Marine Forecasts

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7 Day Forecast for Marine Location Near Hammond, IN

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Area Discussion for - Chicago, IL

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FXUS63 KLOT 220500 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1100 PM CST Tue Jan 21 2020

SHORT TERM. 230 PM CST

Through Wednesday .

High pressure centered over the lower Ohio Valley will drift eastward tonight which will help keep a steady southwesterly wind in place for most areas. This will result in a milder night than last night, with lows in the upper teens west to lower 20s southeast. Some sites may warm a few degrees overnight thanks to the breeze and incoming mid/high level cloud cover, especially west. Breezy south-southwest winds will develop Wednesday morning with cloud cover thickening through the day from west to east. Upper ridging will cross the area through the day with modest warming aloft which will lead to highs in the low to mid 30s. An upper trough will be on the heels of the ridge with surface low pressure developing across the high plains. Light snow may try to develop into far northwest sections of the forecast area west of I-39 late Wednesday afternoon.

MDB

LONG TERM. 245 PM CST

Wednesday Night through Tuesday .

The mid to late week emphasis is on the prolonged snow event, which is one that looks mainly light apart from Friday-Friday night where at least some moderate snow at times seems likely. This is a challenging event to get too specific with details for several reasons: 1.) a closed upper low which is a feature well known for its trickiness, 2.) long duration event so naturally confidence lowers further out in time so difficult to communicate total snowfall amounts, and 3.) marginal surface temperatures with respect to freezing likely resulting in lower snow ratios and some compaction and melting over time, and thus the decent potential for multi-day snowfall totals to be less than incrementally adding up 6-hour forecasts. That all said, confidence on limited/marginal impacts through Thursday night is pretty high.

The current upper jet split flow pattern will have a northern stream buckle Wednesday night into Thursday over the middle of the country, with some phasing predicted in the Mid-Mississippi Valley. From this a closed upper level low has been consistently forecast to develop over the Central Plains into the Missouri River Valley. That phasing period late Thursday night through Friday will result in the system deepening. It is from that point forward that introduces some spread in guidance including from run-to-run especially in the GFS. As the system deepens, there should be a slightly north of east path taken especially with the surface low. Right now a model blend mean for the surface low track is south of the CWA, and the ECMWF has been consistently well south of the CWA. Also the pressures are not particularly deep and the surface low projected around 1010 mb during the day Friday. This points toward limited warm advection aloft for full melting in the upper levels and thus less of a concern for freezing rain - which commonly is a lower threat in closed low situations.

For precipitation onset Wednesday night into early Thursday, the anomalous upper level riding over the area tonight (in the upper 5th percentile for later January) will be gradually nudged out Wednesday night. Onset time has sped up slightly in guidance solutions today, with most CWA locations predicted to see light snow ongoing by first thing Thursday morning. Confidence on this is still somewhat low for the eastern CWA, including Chicago, but do believe snow to be at least moving in late Wednesday night or Thursday morning into the city. This "first half" of the event from Wednesday night through Thursday night will be in the upper right quadrant of the developing upper low, so driven by warm advection and broad upper level diffluence. The warm advection/isentropic ascent again is not overly strong, and the jet positioning would not reflect deep omega, so this points toward light precipitation rates. This looks to be mainly snow though surface temperatures that will not have dropped much Wednesday night should climb to slightly above freezing on Thursday. While it has been cold, the lighter rates and marginal low-level air temperatures will likely result in the snowfall struggling to accumulate on treated roads, and there could even be rain mixed in at times east and south in the CWA. After dark Thursday may be a better chance to get some snow to stick on such treated paved surfaces but again rates at this time look light.

This first half of the event by early Friday morning looks to produce a total of 1-2 inches east and 2-3.5 inches west, with those totals most reflective of grassy surfaces given the long duration. Again lighter rates and air temperatures should allow for fairly effective treatment on roads, where totals look to be less.

The "second half" of the event is when the system is deepening and that's why it may have a slightly different character. Also given the low trajectory, the atmospheric wind field becomes more northeasterly and then northerly, likely keeping precipitation type as snow apart from the southeast half of the CWA during the day Friday. If the mean model solution of forecast system deepening time and track ends up being near correct, there should be better upper level forcing and some mid-level baroclinicity Friday afternoon into night to support at least occasional moderate snow and potentially seeing a few to several inches during that 18 hour period or so. While confidence on accumulating snow for the CWA during that time is fairly high, amount details are quite low for all the aforementioned reasons. Also the best upper to mid-level forcing is not that persistent over the CWA in current model solutions.

The low looks to lose influence on the area into the day Saturday, but a clipper-like wave in the northern stream immediately on the heels keeps snow/snow shower chances going for Saturday in the forecast. This could result in additional minor accumulation but at this time Saturday is not looking like a big deal by itself thanks to the lack of a cold air surge into this system (not that atypical with a closed low). Also common with such a system is struggling to get the clouds out of the area which could be a problem the rest of the weekend into early next week. Temperatures right now for that period look to be slightly above normal.

MTF

AVIATION. For the 06Z TAFs .

Surface winds are responding to high pressure finally building south and east of the region late this evening, with occasional gusts noted to around 20 kts or so. Expect that this trend will continue through the overnight hours and into Wednesday. A general 180-200 direction will likely be favored. There may be a window towards late Wednesday morning and into the early-afternoon where gusts may approach 25 kts at times, but given that these are expected to remain below any E-W crosswind thresholds, elected to not clutter the TAFs up with an additional line at this time.

Have also seen a few wisps of MVFR stratus attempting to developing, but these have thus far been ephemeral and quite isolated. Can't rule out some brief/spotty MVFR cigs through the night, but don't anticipate these being widespread or long-lived enough to warrant a mention in the 06z TAFs. Ceilings will gradually build down through the afternoon and especially early- evening hours on Wednesday with the approach of the next weather disturbance. Guidance is in pretty good agreement regarding the arrival of better precipitation chances towards the end of the RFD and extended ORD/MDW TAFs. Low-level saturation looks to occur pretty quickly through the evening hours, with an initial period of what could be flurries developing just after midnight at the Chicago-area terminals. Have trended the TAFs towards indicating more prevailing light snowfall late Wednesday evening at RFD and towards the very tail end of the ORD/MDW TAF groups.

Carlaw

LOT WATCHES/WARNINGS/ADVISORIES. IL . None. IN . None. LM . Small Craft Advisory . nearshore waters until 3 PM Wednesday.



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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	8 mi	56 min		25°F			1026.5 hPa	21°F
CNII2	17 mi	26 min	SW 11 G 17	26°F				20°F
CHII2 - Chicago, IL	21 mi	36 min	SSW 23 G 24	27°F				23°F
MCYI3 - Michigan City, IN	32 mi	36 min	S 13 G 17	25°F				20°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
Gary Regional Airport, IN	4 mi	31 min	S 8	10.00 mi	Fair	27°F	19°F	74%	1027.4 hPa
Lansing Municipal Airport, IL	7 mi	31 min	S 11	10.00 mi	Fair	24°F	20°F	86%	1027.4 hPa
Chicago, Chicago Midway Airport, IL	18 mi	33 min	SSW 11 G 19	9.00 mi	Mostly Cloudy	25°F	19°F	78%	1028.6 hPa

Link to 5 minute data for KGYY

Wind History from GYY (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.
Link to Loop

Other links: Northern Pacific     Contential US     Full GOES-East

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Wind Forecast for Chicago, IL (2,6,7,8)

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Ground Weather Radar Station Chicago, IL

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