accumulation as of 8 AM Monday. Much of the area had much less than forecast. The rain maxima over Chestnut Hill/Germantown was partly from the localized rainfall that went through Sunday afternoon. (Click on image for a larger view.)
Not much of a drought-breaker so far, But we’ll have to see what develops later today and where.
Update Sun 08/21 @ 8:41 PM — We had some break out showers Sunday afternoon that went through Citizen’s Bank Park. These had very limited coverage as they moved northward.
So…Are we really going to get about an inch of rain by Monday evening?
The latest RAP and GFS were in the 0.8- 1.0 inch range.
The NAM-NEST had the heavy rain splitting into two areas: far north of Philadelphia and far south of Philadelphia. The immediate PHL area was just getting about 0.4 inches—
18z NAM-NEST shows the heaviest rain far north and far south. It’s an outlier, but not to be ignored. It’s sorta what I expect during a drought where this sort precipitation miss has occurred several times before in recent months. (Click on image for a larger view.)
I’m going to stick with the current “about 0.75-1.25 inches” forecast.
And I’m going to avoid my usual temptation to update my forecast later with tonight’s models…the rain event is too close and errors from model spin up time may move the forecast in the wrong direction.
Model spin up is the time a model takes to combine initial conditions at the start of the model into a state of thermal and mass-velocity equilibrium.
Due to spin up time, the first few forecast hours of a new model run may be less accurate.
Models are very complex mathematical constructs that incorporate starting conditions and observations, in a process called “initialization”, to accurately simulate and blend (and not conflict) with its past simulation so that it maximally captures ‘reality’ at the start. Short range models can take 3 or more hours to spin-up. The new models being developed by NOAA have a built in ‘cold start’, followed by an intentional 6 hour spin up!
Most current models do not ‘cold start’ but still have a spin up time to ‘mesh’ past runs into equilibrium with new observations. The 00z models from last night all have new upper air measurements that need to blend into equilibrium with the previous run.
Thus, spin up time is needed. If heavy rain is falling in our area at the start of initialization, it can throw off the first few hours of the precipitation forecasts of the new model run until equilibrium is reached.
Am I still skeptical about this amount of rain during a mini-drought? Yes. (Maybe the NAM-NEST shouldn’t be ignored?)
Update Sun 08/21 @ 9:40 AM — The latest ECMWF accumulated rain forecast—
The latest ECMWF rain forecast by end of day Monday. The ECMWF is on the high end of the forecast spectrum. Despite the drought conditions, the ECMWF has been consistent about this expected rainfall. I’m skeptical, but the models are the best tools we have. (Click on image for a larger view.)
The latest HRRR (12z) just available shows the rain (and thunderstorms) moving in after midnight tonight (Sunday). The HRRR is predicting the possibility of some strong thunderstorms about 8 AM Monday morning.
HRRR Simulated Radar with CAPE and Helicity overlay. Boxed areas show elevated helicity and vertical shear with the possibility of strong to severe thunderstorms. (Click on image for a larger view.)
Updated Sun 8/21 9:03 AM —I expect the sun to break out later this morning. Rain waits for the evening hours, most likely after 8 PM. The GFS and NBM still crank out rainfall amounts in the 0.7-1 inch range for much of the area. The HRRR has reduced the rainfall amount to less than 0.5 inches.
Updated Sat 8/20 10:19 PM — Despite several of last night’s models having forecast widely scattered afternoon showers to our immediate north, none were to be found today except in far northeastern Pennsylvania. While writing this update, today’s 18z (2pm EDT) ECMWF became available. (There’s a 7 hour delay for free ECMWF data downloads.) Incredibly, this afternoon’s ECMWF was still forecasting the afternoon showers that never materialized.
Sunday— Periods of sun and periods of clouds. High temp 87.5° sd 1.5°. A few scattered showers as early as 6 PM, but the main area of rain moves in about 10-11 PM.
The models are cranking out anywhere from 0.75” to 1.25” of rain through Monday.
Currently, a rainy day is forecast for Monday with up to one inch of rain forecast. However, we’re in a dry spell that is tough to break. Soil moisture is extremely low resulting in negative feedback. Additionally, we’re in the uptick phase of a well-recognized but little talked about Hale 22 year Solar Cycle that is highly-correlated with drought conditions (but poorly understood). Do a Google Scholar search on “Solar Cycle and drought” for scientific journal articles on this subject.
Update Sat 08/20 @ 9:32 AM — Last night’s models shows a warm front moving up to our north and west later this afternoon. This feature didn’t show on earlier models, but does show on today’s water vapor image.
WV image 9:30 AM with warm front (drawn). (Click on image for a larger view.)
The latest HRRR shows very little activity, but the ECMWF and NBM show light scattered showers possible.
Today’s 12z NBM at 2PM showing light scattered showers. (Click on image for a larger view.)
As for the onset time for showers on Sunday, there’s still a range of model forecasts, but most wait until evening.
Weather pattern transition
Previously Posted Fri 5:25 PM —
The delightful and low humidity weather pattern we’ve been in this past week will change over the weekend.
Increasingly warm and humid air will move in from the south. A disturbance to our southwest this evening (1) will bring some light showers before daybreak Saturday morning, mostly to far western suburbs.
WV image Friday afternoon shows main disturbance moving off Carolina coastline. However, an additional disturbance (1) along the Appalachians may bring some showers before daybreak to far western suburbs Saturday morning. For Sunday into Monday, the upper low (2) will move eastward [hopefully] bringing some much needed rain late Sunday through Monday. (Click on image for a larger view.)
Saturday
Following some very early morning cloudiness, especially far western suburbs, it will become partly to mostly sunny, very hot and more humid than recent days.
High temperature 90.1º ± 1.5º NBM model Blue Bell, PA
Sunday
The disturbance from the west (2 above) will move in. Sunny early, becoming increasingly cloudy in the afternoon. There is still uncertainty with the timing of any light showers, but there’s a strong signal (especially from the ECMWF and NAEFS) that some scattered shower activity may begin in the early afternoon instead of the evening. The majority of the models (and the NBM) hold off the showers until after 7 PM. More humid, but clouds will hold down the high temperatures.
High temperature 85.7º ± 2.4º NBM model Blue Bell, PA
