Current Conditions at Sanborn Field
Thursday Night: Clear. Low: 42 - 46
Friday: Clear with clouds building in the late afternoon. High: 62 - 66
Friday Night: Clouds building. Low: 48 - 52
Saturday: Overcast with showers throughout the day. High: 56-60
Discussion:
Today will see clouds clearing as a high pressure system moves into the region for today and tomorrow. For Friday, clear skies with light winds out of the west. Friday night, clouds begin to build as southerly winds begin to dominate, bringing moisture and clouds. Rain could begin as early as 6 am, but won't be steady until about noon, when the atmosphere saturates completely. Storm totals are between 1 and 1.5 inches through Sunday. Thunderstorms are possible overnight Saturday, but will be brief and not severe.
=====================================================================
Technical discussion:
The 06z GFS was used for this forecast. The reasoning for its use is to maintain continuity with previous forecasts and because it has been closer to the actual conditions than the RAP and NAM. The focus of this discussion is the rain arriving Friday evening into Saturday morning.
For Thursday, high clouds will move through the area due to upper level divergence at 250mb and broad circulations at 500 mb. Throughout the day, the longwave pattern will move the base of the trough over Missouri, providing strong northwesterly flow for the region. Mid level moisture and vertical velocities also exit the area over the course of the day, giving way to clear skies for Thursday. As the surface low moves off to the east, northwesterly flow takes hold and Missouri will see some cold air advection (CAA).
On Friday, the upper level trough will move to the east and an upper level ridge begins to take hold. At 250 mb, the divergence field remains relatively quiet and the flow is still northwesterly for most of the day Friday. The 500 mb vorticity field is also quiet over Missouri for Friday as the ridge pattern begins to take hold. Down at 700 and 850 mb, the relative humidity field starts to saturate over Missouri and the flow begins to shift from northwesterly to pure westerly. For the first part of Friday, a surface high pressure system will dominate, but will quickly exit to the south as the next system begins to affect the region.
Saturday begins the changeover and rain begins to enter the forecast. Starting between 09z and 12z, the divergence field at 250 mb begins to develop over Missouri. Upper level flow is still from the northwest, and will drive increased divergence into Missouri. At 500 mb, the vorticity field is quiet until about 18z when some small circulations enter Missouri from the west as the flow is westerly. At 700 mb, the relative humidity field stagnates and builds, with increasing vertical velocities throughout the day, until about 21z when a trough pulls the moisture out of the region. At 850 mb, a low level jet sets up out of the southwest, bringing warmer air and moisture to the region. At the surface, some slight warm air advection (WAA) takes place throughout Saturday.
The surface low pressure system moves through Saturday night and passes Sunday morning through early afternoon. Soundings indicate clouds dissipating Thursday with Friday being clear until late afternoon. Rain could start as early as 6 am on Saturday, but the soundings don't saturate until 12 pm. Scattered showers will likely start, but turn to more stratiform rain throughout the afternoon on Saturday. GEFS plumes indicate between 1 in and 1.5 in for storm totals.
No comments:
Post a Comment