Marine Forecasts

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7 Day Forecast for Marine Location Near Joliet, IL

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Area Discussion for - Chicago, IL

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FXUS63 KLOT 090849 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 349 AM CDT Thu Jul 9 2020

SHORT TERM. 325 AM CDT

Through Friday Night .

The current heat episode of widespread temperatures of 90-95 and heat index readings of 95 to near 100 looks to wrap up today, though still warm and muggy conditions on Friday. This continues an impressive two week stretch through yesterday of above normal temperatures for most if not all the CWA. The other item on the short term forecast docket is the likely thunderstorms -- scattered early in the afternoon and then more numerous into the evening. There will be a propensity for gusty winds and larger footprints of heavier downpours than in recent days. Thus the severe weather and flooding risk is generally a 1 to 2 on the scale of 5 ("Marginal"/"Slight" Risks), with the higher confidence in the northern Illinois portion of the forecast area, especially west of I-55.

An active regional radar loop early this morning, with a couple MCSs in northern parts of Minnesota and Wisconsin, and a larger and more mature one diving southeastward into eastern Kansas. This latter one, in particular its mesoscale convective vortex (MCV), is of more interest for our forecast. The KLNX (North Platte, NE) VWP by 3 a.m. captured clear evidence of this MCV in the wind flow and 60 kt of flow just above 500 mb, showing its enhancement to the mid-level wind field and thus likelihood of sustenance across Iowa today as it rides with its parent short wave. Both global and higher resolution models depict this general solution, though have variances with how they are handling the current location and convection with it, with the RAP and GFS doing particularly well. We should start to feel influence of this into the western CWA by later afternoon with peak forcing during the evening. More on that in a sec.

Prior to that wave's arrival, there is a highly sheared, broad 700-600 mb circulation and moisture pocket across central / northern Illinois that will slowly meander northeast. It has about 1.5C cooler temperatures near 600 mb than the ambient environment as captured on the 00Z ILX sounding. So this could result in a few showers and maybe a storm prior to noon but then likely assist in widely scattered storms early to mid afternoon. Some of these could be on the lake breeze boundary, which will not make much inroads today though should be enough to keep the Chicago loop cooler, with highs around 90 by noon before a dip into the 80s with the onshore turn. Elsewhere, 850 mb temperatures of 20C over the area will again support mid 90s, but convective debris cloud cover, developing cumulus, and effects of widely scattered convection are favored to keep temperatures in many places more 90-93. Dew points have mixed slightly less every day since the holiday weekend and that trend should continue today with many places only dipping to around 70. Peak heat index readings are forecast to fall out 96-101. While a lengthy duration of days with afternoon heat, the both nighttime relief and heat index readings falling shy of local Advisory criteria (105) each day, should be limiting cumulative effects and we continue with no headline today.

The expected ongoing widely scattered convection by mid-afternoon is expected to see a gradual uptick in coverage as the aforementioned convectively-enhanced short wave crossing Iowa approaches, especially after 4 p.m. over northern Illinois. Mixed layer CAPE (mlCAPE) values should be solidly around 2,000 J/kg, which is higher than recent days thanks to the higher dew points and supportive of convection to continue well after peak heating. Also supporting the convective coverage to peak later day into the evening is the forcing for ascent and precipitable water maximum (1.75-2 inches) with the mid-level impulse. In terms of storm mode, across the Mississippi River Valley into northwest Illinois in the afternoon there looks to be a greater trend for semi- organized mature convection with the slightly enhanced wind fields (0-6 km shear of 25-30 kt and 0-3 km shear for some cold pool sustainability of 20 kt). If those values pan out, that is likely shy of what's needed for long-lived mature clusters, but temporary severe storm clusters via precipitation-loaded downdrafts and realizing steep low-level lapse rates may evolve into north central Illinois later this afternoon and over the CWA (especially Illinois) this evening. There is some noteworthy spread in the eastern CWA with how much of the area gets impacted, with some convection allowing models (CAMs) showing a southeastward dive to organized convection into central Illinois.

With such high absolute moisture and the likelihood of tangled / webbed outflow boundaries for sources of updraft rooting, localized flash flooding is a concern. Even though inherent conditions have been more dry, a quick (under an hour) 2+ inch dumping over a few locations in the northern half of Illinois is certainly plausible and there is some signal of that in the 00Z HREF probabilities though mainly just southwest of the CWA. Plus the potential to receive multiple storm clusters is there as well.

Convective coverage is likely to ease from west to ease late tonight into early Friday morning. The short wave and associated weak cold front should progress southeastward limiting forcing for redeveloping showers and storms in the afternoon. However, residual high dew points forecast in the upper 60s and still no capping with highs 85-90 could support isolated storms. With the muggy conditions heat index readings are forecast 90-95 Friday afternoon. Confidence continues to increase that Friday evening looks to be dry.

MTF

LONG TERM. 337 AM CDT

Saturday through Wednesday .

This Weekend .

Temporary upper northwest flow will prevail this weekend, but like a lot of July's pattern so far, it avoids being fully "clean". However, the timing of an upper level disturbance in the northwest flow is settling in model solutions to be Saturday night/early Sunday, not an ideal time to result in high coverage of any storms or stronger storms. Certainly still time to wiggle from that solution. For now have the higher PoPs during Saturday night and Sunday morning. The wave is fairly pronounced so cannot rule out a northwest flow stronger storm or two, but if the timing continues, the potential for severe looks low in our area.

