Weather Blog

We say C-YA to NGM MOS

We say C-YA to NGM MOS

A passing of the torch, per se, is under way today in the weather community as we retire a long-time computer tool for forecasting the weather.

The "NGM MOS" made its last forecast Monday evening, and NOAA has turned the switch off.  Not to worry, we have newer computer models that take the reigns now.

MOS stands for "Model Output Statistics" -- it's basically the computer model looking at its own computations of future weather, and then knowing what it knows about how those atmospheric conditions translate to the actual weather for a certain location, puts out an auto generated forecast for a specific location.

What I have in the image above was its last forecast for Seattle.  You can see the Day at the top, then Hour, is the forecast hour in UTC (the old GMT/Greenwich Mean Time).  As of today, that is 8 hours ahead of PST, but it'll be 7 hours ahead next week as we go onto PDT Sunday morning. 

The "MX/MN" is its forecasted high and low for the period. In this case, it's saying the forecasted high for March 3 is 52 degrees. (Note it says it under 00 Mar 4, which is midnight GMT time on the 4th, but is actually 4pm on March 3rd on Pacific Time. The good rule of thumb is 00 time is the afternoon and 12 is the morning (4 or 5 a.m.)

So taking this further, it has a high of 52 on Tuesday, a low of 40 Tuesday night/Wed. morning and a high of 49 for Wednesday afternoon.

The TEMP field is the expected temperature at each three hour period. DEWPT is the expected dew point.  CLDS is cloud cover -- BK is "Broken layer" or mostly cloudy. OV is overcast. SC is "scattered" or partly cloudy, and I believe CL is sunny/clear.

WDIR is wind direction (Multiply by 10 for compass direction), so 02 is an 020 wind or northeast wind. 21 is 210 or southwest wind.. WSPD -- wind speed in knots. (MOS's tend to well underestimate the wind in larger wind events).

POP06 is probability of precipitation in the 6 hour period -- a 48% chance of rain at 12 UTC, a 63% chance at 18 UTC, etc.  POP 12 is the overall precipitation chance over 12 hours. So as you can see, we have a decent chance of getting measurable rain at some point this afternoon (77%).

QPF is a rain intensity measure, on a scale of 0-6 plus 9. (What?!?  yes, they skip 7 and 8).  For instance, 1 means 0.01-0.09" of rain. 3 is 0.25" to 0.49", it goes up to 5, which is greater than 1", but they reserve '6' and '9' for when short term forecast is unavailable but heavy rain over 1.00" ('6' rating) or 2.00" ('9') is expected in a 12 hour period. (If you see a '7' or '8' there, I guess the computer might be signalling for help or playing a practical joke :) )

TSV06/TSV12 is probability of thunderstorms, with chance of severe thunderstorm to the right of the /, but it's a conditional chance. Thus, if you see 3/15 that means there's a 3% chance of a thunderstorm occurring in the 6/12 hour interval, and of that 3%, if one of those thunderstorms occurs, there's a 15% chance it'll be severe. In other words, not very likely.

PTYPE is precipitation type: R is Rain, Z is freezing (Freezing rain or ice pellets), and S is Snow.

POSN is possibility if you do get precipitation, it will be snow. The SNOW category below it means how much snow on a scale of 0-5 -- 0 meaning none, 1 meaning Tr-2", 2 means 2+" within 6 hours, 3 means 2-4" in 12 hours, 4 means 4-6" in 12 hours, 5 means 6"+.

The CIG and VIS are scales of ceiling heights ands visibilities. And OBVIS means anything that might obstruct visibility, such as fog (F) or haze (H) or nothing (N)

You can get more details at The University of Wisconsin Meteorology Site

Are There Others?

So, Scott, if they retired the darn thing, why are you telling us all of this?

Because there are others out there :)

The GFS MOS is the same product, only a newer computer model. There's also the NAM MOS.

Then, there's the GFS Extended MOS which runs out 7 days. The only caveat here is these models tend to drift toward the period's normal temperature in the 5-7 day forecast time frame (that's the number under "CLIMO"). So the fact that it says a high of 45 for Tuesday, March 10 (as of this writing) seems in indicate we are going into another extended cool period as it is forecasting well below normal temperatures even 5-7 days out and with an inherent bias toward warming it up.

But I don't live in Seattle!

No problem. Here are some links to find other cities' MOS's:

Washington:

Washington GFS Extended MOS List

GFS Short Term MOS

NAM Short Term MOS

Oregon:

Oregon GFS Extended MOS List

GFS Short Term MOS

NAM Short Term MOS

So long NGM, you were a good helper :)