Area forecast discussion National Weather Service Detroit/Pontiac Michigan 1230 PM EDT Friday may 24 2013 Aviation... //discussion... 12z DTX sounding showed a real strong inversion around 4000 feet...which allowed cold northerly flow off Lake Huron to support solid stratus deck...which is currently in the process of mixing out. Once this occurs (mid afternoon)...clear skies should be the rule into tonight. Low levels should be warm enough and flow backed to the west-northwest not to support a repeat performance of the low clouds tonight. There will be some middle/high clouds arriving overnight however...with just a bit of diurnal cumulus developing tomorrow (5000 feet). Marginally gusty northwest winds (around 20 knots) early this afternoon diminishing...with light and variable winds tonight into tomorrow. //Dtw threshold threats... * low confidence in ceilings below 5000 feet 18-20z. && Previous discussion...issued 340 am EDT Friday may 24 2013 Short term...today and tonight The weather up for discussion is the prospects for overcast skies today as an opaque blanket of 030-035 feet stratus is aggressively diving southward across Lake Huron. Trajectory of cloud deck in addition to the orientation of the western edge aligns well with the axis of maximum 925-850mb cold air advection and the depression of the longwave trough axis. Nwp data is virtually void of cloud...a result of inadequate vertical resolution within the models. While the cloud is completely opaque it is undoubtedly a shallow layer of moisture that is likely trapped within the base of the inversion at/around 900-890mb. RUC soundings show saturation at this zone...but the sounding structure itself does not inspire much confidence as it is the wrong profile. Given the true northerly trajectory...have decided to introduce overcast conditions for much of the County Warning Area through the morning hours. It will be difficult to pinpoint any west edge of the clouds given degree of dry air immediately to the west. Pattern recognition suggests entrainment at the edge should aid diurnal mixing to force stratus to go broken by late morning...eventually clearing out for the afternoon. Lowered maximum temperatures for many areas due to the cloud and steady cold air advection. Expect temperatures to eventually reach 60-61 degrees across the south and Saginaw Valley very late in the day. Otherwise temperatures are going to struggle to reach the lower 50s in The Thumb. For tonight...the compact vorticity over northern Manitoba will get squeezed with a rogue vorticity streamer off of the pacnw anomaly merging over the western Great Lakes. This will occur down the front edge of the central Continental U.S. Ridge...allowing for a very healthy ageostrophic response and stripe of frontogenesis very late. Any significant temperature gradient will reside well west of lower Michigan which is where the precipitation response will occur. Regardless...increasing clouds late will establish a floor on minimum temperatures tonight. Long term...Saturday through Thursday The overall pattern across North America this weekend will feature a quasi Omega block. Short wave energy now shown rotating into northern Manitoba is forecast to track across the eastern Great Lakes and middle Atlantic early Saturday...leading to deepening of an upper low rotating across New England. Lower Michigan will be located between this system and amplifying middle level ridging across the northern plains/upper MS valley. This will place the forecast area within a strongly confluent upper flow with persistent high pressure at the surface. The resident airmass across the Great Lakes will be cool and very dry. Temperatures on Saturday should only rise to the low 60s over much of the forecast area with 850mb temperatures hovering around +2c. The airmass will moderate during the course of the weekend...with highs expected to be around 70 by Memorial Day. Given the dry airmass and light winds...nighttime lows will be quite chilly this weekend /30s and 40s/. A seasonally strong 140+ knot upper jet is forecast dive into the Pacific northwest early next week...leading to long wave trough amplification across the western US and a building subtropical ridge across the southeastern US. This will allow the middle level ridge to become more progressive and pass east of lower Michigan toward midweek...allowing a surface warm front to lift across the region from the southwest. This warm front will advect a warm...moist and unstable airmass into the forecast area. The GFS continues to bring this warm front through faster than the other model solutions /suggesting convection as early as Monday night/. The GFS has some obvious convective feedback issues due to potential mesoscale convective system development over the plains. The GFS is also less amplified with the long wave trough over the western US. Given the strength of the polar jet and potential phasing with the subtropical jet...the more amplified European model (ecmwf) remains the preferred solution. This suggests the better chances for convection will hold off until the Tuesday night/Wednesday time frame. Despite this uncertainty... the overall trend next week will be for warmer and more humid conditions with increasing chances for thunderstorms. Marine... Unseasonable conditions are in place over the central Great Lakes today as cold air advection is ongoing within a deep trough axis. Efficient northerly flow and a long fetch over the waters will sustain high wave activity from Saginaw Bay down to Port Huron. Recent water temperature readings from the buoys suggests that conditions will be solidly in the neutral regime out over the Open Lake which is atypical for late may. In fact...conditions are unstable for Saginaw Bay with water temperature readings suggesting lsts are at around 13 to 14 c vs an 850mb temperature that will be dipping down to -4c by 12z this morning. Will expand the advisory to include inner Saginaw. Conditions are more marginal on Lake St Clair and Lake Erie. Will give respect to peak of the cold air advection that will occur this morning for the southern zones and extend the small craft for them as well. The stable surface anticyclone will build into the central Great Lakes tonight bringing a return of much more familiar stable season marine weather. && DTX watches/warnings/advisories... Michigan...none. Lake Huron... Small Craft Advisory...nearshore waters from Port Austin to Port Huron...until 8 PM Friday. Small Craft Advisory...outer Saginaw Bay...until 6 PM Friday. Lake St Clair... Small Craft Advisory...until 4 PM Friday. Michigan waters of Lake Erie... Small Craft Advisory...until 4 PM Friday. && $$ Aviation.....Sf short term...cumulonimbus long term....SC marine.......cb You can obtain your latest National Weather Service forecasts online at www.Weather.Gov/Detroit (all lower case).