Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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975 FXUS63 KARX 171658 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 1158 AM CDT Wed Jul 17 2024 .KEY MESSAGES... - Seasonably cool, dry weather will prevail through Friday, with slow warming into the weekend. - Scattered shower/storm chances (20-40%) at times this weekend into early next week, but organized heavy rain/severe weather potential is quite low at this time. && .DISCUSSION... Issued at 210 AM CDT Wed Jul 17 2024 Today-Friday: Seasonably cool and dry Canadian high pressure will build south across the Upper Midwest and Great Lakes regions through Friday bringing seasonably cool temps and dry conditions to the area. Diurnal cumulus development will occur this afternoon with boundary layer warming beneath the large upper trough/cold pool centered over the Great Lakes. Highs today will be mainly in the 70s, about 10 degrees below mid-July averages, with only slow moderation in temps by Friday as the surface ridge slides east of the area. Humidity levels will be very comfortable for mid-summer thanks to the Canadian airmass in place keeping dew points in the 50s. Although the dry air may be a limiting factor, with light boundary layer flow under the ridge, will have to watch for any early morning fog development over the next few mornings, especially in favored low-lying areas and valleys. Saturday-Tuesday: Slight warming with low shower/storm chances Some moisture increase will occur heading into the weekend and early next week back towards seasonal values as the surface ridge moves east. However, a stagnant, blocking flow pattern will evolve featuring an amplified western US ridge and broad, weak troughing across parts of the central plains/Mississippi Valley. Scattered diurnally enhanced showers/storms associated with weak lower predictability waves within the broader trough are possible during this time. However, there is not much signal for organized severe weather in this pattern with minimal shear. Little change in airmass will occur through this period with the global ensemble suite showing relatively small day-to-day temperature variation in the interquartile ranges. Highs generally in the the mid/upper 70s to low/mid 80s are likely this weekend through the middle of next week, near to a touch below average. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1157 AM CDT Wed Jul 17 2024 VFR conditions expected. There are a few signals for valley fog to affect the Mississippi river tonight and specifically the KLSE airfield. Radiational cooling, a deep very dry layer aloft, and light winds all are positives. There is some spread in the depth of the light wind layer overnight with the HRRR/RAP latest solutions showing the more aggressive 5kft depth. This would favor valley fog formation but there are a number of CAMS that suggest the layer is much shallower. Deeper mixing today and the north wind /even light/ overnight works against fog formation at KLSE per research and most of the guidance raw T-Td spreads are over 7F at 03Z. So, right now, have decided to leave valley fog visibility restrictions out of the TAF at KLSE but it cannot be ruled out. .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...JM AVIATION...Baumgardt