Monday, October 22, 2012

City #3: Louisville, KY (KSDF)

I don't know about you, but I couldn't be happier to be moving on from forecasting for KBIL. The USL model, NAM and NWS forecasts had the least errors for KBIL but still rarely verified within 1 degree for temperature or 1 kt for wind. I guess it's just another example that forecasting for a point with discrete values is exhausting. Oh well, we all must soldier on! Let's travel southeast to KSDF!

Louisville, Kentucky is located in north-central Kentucky near the Kentucky-Indiana border which is the Ohio River. We are forecasting for KSDF or Strandiford Field, KY aka Louisville International Airport (NOT KLOU or Bowman Field!) found in the map below. The station ID is 72423. The city is located in a flood plain of the Ohio River with slightly higher terrain around, especially to the east but still less than 1,000 ft AMSL. I think that forecasting for this area will be determined by local radiative forcing for high and low temperatures and advection of warmer air from the south, cooler air from the north and storms from the west. But, we shall see.



View Larger Map

We are forecasting for KSDF from 22 October - 1 November for the 24-h period from 06 UTC - 06 UTC. 06 UTC is 2 AM EDT or local time. We are finally forecasting for our own time zone! The local NWS WFO is located conveniently in Louisville. I really, really like their formatting of their area forecast discussion so I think you will too. 

*PSA (Public Service Announcement): The local 88-D is getting an upgrade so for radar data, you'll have to check out the mosaic or surrounding radars (more information).*

Just to briefly say what the climate normals are-- high temps are usually in the upper 60's and low temps are usually in the upper 40's in late October. However, I don't want to harp on climate normals too much because it looks like we will be dealing with an amplified and slightly anomalous pattern early on. 

Large-scale Pattern:

Holy ridge, Batman! A look at forecast 500-hPa heights according to the GFS shows that the ridge looks to build for almost the entirety of this week. There may be a shortwave embedded in the flow that may provide some lift but with the question of moisture availability, I doubt there will be measurable precip until the ridge moves out and the trough brings a system on Friday. After that system, the GFS is showing troughiness (yes that's a word... now) in the Louisville region and then more zonal flow.


What to watch out for (IMO):

  • Cloud cover affecting daytime highs and nighttime lows.
  • Large diurnal swings in temperature especially with anomalous heights over the region- don't be afraid if you have a couple more degrees added to your temperature range than you are comfortable with.
  • Moisture availability with weak forcing.
  • Wind direction should be very important for the advection of warm, moist air from the south and cooler, dry air from the north. Pretty standard but still pay attention.

 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 Louisville.
  • Look at forecast model soundings for the period for KSDF.
  • 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 Louisville, KY WFO forecast discussion for KSDF.

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. 
  • 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 or try to spot it on the regional radar and know whether to take it into consideration for certain days with weak synoptic flow.
Tips/Comments for Forecasting Precipitation (inches):
  • Take a look at some higher-resolution models (e.g. WRF)
  • What does the HPC show?
  • Take a look at some ensemble data (e.g. SREF)
  • Most products you will be looking at will output the QPF in inches already so no conversion is necessary.
  • KSDF will likely be a target for convection along cold fronts that move through after warm, moist air was advected from the south out ahead of the system. At least that's what one would expect if the ridging pattern we are starting with should ever break!
Alright guys- grab your fried chicken and get to forecasting! Hopefully Louisville is a little bit better to forecast for than Billings was. If you have any questions or want to discuss anything, feel free to comment on this post. Best of luck forecasting! Go SBU!

Monday, October 8, 2012

City #2: Billings, MT (KBIL)

We are done forecasting for Pensacola and now must divert our attention roughly 2,000 miles northwest to Billings, MT. Has anyone ever been to Yellowstone? If so- I'm jealous. We will be forecasting for this city from October 8-18. Forecasts are still due by 00 UTC or 8 PM local time. We are forecasting for the 24-h period 06-06 UTC which is 12 AM - 12 AM local time (MDT) for those looking at the Billings NWS WFO page.

Alright, time to stalk the airport and surrounding area. The airport and city lies in the Yellowstone Valley at an elevation of roughly 1000 m AMSL. Surrounding the city are clusters of 100-500 m high hills with the closest being to the north and southeast.



View Larger Map

So we have some terrain slight that may influence our forecasts. Mental note made.

Now just to get an idea of what to expect, time to look at some monthly climate data. Remember, this is just to get a crude idea about what is the average daily temperature range but there are always exceptions.

Month     Daily Max     Daily Min
Sep             73.1                  47.5

Oct             59.4                  37.1 


Now to move onto what's going on weather-wise.

Large-scale Pattern:

A look at forecast 500-hPa heights according to the GFS shows a persistent  trough over the region. Looking at some model output for other mass fields shows that weak surface fronts (cold fronts) may provide forcing for ascent in the near-term for some rain showers and even snow showers. Pay attention to the wind direction as the northerlies may usher in cold, Canadian air.

What to watch out for (IMO):

  • Shortwaves traveling along the mean trough that can provide forcing for precipitation.
  • Weak fronts if the models pick up on them which would impact temperatures.
  • Wind direction should be very important given the topography, mainly westerly or zonal winds should result in warmer, drier conditions.

 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 Billings.
  • Look at forecast model soundings for the period for KBIL.
  • 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 Billings, MT WFO forecast discussion for KBIL.

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. 
  • Frontal passages can affect your temperature forecast. Pay attention to the forecast timing of such frontal passages.
  • With KBIL, terrain may be an issue. If the winds are downslope or likely westerly and northerwesterly given the location of the airport, then there may be some subsidence warming. Recall that as air falls adiabatically, it warms.
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 or try to spot it on the Billings, MT radar.
Tips/Comments for Forecasting Precipitation (inches):
  • Snow?! Looks like it at KBIL! We forecast for the liquid equivalent of precipitation, or exactly what the models output in inches. So if there is a forecast for 6 inches of snow, do not put "6.00" or you will be filled with regret and sadness.
  • Take a look at some higher-resolution models (e.g. WRF)
  • What does the HPC show?
  • Take a look at some ensemble data (e.g. SREF)
  • Most products you will be looking at will output the QPF in inches already so no conversion is necessary.
What if I'm afraid I'll miss a forecast?
  •  When making a forecast for the first day only, always select the "Guidance" option for the "Optional Forecast for Future Days" days just in case you forget.
  • It is advisable that you enter your forecast for the next couple of days when you enter your Day 1 forecast. They are not counted towards any score and it is just a good way to possibly save your score if you happen to forget to forecast the next day. However, you realistically likely only have enough time to forecast for the first 24-hour period so I always just select "Guidance" anyway.
If you have any questions, comments please feel free to comment on this post! Best of luck with forecasting for Billings! Go SBU!!!