Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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835 FXUS63 KLOT 010533 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1233 AM CDT Mon Jul 1 2024 .KEY MESSAGES... - Dangerous swimming conditions at area beaches through tonight due to breezy onshore winds and high waves. - Return to more typical summer temperatures and humidity Tuesday onward with periods of showers and thunderstorms at times too. && .UPDATE... Issued at 849 PM CDT Sun Jun 30 2024 No significant changes to going forecast tonight into Monday. Sprawling, 1026 mb surface high pressure was centered over far northern WI/upper MI this evening, and will continue to build slowly southeast across Lake Michigan by morning and then into the central Great Lakes region through the day Monday. Breezy north-northeast flow along the southeastern periphery of the high will linger across the area (especially over Lake Michigan and into parts of the metro and northwest Indiana) through the evening, before gradually diminishing overnight as the high approaches. Clear skies, light winds and a cooler/drier air mass will support overnight low temperatures around 50 (some upper 40s possible in the coolest spots) away from the core of the Chicago metro, with upper 50s downtown and along the immediate lake shore. With the surface high off to the east of the area on Monday, modest winds will turn east-southeasterly, with lake cooling limiting temps to the lower 70s along the IL shore, while warming into the mid-70s elsewhere. Mostly sunny skies are expected, with only some increasing thin cirrus later in the day. Ratzer && .DISCUSSION... Issued at 300 PM CDT Sun Jun 30 2024 Through Monday Night: Early this afternoon, a fair weather cumulus deck overhangs the CWA, but drier air being fed into region is slowly eroding the cloud cover. Cold advection driven by a prominent region of high pressure centered up in Minnesota has kept temperatures in the middle 60s to near 70 degrees, cooler than what you would typically expect on the last day of June. Meanwhile, breezy northerly winds over the lake since last evening have been consistently churning waves in the 5 to 7 foot range with several peak waves reported at just under 10 feet. Gusts are gradually waning this afternoon and that, for the most part, should continue through this evening and overnight, and waves will respond accordingly. However, several pieces of high res guidance are resolving one final surge of wind, especially along the far southern lakeshore, during the mid to late evening. Most models suggest more 20 to 25 kt gusts are in store, although the HRRR has been saying over numerous runs now that a period of near 30 kt gusts could be on the table along the Indiana lakeshore. That said, decided to extend the ongoing beach hazards statement and small craft advisory through 12Z Monday across all zones. The aforementioned high will propagate southeastward across the Great Lakes region tonight and tomorrow. This will keep conditions nice and quiet during the day and the milder return flow will bump afternoon temperatures into the middle and upper 70s. Meanwhile, the large upper high in the Plains responsible for the fair weather will get shunted to the east Monday night by a digging trough. The surface response will be a center of low pressure working across the Plains during the night. The more appreciable rain chances arrive during the day on Tuesday as the storm system approaches, but a developing warm frontal boundary could extend eastward from the storm and bring a few showers to our far northwestern CWA before daybreak. The brunt of the storm is covered in the long term discussion below. Doom Tuesday through Sunday: Following a quiet and seasonably cool start to the week on Monday, an active belt of west-southwesterly upper level flow is expected to set up across much of the Midwest into the western Great Lakes downstream of aggregate upper troughing settling over the northern Plains. Accordingly, conditions will become supportive for a few episodes of showers and thunderstorms through the to later portion of the period as a warm and humid airmass works back northward across the region. The first period of showers and thunderstorms is expected to set up mainly to our west-northwest across the upper Midwest Monday night in response to a corridor of enhanced theta-e advection along a strengthening southwesterly low-level jet axis (45-50 kt). This activity is expected to track east-northeastward into WI and perhaps as far south as parts of far northern IL (north of I-88) late Monday night into Tuesday morning. Since most of this activity is likely to outpace the instability axis, much of this convective activity should be in a weakening state by early Tuesday morning. Nevertheless, we continue to carry some chance POPs into Tuesday morning, highest along the WI state line. Following any lingering morning showers it appears much, if not all of the afternoon may be precipitation free across the area as the really humid and unstable axis remains to our west in closer proximately to an approaching cold front. However, temperatures will be on an uptick during the day on breezy southerly winds. Accordingly, readings are likely to top out in the low to mid 80s on Tuesday. Afternoon convection is expected to develop to our west Tuesday as the prefrontal airmass destabilizes in the vicinity of the aforementioned approaching cold front. This front, as well as any associated thunderstorms, will then shift eastward into our area into Tuesday night. This is certainly not a favorable diurnal timing for robust convection in our area. However, given respectable deep layer bulk shear and a stout low level jet, it`s possible scattered thunderstorms could persist well into the night despite the stronger synoptic forcing remaining well north the area. Nevertheless, it appears the higher threat area for any strong to severe storms will largely remain west of the area on Tuesday. Following the cold frontal passage late Tuesday night, the front is expected to lay out in a west-east orientation somewhere across central parts of IL and IN on Wednesday. If it ends up setting far enough south, we could end up with a primarily dry day Wednesday, albeit a very warm one, with highs well into the 80s. Heading into the July 4th holiday on Thursday, the front is forecast to gradually lift back northward as a warm front Wednesday night into the day on Thursday. Depending on how far north the front gets will determine the extent of shower and storm coverage during the Thursday into Friday timeframe as another shortwave trough pivots into the Great Lakes. At this point, guidance is favoring an afternoon and evening show for our area on Thursday with the greatest coverage in our southern CWA. However, this general timing is still low confidence given that we are still several days out and existing storms on Wednesday will play a role in frontal placement. Therefore, those with outdoor plans for the 4th should keep an eye on this period. Regardless of how Thursday plays out, it does appear that another front should push through on Friday and finally bring the periods of showers and storms to a close heading into next weekend. Though the typical late June early July heat and humidity is forecast to remain through the period with highs in the mid to upper 80s and dew points in the 60s to around 70 each day. KJB/Yack && .AVIATION /06Z TAFS THROUGH 12Z TUESDAY/... Issued at 1233 AM CDT Mon Jul 1 2024 No major forecast concerns are expected for this TAF period as high pressure will remain in control overhead. Light northeast winds tonight will gradually become more east-southeasterly after daybreak with speeds increasing to near 10 kts before settling into a southeast direction Monday evening. However, a lake breeze will keep directions favoring a more easterly direction at ORD, MDW, and GYY Monday afternoon. Otherwise, expect clear skies overnight before SCT to BKN VFR cirrus drift overhead Monday afternoon and evening. Yack && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Beach Hazards Statement until 7 AM CDT this morning for ILZ006- ILZ103-ILZ104. IN...Beach Hazards Statement until 7 AM CDT this morning for INZ001- INZ002. LM...Small Craft Advisory until 7 AM CDT this morning for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago