Fri 11:37 AM Forecast Review — While I hadn’t covered Thursday evening’s rain in depth, the new HIRESW (specifically, it was the new “HIRESW-ARW-MEM2”) did nice job in predicting Thursday’s evenings rain 24 hours in advance. Last year, I thought the HIRESW did very well with thunderstorm prediction. NOAA is making the newest version of the HIRESW model “operational” this coming May 11th 2021.
The HIRESW “High RESolution Window is a relatively new model that is being actively developed by NOAA. There are actually several versions. Beginning May 11th, these new models will become operational: the HIRESW, the HIRESW-ARW-MEM2 and the HIRESW-FV3.
The HIRESW forecasts out to 48 hours. The new HIRESW-FV3 forecasts out to 60 hours. The are run twice a day.
Additionally, there will be a new, updated statistical “ensemble” version, the HREF (HIgh Resolution Ensemble Forecast model). The HREF is a model based on statistical averages/means of several different models, the RAP, HRRR, and the HIRESW versions combined with some time-lagged versions to even out model run variances. The HREF is run 4x daily
Update Wed 10:08 PM – The weak cold front never made it south this evening. Nor did any thunderstorms. Thursday’s high will likely be near 80°. Currently, the main cold front will move through late Thursday. Most models are keeping the main storm activity to our north and through central Pennsylvania on Thursday. However, tonight’s HIRESW-ARW shows some thunderstorm activity mid morning and again about 5pm Thursday in our area.
While this is primarily a “weekend weather” site, looking at the weather models is my daily crossword puzzle.
I couldn’t help but notice that there’s been a major shift in the model forecast over this past day and some of the TV media forecasts have not updated their forecasts.
Originally, Wednesday and Thursday were to be very warm days, with many of the on-air forecasts talking about record high temperatures, especially Thursday.
The models forecasts have shifted this afternoon – a cold front will slide down during the day Wednesday, a day earlier than previously expected. Showers and thunderstorms will break out, especially Wednesday evening. The models have most of the energy to our north and to our south, so right now, any thunderstorms are not expected to be severe in the immediate PHL area.
High temperatures in the 80’s Wednesday may not make it out of the low 70’s on Thursday (a huge change in the forecast). (The latest GFS model has high temperatures in the 60s Thursday!)
The front may get hung up just south of our area, causing showers on Thursday.
We now return you to your regularly scheduled programming…
Last night’s HIRESW-ARW-MEM2 came through, accurately forecasting the showers that moved through around 12 – 2 PM.
Here’s last night’s HIRESW—
Here’s the current radar at 1:39 PM—
That’s about as good as model forecasts get.
There’s been uncertainty regarding the shower/thundershower potential on Sunday. High humidity, heat and instability suggests that some showers and thundershowers are likely during the day.
Tonight’s models just becoming available have the greatest dynamics just south of Philadelphia and the majority of the models keep the showers just south of our area.
The exception is the HIRESW-MEM2, which continues to forecast showers and thundershowers further north into our immediate PHL area, from 11 AM through 3 PM. As someone who looks at the models as my daily crossword puzzle(s), the HIRESW-MEM2 has been particularly impressive this summer in predicting these sort of convective storms. So, I’m betting on its forecast for Sunday.
The models have more consensus about another period of showers/thundershowers around 10 PM Sunday evening, as another wave moves through.
[su_note note_color=”#bceaed”]Forecast Review— The HIRESW models did the best with this forecast. The 11 AM -1 PM timeframe was very close. The RAP model picked up the early morning showers. The NAM and NAM NEST over-predicted the second line of showers during the afternoon.[/su_note]
Last night’s early models showed considerable spread with the timing of thunderstorms and showers today. I’ve had more time to look at those models as well as subsequent newer model runs from 2 AM (“06 Z model runs”).
So what’s happening?
The surface front moves through between 11 AM and 1 PM today with showers and thunderstorms as previously forecast. Prior to this time, expect windy and gusty conditions and possibly some scattered showers ahead of the front.
However, at the upper/mid levels of the atmosphere, additional disturbances (areas of “vorticity and vertical motion”) continue to move through in the upper level flow during the afternoon.
The actual upper air trough moves through slowly with these areas of vorticity triggering showers. Additional scattered showers and thunderstorms are possible during the afternoon until the upper air trough moves through. The NAM NEST shows this activity may be most enhanced at 2-4 PM.