Forecasting Weeks for Orlando, FL and Fresno, CA
For our second ePortfolio assignment, we were set the task of choosing a Lesson Learned from each forecast week, two per city, and elaborate on what we learned and how it affects our forecasting technique. Orlando, Florida, KMCO, was our first forecasting city for the first two weeks of the WxChallenge Forecasting Contest. This time of year, Orlando is still in the warm season, with tropical temperatures and solar heating dominating their weather. We also used Orlando, Florida for our practice week the week prior to the beginning of the contest. My first Lesson Learned actually came from that practice week, and it had a big effect on my forecasting technique - the effects and behavior of mid-latitude cyclones/low pressure systems/frontal boundaries between the Midwest and tropical Florida. It changed my whole thinking on frontal boundaries when they reach Florida after traversing the Midwest and Southeast at the end of summer/beginning of fall.
The second Lesson Learned, from the second week of the contest, hinged around my use of the Delta Method, which was required to try at least once for this assignment. My surprise came in the form of the accuracy of my forecast when I used this method - that was my best forecast for the week!
Our second city was Fresno, California, tucked in a valley (San Joaquin Valley) just west of the Sierra Nevada Mountains. The climate for Fresno at this time of year is basically sunny and dry with light winds. However, there was a low pressure system traveling around the vicinity - it got knocked west by a large low pressure system over central Canada, where it moved to the north of Fresno then moved offshore, where it spun a day or two before moving east back onshore just south of Fresno. Our first lesson learned was regarding the presence of showers nearby from this low, whereby evaporatively cooled air busted the high temperature prediction on MOS and by the class (it was first thought that a marine layer invasion had caused this temperature bust - details below).
The second lesson learned for Fresno had to do with winds and MOS' handle on factoring in downward momentum mixing from 850 mb to the surface. This mixing typically manifests as wind gusts, whereas we are forecasting for sustained winds here - a small but important point that caused some confusion and led to this lesson learned. With the presence of the low pressure system nearby, a large pressure gradient showing up on the eWall progs, and the local NWS Area Forecast Discussion indicating that winds would be much higher than normal, we followed suit with predictions for much higher sustained winds and busted by several knots.
Below I will elaborate on each of these Lessons Learned and try to graphically show each occurrence.
Orlando, Florida KMCO
Forecast week 1 for Orlando, FL KMCO
Lesson Learned: Though the sea breeze frontal issues with precipitation, clouds and wind was the biggest issue of the first week of forecasting for Orlando, my personal Lesson Learned was about tropical climatology of the southern states vs. mid-latitude cyclones and frontal boundaries that pack a large temperature change in the Midwest toward the end of the warm season. I realize this occurred during the practice week, but it had a very important consequence to my forecasting mindset.
On September 17th, a frontal boundary packing a potent large temperature gradient passed through Kansas City, Missouri, dropping temperatures by 26 degrees between September 16th and September 17th for afternoon highs (though for some reason the local weather station determined it was 24 degrees). You can see the frontal passage and its effect on these meteograms.
These surface analyses for 21Z September 16th and 21Z September 17th show the progression of the front and the changes in temperature and dew points behind it. I admit, I was doing some upstream forecasting with this front, thinking since it was so potent here in Kansas City, that it would affect temperatures nearly as much when it reached Florida.
Three days later, on September 20th, this same frontal boundary was slated to reach the Orlando area. Below are the surface analyses for 21Z September 19h and 21Z September 20th to show the progression of the front. For all intents and purposes, the conditions pre-front and post-front look the same on these maps, showing that the power it had back in the Midwest weakened considerably by the time it reached Florida.
This meteogram shows the frontal passage at Orlando - with solar heating in control, Orlando barely gave the front a nod of recognition.
My forecasts for 06Z 091906 - 06Z 092006 and 06Z 092006 - 06Z 092106 were for high 88/low 74 and high 86/low 70, respectively. I was fairly close on the lows. However, I busted on the highs due to my thinking that the frontal boundary would significantly affect the air mass temperature over Florida as it had in the Midwest. Actuals for both days were high 92/low 74 and high 90/low 71, respectively. The high on the 20th of 2 degrees cooler has more to do with sea breeze frontal cloud cover than it does with the frontal air mass. Just as a comparative note, the high on the 18th was 92/71 and on the 21st was 91/68 (cooler night with clear skies).
I have always considered frontal boundaries as a distinct dividing line between "warring" large temperature differences. I had also always thought that all frontal passages involved storm activity, or at the very least, rain. One of the most interesting, and sometimes confusing, thing I've learned during this program is that there are varied and sundry weather conditions, as well as varied and sundry cause-and-effect relationships, involved with frontal passages. And that's just fronts - there are so many variables to weather and climate. Though I knew it was warm in Florida year-round with no large temperature fluctuations usually, still I had it in my mind that fronts cause storms and cooler temperatures. Even though I've learned that this isn't always so, it must have still been in the back of my mind when making this forecast.
