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Reflections on my Forecasting Assignments in the Weather Station |
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In order to become a better weather forecaster, both knowledge and
experience are required. In Meteo 101, we were asked to complete a
weekly forecasting exercise. Below I have listed several of these
exercises that had specific impact on my understanding of the dynamics of
the atmosphere, along with a reflection about how this experience changed or
reinforced my understanding. |
| Assignments in The Weather Station Assignment 1 had to do with locating low visibility conditions due to rain/storms or fog, and also with the weather cooperating with our need to find such conditions. Assignment 1
20 May 2005 _____________________________________________________________________________________________0316 UTC KIND Indianapolis, IN NCAR-RAP Real-Time Weather Data Output produced by METARs form (20 May 2005 03:24 UTC) found at http://www.rap.ucar.edu/weather/surface/ Conditions at: KIND observed 20 May 2005 03:04 UTC Temperature: 17.0°C (63°F) Dewpoint: 17.0°C (63°F) [RH = 100%] Pressure (altimeter): 29.78 inches Hg (1008.5 mb) Winds: from the ENE (60 degrees) at 9 MPH (8 knots; 4.2 m/s) Visibility: 2.50 miles (4.02 km) Ceiling: 3900 feet AGL Clouds: few clouds at 900 feet AGL broken clouds at 3900 feet AGL overcast cloud deck at 9500 feet AGL Present Weather: -TSRA BR (light rain associated with thunderstorm(s), mist) KIND 200304Z 06008KT 2 1/2SM -TSRA BR FEW009 BKN039CB OVC095 17/17 A2978 RMK AO2 FRQ LTGICCCCG OHD-S TS OHD-S MOV S P0001 ________________________________________ Actual post time is 10:40 pm CST Thursday, May 19, 2005. At this time, TWC is showing a severe line of thunderstorms with damaging winds moving through the upper Midwest. I chose Indianapolis, IN because it showed a red dot with the thunderstorm symbol at the present time, and I figured it was in the middle of that storm system. My translation, however, shows light rain associated with thunderstorms, and mist. The mist lowers visibility enough (2.5 miles) to qualify for IFR, even though the ceiling is at 3900 feet AGL (which would indicate Visual Flight Rules) with broken clouds. My guess is the storm is in a lull or between cells. [Steve Seman] Great job, Debra!
On this assignment, I used my intuition and what I've already observed about storms along with what I'd learned from the lesson - it worked for this one, but I found out later on that you can't forecast by intuition alone. The science has to be learned and applied. Assignment 9 dealt with forecasting precipitation around a low pressure system and identifying the lifting mechanism in play. This was based on the Cyclone Model.
Assignment 9
The 36 hour precip forecast map (valid 1200Z Thursday,
July 14, 2005) shows a Low occluded back to the northern
Manitoba/Saskatchewan, Canada province line from its
center in mid-Manitoba, Canada, with a cold frontal
boundary trailing down through Manitoba and into North
Dakota.
Per Steve, since the
HPC was late in updating its forecast maps, causing
my 36 hr map to actually be 24 hrs, I have chosen to
repost, with his permission.
