Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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811 FXUS63 KLOT 061111 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 611 AM CDT Sun Oct 6 2024 .KEY MESSAGES... - Very elevated fire danger today due to gusty winds and dry conditions. - Dry weather continues through the week, with temperatures trending above average. && .DISCUSSION... Issued at 252 AM CDT Sun Oct 6 2024 Through Monday: Recent surface analysis shows a cold front stretching from the central Upper Peninsula of MI southward across southeastern WI and northwestern IL which will continue to race across northern IL and northwest IN this morning. Ahead of the front, gusty southwest winds will persist with gusts in the 25 to 35 mph range. While gusts are expected to diminish immediately behind the front for a period towards daybreak, gusty northwest winds will return by midday with gusts once again in the 25 to 30 mph range for the rest of the afternoon. These gusty winds in combination with the dry conditions behind the front (dew points in the low to mid-30s) will set up favorable conditions for very elevated fire danger this afternoon, especially for areas along and south of I-80 where RH values should dip into the 20-25% range. Since fuel moistures are currently in the 9-12% range it appears that we will be just above local Red Flag Warning criteria, however; a Special Weather Statement (SPS) will be issued for the entire forecast area through this afternoon for the elevated fire danger. Therefore, any planned burning should be postponed until conditions improve and extra caution should be used when discarding any burning materials (such as cigarettes) today. Otherwise, expect temperatures this afternoon to be more in the seasonable category with highs in the upper 60s to mid-70s. Heading into tonight, winds are expected to subside as a surface high moves into the Midwest. While this will lower the fire danger, dry conditions are still expected to prevail through the day on Monday with minimum RH values generally in the 25-30% range. So continue to be cautious with any planned burning. The combination of light winds and clear skies under the high will also set up conditions for strong radiational cooling tonight and allow temperatures to dip into the upper 30s and lower 40s areawide. These cool and calm conditions may also lead to the development of some patchy frost late tonight particularly across northwestern IL where the coldest temperatures and lightest winds are forecast. Any frost that does materialize will diminish Monday morning as temperatures rebound into the middle 60s by Monday afternoon with otherwise sunny skies. Yack Monday Night through Saturday: At the start of the period, medium range guidance continues to be in good agreement in depicting a closed upper low centered over southern Quebec, within a larger scale upper trough over much of northeastern North America. While a series of low- amplitude short waves are indicated wrapping south-southeast through the western periphery of this circulation, their impacts are expected to remain well off to the east and northeast of the forecast area. Eventually, an upper level ridge extending from the desert southwest into the northern Plains and eastern Canadian Prairie Provinces is progged to shift east mid-week, nudging the northeastern NOAM trough further to the east. This results in rising heights indicative of increasing subsidence across the upper Midwest and western Lakes Wednesday into Thursday, allowing surface high pressure to build across the western and central Lakes region. Locally, this portends continued dry and gradually warming weather conditions into mid-week, tempered only by daily lake breezes near Lake Michigan. Daytime temperatures are expected to moderate from the lower 70s (upper 60s/near 70 along the lake) Tuesday, to the low to mid/upper 70s (warmest west) by Thursday, under largely cloudless skies. Nighttime lows may dip into the upper 30s in our typically coolest spots Monday night, and generally in the 40s elsewhere (upper 40s/low 50s in the core of the Chicago urban region). Models remain in excellent agreement in tracking a mid-level short wave trough and associated jet streak along/just north of the U.S./Canadian border region Thursday into Friday, flattening the upper ridge across the upper Midwest and northern Lakes. This initially enhances west-southwesterly low-level warm advection into the upper Mississippi Valley and northern Great Lakes, around the northwest periphery of the departing surface high drifting east of our area. The warm advection axis is progged to eventually shift south across IA/WI and northern IL Friday and Saturday, with ensemble mean 850 mb temperatures warming to +15/16C by Saturday. This looks to further warm surface temps into the upper 70s and lower 80s Friday and Saturday, well-above average heading into mid- October. Ratzer && .AVIATION /12Z TAFS THROUGH 18Z MONDAY/... Issued at 611 AM CDT Sun Oct 6 2024 Aviation Forecast Concerns: - Gusty WNW winds 25-30 kts today. Surface cold front has pushed through the terminals early this morning, with winds easing off to west 10 kts or less temporarily. Winds will increase again by mid morning as mixing commences after sunrise, with west-northwest winds gusting 25-30 kts through the remainder of the day. Winds will diminish slowly this evening, with lingering gusts especially at our warmer Chicago urban airports. Eventually though, winds should settle to 10 kts or less from the northwest after midnight and persist into Monday morning. Otherwise, a very dry airmass is moving in behind the cold front with VFR conditions expected through the period under nearly cloudless skies. Ratzer && .FIRE WEATHER... Issued at 252 AM CDT Sun Oct 6 2024 While temperatures today will be around 10 degrees cooler than yesterday, dewpoints are expected to settle into the low to mid-30s which will result in afternoon relative humidities in the 20 to 30 percent range. The driest conditions/lowest RH values will occur south of about I-80. Gusty winds from the west to west-northwest will develop quickly through the morning, peaking towards midday and early afternoon in the 25 to 30 mph range. At this time, sustained 20-foot winds are forecast to come in just under formal Red Flag criteria, and 10-hr fuel moisture values may only briefly tag 8 percent. As a result, have refrained from issuing a Red Flag Warning on this shift, but will issue a Special Weather Statement and continue to highlight a heightened fire danger in our graphical messaging suite. Winds will diminish rapidly near sunset. Yack/Carlaw && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory until 7 AM CDT Monday for the IL nearshore waters. Small Craft Advisory until 10 AM CDT Monday for Calumet Harbor to Gary IN. Small Craft Advisory until 4 PM CDT Monday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN. && $$ Visit us at weather.gov/chicago