Area forecast discussion National Weather Service Chicago/Romeoville, Illinois 621 am CDT Thursday may 5 2016
Short term... 323 am CDT
Today through Friday...
Deep upper trough/closed low over the Ohio Valley will lose its grip on the region today... moving to the East Coast/mid-Atlantic by this evening. Surface high pressure ridge over the upper Mississippi Valley and northern lakes this morning will spread across the forecast area from the northwest later today... beneath subsidence associated with rising heights in the wake of the departing trough. This subsidence and advection of drier air from the north will work to erode lingering cloud cover over the eastern parts of the forecast area today. Temperatures will moderate a bit today though stronger warm advection holds off until tonight. Afternoon highs from the middle 60s west to the upper 50s/around 60 far east are expected... though north-Northeast Lake breeze winds will keep areas near Lake Michigan in the 50s.
Low-level warm advection begins in earnest from the northwest tonight as upper ridge builds across the upper Mississippi Valley and northern Great Lakes. Various models indicate potential for some light precipitation upstream across WI... though 00z soundings from the source region of the northern plains and far upper Midwest appear pretty dry... and model forecasts of the 300-305 k isentropic surfaces depict unimpressive condensation pressure deficits which adds confidence to keeping a dry forecast.
By Friday morning... surface ridge axis is off to the south/southeast of the County Warning Area. Westerly low level flow... dry profiles and 925 mb temperatures of +20 to around +23 c by afternoon support much warmer surface temperatures ranging from the upper 70s across the far eastern County Warning Area... and 83-84 f for maxes across our west/northwest counties. The surface pressure gradient should be weak enough to allow a lake breeze to develop by Friday afternoon... though with enough west wind component to prevent it from pushing too far inland over northeast Illinois. Lake breeze may be a bit stronger into Northwest Indiana where gradient will be a bit weaker.
Long term... 323 am CDT
Friday night through Wednesday...
Guidance remains steadfast in amplifying a short wave trough which moves across southern Canada Friday... then digs southeast and breaks down the upper ridge across the western Great Lakes region over the weekend. At the surface... this manifests as a southeastward moving surface low and cold front which moves into the County Warning Area early Saturday morning. Despite steep middle-level lapse rates... forecast soundings indicate a lack of deep saturation coincident with the front pushing across northern parts of the County Warning Area early Saturday. This... along with diurnal minimum for near-surface based instability suggests limited probability of precipitation initially across the northern half of the County Warning Area. Convection potential looks a little better across the southern counties of the forecast area late morning/early afternoon where diurnally warming boundary layer should support greater near-surface based convective available potential energy. Elevated cape is indicated farther north on the cool side of the boundary into the afternoon atop cool boundary layer which may support rain/embedded thunder potential as large scale forcing increases. Temperatures will be tricky on Saturday with front moving through during the morning/midday. Mild start to the day will likely allow most locations to warm into the 60s before stronger northerly cool push develops behind the front... and southern counties likely tapping the low-middle 70s. Falling temperatures are expected near Lake Michigan however... where readings will likely dip into the 50s.
The front then pushes well south of the County Warning Area into the Ohio Valley Saturday night... with weak surface high pressure spreading across the region. This should take precipitation chances south of the forecast area Saturday night and Sunday while dry... modestly cool weather lingers locally.
Days 5-7 see a continuation of split flow aloft... with a closed upper low over the western Continental U.S. Eventually weakening and lifting northeast across the Midwest through Wednesday. Differences in guidance abound though there is general consensus that the front to our south lifts back into the area as a warm front Sunday night into Monday... becoming nearly stationary as the associated surface low moves into our area late Tuesday/Wednesday. This sets up the potential for a potentially wet early-middle week period with temperatures near normal in the 60s/low 70s... and also some daily lake cooling.
Aviation... for the 12z tafs...
A ridge of high pressure stretches from Lake Superior into Iowa early this morning and will build towards the local area through the day allowing winds to continue to diminish. MVFR/IFR level stratus persists across much of Indiana and built into portions of northeastern Illinois overnight. These lower clouds have since eroded over Ord and dpa... though continue to impact mdw and gyy. Anticipate both terminals to improve over the next couple hours back to VFR where they should remain through the remainder of the forecast period. North winds are expected through the morning and early afternoon... then an afternoon lake breeze will turn winds northeasterly for at Ord/mdw. Winds will diminish and become light and variable around or shortly after sunset... then should become southwesterly at some point overnight... increasing to around 10 knots again Friday morning.
Marine... 356 am CDT
Lake Michigan remains under a moderate northerly gradient early this morning behind departing low pressure centered along the middle Atlantic coast and high pressure building into the upper Midwest. The high will continue to build southeast across Lake Michigan today allowing winds to diminish. The Gale Warning will be allowed to expire early this morning... however a Small Craft Advisory will remain in effect for hazardous winds and waves through middle morning for the Illinois nearshore waters... and through late this afternoon for the Indiana nearshore waters. The ridge axis will settle southeast of Lake Michigan late this evening and tonight allowing southwest to south winds to overspread the lake... increasing into the 15 to 25 knots range by midday Friday. Another area of low pressure is expected to move across Ontario into Quebec on Friday with a trailing cold front pushing south across Lake Michigan Friday night into early Saturday with northerly winds to around 30 knots expected behind the front.
Lot watches/warnings/advisories... Illinois... none. In... none. Lm... Small Craft Advisory... Illinois nearshore waters until 10 am Thursday.
Small Craft Advisory... Indiana nearshore waters until 7 PM Thursday.
Made the guac with 4 avocados to tone down the heat slightly, I could feel myself starting to sweat and my stomach burn a little with three in there because I always get a little carried away when dicing the hot peppers.