textproduct: La Crosse

KEY MESSAGES

- Rain moves into the region tonight into Wednesday morning (40-90%)with a rumble of thunder possible (20%) along/south of I-90. Most stay dry Wednesday apart from those north of I-94 where a transition to light snow occurs late in the day. Snow accumulations are expected to be minimal.

- Windy and very dry conditions are expected south of I-94 Wednesday afternoon. Windiest conditions are west of the Mississippi valley, where a Wind Advisory has been issued due to the likelihood (70%) for 45 mph gusts. Critical fire weather conditions are expected in NE IA due to the presence of more tall grasses while conditions in far SW WI are held back to elevated only due to the damp nature of many fuels.

- Rain changes to snow overnight Thursday and into Friday with measurable snowfall likely (50-70% chance) for much of the area. A narrow band of higher accumulations (3"+) is possible somewhere in the region however confidence in its exact location is very low.

DISCUSSION

Issued at 311 PM CST Tue Feb 17 2026

Rain and a rumble of thunder tonight, light snow north of I-94 tomorrow

WV satellite shows a vigorous upper trough over the Pacific Northwest with a 175+ kt southwesterly upper jet on the equatorward side of this feature advancing over the Front Ranges. A lead wave in the cyclonic flow over the western third of the CONUS is seen over WY/CO. At the surface, lee troughiness is ramping up as the upper trough moves over the Rockies. Expect rapid lee cyclogenesis in SE WY/NE CO/W NE as this area will be under the left exit region of the upper jet shortly. In our CWA, broad lee troughing to our west has led to east-southeasterly winds. With a surface high centered on the GA/SC/NC coast, trajectory of these surface winds traces back to the Gulf and moisture is increasing as a result with dewpoints rising into the mid to upper 30s.

Into tonight, WY/CO wave advances over our CWA and then pivots to N WI. As it arrives, increasing low level moist advection and cooling aloft with the wave should combine to allow a few showers and potentially (20%) a rumble of thunder to develop. With MUCAPE of less than 250 J/kg and storms strongly favored to be elevated and thus unable to access much of the ~50 knots of sfc-6km bulk shear that looks to be present, concern for a stray strong to severe storm is very low.

Windy and very dry Wednesday

Through tonight, aforementioned upper jet advances over NE/KS/IA/IL/S WI with the surface low shifting into central MN accordingly. GIven robust upper support from that jet and the advancing WY disturbance, this low will deepen as it moves into MN with both the surface pressure gradient and height gradients aloft tightening in response. Consequently, 75/45/35kt 700/850/925mb jet advances over the CWA with 17.12z bufkit guidance suggesting average winds in the boundary layer during the day will be around 40-45 knots. Have therefore pushed the forecast toward the high end of guidance winds and wind gusts. As for exact speed, 17.13z NBM suggests a 60% chance for a 45 mph gust along and southwest of a Rochester-Decorah-Plattenville arc while 17.12z HREF/REFS suggest a 50-80% chance for this to occur across all areas west of the immediate Mississippi valley terrain. Given the strong dynamics at play, think the more aggressive probabilities will carry the day. Have therefore issued a Wind Advisory for strong gust potential from mid-morning tomorrow through the afternoon.

In addition, the strong winds will lead to very dry conditions roughly along and south of I-90. Progged soundings suggest the atmosphere will become very well mixed by the afternoon which usually heralds dewpoints well below blended guidance. Indeed, dewpoints across the central High Plains this afternoon are running around 5-10 degrees below NBM. Have moved forecast dewpoints from the 17.13z NBM values to a blend of short term guidance, yielding values in the teens across NE IA and far SW WI. This will lead to elevated and critical fire weather conditions depending on fuels, as discussed further below.

