Tag Archives: HIRESW Model


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—

Last night’s HIRESW-ARW-MEM2 forecast for 2PM Sunday. (Click on image for a larger view.)


Here’s the current radar at 1:39 PM—

NEXRAD radar 1:39 PM Sunday. Courtesy of weathertap.com (Click on image for a larger view.)

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.

NAM NEST Vertical Velocity 700 mb (10,000 feet) at 3 PM  (Black= maxima)  (Click on image for a larger view.)

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.


My regular forecast followers may have noticed that I’m spending more time using  some new, high resolution models for these forecasts— these models are referred to as HIRESW  (High RESolution Window) models.  The models are run by NOAA/NCEP. I’ve been really impressed with these models;  I have only recently gotten access to them.

These models were developed through open-source university development of the WRF (Weather Research Forecast) Model around 2002 and later enhanced and further developed.  (In fact, the old ETA model starting using the WRF physics packages about 2005; subsequently, the ETA then became known as the NAM.  

–> There are two major forks and development paths of the HIRESW models, an ARW (Advanced Research Weather version) and an NMM version (a Non-hydrostatic Mesoscale Model version). 

The ARW and NMM versions use different “physics packages” and different “initializations”.     (There are different sets of equations  or “packages” used in each that make different assumptions and approximations about the atmosphere.  These equation packages are used to predict things such as rain, clouds etc..  The “packages” are referred to by the name of the researcher who developed these advanced, applied equations.)

It’s complicated, but in a loose way,  the HIRESEW-ARW  version is closer to the physics of the GFS model and the HIRESW-NMM version is closer to the physics of the NAM model. 

In recent years, there have been further improvements in both versions (ARW, NMM) of these HIRESW models.   These improvement included increases in resolution, (now 3 kilometers).

More interestingly, new statistical versions have been developed for each model — groups (“ensembles”) of models with intentionally introduced known errors called “perturbations. These allow forecasters to see how known errors statistically affect the computed forecast outcomes.

Out of these ensembles, it emerged that two perturbed versions (called “members”) of each seemed to offer improved forecasts:

  • HIRESW-ARW-MEM2   (MEM 2 refers to member two)
  • HIRESW-NMMB2      (B2  refers to grid B, member two)

Both of these versions are run twice a day at 8 AM and 8 PM EDT., for the continental US by the National Center for Environmental Prediction (NCEP-NOAA).  These high resolution models forecast up to 48 hours out in time.

The forecast output of these models becomes available between 10:25 AM/PM  EDT for the first 24 hour forecast and about 10:58 AM/PM EDT for the next 24 hour forecast.) 

That’s why I’ve been holding back posting my forecasts until after 11 PM in recent days.  (The model data available at 11 PM  Friday forecasts out to 8 PM Sunday. )

Sincere there remain differences in the forecasts of both version’s ensembles, you’d think there would be a model that combines them.  There is.  It’s called the HIREF.  I haven’t found it very useful to date.

The latest development for the HIRESW models still in experimental stages, is use of a new grid arrangement, the FV3 geometry, that is being used for the latest GFS model released in May 2019.