Fall 2018 Weather Diagnosis Component Essay Weather at midlatitude, continental locations can be highly variable during the transition period from late summer into fall. The weather at KMSP during 2018 was no exception. Temperatures for 1800 UTC during our data collection period (2 September to 14 October) varied from the upper 80’s to the low 30’s Fahrenheit.

The period that we will diagnose begins 1200 UTC October 2 and ends 1200 UTC October 4. KMSP experienced the following weather during the 48 hours: – Temperatures varied from a high of 79˚F at 21:53 UTC Oct. 3 to low of 37˚F at 11:53 UTC Oct. 4. Several hours of fog with 100% relative humidity that ended at 13:53 UTC Oct. 3. SLP’s slowly fell to a minimum of 995.7 hPa at 20:53 UTC Oct. 3 and was followed by a rapid rise to a value of 1029.1 hPa at 14:53 UTC Oct. 4 (three hours after the time-series ends). A 70˚ wind-shift from southwest (230˚) at 21:53 UTC Oct. 3 to northwest (300˚) at 22:30 UTC. A peak wind of 53 knots at 22:37 UTC. Thunderstorms with 0.59” of rain starting 22:34 UTC Oct. 3 and ending 22:53 UTC Oct. 3. A 31˚F cooling in 5 hours following the wind shift when the temperature dropped form 78˚F at 21:53 UTC Oct. 3 to 47˚F at 02:53 UTC Oct. 4.
These points can be gleaned from the time-series graphs (below) of temperature, dew point, SLP, wind, weather and hourly precipitation for the 48 hours.

Fall 2018 Weather Diagnosis Component Essay
Upper panel: temperature (red) and dew point (blue) in ˚F on y-axis, wind barbs (knots) and weather symbols. Middle panel: SLP (dark red) in hPa on y-axis, wind barbs (knots) and weather symbols. Bottom panel: hourly precipitation (inches) on y-axis, wind barbs (knots) and weather symbols. The x-axis has date/hour as dd/hh, where 02/12 denotes October 2, 1200 UTC, etc.
In order to keep the diagnosis portion of term project tractable in the remaining time, we will focus our diagnosis efforts on the addressing four straightforward questions:

1) Explain the surface weather evolution that caused the SLP to fall steadily to its minimum value of 995.7 hPa at 20:53 UTC Oct. 3 and the winds to increase from the south prior to the 70˚ wind shift between 21:53 UTC and 22:53 UTC Oct. 3.

2) What preceding weather conditions set the stage for thunderstorms and heavy rain that began at 22:34 UTC on Oct. 3? You need to consider the joint impact of changes in temperature, moisture, vertical stability and vertical motion.

3) What was the source region of the air mass that ultimately led to the formation of thunderstorms over KMSP? Give the source region in terms of a geographical location such as “Antarctica” or “Mediterranean Sea”, instead of a compass direction such as “It came from the north.” A map of North American could prove helpful if your knowledge of the geography of North America is limited.

4) What weather feature produced the 70˚ wind shift between 21:53 UTC and 22:53 UTC on October 3, the abrupt 31˚F cooling starting 21:53 UTC on October 3, a pressure minimum of 955.7 hPa (i.e. trough passage) at 20:53 UTC, and rapid pressure rise thereafter to 1026.0 hPa at 11:53 UTC on October 4 (the last time shown on the prior time-series plots)?

Fall 2018 Weather Diagnosis Component Essay

You must support your diagnosis with a tight set of weather maps and/or supplemental data. Consider adding surface maps, upper-air analyses, radar reflectivity maps and satellite imagery. I have listed in a separate document on D2L several sources to access historical weather maps. Be certain to use course concepts to explain any role that conditions aloft (925 hPa, 850 hPa, 500 hPa, 300 hPa) may have played in producing significant surface weather (e.g. precipitation) or abrupt weather changes (e.g. wind shifts, temperature falls, etc.). You should find concepts in Chapters 10 and 11 of H&P particularly helpful to answering the four questions.

You have ample time to complete Stage II of the project (the time-series analysis and weather diagnosis herein described) before taking your penultimate draft to a tutor at the Writing Center for their analysis and integrating their suggestions into your final draft IF you do not wait until the last minute to start Stage II or delay going to the Writing Center.

Fall 2018 Weather Diagnosis Component Essay

You must submit the email receipt that you will receive from the Writing Center to the appropriate D2L dropbox before the dropbox for the final draft will open for you. Plan to submit your receipt at least one week before the due date for your final draft of Stage II so I have sufficient to check that it is valid.

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