Sunrise 5:50 AM   Sunset 7:47 PM Moonrise 11:09 PM   Moonset 7:00 AM

  Print   HELP   Reset   Save   Recall

LMZ646 Wind Point Wi To Winthrop Harbor Il- 706 Pm Cdt Fri Apr 26 2024
.small craft advisory in effect through Monday evening - .
Tonight - Southeast wind 15 to 20 knots veering south early in the morning. Gusts up to 25 knots. Rain showers likely and a chance of Thunderstorms. Waves 3 to 4 feet building to 4 to 6 feet in the late evening and overnight. Saturday - South wind 15 to 20 knots becoming 10 to 20 knots early in the afternoon, then veering southwest 15 to 20 knots late in the afternoon. Gusts up to 30 knots. Partly Sunny. Waves 3 to 5 feet subsiding to 3 to 4 feet in the late morning and afternoon. Saturday night - Southwest wind 10 to 15 knots with gusts to around 20 knots backing south with gusts to around 20 knots late in the evening, then veering southwest after midnight becoming south 5 to 10 knots early in the morning. Rain showers likely and a chance of Thunderstorms through the night. Waves 2 to 4 feet subsiding to 1 to 2 feet in the late evening and overnight. Sunday - Southeast wind 10 to 15 knots veering south with gusts to around 20 knots late in the afternoon. Rain showers likely in the morning. Chance of Thunderstorms through the day. Chance of showers in the afternoon. Waves 1 to 2 feet building to 2 to 4 feet in the afternoon.

LMZ600
No data

FXUS63 KLOT 270006 AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 706 PM CDT Fri Apr 26 2024

KEY MESSAGES

- Showers and a few thunderstorms will move over the area late this evening into the overnight hours.

- Saturday looks summer-like with highs in the upper 70s to lower 80s, increasing humidity levels, and eventually partly cloudy skies.

- Showers and thunderstorms will develop toward and after sunset Saturday night and continue through Sunday morning. A threat for flash flooding will exist where thunderstorms train.

- Periods of showers and storms will continue through midweek, a few of which could be strong to possibly severe on Sunday.

DISCUSSION
Issued at 248 PM CDT Fri Apr 26 2024

Through Saturday Night:

Regional water vapor and visible satellite imagery, surface observations, and radar data depict a surface low pressure system centered along the Kansas and Nebraska borders underneath an upper level shortwave trough lifting northeastward into the Upper Mississippi River Valley. Bands of showers and a few thunderstorms are evident east of the center of the low, including severe convection across the Plains and warm-air advection driven showers along and east of the Mississippi River. A diffuse surface warm front is draped across southern Illinois, and delineates summer-like moisture to the south and more seasonable (and wet) conditions to the north.

Over the next 18 hours or so, waves of showers will parade over northern Illinois and northwestern Indiana as broad warm air advection continues atop the northward-surging warm front. While coverage of thunderstorms will initially be isolated this afternoon and evening, gradually increasing instability (by virtual of low- level moistening and steepening mid-level lapse rates) will support embedded thunderstorms particularly after sunset and especially midnight. While the threat for severe weather remains low, a localized threat for pea to nickel size hail or gusty winds exists across much of the area through the overnight hours, particularly if any upscale growth of any cluster originating out of Missouri occurs overnight. The SPC Level 1/5 threat level for the overnight hours covers the potential well.

After daybreak, the warm front is expected to stall across central Wisconsin as the low-level jet wanes. At the same time, a secondary upper-level trough moving into the Southern Plains will induce gradual mid-level height rises across the Great Lakes. The net result should be the erosion of any remaining shower or thunderstorm after daybreak affording a dry period from mid-morning to mid- afternoon. As low-level stratus thins from mid-morning onward, a "pop" of southwesterly winds gusting 40-45 mph may occur before noon as mixing builds into the waning low-level jet. Thereafter, southwesterly gusts of 30-35 mph will continue through the afternoon. With 850mb temperatures climbing to +13 to +14C and prospects for even filtered sunshine, temperatures tomorrow are poised to shoot into the upper 70s to even lower 80s. When combined with a humid airmass (surface dew points in the low to mid 60s and PWATs nearing 1.5"), it will feel more like late June than late April by tomorrow afternoon!

Tomorrow afternoon, neutral height tendencies and boundary layer heating may prove sufficient to erode capping. As a result, isolated showers and thunderstorms may develop after 2 or 3 PM, though confidence in anything developing so early is pretty low (equating to a 20% chance for thunderstorms).
Tomorrow evening, coverage of showers and storms will increase markedly first across Missouri and Iowa, and later across northern Illinois, as the next upper-level shortwave pivots northeastward and supports the redevelopment of an expansive low-level jet. With a steady feed of low-level moisture and convergence along the nose of the low-level jet overnight, showers and storms may continue more or less continuously through daybreak Sunday along a southwest to northeast, or even west to east, oriented axis.

