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Displaying AFOS PIL: AFDLOT Received: 2018-06-29 08:01 UTC
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992 FXUS63 KLOT 290801 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 301 AM CDT Fri Jun 29 2018 .SHORT TERM... 254 AM CDT Through Saturday... Very hot and humid conditions are the main forecast story for at least Friday and Saturday across northern Illinois and northwest Indiana. Overall, no big changes in forecast thinking over the next couple days and guidance remains in good agreement suggesting low to mid 90s for high temperatures. The official forecast errs on the warmer side of guidance as models tend to struggle with the magnitude of these higher-end events. Moderate to strong MLCIN owing to 850/700mb temps of 23-25C and 14C, respectively, should keep skies mostly clear today with little concern for afternoon convection. Dew points on track to become quite oppressive across the region today. Early Thursday evening, dew points in the upper 70s to low 80s were observed from the mid Missouri Valley southeast across the mid Mississippi Valley and guidance suggests this moisture axis will lift across northern Illinois and northwest Indiana today. Should be able to get a little higher even as the moisture axis lifts into the corn belt. As with temperatures, staying on the high side of guidance for dew points. For the previous heat event last week, models across the board had a low bias with dew points. Given these factors, felt comfortable nudging dew points up a hair from previous forecast bringing more of the forecast area closer to the 80 mark outside the city. This yields heat indices of around 110F for the city of Chicago and portions of northwest Indiana, and into the 110-120 range farther west and southwest. Conditions don't change too terribly much for Saturday. The local area still lies under the thermal ridge and within the moisture axis, though the upper ridge axis does inch east away from the area. As a result, soundings indicate only weak capping in place during the afternoon hours. Forcing isn't readily apparent, though some models indicate convergence as winds over Lake Michigan try to turn a lake breeze. Couldn't rule out an isolated storm or two forming near the shores of Lake Michigan and moving over the lake if this were to occur, but more likely expect cap to hold. Will upgrade the remainder of the Excessive Heat Watch to and Excessive Heat Warning for Friday and Saturday. Deubelbeiss && .LONG TERM... 254 AM CDT Sunday through Friday... Confidence in the forecast details, especially with respect to the heat, begins to diminish by Sunday as weather could become more unsettled through the day. Upper ridge axis is progged to shift to the East Coast Sunday while broad and shallow longwave trough spreads from the West Coast across the Great Plains. A lead shortwave trough and attendant surface cold front is progged to move across portions of the Upper Midwest on Sunday kicking off showers and thunderstorms. The cold front isn't expected to pass through the local area until Sunday night, but showers and thunderstorms will likely precede fropa adding uncertainty in the temperature forecast. Guidance ranges from mid 80s to mid 90s for highs and will lean towards the middle of the spread given the uncertainty. If convection is able to hold off until late in the day, it's quite possible additional heat headlines will be needed through the day Sunday. In addition, the area could still experience moderate to strong instability Sunday with increasing shear expected as the shortwave trough approaches. Will have to keep an eye on the severe thunderstorm potential as we get closer. Unsettled weather could continue throughout much of the upcoming week. Upper ridge will initially settle over the east coast with the local area falling on the western periphery of the ridge axis Monday. Temperatures briefly moderate in the mid 80s Monday behind the front, but should see temps bounce back around or into the 90s through the latter half of the week as a broad upper ridge builds from the Desert Southwest to the mid Atlantic Coast. Thermal ridge and effective cap remains just to our west through much of the upcoming week which could allow for scattered diurnally favored thunderstorms locally as MLCIN is eroded each afternoon. There isn't any notable synoptic scale forcing for ascent under the influence of the upper ridge, so will have to keep an eye out for smaller scale, lower amplitude features to get a better handle on specific timing and coverage of these thunderstorm chances. Deubelbeiss && .CLIMATE... Record Temps For the Chicago area... Record High Max Temp June 29: 97F (1954) June 30: 99F (1913, 1953) Record High Min Temp June 29: 80F (1931) June 30: 80F (1931) For the Rockford area... Record High Max Temp June 29: 103F (1931) June 30: 102F (1931) Record High Min Temp June 29: 75F (1931) June 30: 74F (1913, 1931) && .AVIATION... For the 06Z TAFs... The items of note for the aviation forecast through tonight are: - Patchy haze and shallow fog early this morning - Occasional southerly gusts of 17-20 kt late this morning and afternoon - High heat and high heat index readings on Friday and Saturday Light southeast winds early this morning will become southerly by 13Z with gusts into the mid teens by mid-late morning. Confidence on a 180-200 degree wind direction for today and tonight is high. After dark when surface winds start to ease, low-level wind shear is possible by Rockford as southwest wind speeds around 1000 ft increase to around 40 kt by 04Z. As for precipitation, confidence is increasing in a dry forecast with any isolated early morning storms in southern MN expected to not organize and progress toward the area, which a few models on Thursday were showing. Well-organized storms into northern/central MN by 11Z are expected to move into northern/central WI into the morning and show a gradual fade in intensity, with any wind shift presently expected to stay north. With full or close to full sun this afternoon, high heat will build in over the airfields, with heat index readings (combination of temperature and dew point) of 105-115 forecast. MTF && .MARINE... 112 AM CDT Southerly winds of 15 to 25 kt will prevail over the lake through the weekend, with the exceptions being occasional gusts to 30 kt this afternoon and evening across the north, where also a few thunderstorms are possible midday that could temporarily shift winds westerly. Confidence in these are low though. Storms are again possible late Saturday night into Sunday,and across much of the lake. For much of the weekend though, dry conditions are expected. For the Illinois and Indiana nearshore, dry weather is likely for much of the weekend. South to south-southwest winds will prevail. On Sunday, these could be close to Small Craft Advisory criteria with gusts at or just over 20 kt presently forecast. With high pressure then expected later Monday through the holiday, lighter onshore flow is expected, especially across the Illinois nearshore. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Excessive Heat Warning...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008- ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021- ILZ022-ILZ023-ILZ032-ILZ033-ILZ039...11 AM Friday to 7 PM Saturday. IN...Excessive Heat Warning...INZ001-INZ002-INZ010-INZ011-INZ019...11 AM Friday to 7 PM Saturday. LM...None. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO
992 FXUS63 KLOT 290801 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 301 AM CDT Fri Jun 29 2018 .SHORT TERM... 254 AM CDT Through Saturday... Very hot and humid conditions are the main forecast story for at least Friday and Saturday across northern Illinois and northwest Indiana. Overall, no big changes in forecast thinking over the next couple days and guidance remains in good agreement suggesting low to mid 90s for high temperatures. The official forecast errs on the warmer side of guidance as models tend to struggle with the magnitude of these higher-end events. Moderate to strong MLCIN owing to 850/700mb temps of 23-25C and 14C, respectively, should keep skies mostly clear today with little concern for afternoon convection. Dew points on track to become quite oppressive across the region today. Early Thursday evening, dew points in the upper 70s to low 80s were observed from the mid Missouri Valley southeast across the mid Mississippi Valley and guidance suggests this moisture axis will lift across northern Illinois and northwest Indiana today. Should be able to get a little higher even as the moisture axis lifts into the corn belt. As with temperatures, staying on the high side of guidance for dew points. For the previous heat event last week, models across the board had a low bias with dew points. Given these factors, felt comfortable nudging dew points up a hair from previous forecast bringing more of the forecast area closer to the 80 mark outside the city. This yields heat indices of around 110F for the city of Chicago and portions of northwest Indiana, and into the 110-120 range farther west and southwest. Conditions don't change too terribly much for Saturday. The local area still lies under the thermal ridge and within the moisture axis, though the upper ridge axis does inch east away from the area. As a result, soundings indicate only weak capping in place during the afternoon hours. Forcing isn't readily apparent, though some models indicate convergence as winds over Lake Michigan try to turn a lake breeze. Couldn't rule out an isolated storm or two forming near the shores of Lake Michigan and moving over the lake if this were to occur, but more likely expect cap to hold. Will upgrade the remainder of the Excessive Heat Watch to and Excessive Heat Warning for Friday and Saturday. Deubelbeiss && .LONG TERM... 254 AM CDT Sunday through