KMSP → KMSN → KOSH

Executive Summary

This is an afternoon VFR day with a narrowing convective window — the flight itself is workable, but the destination is forecast to go convective within roughly 30 minutes of your planned arrival. The primary risk is the afternoon/evening thunderstorm cycle over the KOSH area: WFO Green Bay forecasts TSRA from approximately 22Z with severe-capable storms (winds >50 kt, large hail), and your ETA is 21:34Z — leaving only a ~25-minute margin before the storm clock starts. Compounding this, KOSH is hosting EAA AirVenture (TFR NOTAM 6/5564 active 19:15Z through July 23), which means a mandatory special arrival procedure and non-standard traffic environment. CONDITIONAL GO — the flight is flyable if you depart on time and arrive ahead of convection, but you must brief and comply with the AirVenture arrival NOTAM before departure, and you must have a firm divert plan if convection initiates early. The single most important trigger: if KOSH convection initiates before 22Z or ATC/ATIS indicates storm activity in the arrival area, do not continue — divert to an alternate.

Route Hazards

Before Departure — What to Recheck

• EAA AirVenture arrival NOTAM — mandatory. Brief the full NOTAM before taxi. The KOSH arrival procedure during AirVenture is non-standard (typically the RIPON/FISK VFR arrival corridor with mandatory altitude and speed requirements, and non-standard tower/CTAF procedures with extremely high traffic volume). Verify which procedures apply for your specific arrival window and aircraft type — this is not optional. Download or print the current NOTAM.
• TFR confirmation: NOTAM 6/5564 is active at your 20:00Z departure and covers 0–16,000 ft over Oshkosh. Confirm the lateral boundaries on tfr.faa.gov and verify your routing enters the TFR only via the published arrival procedure.
• Convective timing check: Pull the latest KOSH ATIS and check radar (recalling that datalink NEXRAD can lag 15–20+ minutes from real-time — it shows where weather was). WFO GRB forecasts TSRA onset around 22Z. If any convection is already initiating over central/north-central Wisconsin at your departure time, consider delaying or holding at MSP until the picture clarifies.
• LLWS check: G-AIRMET LLWS is active on the route through 21:00Z. Check the latest departure-area PIREPs before taxi; if shear reports are appearing on the KMSP climb-out, get the specifics before committing.
• KMSP departure TAF re-read: At ETD the FM202000 group is in effect: 28016G28 kt, P6SM, SKC. Confirm no new convective SIGMETs or CWAs have been issued for the KMSP area — convective sigmets 80C and 81C expired before your departure but the underlying instability is still present in the region.
• File IFR or confirm VFR flight following: With a TFR arrival environment, high traffic, gusting winds, and afternoon convection, IFR is strongly recommended for the additional ATC coordination and positive separation. At minimum, obtain VFR flight following from KMSP clearance delivery or Minneapolis Center.
• Alternate fuel: Plan fuel to reach KOSH and continue to your alternate (see If You Go section) plus reserves. Convection or holding delays at KOSH are realistic given AirVenture traffic.

Leaving KMSP — Departure at 2026-07-20 15:00 CDT (2026-07-20 20:00Z)

At generation time (approximately 15:53 CDT / 20:53Z), KMSP was reporting winds 240 at 11 gusting 19 kt, 10 SM visibility, broken ceiling at 1,900 ft, and a second broken layer at 20,000 ft — MVFR ceilings currently. However, the TAF FM202000 group takes effect right at your departure and forecasts a significant improvement: 280 at 16 gusting 28 kt, more than 6 SM, sky clear. The WFO MPX discussion confirms high confidence that morning convection is done and afternoon storms are not expected to affect the KMSP terminal area. This is a VMC departure — the current MVFR ceiling should be lifting and clearing as the westerly wind shift arrives. You should expect a brief layer penetration through the broken deck at approximately 1,900 ft AGL during initial climb, but conditions above that should be clear.

The departure wind of 280G28 kt is from the right and slightly behind your eastbound route. Expect some turbulence during the climb through the wind shear environment, and be alert to the G-AIRMET LLWS advisory active through 21:00Z. At KMSP's elevation of 842 ft MSL, density altitude at generation time is approximately 2,700 ft — factor this for takeoff performance, particularly on the shorter runways. The KMSP Class B requires an ATC clearance for departure; with a flight plan filed this is routine, but plan your routing to account for the Class B shelf (penetrated from roughly 0–30 nm along the route during your climb).