While the pattern doesn't conceptually match classic flash- flood set- ups (as the upper-level jet will be displaced too far to our north and west, and cells may be more broken than within a continuous, training line), the ability for the low-level jet to continuously feed replenishing instability and moisture into a relatively confined band of thunderstorms over a prolonged period of time does raise concern for a localized threat for flash flooding mainly in urban areas. At this point, CAM guidance (including an experimental FV3 core extended CAM ensemble) appears to favor the axis aligning near the Illinois and Wisconsin state line which is reflected in our forecast.
However, we would be remiss to ignore the deterministic HRRR, RAP, and experimental RRFS, which all favor the thunderstorms aligning somewhere near I-80 or I-88. For now, felt the course of least regret was to collaborate a southeastward expansion of the D2 WPC Flash Flooding Threat level 1/5 area to encompass much of northern Illinois.

Not to be forgotten, overnight lows Saturday night will be incredibly (record?) warm and in the low to mid 60s.

Borchardt

Sunday through Friday:

The secondary upper trough, currently over the Great Basin, is expected to be traversing the central Plains into the upper Midwest as a closed upper low on Sunday. This trajectory will place the Mississippi River Valley and western Great Lakes in the diffluent region of the trough and therefore continue to support periods of showers and thunderstorms through Sunday night. However, there is a notable signal amongst the mid-range forecast guidance that a modest cap may develop Sunday morning which could limit (if not inhibit) shower and storm development until better forcing and destabilization arrives Sunday evening into the overnight hours as the aforementioned trough is closest and a low-level jet forms overhead. While it continues to look as if the better forcing and subsequent instability should remain near and west of I-39, 30-35 kts of effective shear are forecast to be in place which could allow a few storms to become better organized and be capable of producing severe weather, primarily during the late afternoon and evening hours Sunday.
Therefore, a marginal (level 1 of 5) severe weather risk remains for the western half of our forecast area.

As the aforementioned upper low lifts into the upper Midwest Sunday night into Monday, a cold front is expected to move through northeast IL and northwest IN bringing yet another period of showers and thunderstorms. Though, the instability on Monday does look to be notably weaker than on Sunday which should keep the threat for any strong to severe storms to a minimum. While temperatures are expected to cool a bit in the wake of the front, high temperatures are forecast to remain in the mid to upper 70s through the middle of next week.

A brief break in the active weather is expected for Monday night and Tuesday as the upper-level pattern transitions into a more zonal (east-west oriented) pattern. However, additional shortwave troughs are forecast to traverse through the pattern Tuesday night through Thursday which looks to return the threat for periodic showers and thunderstorms. It does look as if high pressure may try to establish over the central CONUS towards the end of the week and into next weekend with more seasonable temperatures as well.

Yack

AVIATION /00Z TAFS THROUGH 06Z SUNDAY/
Issued at 705 PM CDT Fri Apr 26 2024

Key Aviation Messages: - Isolated to scattered elevated TS late this evening and early overnight.
- SW wind gusts over 30 knots on Saturday.
- Periods of MVFR ceilings through the period.

SE winds gusting to 20 knots early this evening will increase to around 25 knots late this evening, then veer SSW overnight.
An area of SHRA with embedded TS across eastern Missouri early this evening is expected to lift northeast toward the Chicago terminals late this evening into the overnight hours. Steepening lapse rates combined with renewed forcing ahead of trough over western Missouri should support at least isolated to scattered TS at ORD/MDW in the 04-08Z window. Have therefore included TEMPO TS for this period.

Beyond roughly 08-09Z, dry conditions are expected to prevail through the daytime hours Saturday. Winds will veer SW after sunrise, with gusts quickly increasing to over 30 knots by mid- morning. MVFR ceilings in the morning may lift into lower end VFR levels or become SCT in the afternoon.

Additional isolated SHRA are expected to develop Saturday evening, so have included VCSH at this time.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...Small Craft Advisory until 10 PM CDT Saturday for Winthrop Harbor to Northerly Is. IL.

Small Craft Advisory until 10 PM CDT Saturday for Northerly Is. IL to Michigan City IN.

toggle option: (graph/table)

Full Color Weather Map

Link to Loop


Other links: GEOS-West     Contential US     Full GOES-East

Milwaukee, WI,