Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
327 PM EDT Wednesday Sep 17 2014
Short term... through tonight
High pressure at the surface helped scour out some of the ll
moisture that has been prevalent over the last few days. This was
evident in the afternoon cumulus field which struggled to develop over
our eastern parts. Early cumulus development over western Michigan did make a
push east into Saginaw Valley and fnt which then expanded through
The Thumb. This will quickly dissipate this evening after sunset
allowing clear skies to take US into the overnight.
A fast moving shortwave embedded in the northwest flow aloft
tracked through Ontario this morning laying out a cold front across
the Upper Peninsula. Cold air advection advection behind the front brought
freezing temperatures and even some snow to parts of Ontario. This
front will continue its southward push through the overnight
reaching mbs around 10z and dtw closer to 12z. Cold air advection behind the front
combined with moisture advection from NE flow over Lake Huron will
result in a low stratus deck for most of the area. As the front
drifts south it will become more diffuse which will lessen the
impacts further south. There will likely be a degree of light fog as
well but with the amplified winds associated with the
front...leaning more toward low stratus. This will be a dry frontal passage in
terms of precipitation as hires models show precipitable waters only around a half inch
with the moisture density located in the lowest 5kft of the column.
The clouds will hold min temperatures up in the middle 40s tonight as the cold
front...and cold air advection...will hold off until after 12z for most
Long term...Thursday through Tuesday
Current infrared/WV satellite views and 500mb height contours show
increased moisture content along a jet streak over eastern Canada.
Another moisture-rich area can be found near and east of ts Odile
over The Four Corners region. The western Continental U.S. Is generally in a
ridge pattern that is expected to flatten out and only slightly
raise pressure heights over Southeast Michigan.
Easterly flow off of Lake Huron and a backdoor cold front is
expected to increase cloud cover across the northern half of the County Warning Area
Thursday. This front loses its punch as the day wears on with 850 mb
Theta-E temperature differential going from about 20c in the morning
to less than 10c during the day. This front may have little affect
on our southern 4 counties...but temperatures will be around 10 degrees
cooler north of I-69.
The main edit this cycle was to lower mins on Thursday night.
Sprawling high pressure and likely light winds will allow a good
radiational cooling night. There will still be an easterly component
to the wind field that will advect moisture inland. This will keep
coastal areas and the domain within 20 miles significantly warmer.
Look for inland areas to radiate into the middle or upper 30s though.
Next chance for rain remains on Friday night as an upper wave and
corresponding low pressure moves toward Michigan. American model
suite does not push the moisture plume very far past Lake
Michigan...sporting dry air and retreating high pressure. The Gem
and European model (ecmwf) do plot higher moisture levels and quantitative precipitation forecast amounts across the
County Warning Area. Went likely just for areas north of I-69 on this event and will
continue to monitor wave progression.
The next low pressure system will track across the northern plains
and into the northern Great Lakes region by Saturday morning. This
low will bring a chance of rain showers to the entire County Warning Area. Rain
should begin first in The Thumb region on Saturday morning. Rain
chances will begin for the southern County Warning Area during the afternoon on
Saturday. The best chances for rain showers will occur on Saturday
night as a cold front gets dragged across lower Michigan. Some light
rain showers are expected through the day on Sunday as moisture
wraps around the departing low. High pressure will return on Monday
resulting in dry conditions across the region.
Winds become more southwesterly this afternoon ahead of an
approaching cold front currently draped across the northern Great
Lakes. The front will drop through the eastern lakes tonight and
into Thursday morning veering flow to northeasterly while increasing
the winds with gusts approaching 25 knots tonight. The northeast
wind direction will bring increased wave heights into the nearshore
zones around The Thumb. Small craft advisories have been issued for
all nearshore areas of Lake Huron including Saginaw Bay for both
winds and waves. The advisories will be in effect from this evening
into the late morning hours on Thursday. Winds will ease Thursday
night into Friday before southerly winds begin to ramp up ahead of
the next system late Friday.
Aviation...issued 125 PM EDT Wednesday Sep 17 2014
VFR conditions this evening and through the first half of the
overnight as high pressure holds over the area. A cold front will
drop through the area later tonight bringing a period of IFR
stratocu and possibly some light fog for a few hours into Thursday
morning. Does not look like there is enough moisture for rain to
develop. The front will weaken as it tracks southward which should
result in highest confidence for IFR ceilings for mbs/fnt with less
confidence for the Detroit metropolitan tafs. Winds will increase a bit
after they veer from southwest to northeast with the frontal
passage. High pressure will build back in on Thursday bringing
//Dtw threshold threats...
* high confidence in ceilings below 5kft beginning early Thursday
Small Craft Advisory...nearshore waters from Port Austin to Port
Huron including Saginaw Bay...from 10 PM Wednesday to 10 am
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).