When planning a flight in marginal visual flight conditions, one thing we helicopter pilots realize is that the only weather reports we get in a briefing are Aviation Routine Weather Reports (METARs) and Terminal Area Forecasts (TAFs) from airports, or Area Forecasts (FA) and Weather Synopses covering larger areas. We then have to visualize the ceilings and visibilities between those ground reporting stations. If we are going to or launching from an off-airport site, that complicates our decision-making. While Weather Depiction graphics can help, another great tool in our flight planning toolbox is the Helicopter Emergency Medical Services (HEMS) Tool from the National Weather Service.
You don’t need to be a Helicopter Air Ambulance (HAA) pilot to use or appreciate this tool. Besides being able to show METARs, TAFs, and other weather information that can be found easily in other products, HEMS Tool displays “high resolution grids of critical weather parameters, particularly cloud ceiling and surface visibility.”1 In other words, this tool allows us to see a computer guesstimate of the ceiling and visibility between reporting stations.
In this screenshot, we have HEMS Tool set to display the flight categories derived from each METAR at all reporting airports in view, which ranges from Visual Flight Rules (VFR, indicated by a green circle), Marginal VFR (MVFR, indicated by a blue circle), Instrument Flight Rules (IFR, indicated by a red circle), and Low IFR (LIFR, indicated by a pink circle). HEMS Tool defines these conditions with the following key:
That’s all good and well, but what we are concerned with are the conditions between these reporting airports. That’s where the Flight Category weather layer is especially useful. See the pink, dark pink, yellow, and blue areas on the screenshot? Those areas represent ceilings and/or visibilities ranging from MVFR (1,000’-3,000’ ceilings or 3-5sm visibility) down to obscure (terrain obscured by the ceiling/visibility).
In the above example, if you had to fly from Chillicothe, Ohio to Muncie, Indiana, you’d start in clear, VFR weather for a few miles and then hit IFR and LIFR weather for the rest of the trip, assuming the computer model is accurate. Of course, it can’t know exactly at what latitude and longitude the weather changes categories, but it can give us a good estimate and visual representation on conditions in the pre-flight planning phase of our operations. Additionally, to non-pilots this tool can be used to more simply show why the pilot-in-command may choose to make a go or no-go decision for a flight and reduce complicated explanation.
Another great visual from this tool is the Icing Probability weather layer.
The light blue to orange shaded areas represent an icing probability from 5% to >75% for the selected altitude, which I have set in this screenshot as 1,000’ AGL. While you can usually figure out this risk with just the raw data, the overlay makes it a visually simple process.
HEMS Tool is one of just many sources of information we can use in flight planning, and the two features we’ve discussed are what really make it shine. It is so useful, that my normal flight planning routine is to review the weather as displayed on ForeFlight, followed by a review of HEMS Tool, and then a final logged briefing from CSRA Direct User Access Terminal (DUATs) with the additional focus of getting all Notices to Airmen (NOTAMs) for the flight.
Proper Preflight Prevents Poor Piloting,
Note: This is the last article for January 2017’s push for multiple articles per week. Now we will shift to one article and one quiz published per week, with exceptions for content we don’t want to sit on. Coming up in February we’ll discuss known icing conditions, long-standing NOTAMs, a look at being a 141 instructor, inadvertent encounters with Instrument Meteorological Conditions (IMC), and provide quizzes for Robinson R22 and R44 series helicopters, as well as helicopter basic and advanced aerodynamics.
- Aviation Weather Center. HEMS Tool Help. [Web Page]. Retrieved January 29, 2017 from https://www.aviationweather.gov/hemst/help