In the early part of your training, your questions about weather start with “Will I be able to have my lesson today/tomorrow?”. Your instructor will answer that question for you initially, but you should quickly be able to make a good guess yourself. You have lots of tools available to help answer that question.
For the local weather in the very near future, just looking or walking outside may be enough. Is the visibility poor? Are the clouds low? Is the wind strong and gusty? If so, then it may not be a good day for VFR flying, especially early in your training.
Look at METARs, listen to ATIS/AWOS/ASOS
You may not have enough experience to tell how low clouds are or how good the visibility is, or how strong the winds are, but for many airports (including El Monte), help is at hand in the form of official weather observations.
At El Monte, you are exposed to the ATIS on your first lesson. You can call 626-444-1107 and listen to the current ATIS. Much of the information from the ATIS is also available through a METAR. Go to http://aviationweather.gov/adds/metars/ , put in the airport identifier (KEMT) and click “Submit”. There, in a compact format, is the latest weather. Want to get a version that will help you understand the cryptic format, then click “Translated” before you submit (you do have to learn to read the cryptic version). There are a few caveats through:
- As of July 2013, at EMT, METARs are only pubished when the tower is open, 800-2000 local.
- There’s a delay between the controllers entering the information and it being available online (so check the time the METAR was issued).
- This is only the weather information, so sometimes you’ll miss IMPORTANT information that would be in the Remarks portion of the ATIS. One good example – I made the mistake of just checking the METAR before going to the airport. I arrived to find the weather was fine, but the runway was closed by an airplane that sat damaged on the runway for hours.
ASOS and AWOS are automated weather reporting systems that can provide some of the same information as an ATIS. Just remember that automated systems can make mistakes that no human would make. Some systems will report “sky clear” when there is just a hole in the clouds overhead.
So, you have the weather information, but what do you do with it? Well, you need to know what conditions are acceptable for your level of experience and the type of flying you plan to do.
For the first few lessons, I prefer the cloud ceiling to be at least 3500′ AGL (Above Ground Level). For later pattern work lessons, as low as 1500′ AGL may be acceptable. Cloud levels in METARs and the ATIS are reported as AGL, rather than MSL (Mean above Sea Level). Clouds are reported from the lowest layer to the highest layer. Each layer is assigned a coverage of Few (0-2/8), Scattered (3/8-4/8), Broken (5/8-7/8), or Overcast (8/8), The ceiling is the lowest level of clouds reported as Broken or Overcast. Clouds that are lower, but only Few or Scattered may still be a problem. Also, the clouds at the airport may not reflect what is happening nearby, so don’t forget to look.
In almost every case, we will need 3 sm of visibility to fly in the pattern (and better than that early on). To leave the pattern, I prefer we have at least 5sm of visibility. Visibility is not always the same in every direction from the airport, so there can be cases where the reported visibility is not sufficient information to make the call.
Winds can cause problems both while flying in the practice area and while flying in the pattern. Strong winds are often associated with turbulence; you’ll have to determine whether the level of turbulence is acceptable. Winds during takeoff and landing can be helpful or make it too much of a challenge. Generally, if winds are light (5 kts or less), we’ll be fine. Stronger winds become a problem when they are either very gusty or if they have a significant cross-wind component. Winds right down the runway (190 for RW19) have no crosswind component. Winds perpendicular to the runway (100 or 280 for RW19) are all crosswind. An easy rule for estimating cross-wind component is that you get an extra 1/6 of the wind velocity for each 10 degrees off the runway. If the winds are 12kts and we’re using runway 19, winds from 200 would be 2kts of crosswind and winds from 250 would be 12kts (all) cross-wind (210=>4kts, 220=>6 kts, 230=>8 kts, 140=>10kts). Early in the process of learning to land, crosswinds of even 5 knots may be too much. Later in your training, it’s good to get experience in stronger crosswinds. Crosswinds greater than 15kts can exceed the capability of most pilots in a 172.
Looking at other factors besides airport weather
Looking at weather may be sufficient to tell you that you can’t (or don’t want to) fly. However, there are other factors that may not show up in the METARs which will keep you from flying. Remember that the METAR only give you information at one point in time right at the airport. If you depart the airport pattern, there may be different conditions and weather can change significantly in less than an hour.
Other factors to consider that may impact flying are TFRs (Temporary Flight Restrictions).
Seeing into the future
You’d also like to be able to plan ahead as to whether you’ll be able to fly later in the day or even tomorrow. There are many types of forecasts. The most precise aviation weather forecasts are known as Terminal Area Forecasts (TAFs). These are produced for larger airports and predict weather conditions in the immediate area of the airport 24-30 hours into the future.
El Monte doesn’t have a TAF, but you’ll find that the Burbank (KBUR), Ontario (KONT), and Long Beach (KLGB) TAFs can be used to get a pretty good idea of conditions. If they all agree on the forecast conditions, then you have a reasonable expectation that’s what you’ll get. Burbank and Ontario are generally the best indicators, but they can have significantly different weather. It’s a bit of a guess as to which will be a better indicator in that case. There are even occasionally situations where both predict clear weather and El Monte gets fog that sits in the San Gabriel river channel.
TAFs share much of their format with METARs, but with the addition of time periods and/or probability information. You can use the same link you used to get METARs to also get TAFs; put multiple airport identifiers (e.g. “KEMT KBUR KONT KLGB”) into the station field and click on TAFs before you hit submit.
