Friday Night - Overcast. Low: 46 - 50.
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Cloudy skies will prevail for most of this weekend. You will need your umbrella for showers Saturday morning into the after afternoon. We expected precipitation totals not to be greater than 0.30 inch. By Sunday afternoon should be able to see some peaks of sunshine as some of the clouds have moved out. Clouds completely move out overnight allowing for a sunny start to the week. With the sunshine we can expect warmer temperatures in the upper 60s for Monday.
Forecasters: Johnston & Rojas
Issued: 6:15 p.m.; 10 May 2019
Technical Discussion (The nerdy stuff we are discussing in class!)
We used the 12Z GFS to forecast due to the Weather Prediction Center having an average confidence in a non 12Z CMC model blend.
At 250-mb we are located in the right entrance of the jet streak with some related divergence. Looking at 500-mb we are located below the downstream side of the trough with maximum vorticity circulation over our area at 09Z on Saturday. The relative humidity at 700-mb increases to near 80% by the following 3 hours. At this same time omega values are around -3 ub/s. Showers likely from early in the morning on Saturday until the afternoon. Vorticity advection would be the main factor to yield forcing for upward motion based on the convergence of Qs vector. We expect low amount of total precipitation from these showers with the mean GEFS plumes line reaching 0.2 inch and GFS with 0.28 inch.
Soundings from 18Z on Saturday to 00Z on Sunday show temperature and dew point profiles really close near the surface while profiles in upper atmosphere becomes saturated, which will lead to cloudiness being present and isolated drizzle possible.
By Sunday a clipper system would be to our north over Iowa by 15Z on Sunday. The axis of the positive tilted trough at 500-mb will cross over our area by the afternoon with associated maximum vorticity circulation. The next period of isolated precipitation would be at 15Z on Sunday due to the vorticity advection mentioned and divergence at 250-mb. After 15Z the atmosphere dries out which could inhibit this opportunity of precipitation and provide some clearing. Sunday night the southwesterly winds slowly shift westerly as the system is moving out of the area and a well amplified ridge start to dominate the western 2/3 of CONUS aloft and a high pressure system at surface. The atmosphere will dry out by Monday leaving us sunny conditions for the beginning of next week.