Current Conditions at Sanborn Field
Thursday: Overcast, with periods of scattered rain. High: 50
Thursday Night: Steady downpours of rain. Low: 47
Friday: Continuous rain, becoming more scattered after noon. High: 50
Friday Night: Mostly cloudy with isolated showers. Low: 44
Saturday: Partly sunny. High: 55
Discussion:
Rain will continue for the end of the week and into the beginning of the weekend in Missouri, as a deep trough rolls straight through the heart of the state. Rain will be scattered for most of the day Thursday as we are stuck closer to the center of the LPS, but will pick up later tonight as we enter the backside of the system's flow. This will keep our overnight rainfall fairly steady, but without any risk of thunderstorms or severe weather. Even as the trough begins to exit Friday, moisture from both our south and north will keep the atmosphere wet, continuing the chance of scattered showers and rain. Once we enter Friday afternoon, the risk of rain will slowly decrease. Our temperatures will have been kept in the high 40s to lower 50s up to this point, but will begin to cool Friday night as the influence of this powerful trough decreases, clearing the sky above. Saturday will likely see the return of at least some sunshine as cloud cover further departs to the east with the direction of the LPS. Temperatures will start to warm back to average in the middle 50s.
-McDonald
====================================================================
Forecasters: Duff, Mcdonald
Date Issued: 10/28/21 10:00AM CST
Technical discussion:
The 06z model run of the GFS was used. It was chosen because of the accuracy of GFS model output statistics in forecasting surface temperatures and dew point temperatures for the early part of the forecast period. The NAM tended to run warmer surface temperatures and dew point temperatures.
A large upper-level trough and jet streak ahead of the trough can be seen on a 250-mb plot of heights, winds, and divergence. Some upper-level divergence persist throughout thursday morning. By 21z Thursday the trough becomes a closed low pressure system moving east across the southern part of Missouri. As the center becomes closer to Mid-Missouri, the jet streak moves away taking divergence with it. Late Friday a jet streak wrapping around the backside of the low moves through the area bringing some upper-level divergence. The system moves east as the weekend begins and should exit the Mid-Mississippi River Valley in the early hours of Saturday morning. An upper-level ridge approaches behind the system. After 18z Saturday zonal flow will continue into Sunday.
At 500-mb plots of heights, winds, and vorticity show the low centered over southern Missouri at 12z Thursday. The strong low pressure system will continue to move across the bottom part of the state over the next 48 hours. The low pressure system will bring lots of circulation into the Mid-Mississippi River Valley and higher values of vorticity over Columbia throughout the day on thursday will bring continuous rain. Vorticity becomes spotty starting 12z Friday and will remain until 12z Saturday. The sky will begin to clear and conditions will improve early on Saturday as zonal flow begins.
At 700-mb a stream of moisture from the Gulf of Mexico out ahead of the low pressure system can be seen on a plot of heights, relative humidity, and vertical velocity. The moisture wraps around the low and pools in Mid-Missouri. Higher values of relative humidity and vertical velocity continue through most of the forecast period, but decrease by 09z Saturday.
As the trough and the low progress east winds will become more northernly on Thursday. The northernly winds, precipitation, and cloud cover will keep temperatures cooler and seasonable throughout the next few days. Temperatures will stay in the lower 50s for highs on Thursday and Friday. The temperatures will stay seasonable due to a northwest wind and clearing conditions on Saturday with highs in the Mid-50's.
Future forecasters should pay attention to the exit of the system and the return of zonal flow.
-Duff
No comments:
Post a Comment