Friday, April 26, 2019

Friday Night - Clouds increasing. Low: 52 - 56.

Saturday - Cloudy, with light showers in the morning. High: 68 - 72.

Saturday Night - Partly cloudly. Low: 34 - 38.

Sunday - Clouds increases through out the day. With late overnight showers possible.  High: 60 - 64.

Monday -  Cloudly with showers likely. High: 62 - 66.

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The low temperatures tonight will not drop too much as the increase in cloud cover will help us to keep the warm air. The cloud formation is due to the southerly flow that will bring moisture and warmer conditions to the area. Light showers are expected after midnight and early Saturday with no significant accumulation. The cloudy conditions will remain along Saturday, with an, for a short time though increase in wind speeds by the afternoon. Saturday evening a cold front will pass across the area, drying out the mid and upper atmosphere allowing clear skies, for a short time Saturday’s night. Moisture works its way back in to get cloud formation, then we get enough moisture in the atmosphere to get showers late Sunday night that will last through out Monday.

Forecasters: Johnston, Rojas, and Summall.
Issued: 5:30 p.m.; 26 April 2019

Technical Discussion (The nerdy stuff we are discussing in class!)
The WPC Model Diagnostics suggested a general model blend for the CONUS, excluding the NAM and CMC with a slightly above average confidence. Based on that, the following discussion is using GFS 12Z.

The dry conditions associated with high pressure system formed west of the departing upper level trough were dominant during Friday but as the northerly winds shift southerly tonight, the veering profile confirms warm advection as the southerly flow, the increase in moisture. We can expect an increase of clouds along tonight, which will be acting as a blanket, avoiding the escape of warm air. As a result the temperatures will not descend too much, leaving us mild temperatures Friday’s night.

A short wave approaches to our area by 6Z on Saturday along with unorganized areas of vorticity, seen at 500 mb –height. The column in the atmosphere starts to moist from upper to lower levels by 09Z.A low level jet will be responsible for the warm advection and the increase in moisture over the area, an absence of vertical motion will indicate more light showers. This LLJ with wind velocities of 40 to 50 kts at 925 and 850 mb-height respectively, will also bring breezy condition in the afternoon. Rain is expected to last from 09Z to 18Z. The GFS does not indicate significant accumulated precipitation, just trace. The NAM is being a little bit more optimistic with values of 0.02, the rain expected will not be significant. At 12Z the center of the deep low pressure system would be east of Nebraska and North of Missouri by 18Z. Along with the low pressure system we will have a tight pressure gradient that will increase the wind speed at surface around 20 kts during the early evening. Same time, the deep low will drag a cold front through the area which literally will sweep the moisture, leaving us a dry atmosphere at the end of the day, for a short time though.

A low pressure system over the Rockies Sunday morning will be the cause of our precipitation Sunday night through Monday. Sunday night near midnight the core of the low pressure system is over eastern Colorado and western Kansas. The low pressure system reaches northwest Missouri by noon on Monday. We start off Monday with southerly winds allowing warmer temperatures through the start of the afternoon before the winds begin to shift northerly. This wind shift indicates frontal passage.

Soundings show moistening aloft increasing through out the day on Sunday to support increasing cloud cover. Near 21Z on Sunday, soundings have CAPE values above 500 J/kg and CIN values at -61 J/kg. The CIN provides a small cap, which can be easily eroded when moisture reaches the surface in the next few hours. Some thunder is possible 09Z Monday when high omega values stretch from near the surface up to 250 mb along with a 500 vorticity max moving through Mid-Missouri during that same time. The moisture remains near the surface all through the end of our forecast period. Along with CAPE values ranging from 500 – 1000 J/kg during this time with low CIN values which supports shower activity for our area. SREF plumes has a total QPF mean of 0.46 inch through Monday. Future forecasters will need to look at rainfall totals and rates for next week to monitor for a risk of flash flooding.