This 36 hour precip forecast map is valid for 000Z Fri Jul 15, 2005 (7:00 pm CDT Thu Jul 14 2005). The low has occluded back to about the Manitoba/Nunavut province line, with its original center in Manitoba just southeast of Churchill, Manitoba, Canada CYYQ (another airport station). The frontal boundary is trailing down across the Manitoba/Ontario province line, and on into Minnesota then South Dakota. An area of precip is predicted for the frontal boundary at the Canada/US country line up through its occlusion boundary. Churchill, Manitoba lies within the occlusion boundary, thus making this a Dynamic Lifting Type I lifting mechanism (due to its position near the center of the low and as part of the heavier precip at the head of the comma). However, since occlusion is well underway, precip is dissipating from its strongest point at the low's maximum intensity. 36 Hour Precip Forecast for Churchill, Manitoba
Conditions at: CYYQ observed 0000 UTC 15
July 2005 Temperature: 22.0°C (72°F) Dewpoint: 18.0°C (64°F) [RH = 78%] Pressure (altimeter): 29.32 inches Hg (993.0 mb) [Sea-level pressure: 992.9 mb] Winds: from the S (180 degrees) at 22 MPH (19 knots; 9.9 m/s) gusting to 30 MPH (26 knots; 13.5 m/s) Visibility: 15 miles (24 km) Ceiling: 2900 feet AGL Clouds: few clouds at 1600 feet AGL broken clouds at 2900 feet AGL broken clouds at 8000 feet AGL Weather: -TSRA (light rain associated with thunderstorm(s)) As forecast, rain was setting in at the frontal boundary in Churchill, Manitoba, Canada, by 00Z Fri Jul 15, 2005. Within the next hour, a thunderstorm was reported at this station (0046Z and 0100Z). This precip at the frontal boundary is caused by the convergence of surface air in the trough and convection of the warm, moist air ahead of the front (in the warm air mass). Thunderstorms usually form when a front is coming in due to these two elements. ---------------------------------------------------------- Since I originally posted for Regina, Saskatchewan, Canada at 1200Z Thu Jul 14, 2005, I'll go ahead and post the METAR for 1200Z for Regina. Regina, Saskatchewan, Canada 1200Z Thu Jul 14 2005 Conditions at: CYQR observed 1200 UTC 14 July 2005 Temperature: 12.0°C (54°F) Dewpoint: 12.0°C (54°F) [RH = 100%] Pressure (altimeter): 29.97 inches Hg (1015.0 mb) [Sea-level pressure: 1015.2 mb] Winds: from the WSW (240 degrees) at 7 MPH (6 knots; 3.1 m/s) Visibility: 15 miles (24 km) Ceiling: at least 12,000 feet AGL Clouds: few clouds at 10000 feet AGL few clouds at 26000 feet AGL Weather: no significant weather observed at this time The temp and dewpt have been steadily moving toward each other for the past 6 hours, so it appears that it’s “clouding up and getting ready to rain.” However, the sounding at 1300Z separates the dewpt and temp again by a couple of degrees, though the clouds remain the same as at 1200Z. Seems Regina is just on the edge of the predicted precip pocket at 1200Z. _____________________________________________________________________________________________ On this assignment, I learned about the importance of timing and observing the updates that NWS makes to the data sites. If I had not caught the discrepancy in what I was looking at versus how it was labeled, I would have done the assignment wrong (used incorrect data). _____________________________________________________________________________________________ Assignment 10 gave us the chance to predict precipitation based on the computer models ("progs"). Assignment 10
Date/Time ETA (NAM) run initialized: 050726/1200ZF024
Date/Time ETA (NAM) run valid: 050727/1200V024 State: Tennessee Max Value of Downward Motion at 700mb: +4 mps City: KTRI - Bristol, TN Prog initialized today at 1200 Z (Tuesday 7/26/05) and valid for 24 hours at 1200Z tomorrow (Wednesday, 7/27/05). There is a +4 mps solid contour surrounding the four corners of SE Kentucky/NE Tennessee/SW Virginia/NW North Carolina. Bristol, TN is located within this contour. +4 mps indicates 4 microbars per second of downward motion (air sinking = convergence aloft with divergence at ground level = high pressure area).
