18-31 October 2004 near-record rain

Brigham Young University

Dept. of Physics & Astronomy

A sequence of fronts with strong flow aloft from the southwest for a significant period produced near record rainfall for the month of October. The highest measured rainfall at the official BYU station south of campus (data has only been kept since 1980) was 5.05" in 1981. The highest recorded for Provo City (location unknown) was 5.39" in 1946. We finished October with 4.96" at the official BYU station (4.53" at the ESC station which generally records lower rainfall than the neighboring stations). The unofficial total at my home located 2 miles southeast of campus was actually 5.30". The interesting part was that this rain all fell in the last 14 days of the month - the remainder of the month was completely dry. A breakdown of what happened during the month is included here.

Weather data graph

October 17-19: the cold front passed over Utah Valley at about 6:00 am on October 18th, bringing with it considerable rain and colder temperatures. The front then passed south through Utah by 6:00 pm and moved off to the west. The southwesterly flow aloft brought Pacific moisture in with continuing rainfall for several days. This flow also resulted in heavy rain in southern California, especially in the evening on October 19th as a new cold front approached that area.

Weather data graph

October 20-22: although the weather charts didn't show any frontal activity in Utah, at 4:00 am on October 20th a cold front passed through Utah Valley and the rain began again. During that period an occluded front was located near Reno, Nevada, at 6:00 am, had become a cold front as it passed over Elko, Nevada, at about 6:00 pm, and stalled to a stationary front running north-south through Utah by 6:00 am on October 21st. This cold front moved on into Colorado by 6:00 am on October 22nd.

Weather data graph

October 23-25: a cold front approached Utah from the northwest, entering the northwest corner by about 6:00 pm on October 23rd. We received a lot of rain before the actual cold frontal passage at 6:30 am on October 24th. This front then stalled into a stationary front that slowly rotated so that by 6:00 am on October 25th it was an east-west line through Utah just south of Provo.

Weather data graph

October 26-28: the west end of the stationary front slowly curled northward and about noon on October 26th the warmer air to the south and west of that front reached Utah Valley as the front moved out towards the east. This was accompanied with moderate to strong southerly winds. At the same time the front that had been sliding southward along the coast began to move inland with the charts showing an occluded front north-south over Reno, Nevada, by 6:00 pm on October 26th. This front continued to move westward (the associated low was actually moving northeastward) and there is a cold front passage at 6:00 pm on October 27th although the weather charts generally indicated the front to be an occluded one extending southward from Boise, Idaho, through Nevada which didn't reach Utah Valley until about 5:00 am on October 28th (as what appears to be a cold-type occluded front). By 6:00 pm on October 28th the occluded front had dissipated and the cold front had essentially reformed over Colorado.

Weather data graph

October 29-31: there was a very light rainfall on the 29th that was not associated with any frontal activity (except possibly the tail end of a front in Wyoming that sort of pointed our way but really didn't reach this far down). The 30th was generally cloudy but calm. A cold front finally passed through Utah Valley on the 31st at about 12:45 am (first temperature drop and minimum barometric pressure minimum) and 2:30 am (second temperature drop and wind direction shift) - both times are Mountain Daylight Time (Windows XP decided to switch times at 3:00 am MDT rather than at 2:00 am MDT). The rain begain just before 1:00 am and continued until about 3:10 am MST. There were periods of light snow throughout the remainder of the day.

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