Another resource is the Aviation Forecast Discussion for the area ( LA/Oxnard Area). This provides some insight into reasons for and confidence in the local TAFs.
Check my Resources page for some common links I use for a quick check of weather and TFRs.
So, I’m sitting here on a day that is atypical California weather (meaning there actually IS weather) 😉 and I’m trying to decide if I’ll be able to fly in 2 hours with a student. I start with
KEMT 071747Z 02005KT 13SM DZ BKN060 OVC080 A2994
The winds (from 020 degrees at 5 kts, which means very little crosswind and that runway 1 would be the likely runway), visibility (13 statute miles) and clouds (lowest level is a broken layer that constitutes a ceiling at 6000′ AGL) all meet my criteria. The drizzle (DZ) might make it less fun during preflight and might make things a little slick, but nothing that makes me want to immediately cancel.
I next look to see what is forecast nearby around my planned time (1200 local = 2000 GMT/UTC right now)
KBUR 071747Z 0718/0818 VRB06KT P6SM SCT050 OVC080 FM072000 16015KT P6SM -SHRA OVC040 FM080500 11008KT P6SM -SHRA OVC035 FM080800 VRB03KT P6SM BKN080
KONT 071738Z 0718/0824 VRB06KT P6SM FEW080 OVC100 FM072100 10010G20KT P6SM VCSH OVC080 FM080200 13010KT P6SM -RA SCT015 OVC050 TEMPO 0802/0806 13010G20KT 5SM RA BR BKN015 FM081100 08005KT P6SM SCT040 OVC100 FM081800 VRB05KT P6SM FEW080
KLGB 071747Z 0718/0818 07008KT P6SM -SHRA OVC080 FM071900 15012KT P6SM -SHRA OVC040 FM072200 12012KT P6SM -SHRA OVC040 FM080500 11008KT P6SM -SHRA OVC035 FM080900 VRB03KT P6SM BKN080
In all the highlighted portions of the forecast, the lowest ceiling shows as 4000′ AGL (fine), the rain is forecast to be just in the area (VCSH) or light rain showers (-SHRA), so maybe annoying but not immediately disqualifying. Ontario does show some gusty winds out of the east forecast (10010G20KT). If El Monte were to get that exact wind, that might be too much for a pre- or early-solo student.
I look at the PIREPs (PIlot REPorts) in the area and see that there are some reports of low altitude turbulence of the light-moderate intensity reported by small aircraft in the area, as well as some low level windshear. This is consistent with the developing gusty winds associated with approaching weather and starts to tip me towards not wanting to fly. The last two reports would be very near El Monte.
LGB UA /OV SLI315005/TM 1708/FL025/TP C152/WX -RA/TB LGT-MOD SMO UUA /OV SMO090001/TM 1713/FL011/TP SR22/RM LLWS +30KT FA RWY 21 EMT UA /OV EMT030003/TM 1805/FL018/TP M20P/TB MOD-LGT POC UA /OV POC270005/TM 1810/FL025/TP M20P/TB MOD
These are still not conditions where I would tell a student we aren’t flying, but I let them know the conditions could worsen to the point where we cancel. They also might not be fun, but I can guarantee you’d learn something. The +30 knots low level wind shear on final approach to runway 21 at Santa Monica reported by a Cirrus SR-22 would be eye opening and might cause a go around (much less dangerous than a -30kts LLWS)
Now, all of what we’ve discussed so far is detailed information that ignores the big picture. The big picture is that there’s a cold front and low pressure system heading our way that is bringing rain and winds. All of what we’ve seen is what you’d expect from the big picture; it’s a question of intensity and timing of the weather that’s coming.
Soon after I captured the previous METAR and TAFs, the next EMT METAR came out:
KEMT 071847Z 07010KT 13SM BKN070 OVC100 A2993 RMK LLWS INEFECT
The winds are now getting stronger and coming more from the east (as the ONT TAF predicted). This now gives us a 9 kt cross-wind component landing on runway 1, in addition to a warning about low level windshear. I’m now to the point that I suggest that it might be a waste of time to go to the airport, but still possible we could get a flight in. I also see
KPOC 071847Z 19005KT 15SM -RA BKN030 OVC050 A2996
which shows that there are clouds in the area lower and earlier than had been forecast.
So, now with 20/20 hindsight, I can tell you what happened. I and a post-solo student did fly. When we arrived, winds were out of the east/northeast at around 10 knots and El Monte was using runway 1.
KEMT 071947Z 07010KT 13SM BKN070 OVC100 A2989 KEMT 072047Z 09010KT 20SM BKN070 OVC100 A2989
By the time we were ready to taxi, the winds had shifted and runway 19 was back in use, but with an unusual left crosswind component.
KEMT 072147Z 15010KT 20SM BKN070 OVC150 A2990
We departed and headed over Pasadena and Altadena. As expected, at around 3000′ MSL, we started to get light to moderate turbulence that got worse as we approached the mountains. We stayed over south Pasadena and Alhambra and were able to do some airwork. We cut that short and came back for some good cross-wind takeoff and landing practice at El Monte (a somewhat rare occurrence). They were good conditions to work on expanding the envelope, but might not be for a newer student. YMMV.
Great walk-through on the weather. Thank you!