Forecast week 2 for Orlando, FL KMCO
Lesson Learned: The Delta Method really works! For the forecast period 06Z 10/4 - 06Z 10/5, I chose to use the Delta Method on high temp and max sustained winds both because the Orlando area was embedded in an air mass that was changing little day by day, and forecasted to be the same for the period. This allowed for some persistence forecasting. It turned out to be the WxChallenge day when I had the least amount of error!
I started out as it outlines in the lesson
text, with monitoring the hourly METARS to determine the high for the
current day. On the METAR reading below on October 3rd, the high so far
had come out to be 32.2C, or 89.96F - round it to 90F. This turned
out to be the actual high for the day, by the way.
And now for the math. We've already determined that we're rounding 1.8 to 2 degrees F. So you subtract 2 degrees from 90 degrees to arrive at 88 degrees F for the progged high for tomorrow. I'm happy to say that the actual high for October 4th was ... 88ºF!
Then I went for the winds. Knowing
that this may be off due to the day not being done with, I'm taking the
highest reading of winds of 14 knots at 1753Z as my starting value here
(see METAR line above). On the NGM grid, we look at 850 mb winds:
It was also pointed out that these calculations should be checked with surface/2m/1000 mb values, as well. The value in this is if the 850 mb layer is not well mixed, those winds will not be filtering down to the surface and thus increasing wind speeds. However, it was cautioned in the lesson text that stability must be similar between the comparison days in order to use this method. I believe this was the case for this forecast period. Here are the surface analyses for October 3rd and October 4th, both for 15Z.
I think the biggest problem I have with studying the weather is relating the dynamics I can see and feel outside to the equations and formulas that come to play in the data. There's still a disconnect for me between math and the great outdoors. For the Delta Method to be so close to actual temperature forecast - which to me is a bunch of numbers trying to relate directly to the air outside - truly amazed and delighted me. Not having any formal background, nor natural inclination toward, physics and math, it's been a struggle to put some of these concepts together in my head, but this experience helped to bridge that gap. It also made the numbers more interesting, or rather have more meaning, so that I'm more comfortable using them.
Fresno, California KFAT
Forecast Week 1 for Fresno, CA KFAT
Lesson Learned: Marine layer - to be or not to be.
Fresno, California was a more difficult city to forecast. Fresno sits in a valley with both mountains and desert nearby, but with mountains between the city and the coast. Climatology called for mostly sunny and warm conditions, but there was a low pressure system that affected the area during our forecast parameters. During the forecast period for 06Z 10/13 - 06Z 10/14 (Friday the 13th), MOS indicated predicted high temps close to climatology, which was a high of 80°F for October 13th. The low pressure system was sitting offshore, and slated by the eWall progs to move inland just south of the Fresno area toward the end of the forecast period. The two HPC Front maps below show the predicted location of the low at 12Z 10/13 and 00Z 10/14.
In spite of the low coming onshore, precipitation chances were low on MOS, NWS Area Forecast, and the NWS Point Forecast. There was a lot of dry air with this low, as can be seen on the lower left panel on the eWall progs linked above, and the visible and infrared satellite images below from 2030Z on October 13th confirm that the low brought a few clouds to the Fresno area, but the class consensus was that it was not enough to warrant lowering daytime highs much beyond MOS and climatology.
The actual high temperature for Friday, October 13th came in as 71°F, which is 9 degrees below the climate norm of 80°F. No one expected this huge bust, not even the instructors! So we got busy trying to find the cause, and determined that it was invasion of a marine layer of cooler surface air that caused the high temperature prediction to bust, for us and for MOS. The attached streamlines, sounding, and profiler were all used to support this conclusion. On the streamlines, note the blue arrows that point up to Fresno from the south after coming in offshore from the north (indicating they would travel through a mountain pass). On the sounding, you can see the small surface inversion which is typical of a marine layer. And on the profiler, which is a look back at actual conditions, you can see the pink area at 3000 ft. that deepens from right to left (indicative of increasing height of the inversion with time). The "invasion of the marine layer" was to be our lesson learned for this week.
However, upon further research by the instructor, it was found that a marine layer was not present and thus not the cause of the high temperature bust. According to the station models (click on files to show satellite images), surface winds were from the south all day, whereas a marine layer comes in from the north. Also, even though there was no precipitation measured at Fresno until after the forecast period, there were showers (click on files to show radar images) nearby, and the evaporatively cooled air from these showers was carried by the southerly winds to bring temperatures down and form more clouds than MOS predicted, which also worked to cool temperatures. The real lesson learned here might very well be to always delve deeper for true cause and effect when doing post mortem meteorology.