Otherwise, Saturday looks mainly sunny and that will help temperatures to still reach a tad above normal readings, with upper 80s forecast and would not be surprised to see a 90 or two. The air mass will be less humid though with mid 60s forecast for dew points. On Sunday behind a cold front, temperatures are forecast to dip a bit more to normal (mid 80s) with a lake push keeping lakeside areas at or just shy of 80. This push could end up having slightly stronger winds and may result in some rip current risk for Lake Michigan beaches for Sunday afternoon.

Next Week's Heat and Thunderstorm Potential .

After a rare near normal and low humidity day to start next work week, through mid week and beyond there will be intense heat possible locally at times. However, while north of us will be more favored for multiple rounds of thunderstorms, our area will be in the potential threat zone for thunderstorms in the mid week period.

The brief period of lower heights responsible for more seasonable temperatures Sunday and Monday will slide east as troughing north of the Great Lakes shifts to the northeast on Tuesday. In response to this and an impressive trough over the Canadian Prairies, 500 mb heights will quickly pump to around 590 DM on Tuesday. In addition, rapid warm advection will ensue, with 850 mb temps rising to near or above 20C. Operational ECMWF was on the extreme end of the scale with well into the mid 20s Celsius by 00z Wednesday, however the ECMWF Ensemble mean is not too far shy and typically reliable UKMET also gets to around 20C.

While this is several days out, considering high temps that have been attained in this pattern with 850 mb temps generally slightly cooler, Tuesday has potential for low-mid 90s if not warmer, aided by no established moisture return coming off Monday's dry high pressure. For this reason, dew points should remain in check in the 60s, and may even mix out into the 50s in spots, so at this vantage point, Tuesday's maximum heat indices probably wouldn't fall out much above high temps.

The mid week period could *potentially* get interesting, as the earlier mentioned Canadian trough advancing eastward may suppress heights some and get the area into enhanced mid-level flow. There is a signal with solid ensemble support for a potential cold frontal approach on Wednesday into a more moist and very unstable air mass with temps possibly well into the 90s. The variance between staying capped with very warm 700 mb temps or having enough height falls for a thunderstorm threat with the front is subtle so lower end PoPs appear reasonable. There would likely be sufficient mid-level flow (500 mb winds of 40+ kt) for deep layer shear to support organized strong to severe convection in the region. Obviously too early to say if within the CWA.

Beyond day 7, there are some signs that the very impressive mid 590s DM ridge core could stay suppressed south just enough for a few days to keep us potentially near the fringe of the active "Ring of Fire" zone. As we've been mentioning, how quickly the ridge fully builds north will determine timing of getting into potentially intense heat (mid-upper 90s+), with decided variance in the operational runs well within the ensemble spread. Ensemble agreement in the pattern is excellent despite the advanced lead time by next weekend for the ridge center to push far enough north to support aforementioned intense heat potential.

MTF/Castro

AVIATION. For the 06Z TAFs . 1248 AM CDT

The main concern is:

* Gusty TSRA potential this afternoon and evening and associated effects on wind direction

Quiet weather is expected through this morning and then a similar scenario to what we've had the past few days with scattered TSRA developing at peak heating. Coverage may be a bit higher than the daytime hours on Tuesday and Wednesday, however with lingering uncertainty maintained PROB30 TSRA mention for the mid to late afternoon activity. A stronger disturbance approaching from the west could potentially result in more widespread coverage during the evening, so brought in the TEMPOs from the ORD/MDW TAFs to all the TAF sites. Also similar to the past few days, parameters will favor gusty (potentially strong gusts >40 kt if direct impacts) and variable wind directions during and after the TSRA impacts.

Should a more organized cluster form in the evening, wind direction with the line of storms would favor westerly. Pre- convective winds will be south- southwest, with the lake breeze expected to stay east of ORD/MDW unless convection blows up near it and forces boundary through, which is a plausible but low confidence scenario. A weak cold frontal boundary should move across the terminals early Friday morning, shifting winds to northwesterly.

Castro

LOT WATCHES/WARNINGS/ADVISORIES. IL . None. IN . None. LM . None.

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Weather Reporting Stations

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Stations	Dist	Age	Wind	Air Temp	Water Temp	Waves	Pressure	DewPt
CMTI2 - 9087044 - Calumet, IL	36 mi	51 min	SW 1 G 1.9	76°F			1011.8 hPa	70°F
CNII2	37 mi	24 min	W 8	78°F				66°F
CHII2 - Chicago, IL	41 mi	49 min	SSW 7 G 8	80°F				73°F

Wind History for Calumet Harbor, IL

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Airport Reports

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Airport	Dist	Age	Wind kt	Visibility	Sky/Weather	Temp	DewPt	Humidity	Pressure
Joliet Regional Airport, IL	1 mi	74 min	N 0	7.00 mi	Fair	71°F	69°F	96%	1012.5 hPa
Lewis University Airport, IL	7 mi	74 min	SSE 6	10.00 mi	Fair	71°F	69°F	95%	1012.2 hPa
Morris Muni-James R Washburn Field Airport, IL	15 mi	69 min	N 0	10.00 mi	Fair	72°F	71°F	100%	1011.8 hPa
Aurora Municipal Airport, IL	24 mi	77 min	N 0	7.00 mi	Fair	72°F	70°F	94%	1011.3 hPa

Link to 5 minute data for KJOT

Wind History from JOT (wind in knots)

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Tide / Current Tables for

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Tide / Current Tables for

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Weather Map

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GEOS Local Image of    EDIT
NOTE: East coast views moved to GEOS-16. They are experimental and not well supported by NOAA so they may not be correct so be warned. This change required redoing a large amount of the GOES code. If the image you are expecting is not showing, please let me know. You may need to use the EDIT function to update your location.
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Wind Forecast for Chicago, IL (6,6,7,8)

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Ground Weather Radar Station Chicago, IL

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