Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
271 FXUS63 KARX 051653 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 1155 AM CDT Fri Jul 5 2024 .KEY MESSAGES... - Seasonably cool today with scattered showers and storms. - Unsettled weather continues through the weekend into early next week, however severe weather and additional flooding concerns remain low through the weekend. && .DISCUSSION... Issued at 330 AM CDT Fri Jul 5 2024 Overview: Latest water vapor satellite imagery, 500mb heights, and lightning showed the closed low over southern Minnesota. The convection had pushed off to the east with showers and a few isolated strokes of lightning rotating around the closed low. Rainfall reports included 0.57 at Rochester, 0.51" at La Crosse, and 0.61" here at the NWS. Winona, Sparta, and Boscobel all reported over and inch. At 08Z, surface low pressure extended from southeast MN into southern WI. With the wet ground and low dewpoint depressions we had a variety of low clouds, patchy fog, and some patchy dense fog. Patchy morning fog then seasonably cool today with scattered showers and storms: The 500mb trough over the Upper Mississippi Valley slowly pushes across Wisconsin today into the Great Lakes tonight. A look at the HREF probabilities show the widespread west to east area of precipitation across the northern portion of the area of mid-level low pressure shifts east into the U.P. this morning with the axis becoming more tilted in a southwest to northeast area around the low pressure system. Farther to the southwest, the showers and thunderstorms are more scattered. There are hints of higher probabilities in that axis during peak heating and especially near and northeast of I94 in the 2-4pm timeframe. General thunderstorms are expected today with MLCAPE of up to 500J/kg and little shear. That being said, did look into the non-supercell tornado parameter with the upper low nearby. This value was non-zero from 1 to 3 across parts of the forecast area; near EAU, and I90 around 2 or 3pm. Something to keep in mind during the day if instability increases or there is a local boundary. The HREF shows some 30-60% 25mi neighborhood probabilities of 1"/6hr rates during this time. Our current forecast generally has rainfall amounts of 0.25" or less as the system exits the area, however there could be pockets of higher amounts where the rainfall is a little more efficient along and northeast of I94, where there are thunderstorms, or in general where the precipitation repeats over the same areas. Temperatures are forecast to be below normal today generally 69 to 75, being held down by the clouds and scattered showers/a few storms. If it breaks out more earlier, temps could top out a little warmer with the July sun. Unsettled weather continues through the weekend into early next week, however severe weather and flooding concerns remain low through the weekend: An upstream shortwave trough over Alberta, Canada is forecast to drop southeast Saturday toward Minnesota and continue eastward Sunday into the Upper Mississippi Valley. Trailing trough energy lags and deepens over the Northern Plains. This prolongs the rainfall chance into Sunday night through Tuesday night. Temperatures warm into the mid 70s to lower 80s Saturday with isolated showers in the morning and scattered showers/storms in the afternoon. MLCAPE is modest, 750 to 1500 J/kg with little shear. The shortwave that moves through the flow Sunday appears to have little instability to work with. The low level forcing is a little stronger and the shear increases over parts of central Iowa. At this time, severe weather and flooding concerns appear low through the weekend. With the 500mb trough still in the area Sunday night into Monday and a surface front in the area, we will remain vulnerable to showers and thunderstorms. Spotty showers linger for Wednesday and Thursday with a large 500mb ridge to the west. Temperatures for the weekend into mid-week remain near to below normal in the 70s to lower or mid 80s. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1155 AM CDT Fri Jul 5 2024 CIGS: BKN MVFR looks to hang around for the early part of the afternoon with the RAP/HRRR soundings suggesting a gradual lift into VFR as the afternoon wears on. Should see an exit southeast with a scattering into the evening. WX/vsby: scattered -shra will persist through the rest of the afternoon as weak instability works with an upper level shortwave. Isolated thunder possible. -SHRA or VCSH could cover the likelihood/coverage with most vsby impacts holding at P6sm. However, could see a dip to 3SM with any moderate shower. Showers will shift southeast through the afternoon with decrease in areal coverage with loss of daytime heating. With clearing skies and saturated grounds/near sfc layer - some concerns for fog. Not a lot of consensus for where or how widespread the potential would be in the short term guidance, so opting to not add to forecast yet. Will keep a close eye though and adjust as needed. WINDS: north/northwest becoming light for the night time hours. Expecting a shift to the southwest moving into Sat afternoon. && .HYDROLOGY... Issued at 300 AM CDT Fri Jul 5 2024 Rainfall amounts were generally less than an inch across the bulk of the forecast area, however some pockets of 1 to 2"+ did occur. Some of these localized amounts fell over the Whitewater, Root River, Kickapoo, Pine River, and Wisconsin River Basins, and the Mississippi River mainstem. As a result, we are seeing some river rises and some minor flooding on the Kickapoo and Pine River. In addition, this widespread rain will prolong the flooding along the Mississippi River mainstem. Although rainfall is generally forecast to be a quarter of an inch or less for most locations today. Some isolated locations could pick up more. Some of our hi-res guidance shows some low to medium probabilities of 1" in spots along and east of I94. Locally higher amounts can occur with any storms. Through the weekend, the additional rainfall is not expected to increase flooding concerns. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Zapotocny AVIATION.....Rieck HYDROLOGY...Zapotocny