Friday... Confidence in the forecast details, especially with respect to the heat, begins to diminish by Sunday as weather could become more unsettled through the day. Upper ridge axis is progged to shift to the East Coast Sunday while broad and shallow longwave trough spreads from the West Coast across the Great Plains. A lead shortwave trough and attendant surface cold front is progged to move across portions of the Upper Midwest on Sunday kicking off showers and thunderstorms. The cold front isn't expected to pass through the local area until Sunday night, but showers and thunderstorms will likely precede fropa adding uncertainty in the temperature forecast. Guidance ranges from mid 80s to mid 90s for highs and will lean towards the middle of the spread given the uncertainty. If convection is able to hold off until late in the day, it's quite possible additional heat headlines will be needed through the day Sunday. In addition, the area could still experience moderate to strong instability Sunday with increasing shear expected as the shortwave trough approaches. Will have to keep an eye on the severe thunderstorm potential as we get closer. Unsettled weather could continue throughout much of the upcoming week. Upper ridge will initially settle over the east coast with the local area falling on the western periphery of the ridge axis Monday. Temperatures briefly moderate in the mid 80s Monday behind the front, but should see temps bounce back around or into the 90s through the latter half of the week as a broad upper ridge builds from the Desert Southwest to the mid Atlantic Coast. Thermal ridge and effective cap remains just to our west through much of the upcoming week which could allow for scattered diurnally favored thunderstorms locally as MLCIN is eroded each afternoon. There isn't any notable synoptic scale forcing for ascent under the influence of the upper ridge, so will have to keep an eye out for smaller scale, lower amplitude features to get a better handle on specific timing and coverage of these thunderstorm chances. Deubelbeiss && .CLIMATE... Record Temps For the Chicago area... Record High Max Temp June 29: 97F (1954) June 30: 99F (1913, 1953) Record High Min Temp June 29: 80F (1931) June 30: 80F (1931) For the Rockford area... Record High Max Temp June 29: 103F (1931) June 30: 102F (1931) Record High Min Temp June 29: 75F (1931) June 30: 74F (1913, 1931) && .AVIATION... For the 06Z TAFs... The items of note for the aviation forecast through tonight are: - Patchy haze and shallow fog early this morning - Occasional southerly gusts of 17-20 kt late this morning and afternoon - High heat and high heat index readings on Friday and Saturday Light southeast winds early this morning will become southerly by 13Z with gusts into the mid teens by mid-late morning. Confidence on a 180-200 degree wind direction for today and tonight is high. After dark when surface winds start to ease, low-level wind shear is possible by Rockford as southwest wind speeds around 1000 ft increase to around 40 kt by 04Z. As for precipitation, confidence is increasing in a dry forecast with any isolated early morning storms in southern MN expected to not organize and progress toward the area, which a few models on Thursday were showing. Well-organized storms into northern/central MN by 11Z are expected to move into northern/central WI into the morning and show a gradual fade in intensity, with any wind shift presently expected to stay north. With full or close to full sun this afternoon, high heat will build in over the airfields, with heat index readings (combination of temperature and dew point) of 105-115 forecast. MTF && .MARINE... 112 AM CDT Southerly winds of 15 to 25 kt will prevail over the lake through the weekend, with the exceptions being occasional gusts to 30 kt this afternoon and evening across the north, where also a few thunderstorms are possible midday that could temporarily shift winds westerly. Confidence in these are low though. Storms are again possible late Saturday night into Sunday,and across much of the lake. For much of the weekend though, dry conditions are expected. For the Illinois and Indiana nearshore, dry weather is likely for much of the weekend. South to south-southwest winds will prevail. On Sunday, these could be close to Small Craft Advisory criteria with gusts at or just over 20 kt presently forecast. With high pressure then expected later Monday through the holiday, lighter onshore flow is expected, especially across the Illinois nearshore. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Excessive Heat Warning...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008- ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021- ILZ022-ILZ023-ILZ032-ILZ033-ILZ039...11 AM Friday to 7 PM Saturday. IN...Excessive Heat Warning...INZ001-INZ002-INZ010-INZ011-INZ019...11 AM Friday to 7 PM Saturday. LM...None. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO