Tuesday, November 5, 2019

Tuesday Night - Partly cloudy. Low: 36-40

Wednesday - Increasing Clouds in the Morning. Midday showers. High: 54-58

Wednesday Night - Cloudy with Light Rain. Low:  32-36

Thursday - Cloudy with rain ending in the morning. Clouds clearing out in the afternoon. High: 36-40

 Friday - Partly cloudy. High: 38-42

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Due to the high pressure system moving over Iowa, southerly winds are keeping our temps relatively warm. Tuesday night will be partly cloudy with lows in the upper 30's. A small disturbance will pass through Wednesday keeping temps relatively warm, and also providing a chance of showers, with highs in the mid to upper 50's. Wednesday night a cold front begins to move through causing a drop in temps from the days before and light rain, lows in the low 30's. Thursday the cold front continues to move through, rain ending in the early morning hours, with highs in the upper 30's. As the high pressure system moves through we will once again receive southerly winds, slightly warming the temps but still only topping out in the high 30's and low 40's.
Forecasters: Lujan, Savoy, Vanderpool, Heaven, Munley, Travis
Issued:  5:00 p.m. November 5, 2019

Technical Discussion (The nerdy stuff we are discussing in class!)  
WPC model diagnostics favors a general model blend through 00z 11/8, with emphasis on the GEFS, ECMWF, and 12z NAM thereafter. For this forecast, we will be using the GFS and NAM to diagnose synoptic-scale patterns, with the GEFS and SREF for precipitation and temperature guidance. 

Current WPC analysis shows a large surface high centered over Iowa as of 18z today. Generally easterly flow was observed across Missouri, which will switch around to the south and southwest as the center of the high shifts east. This high was located beneath a large 250mb jet streak which ran through the northern and central plains. A mass of clouds attended this jet streak, which are currently moving into the region out of the northwest.

Tonight, the center of the aforementioned high will shift off to the east. This will allow winds to return to a more southerly direction. Warm air advection from the resulting wind shift will serve to keep temperatures in the high 30s to near 40 overnight, with increasing moisture as well. This increasing moisture comes into play tomorrow as a very small disturbance enters mid-MO from the southwest. Currently, this disturbance looks just strong enough to provide sufficient lift and moisture to generate showers by mid-day and afternoon. The resulting cloudiness and rainfall should cool temperatures slightly, therefore we have lowered Wednesday high temperatures by a couple degrees.

Things get more interesting during the Wednesday evening - Thursday morning period. A large trough at 250mb dives into the central CONUS, driving a powerful cold front south into Missouri. This front shows up especially well on isentropic analysis, with a sharp gradient in moisture, wind direction, and pressure levels noted on the 300 K theta surface. The front will provide a lifting mechanism, and with increasing moisture out ahead of it, we can expect another round of clouds and rainfall for the second half of our Wednesday night. Some models advertise the potential for mixed precipitation (sleet and snow being the dominant types), but the thermal profile just does not look supportive for anything but a very cold rain at this time. Later shifts will need to keep a close eye on this, as a change of just a few degrees will make the difference between all rain and possible frozen precipitation.

Thursday into Friday, a powerful surface high builds in behind the front. This looks to bring us our coldest temperatures thus far this season, with temperatures on Thursday likely not breaking out of the 30s. Thursday night into Friday looks frigid, with lows possibly below 20 degrees. Southerly flow at the surface kicks in on the backside of the retreating high for Friday, though warm air advection will be weak and temperatures will still likely struggle to make 40.

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