Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
326 PM EDT Monday may 4 2015
Short term... tonight
Good push of dry air over the western Great Lakes...as surface dew
points have fallen into the 30s across much of Wisconsin...Upper
Peninsula and parts of norther lower Michigan. With surface high
(1025-1027 mb) building over northern lower Michigan tonight...it
appears we can lower probability of precipitation tonight...as majority of County Warning Area should end up
dry as the front sinks south of the border. Still need the cold
front to clear Southeast Michigan this afternoon into this
evening...and with surface based convective available potential energy climbing to at least 1000
j/kg (mid/upper 70s over middle/upper 50 dew pts)...isolated-low
scattered coverage of thunderstorm/shower activity remains
possible...with 12z regional Gem being one of the biggest
proponents...while the NAM lites up the front around 00z...helped
out by the cool marine layer push of Lake Huron. Could be
experiencing subsidence at the present time due to departing
circulation over Northwest Ohio. None-the-less...will be
maintaining the low chance probability of precipitation along and south of I-69 into the
evening...then allowing the drier air to take hold and confine
chance probability of precipitation toward the Ohio border as upstream activity approaches
Will have to keep an eye on the radar (assuming convective available potential energy reach 1000+
j/kg) through daylight hours for isolated strong/marginal severe
activity as freezing levels are ideal...and front is Colorado-located
along the sharp 0-6 km shear gradient. Solid north-south min temperature
gradient (15 degrees) likely tonight with mostly clear skies/Cool
Lake Huron influence north (around 40/lower 40s)...while
thicker/lower clouds linger south (low/middle 50s).
Long term...Tuesday through Sunday
Tuesdays forecast is shaping up to be kind of tricky in regards to
how far south a frontal feature will slide down across lower
Michigan. Current model runs...while overall are trending more to
the south...are very inconsistent with each other making it
difficult to determine where the front and associated precipitation
will remain focused. Have shifted the main precipitation area further to
the south...to account for the model trend...however...have also
left low chance probability of precipitation /30 percent/ to the north /up to I-69/ to
account for a more northerly track. The frontal set up Tuesday not
only affects where the rain and thunderstorms will develop...but
also will play a big part on our temperatures. In the northerly
solutions...more cloud cover will be around...considerably hampering
our high temperatures /highs only in the middle to upper 50s/.
However...if the front settles south of the Ohio border...we will
experience a more partly cloudy forecast with resulting higher maximum
temperatures /mid to upper 60s/. Since current trends are favoring a more
southerly solution...have bumped up temperatures by a few degrees.
Similarly...the position of the front will affect Tuesday night
lows. For now until more confidence on where this frontal feature
will set up...have maintained the middle to upper 40 low temperature
from the previous forecast.
For the most part...Wednesday will remain dry as upper level ridging
builds into the Great Lakes region resulting in a surface high to
develop over the eastern Great Lakes. Locations that may see some
light shower activity...mainly in the morning hours...would be in
the extreme western counties /Shiawassee...Livingston...Washtenaw
..Lenawee/. Have kept in a slight chance of showers and isolated
thunderstorms from the previous forecast for these locations.
Elsewhere across the County Warning Area...current model runs show enough dry air
and subsidence to keep the forecast dry...however...plenty of clouds
will be around keeping temperatures on the cooler side for most of
the day /mid to upper 60s/. A brief scattering out of the cloud deck
towards late afternoon and early evening Wednesday could allow
temperatures to creep up into the low 70s towards the end of the day
before temperatures quickly drop after sunset. Partly cloudy skies
overnight will allow temperatures to drop into the upper 40s to low
50s on Wednesday night.
Highly amplified flow with a trough out west and ridge over the
Great Lakes and East Coast for the end of the week will allow for
warm and mainly dry conditions. This pattern will break down a bit
by the weekend as impulses in the southwesterly flow will allow for
daily shower/tstorm chances into early next week. At the
surface...cold front will slowly ease into lower Michigan by
Saturday...providing a low-level focus for precipitation and
allowing temperatures to decline Sunday and Monday.
Rain showers and thunderstorms are possible across the southern
Great Lakes as a frontal system tracks across the region.
Northwesterly winds will become northerly by Tuesday morning...with
rain showers continuing through Tuesday afternoon. High pressure
returns for Wednesday allowing winds and waves to remain calm
through Thursday. A low pressure system arrives late Friday bringing
the next chance of rain and thunderstorms to the Great Lakes.
Aviation...issued 1253 PM EDT Monday may 4 2015
Mainly middle clouds left behind this mornings line of showers and
embedded thunderstorms. A cold front will be slowly working
through Southeast Michigan this afternoon/early this
evening...thus their remains a low chance of shower/thunderstorm
activity...but areal coverage and confidence precludes the mention
in the tafs. A short period of lower ceilings are possible with
the frontal passage...as winds shift around to the northwest...allowing
drier air to filter in. Tonight should be dry...with frontal
boundary returning north tomorrow as a warm front. It appears rain
should at least reach the southern taf sites (dtw/det/yip)...but
confidence is average.
//Dtw threshold probabilities...
* low for ceiling at or below 5000ft this afternoon and tonight...medium
* Low for thunderstorms this afternoon and evening and then again
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).