Tag Archives: NBM Model


Update Sun 12/18 @ 6:08 PM — Updated Winter Storm page.

Update Sun 12/18 @ 9:12 AM — Expect considerable instability cloudiness, similar to Saturday, to move in from the west about 11 AM – noon today. Also updated this week’s Winter Storm page.

NOAA and the NWS has just released the preview version (called the parallel run) of the new NBM model (version 4.1) this past Thursday, and major improvements in precipitation type forecasts suggests that I lean heavily on this new NBM model for the storm’s precipitation type forecast.

From National Weather Service /NOAA—

Improvements in NBM Model 4.1 – inclusion of additional Australian Global and Canadian models and NOAA’S new HIRESW-FV3

“Improvements in winter weather guidance for snow, ice, freezing rain, and unconditional precipitation type through the increase in [ensemble] membership (18 to 100 members) and leveraging direct model precipitation type guidance averaging direct model precipitation type guidance.”

“Usage of high-quality Quantitative Precipitation Estimates (QPE) observational and long sampled climatological data sets (e.g., the Multi Radar/Multi Sensor System (MRMS) and Multi-Source Weighted-Ensemble Precipitation (MSWEP) for calibrating probabilistic quantitative precipitation forecasts”

Update Sat 12/17 @ 5:30 PM — We did have the cloudiness today. Sunday will likely be similar to Saturday regarding clouds, possibly even cloudier in the afternoon. Colder. Forecast below still holds.

Update Sat 12/17 @ 5:33 PM Winter Storm page updated for storm expected Thursday to Saturday.

Update Sat 12/17 @ 10:31 AM — Last night’s models are less emphatic about cloudiness this afternoon.

Update Fri 12/16 @ 5:51 PM — Updated Saturday and Sunday forecast below to reflect new model forecasts. Changes are highlighted.

Our weather this weekend will be influenced by a slow moving upper air low and a slowly departing surface low that gave us the rainy weather Thursday into Friday. High pressure will be building in, but disturbances rotating around the upper low will cause windy conditions and some occasional cloudiness.

Water Vapor image shows upper air configuration—

Water Vapor Image Friday morning shows the upper low approaching the Great Lakes area. The arrows depict the general location of the jet stream. (Click on image for a larger view.)

Friday’s GFS forecast for Saturday—

Friday’s 12z GFS forecast for Saturday at 5 PM. The upper low hasn’t moved that much eastward and the surface low is still off the coast of Maine. Cold high pressure will be sinking southward into Missouri. The circulation around the upper low will continue to affect us. (Click on image for a larger view.)

A colder pattern is setting up for the weekend and the coming week with cold high pressure pushing the jet stream to the south of us.

I’m keeping my eye on significant coastal storm that is forecast to form in the late Thursday through early Saturday time frame. The impulse expected to trigger this storm is way off in the Pacific right now and it’s too soon to consider it a reality.

At the same time, this is the first time in a long while where a white Christmas here is a distinct possibility. It currently looks to be a rain–> snow storm for us. Stay tuned.

Previously Posted Fri 12:07 PM —


Mostly sunny in the morning, considerable instability cloudiness in the afternoon, especially west of the city. Windy/breezy and cold. Wind chills in the low 30s.

High temperature 40.1º sd 1.8º NBM model – for location Blue Bell, PA


Sunny and cold. A period cloudiness in the early afternoon. Still breezy. Wind chills in the 20s!

High temperature 37.0º sd 1.8º NBM model – for location Blue Bell, PA


One reader wanted to know how to get the latest hourly probability of precipitation for our area.

One of the best ways is a direct link to the NBM (Model Blend) text output. The NBM is considered the best model for rain probability and the model data from this link is updated every few hours.  (Yes, the NBM model is updated every hour, but to get the absolute latest, you’d have to dive into the bowels of the NOAA NOMADS server.)

I’ve pre-configured the URL for you to provide the model output for Philadelphia Airport, Wings Field Blue Bell, and Northeast Philadelphia airport—


The one you want to focus on is the NBH ( H= hourly).

It provides hourly probability (P01) in percentage (on an hourly basis, anything greater than 18% and increasing is meaningful) and the amount (Q01) in hundredths of an inch. 

It’s important to know, that with accumulated rainfall, the number refers to amount having accumulated in the preceding hour.

The tricky part is converting to the UTC time to Eastern Standard or Eastern Daylight time. 

The example below is for KLOM, Wings Field, Blue Bell.

So in the example below, this is the NBM model run is from 0700 UTC (3 AM EDT).  The first row (labeled UTC)  are the forecast hours and the column labeled “14” is the UTC TIME forecast time. So  14UTC = 10 AM EDT (or 9 AM EST).

Looking down the 1 hour probability (P01) is 48% and the quantity of rain fallen in the preceding hour (Q01) is 2.   2= 0.02″

Beware that for some of the other data displayed, especially in the NBE, the meaning can less less than intuitive.  In the NBE, the column labeled, as an example,  00 day FRI, refers to the 12 hours PRIOR to 00z Friday which means daytime THURSDAY!