Marine Weather and Tide Forecast for La Porte, IN

DISCUSSION
Issued at 303 AM EDT Wed Apr 30 2025

Brief surge of postfrontal negative theta-e advection overnight has resulted in a 30 degree drop in surface dewpoints and will maintain tranquil weather through most of today. SSW flow ramps up once again by late today though as upper low currently seen pivoting through the southwest CONUS begins to eject NE. The initial (elevated) isentropic ascent is not particularly impressive. 300K analysis shows just a brief period of modest cross-isobar flow that will be intersecting a very dry and stable ambient airmass. A few very light showers are possible in our W/SW zones during the late afternoon but by and large expect most locations to remain dry. Late day WAA will help push highs into the mid/upper 60s despite cool start this AM and increasing clouds PM.

Much better chances for rain arrive overnight as the surface warm front strengthens and lifts northward into our area. Much stronger and deeper isentropic upglide noted by late tonight as the nocturnal LLJ ramps up with approaching shortwave. This initial shortwave arriving late tonight is not the primary trough/vort max ejecting out of the Southwest but rather a convectively-modified shortwave associated with the remnants of convection developing over the Ozarks later today. This leads to some increased uncertainty in the exact placement of heaviest rain which some hi-res CAM's suggest may pass just to our northwest. This uncertainty is already reflected well in inherited grids with highest PoP's and QPF in our NW zones and have generally kept that trend. Do think even our SE zones have a chance of at least SCT showers late tonight into Thu morning.

Thu will feature the best rain chances for most of the area.
Southern stream shortwave zips NE as another potent northern stream trough dives SE into the region. This leads to a prolonged period of moist SW flow and broad isentropic ascent. It won't be an all-day soaker but most locations are likely to see at least some rain at some point during the day. Initial cold front passes Thu evening and there is some potential for better instability to build in our E/SE zones and support a chance for a few strong storms as suggested by the 00Z NAM. There will be a lot of prefrontal clouds/precip though and surface dewpoints may struggle to get much above 60F. Will certainly keep an eye on this period but the severe risk appears low in our area at this point (especially north of US-24).

With the secondary trough digging SE, precip chances will linger into Fri night with a prolonged period of cyclonic low level flow until main trough axis finally passes Sat morning. Better moisture will be steadily pushed E/SE though and any showers will remain on the SCT side. Left in a slight chance thunder mention given cold temps aloft (below -20C at 500mb) but severe weather is not expected. Cooler weather also returns briefly with this trough.
Anticipated highs in the 50s on Sat and lows touching 40F both Fri and Sat night.

No significant changes to NBM initialization in the extended though did maintain a dry forecast for now...supported by vast majority of ensemble guidance. It should be noted deterministic ECMWF still has a cutoff upper low over our region during this period which would bring a persistent low chance for rain.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
Issued at 129 PM EDT Wed Apr 30 2025

Dew points fell down into the 30s last night into this morning and this will allow some time before rain arrives at the terminals.
It'll likely take until later tonight to begin to get lowered flight conditions, likely into MVFR, but perhaps a few hours dipping into IFR. Wind-wise, east southeast winds today become southerly Wednesday morning with gusts picking up by that time as a low level jet moves into the area.

IWX WATCHES/WARNINGS/ADVISORIES
IN...None.
OH...None.
MI...None.
MARINE...None.