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Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1150 PM EDT sun Apr 20 2014
Skies remain clear below 10kft tonight and Monday given the
existence of a very dry low level environment. A light south to
southeast wind tonight will veer to southwest while increasing into
the 10 knot range on Monday. The arrival of a frontal boundary will
bring an increasing chance for showers in lower ceilings Monday
evening/night. Isolated potential for thunderstorms...probability
too low to include a mention at this time.
//Dtw threshold threats...
Previous discussion...issued 354 PM EDT sun Apr 20 2014
Short term...today and tonight
Very dry near surface air remains in place over southeastern
Michigan this afternoon evidenced by surface dewpoints that have
fallen down into the 20s at many locations. The 20.12z kdtx sounding
showed the depth of this dry air to be significant...from the
surface through 11 kft above ground level. Geopotential height settling is
forecasted to occur at a broad wavelength which will allow the
frontal boundary blocked to the north...to settle slightly
southward. It remains possible that some virga or enhanced midlevel
cloud could Brush Bay/Midland counties...especially between the
01-06z timeframe. Kept a slight chance of precipitation in the
forecast to account for this. Otherwise...low dewpoints and
persistent ridging suggests temperatures tonight should cool...with
a maximum/min difference of roughly 25 degrees. Forecasted lows tonight
are expected in the lower into the 40s in the far eastern sections
of the County Warning Area...with upper 40s to near 50 west.
Long term...Monday through next Sunday
Deepening of the middle level trough approaching the West Coast on
Monday will lead to an overall amplification in the downstream
height field heading into middle week. Strong agreement is noted among
the 12z model suite in showing weak surface low pressure development
over the upper MS valley on Monday in advance of a middle level wave
tracking along the US/Canadian border. Meanwhile...the middle level
circulation now over the southern High Plains will lift into the Ohio
Valley on Monday. This will force weak middle level short wave ridging
over Southeast Michigan into early to middle afternoon on Monday despite the weakening
of this system. Observations across the region suggest only a narrow
ribbon of deep layer moisture present along the residual frontal
boundary now extending from northern Iowa trough The Straits region.
Enhanced low level S-SW flow in advance of the approaching surface low
and the expected middle level ridging should hold this ribbon of
moisture north of the forecast area well into Monday afternoon. In
light of regional observations...the GFS appears significantly too
bullish on timing the low level moisture into Southeast Michigan. Thus the
NAM/Canadian/ECMWF which hold the arrival of the deeper moisture and
thus precipitation chances later into the afternoon/evening appear
reasonable. The lack of low level moisture and good S-SW flow should
then enable fairly deep mixing depths into Monday afternoon...
supportive of high temperatures well into the 70s.
The surface low is expected to track into northern lower Michigan by Monday evening.
Increasing moisture convergence along the associated surface front and
weak instability will provide increasing chances for showers
/isolated thunder/ late in the day. Amplification of the middle level
wave tracking across the northern Great Lakes Monday night will strengthen
the magnitude of the downstream upper jet maximum. The enhanced response
within the entrance region of this jet will invoke a deeper frontal
circulation over the forecast area Monday night. This should result in
an increase in coverage of showers after 00z. Continued long wave
trough amplification east of the region will usher in drier and much
cooler air by daybreak Tuesday. So temperatures will once again be on the
colder side of the typical middle April spectrum into middle week. The
degree of dry air should keep the forecast area precipitation free Tuesday and
Wednesday. Diurnally enhanced daytime cumulus/strato cumulus are highly possible in
light of the steep low level lapse rates...especially on Tuesday
considering model solutions depict a secondary middle level short
wave traversing lower Michigan.
Thursday afternoon...the low pressure setting up to the west over
the northern plains will bring increasing clouds during the day with
rain chances developing late Thursday night into Friday. Weak
chances for showers will continue through Saturday. A strong
Canadian high builds over the area for Sunday and Monday resulting
in dryer and slightly cooler conditions.
A stalled frontal boundary will linger over Northern Lake Huron into
Monday afternoon. High stability over the Cold Lakes and a
relatively weak gradient will support light winds through the day
Monday. A low pressure system will then pass across Lake Huron
Monday evening...dragging a cold front across the region. Post
frontal northwest winds will increase into the 20 to 30 knots range
early Tuesday morning and persist into Tuesday afternoon as colder air
advances south. The chances of gale force wind gusts still look low
at this time...although the development of some Small Craft Advisory
conditions does look possible. High pressure will then bring calming
conditions through the middle of the week before southwest to west
winds increase late in the week with the approach of the next low
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).
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