Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
700 PM EDT Wednesday Oct 22 2014
Residual stratus /now impacting just fnt and mbs/ will attempt to
slowly dissipate this evening as slight warming above the boundary
layer helps to erode the low level inversion. Limited mixing this
afternoon has held surface dewpoints in the upper 30s. Clearing skies
and light winds as surface high pressure expands over the region will
provide good cooling in the boundary layer and will thus pose the
risk for some fog late tonight into Thursday morning assuming the
anticipated clearing trend holds. Some enhanced moisture off Lake
Huron under lingering north-NE flow will add to the fog potential...
particulary at ptk/fnt/mbs. Although not strongly confident in
fog...there is enough support to include a mention of some reduced
visibilities in the tafs.
For dtw...less influence from Lake Huron and warmer nighttime mins
in metropolitan Detroit will be limiting factors for fog development. In
light of cooling potential...a brief period of MVFR visibility
toward daybreak certainly looks possible.
//Dtw threshold threats...
Previous discussion...issued 354 PM EDT Wednesday Oct 22 2014
Short term...through tonight
Upper level closed low over the East Coast along with upper level
jet influence will continue to shift east through the short term.
Main concern today is the cloud cover as it ever so slowly erodes
away. Clouds have been slow to dissipate due to the north/northeast
flow off of the lake bringing. High pressure has been working its
way in and will result in helping to clear out clouds. With clear
skies and light winds overnight...radiational cooling will take
effect leading to temperatures dropping into the upper 20s over
northern parts of the County Warning Area to the lower 30s. With these parameters
in place there is a chance for fog to develop early Thursday
morning. Currently only a mention of patchy fog is in the forecast
as models have varying opinions on the amount of moisture near the
surface. This will also depend on how fast clouds can clear this
afternoon...especially over nothwestern parts of the County Warning Area where
clouds are still prevalent. If clouds stick around this would keep
temperatures cooler and in turn lead to a better potential for fog as temperatures
would be able to approach the dewpoint faster.
Long term...Thursday through Tuesday
Fairly amplified longwave pattern will get flattened by a train of
shortwaves embedded in strong westerly jet across southern Canada.
It will stay up across Canada though as a strong ridge builds over
the SW Continental U.S.. the ridge will push the cool pool...associated with
the upper low cutting off over the East Coast...further east away
from Southeast Michigan. This will allow temperatures to slowly climb into the weekend
as the middle level heights slowly increase. Overall pleasant
conditions will hold over Southeast Michigan into the weekend as high pressure
will dominate with little more than an elevated front working across
the state Thursday night.
Surface high pressure will be centered over the area to start the day
Thursday with a shortwave ridge axis passing across the area in the
afternoon. This will lead to sunny skies with 850mb temperatures increasing
to around 9c by evening. A weak system working across Canada will
shed a piece of energy southeast through the western Great Lakes. The
results will be a shearing fgen band working over the area Thursday
night. Its hard to find a model solution that gives any credence to
the front as it struggles to fight the dry air and subsidence in
place from the ridge as the bulk of the energy wicks away to the
north and south. Continued the mostly clouds forecast over night
with min temperatures holding up around 40 with the southwesterly flow.
After the front passes...high pressure will build back in over the
area with another low amplitude shortwave ridge working into the
area as well. Temperatures during the day will increase slightly
over Thursday approaching 60...but a sharp thermal ridge around 12c
at 850mb will fold over into Michigan Friday night which will keep min temperatures
up in middle 40s.
Thermal ridge will be short-lived however as a dry cold frontal
passage will occur early Saturday. Despite low-level Post-frontal
cold advection for most of Saturday...still expecting highs to reach
the lower 60s due to decent mixing heights and ample afternoon
sunshine. It will be breezy though with 925mb winds of 30-35 knots
supporting decent gust potential. Continued cold advection Saturday
night will cause a cool down for highs Sunday...dropping to the middle-
50s. Will have to watch for cloud potential Saturday night/early
Sunday with cold advection and multi-lake connection...but for now
continued mostly clear skies. Upper ridge building in will result in
recovery in temperatures for Monday. Still large model spread with inbound
upper troughing Monday night through Wednesday. For now have
targeted Tuesday/Tuesday night timeframe for chance probability of precipitation.
A ridge of high pressure will move over the central Great Lakes
tonight becoming centered over the region by Thursday morning. This
high will bring favorable marine conditions to the lakes for the
remainder of the week. Winds will increase as they veer from
southwest to northwest on Saturday when a cold front drops through
the region. Small craft advisories may be needed for portions of
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).