Quite frankly, my mind is still reeling on this one. First I was trying to understand the marine layer, which is a new concept we learned from the forecast practice week on Fresno (when I was still concentrating on Orlando). Then to find out the marine layer was not the cause of the bust, but it was a simple, mesoscale feature we learned in 361 - advection of evaporatively cooled air by southerly winds, evaporatively cooled air produced locally, and more cloud cover than anticipated by MOS - made me realize that I haven't been applying everything I could to these situations. A lot of this forecasting for daily high/low temperature, precipitation amount and wind speed is part Meteo 101 and part Meteo 361, and I think I've only been focusing on Meteo 101 where we first learned to use MOS. I've tried to anticipate cloud cover and rain chances, but realize that I haven't been looking at them from a mesoscale point of view, nor even in a synoptic context. I have been looking at the low pressure systems and frontal boundaries, but for some reason my thinking is fragmented on these features when it comes to the basics of temperature and winds.
I also realize I haven't been fully utilizing radar and satellite imagery to enhance my perspective of synoptic and mesoscale situations. I think a synoptic briefing at the beginning of each day would have been helpful, and realize that we are each responsible for approaching our forecast in this manner in order to see "the big picture" first. This in itself has been a big lesson learned for me - my routine is opposite of what it needs to be. I need to focus on synoptic, then mesoscale, include climatology, then focus on the details.
Forecast Week 2 for Fresno, CA KFAT
Lesson Learned: Sometimes MOS is the best guidance. And when using the Delta Method, don't use 850 mb for night or winter when mixing is not probable - use 2m, or 1000 mb, for surface conditions, instead.
This week presented a challenge with winds. The local NWS Area Forecast Discussion from 2:00 pm PDT Sunday October 15th indicated the following:
BY MON AFTERNOON...A 120 KT UPPER JET IS FCST TO SAG ACROSS CENTRAL CA.
THIS WILL COUPLE WITH
The prog below, valid at 12Z on October 17th, shows the large pressure gradient present over southern California, which would indicate higher than average winds at the surface. The local NWS Area Forecast called for NW winds of 10-15 mph, which is only 9-13 knots. However, only the ETA MOS predicted a wind higher than 9 knots - 11 knots at 06Z 10/17/06 and 14 knots at 09Z 10/17/06. But since we'd all been experiencing trouble with MOS being too low on the winds (mostly in Orlando - lesson learned there besides), we were all hesitant to take MOS at face value. The local NWS had a handle on the wind situation, as the actual came in at 12 knots. But it was a big bust for some of us on our forecasts.
The lesson learned from this scenario was twofold: trust MOS more and don't fight it so hard as if it were always going to bust, and know that MOS figures in downward mixing of momentum in a statistical sense. It should be noted that since the dynamic models don't handle this downward transfer during the daytime very well, then MOS is bound to be off a bit. However, an adjustment to a wind forecast based on these conditions should only go a degree or two higher than MOS, rather than a huge difference, as we did. Besides, downward mixing manifests as gusts rather than sustained wind speeds.
Many of us were attempting the Delta Method on these winds, and we needed to learn the important difference between using the 850 mb level and the 2m, or 1000 mb, level, to calculate surface winds. In addition to the two-fold lesson learned above, we learned that if downward momentum mixing is expected then the 850 mb level is okay to use since it will reflect surface conditions for a well-mixed boundary layer. However, if this mixing is not expected to occur, then the 2m surface level needs to be used to reflect true surface winds. Also, when using either of these methods, it's a a good idea to double check by calculating the level not used and compare.
I seem to have the most problem with winds, which has always surprised me from the beginning of Meteo 101. And Orlando really threw me for a loop for awhile. But with Fresno, I seem to have been completely lost. This time, I was trying to factor in the low pressure system that was to move back onshore south of Fresno, and I felt certain the winds would pick up, especially when others pointed out the pressure gradient and even the local NWS indicated they'd be way above normal. However, I failed to consider mountains vs. desert vs. valley - the terrain was the hardest thing for me to picture when trying to determine forecasting for Fresno. I failed to take into account that MOS was factoring in terrain (years of statistical data for the same place) as well as the mixing from daytime heating. But with the mixing I'd also forgotten the lesson from Meteo 101 - gusty winds are not what we're forecasting for here, we're looking for sustained. And I think I unconsciously am confusing the two.
ePortfolio Assignment #2
October 24, 2006