textproduct: Chicago

KEY MESSAGES

- Much cooler temperatures expected today before temperatures gradually warm through the weekend and into next week.

- Elevated fire weather conditions Saturday and possibly again on Sunday.

- Stormy weather pattern returns towards the middle of next week.

DISCUSSION

Issued at 248 AM CDT Fri Mar 27 2026

Through Sunday:

The cold front that moved through the area yesterday is racing across the Ohio River Valley early this morning. The band of showers and thunderstorms behind the front also continues to drift southward and as of this writing is just about out of our forecast area. In their wake, a much colder and drier air mass is spreading across the Great Lakes which will result in a much cooler day for us. In fact temperatures today will only top out in the lower to mid-40s for inland locations while those near the lake remain in the mid to upper 30s courtesy of blustery north-northeast winds. Speaking of winds, gusts around 30-40 mph will linger through daybreak before gradually tapering to 20-25 mph this afternoon.

Heading into tonight, a broad surface high will move overhead this evening and allow the aforementioned gusts to fully diminish. Skies will also clear out under the high allowing temperatures to tank into the low to mid-20s overnight into Saturday morning.

Winds will become southwesterly on Saturday as the surface high pulls to our east which in turn will begin to advect in warmer air back to the region. Thus, highs on Saturday will be closer to typical late March readings in the upper 40s to lower 50s. The warmer temperatures will also allow for deeper mixing and increase wind gusts into the 20-25 mph range Saturday afternoon. Given that dew points on Saturday are not expected to recover (remain in the upper teen to lower 20 degree range) there is a concern for elevated fire weather conditions as RH values are forecast to dip into the 25- 35% range. That said, with the rain seen yesterday suspect that most of the more robust fuels may retain their moisture and limit some of the threat but finer fuels could dry out and result in quicker fire spread.

Similar conditions are expected for Sunday but with warmer temperatures (highs in the lower 60s) and higher dew points (in the lower to mid-30s). These conditions should result in higher RH values and thus limit the fire weather concern, however, if dew points struggle to improve Saturday night then another day of elevated fire conditions could linger through Sunday. Bottom line anyone planning to do any outdoor burning this weekend should keep a close eye on the forecast in case conditions worsen.

Sunday Night through Thursday Night:

As we enjoy a quiet weekend weather wise, a deepening shortwave trough is forecast to begin moving onshore across the Pacific Northwest on Sunday ahead of broader troughing that looks to arrive towards the later part of next week. While the shortwave is currently forecast to traverse across the northern CONUS, it is expected to eject a weaker shortwave that will be over the southwest CONUS towards the southern Great Lakes by Tuesday. Ahead of this southern shortwave will be a warm front that is forecast to lift through northern IL and northwest IN on Monday. Moisture immediately along the front looks to be rather limited which should keep dry conditions in place for the daytime hours on Monday. Temperatures will be on the rise Monday with highs forecast to be back into the lower to mid-70s for most. However, as is typical with warm fronts this time of year the cooler waters of Lake Michigan may limit its northward progress and result in onshore winds and notably cooler temperatures along the IL shore.

Heading into Monday night, the continued mid-level southwesterly flow should begin to advect in more moisture. This increasing moisture in combination with the weak shortwave, warm advection, and steepening mid-level lapse rates looks to favor the development of showers and thunderstorms Monday night into Tuesday. However, if low- level moisture struggles to return as quickly as forecast (and/or Sunday comes in drier) then shower/storm coverage may be more hit and miss with most areas remaining dry. Given the uncertainty in moisture return saw no need to adjust the WPC/NBM POPs for this timeframe, but suspect further refinement will be needed as we get closer.

Regardless of how Monday night plays out, the stronger northern stream shortwave is expected to develop a surface low across the Upper Midwest and northern Great Lakes which looks to force a cold front across northern IL and northwest IN on Tuesday. The continued warm-moist advection ahead of the front in combination with the much stronger forcing should result in a higher coverage of showers and thunderstorms Tuesday afternoon into Tuesday night. In fact, forecast soundings Tuesday afternoon do show around 40-45 kts of deep layer shear present which may allow for a few storms to become strong to severe.

After Tuesday the forecast becomes much more uncertain as ensemble guidance varies on what will happen with the cold front as it moves through Tuesday night. About half of the 00z ensemble suite show the front pushing south of the area Tuesday night which in turn allows a surface high to pivot into the Great Lakes and keep conditions more tranquil until the broader Pacific trough mentioned early arrives with another storm system next weekend. However, the other half suggests that the front may stall in the vicinity of central IL/IN and serve as the breeding ground for repeated rounds of showers and thunderstorms through the later half of the week as several shortwaves traverse the pattern. This high degree of uncertainty makes this part of the forecast low confidence and thus could not justify making any adjustments to the nearly constant 40-60% POPs offered from WPC/NBM from Wednesday onward. So while our official forecast will look very soggy next week, suspect some dry hours will be possible especially if the further solutions with the further south front verify. Regardless of how rain chances play out, temperatures through the end of next week look to remain seasonable with highs in the 50s to around 60.

Yack

AVIATION

Key Messages: - North-northeast winds turning northwest for the afternoon, with gustiness (20-25kt) returning mid to late afternoon and evening - Variable winds closer to KMDW with lower confidence on specific winds mid afternoon through early evening. (NNE to NNW)

Winds are the initial concern, with varying winds in the vicinity of ORD/MDW (NNE to NNW). Strong high pressure will move in from the west through tonight, and this will trend winds toward NNW. This should also help erode the lower clouds across the eastern half of the airspace. Given the weakening pressure gradient over the area this afternoon, there may be a period of variability at KMDW, which has a decent chance to shift back to NNE at times. We will account for this with a TEMPO. At this time confidence is higher that KORD will hold a NNW versus a NNE direction for the period. KGYY will hold more of a north-northeast wind as well.

There is a weak system moving through Wisconsin that will graze the area, but at worst would lead to some lower VFR and MVFR cigs for a short time overnight, but VFR is most likely. Winds that normally ease in the evening will remain gusty out of the NNW ahead of this system. Once the high move in overnight, winds will ease and then transition to southwesterly on Saturday. Gusts will hold under 20 kt on Saturday.

KMD

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 7 PM CDT this evening for the IL and IN nearshore waters.