Conditions at: KTRI
observed 1153 UTC 27 July 2005
Temperature: 23.9°C (75°F) Dewpoint: 22.8°C (73°F) [RH = 94%] Pressure (altimeter): 30.02 inches Hg (1016.7 mb) [Sea-level pressure: 1014.4 mb] Winds: calm I believe this was a fairly good prognostication, overall, though the precip moved further southeast than anticipated in the 24 hour period predicted. Visibility: 3 miles (5 km) Ceiling: at least 12,000 feet AGL Clouds: sky clear below 12,000 feet AGL Weather: BR (mist) This METAR is valid for 7 minutes before the prog map validity time of 1200Z. In addition, I've attached below the METAR for 53 minutes past the prog map validity time of 1200Z. These METARs together show the dissipation of water vapor (mist to haze), the rising of pressure (1014.4 mb to 1014.7 mb), the lowering of RH (94% to 85%), and the dropping of dew point (23.3C/74F to 22.8C/73F) -- all indicating convergence aloft causing air to sink, which in turn causes divergence at ground level = high pressure building. This area of convergence is just to the southeast of a band of predicted precip (see 24-HourETAprog), of which a slight part moved over Bristol in the past 6 hours (see attached 6-HourETAprog). This accounts for the mist. However, the sinking air is dissipating the clouds, as both METARS indicate clear skies below 12,000 ft. Temps rose 4 degrees F as the day progressed (8:00 AM EDT to 9:00 AM EDT, approx.). 1253 UTC METAR: Conditions at: KTRI observed 1253 UTC 27 July 2005 Temperature: 26.1°C (79°F) Dewpoint: 23.3°C (74°F) [RH = 85%] Pressure (altimeter): 30.03 inches Hg (1017.0 mb) [Sea-level pressure: 1014.7 mb] Winds: calm Visibility: 3 miles (5 km) Ceiling: at least 12,000 feet AGL Clouds: sky clear below 12,000 feet AGL Weather: HZ (haze) _____________________________________________________________________________________________ This assignment taught about the difficulty of pinpointing the weather to an exact point in time. It does not cooperate, but moves at its own speed. It also taught the value of looking at the METARS from the surrounding times to get a feel for how the system moved in relation to how it was predicted to move. And it was good practice for reading all the other indicators (winds, pressure, temps, RH, etc.). _____________________________________________________________________________________________ Assignment 12 was about predicting precipitation at the time a prog was valid. Mine was a bust, but let me point out that the whole time I lived there in Dallas, the forecast would call for rain and it wouldn't come. I call that typical Summer Dallas Doldrums. Assignment 12
Initialization Time 12Z on August 2 Tuesday (7 AM CDT
8/2)
Valid 00Z on August 4 Thursday (7 PM CDT WED 8/3) KDFW Dallas-Ft. Worth Intl Airport I have chosen my home town, Dallas, Texas, as blue precip shading and a dashed bull's eye of upward motion are present, as well as 70-90% RH. Also present on the graphic is the * (snowflake) indicating the exact location of the predicted max precip in Dallas/Dallas County. The 570 dekameter contour is far north, up in the Dakotas, indicating a very thick, warm atmosphere aloft down in Texas. This precip will be due to convection (the lifting shown by the dashed line) from afternoon heating and enough moisture in the air (70-90% RH) to develop a brief thunderstorm. The attached 36 hour surface analysis shows a trough of low pressure expected to move just ENE of the Dallas-Ft. Worth metroplex by 12Z on Wednesday, August 3 (7 AM CDT), which I did not see indicated on the progs. If a low is trying to form here, the progs are not picking up the vorticity nor the pressure gradient for a trough. However, the second attached surface analysis for 000Z Thur Aug 4 (7 PM CDT Wed Aug 3) is more aligned with the progs in that the low is further north, with no troughs or vort maxes nearby. With the highs in the upper 90s to 100, I know Dallas will be relieved by a brief shower tomorrow night. The MOS prediction for
precip at Dallas at 00Z Aug 4 was a bust. The
METARS below (for 7 minutes prior to 00Z and 53
minutes after) both show no significant weather.
Also, the relative humidity stayed very low (41% and
44%, respectively) with dewpoints at 66 F and temps
in the low 90s. There were scattered clouds both
times at upper levels, with scattered clouds at 7000
ft at 2353Z and a few clouds at 7000 ft at 0053Z,
which lowered the temp 2 degrees F. The prog had
shown RH of 70-90%, blue shading and the closed
dashed line for rising motion. Infrared Satellite Image for 00Z This was another lesson in the unpredictability of predictable weather systems. The rain developed later than anticipated, indicating again that weather systems move in their own good time - we can only attempt to predict based on how they're performing at any given time, and assume they will continue to do so.
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Reflections The most important part of the course for me was learning about the Cyclone Model and how to identify fronts on a map with various data. Being able to put symbols on a map together with clouds on a satellite image has also been one of the most interesting things I've learned. These assignments gave us the experience of using what we'd just learned in a real-time environment, and showed us how to access the various weather data available on the web. These tools are invaluable in determining weather at any given place at any given time.
I knew there were a lot of
scientific principles involved in meteorology, but I didn't realize there
were so many minute variables. It's amazing how one map can show you
so many things, all to be considered for forecasting the simplest weather
movement. The answer to "Is it going to rain?" is complicated and
multi-faceted. The answer is never "Yes" or "No" by any means.
It's full of Ifs and Probabilities and Percentages. A better answer
for that question would be "It depends." Because it does! |