Marine Weather and Tide Forecast for Rochester, MN

DISCUSSION
Issued at 200 AM CST Sun Dec 8 2024

- MILD START TO NEW WEEK: more 40s to near 50 for highs today

The atmosphere squeezed about all the warmth it could out of itself with strong mixing Saturday, pushing highs into the 50s and flirting with some records. A couple more relatively warm/mild days are ahead today and Monday, but even if similar mixing would be realized, the air a loft isn't as warm, and nor should the resulting sfc temps.
EFIs in for Tmax also lower for today/Mon compared to Sat (dropping from near 0.8 to closer to 0.5). Highs Mon could be in the morning for locations to the northwest as a cold front is slated to push through in the afternoon with temps likely to steady/slowly fall after the boundary passes.

- PCPN CHANCES TONIGHT-WED? some drizzle potential in the east tonight, low end snow shower chances and/or periodic flurries Tue night/Wed.

A variety of forcing mechanisms - shortwave troughs, sfc boundaries, low level thermodynamics and increased near sfc lapse rates to name a few - will play roles in pcpn chances over the next few days. No notable (well developed) system of note though, making pinpointing chances/locations problematic. Saturation will be a limiting factor.
Also, QPF looks light so models are struggling with producing much/if any pcpn chances. Per coordination with surrounding offices, will add at least low end chances (20%) to the Tue night/Wed time frame. Periods of higher chances are possible, with some convective elements added to the mix. Expect adjustments to pcpn chances over the next few days.

Turning back to tonight, a shortwave trough is on track to spin over the region with the short/medium range guidance holding the bulk of their QPF well north, associated with the deeper QG convergence/saturation. However, the models also show an increase in low level thermodynamics ahead of an associated sfc front. If saturation can deepen enough, drizzle would be a good bet. The NAM12 suggests as much, but also tends to oversaturate the near sfc layer.
Won't add to the forecast yet, but its something to watch.
Temperatures look to be warm enough to stay liquid (if it manifests).

- MIDWEEK BLAST OF COLD: highs could struggle to reach 20 for most locations Wed and Thu

Cold returns post the first shortwave late Mon night/Tue with a colder slug of air dropping in Wed night as the second shortwave swings through. The models have been trending colder with this second wave. The last several runs of the WPC clusters showing a steady, gradual increase in an anomalously strong 500 mb trough over the western great lakes at 00z Thu. 10 to 90% spread in potential high temps in GEFS and EPS have been tightening, trending toward highs under 20 for Wed/Thu areawide. Further, 850 mb temp anomalies have increased (around -2 now) in the NAEFS/EC at 00z Thu and the EFIs in Tmax also showing a jump to -0.80, although mostly across northeast MN/northern WI. Steady signals for a return to some winter cold - albeit just for a couple days. Long range guidance continues to drive a shortwave ridge across the region by Fri, with more progressive-zonalish flow through the weekend. Temps would rebound to more seasonable levels in this scenario.



AVIATION /06Z TAFS THROUGH 06Z MONDAY/
Issued at 1023 PM CST Sat Dec 7 2024

A stratus deck continues to move in from the north with MVFR cigs being possible (30-50% chance) across portions of northern Clark and Taylor Counties overnight. Otherwise, VFR conditions are expected throughout much of the daytime hours with winds shifting during the evening from southeasterly to westerly and increasing to around 8-10 kts as a low pressure system passes north of the region. MVFR to IFR reductions may be possible (40-60% chance in the 08.00z HRRR) east of the Mississippi River towards 06z Monday with some low-level saturation displayed across some of the CAMs. However, given that RAP/HRRR soundings have winds of around 20-30 kts just off the deck and some mid-level clouds, it remains unclear how this will manifest at this time.

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