Scientific Forecaster Discussion
fxus63 kdtx 270408
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1208 am EDT Tue Jun 27 2017
Long wavelength upper level trough remains in place directly over
the central Great Lakes. Vigorous pv circulation is now over The
Heart of the forecast area which means that Ava will kick in
momentarily. This in combination with loss of diurnal heating will
largely end shower chances overnight. Per cloud trends, also went
more optimistic with VFR clouds north trending sky clear the latter half
of the night.
//Dtw threshold probabilities...
* low for cigs aob 5kft by late evening and the overnight.
issued at 318 PM EDT Mon Jun 26 2017
Another afternoon with scattered showers around.
Upper level low/cold pool (-25 c at 500 mb) sliding through
Southeast Michigan this evening. Best jet forcing south of the
southern Michigan border, but still 0-6 km bulk shear of 40 knots
approaching the southern Michigan border, along with steep mid level
lapse rates. Fortunately, instability expected to be limited.
Surface dew pts started out in the lower 50s early this morning, but
have mixed down into the 40s, limiting sbcapes to 500 j/kg or less.
Thus, updrafts likely not strong enough to handle the stronger wind
shear and dry air in the mid levels. However, isolated thunderstorms
remain possible, especially across Lake St Clair and Western Lake
Erie, as warmer waters provide a moisture boost, and Max negative
showalter values seen tracking through that area early this evening.
The main mid level circulation/cold pool will be tracking off into
the eastern Great Lake overnight, but there is one more weaker
shortwave trough/700 mb thermal trough tracking through during
Tuesday, which should touch of isolated showers, as strong upper
level jet (110+ knots at 250 mb) slides through Lake Michigan with
modest moisture pooling over Southeast Michigan as seen in 850-700
mb Theta-east fields. With surface based Li's just near zero with CAPES
less than 250 j/kg, will forego mention of a thunderstorm.
Strong low level southwest flow developing during Wednesday, with
dry warm front lifting into northern lower Michigan. 850 mb temps
climbing to 12 c should support highs reaching around 80 degrees.
Excellent surge of moisture to occur Wednesday evening/night, with
precipitable water values approaching 1.75 inches by Thursday morning. Showalter
index in the -2 to - 4 c range, with mid level lapse rates around 7
c/km should be plenty of thunderstorms, and with 50+ knots at 850
mb, severe storms could be a concern, but good chance the stable low
levels/surfaced based inversion likely will hold, and maybe hail
would be a slight bigger threat, but right now 850 mb computed cape
looks to be below 1000 j/kg, per 12z Euro.
Extended forecast Thursday, June 29th through Tuesday,July 4th:
current models show active wet weather pattern resuming mid-week and
continuing through most of the Holiday weekend, as several waves of
back-to-back low pressure gear up to move through Southeast
Michigan. Chances of showers/thunderstorms look to increase
significantly for Friday afternoon through early Saturday morning.
Surface high pressure tries to build over the region Saturday
afternoon and sunday; however, upper level troughing could allow at
least some scattered showers to develop. Keeping at least weak pops
in the forecast into Monday. At present, the fourth looks to be dry.
Temperatures are expected to remain near the seasonal norm through
the period with highs in the upper 70s to low 80s and overnight lows
in the 60s.
Wind will diminish through this evening becoming light to moderate
through Wednesday. Moderate southerly wind will transition to fresh
southeasterly Wednesday night into Thursday in advance of the next
low pressure system, the stable southerly fetch limiting gustiness.
Lake St Clair...none.
Michigan waters of Lake Erie...none.