Thursday - Friday: Accumulating Snow Potential

By the time Thursday rolls around, a secondary shortwave trough will swing through the Central Plains and eventually becomes a closed 500mb low as it pushes north/northeast through Wisconsin. Deterministic guidance shows a scenario where a very interesting interaction occurs between this closing off low as well as the remnant upper-level from previously mentioned system which do a fujiwhara-like interaction. In this scenario, an associated surface low with this incoming disturbance both deepens and pivots northeast as it occludes through Wisconsin overnight Thursday and into Friday before exiting to the east. Would need to watch in this scenario how a 600-800mb frontogenesis axis manifests as an initial TROWAL/WAA in the warm sector of the low would allow for a trailing fgen band within the deformation region on its western flank. As the low occludes, this would allow for warm air aloft to push in from the east and reinforce this frontogenesis while pivoting it to a more north/south orientation as shown in the 17.12z deterministic GFS/NAM which would likely result in more efficient snowfall rates where this band occurs for several hours (the exact location of this band is very contingent on the exact position of the corresponding surface low). An alternate scenario to this would be that you do not get occlusion of this surface low and it simply pushes quickly northeast and the stronger frontogenesis would likely not be sustained at any particular location for a longer period. In this case, would expect a broader area of lesser impactful snowfall amounts. Overall though, important to note that the surface low position is still very uncertain with this system as there remains vast spread in both the AIGEFS ensemble data sets with roughly 200 miles of variance (Anywhere from Grant County, WI to central Lake Michigan) for Thursday night, so really cannot say confidence is overly high where the most impactful snow will setup at this point.

Looking at the probabilities in the grand ensemble (GEFS/EC/Canadian ensemble), confidence remains fairly high (70-80%) for measurable snowfall across much of the local area. However, when looking at probabilities for amounts in excess of 1 inch, probabilities in the grand ensemble have actually slightly decreased from yesterday (roughly 30-40% areawide). However, this may be a facet of this secondary scenario where you have the low occluding which provides more areal spread amongst the membership. Now when you look at the higher percentiles and each individual member of the grand ensemble (GEFS/EC/Canadian ensemble), many members display this banded nature to the snowfall but with extensive location variance. As a result, the 90th percentile to ensemble maximum pretty uniformly range from 4 to 10 inches with even higher amounts in a few member across at any given location in the local area. So this illustrates that this banded scenario is out there in the ensemble probabilistic space, but the location of it is not at all defined. Thermal profiles within the stronger forcing in the 17.12z GFS/NAM would suggest snow likely being on the wetter side (about 8-12:1 snow-to-liquid ratio) with much of the column residing between 0C and -5C and only around a 50-100mb depth of saturation in the DGZ.

In short, the main forecast considerations with this system is that there is the potential for a narrow band of impactful snow to develop in the Upper Midwest Thursday night and into Friday. However, the location of where this would setup is very uncertain at this point as there still remains substantial variance in the position of the surface low associated with this system. It is certainly possible that many locations will see minimally impactful snowfall with a narrow, more focused corridor of higher impactful snow. Be sure to stay tuned to the forecast as details will certainly change!

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1132 AM CST Tue Feb 17 2026

MVFR ceilings should develop tonight as increasing moisture also leads to showers during a 4-6 hour period. Arrival of much drier air should scatter out the clouds and shut off rain potential by 12z. Areas around and east of the Mississippi may (25%) see TS during this period as well so have included a PROB30 in the LSE TAF while omitting it from the RST TAF. Winds, initially out of the southeast, will become out of the west-southwest around 12z Wednesday with strong gusts to 35 knots possible west of the Mississippi. Before these winds increase at the surface, a 20-30 knot difference in wind speeds is expected in the lowest 2 kft of the atmosphere. However, very little change in wind direction within this 2 kft is expected so have refrained from adding LLWS to the TAFs.

FIRE WEATHER

Issued at 311 PM CST Tue Feb 17 2026

Windy and very dry conditions are expected Wednesday along and south of I-90. Efficient mixing will likely (60%+ chance) lead to RH values dropping below 25 percent south of I-90, likely below 20 percent in NE IA and far SW WI. As this occurs, wind of 20-30 mph with gusts to 45 mph are expected in this area, especially west of the Mississippi in NE IA. Limiting factor for fire weather is the state of the fuels with many locations still damp and muddy from recent snow melt and additional light (0.25" or less) rain expected tonight. With tall grasses more common in NE IA, thinking critical conditions are favored there while far SW WI favors elevated.

ARX WATCHES/WARNINGS/ADVISORIES

WI...None. MN...Wind Advisory from 9 AM to 6 PM CST Wednesday for MNZ086-087- 094-095. IA...Wind Advisory from 9 AM to 6 PM CST Wednesday for IAZ008>011- 018-019-029-030. Fire Weather Watch from Wednesday morning through Wednesday evening for IAZ008>011-018-019-029-030.