Marine Weather and Tide Forecast for Rochester, MN

DISCUSSION
Issued at 347 AM CDT Fri May 23 2025

Another Cool & Dry Day Today:

Similar conditions to yesterday (Thursday) are expected with daytime mixing causing some lower level cumulus. Unlike yesterday, expect mid to upper level overcast skies to build in through the afternoon. Given current timing of clearer skies concurrent with peak diurnal heating, have reduced dewpoint temperatures slightly as 23.00Z RAOBs, POES, and high resolution forecast models show drier air off the deck that may be tapped into during peak diurnal heating. All in all, quite a persistence forecast.

Low Light Rain Chances Saturday:

A narrow plume of low level drier air cyclonically curved through the Mississippi River Valley, today will be reinforced by even drier air sagging southwest out of northern Ontario on Saturday placing a surface boundary from northwest to southeast across the forecast area. While there is /some/ moisture abutting the frontal boundary, a 6C isodrosothermal gradient across Iowa is the clue that overall moisture will be a limiting factor for rain. The best moisture will lie well to the south with the warm front zonally draped from Nebraska through Kentucky. Most recent high resolution convective allowing models have been clueing in on local rain potential while accompanying soundings do show /some/ steep mid level lapse rates providing some instability. All in all, have increased non-mentionable PoPs for Saturday as confidence is low but can't rule out light rain in the local area.

Very Low Light Rain Chances Sunday:

Similar to Saturday, although with an even drier airmass in place, there may be a chance for light rain with current confidence primarily in central Wisconsin. NAM and GFS model soundings show steep low to mid level lapse rates causing some instability but again, the overall lack of moisture limits any confidence. While overall LREF confidence in measurable precipitation is very low (6-15%), the GEFS suggests a stronger frontal boundary locally abutting /slightly/ more moisture and as a result has 75% probability for measurable precipitation in central Wisconsin. Haven't adjusted from the <10% NBM PoPs at the current forecast hour but could be a small change made in coming forecasts.

Precipitation Chances Through Next Week:

Light precipitation chances occur nearly daily for the rest of the forecast period as a Rex Block sets up through next week.
An amplified ridge downstream over Quebec on GOES WV early this morning acts to separate a negatively-tilted trough from it's parent flow over northern Manitoba on GOES WV imagery, allowing an amplified upstream ridge to encapsulate the eventually closed low beneath it. Long term global ensemble confidence for the 576dam at 500mb spans from 50-80% in the GEFS, 10-40% in the CMC, and 20-80% in the EPS. The low to moderate confidence for the synoptic ridge means local impacts are likely to change over the next few days.

As is expected from Rex Block's, being closer to the Low will likely provide precipitation chances. Current confidence of 10-40% for 0.01" over 6 hours repeats daily in LREF ensembles while increasing near 75% some days in the their clusters. Overall impacts expected to be limited though as PWATs will be near normal (1"-SPC Climatology) with LREF ensemble 25th of 0.8" and 75th of 1.2".

Staying Cool Through Much of Next Week:

The Rex Block also continues the recent below normal temperatures over the next few days with daytime highs from the 60s to low 70s and overnight lows mostly in the 40s. Current LREF confidence calls for the low center to be parked quite close by through much of next week, keeping a corridor of below normal low level temperatures from the Mid- Atlantic to the Central Plains with anomalously warm temperatures to the north.
Given the location of the most anomalous (+15C) warmth of 15C-20C (23.00Z LREF Cluster) in Canada, a somewhat counterintuitive southern shift of the low pressure will provide warmer temperatures locally but would require weakening of the ridge.

While not overly impactful, it might feel slightly colder for some as the 50 degree isodrosotherm flirts the forecast area potentially keeping RHs near 70% for some time. May also see periods of nighttime fog.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/
Issued at 556 AM CDT Fri May 23 2025

VFR expected through the 23.12Z TAF period besides potential fog IFR-LIFR-VLIFR visibilities only in central Wisconsin locally at KMDZ.

ARX WATCHES/WARNINGS/ADVISORIES
WI...None.
MN...None.
IA...None.