Friday, April 24, 2020

Friday Night - Overcast with rain. Low: 52 - 56
Saturday - Overcast with rain. High: 58-62
Saturday Night - Clearing through the nightLow: 44-48
Sunday -  Partly cloudy. High: 62 - 66
Monday - Increasing clouds throughout the day. High: 68-72
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For this weekend, we will be expecting rainfall this weekend as a deep low pressure system 
comes into our forecast area from Saturday into Sunday.  We expect a maximum cumulative 
3 hourly precipitation amount to be 0.2 inches during this period.  We expect temperatures to 
increase from Sunday and Monday as this closed off system moves past us.  

Forecasters: Balkissoon, Savoy, Heaven
Issued:  5:00pm: April 17, 2020
Technical Discussion (The nerdy stuff we are discussing in class)

WPC model diagnostics suggested a general model blend so we decided to go with GFS. 
SREF was used alongside to supply temperature averages as well as precipitation amounts.

At 250 hPa we see westerly winds at the beginning of our forecasting period,  begin to shift to 
southerly around 3Z on Saturday. These northerly winds stick around until 12Z then shifts to 
northerly. We also noticed an upper level trough that enters Missouri around 6Z on Saturday 
which deepens as it moves through our region. 

As we move down to 500 hPa we notice the trough again entering the region at around 6Z on 
Saturday and continues to deepen until it’s exit at 12Z on Sun.  The system around this time 
period is closed off over Missouri.  There is a deep low and enclosed in the system, vorticity 
max is at the center of the rotation.   With this trough, comes vorticity, which will be an important 
factor in any rain we will be expecting. Small amounts of vorticity were noticed scattered 
throughout the state on Friday but increases as the trough approaches. Max values in our area 
were noticed between 6Z- 18Z on Saturday. As the trough continues to deepen we see another 
peak in vorticity around 15Z on Sunday, with small amounts of scattered vorticity as the trough 
exits the state. The vorticity will play an important role along with other factors to determine our 
chance for continued rain. 

We move further down to the 700 hPa RH and Omega map to further investigate rain chances 
from these products.   From this evening into tomorrow morning we note that very high 
percentages of RH over the entire state of MO.  This persists throughout Saturday and into 
Sunday with intermediate periods of reduced RH values starting on Saturday at 18Z before 
becoming fully saturated over the entire state on Monday at 12Z.  This persists there on out into 
Tuesday.  Comparing the RH values with vertical velocities, we note that there are significant 
values of VV from Saturday 3Z to Sunday 0Z over Missouri.  We see significant lift in central 
Missouri next, from Monday at 12Z into Tuesday.  It is these mentioned times , we expect the 
highest rain chances.    Consulting the skew-Ts, it was confirmed from the GFS sounding 
that throughout Saturday the atmosphere was saturated in Boone County with periods of 
significant lift.   It should be noted that there were no very significant CAPE values for the 
sounding and none of the hodographs were curved,  indicating there we are not expecting 
severe weather and supercell formation.  There are also no  significant SRH values both at 
1km and 3km  which was also supported by the low values of BNR Shear values.  

From the last map we looked at in our top-down approach  was the 850 hPa temperatures 
and heights.  It was noted that throughout the forecast period we are above freezing temperatures 
which implies all precipitation will be in the form of rainfall.  We expect  an average range of 2 - 6 
degrees Celsius over the weekend before temperatures rise in the double digits from Monday 
into Tuesday.  

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