Forecast Update

It seems as if tomorrow's situation keeps changing every hour, so I will give you the latest consensus among the data.  It looks like the rain will probably start a bit later than what I said yesterday.  Yesterday, I mentioned that precipitation would probably start after 11 p.m., well now, it looks like rain will start around midnight.  In my opinion, I still think that precipitation will begin around the late evening hours, probably around 10 or 11 tonight.  It just all depends on how quickly the storm system moving into the plains occludes, because storm systems tend to accelerate until they occlude, which by that time, they tend to slow down considerably.  This will lead to timing issues with the onset of strong isentropic upglide, upper level forcing, the works... which will all eventually lead to the point at which the atmosphere above is saturated.  As was the trend in models, the storm looks to strengthen and accelerate for the next few hours, then occluding over the Northern Plains somewhere over southern Minnesota.  The storm looks to become fairly strong before becoming vertically stacked (this means that the storm system does not have a tilt to it when moving up from the earth's surface.  In a strengthening storm system, the surface low is located farthest east, while the 500 and 300 millibar lows and troughs, tend to be located north and west of the surface low.  When a low pressure system becomes vertically stacked, all of the upper level storm systems are located directly above the low, causing it to strengthen for a little while longer, but then weaken as it is source of development has been cut off.), which at the time that it is expected to become vertically stacked, the warm sector will be right over the area.  Tonight, no matter what time the rain arrives, it will become steadier and heavier with time, with embedded heavy thunderstorm development after 3 a.m.  By 7 a.m., scattered heavy thunderstorms will still be located in the area, leading to localized heavy rainfall amounts in some parts of the area.  After 9 a.m., most if not all thunderstorm development will cease, with rapidly clearing skies and strong southerly winds bringing in warm, moist air to the region.  Temperatures will soar into the lower and middle 60's across the area, with upper 50's at the Michigan border.  With increasing lapse rates, strong mixing will occur, bringing much higher winds aloft to the surface, increasing wind speeds as high as 40-50 mph.  Strong mixing could also cause the development of showers and thunderstorms in the warm sector ahead of the mesoscale dry line that is expected to pass through the area.  Right now, the highest chance for scattered thunderstorms after 2 p.m. is expected east of I-69, as the axis of highest instability and highest moisture, will move through the areas at the same time that low level convergence will be strongest.  Some models such as the GFS, are indicating that mixing will be so strong that dry air aloft will mix down to the surface, inhibiting significant convective development.  On the otherhand, the NAM has dew points well above what the GFS is forecasting, with dew points near 60, with temperatures near 65.  This would potential lead to thunderstorm development, but the NAM also has a very narrow opportunity for thunderstorm development, dry air mixing to the surface after 4 p.m., so thunderstorms may not ever form tomorrow afternoon, not in our area to the say the least.  My current thinking is that thunderstorms will form if the NAM is correct with the higher dew points in the area, especially if the left exit region of the jet streak ends up right over our area.  These thunderstorms could produce gusty winds and some small hail as they pass quickly through the area.  After they pass, the cold front will quickly pass through the area, with temperatures quickly dropping, but with strong winds continuing throughout the late afternoon.  Some showers and maybe a snow shower may pivot through the area by nightfall, with mostly cloudy skies and falling temperatures.  After this storm passes through, our attention will focus on the next potentially major storm system, which will further impact the area by Friday and Friday night.  Stay tuned for further updates.