Shallow warm core!

ide-note:
Multiple structural changes occurred and will occur with the consolidating depression, which moves off the Bay of Biscay to the north/northeast. After initiated by a southbound moving upper low with a distinct tropopause fold during the overnight hours of the 21st to the 22nd, roughly 36h of a slightly less barocline atmosphere allowed for some low-end core modification, although negligible (and still classified as a true cold core low). As of writing (23rd), a plume of slightly modified tropical air (modified due to onshore trajectories into the depression's center), encircled most of the center and assisted in disorganized but slightly deeper convection with no distinct banding present. However this pushed the depression near the shallow warm core structure on available phase diagrams. During the afternoon hours of the 23rd however, an approaching frontal boundary from the NW marked the beginning of another round of enhanced baroclinity with models showing the evolution of a distinct tropopause fold over Ireland and UK during the forecast period, bending into the system. This increase of baroclinity results in a rapid deepening phase, which starts around the beginning of my forecast period and offers a central pressure drop of at least 10 K in probably less than 24 h while crossing UK from the SW with a strong turn to the NW during the night.

This results in a quite complex frontal and thermal structure of that low, as the majority of the models now propose some type of thermodynamic core modification. Current thinking is that a moderate warm-core seclusion takes place during the forecast although described history of that depression may offer a better defined LL warm core structure compared to truley extratropical cases. Latest ASCAT scans reveal a quite symmetric near surface wind field with uncontaminated 30-40 kt winds along the W/S and SE-ern fringes (much less defined along the NE quadrant) and this well defined wind field in the lower troposphere remains intact during much of the forecast period.

To complicate that scenario once more, ongoing baroclinic transformation will result in more typical vertical wind field distribution of the extra tropics along the southern fringe, as a strong mid/high-level jet moves in from the west and crosses N-France and Benelux during the night. Along the northern fringe of the depression however (e.g. N-UK and Scotland), no modification is expected until 06Z due to the dominant and still westward pointing wrap-around occlusion, which keeps the shallow warm core intact.