Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
752 PM EDT Tuesday Jun 30 2015
Instability due to daytime heating will rapidly diminish through middle
evening and allow any remaining showers to gradually dissipate. The
best environment for thunderstorms has settled south of the terminal
corridor with the wave of low pressure exiting into Lake Erie. Weak
northwest wind left behind will carry in an air mass prone to
MVFR/IFR stratus development as observed over the northern/western
Great Lakes earlier today. Similar conditions are expected to
redevelop over Southeast Michigan overnight through middle Wednesday morning.
Renewed daytime heating will then help lift ceiling into VFR during
For dtw... an isolated shower remains possible through middle evening
while coverage of thunder will be south and east of the terminal and
moving away. Pushed back timing of MVFR/IFR transition later into
the night then lasting through Wednesday morning once developed.
//Dtw threshold probabilities...
* high for ceilings at or below 5kft
* low for tstorm impacting kdtw airspace
Previous discussion...issued 326 PM EDT Tuesday Jun 30 2015
Short term...this evening and tonight
Forecast reasoning has changed relatively little for this afternoon
with the lone notable exception that a mesoscale low propagating
south over Lake Michigan has modulated the forcing field over
central and Southern Lower Michigan so far today. As a result, the
genesis region for showers and thunderstorms has been along and
south of this feature's pseudo-warm front. Probability of precipitation have correspondingly
been shifted south in accordance with the latest observational
evidence which suggests afternoon convective activity funneling into
the I-69 to I-94 corridor. 4km Storm Prediction Center WRF run appears usable through
late evening. Shear remains quite low while MLCAPE still looks to
maximum out around 600 j/kg near the Ohio border. No severe weather
anticipated, but a localized flooding threat could evolve in a
region of training of slow moving cells.
Large scale forcing associated with the middle-level circulation over
northern lower Michigan will shift east through the late evening
bringing a gradual end to showers after sunset. Marine modified air,
as noted streaming off of Lake Superior all day, will filter into
lower Michigan within westerly flow tonight supporting low clouds
through sunrise and containing lows to the middle and upper 50s.
Large upper level ridge centered over the central rockies this
afternoon folding over...with shortwave over extreme southern
Saskatchewan diving southeast into the Midwest tomorrow morning.
Southeast Michigan looks to be under general subsidence and drying
behind this evenings trough axis passage...with heights and surface
pressure on the rise. However...a northern stream shortwave trough
extending from the large upper level low over Hudson Bay is
forecasted to sweep through the northern Great Lakes late
Wednesday/Wednesday night...with second pv extension rotating
through Southern Lower Michigan during Thursday. Good 500 mb packing
of temperatures...but GFS indicating 925 mb computed lifted indices and
showalter index remaining solidly positive Wednesday evening...while
NAM lowers the lifted indices to around zero as weak frontal passage occurs.
With possible slight moisture contribution from Saginaw Bay...would
not discount the possibility of isolated cells going up....but even
NAM soundings show difficult time over coming the dry middle level air.
During Thursday...shortwave and surface low expected to track across
the Ohio Valley. Although middle level lapse rates will be rather steep
(6.5+ c from 700-500 mb noted) over lower Michigan...low level
anticylonic flow will be building in...and will continue with the
dry forecast. Light northeast flow in the low levels coupled with
partly cloudy skies (south) expected to hold maxes under 80 degrees
with 850 mb temperatures around 10 c.
Will maintain a dry forecast Friday into the Holiday weekend with
weak upper flow/lack of forcing...lack of moisture...and weak
surface high pressure shown by 12z model suite. Temperatures also
expected to warm back to near normal as the negative upper height
anomaly is replaced by slightly rising heights. Models disagree
substantially early next week with 12z Euro tracking a strong upper
low through Ontario while GFS/gefs mean cut this energy off over
northwestern Canada. Will keep probability of precipitation near climatology in the lower chance
range until better agreement can be reached.
Very light winds will persist through tonight with a few showers
around into the evening hours. A weak cold front looks to be
dropping south through the central Great Lakes late
tomorrow/tomorrow night. Little shower/thunderstorm activity is
expected with the front...with northwest winds increasing to around
15 knots over Lake Huron. High pressure building into the region on
Thursday with low pressure tracking through the Ohio Valley will
lead to northeast flow....but still holding around 15 knots.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).