City #2: Cheyenne, WY (KCYS)

With the barely predictable convective rainfall, aren't you happy to be done with forecasting for Houston, TX? I know I am. We are now forecasting for Cheyenne, WY (KCYS) from 14 October - 24 October for the 24-hour period 06 UTC - 06 UTC which translates to 12 AM local Cheyenne time (MDT) if you are looking at NWS Cheyenne forecast products. Forecasts need to be submitted by 00 UTC which is 8 PM local Long Island time (EDT).

Time to stalk the airport! Cheyenne, WY is located near the southeast corner of the state of Wyoming just east of the Laramie Mountains. KCYS is Cheyenne Airport with a WMO ID of 72564. There is very flat terrain south, east and north of the station which may allow for unimpeded advection of heat and moisture with strong systems from winds from those directions. Something to keep in mind!


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Large-scale Pattern: 

I think that forecasting for Cheyenne will prove challenging given the general troughiness in place that may allow for a few disturbances to develop along shortwaves that may develop. A look at forecast 500-hPa heights according to the GFS ensemble shows that the general trend in heights seems to be highly amplified early in the forecasting period (the first week) and returning in a more zonal structure for the second week. With a mean trough set up over the Rockies, a resultant continental cyclone will likely be the main player early on. To see if I'm right, check out what WPC is calling for. The position of Cheyenne relative to the cyclone will affect both temperatures and precipitation amount and the strong pressure gradient will definitely affect wind speeds. Take a look at the 1000-500 mb thickness values and pay special attention to that 540 dam line as a good indication of a rain/snow line. Keep in mind that for the WxChallenge precipitation forecast, it is liquid equivalent in inches! Models all output as such but don't look at any info-graphics calling for Cheyenne to get 3 feet and then put 36 inches; I will laugh at you because you have been properly warned. 

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 Cheyenne.
• Look at forecast model soundings for the period for KCYS.
• How are the models evolving in time? Check out d(model)/dt plots like this one that focuses on the GFS.
• 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 Cheyenne WFO forecast discussion for KCYS. These are the experts for that location, after all!

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.
• Given quiet synoptic players, the evening dew point can act as a rough guess for the nighttime low (some forecasters use this as a first guess when they think the model output statistics (MOS) is bonkers). Therefore the wind direction may be a good indicator of humidity which may affect the nighttime temperatures.
• i.e. southeasterly winds should be more moist which means a higher dew point which means a higher nighttime temperature and northwesterly winds will advect drier air which means a lower dew point which means the possibility for lower nighttime temperatures.

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. For example, westerlies may allow for downslope warming of air towards Cheyenne. 

Tips/Comments for Forecasting Precipitation (inches):

• Take a look at some higher-resolution models (e.g. WRF)
• What does the WPC show? 
• Tropical activity?!? (Part of me wants there to be while another part of me doesn't at all.) 
• Take a look at some GFS model-derived standardized anomalies of precipitable water (PWAT) to get a handle on any significant movement of the forecast of dry air or very moist air.
• Take a look at some ensemble data (e.g. SREF (South Central option) or for a zoomed-in national look try here.)
• Most products you will be looking at will output the QPF in inches already so no conversion is necessary.

Be sure to check out a previous post found here for a long list of great resources that you should check out! Most of them are also found on Dr. Colle's Coastal Meteorology and Atmospheric Prediction (COMAP) group's website.

Alright guys- let's not let CYS make rodeo clowns out of us! If you ever have any questions please feel free to stop by my office in Challenger 121. I have candy. That is all. Good luck with KCYS and let's go Team SBU!!!