KMSP Facility note: Training flights are prohibited; GA aircraft must terminate at the FBO. Noise abatement procedures are in effect (contact 612-726-9411 if needed). Birds are reported on and in the vicinity of the airport.

The Ride at 8,000 ft

Winds Aloft

At 9,000 ft MSL, the route is solidly eastbound and benefits from a consistent westerly tailwind component throughout. Decoded from the 1200Z sounding valid 1800Z:

Bottom line: strong tailwind throughout, particularly early in the flight near MSP (~36 kt). Expect a groundspeed boost of 20–36 kt over your cruise TAS. The 259 nm route with an estimated block time of roughly 94 minutes should come in on or slightly under that estimate. The tailwind decreases as you approach KOSH (GRB shows ~20 kt component), so factor this into your arrival fuel calculation. Crosswind components are all right-to-left or left-to-right in the single-digit to mid-teen range — manageable throughout.

Ride Quality

Expect smooth to light chop at 8,000 ft in the KMSP–KOSH corridor during the flight window. Supporting evidence:

• GTG at FL090 (valid Mon 18Z) shows minimal EDR values — well below the moderate threshold — across the Minnesota/Wisconsin corridor in the flight window.
• LSE PIREP at 1618Z: FL070, SKC, turbulence negative. Clean air below the cloud tops at this level.
• MKE PIREP at 1617Z: FL130, light chop — above your cruise level.
• RFD PIREP at 1601Z: FL110, light to moderate chop — also above cruise altitude and south of route.
• The UUA urgent PIREP at IOW (Iowa City) reported severe turbulence FL100–120 at 1611Z — this is above your 8,000 ft cruise altitude and approximately 100 nm south of the route. It does not directly affect your flight, but notes the convective environment is active in the broader region today.

Near any convective cells that develop: moderate turbulence is likely, severe turbulence is possible. Give building cumulus and any cumulonimbus a wide berth — do not attempt to thread cells using datalink radar.

Icing

Icing is not a significant factor at your planned 8,000 ft cruise altitude.

SLD: No SLD signal exists on the route at any altitude during the flight window.

Altitude Strategy

• Best band: 6,000–9,000 ft. Strong tailwind, clear air, no icing, minimal turbulence. 8,000 ft as planned is appropriate. Temperatures at cruise are well above freezing (~+14°C) so no structural icing concerns in clear air.
• Worst band: Inside or adjacent to convective cells at any altitude. The afternoon storm cycle will produce cells with tops well above FL300; do not enter clouds associated with building convection regardless of altitude.
• Escape option: If convection initiates earlier than forecast and you encounter building cells en route, divert — KMSN (Madison) is roughly mid-route and is forecast VFR with no convection at the overfly time. Do not attempt to continue to KOSH through an active storm line. Descend is also available if high-level ride deteriorates, but at 8,000 ft you are already near the bottom of usable cruise altitudes for this route.

Getting Into KOSH

Generation-Time Conditions at KOSH

At generation time (~15:53 CDT / 20:53Z), KOSH was reporting: winds 210 at 7 kt, 5 SM visibility in haze, few clouds at 2,800 ft. MVFR visibility due to smoke/haze, but ceilings are acceptable. This observation was taken approximately 40 minutes before your departure and roughly 1 hour 40 minutes before your ETA — do not use it as your arrival forecast.

TAF Forecast at ETA (21:34Z)

The TAF group valid at your planned 21:34Z arrival is FM201700: 21014G22 kt, more than 6 SM, SCT150 — VFR. The smoke should be clearing ahead of increasing southerly winds per WFO GRB, and scattered clouds at 15,000 ft present no ceiling issue. This is a benign arrival picture.

The Critical Caveat — Convection Timing

The FM202200 group — beginning just 26 minutes after your planned arrival — forecasts 22013G22 kt, 6 SM, -TSRA, BKN040CB, with a TEMPO from 22Z–02Z of more than 6 SM, BKN060CB. WFO GRB is explicit: any storm passing over KOSH will be capable of producing severe winds over 50 kt, large hail, and heavy rain. The forecasters note possible two rounds of storms between 20Z and 04Z. Your 94-minute estimated block time from a 20:00Z departure gives an ETA of approximately 21:34Z — you will be on the ground before 22Z if everything goes smoothly, but that margin is narrow. AirVenture traffic congestion could add time to the arrival. If your ETA slips past 22Z for any reason, divert.

