City #10: Des Moines, IA (KDSM)! *Final Official Forecast City of the Year!*

I hope you all enjoyed your spring break even though you didn't get a break from forecasting! We are done with Duluth and move south to Des Moines, IA (KDSM). We will be forecasting for the 24-hour period from 06-06 UTC from 25 March - 4 April. Forecasts are due by 00 UTC which is 8 PM local time. 06 UTC corresponds with 1 AM CDT if you are looking at the NWS Des Moines, IA page.

Des Moines is geographically plain in my opinion, mainly due to the fact that it is flat and land-locked and part of the Great Plains. The main atmospheric drivers will be synoptic systems and diurnal patterns. So given that, it should be a straight-forward city to forecast for.

Taking the time to stalk the airport, we see that KDSM is located in central Iowa at the intersections of I-35 and I-80. There's no real significant topographic or water bodies nearby. The airport is located southwest of the city center with suburban areas to its east and a lot of farm fields to its west-southwest. If it was more Springy (yes, that's a word) then I'd expect humidity to be higher when winds blow over the fields due to evapotranspiration but I'm pretty sure the season isn't in full bloom yet.



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Large-scale Pattern:
 
A look at forecast 500-hPa heights according to the GFS shows general troughing in the East for the first week of forecasting with general ridging in the Central and Western US. A few shortwaves move up and over the ridge and slide down the trough which may provide some forcing for weak precipitation or general cloudiness for a couple days. No real systems seem to be affecting KDSM for the first week of forecasting. In fact, a cutoff low off of the West Coast seems to amplify the ridge lee of the Rockies so there may be springlike conditions felt in KDSM by the end of the week.
Tips/Comments for Des Moines (KDSM):

• Look at more than one deterministic model, especially side-by-side comparisons, toggling between models (Mode: Clickable Map), or even better- ensembles (SREF/GEFS Plumes, SREF Maps, GEFS Maps).
• WxChallenge's wind forecast is for sustained, not gusts. Instead of just looking at plan-view maps at or near the surface, try taking a look at forecast soundings. The measured wind speed is a 2-minute average. Gusts often occur because with heavy precip, higher momentum air can be brought down to the surface, i.e. winds reach the surface via more than just mixing, but unless they persist for about 2-minutes they won't verify. 
• Really read the NWS Area Forecast Discussion (AFD). Those forecasters are experts in the intricacies of forecasting for Des Moines.

 Tips/Comments for Forecasting in General:

• Check out the current weather first via satellite, radar, surface observations, METAR, etc. You have to understand the present before you can look to the future.
• Get a feel for general pattern from NAM, GFS, etc. (available from here and here, for example). Identify the general pattern of low and high surface pressure systems and their progression, temperature advection at 850 mb, moisture at 700 mb, vorticity at 500 mb and the general jet structure at 300 mb. Make sure you are focusing your attention on Des Moines.
• Look at forecast model soundings for the period for KDSM.
• Compare your idea for values with MOS (model output statistics).  Keep in mind these are instantaneous output values and you can always have values above/below that between output times. 
• Read the Des Moines, IA WFO forecast discussion for KDSM.

Tips/Comments for Forecasting for High/Low temperature (Fahrenheit):

• Recall such basics as nighttime radiative cooling and daytime solar radiative heating, both of which are affected by cloud cover and fog.
• Frontal passages can affect your temperature forecast. Pay attention to the forecast timing of such frontal passages. 

Tips/Comments for Forecasting Wind Speed (knots):

• NWS outputs wind speed in mph so if you are comparing your forecast value to theirs keep that in mind. Otherwise the models output wind speed (WSP) in knots.
• Look through METAR or surface obs for wind direction and temperature changes.

 
Tips/Comments for Forecasting Precipitation (inches):

• Take a look at some higher-resolution models (e.g. WRF)
• What does the WPC (formerly known as HPC) show?
• Take a look at some ensemble data (e.g. SREF (if no local option then try SPC's SREF page))
• Most products you will be looking at will output the QPF in inches already so no conversion is necessary.

I don't know much about Des Moines  except for what's talked about during election time, but hopefully that won't be a hindering ability to forecast for KDSM. This is the last WxChallenge city before the tournament begins which only counts for those who qualify but everyone is invited to participate, so let's go out with a bang this year! Go Team SBU!!