Monday, October 26, 2020

 


Current Conditions at Sanborn Field



Monday -
Cloudy with a mix of rain, sleet, and snow. High: 30-34


Monday Night -
Cloudy with a mix of rain, sleet, and snow. Low: 30-34


Tuesday -
Cloudy with a few showers possible. High: 40-44


Tuesday Night -
Cloudy. Some drizzle is possible. Low: 34-38


Wednesday -
Cloudy with a few showers possible. High: 50-54
 
 
                          
 
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Discussion: 
Winter makes an early appearance today with our first shot of frozen precipitation expected. Temperatures throughout the day today and into the overnight hours tonight will be sitting right around freezing, meaning that snow, sleet, and rain will be possible during this time. Accumulations, however, should remain below an inch. By Tuesday morning, temperatures should rise above freezing and remain above freezing through the rest of the period. As the low pressure system to our southwest begins to modify and move northeast, it will allow for a continued chance of light rain throughout the early part of the week while also aiding in ushering in some warmer temperatures.
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Forecaster: Ethridge and Ritter
Issued:  10 AM CDT 26 October 2020
 
Technical Discussion (The nerdy stuff we are discussing in class)

Our main issue for this forecast period is precipitation types today; more specifically, we are concerned about the timing and amounts of sleet and snow we may see today. The 06Z GFS was used as primary guidance for this forecast, with additional guidance provided by the 12Z RAP and SREF plumes to give us a better look at forecasted conditions today and tonight.

Currently, a 250-hPa jet streak extends from near the four corners region up into the Great Lakes and southeastern Canada, putting the center of the jet right over central Missouri. At 500 hPa, a trough was deepening to the west of the Rocky Mountains, shifting the flow over central Missouri from westerly to southwesterly. At 700 hPa, significant moisture was building into Missouri from Kansas and Oklahoma. 850-hPa temperatures over the northwestern half of Missouri were subfreezing, with light northerly flow noted at this height. At the surface, a frontal boundary was noted stretching across the far southern CONUS, with several areas of low pressure lined up along the front. Radar images from MZZU showed a precipitation shield overspreading much of Missouri, with the highest intensities between Interstates 44 and 70. Areas in and around Columbia have been seeing precipitation, mainly in the form of rain or sleet, since about 7 AM CDT. The temperature at Sanborn has been sitting right at 33F for the past couple of hours, allowing for this mix of precipitation types.

Today presents a very challenging forecast. The 06Z GFS shows the 250-hPa jet modifying such that winds right at the center of the jet between the Texas panhandle and southwestern Missouri will be weaker than the winds to the northeast and southwest of this region. Therefore, the GFS almost gives this the appearance of jet coupling over central Missouri, which would enhance upper-level divergence. The 500-hPa low should become cutoff over Utah/Arizona this afternoon, and as the trough elongates during this process, vorticity should be enhanced somewhat over central Missouri. Moisture should be abundant at 700 hPa throughout the day today. The GFS also suggests 850-hPa temperatures should remain slightly below freezing today with weak northerly flow, perhaps backing to the west by early evening. Using the top-down method of precipitation type forecasting in analyzing the GFS Skew-T's, it is clear that ice is introduced into the top of the cloud layer. GFS Skew-T's show a thermal inversion between 800 and 650 hPa, but this inversion is not very pronounced and remains near freezing at its warmest point. These Skew-T's also show surface temps below freezing. This would suggest purely snow, but being that rain and sleet were falling at the time of writing, this obviously isn't the case. Turning to RAP Skew-T's (the RAP having better resolution), the inversion layer is more pronounced, and surface temperatures are not as cold (still near freezing). Therefore, I believe the RAP has a better handle on this system, and with its inversion, it seems as though a transition to a sleet/snow mix can be expected by late morning. Temperatures at Sanborn, again, have been fixed at 33F for the past couple of hours, but with near surface backing winds shown by both the GFS and RAP, it should get cold enough in the next hour or two to better support frozen precipitation. Because of clouds and precipitation persisting into early Tuesday morning, temperatures should not change very much, if at all, during this timeframe, so sleet and snow will remain a possibility. Accumulations, however, should be quite light, owing to warm ground temperatures greater than 40F and rather light precipitation intensity.

By Tuesday morning, central Missouri should be right under the center of the 250-hPa jet. The 500-hPa low will become completely cutoff and will slowly move northeast, but it shouldn't get to Missouri before the end of the forecast period. It will, however, continue to disrupt the flow, keeping our weather unsettled. Low-level moisture will not be as easy to come by from Tuesday morning onward, but there will be enough to support continued cloud cover and perhaps a few showers from time to time Tuesday into Wednesday. Temperatures Tuesday will not be able to warm much due to cloud cover and rain, but Columbia should get into the 40s by the afternoon. Wednesday is even warmer as the low draws warmer air into the region-afternoon highs should be in the 50s.

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