EAA AirVenture Procedures

KOSH is in the midst of EAA AirVenture. This is one of the busiest aviation events in the world. The arrival procedure is completely non-standard — not just a busy tower, but a published special NOTAM arrival corridor (historically the RIPON/FISK VFR arrival for VFR traffic, with separate IFR procedures). Do not attempt to arrive at KOSH without fully briefing the current AirVenture arrival NOTAM. Expect:

• Non-standard tower frequencies and CTAF procedures
• Extremely high traffic volume — possible sequencing delays
• Mandatory altitude, speed, and communication requirements per the NOTAM
• Plan fuel for possible holding if sequencing delays occur

Verify the current AirVenture arrival NOTAM at notams.faa.gov or through Flight Service before departure — procedures change year to year and the specific NOTAM text governs.

Runway/Wind at Arrival

With TAF winds 210 at 14G22 kt at ETA, the favored runway will likely be from the south — Rwy 18 (8,002 ft, ILS and PAPI available) is well aligned with a 210° wind. Rwy 09/27 (6,179 ft, PAPI, concrete) would carry a crosswind component. AirVenture procedures may dictate specific runways regardless of wind — defer to current NOTAM and tower/ATIS. Verify approach availability in the current Chart Supplement and per the AirVenture arrival NOTAM. Maximum weight bearing capacity at KOSH is 50,000 lbs — not an issue for typical GA aircraft.

Estimated Block Time

Distance: 259 nm. Estimated block time: roughly 94 minutes. With ~20–36 kt tailwind, actual flight time may be slightly shorter, but allow additional time for AirVenture sequencing.

Practical Alternates

Primary alternate: KMSN (Dane County Regional, Madison, WI) — approximately 70 nm southwest of KOSH, forecast VFR at your flight time (TAF: 21011G19 kt, more than 6 SM, SCT070 in the overfly window, no convection until after midnight). This gives solid weather separation from the KOSH storm cycle, is GA-friendly, and is already in your route data. Confirm the 14 CFR 91.169 alternate requirement using the KOSH TAF and your ETA window — with CB forecast at the destination within an hour of ETA, an alternate is highly advisable. Carry fuel to KOSH plus KMSN plus 45-minute reserves.

Fly or No

CONDITIONAL GO

Hard Stops

1. AirVenture arrival NOTAM not briefed — do not depart. TFR NOTAM 6/5564 is active from 19:15Z (already in effect at your 20:00Z departure) through July 23 at 23:30Z, covering 0–16,000 ft. Entry into the KOSH area requires full compliance with the published AirVenture special arrival procedures. Brief the complete NOTAM before taxi; do not enter the TFR without it. This is a regulatory hard stop, not a weather issue, but it blocks departure until compliance is confirmed.
2. Do not continue to KOSH if convection has initiated over the arrival area at or before your ETA. If KOSH ATIS, ATC, or radar (with appropriate lag caution) shows storm activity in the terminal area at or before 21:34Z, divert to KMSN or another alternate. Do not attempt to land ahead of a severe-capable storm line.

Why Not NO-GO

The weather picture is workable: KMSP departure is forecast VFR with no convection at ETD; the en route environment at 8,000 ft is clear with a strong tailwind; KOSH is forecast VFR at ETA (21:34Z) with the storm window opening approximately 26 minutes later. The WFO forecasters note timing uncertainty — the storms may hold off until 22Z or later. The flight is executable and the margins, while slim, are real. The conditions that would warrant NO-GO (convection at KOSH before ETA, TFR non-compliance, or LLWS confirmed at the departure runway) are not currently present.

Watch Items

• LLWS G-AIRMET active through 21:00Z on the route — monitor departure-area PIREPs and be alert for airspeed/altitude excursions during climb-out from KMSP.
• Smoke aloft along the entire route — slant-range and forward visibility may be reduced even when reported surface visibility is VFR. Use caution on final approach, particularly if sun angle is unfavorable.
• Gusts to 28 kt at KMSP on departure and 22 kt at KOSH on arrival — verify crosswind components against your aircraft's demonstrated crosswind capability.

