textproduct: Columbia

WHAT HAS CHANGED

Forecast rainfall amounts Thursday into Friday have trended upward, but still remain generally light. Aviation discussion updated for 06z TAF issuance.

KEY MESSAGES

- 1. Generally light rainfall amounts possible late this week.

DISCUSSION

Key Message 1: Generally light rainfall amounts possible late this week.

An upper level low over the Upper Midwest continues to move to the north while its associated surface front draped along the Mississippi Valley is creeping eastward. Another upper low moving over the Great Basin is moving eastward early this morning. Expect this low to begin phasing with the low over the Upper Midwest as we head into the last half of the week. The surface front is forecast to continue to move slowly as the flow over it is nearly parallel front until the upper lows eventually phase together. This should allow for the front to get the push it needs to move through the area for the end of the week. As a result of all of this, most of the rainfall associated with this system is expected to stay west of the area today. However, some shower activity is possible for the far western portions of the forecast area. The chances for rain increase for the rest of the forecast area as we head into tomorrow and Friday. Moisture advection is forecast to increase as this front approaches, causing PWATs to potentially exceed 1.5". Therefore, the chances for total rainfall amounts over a half an inch by Friday night have increased to 40-60% over the western and northern portions of the forecast area. With 20-40% chances for the southern and eastern portions of the area. After this system moves out of the area, dry conditions return for the weekend and into next week.

AVIATION /07Z WEDNESDAY THROUGH SUNDAY/

MVFR/IFR restrictions in stratus and patchy fog possible this morning, with VFR conditions expected to return late morning through the end of the period.

Scattered clouds 3-5kft MSL with SCT-BKN mid level clouds expected this morning, but most guidance continues to indicate MVFR CIGs developing after 08z at all terminals, and in particular during the 10z-15z time frame. Brief IFR CIGS could develop around 12z, so continued with a tempo group to cover this potential, along with the possibility of some patchy MVFR VSBYs. A return to low VFR CIGS is expected after 16z and continues through the afternoon. Winds should remain around 5 knots or less early this morning before picking up to around 8 to 10 knots after 14z with direction shifting more southeasterly. Light and variable winds return this evening into tonight. The rain threat should remain west of the terminals during the current TAF period.

EXTENDED AVIATION OUTLOOK...Increasing chances for rain particularly late tonight into Thursday and again Friday may lead to some lower CIGS or VSBY restrictions.

CAE WATCHES/WARNINGS/ADVISORIES

SC...None. GA...None.