Marine Weather and Tide Forecast for Pottawattamie Park, IN

DISCUSSION
Issued at 254 PM EDT Mon Apr 28 2025

An area of low pressure moves from the Dakotas to the Northern Great Lakes area between today and tonight as a large trough gets sheared out across the Plains States. Locally, a warm from front associated with the aformentioned low pressure system is pushed northward through the area this evening. This allows better 60 degree dew points to creep into the area between 8pm this evening through 8pm Tuesday. Meanwhile, the better moisture axis works into the area just before 6z tonight through Tuesday afternoon out in front of a cold front moving through the area. There is 1500 J/kg of MUCAPE and around 750 J/kg of SBCAPE forecast to be moving through the area with the arrival of the moisture axis and better shear begins to poke into the area between 9 and 12z. During the overnight hours, it's often what's left of convection from the north that determines what sort of severe potential arrives with overnight convection in our neck of the woods. With convective inhibition and some question about a trigger for storms in the Northern Plains, what arrives here contains some uncertainty. The better low level turning of winds is actually with the overnight chance, but without the better heating with some question about if we'll even see storms during that time, the tornado threat is low. Cannot rule out a strong wind or hail threat with any convection that does arrive during the overnight into the morning though as mid level lapse rates reach around 8C/km with the EML. The cold front arrives during the late morning in our extreme northwest and may be able to spark some showers and storms during the afternoon (maybe 1 or 2pm at the earliest), but what the overnight convection leaves behind debris cloud-wise will help determine what instability is around for storms to use for the afternoon. The ultimate resting place for the outflow/cold pool boundary will also be key. The EML appears to be washed out and mid level lapse rates are reduced for the afternoon. The DCAPE values are also underwhelming. Even shear values appear reduced with 30 to maybe 40 kts of effective shear and marginal to weak helicity values. Some of these values could be convectively impacted by the model carrying through the convection/outflow boundary. It still appears that east of IN-15 or south of US-24 will be the main area of concern should things be able to refire. It should be out of the area by around 00z or 01z.

The cold front ends up draped to our south on a west to east plane Wednesday morning with surface high pressure to our north. We'll waiting for the southern part of the sheared energy, which has cutoff from the flow, to be captured by the next arriving trough and brought to the area Wednesday night. With an area of low pressure passing by to our northwest, we'll be in the warm sector for the morning into the afternoon and so we'll probably have some thunder, but there remains some uncertainty on severe weather potential. Some lingering rain may continue through Friday when the final area of deformation/final trough swings through.

The surface high pressure finally noses in on Saturday and dries things out for the weekend. We currently have upper 30s for highs Saturday morning so we'll need to watch for frost formation then, but the late departure of the moisture and arrival of the surface high may keep us out of the frost. Timing will be key.

One interesting aspect of this forecast is that blocking begins to set up across the Atlantic so that by day 7 (may 4th or 5th), strong anomalously positive heights build over Greenland. A strong ridge sets up across the southeastern US and a trough sets up across the western CONUS. On the early side of this block being set up, there could be some rain chances, but the longer this lasts, the greater chance that antecedent conditions could keep the area dry from pop showers and storms.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
Issued at 156 AM EDT Tue Apr 29 2025

Pre-frontal moisture transport will continue to ramp up during the overnight hours as low level jet axis shifts eastward. This low level will support LLWS conditions at both terminals through daybreak before better diurnal mixing occurs. However, even before this better daytime mixing during the remainder of the overnight hours, occasional sfc gusts to 25 knots are expected.
The increase in low level moisture will allow cap to erode for some highly elevated parcels that should support a isolated shower development and perhaps a thunderstorm. Coverage currently is expected to be limited enough to keep probability of occurrence at any one terminal point low through daybreak.
Best chance of thunderstorms still looks to be generally along and south of the US 24 corridor this afternoon. Did include a tempo thunder mention at KFWA during the mid-late afternoon hours with potential of thunder diminishing after 22 or 23Z.
Southwest winds gusting to 30 knots will continue through the day veering northwest post-frontal, with speeds diminishing to less than 10 knots later Tuesday evening as directions become northerly. Generally VFR conditions are expected through the period, with the exception of brief reductions to cigs/vsbys in any showers/storms this afternoon.

IWX WATCHES/WARNINGS/ADVISORIES
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 4 PM EDT this afternoon for LMZ043- 046.