What Changes This Call

• Convection at KOSH at or before 21:15Z (15+ minutes before ETA) — abort or hold; do not continue into an active storm environment. If radar and ATIS show cells within 20 nm of KOSH at your ETD, consider delaying until the first round passes or canceling.
• KOSH ATIS reporting ceilings below 2,000 ft AGL or visibility below 3 SM at any point after 21:00Z — storm outflow is ahead of you; divert to KMSN.
• Gusts at KOSH exceeding 35 kt on arrival (above the TAF forecast) — this is the leading edge of storm outflow and a divert trigger.
• AirVenture arrival NOTAM cannot be confirmed/briefed before departure — delay until NOTAM is in hand and fully understood.

If You Go — Do This

1. Brief the AirVenture arrival NOTAM completely before taxi. Download or print it. Know the entry fix, altitude, speed, communication requirements, and what to do if you can't comply. This is non-negotiable.
2. File IFR. With a TFR arrival environment, high traffic, and afternoon convection, IFR gives you ATC coordination, positive separation, and a cleaner path through the AirVenture procedures. If VFR, obtain flight following from KMSP clearance or Minneapolis Center at startup and keep it throughout.
3. Fuel for KOSH + KMSN alternate + 45-minute reserve. AirVenture sequencing can add time; budget for it.
4. Check radar immediately before departure — no cells currently depicted in the corridor is the baseline, but conditions can change within minutes. Note: ground NEXRAD is several minutes old, and cockpit datalink NEXRAD can lag 15–20+ minutes beyond its displayed timestamp (NTSB Safety Alert SA-017) — use it as strategic context, not real-time cell avoidance.
5. Get KOSH ATIS before top of descent. Confirm runway in use, winds, and no convective activity. If ATIS mentions any CB or storm activity, hold at a safe distance or divert.
6. Divert plan in hand: KMSN is your primary alternate — have the frequencies, current KMSN ATIS frequency, and fuel state at divert point already calculated before you leave KMSP.
7. Timing window: Departing at 20:00Z as planned is your best window — any delay pushes your ETA closer to the 22Z storm onset. If departure slips by more than 30 minutes (ETA beyond ~22Z), reassess whether the first storm round has occurred or is still building before committing to continue.
8. Contact Flight Service (1-800-WX-BRIEF) en route for updated weather and NOTAMs if conditions change — not Flight Service, which was discontinued in 2015. ATC can also provide weather updates workload permitting.
9. Verify tower hours and AirVenture procedures at KOSH in the current Chart Supplement and NOTAMs — confirm tower hours before departure, as non-standard event procedures may apply beyond the standard staffing schedule (0700–1900 per A/FD).
10. KMSP Class B: The direct route enters the Minneapolis Class B during your climb; ensure your IFR clearance or VFR flight following covers you through the Class B. If routing around it, verify on a current sectional chart.

Confidence

Medium.

The departure and en route picture are well-supported and high-confidence: KMSP clears to SKC at ETD, the ride is smooth with a strong tailwind, and no icing or significant en route convection is forecast. Confidence is capped at Medium due to:

• Convective timing uncertainty at KOSH: WFO GRB notes CAMs show two potential storm rounds and uses TEMPO groups specifically to account for lulls in storm activity — indicating real uncertainty about exactly when the first round arrives. The margin between your 21:34Z ETA and the 22Z storm onset is slim enough that a 30-minute early initiation changes the call.
• AirVenture traffic complexity: High traffic volume, non-standard procedures, and potential sequencing delays are inherently difficult to quantify in advance. A 10–15 minute sequencing delay pushes the arrival uncomfortably close to the storm window.
• LLWS altitude band unknown: The G-AIRMET LLWS has an unspecified altitude band in the available data, making it impossible to fully characterize the shear layer during climb-out from KMSP.

Confidence would increase to High if: convective CAMs consistently hold the storm onset at or after 22:30Z at the time of departure, and KOSH ATIS at departure time confirms VFR with no convective activity within 50 nm. Confidence would decrease (and the call would flip to NO-GO) if radar or ATIS at departure time shows convection already initiating near KOSH.